Acceleromyography to assess neuromuscular recovery: is calibration before measurement mandatory?

Acceleromyography has been shown to be an appropriate method in the detection of residual paralysis. However, the clinical importance of an individual calibration of the device in the single patient to improve reliability in detecting residual paralysis remains unclear.

Observational study in 100 patients undergoing general anaesthesia with endotracheal intubation and a neuromuscular block with atracurium. In all patients, an individually calibrated acceleromyograph was used to estimate a possible residual block at the end of surgery. Immediately after finishing the calibrated measurements at the end of surgery, a non-calibrated measurement was performed. Agreements between the two measurements were tested using Cohen's κ and a Bland-Altman analysis.

Data from 96 patients were analysed. At the end of surgery, a discordance in the calibrated and the non-calibrated train-of-four ratio was found in 88 patients. Bland-Altman analysis showed a mean (bias) of 0.01, with limits of agreement of 0.15/-0.15. κ was calculated with κ=0.84 for the absence or presence of a potential residual block if defined as a train-of-four ratio of 1.0 as a threshold.

The results imply a good agreement in the detection of the presence or absence of a residual neuromuscular block between calibrated and non-calibrated acceleromyography if a train-of-four ratio of 1.0 has been chosen as the threshold. However, the estimated train-of-four values are not transferable between calibrated and non-calibrated measurements.