What is the effect of succinylcholine on the glottis in a patient with a full stomach or at risk for regurgitation?

Succinylcholine Effect on the Glottis in Full Stomach/Aspiration Risk Patients

Succinylcholine (1.0-1.5 mg/kg IV) produces rapid, complete relaxation of the glottic muscles within 60 seconds, facilitating optimal intubating conditions and minimizing the critical period when the airway is unprotected in patients at risk for aspiration. 1, 2

Mechanism of Glottic Relaxation

Succinylcholine causes progressive paralysis of skeletal muscles, with the glottic muscles (vocal cords and laryngeal adductors) relaxing after facial levator muscles but before the intercostals and diaphragm. 2 This sequential paralysis pattern is critical because:

• The glottis relaxes within 45-60 seconds of IV administration, creating optimal conditions for laryngoscopy and tube passage 2, 3
• Complete glottic relaxation prevents laryngospasm during intubation attempts, which is particularly dangerous in full stomach patients where repeated attempts increase aspiration risk 1
• The depolarizing mechanism produces initial fasciculations followed by flaccid paralysis lasting approximately 4-6 minutes 2

Clinical Implications for Aspiration Risk Scenarios

In rapid sequence induction for full stomach patients, succinylcholine 1.0-1.5 mg/kg remains the gold standard because it provides the shortest interval between loss of protective airway reflexes and secured airway. 1, 4

Optimal Dosing for Glottic Relaxation

• 1.0 mg/kg provides excellent intubating conditions in 63.3% of patients at 60 seconds 3
• 1.5 mg/kg increases excellent conditions to 80.0% of patients 3
• 2.0 mg/kg achieves 86.7% excellent conditions, but offers no clinically significant advantage over 1.5 mg/kg 3
• The calculated ED80 (dose achieving excellent conditions in 80% of patients) is 1.6 mg/kg (95% CI: 1.2-2.0 mg/kg) 3

Critical Timing Considerations

The period between loss of consciousness and glottic relaxation represents the highest aspiration risk window—succinylcholine minimizes this to approximately 60 seconds compared to 90-120 seconds with alternatives. 1, 5

• Glottic muscles demonstrate more rapid onset of paralysis than peripheral muscles (adductor pollicis), making hand monitoring an unreliable predictor of optimal intubating conditions 5
• Laryngeal muscles achieve adequate relaxation 15-30 seconds before complete peripheral paralysis 5

Rocuronium as Alternative When Succinylcholine Contraindicated

When succinylcholine is contraindicated, rocuronium 0.9-1.2 mg/kg provides comparable glottic relaxation, though with a longer duration of paralysis (30-60 minutes versus 4-6 minutes). 1, 4, 6

Key Differences in Glottic Effect

• Rocuronium 0.6 mg/kg produces clinically acceptable intubating conditions in 96.1% of emergency patients at 60 seconds when combined with propofol and alfentanil 7
• Rocuronium ≥0.9 mg/kg is required to match succinylcholine's glottic relaxation quality in lighter anesthesia typical of true rapid sequence induction 1, 8
• Lower rocuronium doses (0.6-0.7 mg/kg) produce less frequent excellent intubating conditions 1

Critical Pitfalls to Avoid

Do not use reduced doses of succinylcholine (<1.0 mg/kg) in full stomach patients—inadequate glottic relaxation increases the risk of difficult intubation, repeated attempts, and aspiration. 3

• Doses of 0.3-0.5 mg/kg provide excellent conditions in only 43.3-60.0% of patients, unacceptably low for aspiration risk scenarios 3
• Do not give repeat doses of succinylcholine after failed intubation—this increases laryngospasm risk and prolongs the unprotected airway period 4
• Do not assume cricoid pressure prevents aspiration—it may make intubation more difficult and should be released if direct laryngoscopy is difficult 1

Contraindications Requiring Rocuronium Instead

Absolute contraindications where succinylcholine will NOT produce safe glottic relaxation: 4, 6

• Malignant hyperthermia susceptibility (personal or family history)
• Crush injuries >24-48 hours old (receptor upregulation causes fatal hyperkalemia)
• Denervation syndromes or spinal cord injuries
• Immobilization >3 days
• Known skeletal muscle myopathies (Duchenne muscular dystrophy)
• Burns beyond acute phase

Post-Intubation Considerations

Succinylcholine may transiently increase intragastric pressure during fasciculations, potentially worsening regurgitation risk in the 10-15 seconds before complete glottic relaxation. 2

• This effect is brief and does not contraindicate use in full stomach patients 2
• Adequate anesthetic depth before succinylcholine administration minimizes fasciculation intensity 2
• When rocuronium is used instead, implement immediate post-intubation analgosedation protocols to prevent awareness during the 30-60 minute paralysis period 4, 6