Narrative Review of Prolonged Times to Tracheal Extubation After General Anesthesia With Intubation and Extubation in the Operating Room

Estimating sample means and standard deviations from the log-normal distribution using medians and quartiles: evaluating reporting requirements for primary and secondary endpoints of meta-analyses in anesthesiology

PURPOSE

Clinical trials often report medians and quartiles due to skewed data distributions. We sought to evaluate the methods currently used in meta-analyses in anesthesiology to estimate means and standard deviations (SDs) from medians and quartiles.

METHODS

We simulated sample sizes (n = 15, 27, 51) and coefficients of variation (CV = 0.15, 0.3, 0.5), representative scenarios in anesthesiology studies, generating data that have a log-normal distribution with zero log-scale means. We calculated generalized confidence intervals for the ratios of means and ratios of SDs using means and SDs estimated from three quartiles in time scale, using Luo et al.'s and Wan et al.'s methods, McGrath et al.'s quantile estimation and Box-Cox transformation, and Cai et al.'s maximum likelihood estimation method.

RESULTS

The method by Luo et al. and Wan et al. produced 95% confidence intervals for the ratio of means with coverage ranging from 92.4% to 93.6%, and for SDs from 79.2 to 89.6. McGrath et al.'s quantile estimation method yielded coverage for mean ratios between 88.5% and 91.5% and SDs between 78.0 and 82.7. McGrath et al.'s Box-Cox transformation method showed coverage for mean ratios from 86.6% to 94.4% and SDs from 67.1 to 83.1. The maximum likelihood estimation method by Cai et al. for nonnormal distributions showed coverage for mean ratios from 78.9% to 86.4% and SDs from 67.6 to 78.0.

CONCLUSIONS

All evaluated methods of estimating means and standard deviations from quartiles of log-normal distributed data result in confidence interval coverages below the expected 95%. Because these methods are widely used in meta-analyses of anesthesiology data, P values reported as < 0.05 cannot be trusted. Anesthesiology journals and investigators should revise reporting requirements for continuous skewed variables. We advise reporting the quartiles, mean, and SD, or the quartiles and including the raw data for the relevant variables as supplemental content. This holistic approach could improve the reliability of statistical inferences in meta-analyses of anesthesiology research, particularly when skewed distributions are involved.

Economic impact of prolonged tracheal extubation times on operating room time overall and for subgroups of surgeons: a historical cohort study

BACKGROUND

Prolonged tracheal extubation time is defined as an interval ≥ 15 min from the end of surgery to extubation. An earlier study showed that prolonged extubations had a mean 12.4 min longer time from the end of surgery to operating room (OR) exit. Prolonged extubations usually (57%) were observed during OR days with > 8 h of cases and turnovers, such that longer OR times from prolonged extubation can be treated as a variable cost (i.e., each added minute incurs an expense). The current study addressed limitations of the generalizability of these earlier investigations.

METHODS

The retrospective cohort study included cases performed at a university hospital October 2011 through June 2023 with general anesthesia, tracheal intubation and extubation in the OR where the anesthetic was performed, and non-prone positioning. The primary endpoint was the interval from end of surgery to OR exit. Mean OR time differences with/without prolonged extubation were analyzed pairwise by surgeon. The variance among surgeons was estimated using the DerSimonian-Laird method with Knapp-Hartung adjustment for the sample sizes of surgeons. Proportions were analyzed after arcsine transformation, and the inverse taken to report results.

RESULTS

There were prolonged extubations for 23% (41,768/182,374) of cases. Prolonged extubations had a mean 13.3 min longer time from the end of surgery to OR exit (95% confidence interval 12.8-13.7 min, P < 0.0001). That result was among the 71 surgeons each with ≥ 9 cases having prolonged extubation times and ≥ 9 cases with typical extubation times. Results were similar using a threshold of ≥ 3 cases, comprising 257 surgeons (13.2 min, P < 0.0001). Among the 71 surgeons with at least nine prolonged extubations, on most days with a prolonged extubation during at least one of their cases, there were > 8 h of cases and turnover times in the OR (77%, 73%-81%, P < 0.0001). Results were similar when analyzed for the 249 surgeons each with ≥ 3 cases with prolonged extubation (76%, P < 0.0001).

CONCLUSIONS

Matching earlier findings, prolonged tracheal extubation times are important economically, increasing OR time by 13 min and usually performed in ORs with lists of cases of sufficient duration to treat the extra time as a variable cost.

