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RESPECTED SIR, FOLLOWING OBSERVATION HAS BEEN GIVEN BY THE GUIDE-:(HIGHLIGHTED IN RED)
- USG 3 D PROBE DETAILS NOT REQUIRED (PLEASE REMOVE THAT TABLE)
- REFENCES 18,19 IN RED ARE RELATED TO ASSOCIATION BETWEEN OBESITY AND SOCIOECONOMIC STATUS WHICH IS NOT RELATED TO SPINE ANAESTHESIA (SIR I COULD NOT UNDERSTAND ITS RELEVENCE,IF POSSIBLE PLEASE DELETE).
- IN DICUSSION PLS DON,T MENTION ABOUT REALTIME ULTRASOUND TECHNIQUE ITS TOTALLY DIFFERENT TOPIC
- SPACING NEED TO BE DONE PROPERLY.
- REST ALL OK SIR
THANKS AND REGARDSDR SEEMA SINGH
INTRODUCTION:
Spinal anaesthesia is widely performed using a surface landmark-based “blind” technique.
Multiple passes and attempts while administering spinal anaesthesia are associated with a
greater incidence of postdural puncture headache, paraesthesia, and spinal hematoma 1, 2.
Real-time and preprocedural neuraxial ultrasound techniques have been used to improve the
success rate of spinal anaesthesia. Information on the use of real-time ultrasound- guided
spinal anaesthesia has, to date, been limited to case series and case reports 3-5. Its use may be
limited by the requirement for wide-bore needles and the technical difficulties associated with
simultaneous ultrasound scanning and needle advancement 6. The use of preprocedural
ultrasound has been shown to increase the first-pass success rate for spinal anaesthesia only
in patients with difficult surface anatomic landmarks 7.
Studies on preprocedural ultrasound-guided spinal techniques have focused on a midline
approach using a transverse median (TM) view. The parasagittal oblique (PSO) view
consistently offers a better ultrasound view of the neuraxis compared with TM views 8, 9.
However, very few studies have been conducted to assess whether these superior PSO views
translate into easier paramedian needle insertion.
The use of ultrasound imaging techniques in regional anaesthesia is rapidly becoming an area
of increasing interest. It represents one of the largest changes that the field of regional
anaesthesia has seen. For the first time, the operator is able to view an image of the target
nerve directly, guide the needle under real-time observation, navigate away from sensitive
anatomy, and monitor the spread of local anaesthetic (LA). This comes at a time when an
ageing population presents with an increasing range of comorbidities, thereby demanding a
wider choice of surgical and anaesthetic options to ensure optimal clinical care and a
decreased risk of complications. The key to successful regional anaesthesia is deposition of
LA accurately around the nerve structures. In the past, electrical stimulation or paraesthesia,
both of which relied on surface landmark identification, was used for this. However,
landmark techniques have limitations; variations in anatomy and nerve physiology 4, as well
as equipment accuracy have had an effect on success rates and complications. The
introduction of ultrasound may go some way towards changing this.
If the use of ultrasound is to become more widespread amongst anaesthetists, then it must be
shown to be clinically effective, practical and cost-effective 10. The use of ultrasound
guidance in daily clinical practice requires a degree of training and an understanding of the
equipment and technology.
US-guided Central Neuraxial block is a promising alternative to traditional landmark-based
techniques 6. It is non-invasive, safe, simple to use, can be quickly performed, does not
involve exposure to radiation, provides real-time images, and is free from adverse effects. US
guidance may also allow the use of central neuraxial block in patients who in the past may
have been considered unsuitable for such procedures due to abnormal spinal anatomy.
Spinal anaesthesia may be challenging in patients with poorly palpable surface landmarks or
abnormal spinal anatomy. Pre-procedural ultrasound imaging of the lumbar spine can help by
providing additional anatomical information, thus permitting a more accurate estimation of
the appropriate needle insertion site and trajectory.
We hypothesized that the routine use of a preprocedural ultrasound-guided technique for
spinal anaesthesia would reduce the number of passes required to achieve entry into the
subarachnoid space when compared with the conventional landmark-guided midline
approach.
REVIEW OF LITERATURE:
ANATOMY of SPINE11
The vertebral column consists of 33 vertebrae: 7 cervical, 12 thoracic, 5 lumbar, 5 sacral, and
4 coccygeal segments. The vertebral column usually contains three curves. The cervical and
lumbar curves are convex anteriorly, and the thoracic curve is convex posteriorly.
Fig 1. Anatomy of spine
VERTEBRA The typical vertebra consist of two parts
(1) Body: placed anteriorly and bear weight
(2) Arch: It consist of 2 pedicles, 2 superior and 2 inferior articular process, 2 transverse
process, 2 laminae, 1 spinous process . It surround the cord laterally and posteriorly
Fig 2. The vertebral arch (green) forms the spinal canal (blue) through which the spinal cord
runs. Seven bony processes arise from the vertebral arch to form the facet joints and
processes for muscle attachment.
The vertebral arch, spinous process, pedicles, and laminae form the posterior elements of the
vertebra, and the vertebral body forms the anterior element. The vertebrae are joined together
anteriorly by the fibrocartilaginous joints with the central disks containing the nucleus
pulposus, and posteriorly by the zygapophyseal (facet) joints. The thoracic spinous process is
angulated steeply caudal as opposed to the almost horizontal angulation of the lumbar
spinous process This is a clinically important distinction for needle insertion and
advancement in the thoracic versus lumbar levels. The sacral canal contains the terminal
portion of the dural sac, which typically ends at S2.
SPINAL CORD
The spinal cord is continuous with the brainstem proximally and terminates distally in the
conus medullaris as the filum terminale (fibrous extension) and the cauda equina (neural
extension). This distal termination varies from L3 in infants to the lower border of L1 in
adults because of differential growth rates between the bony vertebral canal and the central
nervous system. It is about 40 cm long and 1-1.5 cm in diameter. Surrounding the spinal cord
in the bony vertebral column are three membranes (from innermost to outermost): the pia
mater, the arachnoid mater, and the dura mater (Fig. 56-1). The cerebrospinal fluid (CSF)
resides in the space between the pia mater and the arachnoid mater, termed the subarachnoid
(or intrathecal) space. The pia mater is a highly vascular membrane that closely invests the
spinal cord and brain. Approximately 500 mL of CSF is formed daily by the choroid plexuses
of the cerebral ventricles, with 30 to 80 mL occupying the subarachnoid space from T11-T12
downward. The arachnoid matter is a delicate, nonvascular membrane that functions as the
principal barrier to drugs crossing into (and out of) the CSF and is estimated to account for
90% of the resistance to drug migration.12
Fig 3. The ventral (motor) and dorsal (sensory) roots join to form the spinal nerve.
Spinal cord is composed of white and grey matter and is divided into spinal segments each
segment forms a pair of spinal nerves. The spinal nerves are numbered according to the
vertebrae above which it exits the spinal canal. The 8 cervical spinal nerves are C1 through
C8, the 12 thoracic spinal nerves are T1 through T12, the 5 lumbar spinal nerves are L1
through L5, and the 5 sacral spinal nerves are S1 through S5. There is 1 coccygeal nerve.
Thirty-one pairs of spinal nerves branch off the spinal cord. Each spinal nerve has two roots.
The ventral (motor) and the dorsal (sensory). (Fig. 9). Once the nerve passes through the
intervertebral foramen, it branches; each branch has both motor and sensory fibers. The
smaller branch (called the posterior primary ramus) turns posteriorly to supply the skin and
muscles of the back of the body. The larger branch (called the anterior primary ramus) turns
anteriorly to supply the skin and muscles of the front of the body and forms most of the major
nerves.
Fig 4. The spinal nerves exit the spinal canal through the intervertebral foramen below each
pedicle.
LIGAMENTS
The ligaments are strong fibrous bands that hold the vertebrae together, stabilize the spine,
and protect the discs. The three major ligaments of the spine are the ligamentum flavum,
anterior longitudinal ligament (ALL), and posterior longitudinal ligament (PLL) (Fig. 7). The
ALL and PLL are continuous bands that run from the top to the bottom of the spinal column
along the vertebral bodies. They prevent excessive movement of the vertebral bones. The
ligamentum flavum attaches between the lamina of each vertebra. ligamentum flavum (the
so-called yellow ligament) extends from the foramen magnum to the sacral hiatus. Although
classically portrayed as a single ligament, it is actually comprised of two ligamenta flava—
the right and the left—which join in the middle and form an acute angle with a ventral
opening13 The ligamentum flavum is not uniform from skull to sacrum, nor even within an
intervertebral space. Ligament thickness, distance to the dura, and skin-to-dura distance vary
with the area of the vertebral canal. The vertebral canal is triangular and largest in area at the
lumbar levels, and it is circular and smallest in area at the thoracic levels. The two ligamenta
flava are variably joined (fused) in the midline, and this fusion or lack of fusion of the
ligamenta flava even occurs at different vertebral levels in individual patients. Immediately
posterior to the ligamentum flavum are the lamina and spinous processes of vertebral bodies
or the interspinous ligaments. Extending from the external occipital protuberance to the
coccyx posterior to these structures is the supraspinous ligament, which joins the vertebral
spines.
Fig 5. The ligamentum flavum, anterior longitudinal ligament (ALL), and posterior
longitudinal ligament (PLL) allow the flexion and extension of the spine while keeping the
vertebrae in alignment.
EPIDURAL SPACE: It is also called as peridural or extradural space .It is circular space
extending from foramen magnum to sacral hiatus and surround the duramater anteriorly,
laterally and posteriorly
Boundaries of epidural space:
Anteriorly : Posterior longitudinal ligaments,
Laterally : Pedicles and intervertebral foramina
Posteriorly : Ligamentum flavum.
Contents: nerve roots and fat, areolar tissue, lymphatics, and blood vessels including the well-
organized Batson venous plexus.
BLOOD SUPPLY14
Blood is supplied to the spinal cord
Arterial Supply
1) One anterior spinal artery (originating from the vertebral artery),
2) Two posterior spinal arteries (originating from the inferior cerebellar artery)
3) Segmental spinal arteries (originating from the intercostal and lumbar arteries).
