beginning neuraxial anesthesia (an overview) local anesthetics (an introduction)
DESCRIPTION
Beginning Neuraxial Anesthesia (an overview) Local Anesthetics (an introduction). Neuraxial Anesthesia Indications. Any operation in the lower abdomen and below. Contraindications. Absolute Patient doesn’t want it Infection at site of puncture Increased ICP Uncorrected hypovolemia - PowerPoint PPT PresentationTRANSCRIPT
Beginning Neuraxial Anesthesia(an overview)
Local Anesthetics(an introduction)
Neuraxial Anesthesia Indications
• Any operation in the lower abdomen and below
Contraindications
• Absolute– Patient doesn’t want it– Infection at site of
puncture– Increased ICP– Uncorrected
hypovolemia– Uncorrected
coagulopathy
• Relative– Systemic infection– Neuruologic diseases
like MS
Spinal vs. Epidural
• Spinal– More definite endpoint– Easier to do– Faster onset– More intense sensory
and motor block– Limited duration– Fewer failures
• Epidural– Less definite endpoint– More difficult to do– Slower onset– Less intense sensory
and motor block possible (labor)
– Unlimited duration– Postop analgesia
possible– More failures
Sedation/Analgesia
Position
ABSOLUTELY NO RITUALS!
Where?
Spinal - L2-3 and below
Epidural - anywhere
Skin anesthesia
• Do a good intradermal skin wheal• Other, deeper soft tissues are not painful• The periostium is painful but impossible to
anesthetize easily, so don’t try
Please memorize this image. When you are performing an epidural or spinal puncture use the image of the ligaments as a guide to imagine where the needle tip is at all times.
If at any time you think the plunger is stuck, STOP. Remove the syringe and check that the plunger moves freely.
Pay attention to what you are FEELING as the needle advances. If you feel as though the ligamentum flavum has been penetrated but there has been no LOR to injection, STOP. Reassess plunger action and resistance to injection.
Pay attention to DEPTH as the needle advances. If you feel as though you should have penetrated the ligamentum flavum by now but there has been no LOR to injection, STOP. Reassess plunger action and resistance to injection.
Spinal Anesthesia
We do it the same as we do an epidural except we use flimsy
needles and we don’t stop in the epidural space
Because the needles are so flimsy, we use an introducer needle
Interspinous lig
Epidural spaceDura
CSF
Ligamentum flavum
FAILURE!
So, we’re in!
What do we inject?
Ask your attending
Epidural injections:ChloroprocaineLidocaineBupivacaine
Epidural injections:What concentration?How much?
Ask your attending
Epidural injections:What concentration?
Chloroprocaine – 3%Lidocaine – 1-2%Bupivacaine – 0.625-0.5%
(low conc. for labor)How much?
Roughly 10-20 ml
Spinal injections:What solution?How much?
Ask your attending
Spinal injections:What solution?
Chloroprocaine – 2-3% (no dextrose)
Lidocaine – 5%/0.75% dextrose
Bupivacaine – 0.75%/0.825 dextrose
Spinal injections:How much?
Chloroprocaine – 2 ml (40-60 mg)
Lidocaine – 1-2 ml (50-100 mg)
Bupivacaine – 1-2 ml (7.5-15 mg)
Conversion of % concentration to mg/ml:
1% solution = 1gm per 100 ml (1000 mg per 100 ml) = 10 mg/ml
% solution X 10 = mg/ml
e.g., 0.5% bupivacaine X 10 = 5 mg/ml Dose is volume X concentration:
10 ml of 0.5% bupivacaine = 50 mg dose
Dose is important in determining toxicity
Manufacturer Maximum Recommended Doses
• Chloroprocaine– 800 mg no epinephrine– 1000 mg with epinephrine
• Lidocaine– 300 mg no epinephrine– 500 mg with epinephrine
• Bupivacaine– 175 mg no epinephrine– 225 mg with epinephrine
Concept of baricity
• Baricity is the relationship of the density of the local anesthetic solution to the density of the cerebrospinal fluid.
If the LA solution is:• Less dense than CSF it is hypobaric (floats)• Equal in density to CSF it is isobaric (stationary)• More dense than CSF it is hyperbaric (sinks)
• As a concept, baricity refers only to spinal anesthesia and not to epidural anesthesia
Spinal solutions
• Hyperbaric solutions (with dextrose)– Intra-abdominal operations (including inguinal
hernia and vaginal procedures)– All operations can be done with this solution
• Isobaric solutions (epidural solutions without dextrose)– Lower extremity operations (hip and below)
• Hypobaric solutions (diluted with DW)– Not really useful
1 ml 5% lido with dextrose during injection
1 ml 5% lido with dextrose immediately after injection
• The effect of baricity on the distribution of bupivacaine in spinal model
Hyperbaric
IsobaricH
ypobaric
In spite of the crudeness of this model, the levels of anesthesia predicted by the model are remarkably similar to the levels of anesthesia observed in patients
Immediately after injection
20 min. after injection
Hyperbaric
IsobaricH
ypobaric
What could go wrong?
