Ketamine Emergence Reaction

Ketamine emergence reaction is a group of psychological phenomena during recovery from ketamine: vivid dreams, hallucinations, floating sensations, confusion, delirium, agitation, fear and dysphoria. It usually begins within minutes of waking and lasts from minutes to a few hours.

Epidemiology. It occurs in about 10% to 30% of adults given ketamine, and less often in children under 15 years (about 5% to 10%). Severe reactions are less frequent.

Risk factors. Age over 15 years, female sex, dose over 2 mg/kg IV, rapid injection, history of psychiatric disease, vivid dreams or personality disorders, absence of premedication, stimulation during recovery and patient anxiety.

Pathophysiology.

Ketamine blocks N-methyl-D-aspartate receptors and disinhibits cortical and limbic glutamatergic neurons. This releases sensory and emotional processing, producing dissociation and hallucination.

Reactions often appear on recovery, since the drug reaches its lowest level while the cortex awakens in a dissociated state.

Vivid dreams, nightmares, visual and auditory hallucinations, out-of-body sensations, agitation, crying, combative behaviour, nausea, nystagmus, hypertension and tachycardia.

Red flags.

• Violent behaviour with risk of injury.
• Persistent psychosis beyond 24 hours.
• Respiratory depression after added sedatives.
• Signs of raised intracranial pressure or laryngospasm.

Clinical, in a patient recovering from ketamine. Exclude hypoxia, hypoglycaemia, pain, urinary retention, withdrawal, stroke, infection, other drugs and anticholinergic delirium. Check oxygen saturation, glucose and observation chart.

Differential diagnosis.

• Emergence delirium from other agents.
• Hypoxia.
• Pain.
• Hypoglycaemia.
• Alcohol or drug withdrawal.
• Anticholinergic toxicity.
• Neurological event.

Prevention. Use the lowest effective dose (analgesia 0.1 to 0.3 mg/kg IV, induction 1 to 2 mg/kg IV), inject slowly over 60 seconds, and recover the patient in a quiet, low stimulation area. Prepare patients and pre-medicate when ketamine is used.

• Midazolam prophylaxis: 0.03 to 0.05 mg/kg IV (usually 1 to 3 mg in adults) before or with ketamine; single dose; maximum 5 mg; monitor sedation and respiratory rate; use half the dose in older adults and in hepatic impairment.

Treatment. Reassure, reduce stimulation, ensure safety and treat pain.

• Midazolam: 1 to 2 mg IV, repeated every 2 to 5 minutes as needed; maximum 5 mg total in adults; monitor respiratory rate, saturation and sedation; reduce by half in older adults and hepatic impairment.
• Propofol (if severe and monitored): 0.25 to 0.5 mg/kg IV; may repeat once; maximum 1 mg/kg; monitor airway and blood pressure; reduce in older adults and shock.
• Haloperidol is an option for persistent agitation: 2.5 to 5 mg IV or IM; repeat once after 30 minutes; maximum 10 mg in 24 hours in this setting; check QTc; reduce in older adults, avoid in Parkinson disease and long QT.

Monitoring. Respiratory rate, saturation, sedation score, blood pressure and heart rate until the patient is calm and orientated.

Referral and escalation. Psychiatric or senior anaesthetic review for reactions lasting over 24 hours or severe behaviour. Document the event and use benzodiazepine cover in future ketamine use.