Rapid inhalation induction with halothane-nitrous oxide for myasthenic patients

Rapid inhalation induction (RII) was successfully employed for patients without myopathy. Inhalatory agents can be used for anaesthetic induction of myasthenics, avoiding the use of neuromuscular blocking agents. We studied the use of RII in 15 myasthenics (MG) and in 15 normal subjects (nMG), measuring induction time (TI), cardiorespiratory effects, complications, and evaluated the patient's reaction to RII. The patients were submitted to elective transsternal thymectomy (MG) and gynaecological or lower abdominal surgery (nMG). No premedication was used. After preoxygenation, RII was started using a mixture of 4% halothane and O2:N2O (1:2). They performed three vital capacity breaths, followed by normal spontaneous ventilation. The TI was assessed by timing the loss of verbal command (TLVC) and loss of eyelid reflex (TLER). Systolic and diastolic pressure, pulse oximetry, capnometry, respiratory rate (RR) and heart rate (HR) were measured during induction at each minute, for four minutes. After a postanaesthetic questionnaire only two normal subjects did not like the RII technique. Mean values for TLVC and TLER were 67 and 73 sec for MG and 64 and 69 sec for nMG, respectively. There was no change in HR for MG or blood pressure. The RR increased in both groups, but no change in PetCO2 was observed; SaO2 was > 97%. In conclusion, RII can be performed rapidly and safely in myasthenic patients and is a technique that should be considered for the induction of anaesthesia in myasthenic patients.