Perioperative Problems and Management in a 1-Year-Old with Hydrocephalus

1. Pathophysiology and Why It Matters for the Anaesthetist

2. Preoperative Assessment and Preparation

History and Examination

• Assess level of consciousness, irritability, vomiting (sign of raised ICP), bulging fontanelle, "sunsetting" eyes (Parinaud's sign), feeding difficulties
• Review CT/MRI: degree of ventricular dilatation, midline shift, brain edema, aqueductal stenosis vs. communicating hydrocephalus
• Review existing shunt function (if revision surgery)
• Document prior seizures, anticonvulsant therapy
• Assess for coexisting conditions: spina bifida (latex allergy precautions), Chiari malformation (airway/respiratory issues), prematurity-related lung disease

Laboratory

• Full blood count, electrolytes, renal function
• Corticosteroid-induced hyperglycemia if on dexamethasone
• Electrolyte disturbances if on diuretics (acetazolamide, furosemide)
• Blood group and crossmatch

Preoperative Optimization

• Continue anticonvulsants until the day of surgery
• Dexamethasone if cerebral edema present - continue perioperatively
• Avoid sedative or opioid premedication if intracranial hypertension is suspected - hypercapnia from respiratory depression raises ICP further
• If acetaminophen/NSAID premedication is used, it should not cause respiratory depression
• Fasting according to pediatric guidelines (4-6-8 rule: clear fluids 2h, breast milk 4h, formula/solids 6h) - but in emergency, treat as full stomach (risk of vomiting from raised ICP)

"Sedative or opioid premedication is best avoided, particularly when intracranial hypertension is suspected. Hypercapnia secondary to respiratory depression increases ICP." - Morgan & Mikhail's Clinical Anesthesiology, 7e

Latex Precautions

• Mandatory in patients with myelomeningocele or prior multiple abdominal surgeries (sensitization risk) - use latex-free environment throughout

3. Perioperative Problems

3.1 Raised Intracranial Pressure

• Bulging fontanelle, enlarged head circumference
• Irritability, vomiting, high-pitched cry
• Cushing's triad (bradycardia + hypertension + irregular respiration) - late, ominous sign
• Papilledema (may be absent in infants due to open sutures)
• "Sunsetting" eyes

3.2 Full Stomach Risk

3.3 Difficult Airway

• Large head (macrocephaly) makes positioning difficult - a shoulder roll is essential
• Chiari malformation may cause brainstem/cervical compression - avoid neck flexion/extension
• Limited mouth opening in some syndromic cases

3.4 Cardiovascular Instability

• The bradycardia-hypertension Cushing response may be present pre-induction
• Induction agents can cause sudden hypotension, critically lowering CPP
• CPP = MAP - ICP; in severe hydrocephalus ICP may be very high, so even a modest drop in MAP can drop CPP below ischemic threshold
• Pediatric CPP thresholds: minimum 40 mmHg; 50 mmHg may be safer in older infants/children

3.5 Venous Air Embolism (VAE)

• Particularly relevant in sitting or semi-sitting positions (posterior fossa procedures, ETV)
• The large dural sinuses and open diploic veins in infants are particularly susceptible
• Detected by: precordial Doppler (most sensitive), sudden fall in ETCO2, "mill-wheel" murmur, hypotension

3.6 Intraoperative ICP Surges

• Triggered by: laryngoscopy, inadequate depth, hypercapnia, hypoxia, coughing, Valsalva, venous obstruction from head position, high airway pressures

3.7 Temperature Dysregulation

• Neonates and infants have a large body surface area:weight ratio - prone to rapid heat loss
• Hypothermia increases drug metabolism unpredictably; hyperthermia worsens cerebral ischemia

3.8 Blood Loss

• Scalp incisions in infants can cause significant blood loss relative to small blood volume
• Estimated blood volume (EBV) of a 1-year-old ~75-80 mL/kg
• Allowable blood loss calculated accordingly; have blood available

3.9 Electrolyte Disturbances (Postoperative)

• SIADH - free water retention, hyponatremia - worsens cerebral edema; occurs 24-48h post-op
• Diabetes Insipidus (DI) - excessive diuresis, hypernatremia, low urine osmolality; may follow suprasellar surgery
• Cerebral salt wasting - hyponatremia + volume depletion (unlike SIADH where euvolemic/hypervolemic)

3.10 Seizures

• Perioperative seizures increase cerebral metabolic demand, O2 consumption, and ICP
• Prophylactic levetiracetam or anticonvulsants in high-risk cases

