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 induc tion, we investigated three induction techniques, all including the us e of succinylcholine, with respect to masseter muscle tone, neuromuscu lar blockade, intubation conditions, and time course of intubation. Me thods: Sixty adult patients were allocated to one of three induction g roups: Group THIO received 5 mg.kg(-1) thiopentone, Group THIO/ATR rec eived 5 mg.kg(-1) thiopentone plus 0.05 mg.kg(-1) atracurium for precu rarization, and Group PROP received 2.5 mg.kg(-1) propofol. All patien ts received 3 mu g.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 admi nistration 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 prelo ads following induction of anaesthesia were similar in all three group s (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 mas seter 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: ja w tension after administration of succinylcholine is influenced by the choice of induction agent. The increase of masseter muscle tone is lo wer following propofol or thiopentone/atracurium induction than with t hiopentone alone.