The priming principle suggests that the onset of neuromuscular block may be accelerated if an intubating dose is preceded by a priming dose (approximately 100/. to 30% of the 95% effective dose [END administered a few minutes earlier. In any normal population, there is wide variability in the response to neuromuscular blocking drugs. A dose equivalent to 10% of the ED,, will rarely produce a measurable neuromuscular effect. As this dose is increased, the potential for clinical weakness rapidly escalates. So, we designed this study to demonstrate the effect of administering two different precurarizing doses of rocuronium (20% and 30% of ED95) on the speed of onset of cisatracurium and to ascertain the effect of high-dose priming on neuromuscular transmission by measuring the Tl% and TOE values. The study included 90 ASA physical status 1 and II patients undergoing elective surgery requiring endotracheal intubation. Following induction of anesthesia with fentanyl and propofol, patients were randomized into three groups (30 patients each), Group I received rocuronium 0.06 mg/kg (20% of EN); Group 2 received rocuronium 0.09 mg/kg (30% of ED,,) and Group 3 (control) received normal saline. Four minutes after priming, Group I received cisatracurium 0.140 mg/kg; Group 2 received cisatracurium 0.135 mg/kg whereas Group 3 received cisatracurium 0.15 mg/kg. In each group, first twitch height and the train-of-four ratios were recorded every 10 seconds after the initial priming dose. Intubation was attempted after the first twitch height became less than 15% of baseline. The decrease in the train-of-four ratios at 4 minutes was 0.93 for group I and 0.85 for group 2. The onset of muscle relaxation was significantly faster in groups 1 and 2 (73.7±21.3and 65.0±19.8, respectively) compared with control group (148.7±43.1sec) with no significant difference between groups I and 2. lntubation conditions were either excellent or satisfactory in all patients. Four-minutes after precurarization, there is no significant difference (regarding the onset of action of subsequent cisatracurium) between the two priming doses of rocuronium used in this study She use of priming doses 30% of EINs may cause symptomatic muscle weakness. |