What could go wrong with spinal anesthesia?
• It doesn’t work• It goes too high (total spinal)• It doesn’t go high enough• It causes hypotension• It doesn’t last long enough• It causes a spinal headache
The Two Components of
Spinal Headache• There must have
been a lumbar puncture
• The headache is related to posture– Worst when
standing or sitting– Gone or improved
with recumbency
Effect of Age on the Incidence of Spinal
Headache
Vandam and Dripps, JAMA 1956;161:586-591
0
2
4
6
8
10
12
14
16
Perc
ent H
eada
che
10-19 20-29 30-39 40-49 50-59 60-69 70-79 80-89
Age
This and AARP discounts are two of the few advantages to aging!
Needle tip design is important
• 25 gauge Quincke or cutting needle has 5% incidence of spinal headache in OB patients.
• 25 gauge Whitacre or pencil tipped needle has <1% incidence of spinal headache in OB patients
What could go wrong with epidural anesthesia?
• It doesn’t work• It goes too high (total spinal)• It doesn’t go high enough• It causes hypotension• It doesn’t last long enough• It causes a spinal headache (but it’s not
supposed to)• It produces spinal anesthesia• It goes intravascular causing systemic toxicity
Or the catheter could have penetrated the dura and be located intra-thecally
Epidural Test Dose
• 3 ml of 1.5% lidocaine with 1:200,000 epi
– 1:200,000 = 5 ug/ml X 5 ml = 25 ug epi• will cause tachycardia and is used to detect and
intravascular injection
– 3 ml X 15 mg/ml = 45 mg lido• will cause spinal anesthesia and is used to detect
an intrathecal injection
The Local Anesthetic Molecule• Local
anesthetics consist of an aromatic ring and an amine, separated by a hydrocarbon chain
Two types of local anesthetics based on the hydrocarbon chain linkage:
Esters have [-CO-O-] linkageAmides have [-N-CO-] linkage
N C
O
O C C NCH3
CH3
H9C4
NH2 C
O
O C C N
C2H5
C2H5
NH2 C
O
O C C N
Cl
C2H5
C2H5
Procaine
Chloroprocaine
Tetracaine
ESTERS
N
O
NH
CH3
CH3 CH3
H
N
O
NH
CH3
CH3 CH2
CH2
CH2
CH3
H
M epivacaine
Ropivacaine
Bupivacaine
N
O
NH
CH3
CH3 CH2
CH2
CH3
HHAmide
Bupivacaine Analogues
AmideLidocaineAnalogues
Toxicity
• Directly related to lipid solubility (potency)– Bupivacaine > Lidocaine > Chloroprocaine
• The more potent the LA, the more toxic the LA is– It takes a lower dose to produce the toxicity
• Two types of toxicity– Central nervous system– Cardiovascular
• Central Nervous System– Earliest signs and symptoms are those of
excitation owing to depression of inhibitory cells allowing excitatory cell preponderance
• Tinnitus• Light headedness• Confusion• Circum-oral numbness• Tonic-clonic convulsions
Toxicity of Local Anesthetics
• Central Nervous System– Excitation is followed by depression
Drowsiness Unconsciousness Respiratory Arrest
SZ
SZ
Treatment of CNS Toxicity• STOP INJECTING• If seizure, depress the CNS with
benzodiazepines (midazolam, ativan, diazepam), or propofol, or thiopental
• Support airway and breathing• Intubation if necessary• Wait until consciousness returns
– It is unlikely there will be a good block as the local obviously went intravascular
• Or convert to general and continue with the operation
Cardiovascular ToxicityHYPERTENSION - TACHYCARDIA OWING TO CNS EXCITATION
NEGATIVE INOTROPY
DECREASED CARDIAC OUTPUT
MILD - MODERATE HYPOTENSION
PERIPHERAL VASODILATATION
PROFOUND HYPOTENSION
SINUS BRADYCARDIA
CONDUCTION DEFECTS VENTRICULAR ARRYTHMIAS
CARDIOVASCULAR COLLAPSE
Treatment of Bupivacaine CardiotoxicityWeinberg, GL. RAPM 27:568, 2002
• Early Response• ABC• ACLS Protocol
An Intralipid Protocol• Intralipid bag available
• LA arrest unresponsive to ACLS:
1 ml/kg intralipid IV over one minute
Repeat X2 at 3-5 min. intervals
0.25 ml/kg/min intralipid IV until stable
Picard J, Meek T: Lipid emulsion to treat overdose of local anaesthetic: the gift of the glob. Anaesthesia 2006; 61: 107-9
Prevention Is Better Than Treatment
Good Luck!
Have Fun!!
Be Careful!!!