Special Perioperative Considerations : Paediatric Patient

Physiological Differences Pediatric vs Adult Patients and It’s Effect

RESPIRATORY CONSIDERATIONS• Tidal Volume : 7ml/kg, Dead Space: 2.2ml/kg• FRC: 30ml/kg • Greater Minute Ventilation (VA ) in neonate (100-

150ml/kg/min) vs Adult (60-70ml/kg/min)• VA : FRC Ratio 5:1 vs 2:1 in adult• Oxygen Consumption : 2x adult (6ml/kg)• Alveolar ventilation : 2x adult

• Closing Capacity = Residual Volume + Closing Volume (CV)

• In healthy young adults CV= 10% of Vital Capacity but in infants and orderly it may exceed FRC – Airway closure occurs at normal tidal volumes.

• FRC decreases under anesthesia -> more atelectasis. PEEP and CPAP important

Hematological ConsiderationsCATEGORY BLOOD VOLUME

PRE TERM 100-120 ml/kg

NEONATE 90 ml/kg

INFANT 85 ml/kg

CHILD 80 ml/kg

• Adult : 70 ml/kg• Shock manifests at about 25% blood loss

GASTROINTESTINAL CONSIDERATIONS• Liver is immature. Enzyme systems not fully

matured – some drugs metabolized more slowly.

• Carbohydrate reserves are low in neonates- vulnerable to hypoglycemia.

• The ability to coordinate swallowing with respiration does not fully mature until the infant is 4-5 months of age – high incidence of gastro esophageal reflux in newborns is very common

RENAL CONSIDERATIONS

• Renal function is immature. Renal blood flow is reduced due to high renal vascular resistance.

• Neonates cannot excrete a large solvent or Na load. Thus, reduced dosages or prolonged frequency intervals may apply.

NEUROLOGICAL CONSIDERATIONS

• The BBB is more permeable in neonates – barbiturates, opioids, antibiotics all cross more readily

• The brain contain higher proportion of fat – may allow volatile agents to reach concentration more rapidly.

Thermoregulation• Poorly developed temperature regulatory mechanism• High body surface area ratio with minimal SC fat and

poor insulation – vulnerable to hypothermia - Hypothermia: assoc. with delayed awakening, cardiac irritability, resp depression, altered drug responses. - Premature infant even more susceptible d/t very thin skin & limited fat stores.• Measures : warm mattress, warming the OR, hot air

blankets, warm anesthetic gases.

Pre-op Assessment of Pediatric Patient

1) Medical History and Anesthetic History

2) Physical Examination3) Investigation AND Risk assesment

1. Medical History and Anesthetic History

• Any previous problems with anesthetics (inc family history)

• Allergies• Previous medical problems (Incl congenital

anomalies)• Recent respiratory illness• Current medications• Recent Immunizations• Loose teeth?• Fasting times

2. Physical Examination

• Children MUST be weighed – all drug doses relate to body weight.

• BP monitoring during preoperative period : detect any decreased cardiovascular reserve or exaggerated hypotensive responses.

• Temperature Monitoring : To detect hypothermia or malignant hyperthermia.

3. Pre-op Investigations• Hemoglobin : Large expected blood loss, premature

infants, systemic disease, CHD. - Preop Hb <10g/dl is abnormal and needs to be investigated. • Electrolytes: Renal/metabolic disease, IV fluids,

dehydration• Urinalysis: Renal disease or UTI• Cardiac Evaluation: Arrhythmias, conduction defects.

