Comparison of electromyography in three hand muscles for monitoring recovery from neuromuscular blockade in the obese

Abstract

Residual effects of neuromuscular blocking agents can persist into the postoperative period resulting in serious complications such as aspiration and airway obstruction. Mortality and morbidity associated with residual neuromuscular blockade can be reduced with quantitative intraoperative neuromuscular transmission monitoring and should be available to all patients receiving neuromuscular blockade as recommended by the Australian and New Zealand College of Anaesthetists. Electromyography (EMG) is a quantitative neuromuscular function monitor which measures onset, depth, and recovery of neuromuscular blockade. Recent data suggests that the precision and/or agreement of EMG monitoring may be impaired by an increasing body mass index (BMI). Obesity is a risk factor for airway and other operative complications irrespective of neuromuscular blockade use. Aim(s): To compare the precision and agreement of EMG in the Abductor Digiti Minimi (ADM), Adductor Pollicis (AP) and First Dorsal Interosseous (FDI) muscles in obese subjects during recovery from neuromuscular blockade. Method(s): Patients between the ages of 18 and 90, with a BMI-30, undergoing surgery requiring neuromuscular blockade were invited to participate in this study. Train of four (TOF) ratios were recorded every 20 seconds using EMG at the ADM, AP, and the FDI of the same hand during recovery from neuromuscular blockade. The Bland-Altman technique was used to compare TOF ratios. Precision was compared by calculating the repeatability coefficient (RC). A lower RC value denotes higher precision. Agreement between the muscles were compared using the bias and limits of agreement. Clinically acceptable agreement was defined a priori as a bias of <0.025 and limits of agreement within 0.05. Result(s): Data from 22 patients were recorded. FDI was the most precise (Table1). Over all TOF ranges, the bias of EMG at AP (-0.084) and FDI (-0.093) underestimate ADM with unacceptably wide limits of agreement (Figure 1). Conclusion(s): FDI was the most precise. The wide bias and limits of agreement suggest that these muscles cannot be used interchangeably in the obese. Further investigation in this high risk group is warranted.