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The effects of succinylcholine on mouth opening
A F Van der Spek1, W B Fang, J A Ashton-Miller
1Department of Anesthesiology, Mott Hospital, University of Michigan Medical Center, Ann Arbor 48109.
Insights
Succinylcholine administration during halothane anesthesia significantly reduces mouth opening and increases jaw stiffness in children. This effect, unlike malignant hyperthermia, should be reconsidered in clinical assessments.
Area of Science:
- Anesthesiology
- Pediatric Anesthesia
- Pharmacology
Background:
- Malignant hyperthermia is a rare, life-threatening condition during anesthesia.
- Masseter spasm is a potential early sign of malignant hyperthermia.
- The effects of neuromuscular blocking agents on jaw mobility during pediatric anesthesia require clarification.
Purpose of the Study:
- To investigate the impact of succinylcholine, pancuronium, and vecuronium on mouth opening and jaw stiffness in children under halothane anesthesia.
- To determine if succinylcholine-induced jaw stiffness is indicative of malignant hyperthermia.
Main Methods:
- Mouth opening and jaw resistance were measured in 63 anesthetized children.
- Measurements were taken before and after administration of succinylcholine, pancuronium, or vecuronium.
- Jaw stiffness was assessed by the resistance to a constant test force.
Main Results:
- Succinylcholine significantly reduced mouth opening (P < 0.0001) and increased jaw stiffness (P < 0.0001) in children.
- These effects persisted for at least 45 seconds after succinylcholine administration.
- Pancuronium and vecuronium did not significantly alter mouth opening or jaw stiffness.
- Three patients receiving succinylcholine required multiple intubation attempts due to jaw stiffness.
Conclusions:
- Succinylcholine, not malignant hyperthermia, is a likely cause of reduced mouth opening and increased jaw stiffness during halothane anesthesia in children.
- Clinical assessment of jaw stiffness as an isolated sign of malignant hyperthermia should be re-evaluated.
- Alternative muscle relaxants like pancuronium or vecuronium may be preferable when jaw mobility is a concern.
Abstract:
Mouth opening and the resistance to opening developed by the muscles of mastication were measured in 63 children anesthetized with halothane and relaxed with succinylcholine, pancuronium, or vecuronium. Measurement of mouth opening, induced by a constant test force, was made when each patient was deeply anesthetized, as judged by clinical parameters. Succinylcholine, vecuronium, or pancuronium was then administered. The mouth opening measurement was repeated immediately after the loss of limb muscle twitch response and 45 s following the loss of twitch response. For the 24 patients receiving succinylcholine, there was a significant reduction in mean mouth opening (P less than 0.0001) and a significant increase in jaw stiffness (P less than 0.0001) immediately after limb relaxation. Forty-five seconds after full limb relaxation was attained, the mean mouth opening was still reduced (P less than 0.0001) and the mean jaw stiffness was still increased (P less than 0.0003) in the succinylcholine group. Patients receiving either vecuronium or pancuronium did not show a significant change of mouth opening or jaw stiffness following limb relaxation. Three patients, who received succinylcholine, required several attempts at tracheal intubation due to increased resistance to mouth opening. Anesthesia and surgery proceeded in all patients. None of the patients developed malignant hyperthermia. In view of the fact that a reduction in mouth opening was a constant finding when succinylcholine was administered during halothane anesthesia, the assumption that isolated "masseter spasm" or jaw stiffness heralds malignant hyperthermia should be reconsidered.