Taylor Series Approximation for Accurate Generalized Confidence Intervals of Ratios of Log-Normal Standard Deviations for Meta-Analysis Using Means and Standard Deviations in Time Scale

With contemporary anesthetic drugs, the efficacy of general anesthesia is assured. Health-economic and clinical objectives are related to reductions in the variability in dosing, variability in recovery, etc. Consequently, meta-analyses for anesthesiology research would benefit from quantification of ratios of standard deviations of log-normally distributed variables (e.g., surgical duration). Generalized confidence intervals can be used, once sample means and standard deviations in the raw, time, scale, for each study and group have been used to estimate the mean and standard deviation of the logarithms of the times (i.e., "log-scale"). We examine the matching of the first two moments versus also using higher-order terms, following Higgins et al. 2008 and Friedrich et al. 2012. Monte Carlo simulations revealed that using the first two moments 95% confidence intervals had coverage 92%-95%, with small bias. Use of higher-order moments worsened confidence interval coverage for the log ratios, especially for coefficients of variation in the time scale of 50% and for largern = 50 $$ \left(n=50\right) $$ sample sizes per group, resulting in 88% coverage. We recommend that for calculating confidence intervals for ratios of standard deviations based on generalized pivotal quantities and log-normal distributions, when relying on transformation of sample statistics from time to log scale, use the first two moments, not the higher order terms.

The Value of Auditing the Frequency of Inhalational Anesthetics With a Combination of Very Low Bispectral Index and High Fraction of the Age-Adjusted Minimum Alveolar Concentration

BACKGROUND

Previously, a depth of anesthesia bispectral index (BIS™) <45 was considered low and found to have no clinical benefit. A BIS <35 was considered very low and was not only without evident clinical benefit but also associated with a greater risk of postoperative delirium. We considered the association between BIS and the anesthetic dose of inhalational agents, quantified using the minimum alveolar concentration (MAC) fraction, which was the patient's end-tidal inhalational agent concentration divided by the agent's altitude- and age-adjusted minimum alveolar percentage concentration. The MAC fraction was displayed on the anesthesia machine. When the MAC fraction >1.0 and the BIS <35, it implies that the inhalational anesthetic agent concentration can be reduced without harmful clinical effects. We hypothesized a substantive percentage of cases (>10%) have long (≥15 minutes) periods having the combination of MAC fraction >1.0 and BIS <35.

METHODS

The retrospective database cohort study included N = 8,566 cases from September 13, 2016, to August 12, 2024 that met the following criteria: (1) ≥100 minutes of BIS monitoring (BIS minutes); (2) use of general anesthesia; (3) tracheal intubation and extubation performed in the operating room where the anesthetic was administered; and (4) absence of prone positioning. The latter three were characteristics of studies examining prolonged extubation, defined as ≥15 minutes from the end of surgery. From the N = 8,566 cases studied, 1,862,022 BIS minutes were automatically recorded in the electronic health record. Comparisons were made with the matching MAC fractions. A Clopper-Pearson two-sided exact 95% confidence interval was calculated for the planned primary endpoint, the percentage of cases with ≥15 minutes wherein simultaneously the BIS <35 and MAC fraction >1.0. Post hoc, we added a 97.5% confidence interval for the incidence with ≥30 minutes to compare with 10%.

RESULTS

Among the 8,566 cases with ≥100 minutes of BIS monitor use, 29.5% (2,527) had prolonged extubation. There were contemporaneously 152,443 other cases without BIS monitoring. Those other cases had a nearly identical incidence of prolonged extubations (29.3%, 44,675). A total of 375 distinct anesthesia practitioners used the BIS monitor during the 8,566 cases, with each contributing, on average, only 0.27% (standard deviation [SD] = 0.33%) of anesthetic minutes. Among the N = 7,031 cases with BIS measured when the MAC fraction ≥0.6, 25% (1,780/7,031) had ≥15 minutes of very low BIS and MAC fraction >1.0. The 95% confidence interval was 24% to 26%. Being considerably larger than 10% (P < 0.0001), post hoc, we repeated the calculations using the threshold of ≥30 minutes of very low BIS and MAC fraction >1.0. The estimated incidence was 15%, with a 97.5% confidence interval of 14% to 16%, also significantly exceeding 10% (P < 0.0001).

CONCLUSIONS

If department practices are such that processed electroencephalographic monitoring (e.g., BIS) is commonly used during general anesthesia to assess anesthetic depth, our results recommend auditing the volatile agent concentration and the corresponding anesthetic depth index, as we did in this study. We recommend that feedback and education regarding suitable titration of anesthetic agent concentrations relative to the index should be provided at the departmental level.

Inhalational Agent Dosing Behaviors of Anesthesia Practitioners Cause Variability in End-Tidal Concentrations at the End of Surgery and Prolonged Times to Tracheal Extubation

INTRODUCTION

Prolonged times to tracheal extubation are intervals from the end of surgery to extubation ≥15 minutes. We examined why there are associations with the end-tidal inhalational agent concentration as a proportion of the age‑adjusted minimum alveolar concentration (MAC fraction) at the end of surgery.

METHODS

The retrospective cohort study used 11.7 years of data from one hospital. All p‑values were adjusted for multiple comparisons.