EEG, ECHO.• Pulmonary Function Test : Lung impairment• Chest X-Ray : Active respiratory disease, scoliosis, CHD

Pre-Medication of Paediatric Patient

• Routine sedative is unnecessary – Parents is the best premedication

• Some children will require pre-op sedation : - Excessively upset child - Childen with previous unpleasant experiences - Children with developmental delay• Infants have not yet developed strangers

anxiety– low risk, Pre school kids – most at risk

Pre-medications : • Oral Midazolam (0.5mg/kg)• Temazepam (10-30mg)• Ketamine (2mg/kg)• Clonidine (4ug/kg)• Children undergoing cardiac surgery – heavily

premedicated. - Morphine - PethCo (Pethidine, Promathazine & Chlormazine)

Post-op Care for Paediatric Patient• PostOperative Nausea & Vomitting(PONV) - Morphine increases risk of PONV by 30% - Mgmt: Combination antiemetic + 5HT3

antagonists with dexamethasone 0/1mg/kg• PostOp Pain Relief - Paracetamol & NSAIDS: minor cases/day surgery - Caudal Analgelsia - Morphine Infusions

Anesthetic Considerations in Obstetric Patients

CVS – Plasma Volume

• An increase in plasma volume (50%), RBC volume (20%) and total blood volume (35%).

• Most of the rise take place before 32 – 34 weeks gestation; after that there is relatively little change.

• The increase is related to the size of fetus and can be associated with multiple pregnancy.

• The changes in plasma volume result in haemodilution with subsequent decrease in RBC volume, haematocrit, haemoglobin and serum protein levels.

• Physiological anaemia of pregnancy.

CVS – Cardiac Ouput

• Cardiac output increases during pregnancy ( 40 – 50 %).

• The increase begins at 8th week of gestation and reaches a maximum of 30 – 50% above normal near term.

• During early labour, CO increases further due to catecholamine secretion in response to pain.

CVS – Aortocaval Compression• During pregnancy, increase in CO is sustained by increasing HR

as SV reduces towards term.• In supine position late in pregnancy, uterine contraction and

maternal hypotension (due to aortocaval compression) markedly enhance the obstruction effects on the aorta and its branches.

• The vascular region exposed to uterine compression is the most protruding part of vertebral column at L4-L5.

• The force of the contracting myometrium and the uterine gravitation may exert a pressure 2 – 3 times greater than the same force distributed over the large surface area of the amniotic cavity.

CVS –Peripheral Vascular Resistance

• A decreased in peripheral vascular resistance results in a small decrease in SBP and in mid-pregnancy a more marked decrease in DBP.

• Central venous pressure (CVP) remain normal during pregnancy but is elevated 4 – 5 cm of H20 with each contraction due to transient blood volume increases.

• Maternal bearing down and oxytocin infusion also increase CVP.

CVS – Anaesthethic Considerations

• Blood loss at vaginal delivery ranges from 250 – 500 ml, with caesarean section it ranges from 500 – 1000 ml.

• At delivery, autotransfusion of as much as 500 ml of blood into maternal circulation from uterus and placenta into maternal circulation minimizes the impact of maternal haemorrhage.

• Must constantly reasess the parameters of O2 availability; Hb, SPO2, CO etc when deciding if transfussion is necessary.

• Vasomotor block from induction of spinal or epidural anaesthesia or other procedures may deprive patient of compensatory vasoconstriction.

• Patient with severe aortocaval syndrome are particularly vulnerable to this. Anaesthetist should ascertain the degree of the block by measuring BP first with the patient on her left side and then again after she ahs been supine for 5 – 15 minutes.

• Avoid techniques that produce vasomotor block, if not possible, prevention measures such infusion of fluids prior to block and lateral displacement of uterus or left lateral tilt after induction must be taken to avoid severe arterial hypotension.

• During pregnancy, the peridural venous plexus is distended. This leads to:1. Increased epidural space pressure, with less reliability on

the ‘hanging drop’ technique.2. Decreased epidural capacity, results in use of smaller

volumes of local anaesthetics.3. Increased risk of intravascular placement of the epidural

needle and catheter, with greater potential for local anaesthetic toxicity.

• The dosage for spinal anaesthetics must also be reduced.

Respiratory System

1. Airway 2. Lung volumes 3. Ventilatory mechanics

Airway – Capillary Engorgement• Throughout the respiratory tract. So nasopharynx, larynx,

trachea and bronchi become swollen and reddened. • These changes stimulate inflammation often causing

changes in the voice and make breathing through the nose difficult for the women at term.

