Impact of normalizing the acceleromyographic train-of-four ratio on detecting residual paralysis—a cohort study

Quantitative monitoring is recommended to prevent residual postoperative neuromuscular blockade. Guidelines advocate a train-of-four ratio ≥ 0.90 before extubation. Acceleromyography, the most common modality, tends to overestimate recovery. Therefore, normalizing the train-of-four ratio to a pre-blockade baseline is recommended. However, this is not a routine practice. We hypothesized that failure to normalize acceleromyographic measurements may lead to misclassification of neuromuscular recovery. We aimed to describe the incidence of inadequate recovery after blockade and the relationship between non-normalized and normalized train-of-four ratios. We examined data from Oslo University Hospital from January 2017 to December 2020 and included patients ≥ 13 years, who underwent general anesthesia with intubation, non-depolarizing blockade, and acceleromyography with an available baseline train-of-four ratio. The primary outcome was the incidence of residual paralysis, defined as a normalized train-of-four ratio < 0.90 at extubation. Among secondary objectives was describing the bias between non-normalized and normalized train-of-four ratios. After screening 50,872 episodes, 1632 cases were included (median age Q1-Q3 54.9 yr 40.7–66.8, 43.1% women). The incidence of residual paralysis was 52.8% (862/1632). Regression-based Bland–Altman analysis revealed a mean bias (non-normalized –normalized train-of-four ratio) of 0.14 (95% confidence interval 0.11–0.17; p = 0.043), with limits of agreement (± 1.96SD) of –0.13 to 0.35. The variability of the differences increased with higher mean train-of-four ratios, indicating that non-normalized ratios are poor predictors of normalized values. More than half the subjects in our cohort were extubated at a normalized acceleromyographic train-of-four ratio below the recommended minimum of 0.90. Our analyses demonstrate that normalized values cannot be reliably predicted from non-normalized measurements.