Use of a train-of-four ratio of 0.95 versus 0.9 for tracheal extubation: an exploratory analysis of POPULAR data

Background: The prospective observational European multicentre cohort study (POPULAR) of postoperative pulmonary complications (NCT01865513) did not demonstrate that adherence to the recommended train-of-four ratio (TOFR) of 0.9 before extubation was associated with better pulmonary outcomes from the first postoperative day up to hospital discharge. We re-analysed the POPULAR data as to whether there existed a better threshold for TOFR recovery before extubation to reduce postoperative pulmonary complications in patients who had quantitative neuromuscular monitoring (87% acceleromyography). Methods: To identify the optimal TOFR, the complete case cohort of patients with quantitative neuromuscular monitoring (n=3150) was split into several pairs of sub-cohorts related to TOFR values from 0.86 to 0.96; values of 0.97 and higher could not be used as the sub-cohorts were too small. The optimal TOFR was considered to have the lowest P-value from multivariate logistic regression calculated for each of the TOFR values. Data are presented as adjusted absolute risk reduction or median difference with 95% confidence interval. Results: Extubating patients with TOFR >0.95 rather than >0.9 reduced the adjusted risk of postoperative pulmonary complications by 3.5% (0.7–6.0%) from that reported in POPULAR (11.3%). Increasing the recommended TOFR from 0.9 to 0.95 reduced the adjusted risk by 4.9% (1.2–8.5%). Sub-cohorts resulting from 1:1 propensity score matching revealed that sugammadex had been given in higher doses by 0.30 (0.13–0.48) mg kg⁻¹ in the sub-cohort with TOFR > 0.95. Conclusions: A post hoc analysis of patients receiving quantitative monitoring of neuromuscular function suggests that postoperative pulmonary complications are reduced for TOFR > 0.95 before tracheal extubation compared with TOFR > 0.9. Trial registration number: NCT01865513.