Venous drainage
Venous drainage of the spinal cord follows a similar distribution as the spinal arteries. There
are three longitudinal anterior spinal veins and three posterior spinal veins that communicate
with the segmental anterior and posterior radicular veins before draining into the internal
vertebral venous plexus in the medial and lateral components of the epidural space. There are
no veins in the posterior epidural space except those caudal to the L5-S1
CEREBROSPINAL FLUID
Lumbosacral CSF has a constant pressure of approximately 15 cm H2O, but its volume
varies by patient, in part because of differences in body habitus and weight.15 It is estimated
that CSF volume accounts for 80% of the variability in peak block height and regression of
sensory and motor blockade. Nevertheless, except for body weight (less CSF in subjects with
high body mass index [BMI]), the volume of CSF does not correlate with other
anthropomorphic measurements available clinically.16
PHYSIOLOGY AND MECHANISM OF SPINAL ANAESTHESIA
Local anaesthetic binding to nerve tissue disrupts nerve transmission, resulting in neural
blockade. For spinal and epidural anaesthesia, the target binding sites are located within the
spinal cord (superficial and deep portions) and on the spinal nerve roots in the subarachnoid
and epidural spaces. The spinal nerve roots and dorsal root ganglia are considered the most
important sites of action. Nerves in the subarachnoid space are highly accessible and easily
anesthetized, even with a small dose of local anaesthetic, as compared to the extradural
nerves, which are often ensheathed by duramater (the “dural sleeve”).17
The speed of neural blockade depends on-:
- Size of nerve fibre
- Surface area of the nerve fibres exposed to the local anaesthetic
- degree of myelination of the nerve fibres exposed to the local anaesthetic.
Injection of local anaesthetics into the spinal CSF allows access to sites of action both within
the spinal cord and the peripheral nerve roots 18. The traditional concept of spinal anaesthesia
causing complete conduction block is simplistic, as studies with somatosensory evoked
potentials demonstrate little change in amplitudes or latencies after induction of dense spinal
or epidural anaesthesia. There are multiple potential actions of local anaesthetics within the
spinal cord at different sites. For example, within the dorsal and ventral horns, local
anaesthetics can exert sodium channel block and inhibit generation and propagation of
electrical activity. Other spinal cord neuronal ion channels, such as calcium channels, are also
important for afferent and efferent neural activity. Spinal administration of N-type calcium
channel blockers results in hyperpolarization of cell membranes, resistance to electrical
stimulation from nociceptive afferents, and intense analgesia. Local anaesthetics may have
similar actions on neural calcium channels, which may contribute to analgesic actions of
central neuraxially administered local anaesthetics 19.
Multiple neurotransmitters are involved in nociceptive transmission in the dorsal horn of
the spinal cord 20. Substance P is an important neurotransmitter that modulates nociception
from C fibers and is released from presynaptic terminals of dorsal root ganglion cells.
Administration of local anaesthetics in concentrations that occur after spinal and epidural
anaesthesia inhibits the release of substance P and inhibits the binding of substance P to its
receptor in the central neuraxis in a non-competitive fashion 21. Other inhibitory
neurotransmitters that may be important for nociceptive processing in the spinal cord, such as
γ-aminobutyric acid, are also affected by local anaesthetics. Local anaesthetics can potentiate
the effects of γ-aminobutyric acid by preventing uptake and clearance 22. These studies
suggest spinal anaesthesia may be partially mediated via complex interactions at neural
synapses in addition to ion channel blockade and may explain the ability of spinal anaesthesia
to reduce central temporal summation in humans.
Although spinal local anaesthetics can block sodium channels and electrical conduction in
spinal nerve roots, other mechanisms may also come into play. It is theorized that a large part
of the sensory information transmitted via peripheral nerves is carried via coding of
electrical signals in after-potentials and after-oscillations 23. Evidence for this theory is found
in studies demonstrating loss of sensory nerve function after incomplete local anaesthetic
blockade. For example, sensation of temperature of the skin can be lost despite unimpeded
conduction of small fibres 24. Furthermore, a surgical depth of epidural and spinal anaesthesia
can be obtained with only minor changes in somatosensory evoked potentials from the
anesthetized area 23. Previous studies have demonstrated that application of sub-blocking
concentrations of local anaesthetic will suppress normally occurring after-potentials and
after-oscillations without significantly affecting action potential conduction 24. Thus,
disruption of coding of electrical information by local anaesthetics may be a primary
mechanism for block of spinal nerve roots during spinal anaesthesia.
DRUG UPTAKE
When local anaesthetic is injected directly into the subarachnoid space during spinal
anaesthesia, it diffuses through the pia mater and penetrates through the spaces of Virchow-
Robin (extensions of the subarachnoid space accompanying the blood vessels that invaginate
the spinal cord from the pia mater) to reach the deeper dorsal root ganglia. Furthermore, a
portion of the subarachnoid drug diffuses outward through the arachnoid and dura mater to
enter the epidural space, whereas some is taken up by the blood vessels of the pia and dura
maters.25
Drug penetration and uptake is directly proportional to
- the drug mass
- CSF drug concentration
- contact surface area
- lipid content (high in spinal cord and myelinated nerves)
- local tissue vascular supply
Drug penetration is inversely related to nerve root size.
The concentration of local anaesthetic in the CSF is highest at the site of subarachnoid
injection in the case of spinal anaesthesia (generally L2-L4 levels).
DRUG DISTRIBUTION
Diffusion is the primary mechanism of local anaesthetic distribution in the CSF from areas of
high concentration (i.e., at the site of injection) toward other segments of the spinal cord with
low drug concentration.26 Rostral spread after the administration of a small local anaesthetic
dose, often evident within 10 to 20 minutes, is related to the CSF circulation time.
Longitudinal oscillations generated by the pulsations of the arteries in the skull are believed
to be responsible for CSF bulk flow.
DRUG ELIMINATION
Regression of neural blockade results from a decline in the CSF drug concentration, which in
turn is caused by nonneural tissue uptake and, most importantly, vascular absorption. Time
for block regression is also inversely correlated with CSF volume. Drug is absorbed by the
vessels in the pia mater or the epidural vessels through back diffusion before entering the
systemic circulation. No drug metabolism takes place in the CSF. The rate of elimination is
also dependent on the distribution of local anaesthetic; greater spread will expose the drug to
a larger area for vascular absorption and thus a shorter duration of action. 27
INDICATIONS
When considering spinal anaesthesia, the nature and duration of surgery, patient
comorbidities, the ease of spinal insertion (i.e., positioning and spinal pathology), and the
relative benefits and risks to the individual are important. Spinal anaesthesia is most
commonly used for patients who require surgical anaesthesia for procedures of known
duration that involve the lower extremities, perineum, pelvic girdle, or lower abdomen.
Spinal anaesthesia may be useful when patients wish to remain conscious or when
comorbidities such as severe respiratory disease or a difficult airway increase the risks of
using general anaesthesia.28
CONTRAINDICATIONS
ABSOLUTE
Patient refusal
Localized sepsis
Allergy to any of the drugs planned for administration.
A patient’s inability to maintain stillness during needle puncture, which can expose the neural
structures to traumatic injury. Raised intracranial pressure which may theoretically
predispose to brainstem herniation.29
RELATIVE
1) Neurologic Myelopathy or peripheral Neuropathy. The proof that neuraxial
anaesthesia or analgesia in the setting of pre-existing neurologic deficit can worsen
the extent of injury (so-called double-crush phenomenon) is absent.
2) Spinal Stenosis. Patients with spinal stenosis may be at increased risk of neurologic
complications after neuraxial blockade.
3) Previous spine surgery
4) Multiple Sclerosis.
5) Spina Bifida.
6) Aortic Stenosis or fixed cardiac output.
7) Hypovolemia.
8) Hematologic Thromboprophylaxis.
9) Inherited coagulopathy.
10) Infection
TECHNIQUE
Technique should be classified into a series of steps (i.e., the four Ps):
preparation
position
projection
puncture
Preparation
Informed consent must be obtained, with adequate documentation of the discussion of risk.
Resuscitation equipment must always be readily available whenever a spinal anaesthetic
procedure is performed.
The patient should have adequate intravenous access and be monitored with pulse oximetry,
non-invasive arterial blood pressure, and electrocardiogram. Record an initial set of vital
signs. Preload the patient with 1-1.5 litres of crystalloid intravenous solution.
Pre-prepared packs are now commonly used which contain fenestrated drapes, swabs and
towels, syringes, needles, filters, spinal needles, sterilizing solution, and local anaesthetic for
skin infiltration. Single use preservative free local anaesthetic ampoule should be used. Local
anaesthetics from multi dose vials or those that contain preservatives should NEVER be used
for spinal anaesthesia. Ensure that the local anaesthetic preparation is made specifically for
spinal anaesthesia.
When the local anaesthetic for subarachnoid injection is chosen, the duration of block should
be matched with both the surgical procedure and patient variables.
The most important characteristics of a spinal needle are the shape of the tip and the needle
diameter. Needle tip shapes fall into two main categories:
Cutting that cut the dura- Pitkin and Quincke-Babcock needle
Conical, pencil-point tip - Whitacre and Sprotte needles.
Spinal needles are available in a variety of sizes (from 16-30 gauge) and lengths. Commonly,
a 22 gauge needle is used in patients that are 50 years and older. A 25-27 gauge needle is
used in patients that are less than 50 years of age. A smaller needle is used in the younger
patient to decrease the incidence of post dural puncture headache. The removable stylet
occludes the lumen and avoids tracking tissue into the subarachnoid space. Blunt tipped
needles (pencil point) decrease the incidence of postdural puncture headaches compared to
cutting needle Sterility is an issue of utmost importance. One of the most common organisms
responsible for post-spinal bacterial meningitis is Streptococcus viridans, which is an oral
commensal, emphasizing the purpose of wearing a mask as part of a full aseptic technique.
Hands and forearms must be washed and all jewellery removed. A variety of solutions may
be used to clean the back, such as chlorhexidine or alcohol (alone or in combination), or
iodine solutions. Chlorhexidine and alcohol together have been concluded to be most
effective. If chlorhexidine is used, it is important that the solution is allowed to dry
completely before skin puncture because chlorhexidine is neurotoxic.
