Ketamine is Safe for RSI in Head Injury Patients
Ketamine is safe and appropriate for rapid sequence intubation in head-injured patients, particularly when used in mechanically ventilated patients with controlled ventilation. 1, 2 The historical contraindication based on concerns about increased intracranial pressure (ICP) has been refuted by modern evidence.
Why Ketamine is Recommended for Head Injury RSI
Ketamine is an appropriate induction agent for RSI due to its quick onset, short duration of action, preservation of respiratory drive, and sympathomimetic properties that maintain hemodynamic stability. 1 This hemodynamic stability is particularly valuable in trauma patients who may be hypovolemic or in shock.
Evidence Refuting ICP Concerns
The traditional teaching that ketamine increases ICP has been definitively challenged:
In mechanically ventilated pediatric patients with intracranial hypertension, ketamine actually decreased ICP by 30% (from 25.8 to 18.0 mm Hg) and increased cerebral perfusion pressure (CPP) from 54.4 to 58.3 mm Hg. 3 This prospective controlled trial in 30 patients with 82 ketamine administrations demonstrated that ketamine effectively lowered ICP without compromising blood pressure or CPP.
A prospective study in severely head-injured adults found that ketamine (at doses averaging 104 mg/kg/day for sedation) resulted in 8 mm Hg higher CPP and only 2 mm Hg higher ICP compared to fentanyl/midazolam, with lower catecholamine requirements. 4
The concern about ketamine increasing ICP originated from early, inadequately controlled studies, and recent literature demonstrates ketamine is safe in controlled ventilation settings. 5
Recommended Dosing for RSI in Head Injury
Administer ketamine at 1-2 mg/kg IV for RSI, using the lower end of the dosing range (1 mg/kg) in patients with cardiovascular compromise. 1, 2 The Society of Critical Care Medicine guidelines support ketamine as a first-line induction agent alongside etomidate. 2
Critical Dosing Caveat
Avoid ketamine doses greater than 2 mg/kg, as higher doses are associated with significantly increased adverse events. 6 A prehospital study found that ketamine doses >2 mg/kg were associated with:
- 7-fold increased odds of hypotension (OR = 7.0)
- 10.8-fold increased odds of laryngospasm
- 6-fold increased odds of oxygen desaturation
- 3.6-fold increased odds of failed airway 6
Essential Clinical Considerations
Medication Sequence
Always administer ketamine BEFORE the neuromuscular blocking agent to prevent awareness during paralysis, which occurs in approximately 2.6% of emergency intubations. 1, 7 This is a critical safety principle emphasized by the Society of Critical Care Medicine. 2
Controlled Ventilation Requirement
The safety of ketamine in head injury is predicated on controlled mechanical ventilation. 3, 5 The FDA label warns against using ketamine alone for procedures of the pharynx, larynx, or bronchial tree, emphasizing the need for airway control. 8
Hemodynamic Monitoring
In critically ill patients with depleted catecholamine stores, ketamine may paradoxically cause hypotension despite its sympathomimetic properties. 2 Have vasopressors immediately available during RSI. 2
Historical Context
The 2008 Pediatrics guidelines stated to "avoid use in patients with increased ICP," 9 but this recommendation predates the robust evidence from 2009-2013 demonstrating ketamine's safety and ICP-lowering effects in controlled ventilation settings. 3, 5, 4
Practical Algorithm for Head Injury RSI
- Preoxygenate the patient and prepare for controlled mechanical ventilation 2
- Administer ketamine 1-2 mg/kg IV (use 1 mg/kg if hemodynamically unstable) 1, 2
- Follow immediately with neuromuscular blocking agent (succinylcholine 1-1.5 mg/kg or rocuronium 1.0-1.2 mg/kg) 1, 2
- Wait 60 seconds after NMBA before attempting intubation 2
- Initiate post-intubation sedation promptly to prevent awareness 7
- Have vasopressors immediately available for potential hypotension 2