Hydrocephalus: Classification, Anaesthetic Considerations, and Anaesthetic Management

Miller's Anesthesia, 2-Volume Set, 10e

1. DEFINITION

2. CLASSIFICATION

2.1 Communicating Hydrocephalus

• Subarachnoid haemorrhage (SAH) — a particularly frequent association; 15%–87% of SAH patients develop acute hydrocephalus
• Meningitis / infection in the CSF space
• Blood in the CSF space obstructing arachnoid villi
• Normal pressure hydrocephalus (NPH) — chronic form in adults

2.2 Noncommunicating (Obstructive) Hydrocephalus

• Aqueductal stenosis (congenital malformations — e.g., Arnold-Chiari malformation, Dandy-Walker syndrome)
• Compression by posterior fossa tumours (astrocytoma, medulloblastoma — ~70% of paediatric brain tumours are in the posterior fossa)
• Intraventricular haemorrhage (neonatal)
• Infection within the ventricular system
• Obstructed ventricular shunts

"In a noncommunicating hydrocephalus, CSF egress from the ventricular system is obstructed. This can occur because of blood or infection in the ventricular system or tumors in or adjacent to the ventricular system. In communicating hydrocephalus, the CSF escapes from the ventricular system but is not absorbed by the arachnoid villi." — Miller's Anesthesia, 10e, Chapter 53 (block 22)

2.3 Special Subtype — Acute Post-SAH Hydrocephalus

3. PATHOPHYSIOLOGY RELEVANT TO ANAESTHESIA

Intracranial Volume-Pressure Relationship (Monroe-Kellie Doctrine)

1. Herniation — sub-falcine, uncal (transtentorial), cerebellar, or transcalvarial
2. Ischaemia — reduced cerebral perfusion pressure (CPP = MAP − ICP)

4. ANAESTHETIC CONSIDERATIONS

4.1 Preoperative Assessment

• Neurological status: GCS, pupillary responses, papilloedema, level of consciousness (stupor/coma demand IV induction — inhaled inductions should be avoided in stuporous patients)
• Imaging: Head CT showing ventricular dilatation is diagnostic. Assessment of basal cisterns is important — obliterated cisterns indicate exhausted compensatory reserve
• Comorbidities in children: Meningomyelocele, prior intraventricular haemorrhage, posterior fossa tumours — the most frequent paediatric indications for VP shunts
• Shunt dependency: Patients presenting with obstructed shunts are in acute ICP crisis — emergency planning is mandatory
• Fontanelle assessment in infants: Open fontanelles provide a compensatory margin and allow real-time ICP trend monitoring by palpation

4.2 Physiological Targets

• Moderate hyperventilation is a cornerstone: target PaCO₂ 25–30 mmHg for shunt procedures (customary for ICP reduction)
• Mechanism: hypocapnia → cerebral vasoconstriction → reduced CBF and CBV → lower ICP
• Caution: reduction below 23–25 mmHg offers minimal additional ICP benefit and risks ischaemia; EEG abnormalities occur below 20 mmHg
• The PaCO₂ target should be agreed upon with the surgeon at the outset
• Prolonged hyperventilation loses efficacy as cerebrospinal compensation occurs (adaptation within hours)

• CPP = MAP − ICP. Maintain CPP at normal to high-normal levels
• After acute CNS insult (TBI, SAH), CBF may be critically low in some regions; autoregulation may be impaired → even modest hypotension can cause ischaemia
• Avoid hypotension — support MAP to maintain CPP

• Head-up posture (15°–30°) standard in neuroanesthesia to optimise venous drainage
• Avoid extreme head rotation, neck flexion/extension, cervical collar compression, tight endotracheal tube ties
• Avoid elevated intrathoracic pressure: treat bronchospasm, avoid excessive PEEP, prevent coughing/straining against ETT

• Listed in Miller's Box 53.1 as a recurrent neuroanesthesia issue. Both hypo- and hyperglycaemia worsen neurological outcomes

• Hyperthermia increases CMR (cerebral metabolic rate) and CBF — avoid. Active normothermia is standard

4.3 Drug Considerations

• Propofol, barbiturates, opioids, benzodiazepines — all produce parallel reductions in CBF and CMR; no adverse effect on ICP; preserve autoregulation and CO₂ responsiveness
• Propofol–relaxant induction is the preferred sequence when IV access is available