Position
The three primary patient positions include the lateral decubitus, sitting, and prone positions,
each of which has advantages in specific situations. Proper positioning is essential for a
successful block.
1. Place the patient in the position in which the neuraxial block will be performed:
sitting or lateral, with forward flexion of the lumbar spine.
2. Attempt to identify the midline and lumbar spine by
- Palpation of standard anatomical landmarks.
- Using ultrasound low-frequency (2–5 MHz), curved-array probe.
There are three positions used for the administration of spinal anaesthesia: lateral decubitus,
sitting, and prone.
Lateral Decubitus
Allows the anaesthetist to administer more sedation-less dependence on an assistant for
positioning (Never over sedate a patient)
The patient is positioned with their back parallel with the side of the OR table. Thighs are
flexed up, and the neck is flexed forward (fetal position).
Patient should be positioned to take advantage of the baricity of the spinal local anaesthetic.
Fig 6. Posture of the patient
Sitting
Used for anaesthesia of the lumbar and sacral levels (urological, perineal). Higher levels of
anaesthesia can be obtained if an appropriate dose of local anaesthetic is administered, and
the patient is quickly positioned to maximize the spread of local anaesthetic.
Identify anatomical landmarks. This may be a challenge in the obese or those with abnormal
anatomical curvatures of the spine.
Position- a stool can be provided as a footrest and a pillow placed in the lap. The assistant
helps to maintain the patient in a vertical plane while flexing the patient’s neck and arms over
the pillow, relaxing the shoulders, and asking the patient to “push out” the lower back to open
up the lumbar vertebral spaces. Care must be taken not to oversedate a patient in this position.
This will maximize the “opening” of the vertebral interspaces.
Fig 7. For a lower lumbar/sacral block (i.e. saddle block), leave the patient sitting for 5
minutes before assuming a supine position.
Prone
The prone position is used when the patient will be in this position for the surgical procedure
(i.e. rectal, perineal, lumbar procedures).
Hypobaric local anaesthetics are administered. Patient positions self, lumbar lordosis should
be minimized, a paramedian approach is often used.
Projection and Puncture
Midline approach
It relies on the ability of patients and assistants to minimize lumbar lordosis and allow access
to the subarachnoid space between adjacent spinous processes, usually at the L2-L3, L3-L4,
or the L4-L5 space. The spinal cord ends at the level of L1-L2 and so needle insertion above
this level should be avoided. The inter-crestal line is the line drawn between the two iliac
crests which corresponds to the level of the L4 vertebral body or the L4-L5 interspace.30 Once
the appropriate space has been selected, a subcutaneous skin wheal of local anaesthetic is
developed over this space, and the introducer is inserted at a slight cephalad angle of 10 to 15
degrees through skin, subcutaneous tissue, supraspinous ligament and interspinous ligament.
The introducer is grasped with the palpating fingers and steadied while the other hand is used
to hold the spinal needle like a dart, and the fifth finger is used as a tripod against the
patient’s back to prevent patient movement and unintentional insertion to a level deeper than
intended. The needle, with its bevel parallel to the midline, is advanced slowly to heighten the
sense of tissue planes traversed and to prevent skewing of nerve roots, until the characteristic
change in resistance is noted as the needle passes through the ligamentum flavum and dura.
On passing through the dura, there is often a slight “click” or “pop” sensation. The stylet is
then removed, and CSF should appear at the needle hub. The smaller the needle diameter, the
longer the wait for CSF flow, particularly if the patient is not in the sitting position. If the
CSF does not flow, the needle might be obstructed and rotation in 90-degree increments can
be undertaken until CSF appears. If CSF does not appear in any quadrant, the needle should
be advanced a few millimetres and rechecked in all four quadrants. If CSF still has not
appeared and the needle is at a depth appropriate for the patient, the needle and introducer
should be withdrawn and the insertion steps should be repeated. A common reason for failure
is insertion of the needle off the midline. After CSF is freely obtained, the dorsum of the
anaesthesiologist’s nondominant hand steadies the spinal needle against the patient’s back
while the syringe containing the therapeutic dose is attached to the needle. CSF is again
freely aspirated into the syringe, and the anaesthetic dose is injected at a rate of
approximately 0.2 mL/sec. After completion of the injection, 0.2 mL of CSF can be aspirated
into the syringe and reinjected into the subarachnoid space to reconfirm location and clear the
needle of the remaining local anaesthetic.
Paramedian approach
It exploits the larger “subarachnoid target” that exists if a needle is inserted slightly lateral to
the midline. The paramedian approach may be especially useful in the setting of diffuse
calcification of the interspinous ligament. In this approach the spinal needle traverse the skin,
subcutaneous fat, ligamentum flavum, dura mater, subdural space, arachnoid mater, and then
passes into the subarachnoid space The most common error when using the paramedian
technique is that the needle entry site is placed too far off the midline, which makes the
vertebral laminae barriers to insertion of the needle. In the paramedian approach, a skin wheal
is raised 1 cm lateral and 1 cm caudal to the corresponding spinous process. A longer needle
(e.g., 3 to 5 cm) is then used to infiltrate deeper tissues in a cephalomedial plane. The spinal
introducer and needle are next inserted 10 to 15 degrees off the sagittal plane in a
cephalomedial plane. Similar to the midline approach, the most common error is to angle the
needle too far cephalad on initial insertion. Nevertheless, if the needle contacts bone, it is
redirected slightly in a cephalad direction. If bone is again contacted, but at a deeper level,
the slight cephalad angulation is continued because it is likely that the needle is being
“walked up” the lamina. After CSF is obtained, the block is carried out in a manner similar to
that described for the midline approach.
OBESITY PREVALENCE AND PROBLEMS
Over the last three to four decades, over nutrition and obesity have been transformed from
relatively minor public health issues that primarily affected the most affluent societies to a
major threat to public health that is being increasingly seen throughout the world. The plight
of the most affected populations, like those in high-income countries in North America,
Australasia and Europe, has been well publicized. However, the more recent increases in
population obesity in low- and middle-income countries that are now increasingly being
observed have been less recognized.
Two relatively recent papers documented the global prevalence of obesity 31, 32. The Global
Burden of Metabolic Risk Factors of Chronic Diseases Collaborating Group analyzed data
from 199 countries and territories and 9.1 million adults with respect to the prevalence of
overweight and obesity between 1980 and 2008 31. During that 28-year period, the prevalence
of obesity nearly doubled worldwide. In 2008, about 1.5 billion adults were estimated to have
a body mass index (BMI) of 25 or more (about 34%). Of these, 500 million were considered
obese (about 10% in men and 14% in women).
In 2008, the highest rates of obesity in women were observed, in descending order of
magnitude, in Southern Africa, North Africa and the Middle East, Central Latin America,
North America (US and Canada) and Southern Latin America. In men, the top 5 regions were
North America (US and Canada), Southern Latin America, Australasia, Central Europe and
Central Latin America. Note that many of these regions comprise low- or middle-income
countries.
More recently, the analyses for the Global Burden of Disease Study 2013 32 further
documented that worldwide, the proportion of adults with a BMI of 25 or greater increased
between 1980 and 2013 from about 29 to 37% in men and from about 30 to 38% in women.
These estimates are slightly higher than those calculated by Finucane et al. 31. The estimates
by Ng et al. 32 may reflect further increases between 2008 and 2013, but this may also be due
to methodological differences between the two studies. In adults, the estimated prevalence of
obesity exceeded 50% in men in Tonga (Polynesia) and in women in some countries in the
Middle East, Polynesia and Micronesia. Since 2006, the increase in adult obesity seems to
have leveled off in several high-income countries, but the incidence generally remains higher
than in most low- and middle-income countries.
In the analyses for the Global Burden of Disease Study, estimates were also made of the
global prevalence of overweight and obesity in children and adolescents. Ng et al. 32 showed
that among children and adolescents in developed countries, the prevalence in 2013 was high;
about 24% of boys and 23% of girls were either overweight or obese. In general, the
prevalence of overweight and obesity had increased considerably since 1980. There were,
however, large differences in the prevalence of obesity and secular trends. The prevalence of
overweight and obesity had also increased in children and adolescents in developing
countries, from about 8% in 1980 to 13% in 2013 for boys and girls. Ng et al. 32 estimated
that in 2013, more than 2 billion people in the world were overweight or obese and about 671
million of them were obese.
About 25 years ago, obesity was considered to be particularly a problem of high-income
countries. In those high-income countries, as illustrated by Molarius et al. 33, an inverse
association was seen between obesity and socioeconomic status, particularly in women. In
contrast, in low- and middle-income countries, the prevalence of obesity tended to be low and
was confined to those with relatively high socioeconomic status 34. Monteiro et al. 34 were
among the first to show that this was no longer true in 2003 and that obesity had also become
a problem of lower socioeconomic groups, particularly of women in middle-income
countries. More recently, Dinsa et al. 35 observed that by 2012, the association between
socioeconomic status and obesity remained positive for both men and women in low-income
countries. However, in middle-income countries, the association varied greatly in men and
was generally negative in women. In children and adolescents, however, obesity remained
predominantly a problem of those with relatively high socioeconomic status in low- and
middle-income countries.
The epidemiology of obesity has for many years been difficult to study because many
countries had their own specific criteria for the classification of different degrees of
overweight. Gradually, during the 1990s, however, the BMI (weight/height2) became a
universally accepted measure of the degree of overweight, and now, identical cutoff points
are generally recommended. This most recent classification of overweight in adults by the
World Health Organization (WHO) is given in table 1[6]. In many community studies in
affluent societies, this scheme has been simplified and cutoff points of 25 and 30 are used for
descriptive purposes. Both the prevalence of a very low BMI (<18.5) and of a very high BMI
(40 or higher) is usually low, in the order of 1-2% or less.
