🧠 Chapter 61: Intracranial Hypertension

Monro-Kellie doctrine · Cerebral compliance · CPP (CPP = MAP - ICP) · ICP waveform (P1>P2 normal, P2>P1 = ↓ compliance) · Lundberg A-waves (plateau) · First-tier therapy (sedation, head-up, osmotherapy, CSF drainage) · Second-tier (barbiturates, decompressive craniectomy, hypothermia) · Mannitol vs hypertonic saline

🔍 Core Concepts: Intracranial Hypertension

📌 Monro-Kellie Doctrine
Skull is fixed volume: brain + blood + CSF = constant. If any component increases, others must compensate (CSF → spinal canal, then venous blood). Once exhausted, ICP rises exponentially.
📊 CPP = MAP - ICP
Cerebral Perfusion Pressure target: infants 40-45 mmHg, children 45-50 mmHg, adults 50-70 mmHg. Low CPP → cerebral ischaemia. Treat hypotension aggressively.
📈 ICP Waveform (Lundberg)
Normal: P1 > P2 (percussive > tidal). With poor compliance: P2 > P1. A-waves (plateau waves): pathological, ICP >50 for 5-20 min → herniation risk.
💊 First-tier Therapy
Head-up 30°, sedation/analgesia, CSF drainage (if EVD), hyperosmolar therapy (mannitol 0.25-1 g/kg or 3% NaCl), avoid hypercapnia, maintain euvolemia, target CPP.
⚡ Second-tier Therapy
Barbiturates (thiopentone, burst suppression), decompressive craniectomy, hypothermia (32-34°C), aggressive hyperventilation (last resort, risk ischaemia).
⚠️ Herniation Signs
Cushing triad: hypertension, bradycardia, irregular breathing. Ipsilateral pupil dilatation = uncal herniation. Immediate: hyperventilation, mannitol, EVD drainage, CT.

🩺 Stepwise Approach: Raised ICP

1
Emergency measures for impending herniation
If unequal pupils, Cushing triad: intubate, hyperventilate (target PaCO2 30-35), mannitol 0.5-1 g/kg IV, elevate head 30°, urgent CT, call neurosurgery.
2
General first-tier measures (ICP >20)
Head midline, elevated 30°. Sedation (fentanyl/midazolam, consider neuromuscular blockade). Avoid fever, hypoglycaemia, hyponatraemia. Maintain euvolemia (avoid overload).
3
CSF drainage (if EVD in place)
External ventricular drain (EVD) is gold standard for ICP monitoring + therapy. Drain CSF in increments to keep ICP <20. Monitor ICP waveform (P2 > P1 indicates poor compliance).
4
Hyperosmolar therapy
Mannitol 0.25-0.5 g/kg bolus (1 g/kg for herniation). Monitor osmolality (target <320). Hypertonic saline (3%) 0.1-1 mL/kg/h, target Na 145-150. Preferred in hypotensive patients.
5
Second-tier (refractory ICP)
Barbiturate coma (thiopentone, burst suppression on EEG). Decompressive craniectomy. Hypothermia (32-34°C). Optimised hyperventilation (jugular venous saturation monitoring).
6
CPP optimisation
Target CPP age-appropriate. If CPP low, give fluids (isotonic) or vasopressors (norepinephrine) to increase MAP. Avoid excessive vasopressors that increase ICP.