Respiratory System

Lung volumes:• The growing uterus causes the diaphragm to rest

4 cm higher, but it does not impair its excursions.• The abdominal muscles have much less tone and

are less active in pregnancy.• Total Lung Capacity (TLC) is reduced due to the

rise in diaphragm, but is compensated by the increased anterior-posterior and transverse diameters of the rib cage.

RSP – Ventilatory Mechanics

• Significant ventilatory changes are not seen until the 5th or 6th month of pregnancy.

• After that, there is a progressive decrease of both the Expiratory Reserve Volume (ERV) and Residual Volume (RV).

• At term, the sum of these two volumes, the Functional Residual Capacity (FRC) is decreased by 17%.

• However, there is a concomitant increase in Inspiratory Capacity (IC) with the result that the Vital Capacity (VC) and TLC remain unaltered.

• Minute Ventilation (VE) is increased by 50% at term.• Tidal volume increased (40%) more than respiratory rate (15%)

and this decreases the dead space component of ventilation. So, alveolar ventilation reaches a level 70% above that in non-pregnant state.

• During labour and delivery, pain acts as a potent ventilatory stimulus. O2 consumption increases by 10 – 20% during pregnancy and is further elevated as much as 100% over normal during labour.

• This occurs in response to demand by the growing fetus, placenta and uterus and to increase cardiac and respiratory work, particularly during labour.

• Hyperventilation during pregnancy, mainly due to increase in tidal volume, is attributed to the action of progesterone as has been shown in a study.

RSP – Anaesthetic Consideration

• Increased alveolar ventilation augments the transfer of gases between mother and fetus.

• Because of these changes, patient is much more susceptible to rapid changes in respiratory blood gas levels during respiratory complications than the non-pregnant woman.

• Consequently, hypoxia, hypercarbia and respiratory acidosis as a result of hypoventilation, breath-holding or respiratory obstruction develop more readily.

RSP – Anaesthetic Consideration• During an endotracheal intubation, even by a skilled anesthetist,

the oxygen tension may fall precipitously after only a brief period of apnea.

• Conversely, moderate to severe hyperventilation can quickly lead to severe respiratory alkalosis with arterial carbon dioxide tensions as low as 10-15 mmHg and pH as high as 7.7.

• Inhalational anesthesia is rapidly induced because hyperventilation, particularly during labor, delivers more anesthetic to the alveoli.

• At the same time, a smaller than usual functional residual capacity results in less dilution of incoming gases, allowing higher alveolar concentrations to be reached more quickly.

Gastrointestinal System

• Prolonged gastric emptying is noted from at least the 34th week of pregnancy and is most likely hormonal in origin (progesterone).

• Anxiety and excitement have a severe depressant effect on gastric motility and this effect is mediated by the splanchnic nerves. Pain and emotional disturbances which accompany labour also depress gastric motility and delay gastric emptying.

• During pregnancy there is an increase in intragastric pressure. In pregnant women without heartburn, the gastroesophageal sphincter responded to this increase in pressure by an increase in maximum sphincteric pressure. In the group of pregnant women with heartburn, there was no significant increase in sphincter pressure, and the stomach-to-sphincter pressure gradient was decreased. Under these circumstances, the sphincter does not maintain competence of the gastroesophageal junction and the symptoms of reflux occur.

GIT – Anaesthetic Consideration• With regard to general anesthesia, pregnant women from 32

weeks gestation onward must be considered as having "full stomachs” and when general anesthesia is employed, have a rapid intravenous induction followed by cricoid pressure and tracheal intubation.

• The patient should be extubated awake when reflexes are intact.• Whenever feasible and appropriate, the use of regional

anesthesia should be employed. The use of prophylactic antacids at the present time is a controversial issue due to the untoward effects of aspiration of antacid materials themselves.

