JAW THRUSTING AS A CLINICAL-TEST TO ASSESS THE ADEQUATE DEPTH OF ANESTHESIA FOR INSERTION OF THE LARYNGEAL MASK

We have studied the efficacy of the loss of response to jaw as a clini cal test to assess adequate depth of anaesthesia for insertion of the laryngeal mask in 60 patients. After induction of anaesthesia with pro pofol (infused using a syringe driver), the patients were randomly all ocated to one of two groups. In one group, insertion of the laryngeal mask was attempted immediately after the loss of verbal contact and in the other group, after the loss of motor response to a jaw thrust. Co nditions for insertion of the laryngeal mask were assessed. The mean d ose of propofol required to obtain loss of verbal contact was 1.94 mg. kg(-1) (SD 0.39, 95% confidence intervals (CI) 1.79-2.08 mg.kg(-1)) an d that for the loss of response to jaw thrust was 2.55 mg.kg(-1) (SD 0 .46, 95% CI 2.38-2.72 mg.kg(-1)). When depth of anaesthesia was assess ed using jaw thrusting, it was always possible to insert the mask and the conditions were optimal in 87% (95% CI 72-95%) of patients. Neithe r coughing nor gagging occurred. In contrast, conditions were almost a lways less that optimal when insertion was attempted after the loss of verbal contact (p much less than 0.001). No marked haemodynamic depre ssion occurred in any patient. Thus, jaw thrust is a reliable clinical test to assess the adequate depth of anaesthesia for uncomplicated in sertion of the laryngeal mask after induction of anaesthesia with prop ofol.