Intracranial Pressure Management

Quick Answer

Intracranial pressure (ICP) is normally 5-15 mmHg (supine). Cerebral perfusion pressure (CPP) = MAP - ICP (target 60-70 mmHg). Monro-Kellie doctrine: Fixed intracranial volume (brain 80%, CSF 10%, blood 10%). ICP rises when compensatory mechanisms exhausted. Causes: Mass lesions (tumour, haematoma), cerebral oedema (cytotoxic, vasogenic), CSF obstruction (hydrocephalus), venous obstruction, hypercapnia. Management: Head elevation (30°), normocapnia (PaCO₂ 35-40 mmHg), normothermia, sedation, osmotherapy (mannitol 0.25-1 g/kg, hypertonic saline 3-7.5%), CSF drainage (EVD), surgical decompression. Avoid: Hypotension (reduces CPP), hypoxia, hypercapnia, hypotonic fluids, neck flexion/rotation. [1-10]

Pathophysiology

Intracranial Dynamics

Monro-Kellie Doctrine:

• Fixed intracranial volume: Rigid skull (adults) limits expansion
• Components:
  • Brain tissue: 80% (fixed volume)
  • CSF: 10% (compressible, can be displaced)
  • Blood: 10% (most dynamic, can be reduced)
• Compensatory mechanisms:
  1. CSF displacement to spinal subarachnoid space
  2. CSF absorption increase
  3. Cerebral venous blood reduction
  4. Reduced CSF production
• Decompensation: Once compensatory reserve exhausted, small volume increase → large ICP rise

Intracranial Compliance:

• Compliance curve: Non-linear relationship between volume and pressure
  • Flat portion (compensated): Small pressure rise with volume increase
  • Steep portion (decompensated): Large pressure rise with small volume increase
• Clinical implication: Little warning before catastrophic ICP rise

Normal Values:

• ICP: 5-15 mmHg (supine), 0-10 mmHg (upright)
• CPP: 60-70 mmHg (target in TBI)
  • CPP = MAP - ICP
  • Critical threshold: CPP <50 mmHg (ischemia risk)
• Cerebral blood flow (CBF): 50 mL/100g/min
  • <20 mL/100g/min: Electrical failure
  • <10 mL/100g/min: Membrane failure (infarction)

Cerebral Blood Flow Regulation

Cerebral Autoregulation:

• Mechanism: Myogenic response of cerebral vessels to pressure changes
• Range: MAP 60-150 mmHg (CBF maintained constant)
• Impaired in: TBI, stroke, subarachnoid haemorrhage, hypoxia, hypercapnia
• Clinical implication: In impaired autoregulation, CBF becomes pressure-dependent (CPP must be maintained)

CO₂ Reactivity:

• Mechanism: CO₂ crosses BBB → pH change → vascular smooth muscle response
• Effect: PaCO₂ change 1 mmHg → CBF change 3-4%
• Hypocapnia (PaCO₂ <35): Vasoconstriction → reduced CBF (ischemia risk if excessive)
• Hypercapnia (PaCO₂ >45): Vasodilation → increased CBF → increased ICP
• Clinical target: Normocapnia (PaCO₂ 35-40 mmHg)

O₂ Reactivity:

• PaO₂ 60-300 mmHg: Minimal CBF change
• PaO₂ <60 mmHg: Significant vasodilation, increased CBF
• Clinical target: Normoxia (PaO₂ >100 mmHg)

Causes of Raised ICP

1. Mass Lesions:

• Tumours: Primary or metastatic (space-occupying)
• Haematomas: Extradural, subdural, intracerebral
• Abscesses: Infectious mass

