Episode Details

Expected Action & Physiology

Ketamine is a nonbarbiturate phencyclidine derivative that acts as an NMDA receptor antagonist, blocking glutamate to selectively interrupt thalamoneocortical pathways while stimulating the limbic system. This induces "dissociative anesthesia" where the patient is unresponsive to pain, but eyes remain open with intact corneal, light, and airway reflexes.

It stimulates the sympathetic system, causing bronchodilation (ideal for asthma/bronchospasm), tachycardia, and hypertension. Direct negative inotropic effects can predominate in critically ill or catecholamine-depleted patients, causing hypotension. Cholinergic activation causes hypersalivation and elevated ICP/IOP.

Therapeutic Uses & Dosing

Uses: Anesthesia induction/maintenance, procedural sedation, RSI (preferred in shock/bronchospasm), plus off-label status asthmaticus, pain, and delirium/agitation.

• IV: Onset: 30–60s (rapid brain circulation); duration: 5–10 min. Dilute 100 mg/mL push and infuse slowly over ≥60s (max 0.5 mg/kg/min) to prevent respiratory depression.
• IM: Onset: 3–5 min; duration: 12–30 min. No dilution.
• Other: Intranasal (bioavailability 35–50%, onset 5–20 min). Oral/Rectal are less predictable due to high first-pass metabolism.

Pharmacokinetics & Metabolism

Highly lipid-soluble with low protein binding (12%), it rapidly distributes to the brain. It is metabolized by CYP3A4 into norketamine (active metabolite, one-third potency of ketamine). Half-life is 2–3 hours. Chronic use induces hepatic enzymes. No renal/hepatic dose adjustments are required.

Complications & Nursing Pearls

• Emergence Reactions: Hallucinations, delirium, or nightmares occur in ~12% of patients. Intervention: Minimize verbal, tactile, and visual stimulation during recovery. Severe reactions can be terminated with benzodiazepines or barbiturates.
• Tonic-Clonic Movements: Purposeless movements can occur but do not indicate a light plane or need for more ketamine.
• Severe Risks: Laryngospasm, apnea, cardiac arrest, and increased ICP/IOP. Contraindication: Do not use as sole agent for procedures involving the larynx/pharynx or requiring muscle relaxation.
• Administration: Give on empty stomach to prevent vomiting/aspiration. Give an anticholinergic beforehand to limit oral secretions.
• Synergy ("Ketofol"): Combining ketamine and propofol reduces doses and improves safety. Propofol counteracts ketamine's nausea/emergence delirium; ketamine offsets propofol's hypotension/respiratory depression.