Predictive value of mechanomyography and accelerometry for pulmonary function in partially paralyzed volunteers

Background: Accelerometry (ACM) of adductor pollicis muscle has been used for monitoring of neuromuscular blockade but its validity compared with the gold standard, mechanomyography (MMG), has been questioned. During neuromuscular blockade we compared these methods and we assessed pulmonary function. Methods: In awake partially paralyzed volunteers we spirometrically assessed pulmonary function every 5 min until recovery. Rocuronium (0.01 mg kg^-1 + 2-10 μg kg^-1 min^-1) was administered to maintain train-of-four (TOF)-ratios (assessed every 15 s) of approximately 0.5 and 0.8 over a period of more than 5 min. The TOF-ratio associated with 'acceptable' pulmonary recovery [forced vital capacity (FVC) and forced inspiratory volume in 1 s (FIV₁) of ≥90% of baseline] was calculated using a linear regression model. During 5-min periods of repetitive nerve stimulation we compared the squared residuals of the FVC and FIV ₁ estimates from TOF_ACM vs. TOF_MMG, and compared variance of values derived from ACM and MMG using Wilcoxon's test. Results: Limits of agreement of TOF-ratio derived from ACM and MMG were wide [0.15 ± 0.016 (SD)], and variability of TOF_ACM exceeded that of TOF_MMG [variance: 77 ± 105, vs. 51 ± 55% (P < 0.01)]. Calculated TOF_ACM and TOF_MMG ratios of 0.56 (0.22-0.71) [mean (95%CI) and 0.6 (0.28-0.74)], respectively, predict 'acceptable' (90%) recovery of FVC while FIV₁ remains impaired until TOF-ratios of 0.91 (0.82-1.07) and 0.95 (0.82-1.18), respectively. In turn, TOF_MMG (TOF_ACM) of unity predicted 'acceptable' recovery of FVC and FIV₁ in 94 (93) % and 68 (73) % of measurements, respectively. Conclusions: Accelerometry predicts effects of relaxation on pulmonary function as valid as the gold standard mechanomyography. We recommend that recovery of TOF ratio to 0.9-1.0 should be used as an indication of sufficient neuromuscular recovery in daily practice.