Purpose: To evaluate the tracheal intubating conditions when intubation time is determined by the onset time of the neuromuscular block either of the adductor pollicis (AP) or of the orbicularis oculi muscle (OO).
Methods: In this prospective, double blind, randomised study, 40 adults ASA I-II undergoing general anaesthesia with tracheal intubation were allocated to two groups (n = 20) according to the reference muscle (AP or OO) used to determine the appropriate intubation time. Induction of anaesthesia was achieved with 5-7 mg.kg-1 thiopentone, 1.5-2.5 micrograms.kg-1 fentanyl and 0.9 mg.kg-1 rocuronium (3 x ED95) for muscular relaxation. Supramaximal train of four stimulation of the ulnar and facial nerve every 10 sec was used to monitor the neuromuscular block. After visual loss of AP or OO contraction, tracheal intubation and quality of intubation assessment were performed by two independent anaesthetists. Data are expressed as mean and standard error of the mean (X +/- SEM).
Results: Curarisation time of the OO was shorter (110 +/- 4.9 sec) than that of the AP (144 +/- 5.5 sec; P < 0.0001). Intubation conditions were excellent in 95% and good in 5% of the patients in the AP group whereas in the OO group only 65% of the patients had excellent and 20% good intubation conditions (P < 0.05). Coughing was observed in 15% of patients in the OO group during tracheal intubation.
Conclusion: Monitoring neuro-muscular activity of the AP using TOF to determine the appropriate tracheal intubation time and conditions in patients paralysed with rocurorium is more clinically relevant than monitoring the OO muscle.