HISTORY OF SPINAL ANAESTHESIA AND ITS EVOLUTION TO USG GUIDED
SPINAL ANAESTHESIA
Spinal anesthesia was first performed by August Bier in Germany in 1889. However, its
earliest roots can be traced to J. Leonard Corning, a New York neurologist who conceived of
the idea of spinal anesthesia by administering cocaine in the central nervous system. Rudolf
Matas first published a case report on spinal anesthesia in the United States in 1899, followed
shortly thereafter by the publication of Tate and Caglieri's study of the subarachnoid space
and their experience with spinal anesthesia. In the 2 years after Bier's report was published,
over 1000 articles on spinal anesthesia appeared in the literature 36. As in other developments
in regional anesthesia, spinal anesthesia appeared in many areas of the world at about the
same time. Six months after Bier's work was published (October 1899), Dr. J.B. Seldowitsch,
in St. Petersburg, Russia, reported four cases of spinal anesthesia for lower extremity surgery
37. Tuffier, in France, published his studies in November 1899 38, 39. These studies were little
more than case reports, offering no solutions for the troubling side effects associated with the
technique. With the development of safer drugs, sterile equipment, and aseptic techniques,
spinal anesthesia would earn a place in the armamentarium of most practicing
anesthesiologists. These early pioneers led the way, and others would follow and improve the
technique.
Spinal anaesthesia became more popular as new developments occurred, including the
introduction in 1946 of saddle block anaesthesia by Adriani and Roman-Vega 40. However, in
1947 the well-publicized case of Woolley and Roe (United Kingdom) resulted in two patients
becoming paraplegic in one day 41.
The classical method for spinal anaesthesia relies on the use of bony landmarks to identify
the level and point of entry of the spinal needle. Over the years, in experienced hands, this
method has proved to be successful and safe. The introduction of ultrasound to guide
neuraxial anaesthesia has been relatively slow compared to its use in peripheral nerve blocks
or central venous catheterization. This could be due to the technical difficulties as the bony
structures surrounding the spinal cord and dura block the path of the ultrasound beam. Many
anaesthetists are reluctant to change from the conventional landmark technique, particularly
with studies showing minimal change in the success rate between ultrasound-guided and
landmark techniques.
PRINCIPLE OF ULTRASOUND, EQUIPMENT, PROBES
Medical ultrasound (also known as diagnostic sonography or ultrasonography) is based on the
use of high-frequency sound to aid in the diagnosis and treatment of patients. Ultrasound
frequencies range from 2 to approximately 15 MHz, although even higher frequencies may be
used in some situations.
Principle of Ultrasound
Two basic principles need to be understood regarding how ultrasound is generated and an
image is formed. The first is the piezoelectric effect, which explains how ultrasound is
generated from ceramic crystals in the transducer 42, 43. An electric current passes through a
cable to the transducer and is applied to the crystals, causing them to deform and vibrate. This
vibration produces the ultrasound beam. The frequency of the ultrasound waves produced is
predetermined by the crystals in the transducer.
The second key principle is the pulse-echo principle, which explains how the image is
generated. Ultrasound waves are produced in pulses, not continuously, because the same
crystals are used to generate and receive sound waves, and they cannot do both at the same
time. In the time between the pulses, the ultrasound beam enters the patient and is bounced or
reflected back to the transducer. These reflected sound waves, or echoes, cause the crystals in
the transducer to deform again and produce an electrical signal that is then converted into an
image displayed on the monitor. The transducer generally emits ultrasound only 1% of the
time; the rest of the time is spent receiving the returning echoes 43.
Ultrasound transducers contain a range of ultrasound frequencies, termed bandwidth. For
example, 2.5-3.5 MHz for general abdominal imaging and 5.0-7.5 MHz for superficial
imaging 44.
Ultrasound waves are reflected at the surfaces between the tissues of different density, the
reflection being proportional to the difference in impedance. If the difference in density is
increased, the proportion of reflected sound is increased, and the proportion of transmitted
sound is proportionately decreased 44.
If the difference in tissue density is very different, then the sound is completely reflected,
resulting in total acoustic shadowing. Acoustic shadowing is present behind bones, calculi
(stones in kidneys, gallbladder, etc.) and air (intestinal gas) (See Fig. 1 with acoustic
shadowing).
Echoes are not produced if there is no difference in a tissue or between tissues. Homogenous
fluids like blood, bile, urine, contents of simple cysts, ascites and pleural effusion are seen as
echo-free structures.
Fig 8: A model of an ultrasonograph
CURVILINEAR PROBE
Fig 9: Curvilinear probe
PROBE MARKER
Fig 10. Probe marker
ULTRASOUND PROBES
FOR 2D IMAGING
Probe type Feature Application Centralfrequency Element
Linear typewide footprint and keep same field of view at deep part.
Vascular applicationArteria carotisarterial sclerosisvenipuncture,blood vessel visualizationBreast,ThyroidTendon,arthrogenousntraoperative,laparoscopy
2.5MHz|12MHz
64ch|256ch
Convex(Curved)Type
wide footprint, field of view will be spreaded at deep part.
Abdominal application.Transvaginal and Transrectal application.Diagnoses organs.
2.5MHz|7.5MHz
64ch|192ch
Phased(Sector)Type
small footprint, field of view will be spreaded widely at deep part.
Cardiac application.Transesophageal
application.Abdominalapplication.
Brain diagnosis
2MHz|7.5MHz
32ch|128ch
Single type
OphthalmologyTransesophageal application.Transvaginal and Transrectal application.Transurethral application.The blood flow
2MHz|22MHz
-
measurement with Doppler.
Frequency and Resolution
High frequency probe can get the fine imaging with good resolution.
However the imaging of deep part will be smudgy due to wave length is short.
Meanwhile the imaging resolution of low frequency probe is low but ultrasonic wave can
reach deep part. The scanning depth and resolution are mainly determined by the frequency
of probe.
Frequency ResolutionPenetratio
n
Possible
scanning depth
High Fine Weak Shallow
Low Rough Strong Deep
Ultrasound Imaging of the spine (various planes of US guided spinal anaesthesia)
Basic considerations
Because the spine is located at a depth, US imaging of the spine typically requires the use of
low-frequency ultrasound (2-5 MHz) and curved array transducers. Low-frequency US
provides good penetration but unfortunately, it lacks the spatial resolution at the depth (5-7
cm) at which the neuraxial structures are located. The osseous framework of the spine, which
envelops the neuraxial structures, reflects much of the incident US signal before it reaches the
spinal canal, presenting additional challenges in obtaining good quality images. Recent
improvements in US technology, the greater image processing capabilities of US machines,
the availability of compound imaging, and the development of new scanning protocols have
improved the ability to image the neuraxial space significantly. As a result, today it is
possible to reasonably accurately delineate the neuraxial anatomy relevant for CNB.
Ultrasound Scan Planes
Figure 11. Anatomic planes of the body
Gross anatomy of the lumbar spine 45
The lumbar spine comprises five vertebrae (L1–L5).Each vertebra has two functional parts: a
vertebral body and a vertebral arch. Each vertebral arch is composed of a spinous process,
pedicles laminae, transverse processes, and superior and inferior articular processes. The
lumbar spinous processes are broad (in the superior–inferior dimension), flat, oblong-shaped
structures that project posteriorly from the union of the laminae. The superior and inferior
articular processes extend posteriorly in a cranial and caudad direction, respectively, from the
point at which the pedicles and laminae fuse. Long, slim transverse processes protrude
laterally from the vertebral arch at the junction of the laminaeandpedicles. The laminae slope
from posterior to anteriorin acaudad – to –cephalad direction. In contrast to the thoracic
spine, the laminae and spinous processes of adjacent lumbar vertebrae do not overlap. This
gives rise to distinct gaps—the interlaminar and interspinous spaces—through which the
vertebral canal can be accessed. These spaces can be enlarged by forward flexion of the
lumbar spine.
The anterior wall of the vertebral canal is formed by the posterior longitudinal ligament and
the posterior surface of the vertebral bodies and intervertebral discs.
The posterior wall of the vertebral canal comprises the laminae and the ligamentum flavum,
which forms a thick, fibrous bridge over the interlaminar spaces
Pre procedural USG scanning45
The patient is placed in a sitting or lateral decubitus position for the block, with forward
flexion at the lumbar spine. This eliminates lumbar lordosis, opens up the lumbar interspinous
spaces, and generally improves the acoustic window. The use of a curved, low-frequency (2–
5 MHz) probe is recommended to provide enhanced beam penetration, and wide field of
view, both of which improve identification of anatomy.
Sonoanatomy of the spine and ultrasonographic views for neuraxial block
Bone is not penetrated by ultrasound and casts a dense acoustic shadow. The contours of the
posterior bony surfaces of the lumbar vertebra thus have characteristic patterns of acoustic
shadowing that are key to interpretation of the sonoanatomy of the lumbar spine.
Visualization of the vertebral canal is only possible through the soft-tissue acoustic windows
of the interlaminar and interspinous spaces. There are five basic ultrasonographic views of the
spine that can be systematically obtained:
(i) parasagittal transverse process view,
(ii) parasagittal articular process view,
(iii) parasagittal oblique (interlaminar) view,
(iv) transverse spinous process view,
(v) transverse interlaminar (interspinous) view.
