The Train - of - Four Response on the Priming Dose of Various Nondepolarizing Muscle Relaxants

Lee, Kyung Woo; Kang, Kyu Sik; Hwang, Kyung Ho; Kim, Sung Yell

Abstract

The priming principle refers to the administration of a small subparalyzing dose (priming dose) of a nondepolarizing muscle relaxant, such dose not cause respiratory depression or any other clinical signs, a few minutes prior to the administration of the larger intubating dose. This study was designed to investigate the influence of a priming dose of vecuronium (0.008 mg/kg), pancuronium (0.008 mg/kg) and d-tubocurarine (0.04 nig/kg) on the relationship between the depres- sion in the first twitch (T2%) of the train-of-four (TOF) and TOF ratio (T4R,%) in 27 ASA class I or II patients. After induction with thiopental sodium 5-6mg/kg, neuromuscular monitoring was carried out by stimulation of ulnar nerve at a frequency of 2 Hz every 20 seconds using a ABM (Datex) to measure the compound evoked electromyographic response of hypothenar muscle. Following calibration of control twitch height, tracheal intubation was performed after succinyl-choline 1 mg/kg IV. Anesthesia was maintained with oxygen, NO (50%) and enflurane (1-2%) in all patients. When the TOF response recovered to 100% of the control, the priming dose was administer-ed. The patients were randomly divided into three groups according to nondepolarizing muscle relax-ant used; vecuronium (n=9), pancuronium (n=8) and tubocurarine (n=10) group respectively. T1 and T4R were measured for 25 minutes after administration of priming dose in each group. The results were as follow: 1) There was no change in T, after priming in all groups. 2) T4R began to decrease significantly at 2 minutes after priming and still decreased significantly at 25 minutes compared to before priming. 3) The time for maximal decrease in T4R (%) proceded by the priming dose was 7 minutes in all groups; 60.7+/-8.6% in vecuronium group, 74.8+/-12.3% in pancuronium group and 78.3+/-11.3% in tubocurarine group.