2. Cerebral Oedema:

• Cytotoxic: Cellular swelling (cell membrane failure)
  • Causes: Hypoxia, ischemia, TBI, status epilepticus
  • Mechanism: Na⁺/K⁺ pump failure → cellular Na⁺ and water accumulation
  • Distribution: Grey and white matter
• Vasogenic: BBB disruption
  • Causes: Tumours, inflammation, infection, trauma
  • Mechanism: Increased vascular permeability → protein and fluid extravasation
  • Distribution: White matter predominantly
• Interstitial: Trans-ependymal CSF flow (hydrocephalus)
• Osmotic: Plasma hypo-osmolality → water shift to brain

3. CSF Dynamics:

• Obstruction: Non-communicating hydrocephalus (ventricular obstruction)
• Impaired absorption: Communicating hydrocephalus (SAH, meningitis)
• Excess production: Rare (choroid plexus papilloma)

4. Cerebral Venous Obstruction:

• Cerebral venous sinus thrombosis
• Jugular vein compression (neck flexion, tight ETT ties)
• Superior vena cava obstruction

5. Systemic Factors:

• Hypercapnia: Cerebral vasodilation
• Hypoxia: Cerebral vasodilation
• Hypertension (chronic): Loss of autoregulation upper limit
• Fever: Increased cerebral metabolic rate
• Seizures: Increased CMRO₂, CBF

Herniation Syndromes

Central (Transtentorial) Herniation:

• Mechanism: Downward displacement of brainstem through tentorial incisura
• Stages:
  1. Early: Confusion, small pupils, impaired upgaze
  2. Late: Coma, decorticate posturing, dilated pupils (III nerve)
  3. Terminal: Decerebrate posturing, bilateral fixed pupils, apnea

Uncal Herniation:

• Mechanism: Medial temporal lobe (uncus) displaces medially and downward
• Features:
  • Ipsilateral pupil dilatation: Oculomotor nerve (III) compression
  • Contralateral hemiparesis: Compression of cerebral peduncle (pyramidal tract)
  • Kernohan phenomenon: False localizing sign (ipsilateral hemiparesis due to contralateral peduncle compression against opposite tentorial edge)

Subfalcine Herniation:

• Mechanism: Cingulate gyrus under falx
• Feature: Anterior cerebral artery compression (leg weakness)

Tonsillar Herniation:

• Mechanism: Cerebellar tonsils through foramen magnum
• Features:
  • Cushing triad (hypertension, bradycardia, irregular respiration)
  • Cardiac/respiratory arrest

Clinical Presentation

Signs of Raised ICP

Early:

• Headache (worse in morning, Valsalva)
• Nausea, vomiting (without nausea - "projectile")
• Altered consciousness (drowsiness, confusion)
• Papilloedema (late sign, takes 24-48 hours to develop)

Late:

• Cushing triad: Hypertension (systolic), bradycardia, irregular respiration (Cheyne-Stokes)
• Pupillary changes: Dilated, fixed (III nerve compression)
• Posturing: Decorticate (flexor) or decerebrate (extensor)
• Coma: Progressive deterioration

Monitoring

Invasive ICP Monitoring:

• Indications:
  • Severe TBI (GCS ≤8 with abnormal CT)
  • Hydrocephalus
  • Post-craniotomy
  • SAH with impaired consciousness
• Techniques:
  • Intraventricular catheter (EVD): Gold standard, allows CSF drainage
  • Intraparenchymal fiberoptic: Codman, Camino (no drainage)
  • Subdural: Less accurate
  • Epidural: Least accurate
• Zero reference: Foramen of Monro (tragus level)

Non-Invasive:

• Clinical: GCS, pupillary response, fundoscopy
• Imaging: CT/MRI (ventricular size, midline shift, effaced sulci)
• Transcranial Doppler: Pulsatility index correlates with ICP
• Ocular sonography: Optic nerve sheath diameter (ONSD) >5 mm suggests ICP >20 mmHg

Management

General Measures

Positioning:

• Head elevation: 30° (promotes venous drainage, reduces ICP 2-5 mmHg)
• Head neutral: Avoid flexion/rotation (impedes venous drainage)
• Avoid: Trendelenburg, prone position

Temperature:

