INTUBATING CONDITIONS AFTER ATRACURIUM AN D VECURONIUM ADMINISTERED BY BOLUS INJECTION OR THE PRIMING TECHNIQUE

Prompted by the ongoing discussion of the pros and cons of using succi nylcholine, this study was conducted to compare the responses to bolus injections of atracurium or vecuronium with those after sequential in jection of these drugs (priming principle). We evaluated the earliest possible intubation times, intubating conditions, and the onset times (i.e. times from the end of injection to the maximum blockade) under c onditions approaching real use as closely as possible. Methods. The ra ndomized and double-blind study was carried out with 80 ASA risk class 1 and 2 patients. Approval of the institutional ethics committee was obtained, and each patient gave informed consent. Patients were random ly allocated to four study groups of 20 patients each. Isotonic saline was administered to those patients assigned to the atracurium or vecu ronium bolus groups, whereas the patients assigned to the other two gr oups received a priming injection of either atracurium (0.05 mg/kg) or vecuronium (0.01 mg/kg). We observed the patients for signs of incipi ent muscular weakness before the induction of anaesthesia. Anaesthesia was induced with thiopental 3.5 min after the first injection (5 mg/k g and 50-100 mg before intubation). After a further 1 min during which adequate mask ventilatin with oxygen was assured, corresponding to a priming interval of 4.5 min, 0.5 mg/kg of atracurium or 0.1 mg/kg of v ecuronium was administered to the patients in the bolus groups and 0.4 5 mg/kg of atracurium or 0.09 mg/kg of vecuronium as intubating doses to those in the priming groups. Intubation was attempted at 90, 120, 1 50 and 180 s thereafter. Intubating conditions were evaluated on the b asis of laryngoscopy, vocal cord movement and coughing or bucking of t he patients. Neuromuscular function was monitored via accelerometry at the adductor pollicis muscle (TOF stimulation of the ulnar nerve ever y 15 s). Results. The priming doses did not diminish the elicited twit ches of the adductor pollicis muscle, but led to heavy eyelids and dou ble vision in 35% of the atracurium patients and 47% of the vecuronium patients; these symptoms were well tolerated by the patients. At the time of intubation the adductor pollicis muscle was relaxed to approxi mately the same degree in all groups (mean+/-SD for the TOF ratios in the bolus groups was 0.46+/-0.37 for atracurium, 0.45+/-0.4 for vecuro nium; in the priming groups 0.52+/-0.39 for atracurium, 0.53+/-0.36 fo r vecuronium). The administration of the relaxants in divided doses si gnificantly shortened the intubating time after atracurium (100 vs 124 a) and improved the intubating conditions of vecuronium (good vs tole rable), but had no effect on the time course of the neuromuscular bloc kade (onset times in the bolus groups 224+/-84 s for atracurium and 20 9+/-64 s for vecuronium; in the priming groups 249+/-112 s for atracur ium and 205+/-52 s for vecuronium). Conclusions. The priming technique presented here is clinically superior to the bolus method and therefo re should be preferred in all elective cases and in those patients in whom succinylcholine is contraindicated.