The parasagittal oblique (interlaminar) view (PSO view) and the transverse
interlaminar/interspinous view (TI view) are the most important views in clinical practice
since they provide a view of the neuraxial structures through acoustic windows. These
structures include: ligamentum flavum, posterior dura, spinal canal, anterior dura, and
posterior longitudinal ligament.45
Parasagittal transverse process view
The ultrasound probe is placed over the lower lumbar spine in a parasagittal orientation, a 3-4
cm lateral to the midline. The transverse processes appear as finger-like acoustic shadows,
separated by the striated psoas major muscle, which lies deep to the transverse processes. The
erector spinae muscle lies superficial (posterior) to the transverse processes
Fig 12. Parasagittal transverse process view
FIG Parasagittal transverse process view (A) with corresponding anatomical section(B) and
ultrasound probe orientation(c)TP; transverse processes ESM, erector spinae muscle; Pm,
Psoas major muscle; L, Lamina; SP, spinous process
Parasagittal articular process view 45
Maintaining a strictly sagittal orientation, the ultrasound probe is now moved medially until
the acoustic shadows of the transverse processes give way to a pattern of continuous hump-
like shadows, formed by the overlapping superior and inferior articular processes. Observe
the transition from the discontinuous pattern of the transverse process view to the continuous,
hyperechoic line formed by the articular processes The articular process view is also
distinguished from the transverse process view by the more superficial depth of the acoustic
shadows
Fig 13. Parasagittal articular process view (A) with corresponding anatomical section (B)
and ultrasound probe orientation(C) AP; articular processes TP; transverse processes ESM,
erector spinae muscle; Pm, Psoas major muscle; L, Lamina; SP, spinous process
Parasagittal oblique (interlaminar) view (PSO view) 45
Starting from the parasagittal articular process view, the ultrasound probe is now slowly tilted
to direct the beam in a lateral to-medial direction until the humped pattern of the articular
processes changes into a ‘sawtooth’ pattern of acoustic shadows. The ‘teeth’ correspond to
the down sloping laminae and the gaps between represent the interlaminar spaces. The PSO
view therefore gives us an acoustic window into the vertebral canal. Structures that are
penetrated by the ultrasound beam are (from posterior to anterior): ligamentum flavum,
epidural space, dura (posterior), intrathecal space, dura (anterior), and posterior longitudinal
ligament. The ligamentum flavum, epidural space, and posterior dura appear as a hyperechoic
linear structure and are collectively referred to as the posterior complex; while the anterior
dura, posterior longitudinal ligament and posterior border of the vertebral body and discs
constitute a deeper hyperechoic linear structure called the anterior complex. In the PSO view,
slide the probe caudad until the sacrum is identified as a long horizontal hyperechoic line.
This is an important and easily recognizable ultrasonographic landmark. The gap between the
hyperechoic line of the sacrum and the ‘sawtooth’ of the adjacent L5lamina represents the
L5–S1 interspace. Starting at this point, each interspace is centered on the ultrasound screen
and a corresponding skin mark made at the midpoint of the long edge of the probe to indicate
its location.
Fig 14. Parasagittal oblique (interlaminar) view (PSO view) (A) with corresponding
anatomical section(B) and ultrasound probe orientation(c) ESM; erector spinae muscle; L,
Lamina; AC, anterior complex; PC, posterior complex
Transverse spinous process view
In order to obtain a transverse spinous process view, the ultrasound probe is placed in a
horizontal orientation with the centre of the probe placed over the midline. If the ultrasound
beam is placed over a spinous process, the tip of the spinous process appears as a superficial
hyperechoic ‘cap’ surmounting at all dense acoustic shadow. Lateral to the spinous process,
the erector spinae muscle can be visualized, with the lamina of the vertebral body casting its
own dense acoustic shadow at the level of the anterior border of the erector spinae muscle.
Fig 15. Transverse spinous process view(A) with corresponding anatomical section(B) and
ultrasound probe orientation(c) ESM; erector spinae muscle; L, Lamina; SP, spinous process
Transverse interlaminar/interspinous view (TI view)45
Starting from the transverse spinous process view, the TI view is obtained by sliding the
probe in a cephalad or caudad direction as needed until the beam enters the acoustic window
between the spinous processes. A slight cephalad tilt in the horizontal plane may have to be
applied to compensate for the angulation of the spinous processes. The interspinous ligament
appears as a hypoechoic midline stripe. The hypoechoic intrathecal space is bounded
anteriorly and posteriorly by the parallel hyperechoic lines of the anterior and posterior
complexes, respectively
Centre the neuraxial midline on the screen. – Make skin marks at the:
(i) midpoint of the probe’s long edge(corresponding to the neuraxial midline);
(ii) midpoint of the probe’s short edge (corresponding to the interspinous
/interlaminar space).
The intersection of these two marks gives the needle insertion point for a midline
approach. – Estimate needle insertion depth by measuring the distance from skin to the
deep aspect of the posterior complex. – If a satisfactory TI view (i.e.one in which the
posterior complex is visible)cannot be obtained, the location of the interlaminar space
may be instead determined from the PSO view, which usually offers a larger and better
window into the vertebral canal. This is the same skin marking used to indicate the
identity of the intervertebral levels (see point 5). The intersection of this mark with the
skin mark of the neuraxial midline obtained in the TI view is a suitable alternative needle
insertion point for a midline approach
Fig 16. Transverse interlaminar/interspinous view (TI view) (A) with corresponding
anatomical section(B) and ultrasound probe orientation(c)TP, transeverse process;AP,
articular process L, Lamina; AC, anterior complex; PC, posterior complex ESM; erector
spinae muscle; ITS, intrathecal space
Needle insertion – 45
Insert the needle at the marked site in the midline. Maintain the same cephalad angle with
respect to the horizontal plane that was applied to the probe to obtain the optimal TI view. –
Needle insertion and re-direction should be guided by tactile feedback(contact with bone,
‘feel’ of the ligamentum flavum, loss of resistance, etc.) in a similar manner to the
conventional landmark-based technique of neuraxial block. – Ensure that needle redirections
are not inappropriately large, and that there is no deflection from its intended trajectory,
particularly when using smaller-gauge spinal needles.
Fig 17. Needle insertion for a midline needle approach at the intersection point between
the skin markings of the neuraxial midline and the interspinous and interlaminar space
MOST RELEVANT STUDIES:
1. Furness G et al. 46 intended to know the accuracy of ultrasound imaging to identify
lumbar intervertebral level in 50 patients undergoing X-ray of the lumbar spine. Using an
ultraviolet marker, an anaesthetist attempted to mark the L2/3, L3/4 and L4/5
intervertebral spaces. A radiologist unaware of these marks attempted to mark the same
spaces with the aid of ultrasound imaging. X-ray-visible pellets were taped to the back at
the various marks prior to lateral lumbar X-ray. Ultrasound imaging identified the correct
level in up to 71% of cases, but palpation was successful in only 30% (p < 0.001). Up to
27% of marks using the palpation method were more than one spinal level above or
below the assumed level using palpation, but none were more than one level high or low
using ultrasound guidance.
2. Nomura JT et al. 47 wanted to know whether ultrasound-assisted LP would increase the
success rate and ease of performing LP with a greater benefit in obese patients through
randomized, prospective, double-blind study conducted at the emergency department of a
teaching institution. Patients were randomized to undergo LP using palpation landmarks
(PLs) or ultrasound landmarks (ULs). Data collected included age, body mass index,
number of attempts, ease of performance and patient comfort on a 10-cm. A total of 46
patients were enrolled, 22 randomized to PLs and 24 to ULs. There were no differences
between the groups in mean age or body mass index. Six of 22 attempts failed with PLs
versus 1 of 24 with ULs (RR, 1.32; 95% confidence interval, 1.01-1.72). In 12 obese
patients, 4 of 7 PL attempts failed versus 0 of 5 UL attempts (RR, 2.33; 95% confidence
interval, 0.99-5.49). The ease of the procedure was better with ULs versus PLs. There
were no statistical differences in the number of attempts, traumatic LPs, patient comfort,
or procedure length. They concluded that the use of ultrasound for LP significantly
reduced the number of failures in all patients and improved the ease of the procedure in
obese patients.
3. Chin KJ et al. 48 assessed real-time ultrasound-guided spinal anesthesia in patients with
a challenging spinal anatomy. They described two patients with an abnormal spinal
anatomy in whom ultrasound-assisted spinal anaesthesia was unsuccessful. Successful
dural puncture was subsequently achieved using a technique of real-time ultrasound-
guided spinal anaesthesia. This may be a useful option in patients in whom landmark-
guided and ultrasound-assisted techniques have failed.
4. Arzola C et al. 49 did a randomized controlled trial to assess spinal ultrasound versus
palpation for epidural catheter insertion in labour by a group of trainees. A group of 17
second-year anaesthesia residents and five anaesthesia fellows underwent a training
programme in ultrasound assessment of the spine. Parturients with easily palpable
lumbar spines were randomized to either ultrasound or palpation group. Residents and
fellows performed both the assessment (ultrasound or palpation) and the epidural
procedure. On the whole, they analysed 128 epidural catheter insertions (residents 84,
fellows 44). There was no difference in median (interquartile range, IQR) epidural
insertion time between the ultrasound and palpation groups [174 (120 to 241) versus 180
(130 to 322.5) s, respectively; P = 0.14]. The number of interspace levels attempted and
needle passes were also similar in both groups. The total procedural time was longer in
the ultrasound group. They concluded that the use of preprocedural spinal ultrasound by
a cohort of anaesthesia trainees did not improve the ease of insertion of labour epidural
catheters in patients with easily palpable lumbar spines, as compared with the traditional
palpation technique based on anatomical landmarks.
5. Srinivasan KK et al. 50 compared Conventional Landmark-Guided Midline and
Preprocedure Ultrasound-Guided Paramedian Techniques in Spinal Anesthesia among
100 patients scheduled for elective total joint replacements (hip and knee). They were
randomized into group C (conventional) and group P (preprocedural ultrasound-guided
paramedian technique) with 50 in each group. In group C, spinal anesthetic was done via
the midline approach using clinically palpated landmarks. In group P, a preprocedural
ultrasound scan was used to mark the paramedian insertion site, and spinal anesthetic
was performed via the paramedian approach. The average number of passes in group P
was approximately 0.34 times that in group C, a difference that was statistically
significant (P = 0.01). Similarly, the average number of attempts in group P was
approximately 0.25 times that of group C (P = 0.0021). In group P, on an average, it took
81.5 (99% confidence interval, 68.4-97 seconds) seconds longer to identify the
landmarks than in group C (P = 0.0002). It was opined that routine use of paramedian
spinal anesthesia in the orthopedic patient population undergoing joint replacement
surgery, guided by preprocedure ultrasound examination, significantly decreases the
number of passes and attempts needed to enter the subarachnoid space.
6. Grau T et al. studied the real-time ultrasound control of the procedure for puncture
among thirty parturients scheduled for Caesarean section who were randomized to three
equal groups. Ten control patients received conventional combined spinal-epidural
anaesthesia. Ten of the remaining patients received ultrasonic scans by an offline scan
technique, and 10 received online imaging of the lumbar region during epidural puncture.
