Methohexital vs midazolam/flumazenil anaesthesia during laryngoscopy under jet ventilation

In a randomised clinical study, two total intravenous anaesthesia techniques for microlaryngoscopic laser surgery were compared. After an induction dose of 100 mg methohexital, Group I received a maintenance infusion of 10 mg·min ‐1 . In Group II anaesthesia was obtained by 15 mg midazolam followed by 0.1 mg·min ‐1 continuously and terminated by the injection of flumazenil. For analgesia 5 mg alfentanil were administered. Opiate‐induced respiratory depression was antagonised by 0.08 to 0.12 mg naloxone. Prior to, during, and after surgery, adrenergic response was assessed by HPLC‐analysis of blood taken from a peripheral vein. Haemodynamic responses to the operation and during the post‐operative period were almost identical in both groups. In Group I, the mean recovery period of 14 min was significantly longer than in Group II (9 min), where patients received a mean dose of 0.53 mg (0.15) flumazenil. Resedation could be observed in all patients receiving flumazenil within 60 min after antagonisation, which was associated with a mean decrease in O 2 ‐saturation from 95% to 88%. There was no difference in epinephrine and norepinephrine blood levels between the two groups prior to and during anaesthesia. In all patients, arousal was associated with a significant increase in the epinephrine plasma concentration. While blood levels in Group I decreased during the post‐operative period to levels prior to surgery, the concentrations in Group II remained elevated. In one patient who received no naloxone, the reversal of midazolam action induced a 16‐fold increase in catecholamine levels (from 50 to 800 ng.1 ‐1 ) associated with a tachycardia of 170 b·min ‐1 and hypertension of 160 mmHg. It is concluded that both anaesthetic techniques provide appropriate and equivalent anaesthesia for laryngeal surgery under jet ventilation. The shorter post‐operative period of unconsciousness after flumazenil administration can be regarded as an advantage. Yet, in single cases the use of flumazenil may lead to excessive adrenergic reactions combined with tachycardia and hypertension. This has to be considered when the antagonist is administered to high‐risk patients. The higher degree of post‐operative vigilance is less accepted by some patients. Post‐operative observation after antagonisation is mandatory as resedation may result in hypoxic episodes.