Priming with atracurium: improving intubating conditions with additional doses of thiopental

The effects of different intubating doses of atracurium on the time of onset, and the effect of an additional dose of thiopental on intubating conditions, were studied in 72 patients divided into six groups (n = 12 in each). Stratified sampling was used to obtain an even sex distribution. Groups I, III, and V (controls) received atracurium as a single bolus dose of 0.4, 0.5 or 0.6 mg/kg respectively. Groups II, IV, and VI received an initial (priming) dose of 0.05 mg/kg followed 3 min later by 0.35, 0.45, or 0.55 mg/kg respectively. The time of onset, that is the time from the intubating dose to complete suppression of the train-of-four (TOF) response, was significantly accelerated after administration of atracurium in divided doses. Increasing the intubating dose of atracurium after an initial 0.05 mg/kg from 0.35 to 0.55 mg/kg did not result in further significant acceleration of the onset time, but resulted in prolongation of the duration of neuromuscular blockade. When divided doses of atracurium were given, administration of 2 mg/kg thiopental (in addition to the 5 mg/kg used for induction) before the injection of the intubating dose resulted in improvement of intubating conditions as reflected by statistically significant changes in intubating scores. This result was probably due to the increase by thiopental in the depth of anesthesia. Therefore, when thiopental is given as supplement, the priming technique can be made to provide better conditions for tracheal intubation in less than 90 sec.