The number of attempts to advance the needle to achieve a successful puncture was
measured and compared, as well as the number of vertebral interspaces punctured before
successful entry into the epidural space. Results showed that in the ultrasound group, the
reduction in the number of attempts at puncture was significant (P < 0.036). The number
of interspaces necessary for puncture was reduced (P < 0.036) in the ultrasound online
group compared with controls. The number of spinal needle manipulations was
significantly reduced (P < 0.036). The authors noted the real-time ultrasonic scanning of
the lumbar spine is an easy procedure and it provides an accurate reading of the location
of the needle tip and facilitates the performance of combined spinal-epidural anaesthesia.
7. Srinivasan KK et al. 51 did a randomized controlled trial on the superiority of pre-
procedure ultrasound-guided paramedian spinal anaesthesia at L5-S1 over landmark-
guided midline approach among120 consenting patients scheduled for elective total joint
replacements (Hip and Knee). They were randomized into either Group C where
conventional midline approach with palpated landmarks was used or Group P where pre-
procedural ultrasound was used to perform subarachnoid block by paramedian approach
at L5-S1 interspace (real time ultrasound guidance was not used). There was no
difference in primary outcome (difference in number of passes) between the two groups.
Similarly there was no difference in the number of attempts (i.e., the number of times the
spinal needle was withdrawn from the skin and reinserted). The first pass success rates (1
attempt and 1 pass) was significantly greater in Group C compared to Group P [43% vs.
22%, P = 0.02]. They concluded that routine use of paramedian spinal anaesthesia at L5-
S1 interspace, guided by pre-procedure ultrasound, in patients undergoing lower limb
joint arthroplasties did not reduce the number of passes or attempts needed to achieve
successful dural puncture.
8. Niazi AU et al. 52 investigated whether SonixGPS(R), a new needle tracking system that
displays needle tip position on the ultrasound screen might aid performance of real-time
ultrasound-guided spinal anesthesia. Twenty patients with body mass index < 35 kg/m(2)
undergoing elective total joint arthroplasty under spinal anesthesia were recruited.
Following a pre-procedural ultrasound scan, a 17G proprietary needle-sensor assembly
was inserted in-plane to the transducer in four patients and out-of-plane in 16 patients.
Then a 25G 120 mm Whitacre spinal needle was inserted through the 17G SonixGPS(R)
needle. The findings revealed an overall success rate of 14/20 (70%) was with two
failures (50%) and four failures (25%) in the in-plane and out-of-plane groups
respectively. Dural puncture was successful on the first skin puncture in 71% of patients
and in a single needle pass in 57% of patients. The median total procedure time was 16.4
and 11.1 min in the in-plane and out-of-plane groups respectively. The SonixGPS(R)
system simplifies real-time ultrasound-guided spinal anesthesia to a large extent,
especially the out-of-plane approach. Nevertheless, it remains a complex multi-step
procedure that requires time, specialized equipment, and a working knowledge of spinal
sonoanatomy.
9. Wong SW et al. 53 elaborated on a case report on a patient with difficult spinal anatomy
about the use of the SonixGPS system for successful performance of real-time
ultrasound-guided spinal anesthesia. The patient was a 67-yr-old male was admitted to
our hospital to undergo revision of total right hip arthroplasty. A 19G 80-mm proprietary
needle (Ultrasonix Medical Corp, Richmond, BC, Canada) was inserted and directed
through the paraspinal muscles to the ligamentum flavum in plane to the ultrasound
beam. Successful dural puncture was achieved on the second attempt, as indicated by a
flow of clear cerebrospinal fluid. The patient tolerated the procedure well, and the spinal
anesthetic was adequate for the duration of the surgery. The SonixGPS is a novel
technology that can reduce the technical difficulty of real-time ultrasound-guided
neuraxial blockade.
10. Weed JT et al. 54 performed a pre-procedure ultrasound examination of the spine on 60
patients undergoing lower extremity orthopaedic surgery under spinal anaesthesia to test
whether the posterior longitudinal ligament or vertebral body easily with ultrasound
would be associated with difficulty placing a spinal anaesthetic. The procedure difficulty
was defined by total procedure time (> 400 s) and number of needle passes (>/= 10)
required to achieve return of cerebrospinal fluid, or abandonment of the procedure due to
unsuccessful dural puncture. When images of the posterior longitudinal ligament were
poor (low score group), the mean (SD) number of passes was 21.2 (30.6), compared with
4.8 (7.5) with good ultrasound images (high score group) (p < 0.01). The mean (SD) time
for placement was 420 (300) s in the low score group vs 176 (176) s in the high score
group (p < 0.01).
11. Creaney M et al. compared the pre-procedural lumbar ultrasonography with landmark
palpation to locate the needle insertion point in women with impalpable lumbar spinous
processes presenting for caesarean delivery. Twenty patients were randomized to
palpation or ultrasound. There were significantly fewer needle passes in the ultrasound
group (median 3 [IQR 1.8-3.2]) compared to the palpation group (median 5.5 [IQR 3.2-
7.2] (P=0.03)). More time was required to locate the needle insertion point in the
ultrasound group (ultrasound 91.8+/-30.8s vs. palpation 32.6+/-11.4s, P<0.001). There
was no difference in the total procedural time between groups (ultrasound 191.8+/-49.4s
vs. palpation 192+/-110.9s, P=0.99). The use of ultrasonography to locate the needle
insertion point reduced the number of needle passes in women with impalpable lumbar
spinous processes undergoing elective caesarean delivery under spinal anaesthesia. Its
use did not prolong overall procedural time.
12. Chin KJ et al. 55 studied how far ultrasound-assisted approach facilitates spinal
anesthesia among fifty patients undergoing elective total joint arthroplasty. Using a
curved-array 2-5 MHz transducer, the lumbar spine was imaged in two views, i.e.,
longitudinal parasagittal (LP) and transverse midline (TM). The findings showed that the
surface landmarks were difficult or impossible to palpate in 38% of the patients. Dural
puncture was achieved with one needle insertion attempt and within two needle insertion
attempts in 84% and 98% of the patients, respectively. The ultrasound-measured depth to
the intrathecal space correlated well with the actual needle insertion depth (concordance
correlation coefficient = 0.82, accuracy 0.95, precision 0.86), with a tendency to
overestimate the depth by just 2.1 +/- 5.4 mm. They concluded that ultrasound imaging
of the lumbar spine provides clinically useful information that can facilitate spinal
anesthesia in the older orthopedic patient population.
13. Chin KJ et al. 56 assessed if ultrasound imaging facilitates spinal anesthesia in adults
with difficult surface anatomic landmarks. They recruited 120 orthopedic patients with
one of the following: body mass index more than 35 kg/m(2) and poorly palpable
spinous processes; moderate to severe lumbar scoliosis; or previous lumbar spine
surgery. Patients were randomized to receive spinal anesthetic by the conventional
surface landmark-guided technique (group LM) or by an ultrasound-guided technique
(group US). The first-attempt success rate was twice as high in group US than in group
LM (65% vs. 32%; P < 0.001). There was a two-fold difference between groups in the
number of needle insertion attempts (group US, 1 [1-2] vs. group LM, 2 [1-4]; P < 0.001)
and number of needle passes (group US, 6 [1-10] vs. group LM, 13 [5-21]; P = 0.003).
More time was required to establish landmarks in group US (6.7 +/- 3.1; group LM, 0.6
+/- 0.5 min; P < 0.001). Preprocedural ultrasound imaging facilitates the performance of
spinal anesthesia in the nonobstetric patient population with difficult anatomic
landmarks.
14. Ansari T et al. 57 pregnant patients are in exclusion criteria compared the use of
ultrasound to the landmark method in patients with no anticipated technical difficulty,
presenting for caesarean delivery under spinal anaesthesia among total of 150 pregnant
women for the randomized, controlled study. Patients were randomized to either the
Ultrasound Group (n=75) or the Landmark Group (n=75). In both groups the level of L3-
4 or L4-5 was identified by ultrasound (transverse and longitudinal approach) or
palpation. Findings revealed that average procedure time, number of skin punctures and
needle passes, were similar in both groups. When performed by anaesthetists experienced
in both ultrasound and landmark techniques, the use of ultrasound does not appear to
increase the success rate of spinal anaesthesia, or reduce the procedure time or number of
attempts in obstetric patients with easily palpable spines.
15. Brinkmann S et al. 58 in their case series reported performance of the SonixGPS system
for real-time ultrasound-guided spinal anesthesia in 20 American Society of
Anesthesiologists' class I-II patients scheduled for lower limb joint arthroplasty.
Successful spinal anesthesia for joint arthroplasty was achieved in 18/20 patients, and 17
of these required only a single skin puncture. In 7/20 (35%) patients, dural puncture was
achieved on the first needle pass, and in 11/20 (55%) patients, dural puncture was
achieved with two or three needle redirections. Median (range) time taken to perform the
block was 8 (5-14) min. All patients with successful spinal anesthesia found the
technique acceptable and were willing to undergo a repeat procedure if deemed
necessary. This case series showed that real-time ultrasound-guided spinal anesthesia
with the SonixGPS system is possible within an acceptable time frame. It proved
effective with a low rate of failure and a low rate of complications.
16. Soni NJ et al. 59 reviewed the literature and describe techniques to use ultrasound to
guide performance of lumbar puncture (LP). They noted that Ultrasound mapping of the
lumbar spine reveals anatomical information that is not obtainable by physical
examination, including depth of the ligamentum flavum, width of the interspinous
spaces, and spinal bone abnormalities, including scoliosis. Using static ultrasound, the
lumbar spine anatomy is visualized in transverse and longitudinal planes and the needle
insertion site is marked. Using real-time ultrasound guidance, the needle tip is tracked in
a paramedian plane as it traverses toward the ligamentum flavum. Future research should
focus on efficient methods to train providers, cost-effectiveness of ultrasound-guided LP,
and the role of new needle-tracking technologies to facilitate the procedure.
17. Lim YC et al. 8 studied whether pre-procedural ultrasound scanning improved first-
attempt success rate and decreased time taken for the procedure in the general adult
population. Patients were randomised into two groups, ultrasound-guided identification
of landmarks (Ultrasound Group) and manual palpation of landmarks (Manual Palpation
Group). Finding showed that the first-attempt success rate was 64% in the Ultrasound
Group and 52% in the Manual Palpation Group (P=0.16). Time taken for procedure was
shorter in the Ultrasound Group compared to the Manual Palpation Group (2.9±3.6
minutes versus 3.9±3.7 min, P= 0.007). Patient satisfaction was higher in the Ultrasound
Group. There were no differences in complications. The current use of pre-procedural
ultrasound scanning will probably be limited to selected patients where spinal
anaesthesia may be technically challenging with conventional methods.
