Background: Succinylcholine chloride (Sch) is ideal for electroconvulsive therapy (ECT). However, the appropriate interval between Sch administration and electrical stimulation has not been reported. Cardiac output at the time of drug administration seems to be the major contributing factor for variability in onset time. The present study therefore investigated relationships between cardiac output before Sch administration and the onset of Sch action.
Methods: Cardiac output and cardiac index (CI) were continuously monitored in 24 patients using a noninvasive impedance cardiac output monitor. Anesthesia was induced using intravenous propofol at 1 mg·kg−1. After loss of consciousness, dorsiflexion of the hallux was monitored as single-twitch stimulations using a peripheral nerve stimulator equipped with an acceleration sensor. A 1 mg·kg−1 dose of Sch was administered, and patients were assisted by mask ventilation with 100% oxygen. A bilateral ECT was performed after single-twitch response reached zero. We measured the intervals between Sch administration and the appearance of the first fasciculation (int-F), and between Sch administration and the loss of the single twitch response (int-S0) as time of Sch onset. To determine the effective duration of Sch action, we measured the intervals between the first fasciculation and the single-twitch response above zero (int-A) and between loss of the single-twitch response and recovery above zero (int-R).
Results: The alteration in CI during ECT was biphasic. The CI before Sch administration (pre-CI) varied from 2.01 to 5.94 L·min−1·m−2 (4.23 ± 1.20 L·min−1·m−2). The int-F was 40 ± 5 seconds (range, 31-49 seconds) and int-S0 was 90 ± 17 seconds (range, 58-124 seconds). The correlations were significantly inverse between int-F and pre-CI (n = 10, R2 = 0.504, P = 0.0189), and between int-S0 and pre-CI (n = 17, R2 = 0.339, P = 0.0127). The int-A was 236 ± 95 seconds (range, 119-391 seconds) and int-R was 184 ± 106 seconds (range, 60-369 seconds). We also found correlations between int-A and pre-CI (n = 10, R2 = 0.413, P = 0.0438) and between int-R and pre-CI (n = 17, R2 = 0.405, P = 0.0466).
Conclusions: The onset of muscle relaxation varies among patients receiving ECT and is related to CI before Sch administration. In patients for whom fasciculation is difficult to determine, the effects of a muscle relaxant should be objectively confirmed before electrical stimulation of the brain.