Propofol reduces succinylcholine induced increase of masseter muscle tone.

Purpose: Succinylcholine is known to increase the tone of the masseter muscles. As excessive jaw tension may complicate rapid sequence induction, we investigated three induction techniques, all including the use of succinylcholine, with respect to masseter muscle tone, neuromuscular blockade, intubation conditions, and time course of intubation.

Methods: Sixty adult patients were allocated to one of three induction groups: Group THIO received 5 mg.kg-1 thiopentone, Group THIO/ATR received 5 mg.kg-1 thiopentone plus 0.05 mg.kg-1 atracurium for precurarization, and Group PROP received 2.5 mg.kg-1 propofol. All patients received 3 micrograms.kg-1 fentanyl and 1.5 mg.kg-1 succinylcholine. Time for induction of anaesthesia was recorded, and, after inserting a Grass Force Transducer between upper and lower incisors, jaw tone and the time course of jaw tension was recorded before and after the administration of succinylcholine.

Results: No differences in the onset of sleep were observed among the three groups (Group THIO 33 +/- 2 sec: THIO/ATR 30 +/- 2 sec: PROP 35 +/- 2 sec, mean +/- SE). Masseter preloads following induction of anaesthesia were similar in all three groups (THIO 16.4 +/- 2.1 N: THIO/ATR 15.1 +/- 2.0 N: PROP 12.7 +/- 1.6 N). However, after administration of succinylcholine, the increase in masseter tone was less in Groups PROP (5.0 +/- 1.1 N) and THIO/ATR (6.4 +/- 2.1 N) than in Group THIO (12.4 +/- 3.0 N; P < 0.05).

Conclusion: Jaw tension after administration of succinylcholine is influenced by the choice of induction agent. The increase of masseter muscle tone is lower following propofol or thiopentone/atracurium induction than with thiopentone alone.