Bradycardia in patients receiving atracurium or vecuronium in conditions of low vagal stimulation

Four groups of 20 patients each received either vecuronium or atracurium together with either glycopyrronium or saline, and underwent anaesthesia free of vagolytic drugs, and surgery devoid of vagal activity. Determinations of plasma histamine concentrations were made to examine the possible correlation between these levels and changes in heart rate and blood pressure as well as a possible relationship with skin reactions after the administration of the relaxants. Patients who received vecuronium without the anticholinergic drug, glycopyrronium, showed a greater tendency towards bradycardia (though not statistically significant) than those given atracurium. More cutaneous reactions were observed with patients who received atracurium than in those with vecuronium, but there was no correlation with plasma histamine concentrations of either relaxant group. There was no correlation either between histamine concentrations and heart rate or blood pressure associated with atracurium. The incidence of bradycardia with either relaxant is low if the anaesthetic technique and the surgery are devoid of vagal activity.