Drugs That Increase Intracranial Pressure (ICP)

1. Volatile (Inhalational) Anesthetics

• Cause cerebral vasodilation → ↑ cerebral blood flow (CBF) → ↑ ICP, particularly at higher concentrations (≥1.5 MAC)
• At 0.5 MAC, the reduction in cerebral metabolic rate (CMR) exceeds vasodilation, so CBF may decrease. At 1.5 MAC, vasodilation dominates and CBF increases
• This effect is most clinically relevant in patients with brain tumors, intracranial hemorrhage, or head injury
• Hyperventilation (↓ PaCO₂ → cerebral vasoconstriction) can attenuate this effect

Katzung's Basic and Clinical Pharmacology, 16e; Barash Clinical Anesthesia, 9e

2. Nitrous Oxide (N₂O)

• Increases CBF and ICP via sympathetic nervous system activation
• Produces mild elevation of ICP and also increases cerebral oxygen consumption (CMRO₂)
• Can be mitigated by combining with IV anesthetics or hyperventilation

Katzung's Basic and Clinical Pharmacology, 16e; Morgan & Mikhail's Clinical Anesthesiology, 7e

3. Ketamine

• Traditionally considered to increase cerebral oxygen consumption, CBF, and ICP through NMDA receptor activation and sympathetic stimulation
• However, modern evidence suggests that when combined with benzodiazepines and controlled ventilation (excluding N₂O), ketamine does not consistently raise ICP
• Still used cautiously or avoided as a solo agent in patients with intracranial hypertension

Morgan & Mikhail's Clinical Anesthesiology, 7e; Tintinalli's Emergency Medicine

4. Succinylcholine (Suxamethonium)

• The depolarizing muscle relaxant can transiently increase ICP
• Mechanism: muscle fasciculations stimulate muscle stretch receptors → activation of cerebral activity → modest ↑ CBF and ICP
• Can be attenuated by pre-treatment with a non-depolarizing neuromuscular blocking drug (defasciculation dose) and by maintaining airway control with hyperventilation

Morgan & Mikhail's Clinical Anesthesiology, 7e; Miller's Anesthesia, 10e

5. Drug-Induced Idiopathic Intracranial Hypertension (Pseudotumor Cerebri)

Goldman-Cecil Medicine, 2e

6. Other Anesthesia-Related Mechanisms

• Airway stimulation / inadequate anesthesia during intubation: Causes EEG activation, ↑ CMR, ↑ CBF → ↑ ICP (especially in patients with decreased intracranial compliance)
• Sedatives causing cerebral vasodilation: e.g., high-dose benzodiazepines, though generally ICP-neutral or reducing at clinical doses

Key Concept: Monro-Kellie Doctrine

Clinical Takeaway