Ketamine

Mechanism of action: Blocks postsynaptic reflexes in the spinal cord and inhibit excitatory neurotransmitters in selected areas of the brain. Dissociates thalamus from limbic system involved in awareness. NMDA receptor antagonist.

Structure: Structural analogue of PCP.

Cerebral, respiratory, and cardiovascular Effects: Increased CMRO₂, increased CBF, and increased ICP. Ventilatory drive is minimally affected. Potent bronchodilator, so good induction agent in patients with asthma. Increased MAP, increased heart, increased CO because of central stimulation of the sympathetic nervous system and inhibits reuptake of norepinephrine. Increase PAP and myocardial work.

Metabolism: Duration limited by redistribution (half-life, 10–15 min). Biotransformed in the liver and excreted by the kidneys.

Side effects: Can cause direct myocardial depression and may lead to decreased CO in sympathetic blockade, spinal cord transection, or exhaustion of catecholamine stores (severe end-stage shock). Relatively contraindicated in coronary artery disease, CHF, uncontrolled hypertension, and aneurysms.

Dosage: Induction: 1 mg/kg (5–10 mg/kg intramuscularly or per rectum); sedation load: 200 to 1000 mcg/kg; then 30 to 80 mcg/kg/min for maintenance.

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