A 35-year-old man with no significant past medical history presents for emergency repair of a perforated duodenal ulcer. He is alert and oriented, with a blood pressure of 110/70 mmHg, heart rate 92 bpm, and respiratory rate 18/min. During rapid sequence intubation, the anesthesiologist administers an IV induction agent and the patient develops dissociative anesthesia with preserved airway reflexes, spontaneous breathing, and analgesia. Which agent was most likely administered?

Explanation

## Dissociative Anesthesia: Ketamine's Unique Profile **Key Point:** Ketamine is the only IV induction agent that produces dissociative anesthesia — a state characterized by profound analgesia, preserved airway reflexes, spontaneous breathing, and intact protective reflexes despite apparent unconsciousness. ## Defining Features of Ketamine-Induced Dissociation Ketamine produces a unique anesthetic state with these hallmark characteristics: 1. **Preserved Airway Reflexes** — Cough and gag reflexes remain intact; aspiration risk is lower than with other agents 2. **Spontaneous Breathing** — Respiratory drive is maintained; minimal respiratory depression 3. **Analgesia** — Profound analgesia at sub-anesthetic doses; unique among IV induction agents 4. **Dissociation** — Patient appears awake but is unaware of surroundings (eyes may remain open) 5. **Preserved Hemodynamics** — Sympathomimetic effects maintain or increase BP and HR **High-Yield:** Ketamine is the ONLY IV induction agent with intrinsic analgesic properties — this makes it ideal for trauma, emergency surgery, and pediatric cases where analgesia during induction is critical. ## Mechanism of Dissociation Ketamine acts as a non-competitive antagonist at the **NMDA receptor** (N-methyl-D-aspartate), causing: - Functional dissociation between thalamus and limbic system - Preservation of brainstem reflexes - Analgesia via spinal cord and supraspinal mechanisms - Sympathomimetic effects via monoamine reuptake inhibition ## Comparison: IV Induction Agents | Feature | Ketamine | Propofol | Thiopentone | Etomidate | | --- | --- | --- | --- | --- | | **Dissociative state** | ✓ Yes | ✗ No | ✗ No | ✗ No | | **Analgesia** | ✓ Yes | ✗ No | ✗ No | ✗ No | | **Airway reflexes** | ✓ Preserved | ✗ Blunted | ✗ Blunted | ✓ Preserved | | **Spontaneous breathing** | ✓ Maintained | ✗ Depressed | ✗ Depressed | ✓ Maintained | | **Hemodynamics** | ↑ (sympathomimetic) | ↓↓ (vasodilation) | ↓↓ (vasodilation) | → (neutral) | **Clinical Pearl:** In rapid sequence intubation (RSI) for emergency surgery, ketamine is increasingly preferred because it maintains airway reflexes, breathing, and hemodynamics while providing analgesia — reducing the need for additional analgesic agents during induction. **Warning:** Emergence reactions (vivid dreams, hallucinations, dysphoria) occur in ~10–30% of adults. These are reduced by benzodiazepine premedication and are less common in younger patients and those with lower doses.