The use of quantitative neuromuscular monitoring during induction of anesthesia to establish a baseline neuromuscular response and ensure paralysis of the vocal cords during laryngoscopy and tracheal intubation has yet to become standard practice. The current study compared intubating conditions based on quantitative measurements (train-of-four count) with intubating conditions based on the time since rocuronium administration.

Consenting adult patients undergoing general anesthesia requiring neuromuscular block were randomized into 2 groups. Following placement of a quantitative electromyographic neuromuscular monitor, general anesthesia was induced with propofol 1–1.5 mg/kg followed by rocuronium 0.6 mg/kg. In one group, intubation commenced 2 min after rocuronium administration (Time Group). In the other, intubation commenced when the first train-of-four (TOF) count was ≤1 (Count Group). Video laryngoscopy was used in both groups and the intubating conditions were noted. A Wilcoxon rank sum test or Fisher's exact test was used to compare intubating conditions between the 2 groups. Spearman's rank correlation test was used to describe the relationship between intubation conditions and the ratio of the amplitude of the first twitch of the TOF sequence, T ₁ , to the control T ₁ amplitude (T ₁ /T _c ).

There were 84 patients in the Count Group and 83 in the Time Group. More patients had ideal intubating conditions (relaxed jaw, abducted vocal cords, and no response to tracheal intubation) in the Count Group (61/84, 73 %) than the Time Group (47/83, 57 %, P  = 0.036). The mean composite intubating score was better (lower) in the Count Group than in the Time Group (3.5 vs. 3.9, respectively, P  = 0.016). The T ₁ /T _c at intubation correlated with the composite intubating conditions score (Spearman's ρ  = 0.34, P   <  0.001).

Intubating conditions were better when the timing of intubation was guided by quantitative neuromuscular monitoring to ensure a TOF count ≤1 versus waiting a fixed time interval of 2 min following administration of rocuronium.