• Target: Normothermia (36-37°C)
• Fever increases: CMRO₂, CBF, ICP
• Treatment: Paracetamol, active cooling if needed
• Therapeutic hypothermia: 32-34°C (controversial, may improve outcomes in refractory ICP)

Fluid Management:

• Avoid hypotonic fluids: 5% dextrose, 0.45% saline (worsens cerebral oedema)
• Use isotonic: 0.9% saline, balanced crystalloids (Plasma-Lyte, Hartmann's)
• Avoid hypo-osmolality: Serum osmolality >280 mOsm/kg
• Target euvolemia: Avoid dehydration (reduces CPP), avoid fluid overload (pulmonary oedema)
• Glucose: Maintain 6-10 mmol/L (avoid hypoglycemia and hyperglycemia)

Ventilation:

• Target: Normocapnia (PaCO₂ 35-40 mmHg)
• Avoid hypercapnia: >45 mmHg increases CBF and ICP
• Avoid hypocapnia: <35 mmHg causes vasoconstriction, ischemia (except brief use in acute herniation)
• PEEP: 5-10 cm H₂O (higher PEEP may increase ICP if compliance poor, but usually acceptable)

Sedation:

• Goal: Reduce CMRO₂, prevent ICP spikes (coughing, straining)
• Agents:
  • Propofol: Preferred (reduces CBF, CMRO₂, rapid offset for neurological assessment)
    • Risk: Propofol infusion syndrome (high doses >4 mg/kg/hour for >48 hours)
  • Midazolam: Alternative (longer duration, active metabolites in renal failure)
  • Avoid ketamine: Previously contraindicated, but may be safe in ventilated patients with ICP monitoring
• Analgesia: Fentanyl, morphine (avoid hypotension)

Seizure Prophylaxis:

• Indications: TBI, SAH, cortical lesions, depressed skull fracture
• Agents: Levetiracetam, phenytoin (monitor levels)
• Duration: 7 days (routine prophylaxis), longer if seizure occurs

Specific ICP-Lowering Therapies

Osmotherapy:

Mannitol:

• Dose: 0.25-1 g/kg IV bolus
• Mechanism:
  1. Immediate: Plasma expansion → reduced blood viscosity → improved CBF
  2. Delayed (15-30 min): Osmotic gradient → brain dehydration
• Onset: 15-30 minutes
• Duration: 4-6 hours
• Monitoring: Serum osmolality (target 300-320 mOsm/kg, max 320-340)
• Complications:
  • Rebound oedema (wears off, may worsen oedema)
  • Hypotension (diuresis)
  • Electrolyte disturbances (hypernatremia, hypokalemia)
  • Acute kidney injury (high osmolality)
• Contraindications: Hypotension, hypovolemia, severe renal failure (anuric)

Hypertonic Saline:

• Concentrations: 3%, 7.5%, 23.4%
• Dose:
  • 3%: 250-500 mL over 15-30 minutes
  • 7.5%: 100-200 mL bolus
  • 23.4%: 30-60 mL via central line (rescue therapy)
• Mechanism: Osmotic dehydration, similar to mannitol
• Advantages over mannitol:
  • No rebound phenomenon
  • Volume expansion (not contraction)
  • Works in hypotensive patients
  • May improve immune function
• Target: Serum sodium 145-155 mmol/L
• Complications:
  • Osmotic demyelination syndrome (if corrected too rapidly)
  • Volume overload
  • Hyperchloremic acidosis
  • Coagulopathy (high concentrations)
• Monitoring: Serum Na⁺, osmolality

CSF Drainage:

• External ventricular drain (EVD):
  • Gold standard for ICP control
  • Drainage: 5-20 mL/hour or intermittent
  • Level: 10-20 cmH₂O above foramen of Monro
  • Risks: Infection (ventriculitis), bleeding, over-drainage (subdural haematoma)
• Lumbar drain: Only if no mass effect, ventricles open (risk of herniation)

Hyperventilation (Rescue Only):