Plasma Cholinesterase• Plasma cholinesterase activity declines during pregnancy

and in the immediate postpartum period. • Anesthetic considerations: Since plasma cholinesterase is

responsible for the hydrolysis of succinylcholine, a low degree of enzymatic activity may result in an undesirably long duration of paralysis following succinylcholine administration.

• It is strongly recommended that whenever succinylcholine is being administered to a patient, that the neuromuscular status be monitored by a peripheral nerve stimulator.

Maternal Physiological ChangesValue Non-pregnant Pregnant

Haematocrit 0.37 – 0.47 0.32 – 0.41

Haemoglobin (g/dL) 11.5 – 16.0 11.0 – 15.0

WCC ( /L) 4.0 – 11.0 X 109 5.0 – 16.0 X 109

Platelets ( /L) 150 – 400 X 109 134 – 400 X 109

ESR (mm/hr) (age in years + 10) 2 44 – 114

Fibrinogen (g/L) 2 – 4 4 – 6

Albumin (g/L) 35 – 50 28 – 40

Urea (mmol/L) 2.5 – 6.7 1.6 – 6.0

Creatinine (mmol/L) < 110 38 – 90

pCO2 (mm/Hg) 34 – 46 27 – 32

pO2 (mm/Hg) > 80.6 > 80.6

HCO3 (mmol/L) 24 – 28 18 – 23

Pain of childbirth

Nociceptive pathways involved

Uterine pain:T10 – L1 during labor(sensory fibres ending in dorsal horns)

Vaginal pain:S2-S4 for delivery(pudendal nerve)

Analgesia for labor and delivery

• Non-medication• Inhalational• Parenteral• Regional

Analgesia- Non medication options

• Breathing exercises• Autohypnosis• Acupuncture• White Noise/ Music• Massage/ walking• TENS transcutaneous electrical nerve

stimulation • Water bath

Inhalation Medications

• Nitronox/Entonox: 50:50 mixture of oxygen and nitrous oxide

Advantages: on demand delivery, relatively safe

Disadvantages: variable efficacy, nausea, drowsiness, neonatal depression

Parenteral Medications

• Narcotics: meperidine/pethidine/demerol, fentanyl

Advantages: relatively good analgesia, beneficial when regional analgesia is contraindicated

Disadvantages: nausea, vomiting, sedation, neonatal depression, short duration of action

Regional Analgesia

• Epidural, spinal, combined spinal-epidural

Advantages: provide most effective pain relief, reduces maternal sympathetic stimulation and hyperventilation, less drug transfer to fetus, improved uterine blood flow, decrease in birth trauma e.g. use of forceps, minimal neonatal depression

Disadvantages: invasive technique, side effects (hypotension, headache, itching, nausea, urinary retention, limited mobility), nerve damage, infection, association with prolonged labour

Regional Analgesia

Indications • Maternal request• Expectation of operative delivery• Maternal disease• Specific CVS disease

(regurgitation valvular lesion)• Severe resp disease (CF)• Specific neurological disease

(intracranial AV malformations)• Obstetric disease (pre-eclampsia)• Morbid obesity

Contraindications • Maternal refusal• Allergy• Local infection• Uncorrected hypovolaemia• Coagulopathy (platelet

>80x109 /L and INR < 1.4 are safe for neuraxial procedure; still need clinical judgment for each cases)

Combined Spinal Epidural Analgesia (CSE)

• Low dose subarachnoid LA and/or opioid together with subsequent top-ups of weak epidural LA.

• Rapid onset with minimal motor block and effective analgesia.

• Epidural alone produce similar degree of analgesia and motor block, but take 10 – 15 min longer to establish.