3.11 Anesthetic Neurotoxicity

• Significant concern in a 1-year-old: animal studies and some human evidence show that repeated/prolonged GA in children <3 years may cause neurotoxicity
• Minimise exposure duration and number of agents where possible; discuss with parents

4. Anesthetic Management

4.1 Monitoring

• Standard: SpO2, ECG, ETCO2, NIBP, temperature
• Arterial line (radial/femoral): mandatory for continuous BP monitoring and arterial blood gas analysis - ETCO2 alone is insufficient for precise PaCO2 regulation due to A-aDCO2 gradient
• Urinary catheter: essential - to monitor urine output, guide fluid management, and measure core temperature
• Zero arterial transducer at the level of the external auditory meatus (approximating Circle of Willis) to calculate CPP accurately
• ICP monitor if not already placed
• Temperature probe (axillary/rectal)
• Precordial Doppler if posterior fossa or sitting position
• Neuromuscular monitoring (TOF)

4.2 Induction

1. Blunt rise in ICP from laryngoscopy
2. Maintain CPP
3. Prevent aspiration (RSI approach)
4. Avoid hypoxia and hypercapnia
5. Pre-oxygenate thoroughly

• Pre-oxygenate 100% O2 for 3 minutes (nitrogen washout)
• Avoid BMV unless impending herniation or desaturation (risk of aspiration and hypocapnia-induced ischemia)
• Propofol or thiopentone + lidocaine + rocuronium (1 mg/kg) or succinylcholine (2 mg/kg in infants)
• Succinylcholine remains an option in children with suspected difficult airway given its rapid offset; theoretically raises ICP transiently via fasciculations but this is clinically minor when pre-treated
• Cricoid pressure (third person, only if trained); abandon if it hinders intubation
• Orotracheal intubation preferred (avoid nasotracheal if basilar skull fracture risk)
• Confirm position with capnography and chest X-ray

• Head 30° elevated, midline (prevents venous obstruction)
• Shoulder roll for macrocephalic infant to bring head into neutral position
• "Even slight movement of the head a few degrees off midline may double ICP"

4.3 Maintenance of Anaesthesia

• Target normocapnia (PaCO2 35-38 mmHg confirmed by ABG)
• Avoid prophylactic hyperventilation (PaCO2 <35 mmHg causes ischemia from vasoconstriction)
• Reserve hyperventilation (PaCO2 30-35 mmHg) only as a temporary bridge if signs of herniation appear (Cushing's triad, pupillary changes, extensor posturing)
• Maintain SpO2 >94%; avoid hyperoxia once airway secured (titrate FiO2)
• Lung-protective ventilation: tidal volume ≤6 mL/kg, avoid high mean airway pressures (raises CVP → raises ICP)

• TIVA with propofol + remifentanil is preferred: reduces CBF and CMRO2, allows rapid emergence and neurological assessment
• If inhalational agent used: sevoflurane ≤1 MAC is acceptable with normocapnia; avoid >1 MAC (dose-dependent uncoupling of cerebral autoregulation)
• Avoid nitrous oxide: in closed gas-containing spaces (pneumocephalus risk); debated ICP effects
• Dexmedetomidine: reduces CBF and CMR; useful adjunct for sedation; watch for bradycardia and hypotension
• Maintain neuromuscular blockade throughout (rocuronium; reverse with neostigmine or sugammadex)

• Use isotonic, glucose-free crystalloid (0.9% normal saline or Plasma-Lyte)
• Avoid hypotonic solutions (worsen cerebral edema)
• Avoid dextrose-containing fluids (hyperglycemia amplifies ischemic brain injury)
• Maintain euvolemia; account for osmotic diuresis if mannitol is given
• Blood available; transfuse to maintain Hb >8-10 g/dL in neurosurgical cases
• EBV = ~75 mL/kg; 10 mL/kg bolus for resuscitation

• Mannitol 0.25-1 g/kg IV over 20 min: osmotic agent, reduces blood viscosity → transiently increases CBF and O2 transport; osmotic brain dehydration kicks in 20-30 min later; repeat doses can be given; target serum osmolality <320 mOsm/L
• Hypertonic saline (3% NaCl, 2-5 mL/kg over 10-20 min): reduces ICP by osmotic gradient; also reduces inflammation; sustained serum Na <160 mEq/L
• CSF drainage: ventriculostomy catheter allows CSF removal intraoperatively - particularly useful; often a pre-placed EVD is opened before induction in severe cases
• In infratentorial procedures/obstructive hydrocephalus: ventriculostomy may be placed under local anaesthesia before induction of GA to reduce ICP prior to airway manipulation