RESULTS

There was a greater odds of prolonged time to extubation if the anesthesia practitioner was a trainee (odds ratio 1.68) or had finished fewer than five cases with the surgeon during the preceding three years (odds ratio 1.12) (both P<0.0001). There was a greater risk of prolonged time to extubation if the MAC fraction was >0.4 at the end of surgery (odds ratio 2.66, P<0.0001). Anesthesia practitioners who were trainees and all practitioners who had finished fewer than five cases with the surgeon had greater mean MAC fractions at the end of surgery and had greater relative risks of the MAC fraction >0.4 at the end of surgery (all P<0.0001). The source for greater MAC fractions at the end of surgery was not greater MAC fractions throughout the anesthetic because the means during the case did not differ among groups. Rather, there was substantial variability of MAC fractions at the end of surgery among cases of the same anesthesia practitioner, with the mean (standard deviation) among practitioners of each practitioner's standard deviation being 0.35 (0.05) and the coefficient of variation being 71% (13%).

CONCLUSION

More prolonged extubations were associated with greater MAC fractions at the end of surgery. The cause of the large MAC fractions was the substantial variability of MAC fractions among cases of each practitioner at the end of surgery. That variability matches what was expected from earlier studies, both from variability among practitioners in their goals for the MAC fraction given at the start of surgical closure and from inadequate dynamic forecasting of the timing of when surgery would end. Future studies should examine how best to reduce prolonged extubations by using anesthesia machines' display of MAC fraction and feedback control of end-tidal agent concentration.

Anesthesia Practitioners' Goals for Sevoflurane Minimum Alveolar Concentration at the End of Surgery and the Incidence of Prolonged Extubations: A Prospective and Observational Study

BACKGROUND

Prolonged times to tracheal extubation (≥15 minutes from dressing on the patient) are consequential based on their clinical and economic effect. We evaluated the variability among anesthesia practitioners in their goals for the age-adjusted end-tidal minimum alveolar concentration of sevoflurane (MAC) at surgery end and achievement of their goals.

METHODS

We prospectively studied a cohort of 56 adult patients undergoing general anesthesia with sevoflurane as the sole anesthetic agent, scheduled operating room time of at least 3 hours, and non-prone positioning. At the start of surgical closure, an observer asked the anesthesia practitioner their goal for MAC when the surgical drapes are lowered (i.e., the functional end of surgery for the studied procedures). When the drapes were lowered, the MAC achieved was recorded, and the values were compared.

RESULTS

The standard deviation of the practitioners' MAC goal was large, 0.199 (N = 56 cases, 95% confidence interval 0.17-0.24), not significantly different from the standard deviation of the MAC achieved of 0.253, P = 0.071. The MAC goal and MAC achieved were correlated pairwise, Pearson r =0.65, P < 0.0001. There was no incremental effect of operating room conversation(s) related to case progress on the association (partial correlation ‑0.01, P = 0.96). Differences among practitioners in the MAC achieved at surgery end were consequential. Specifically, for the N = 12 cases with prolonged extubation, the mean MAC was 0.60 (standard deviation 0.10) versus 0.48 (0.21) among the N = 44 cases without prolonged extubation (P = 0.0070).

CONCLUSIONS

The standard deviation of the MAC goal among practitioners was sufficiently large to contribute significantly to the variability in the MAC achieved at the end of surgery. We confirmed prospectively that the age-adjusted end-tidal MAC at the end of surgery matters clinically and economically because differences of 0.60 versus 0.48 were associated with more prolonged extubations. Our novel finding is that the MAC achieved ≥0.60 were caused in part by the anesthesia practitioners' stated MAC goals when surgical closures started.

Preventing Prolonged Times to Awakening While Mitigating the Risk of Patient Awareness: Gas Man Computer Simulations of Sevoflurane Consumption From Brief, High Fresh Gas Flow Before the End of Surgery

Prolonged times to tracheal extubation are associated with adverse patient and economic outcomes. We simulated awakening patients from sevoflurane after long-duration surgery at 2% end-tidal concentration, 1.0 minimum alveolar concentration (MAC) in a 40-year-old. Our end-of-surgery target was 0.5 MAC, the Michigan Awareness Control Study's threshold for intraoperative alerts. Consider an anesthetist who uses a 1 liter/minute gas flow until surgery ends. During surgical closure, the inspired sevoflurane concentration is reduced from 2.05% to 0.62% (i.e., MAC-awake). The estimated time to reach 0.5 MAC is 28 minutes. From a previous study, 28 minutes exceeded ≥95% of surgical closure times for all 244 distinct surgical procedures (N=23,343 cases). Alternatively, the anesthetist uses 8 liters/minute gas flow with the vaporizer at MAC-awake for 1.8 minutes, which reduces the end-tidal concentration to 0.5 MAC. The anesthetist then increases the vaporizer to keep end-tidal 0.5 MAC until the surgery ends. An additional simulation shows that, compared with simulated end-tidal agent feedback control, this approach consumed 0.45 mL extra agent. Simulation results are the same for an 80-year-old patient. The extra 0.45 mL has a global warming potential comparable to driving 26 seconds at 40 kilometers (25 miles) per hour, comparable to route modification to avoid potential roadway hazards.