THE INCIDENCE OF MASSETER MUSCLE RIGIDITY AFTER SUCCINYLCHOLINE IN INFANTS AND CHILDREN

To determine whether the incidence of masseter muscle rigidity is affe cted by the anaesthetic induction sequence, we prospectively studied f or ten months the anaesthetic course in 5,641 infants and children who received muscle relaxation to facilitate tracheal intubation. The ana esthetic induction sequence consisted of intravenous sodium thiopenton e (STP) 5 mg . kg(-1) alone, halothane induction alone 1-4%, or haloth ane followed by STP Inhalational inductions with halothane included ni trous oxide and oxygen. Tracheal intubation was facilitated by either intravenous succinylcholine (Sch) at least 1.5 mg . kg(-1) or by a non -depolarizing muscle relaxant. The induction sequence and all episodes of MMR were recorded. Ninety percent of the patients received Sch and 10% received a non-depolarising agent. Of those who received Sch, 88% (5,064 patients) were anaesthetised with STP and 12% (607 patients) w ere anaesthetised with halothane alone or halothane followed by STP Ma sseter muscle rigidity was defined clinically by the transient inabili ty to distract the mandible from the maxilla such that the mouth could not be opened or could only be opened with force. No children anaesth etised with STP followed by Sch developed MMR. One child (0.9%) develo ped MMR after halothane and Sch and two developed MMR after halothane, STP and Sch (0.4%). The incidence of MMR after Sch was less with STP than with halothane alone or with halothane and