## Airway Reflex Preservation Among IV Induction Agents ### Ketamine's Unique Profile **Key Point:** Ketamine is the only IV induction agent that preserves airway reflexes and maintains spontaneous ventilation, making it the agent of choice in hemodynamically unstable patients and those at risk of aspiration. ### Mechanism Ketamine produces **dissociative anesthesia** through non-competitive NMDA receptor antagonism. Unlike other induction agents: - Maintains pharyngeal and laryngeal reflexes - Preserves spontaneous ventilation and airway tone - Produces analgesia concurrent with sedation - Maintains or increases sympathetic tone (↑ HR, ↑ BP) ### Comparative Airway Effects | Agent | Airway Reflexes | Spontaneous Ventilation | Cardiovascular Effect | |-------|-----------------|-------------------------|----------------------| | **Ketamine** | **Preserved** | **Maintained** | **↑ BP, ↑ HR** | | Propofol | Abolished | Depressed/Apnea | ↓ BP, ↓ HR | | Thiopentone | Abolished | Depressed/Apnea | ↓ BP, ↓ HR | | Etomidate | Abolished | Depressed | Minimal CV change | **High-Yield:** Ketamine is the safest induction agent in: - Hypovolemic/hemorrhagic shock - Septic shock - Aspiration risk (emergency surgery, full stomach) - Difficult airway anticipated - Pediatric patients (maintains airway protection) ### Clinical Pearl While propofol and thiopentone cause rapid, profound airway reflex loss (requiring immediate airway management), ketamine allows spontaneous breathing and coughing, reducing aspiration risk during induction. **Warning:** Ketamine causes emergence reactions (hallucinations, dysphoria) in 10–30% of adults; mitigated by premedication with benzodiazepines or anticholinergics. [cite:Gupta & Sharma Essentials of Anaesthesia Ch 8]
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