Minute ventilation assessment in the PACU is useful to predict postoperative respiratory depression following discharge to the floor: A prospective cohort study

Study Objective. Reliably identifying patients at risk for postoperative respiratory depression (RD) remains an unmet need. We hypothesized that defined low minute ventilation events (LMVe) near the end of the post-anesthesia care unit (PACU) stay identifies patients at RD risk on the general hospital floor (GHF). Design Prospective observational study. Setting Tertiary care, urban academic medical center. PACU and GHF during the first postoperative night. Patients One hundred-and-nineteen adult, ASA I – III patients undergoing elective surgery under general anesthesia completed the study. Interventions Data collection from a non-invasive respiratory volume monitor and the patients' medical record perioperatively through the first postoperative night. Measurements Minute ventilation (MV), tidal volume (TV) and respiratory rate (RR) were measured continuously in the PACU and on the GHF. MV was counted as the percent of individual predicted MV (MVPRED), and RD was defined as ≥1 LMVe/h on the GHF. Based on the number of LMVes within 30 min before PACU discharge, patients were grouped into A, ‘Not-At-Risk’: 0 LMVe and B, ‘At-Risk’: ≥1 LMVes. Unpaired t-test, Mann-Whitney U test, ANOVA, Kruskal-Wallis test, Fisher's exact test, sensitivity and specificity and ROC curve analyses were applied as appropriate. Main results One hundred-and-six (89%) and 13 (11%) patients met Group A and B criteria respectively. The latter had more LMVe/h on the GHF (median 0.81 vs 0, p ≤ 0.001), and their MVPRED was significantly less. Following opioid administration, the LMVe likelihood was 43% in Group B and 5.6% in Group A. As a predictor for RD on the GHF, the number of LMVe in the last 30 min of PACU, had positive and negative predictive values of 61.5% and 90.6%, respectively. Conclusion Minute ventilation assessment in the PACU as described in this study can be useful to identify patients at risk for postoperative respiratory depression.