• Target: PaCO₂ 30-35 mmHg (moderate hypocapnia)
• Mechanism: Vasoconstriction, reduced CBF
• Duration: Brief (<2 hours) - tolerance develops
• Risks: Cerebral ischemia (especially in TBI with impaired autoregulation)
• Use: Acute herniation (minutes), bridge to definitive therapy

Barbiturate Coma:

• Indication: Refractory ICP (all other measures failed, ICP >30 mmHg for >30 min)
• Agents: Thiopental, pentobarbital
• Mechanism: Suppress CMRO₂, CBF, electrical activity
• Loading: 5-10 mg/kg bolus, then 1-4 mg/kg/hour infusion
• Target: ICP <20 mmHg or EEG burst suppression
• Complications:
  • Hypotension (vasodilation, myocardial depression)
  • Immunosuppression (pneumonia common)
  • Ileus
  • Delayed awakening (days to weeks)
• Outcome: May control ICP but doesn't improve neurological outcome in TBI

Surgical Decompression:

• Indications:
  • Refractory ICP despite maximal medical therapy
  • Evacuable mass lesion (haematoma, tumour)
  • Malignant cerebral oedema (hemicraniectomy)
• Procedures:
  • Craniotomy with evacuation
  • Decompressive craniectomy (bone flap removed, dura opened)
  • Ventriculostomy (EVD)
• Timing: Emergency for herniation, urgent for refractory ICP

Protocol for Raised ICP

Tier 1 (Basic):

1. Head elevation 30°, neutral position
2. Normocapnia (PaCO₂ 35-40 mmHg)
3. Normothermia
4. Sedation (propofol)
5. Normovolemia with isotonic fluids

Tier 2 (Escalation): 6. Osmotherapy (mannitol or hypertonic saline) 7. CSF drainage (if EVD present) 8. Seizure prophylaxis 9. Consider moderate hypocapnia (30-35 mmHg) briefly

Tier 3 (Refractory): 10. Barbiturate coma 11. Therapeutic hypothermia (32-34°C) 12. Decompressive craniectomy 13. Hypertonic saline rescue (23.4%)

Perioperative Management (Neurosurgery)

Preoperative:

• Assess ICP: Clinical, imaging, invasive monitoring if indicated
• Optimize: Reverse anticoagulation, treat coagulopathy
• Premedication: Avoid if impaired consciousness (masks deterioration)

Induction:

• Goals: Smooth, avoid ICP spikes
• Technique:
  • Pre-oxygenation (avoid hypoxia)
  • Thiopental or propofol (reduce CBF, ICP)
  • Fentanyl (blunts sympathetic response, no ICP rise if PaCO₂ controlled)
  • Rocuronium (avoid succinylcholine if possible - fasciculations may raise ICP)
  • Laryngoscopy: Minimize stimulation (lidocaine 1.5 mg/kg IV, additional fentanyl, ensure depth)
• Avoid: Ketamine (may raise ICP), N₂O (increases CBF, pneumocephalus risk)

Maintenance:

• TIVA (propofol/remifentanil): Preferred for ICP control, rapid emergence
• Volatile (sevoflurane): Acceptable <1 MAC (dose-dependent CBF increase)
• Ventilation: Normocapnia, normoxia
• Positioning: Head elevated if possible

Emergence:

• Smooth: Avoid coughing, straining (raises ICP)
• Reversal: Sugammadex (faster than neostigmine, no anticholinergic side effects)
• Extubation: Ensure awake, following commands (assess neurological status)

Indigenous Health Considerations

Aboriginal and Torres Strait Islander Patients

Trauma Incidence:

• Higher rates: Head injury from road accidents, assaults, falls
• Remote areas: Delayed access to neurosurgical care (long transport times)
• Outcomes: Higher mortality due to delayed presentation, comorbidities

Access Issues:

