Stabilization of the neuromuscular response when switching between different modes of nerve stimulation at surgical degrees of neuromuscular blockade.

During general anesthesia, different modes of nerve stimulation are used for estimation of the degree of neuromuscular blockade. When switching between the different modes, it is important to know whether the preceding mode influences the responses to the succeeding mode, and if so, for how long. The object of our study was to determine the number of stimulations required for stabilization of the muscular response when switching between double-burst stimulation (DBS) applied every 20 sec, train-of-four (TOF) applied every 12 sec, and posttetanic count (PTC) at surgical degrees of neuromuscular blockade. A total of 33 women were anesthetized with fentanyl, thiopental, halothane, and nitrous oxide. A constant degree of neuromuscular blockade was maintained at a twitch height of 4 to 11% of the control twitch height using a continuous infusion of atracurium. The ulnar nerve was stimulated supramaximally at the wrist, and the contraction in the adductor pollicis was measured mechanomyographically. At surgical degrees of neuromuscular blockade, only the first twitch response to TOF stimulation (T1) and the first twitch response to DBS stimulation (D1) are consistently present. When switching from DBS to TOF, 4 to 7 stimulations (56 to 92 sec) were required for stabilization of the T1 response. When switching from TOF to DBS, 3 stimulations (36 to 52 sec) were required for stabilization of the D1 response, and, finally, when switching from PTC to DBS, 5 to 11 stimulations (81 to 201 sec) were required for stabilization of the D1 response. Stabilization of D1 was faster following TOF than following PTC (p < 0.01).(ABSTRACT TRUNCATED AT 250 WORDS)