"In such cases, a ventriculostomy is often performed under local anesthesia to decrease ICP prior to induction of general anesthesia." - Morgan & Mikhail's Clinical Anesthesiology, 7e, p.1116

• Maintain normoglycemia (60-180 mg/dL); hyperglycemia amplifies ischemic injury; hypoglycemia causes direct neuronal injury
• Avoid dextrose-containing maintenance fluids; check glucose intraoperatively

• Maintain MAP to keep CPP ≥40-50 mmHg
• Treat hypotension promptly with vasopressors (phenylephrine/noradrenaline) + adequate preload
• Avoid hypertension (can worsen edema, hemorrhage)

• Maintain normothermia
• Active warming: forced-air warming blanket, warm IV fluids, warm OR
• Therapeutic hypothermia is NOT recommended routinely (multicenter RCTs show no benefit, possible harm from hemodynamic instability)

4.4 Specific Situations

• Usually supine with head turned; ensure neck not hyperflexed/rotated to impede venous return
• Tunnelling the shunt (abdominal component) is a separate stimulating step requiring adequate depth
• Peritoneum entry may cause sudden vagal response - have atropine ready
• Abdominal compartment: watch for sudden change in respiratory compliance

• Patient supine with head in Mayfield pins or Sugita frame - significant pain stimulus; ensure depth
• Head flexion required for endoscope entry - watch for venous obstruction and neck flexion effects on breathing circuit
• Intraventricular irrigation with warm normal saline can cause transient bradycardia - have atropine available
• Risk of sudden cardiac arrest from direct hypothalamic stimulation
• Risk of acute ICP rise if endoscope blocks CSF drainage

• Pre-place EVD under LA before GA induction if severely elevated ICP
• Sitting position or "beach-chair" position: highest VAE risk
  • Precordial Doppler placed over right heart
  • Central venous catheter positioned at SVC-RA junction for aspiration of air
  • Treatment of VAE: flood field with saline, compress jugular veins, aspirate from CVP line, left lateral/Trendelenburg position, 100% O2, vasopressors
• Post-op: monitor for SIADH, DI, cerebral salt wasting

4.5 Emergence and Extubation

• Reverse neuromuscular blockade (confirm TOF ratio ≥0.9)
• Prevent coughing/bucking/straining - these cause sudden ICP surge and risk intracranial hemorrhage
  • IV lignocaine 1 mg/kg before extubation
  • Remifentanil infusion continued to the point of extubation blunts response
  • Dexmedetomidine infusion during closure (0.5-1 mcg/kg/h)
  • Deep extubation is an option in selected cases but risks aspiration
• Ensure normocapnia before extubation
• Head 30° elevation maintained
• Delay extubation and continue sedation if: prolonged procedure, significant brain swelling, hemodynamic instability, preoperative neurological compromise

• GCS significantly decreased from baseline
• Ineffective cough/gag
• Significant posterior fossa edema
• Hemodynamic instability
• Significant intraoperative blood loss with coagulopathy

5. Postoperative Management

• Neurological observations every 15-30 min: GCS equivalent, pupils, fontanelle tension
• Monitor for: re-expansion hemorrhage, shunt malfunction, shunt infection (fever, irritability, altered consciousness), CSF leak
• Analgesia: paracetamol + opioids cautiously (titrate to effect; avoid respiratory depression)
• Continue anticonvulsants
• Maintain head 30° elevation, midline

• Watch for SIADH (low Na, concentrated urine, euvolemic/hypervolemic): fluid restrict; cautious hypertonic saline
• Watch for DI (polyuria, high serum Na, dilute urine SG <1.005): volume replacement + vasopressin infusion
• Watch for cerebral salt wasting (low Na + hypovolemia): replace Na and volume

• Over-drainage: can cause subdural hematoma, slit-ventricle syndrome; postural headache
• Under-drainage: recurrence of hydrocephalus
• Shunt infection: early infection within 6 months of insertion is common (S. epidermidis, S. aureus); presents with fever, irritability, CSF pleocytosis

6. Summary Table: Pharmacological Principles

• Miller's Anesthesia, 10e - Hydrocephalus (block 31, p.11402); Pediatric CNS/TBI (block 31, pp.11380-11401)
• Morgan & Mikhail's Clinical Anesthesiology, 7e - Intracranial pressure, Preoperative/Intraoperative management, Obstructive Hydrocephalus (block 4, pp.1085-1116)
• Morgan & Mikhail's Clinical Anesthesiology, 7e - Effect of anesthetic agents on cerebral physiology (Table 26-1, p.1087)