Relationship between the muscle relaxation effect and body muscle mass measured using bioelectrical impedance analysis: A nonrandomized controlled trial

Abstract

Objective: The dose of neuromuscular blocking drugs is commonly based on body weight, but using muscle mass might be more effective. This study investigated the relationship between the effect of neuromuscular blocking drugs and muscle mass measured using bioelectrical impedance analysis.

Methods: Patients who were scheduled for elective surgery using a muscle relaxant were screened for inclusion in this study. Under intravenous anaesthesia, 12 mg or 9 mg of rocuronium was administered to males and females, respectively; and the maximal relaxation effect of T1 was measured using a TOF-Watch-SX® acceleromyograph.

Results: This study enrolled 40 patients; 20 males and 20 females. For both sexes, the maximal relaxation effect of T1 did not correlate with the body weight-based dose of neuromuscular blocking drugs (males, r2 = 0.12; females, r2 = 0.26). Instead, it correlated with the dose based on bioelectrical impedance analysis-measured muscle mass when injected with the same dose of rocuronium (males, r2 = 0.78, female, r2 = 0.82).

Conclusions: This study showed that the muscle relaxation effect of rocuronium was correlated with muscle mass and did not correlate with body weight when using the same dose. Therefore, a muscle mass-based dose of neuromuscular blocking drugs is recommended.

Keywords: Body composition; muscle relaxation; neuromuscular blocking agents; rocuronium.

Figures

Figure 1.

Flow diagram of the progression of patients undergoing elective surgery through this study of the relationship between the muscle relaxation effect and body muscle mass measured using bioelectrical impedance analysis.

Figure 2.

Maximal suppression of T1 at different body weights and muscle masses. (a) Maximal suppression of T1 at different body weights in male patients (n = 20) and (b) maximal suppression of T1 at different muscle masses in male patients (n = 20). (c) Maximal suppression of T1 at different body weights in female patients (n = 20) and (d) maximal suppression of T1 at different muscle masses in female patients (n = 20). T1, first twitch of the train of-four. Overlapping data points might result in less than 20 individual points per figure.

Figure 3.

Difference in T1 at different body weights and muscle masses. (a) Difference in T1 at different body weights in male patients (n = 20) and (b) difference in T1 at different muscle masses in male patients (n = 20). (c) Difference in T1 at different body weights in female patients (n = 20) and (d) difference in T1 at different muscle masses in female patients (n = 20). T1, first twitch of the train of-four; difference in T1, difference in T1 value from first twitch to maximal stimulation. Overlapping data points might result in less than 20 individual points per figure.

Figure 4.

The elapsed time for which T1 was decreased to 50% at different body weight and muscle mass. (a) The elapsed time for which T1 was decreased to 50% at different body weight in male patients (n = 20) and (b) the elapsed time for which T1 was decreased to 50% at different muscle mass in male patients (n = 20). (c) The elapsed time for which T1 was decreased to 50% at different body weight in female patients (n = 20) and (d) The elapsed time for which T1 was decreased to 50% at different muscle mass in female patients (n = 20). T1, first twitch of the train of-four; the elapsed time for which T1 was decreased to 50%, duration from first twitch of T1 to decrease by 50%. Overlapping data points might result in less than 20 individual points per figure.