Abstract
When multiple patients are scheduled to receive regional blocks as part of their anesthetic, planning insufficient preoperative time can cause first-case operating room delays. Prediction of the time to perform multiple regional blocks depends on the probability distributions (e.g., 90th percentiles) of the procedure completion times. We tested hypotheses that, if supported, can be applied for planning how early regional blocks should start to mitigate late first-case of the day starts. The retrospective cohort study used data from two academic hospital surgical suites for all regional anesthetic procedures performed before the adult patients entered the operating room for a first-case of the day. Days with more total minutes of regional procedures had greater total lateness (negative if early) and tardiness (zero if early) of first-case starts for both suites (all four Bonferroni adjusted P < 0.0001). Increases in the numbers of procedures per day were not associated with significant differences in the 0.5 quantile (median) among days of the time per procedure for both the inpatient surgical suite (unadjusted P = 0.46) and the ambulatory surgery center (P = 0.14). The result supported our hypothesis that average times add arithmetically among procedures. Increases in the numbers of procedures per day were associated with significant decreases in the 0.9 quantile among days of the time per procedure for both the inpatient surgical suite (-0.83 min per procedure, Bonferroni adjusted P < 0.0001) and the ambulatory surgery center (-0.90 min per procedure, adjusted P = 0.0002). Because both slopes were reliably negative, the result supported our second hypothesis that the longest time to plan to complete a series of procedures (represented by the 0.9 quantile) is considerably less than as calculated by taking the sum of the individual procedures' 0.9 quantiles. Quantile regression or an Excel 365 formula based on the log-normal distribution for block times can consequently be used to predict the time when anesthesiologists should start procedures and have a low risk of causing first-case start delays. For example, with 7 blocks, the sum of individual 0.9 quantiles would suggest that the anesthesiologist needs to start ≈35 min earlier than necessary based on the 0.9 quantile. Sufficient time can be planned to perform multiple procedures before the first-case of the day starts using quantile regression or an Excel formula. The estimated times are briefer than the sum of the 0.9 quantiles, but longer than the sum of the 0.5 quantiles.