Influence of tetanic stimulation on the staircase phenomenon and the acceleromyographic time-course of neuromuscular block: a randomized controlled trial.

During neuromuscular monitoring, repeated electrical stimulation evokes muscle responses of increasing magnitude ('staircase phenomenon', SP). We aimed to evaluate whether SP affects time course and twitches' values of an acceleromyographic assessed neuromuscular block with or without previous tetanic stimulation. Fifty adult patients were randomized to receive a 50 Hz tetanic stimulus (S group) or not (C group) before monitor calibration. After 20 min of TOF ratio (TOFr) stimulation rocuronium was administered. Onset time of block (primary endpoint), recovery of T1 to 25%, TOFr to 0.9, and recovery index were compared. We also compared T1 and TOFr at baseline, post-stimulation, and during recovery from block. Moreover the correlation between T1 at maximum recovery and (a) baseline T1 and (b) post-stimulation T1 along with T1/TOFr ratio during recovery were evaluated. After stimulation median T1 increased (32%) in group C and decreased (16%) in group S (P = 0.0001). Onset time (Median [IQR] in seconds) was 90 (29-77) vs. 75 (28-60) in C and S group (P = 0.002). Time [Mean (SD) in minutes] to normalized TOFr 0.9 were 70.13 (14.9) vs. 62.1 (21.2) in C and S groups (P = 0.204). TOFr showed no differences between groups at any time point. T1 at maximum recovery showed a stronger correlation with post-stabilization T1 compared to baseline. (ρ = 0.80 and ρ = 0.85, for C and S groups.) Standard calibration does not ensure twitch baseline stabilization and prolongs onset time of neuromuscular block. TOF ratio is not influenced by SP.