PRIMING WITH CISATRACURIUM A DOSE RANGING STUDY: AN INTERIM REPORT*

S322 INTRODUCTION: Cisatracurium besylate (CAB) is a potent non-depolarizing muscle relaxant with an ED95 of 0.05 mg/kg in adults. Compared with its stereoisomer atracurium besylate (AB), CAB lacks histamine release and consequently offers a more stable hemodynamic profile. However, the time to maximal block for equipotent doses with CAB is up to 2 min longer than with AB [1]; therefore in order to shorten CAB onset time, 4XED95 dose has been recommended for tracheal intubation in adults. This study assesses the pharmacodynamic effects of the priming technique on different intubating doses of CAB. MATERIALS AND METHODS: This is an open label randomized study. After obtaining IRB approval and written informed consent, 40 adult female patients, ASA I-III, undergoing elective surgery under general anesthesia, were enrolled into one of 4 groups (Table 1). All patients were premedicated with midazolam 2-4 mg iv and induced with thiopental 3-5 mg/kg and sufentanil up to 0.5 mcg/kg. An inhalational mixture of N2 O/O2 (60/40%) was delivered after 3 min of pre-oxygenation. Mechanomyography assessed the neuromuscular function of the adductor pollicis by stimulating the ulnar nerve with TOF every 12 sec. After obtaining a stable baseline, a priming dose (CAB or placebo) was administered, followed 4 min later by the intubating dose. All patients were intubated at T1 33.5[degree sign]C. If deemed necessary, reversal with neostigmine or edrophonium was allowed only after T1 spontaneous recovery >25%.Table 1: Priming and intubating doses of CAB in each group. Number of patients in parenthesis.RESULTS: Table 2 and Table 3 show the intubating conditions and the pharmacodynamic data in all groups. As this is an interim report, statistical analysis has been withheld until an additional 20 patients are enrolled.Table 2: Intubating conditions in different groups.Table 3: Pharmacodynamic data represented as mean +/- standard deviation.DISCUSSION: Group 2 seems to benefit the most from the priming technique of CAB when compared to the other groups. In this group, 3XED95 offered an onset time comparable with that of Groups 3 and 4 and allowed an earlier spontaneous recovery. Neither Single Twitch nor TOF ratio have shown any significant depression or fade respectively after the priming dose, which may preclude a possible muscle weakness in an awake patient. Even though the priming technique did not accelerate the onset in Group 3 in comparison with Group 4, it is evident that overall intubation conditions at T1