Methohexitone anaesthesia for microlaryngoscopy: Circulatory modulation with metroprolol and dihydralazine

Abstract

Anaesthesia for microlaryngoscopy was induced and maintained with fentanyl 3 μg kg- and methohexitone (initial bolus of 1-1.5 mg-kg-1 plus subsequent infusion of 4 mg kg-1 h-1). Suxamethonium was used to induce neuro-muscular blockade. Twenty minutes before induction of anaesthesia, previously normotensive patients (n = 35), and patients with hypertension well controlled by beta-receptor antagonists (n = 16) were pretreated with metoprolol (M) 0.2 mg kg-1i.v. and dihydralazine (DH) 0.2 mg kg-1i.v., dihydralazine 0.2 mg kg-1 i.v. alone, or saline. Arterial pressure (AP) and heart rate (HR) were monitored: any arrhythmia and ST60T changes were noted. After the methohexitone infusion was stopped, the times for emergence and full recovery were short (median 2 min 15s and 5 min later, respectively). Pretreatment with M+DH abolished increases in AP and HR during endoscopy. Arrhythmias were observed in fewer pretreated patients than in controls (P < 0.05). ST60-Tchanges in the ECG indicating myocardial ischaemia were found in two of 19 M+DH and in six of 21 saline-pretreated patients. One of these six patients developed a myocardial infarction. Pretreatment with dihydralazine alone attenuated the pressor response to microlaryngoscopy, but was associated with consistently high HR and an incidence of arrhythmias as well as ST60T changes similar to that found after saline. © 1985 British Journal of Anaesthesia.