MATERIALS AND METHODS
STATISTICAL METHODS:
Number of attempts, number of passes time taken for identifying landmark (sec), time for
successful lumbar puncture (sec), were considered as outcome variable.
Procedure (Land Mark (LM), Ultra Sound Guided (US)) was considered as primary
explanatory variable.
Normality test for quantitative variables:
A Shapiro- Wilk’s test (p>0.05) and a visual inspection of their histograms, normal Q-Q plots
and box plots showed that age, BMI, number of passes, number of attempts, time taken for
identifying space (sec), time for successful lumber puncture(sec) were non-normally
distributed for study group.
The comparison between procedure (LM, US) and age, BMI number of passes, number of
attempts, time taken for identifying space (sec) and time for successful lumber puncture (sec)
parameters was assessed by comparing the median values. Mann Whitney U test was used to
assess statistical significance. Data was also represented using appropriate diagrams like
comparative box plots and bar chart.
Comparison of categorical variable:
The association between procedure and gender, success was assessed by cross tabulation and
comparison of percentages. Chi square test was used to test statistical significance. Data was
also represented using appropriate diagram like clustered bar chart.
P value < 0.05 was considered statistically significant. IBM SPSS version 22 was used for
statistical analysis60.
RESULTS:A total of 80 subjects were included in the final analysis Table 1: Descriptive analysis of group in study population (N=80)Group Frequency PercentagesLand Mark ( LM) 40 50.00%Ultra Sound Guided (US) 40 50.00%
Among the study population, 40 (50%) were land mark (LM) and remaining 40 (50%) were
ultra sound guided (US). (Table 1)
Table 2: Comparison of median value in age between study group (N=80)
Group AgeMedian (IQR)
Mann Whitney U test (P value)
Land mark ( LM) 59.50 (52.25, 65.75) 0.965Ultra sound guided (US) 58.50 (50.25, 65.75)
Among the people with, land mark (LM), the median age was 59.50 (IQR 52.25 to 65.75) and
it was 58.50 (IQR 50.25 to 65.75) in people with ultra sound guided (US). The difference in
the age between group was statistically not significant (P Value 0.965). (Table 2 & Figure 1)
Figure 1: Box plots of comparison of median value in age between study group (N=80)
Table 3: Comparison of group with gender of study population (N=80)
GenderGroup
Chi square P-valueLM(N=40) US (N=40)
Male 15 (37.5%) 12 (30%)0.503 0.478
Female 25 (62.5%) 28 (70%)
In land mark (LM) group 15 (37.5%) were in male, and remaining 25 (62.5%) were in
female. In ultra sound guided (US) group 12 (30%) were in male, and remaining 28 (70%)
were female. The difference in the proportion of group between gender was statistically not
significant (P value 0.478). (Table 3 & figure 2)
Figure 2: Cluster bar chart of comparison of group with gender of study population (N=80)
Land Mark (LM) Ultra Sound Guided (US )0.00%
10.00%20.00%30.00%40.00%50.00%60.00%70.00%80.00%
38%30%
63%70%
Male Female
Group
Perc
enta
ge
Table 4: Comparison of median value in BMI between study group (N=80)
Group BMIMedian (IQR)
Mann Whitney U test (P value)
Land mark ( LM) 34.9 (33.1, 36.40) 0.958Ultra sound guided (US) 34.9 (33.1, 36.35)
Among the people with, land mark (LM), the median BMI was 34.9 (IQR 33.1 to 36.40) and
it was 34.9 (IQR 33.1 to 36.35) in people with ultra sound guided (US). The difference in the
BMI between group was statistically not significant (P Value 0.958). (Table 4 & Figure 3)
Figure 3: Box plots of comparison of median value in BMI between study group (N=80)
Table 5: Comparison of median value in number of attempts between study group (N=80)
Group Number of AttemptsMedian (IQR)
Mann Whitney U test (P value)
Land mark ( LM) 3 (2,4)<0.001
Ultra sound guided (US) 2 (1,2)
Among the people with, land mark (LM), the median number of attempts was 3 (IQR 2 to 4)
and it was 2 (IQR 1 to 2) in people with ultra sound guided (US). The difference in the
number of attempts between group was statistically significant (P Value <0.001) (Table 5 &
Figure 4)
Figure 4: Bar chart of comparison of median value in number of attempts between study group (N=80)
Land mark ( LM) Ultra sound guided (US)0
0.5
1
1.5
2
2.5
3
3.53
2
Group
Num
ber
of A
ttem
pts (
Med
ian)
Table 6: Comparison of median value in number of passes between study group
Group Number of PassesMedian (IQR)
Mann Whitney U test (P value)
Land mark ( LM) (N=40) 5.50 (4, 6.75) <0.001Ultra sound guided (US) (N=40) 4 (3,4)
Among the people with, land mark (LM), the median number of passes was 5.50 (IQR 4 to
6.75) and it was 4 (IQR 3 to 4) in people with ultra sound guided (US). The difference in the
number of passes between group was statistically significant (P Value <0.001). (Table 6 &
Figure 5)
Figure 5: Bar chart of Comparison of median value in number of passes between study group
Land mark ( LM) (N=38) Ultra sound guided (US) (N=37)0
1
2
3
4
5
6 5.5
4
Group
Num
ber
of P
asse
s Med
ian
Table 7: Comparison of median value in time taken for identifying space (sec) between study group
GroupTime taken for
Identifying Space (sec)Median (IQR)
Mann Whitney U test (P value)
Land mark ( LM) (N=38) 38.19 (25.05, 57.95)<0.001Ultra sound guided (US)
(N=37) 78.35 (60.20, 90.67)
Among the people with, land mark (LM), the median identifying space was 38.19 sec (IQR
25.05 to 57.95) and it was 78.35 sec (IQR 60.20, 90.67) in people with ultra sound guided
(US). The difference in the identifying space (sec) between group was statistically significant
(P Value <0.001). (Table 7 & Figure 6)
Figure 6: Box plots of comparison of median value in time taken for identifying space (sec) between study group
Table 8: Comparison of median value in time for successful lumber puncture (sec)between study group
GroupTime for successful lumber
puncture (sec)Median (IQR)
Mann Whitney U test (P value)
Land mark ( LM) (N=38) 88.31 (51.74, 120.19)0.048Ultra sound guided (US)
(N=37) 64.32 (51.46, 88.31)
Among the people with, land mark (LM), the median spinal injection was 88.31 sec (IQR
51.74 to 120.19) and it was 64.32 sec (IQR 51.46 to 88.31) in people with ultra sound guided
(US). The difference in the time for successful lumber puncture (sec) between group was
statistically significant (P Value 0.048). (Table 8 & Figure 7)
Figure 7: Box plots of comparison of median value in time for successful lumber puncture between study group
Table 9: Comparison of group with success (N=80)
SuccessGroup
Chi square P-valueLand Mark (LM) Ultra Sound Guided
(US)Success 38 (95%) 37 (92.5%)
0.213 0.644Converted to GA 2 (5%) 3 (7.5%)
Among land mark (LM) group, 2 (5%) people were converted to GA. Among ultra sound
guided (US) group, 3 (7.5%) people were converted to GA. Hence these patients were
excluded from subsequent analysis.
Note: 38 patients in land mark (LM) group and 37 patients in ultra sound guided (US) group
were analysed.
DISCUSSION
Since the first description of spinal anaesthesia in humans by Bier in 189861, the identification
of the subarachnoid space has traditionally been achieved by an anatomical landmark guided
approach. While surface anatomical landmarks are useful, they are nevertheless surrogate
markers. They may be difficult to palpate in obese patients as well as those with edema.
Landmark-based approaches do not take into account all anatomical variations or
abnormalities, and frequently lead to incorrect identification of a given lumbar interspace 62.
Accurate identification of the subarachnoid space is paramount as multiple attempts at needle
placement may cause patient discomfort, higher incidence of spinal hematoma, postdural
puncture headache 62, and trauma to neural structures 63. Having alternative approaches may
help improve success and mitigate the limitations of the current techniques.
For the identification of a safe lumbar interspace, clinicians often rely on three beliefs.
Firstly, an imaginary line (described by Tuffier) joining the iliac crests is assumed to be close
to the fourth lumbar spine, but it may cross higher or lower64. Secondly, classical teaching is
that the spinal cord ends at L1–2, but it has been known for over half a century4that this is the
mean position of a normal distribution. Several series describe the spinal cord extending to
the body of L3 in 1–3% of cases, and to L2 or lower in almost 50% of cases, with increased
variability in women65. Thirdly, reliance may be placed on a lack of paraesthesia, but this
confidence may be misplaced if the latter does not occur during cordotomy with a 22 G
needle until electrical stimulation is applied66. A technique to improve the localization of a
lumbar interspace would be an advantage.
Neuraxial ultrasound is a recent development in the field of regional anesthesia. This
technique allows the operator to preview spinal anatomy, identify midline, and determine the
inter- space for needle insertion. A “pre-procedural” ultrasound examination of the spine
accurately delineates the underlying relevant anatomy, thus aiding in successful insertion of a
spinal or epidural needle; this has also been termed “ultrasound-assisted ” neuraxial blockade.
Since 2011, Only five randomized controlled trials and one cohort study have been published
on use pre-procedural ultrasound to guide spinal anaesthesia in non-obstetric patients8, 50, 56, 67-
69. Among these, four studies looked at the routine use of US approach8, 50, 67, 69 and two
others were performed in patients in whom the procedure was presumed to be difficult. While
the use of US method in patients with difficult anatomy has been largely positive, the data on
its routine use are equivocal8, 50, 67, 69.