Epidural Anesthesia

• Potential Complications:– Hypotension– Headache (approx 1:100)– Transient backache ~24hrs– Urinary retention– Unintentional spinal injection– Intravascular injection of local anesthetic– Neurological damage– Infection

CSE

• Potential Complications:– Hypotension– Headache (rare ~1:100)– Backache (temporary ~24hrs)– Nausea/vomiting (secondary to BP, narcotics)– Neurological damage (very rare)– Anaphylaxis (very rare)

Pre medication of C-sect patient• Use antacid and prokinetic agent – elevate gastric pH & reduce

the intragastric volume• A suggested regime is : Elective surgery :-150mg ranitidine orally 2hr & 12hr before surgery-10mg metoclopramide orally 2hr before surgery-30ml 0.3M sodium citrate immediately before surgery Emergency surgery (if prophylaxis has not been given) :-50mg ranitidine by slow IV injection immediately before surgery.-10mg metoclopramide IV injection immediately before surgery-30ml 0.3M sodium citrate orally immediately before surgery

Modalities of anaesthesia for C-sect

A. Regional I. EpiduralII. SpinalIII.Combined spinal epiduralB. General

Regional - EPIDURAL

Advantages Disadvantages

Easy to top up labour epidural Slow onset

Stable BP Large doses of LA

Intraoperative top up possible Poorer quality of block than spinal anaesthesia

Epidural can be used for post op analgesia

Indications

• Already have epidural analgesia established for labor

• Specific maternal disease. Eg : cardiac disease

Technique • History, examination, explanation and consent• Antacid prophylaxis has been given• 16G/larger IV access. Start 10-15ml/kg crystalloid co load• Epidural catheter at L2/3 or L3/4 vertebral interspace• Top up the epidural incrementally with local anaesthetic & opiod-8-10 ml boluses of 2% lidocaine with 1:200000 every 2-3minutes, max 20ml or-8-10ml o.5% bupivacaine/levobupivacaine every 4-5 min, max 2ml/kg in any 4hr period• 100μg fentanyl or 2.5mg diamorphine improves the quality of

the analgegesia

Cont

• S4-T4 block. Check sacral dermatomes, as epidural sacral dermatome doesn’t spread caudally. Document level of block & adequacy of perioperative analgesia

• Patient in supine position with left lateral tilt or wedge. Give facemask if SpO2 <96% on air.

• If hypotension- Fluid- 50-100μg phenylepinephrine IV bolus or 6mg ephedrine

IV- Increasing left uterine displacement

• 9IU (3, 3, 3 )oxytocin IV bolus at delivery. If tachycardia

must be avoided then an IV ( ?? IU ) oxytocin in 500ml crystalloid over 4hr.• NSAID given at the end of procedure - (CI -100mg diclofenac PR)

Regional - SPINAL

• Commonly used for elective C-sect• Rapid in onset and dense block• With intrathecal opiod- long acting post

operative analgesia

Advantages Disadvantages

Quick onset Single shot

Good quality analgesia Limited duration

Easy to perform Inadequate analgesia is difficulty to correct

Rapid changes in BP and cardiac output

Technique• History/examination/explanation and consent. • Ensure that antacid prophylaxis has been given. • Establish 16G or larger IV access. Start 10–15ml/kg

crystalloid co-load. • Perform spinal anaesthetic at L3/4 interspace using a 25G or

smaller pencil-point needle. With the orifice pointing cephalad, inject the anaesthetic solution, e.g. 2.5ml 0.5% hyperbaric bupivacaine with 300µg diamorphine or 15µg fentanyl. Intrathecal diamorphine improves postoperative analgesia, while intrathecal fentanyl has little postoperative analgesic benefit.

Cont • During the insertion of a spinal anaesthetic, some anaesthetists place

patients in a sitting position, while others lie patients on their side. The sitting position usually makes the midline easier to find (important in obese patients), and may be associated with a faster onset, although the height of block is less predictable. A lateral position is associated with a slower onset of block, particularly if a full lateral position is maintained until the block has fully developed. This position also avoids aortocaval compression. With both positions, when hyperbaric local anaesthetic solutions are used, it is important that the cervical spine is kept elevated (pillow) to prevent local anaesthetic spreading to the cervical dermatomes.

• Hypotension is more common with spinal anaesthesia than epidural anaesthesia. Patients may benefit from a continuous infusion of pressor agent initiated at the time of insertion of spinal block.

