Muscle relaxation and increasing doses of propofol improve intubating conditions

Purpose: Muscle relaxants and anesthetics are usually associated during intubation. However, their relative role to facilitate the process is not clearly defined. This study was designed to determine, during intubation: i) the relative role of anesthetics and atracurium-induced neuromuscular block and; ii) the effect of different doses of propofol in the presence of complete muscle block. Methods: Patients were randomized to four groups and received fentanyl and a standardized anesthetic procedure. Patients from groups high (H; n = 45), medium (M; n = 48) and low (L;n = 47) received 2.5 mg·kg^-1, 2.0 mg·kg^-1 , and 1.5 mg·kg^-1 of propofol respectively. Atracurium (0.5 mg·kg^-1) was then injected and tracheal intubation performed once complete block was achieved at the orbicularis oculi. Patients from group without atracurium (WA; n = 20) received propofol as in group H. Intubation was performed at the expected onset time of action of atracurium. Results: Using the same dose of propofol, the incidence of good or excellent intubating conditions was 35% without atracurium and 95% with atracurium (P < 0.0001). In patients receiving atracurium, clinically acceptable intubating conditions were more frequently achieved in groups receiving the highest propofol doses (group H or M vs group L; P < 0.03). Conclusion: Our study confirms the interaction between anesthesia and muscle relaxation to produce adequate intubating conditions. In the conditions described, intubating conditions were more dependent on atracurium-induced neuromuscular blockade than on anesthetics, but both atracurium and propofol improved intubating conditions.