Of the total 80 patients included in the study, equal proportion of (40 each) belonged to
landmark (LM) guided and US-guided spinal anaesthesia groups. Comparatively all studies
have included more patients. In their randomized controlled trial, Abdelhamid et al.67 studied
90 patients, it was 10050 and 12069 in two separate studies by Srinivasan et al. while Lim et
al.8 studied 170 patients. However, Chin et al.56 in their clinical trial studied lesser (60)
patients undergoing lower limb orthopedic surgery.
Regarding age of the patients, the median age of those receiving LM guided (59.50 years)
was similar to that of US-guided group (58.50 years). In comparison the age of the subjects
was higher (68 years in LM group and 65.3 years in US-guided group) in the study by
Srinivasan et al.69 and Srinivasan et al.50 (65.2 years in the former and 63.4 years in the latter
group), in that of Chin et al. 56 (61.2 years in LM group, 62.5 years in US group) and in the
study by Lim et al.8 (62.2 years). However, Abdelhamid et al.67 study had younger patients
(34.7 years).
Gender wise females were higher in both the groups as compared to males (62.5% females vs
37.5% males in LM group) (70% females vs 30% males in US guided group). This is similar
to that of Chin et al. 56 who had 63.3% females in the former group and 66.6% in the latter.
Contrastingly Srinivasan et al. 50 had equal proportion of either sex in the LM group (52%
males and 48% females), however, in the US group, proportion of females was higher (60%
vs 40%), which was similar to our findings.
The median BMI of patients in both the groups was same (34.9), indicating that most of them
were obese. Contrastingly Srinivasan et al.69 observed a lesser average BMI in both LM
group (30.6) and US-guided group (30.1). Also in their earlier study, Srinivasan et al. 50 noted
the overall BMI of subjects in LM group (30.14) and US group (28.57) being lower.
However, Chin et al. 56 reported a higher BMI (obese patients) in both groups (41.2 in the
former group, 38.5 in the latter).
Regarding the number of attempts for successful anaesthesia, Srinivasan et al.69 noted equal
attempts in both groups (2 in LM group and 2.07 in US-guided group. In comparison, the
number of attempts was similar in the study among the US-guided group (2), which was
however, significantly (P Value <0.001) lesser when compared to the LM group (3).
However, in their previous study Srinivasan et al. 50 reported US method required
significantly (P=0.0021) lesser attempts (1.28) compared to the LM method (1.98). Chin et
al. 56 also found the US guided method requiring significantly (P Value <0.001) lesser
attempts (1) compared to LM method (2).
The number of passes were significantly (P Value <0.001) more in LM group (5.50)
compared to the US-guided group (4). A similar finding of 4 passes was observed in the
study by Srinivasan et al. 50 for the latter method, however, the former required considerably
more passes (8.2) and the difference was statistically significant (P=0.01) indicating the
inaccuracies in locating the landmarks. Chin et al. in their study on orthopaedic patients also
found US guided method requiring significantly (P Value <0.001) lesser passes (6) than the
LM method (13).Though, the average number of passes similar in both groups reported by
Srinivasan et al.69 (6.13 in LM group and 6.95 in US-guided group), the latter method
required more number of passes in relation to the present study.
The number of passes was being more in the LM group could be due to many reasons. First,
the patient population was different. Mean age and body mass index in our study were 59
years and 34.9 kg/m2, respectively, versus 63-68 years and 28.5-30.5 kg/m2 in the referenced
studies50, 69. Second, in the study by Kim et al.70 , the number of passes was self-reported,
whereas in our study, it was recorded by an independent observer. This is important, because
it has been shown that the self-reported number of passes is always lower than the actual
number of passes50.
We note a reduction in number of passes required to enter the subarachnoid space because of
the following probable reasons. First, the age of our population group was, on average, 64.3
years (SD = 12.8), and spinal anesthesia has been shown to be more difficult in an older
population compared with a general adult population.16 Second, we used a paramedian
approach to the neuraxis (guided by ultrasound), which has not been studied so far. In the
presence of interspinous ligament calcification and an inability to achieve adequate flexion
(both of which are common in the elderly), this paramedian approach might be valuable. It
has also been shown that both the length and the width of the lumbar spinous process increase
significantly with aging, which further narrows the interspinous space available for a midline
approach71. The interlaminar space is least affected by changes attributable to aging and
offers a potential window for spinal anesthesia.
When the median time taken for identifying space for each group was compared, it was 38.
19 seconds for LM group, while it was twice as high (78.35 seconds) for US-guided group
which was statistically significant (P Value <0.001). The average time taken in the study by
Srinivasan et al.69 was very less (12.3 seconds) for LM group than that of US-guided group
(105.1 seconds), which were in turn were in line with their earlier study findings (14.6
seconds for the former method, 96.1 seconds for the latter) and this finding was statistically
significant (P=0.0002) 50. In a study by Chin et al.56 , using similar endpoints, this process in
the ultra- sound group took 240 seconds longer. The difference might be because of the fact
that in their study, scanning was done in patients with difficult surface landmarks, and it
involved marking 3 interspinous spaces.
The technical difficulty of neuraxial blockade is measured using two main parameters: the
number of needle manipulations required for success and the time taken to perform the block.
Of the two, the former is more important because multiple needle insertions are an
independent predictor of complications, such as inadvertent dural puncture, vascular
puncture, and paresthesia1. Elicitation of paresthesia, in turn, is a significant risk factor for
persistent neurologic deficit after spinal anesthesia72, 73.
Regarding the time taken for successful lumbar puncture between the groups, the US-guided
method took significantly (P Value =0.048) less time (64.32 seconds) compared to LM
method (88.31 seconds). A similar finding was seen the study by Srinivasan et al. 50 with the
former method requiring less time (97.8 seconds) for successful procedure compared to the
latter method (169.9 seconds). However, the overall time taken by both the procedures was
higher in the study of Srinivasan et al.69 [US-guided procedure took more time (137.2
seconds) than LM group (127.4 seconds)], which was contrasting to our study findings.
The successfulness of the both the methods were comparable (95% in LM group; 92.5% in
US-guided group) with only 2 (5%) cases converted to GA in the LM group and 3 (7.5%) of
them needed the same in US-guided group. Similarly, Srinivasan et al.69 noted slightly more
cases in the US-guided group (3) requiring GA in relation to LM group (2). Also using
midline approach of US-guided spinal anaesthesia Abdelhamid et al. 67 reported significantly
improved success rate (the subjects were younger), however, Lim et al.8 who studied elderly
subjects like the present study, found no difference between the LM group and US-guided
paramedian approach.
As suspected by many clinicians, precise lumbar interspace identification by palpation is
prone to error. Broadbent and colleagues74 confirmed this, showing that anaesthetists were
29% accurate, as determined by MRI. Ultrasonography was not investigated in this study.
The inaccuracy was corroborated by Furness et al.46, who showed that clinical identification
by anaesthetists using palpation was 30% accurate, determined by lumbar spine x ray. Both
previous studies also showed that clinical identification by anaesthetists was often inaccurate
by two, three or four interspaces. Using ultrasound, markers were always within one
interspace of the intended position.
There are consistent data to suggest that neuraxial ultrasound identifies lumbar intervertebral
levels, with greater accuracy than palpation of surface anatomical landmarks75. Using plain
X-ray of the lumbar spine as a reference standard, Furness et al.46 demonstrated that
ultrasound correctly identified individual inter- spaces (from L2-3 to L4-5) 71% of the time,
whereas palpation was only correct 29% of the time. Furthermore, the margin of error never
exceeded one level with ultrasound, but was up to 2 spaces higher or lower in 27% of
palpation assessments. These findings are consistent with those reported by Watson et al.76
who, using MRI as their reference standard, found that ultrasound accurately identified the
L3-4 interspace in 76% of cases with a margin of error that did not exceed one level.
In a learning curve study that used CT as a reference standard, Halpern et al. 77 reported an
overall identification accuracy rate for ultrasound of 68%. However, analysis of the learning
curve showed that the 2 anesthesiologists in the study with no previous experience with
neuraxial ultrasound achieved accuracy rates of 90% or greater after 22 and 36 procedures,
respectively.
It is possible to use ultrasound scanning to accurately identify the lumbar spinous processes
in unselected patients. This result suggests that, with appropriate training, this tool can be
used to enhance the accuracy of needle placement during neuraxial techniques77. Watson et
al.76 concluded that ultrasonography may be a useful adjunct to safe subarachnoid
anaesthesia. Also Chin et al.56 inferred that preprocedural ultrasound imaging facilitates the
performance of spinal anesthesia in the non-obstetric patient population with difficult
anatomic landmarks.
The study does have limitations. First, neither the observer nor the attending anesthesiologists
were blinded to either of the group. The fact that the ultrasound group would have skin
markings and the difference in the direction of needle insertion would have made blinding
very difficult but still a potential for bias cannot be excluded. Second, the procedure is
heterogeneous with multiple factors affecting the number of passes, including individual
anesthesiologist preference and style of practice and the number of attempts and/or time
taken before using alternate methods. This may reflect daily clinical practice. Having a
single anesthesiologist perform all procedures might limit the differences because of the
aforementioned reasons, but it might also be more appropriate to reflect individual bias and
lack of validation. Third, neuraxial ultrasound has limitations. TM views for a midline
approach to dural puncture have a positive predictive value of up to 85% but a negative
predictive value of just 30%9. Also, ultrasound views are generally more difficult to acquire
in the elderly because of anatomical changes (facet hypertrophy, interspinous, and
supraspinous ligament calcification)78. In addition, the necessity to remember the angle of
approach of the needle and the inaccuracies of skin markings can further decrease the utility
of ultrasound views in patients with a longer distance between skin and duramater.
CONCLUSIONS
Pre-procedural Ultrasound-guided method of needle insertion needed significantly
lesser number of attempts compared to the landmark guided method for successful
spinal anaesthesia.
The US-guided method needed significantly less number of passes in relation to the
LM methods.
The landmark guided method took needed significantly less time of identifying space,
while the US-guided method took twice of the time.
The US-guided method took significantly less time for successful lumbar puncture
compared to LM method.
Ultrasonography can be a useful adjunct to safe spinal anaesthesia and also it
facilitates the performance of spinal anesthesia in the non-obstetric patient population
with difficult anatomic landmarks, like obese patients.
RECOMMENDATIONS:
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