• Continue as for epidural anaesthesia for Caesarean section

Regional - CSE

Advantages Disadvantages

Quick onset Rapid change in BP & cardiac output

Good quality analgesia More difficult with higher failure rate of spinal injection

Intraoperative top up possible Untested epidural catheter

Epidural can be used for postop analgesia

Indications

• Prolonged surgery. • Using the epidural catheter for postoperative analgesia. • Limiting the speed of onset of a block. A small initial intrathecal dose of local anaesthetic can be supplemented through the epidural catheter as required.

Technique

• History/examination/explanation and consent. • Ensure that antacid prophylaxis has been given. • Establish 16G or larger IV access. Give 10–15ml/kg crystalloid co-load.I. Needle through needle techniqueII. Two needle technique

General Anaesthesia Indications for general anaesthesia include: • Maternal request. • Urgent surgery. (In experienced hands and with a team that is familiar with rapid regional anaesthesia, a spinal or epidural top-up can be performed as rapidly as a general anaesthetic.) • Regional anaesthesia contraindicated (e.g. coagulopathy, maternal hypovolaemia). • Failed regional anaesthesia. • Additional surgery planned at the same time as Caesarean section

Technique• History and examination. In particular assess the maternal airway— mouth opening, Mallampati score, thyromental distance, neck mobility • Antacid prophylaxis • Start appropriate monitoring • Position supine with left lateral tilt or wedge. • Preoxygenate for 3–5min or, in an emergency, with 4–8 vital capacity breaths with a high flow through the circuit. Ensure a seal with the facemask. At term, women have a reduced FRC and a higher respiratory rate and oxygen consumption. This reduces the time required for denitrogenation, but also reduces the time from apnoea to arterial oxygen desaturation.

• Perform rapid sequence induction with an adequate dose of induction agent (e.g. 5–7mg/kg thiopental). A 7.0mm endotracheal tube is adequate. • Propofol has also been used for Caesarean section without any major reported complications, although at present thiopental probably is still the most commonly used agent in the UK. • Ventilate with 50% oxygen in nitrous oxide. If severe fetal distress is suspected then 75% oxygen or higher may be appropriate. Maintain ETCO 2 at 4.0–4.5kPa (30–34 mmHg). • Use ‘overpressure’ of inhalational agent to rapidly increase the end tidal concentration of anaesthetic agent to at least 0.75 of MAC (e.g. 2% isoflurane for 5min, then reduce to 1.5% for a further 5min).

• At delivery: Give 9IU (3, 3, 3) oxytocin IV bolus. If tachycardia must be avoided

then an IV infusion of ( ?? IU )syntocinon in 500ml crystalloid, infused over 4hr, is effective.

Administer opioid (e.g. 0.1 – 0.2mg/kg morphine). Ventilate with 35% inspired oxygen concentration in nitrous oxide.

Inhalational agent can be reduced to 0.75 MAC to reduce uterine relaxation.

At end of procedure give an NSAID (e.g. 100mg diclofenac PR). Bilateral ilioinguinal nerve blocks for postoperative analgesia.

Extubate awake in the head-down left lateral position. Give additional IV analgesia as required.

Effect of general analgesia on the fetus

• Anaesthetic agents cross the placenta – Thiopental can be detected in the fetus

• Opiods may cause fetal depression• Neonatal respiratory depression – reversed

with ??

Post op analgesia for C-sect patient

a) Opioids• IV patient-controlled or oral can be used. May be transferred

to the neonate through breast milk, but with negligible effect

• Intrathecal/epidural opioid :-Bolus at the beginning, Fentanyl last longer than LA & no post-op analgesia. Epidural fentanyl, ( ? Mg/kg) up to 2hourly for 2-3 doses.-Intrathecal diamorphine (0.1-0.2 mg/kg) can be expected to provide 6–18hr of analgesia. More than 40% of women will require no other postoperative opioid.