• All are dose-dependent cerebral vasodilators (potency: halothane > enflurane > desflurane ≈ isoflurane ≈ sevoflurane)
• Safe at <1 MAC as part of a balanced technique in most elective cases
• AVOID (or defer until cranium/dura open) in: somnolent/vomiting patients with papilloedema, large mass lesions, compressed basal cisterns, obliterated sulci/cisterns on CT → use total intravenous anaesthesia (TIVA) instead

• Cerebral vasodilator; effect attenuated when given with propofol or opioids
• Contraindicated if pneumocephalus is present or suspected

• Neuromuscular blockade is standard during craniotomy to prevent coughing → avoids catastrophic herniation through craniotomy
• Histamine-releasing agents (e.g., atracurium): give in small divided doses
• Succinylcholine: can transiently increase ICP (small and short-lived); can be blocked by a prior dose of nondepolarising NMBD; acceptable for rapid-sequence intubation when airway urgency outweighs risk

• Mannitol (osmotic diuretic): widely used for acute ICP reduction
• Hypertonic saline: increasingly used, particularly in paediatrics
• Both reduce brain intracellular/extracellular fluid volume

• Effective for perilesional oedema from tumours and radiation necrosis only
• Not indicated for TBI-related oedema (controlled trials showed no benefit or harm)
• Onset of ICP reduction: 48–72 hours after initiation; too slow for acute intraoperative events
• Preoperative course starting 48 hours before elective surgery can improve intraoperative conditions

5. ANAESTHETIC MANAGEMENT

5.1 Procedures for Hydrocephalus

1. Ventriculoperitoneal (VP) Shunt — most common
2. Lumboperitoneal Shunt — communicating hydrocephalus
3. External Ventricular Drain (EVD/Ventriculostomy) — acute/emergency drainage
4. Endoscopic Procedures — e.g., endoscopic third ventriculostomy (ETV)

5.2 Ventriculoperitoneal (VP) Shunt — Anaesthetic Management

• Burr hole into frontal horn of the lateral ventricle (nondominant/right side)
• Subcutaneous reservoir placed adjacent to burr hole
• Drainage limb tunnelled subcutaneously to epigastrium and inserted into the peritoneal cavity via small laparotomy
• Double-barrelled shunts: two proximal ends (lateral + fourth ventricle), usually performed prone; standard VP shunts done supine

• Invasive monitoring is generally not required for elective shunt placement
• Routine monitors: NIBP, ECG, SpO₂, EtCO₂ (critical for maintaining PaCO₂ target), temperature

• Anesthetic technique must avoid further ICP elevation
• Moderate hyperventilation: PaCO₂ 25–30 mmHg (agree with surgeon preoperatively; less concern about ischaemic effects than in acute injury states)
• A predominantly IV technique (propofol ± opioid ± NMBD) is preferred, especially in symptomatic patients with elevated ICP

• A moderate degree of muscle relaxation is helpful to facilitate peritoneal catheter placement and prevent inadvertent gastrostomy (a distended stomach increases this risk)

1. Ventricular cannulation: blood pressure may drop abruptly as brainstem pressure is relieved — brief vasopressor support may be needed
2. Subcutaneous tunnelling: produces a sudden painful stimulus → surge in blood pressure — should be anticipated and treated preemptively (e.g., deepen anaesthesia or preemptive analgesia before tunnelling)

• Unlike most neurosurgical patients, shunt patients are nursed flat postoperatively
• Rationale: prevent excessively rapid collapse of the ventricular system → risk of tearing bridging veins → subdural haematoma (small but recognised incidence)
• Minor postoperative discomfort; analgesia needs are modest

5.3 Lumboperitoneal Shunt

• Patient positioned laterally
• Catheter inserted into lumbar CSF space via Tuohy-type needle
• Tunnelled subcutaneously to anterior abdominal wall → peritoneal cavity via small laparotomy
• Used when communicating hydrocephalus and no risk of herniation through foramen magnum

5.4 Paediatric VP Shunts — Special Considerations

• Meningomyelocele (myelomeningocele/spina bifida)
• Neonatal intraventricular haemorrhage
• Posterior fossa tumours

• IV access available and not stuporous: propofol–relaxant sequence preferred
• No IV access, not stuporous: inhalational induction with sevoflurane is well-tolerated empirically, even in children with closed fontanelles; initiate controlled ventilation by bag-mask as rapidly as possible, then establish IV access and give relaxant before intubation
• Stuporous child: AVOID inhaled induction — use IV technique only
• Fentanyl supplementation for children >6 months (not stuporous): believed to facilitate smoother emergence and provide postoperative analgesia background

