A 32-year-old woman with severe burns over 40% of her body surface area is brought to the operating theatre for emergency debridement and grafting. Her baseline blood pressure is 110/70 mmHg, heart rate 115 bpm, and she is in significant pain despite analgesia. The anesthesiologist chooses ketamine 1.5 mg/kg IV for induction instead of propofol. Which of the following BEST explains the rationale for choosing ketamine in this critically ill, hypovolemic, and pain-stricken patient?

Explanation

## Ketamine as an Induction Agent in Critical Illness **Key Point:** Ketamine is the induction agent of choice in hemodynamically unstable, hypovolemic, or pain-stricken patients because it maintains or elevates blood pressure through sympathomimetic effects (catecholamine release and sympathetic stimulation) while preserving airway reflexes and providing analgesia. ### Why Ketamine is Ideal in This Scenario **Cardiovascular Stability:** 1. **Sympathomimetic action** — stimulates release of endogenous catecholamines (noradrenaline, adrenaline) 2. **Maintains or increases blood pressure** — systolic BP often rises 10–20 mmHg 3. **Preserves heart rate** — tachycardia is maintained or increased, supporting cardiac output 4. **Minimal direct myocardial depression** — any depression is offset by sympathetic stimulation **Airway & Respiratory Benefits:** - **Preserved airway reflexes** — cough and gag reflexes remain intact; aspiration risk is lower than with propofol - **Maintained spontaneous ventilation** — less respiratory depression than barbiturates or propofol - **Bronchodilation** — beneficial in trauma/burn patients at risk of aspiration **Analgesia & Dissociation:** - **Intrinsic analgesic properties** — reduces pain perception at spinal and supraspinal levels - **Dissociative state** — patient is unconscious but protective reflexes remain - **Reduced opioid requirement** — synergistic with analgesics **Clinical Pearl:** In this burn patient: - Hypovolemia makes propofol or thiopentone dangerous (profound hypotension) - Severe pain and sympathetic activation make etomidate suboptimal (no analgesia) - Ketamine's sympathomimetic effect counteracts hypovolemia-induced hypotension - Preserved airway reflexes reduce aspiration risk in a patient with potential gastric contents ### Comparison of IV Induction Agents in Hemodynamic Instability | Agent | BP Effect | Airway Reflexes | Analgesia | Ideal Use | | --- | --- | --- | --- | --- | | **Ketamine** | ↑ or stable | Preserved | Yes (intrinsic) | Trauma, burns, shock, pain | | **Propofol** | ↓↓ (profound) | Blunted | No | Routine, stable patients only | | **Thiopentone** | ↓↓ (profound) | Blunted | No | Rarely used now | | **Etomidate** | Stable | Blunted | No | Shock/sepsis (but no analgesia) | **High-Yield:** Ketamine is the **gold standard** for: - Trauma and hemorrhagic shock - Severe burns - Acute pain states - Patients with marginal perfusion pressure - Rapid sequence intubation in unstable patients **Mnemonic: KETAMINE = Keep Everything Therapeutic And Maintain Intact Neurologic Equilibrium** — sympathomimetic, analgesic, airway-preserving. **Warning:** Ketamine does NOT eliminate the need for opioids; it provides analgesia but is not a complete analgesic. Emergence reactions (hallucinations, dysphoria) can occur in adults and are mitigated by benzodiazepines or low-dose propofol at emergence. [cite:Gupta & Sharma Essentials of Anesthesia Ch 8; Stoelting Pharmacology & Physiology in Anesthetic Practice Ch 5]