-Epidural diamorphine (2.5mg in 10ml saline) provides 6–10hr of analgesia after a single dose.-Intrathecal preservative-free morphine (0.1-0.2 mg/kg) provides long- lasting analgesia (12–18hr). Doses above 150µg are associated with increased side effects without improved analgesia.b) NSAIDs-effective postoperative analgesics, reducing opioid requirement

SPECIAL PERIOPERATIVE CONSIDERATIONS : PAEDIATRIC PATIENT

Anatomical Differences between Paediatric and Adult Patients

RESPIRATORY SYSTEM• Terminal bronchiole opens into single alveolus. The alveoli are thick

and only 10% of adult (growth cont until 6-8yr).• Cartilagenous ribs are horizontally aligned ; ‘bucket handle’ of adult

thorax isn’t possible. Intercostal muscles are poorly developed- fatigue easily. Diaphragm is more horizontal- reduce mechanical advantage.

• Ventilation is essentially diaphragmatic and rate dependent. Abdominal distension may cause splinting diaphragm- respiratory failure.

• Closing volume is within tidal breathing. Decrease FRC- increase pulmonary shunt & lung collapse. CPAP improves oxygenation & reduce effort.

Cont

• Narrow airways- increased resistance(up to 8y/o). Nasal resistance accentuate children with nasal congestion.

• Apnea : common post-op problem in preterm neonate. (Episode >15s, induce cyanosis, bradycardia). Use CPAP.

• High metabolic rate & alveolar minute volume – volatile agents has rapid induction & emergence than with adult.

Cardiovascular System• PVR falls in response to rise PaO2 & fall in PaCO2. closure

of foramen ovale & ductus arteriosus- lead to pulmonary HPT & right to left shunt.

• Small ventricle- reduced contractile mass & poor ventricular compliance. CO is higher than adult (200ml/kg/min).

• Heart rates up to 200bpm is tolerated. Bradycardia should be treated with oxygen. Heart rate <60bpm (neonate, infant) require external cardiac compression.

• Autonomic & baroreceptor is fully functional at term, mediated parasympathetic tone predominates.

Gastrointestinal System• Liver is immature. Enzyme matured by 12wk. Some drugs

are metabolized slowly by different enzyme pathways from adults.

Eg : barbiturates & opioids have a longer duration in the neonate.• Glucuronyl transferase system was poorly developed- rise in

unconjugated bilirubin.Eg : sulphonamides, diazepam, vit K- displace bilirubin from plasma protein.• Carbohydrate reserves are low – vulnerable to

hypoglycaemia.

Renal System

• Nephron formation is complete at term but renal function is immature.

• Renal blood flow & glomerular filtration are low in first 2 years of life d/t high renal vascular resistance.

• Tubular function is immature until 8 months.• Neonates cant excrete large solvent or sodium

load – reduced drug dosages or prolonged frequency intervals.

Haematology

• At birth, 70-90% Hb are HbF. Within 3 months HbA predominates.

• HbF combines more readily with oxygen but released readily.

• O2/Hb dissociation curve shifts to the right – HbA & 2,3-DPG rise.

• Factor II, VII, IX, X & platelet function are deficient in the first few months.

• Transfusion is recommended when 15% of circulating blood volume has been lost.

CNS• Neurons are complete at term, but brain cells are reduced.

Dendritic proliferation, myelination & synaptic connections developed in the 3rd trimester & first 2 years of life.

• BBB are permeable in neonates – barbiturates, opioids, antibiotics and bilirubin all cross readily.

• Neonates can appreciate pain & associated with increase heart rate, BP and neuro-endocrine response.

• Cerebral autoregulation is function from birth.• Cerebral vessels are thin walled,fragile – prone to

intraventricular haemorrhages. Risk is increased with hypoxia, hypercarbia, hypernatraemia, low haematocrit.

REFERENCES

• Oxford Handbook of Anesthesia 3rd Edition 2012

• Royal Children Hospital’s Guideline of Pediatric Anesthesia

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