• Open fontanelles provide a compensatory margin and allow bedside ICP trend assessment by palpation — a practical intraoperative monitoring advantage

• The most frequent paediatric neurosurgical procedure
• Presenting for emergency revision implies acute shunt obstruction and raised ICP → treat as full-stomach rapid-sequence intubation with ICP precautions

5.5 Acute Hydrocephalus (Emergency/Post-SAH)

• Develops in 15%–87% after SAH
• Presents with: progressive deterioration → stupor → coma; gaze palsy, pupillary dysfunction, cognitive slowing
• Head CT (ventricular dilation) confirms diagnosis → facilitates early ventriculostomy
• Emergency management: ventriculostomy ± lumbar drain
• Anaesthetic goals: protect airway (GCS ≤8 → intubation), control ICP, maintain CPP, avoid vasodilatory anaesthetics, target PaCO₂ 35 mmHg (normoventilation) or mild hyperventilation as bridge to drainage

5.6 Box 53.3 — High ICP Intraoperative Checklist (Miller's)

1. Are pressures controlled?
   • Jugular venous pressure: extreme head rotation? Direct jugular compression? Head-up posture?
   • Airway pressure: airway obstruction? Bronchospasm? High PEEP?
   • Arterial blood pressure
2. Is metabolic rate controlled?
   • Pain/arousal? Seizures? Fever?
3. Are vasodilators in use?
   • N₂O, volatile agents, nitroprusside, calcium channel blockers?
4. Are there unrecognised mass lesions?
   • Contralateral haematoma? Pneumocephalus expanded by N₂O? Clamped ventricular drain?

5.7 Rapid ICP Reduction Methods (Box 53.4)

1. Further reduction of PaCO₂ (not below 23–25 mmHg)
2. CSF drainage (ventriculostomy, brain needle)
3. Diuresis (mannitol, hypertonic saline, furosemide)
4. CMR suppression (barbiturates, propofol)
5. MAP reduction (if cerebral dysautoregulation confirmed)
6. Hyperosmolar therapy (mannitol 0.25–1 g/kg; hypertonic saline)
7. Surgical control (lobectomy, bone flap removal as last resort)

6. SPECIAL ASSOCIATED CONDITIONS

Meningomyelocele (Spina Bifida) with Hydrocephalus

• Vocal cord paralysis may result from brainstem pressure due to hydrocephalus or Arnold-Chiari malformation
• Treatment of the hydrocephalus (shunting) often resolves the vocal cord dysfunction
• Airway management requires careful assessment for subglottic or vocal cord abnormalities — Miller's Anesthesia, 10e, block 31

Posterior Fossa Tumours in Children

• ~70% of paediatric brain tumours are in the posterior fossa
• Frequently associated with hydrocephalus
• Venous air embolism (VAE) risk is significant — Doppler probe and right heart catheters used in sitting-position procedures
• Postoperatively: monitor for SIADH (24–48h), central DI, cerebral salt wasting, and posterior fossa haemorrhage
• Triphasic response after suprasellar surgery: SIADH → DI → SIADH

Normal Pressure Hydrocephalus (NPH)

• Communicating hydrocephalus in adults; presents with the classic triad: gait apraxia, urinary incontinence, dementia
• LP shunt or VP shunt; anaesthetic principles as above

7. SUMMARY TABLE

8. KEY TAKE-AWAYS FROM MILLER'S

"The anesthetic technique should be chosen to avoid further increases in ICP. Moderate hyperventilation (PaCO₂ 25 to 30 mmHg) is customary... Blood pressure may decrease abruptly when the ventricle is first cannulated (as brainstem pressure is relieved)... Burrowing the subcutaneous tunnel can produce a sudden painful stimulus, and a surge in blood pressure, which should be anticipated and treated preemptively... shunt patients are often nursed flat after their procedures to prevent an excessively rapid collapse of the ventricular system." — Miller's Anesthesia, 10e, Chapter 53 — Anesthetic Management (block 22)

"We avoid the inhaled induction technique in a child who is already stuporous. When an intravenous line is available, a propofol–relaxant induction sequence is preferable." — Miller's Anesthesia, 10e, Chapter 53 (block 22)

• Chapter 53: Neurosurgical Anesthesia — Cerebrospinal Fluid Shunting Procedures, Anesthetic Management, Pediatric Ventriculoperitoneal Shunts, Pediatric Neurosurgery (block 22)
• Chapter 75 (Pediatric Critical Care): Hydrocephalus (block 31)
• Chapter 80 (Neurocritical Care): Acute Hydrocephalus after SAH (block 33)