In rapid sequence induction, which muscle relaxant is preferred due to its rapid onset and short duration of action?

Explanation

## Muscle Relaxants in Rapid Sequence Induction **Key Point:** Succinylcholine remains the gold standard depolarizing agent for RSI due to its ultra-rapid onset (30–40 seconds) and very short duration (5–10 minutes), allowing quick recovery if intubation fails. ### Pharmacokinetic Profile of Succinylcholine | Parameter | Succinylcholine | Rocuronium | Atracurium | |-----------|-----------------|-----------|----------| | Onset | 30–40 sec | 60–90 sec | 90–120 sec | | Duration | 5–10 min | 30–40 min | 45–60 min | | Metabolism | Plasma pseudocholinesterase | Organ-independent | Hofmann elimination | | RSI Suitability | Ideal | Acceptable (if rocuronium 1.2 mg/kg used) | Poor | **High-Yield:** The rapid onset of succinylcholine (fastest of all agents) is critical in RSI because it allows intubation within 30–40 seconds, minimizing the window of apnea and aspiration risk. **Clinical Pearl:** Although rocuronium 1.2 mg/kg (double the standard dose) can achieve onset in ~60 seconds, succinylcholine's 30–40 second onset is still superior for true emergency RSI scenarios. **Warning:** Succinylcholine causes transient hyperkalemia (0.5–1 mEq/L rise), which is clinically significant in burn patients, crush injuries, and denervation injuries — these are relative contraindications. ### Why Rocuronium Is Not Preferred for RSI - Standard dose (0.6 mg/kg) has onset of 60–90 seconds — too slow. - Even at 1.2 mg/kg, onset is ~60 seconds, still longer than succinylcholine. - Duration of 30–40 minutes means prolonged paralysis if intubation fails.