In Reply:-Dr. Storella raises interesting questions regarding our recent manuscript. First, he asks whether the duration of predrug stimulation affects train-of-four (TOF) fade during recovery. Our results indicate that the time to recovery of 70% TOF is not influenced by the duration and mode of predrug stimulation. Stimulating for different durations before injecting vecuronium produces differences in time to a given recovery of T1, but not in TOF ratio. Thus, previous duration or frequency of stimulation should not influence clinical assessment of residual block using TOF monitoring.
Second, Dr. Storella reports that maximizing preload eliminates any progressive increase in twitch tension. Because we applied a narrow range of preload values, in our study we did not address this issue. However, the preload that we apply is typical for neuromuscular studies in humans, making our results clinically relevant.
Third, Dr. Storella asks whether similar results might be expected using EMG monitoring. Without knowing whether the recruitment we observed is pre- or postsynaptic in origin, we are unable to speculate. However, now that two studies indicate that mode and duration of predrug stimulation influence onset and recovery (as assessed by mechanical twitch tension), investigators who use EMG should examine this issue.
Finally, we agree with Dr. Storella that “a control” period should not be considered a control until it can be expected to be stable over time." Unfortunately, the brief period used by many investigators does not satisfy this criterion.
Dennis M. Fisher, M.D.
Professor of Anesthesia and Pediatrics
Ronald Brown, B.S.
Staff Research Associate; Department of Anesthesia; University of California, San Francisco; 521 Parnassus Avenue; San Francisco, California 94143–0648
(Accepted for publication April 25, 1997.)