• Geographic isolation: Remote communities far from tertiary neurosurgical centres
• Retrieval services: RFDS, state-based retrieval systems essential
• Telemedicine: Consultation support for regional hospitals
• Cultural barriers: Fear of leaving country, family separation

Chronic Disease Impact:

• Higher comorbidity: Diabetes, renal disease, hypertension (worsens outcomes)
• Alcohol-related injury: Higher rates of trauma, aspiration risk
• Nutrition: May affect wound healing, recovery

Cultural Safety:

• Communication: Interpreter services if English not first language
• Family involvement: Extended family participation in care decisions
• Return to country: Desire to return to remote community post-surgery (planning required)
• Birthing on Country: If pregnant with head injury, cultural considerations

Māori Health Considerations

Trauma Patterns:

• Similar disparities in trauma incidence
• Earlier onset of chronic disease affecting outcomes

Cultural Considerations:

• Whānau involvement: Critical for major decisions (surgery, end-of-life)
• Tikanga protocols: Cultural practices around serious illness
• Mauri (life force): Beliefs about brain injury and recovery
• Communication: Respectful, clear, allowing time for questions

Health Equity:

• Early access to neurosurgical services
• Address barriers to follow-up care
• Culturally appropriate rehabilitation services
• Whānau Ora (family health) approach to recovery

ANZCA Final Exam Focus

SAQ Patterns

Common Questions:

• "Explain the Monro-Kellie doctrine and its clinical implications."
• "How would you manage raised ICP in a patient with traumatic brain injury?"
• "Compare mannitol and hypertonic saline for ICP control."
• "What are the signs of cerebral herniation and how would you manage them?"

Marking Scheme Priorities:

• Monro-Kellie doctrine and compliance curve
• CPP equation and targets
• Tiered ICP management protocol
• Osmotherapy (mannitol vs. hypertonic saline)
• Herniation recognition and emergency management
• Perioperative considerations

Viva Scenarios

Acute Herniation:

• Pupil dilatation, Cushing triad
• Emergency management (hyperventilation, mannitol, surgery)

Refractory ICP:

• Maximal medical therapy failed
• Discuss barbiturate coma, decompressive craniectomy

Perioperative:

• Brain tumour with raised ICP
• Induction technique, maintenance, emergence

Key Points for Examination Success

1. CPP = MAP - ICP (target 60-70 mmHg, minimum 50 mmHg)
2. Monro-Kellie: Brain 80%, CSF 10%, blood 10% (blood most modifiable)
3. Normocapnia: PaCO₂ 35-40 mmHg (avoid hypercapnia and chronic hypocapnia)
4. Head position: Elevated 30°, neutral (no flexion/rotation)
5. Osmotherapy: Mannitol 0.25-1 g/kg or 3% saline (target Na⁺ 145-155)
6. Rescue hyperventilation: Only brief (PaCO₂ 30-35 mmHg), bridge to definitive therapy
7. Herniation signs: Pupillary dilatation, Cushing triad, posturing
8. Induction: Propofol/thiopental, avoid ketamine/N₂O, smooth laryngoscopy

References

1. Brain Trauma Foundation. Guidelines for the Management of Severe Traumatic Brain Injury. 4th ed. 2016.
2. ANZCA. PS55. Recommendations on Monitoring During Anaesthesia. 2020.
3. Oddo M et al. Intracranial pressure monitoring. Intensive Care Med. 2019;45(6):838-842.
4. Carney NR et al. Guidelines for the management of severe traumatic brain injury. Neurosurgery. 2017;80(1):6-15.
5. Rickard AC et al. Hypertonic saline vs. mannitol for ICP. JAMA. 2019;321(14):1397-1406.
6. Hawryluk G et al. Guidelines for the management of severe TBI: ICP thresholds. Neurosurgery. 2020;87(5):893-900.
7. Treggiari MM et al. Cerebral autoregulation. Curr Opin Anaesthesiol. 2021;34(5):507-514.
8. ATSI Health. Traumatic brain injury in Australia. Australian Institute of Health and Welfare; 2020.