Frequently Touched Sites in the Intensive Care Unit Environment Returning 100 Colony-Forming Units per Surface Area Sampled Are Associated With Increased Risk of Major Bacterial Pathogen Detection.

BACKGROUND: A threshold for surface hygiene has not been defined for the healthcare arena. We aimed to identify the magnitude of bacterial contamination of frequently touched sites in the intensive care unit (ICU) environment that could be used to guide quality improvement initiatives. METHODS: Nineteen patients in a mixed ICU environment (providing care for medical and surgical patients) were followed from admission for 72 hours in 2010. Baseline cultures of frequently touched environmental sites were obtained at time zero following active decontamination and at 12, 24, 48, and 72 hours without further disinfection. We tested for an association of environmental reservoirs returning ≥ 100 colony-forming units (CFU) per surface area sampled with major bacterial pathogen detection. RESULTS: There were 446 ICU room, day, and reservoir combinations sampled from 19 patients. There were pathogens detected in 40% (79/199) of samples with ≥ 100 CFU vs. 14% (35/247) of samples returning < 100 CFU. The relative risk was 2.80 (95% CI: 1.97-3.98, P <0.0001). The odds ratio adjusted for time in hours was 3.11 (95% CI: 1.84-5.34, P < 0.0001). CONCLUSIONS: Frequently touched ICU environmental sites returning ≥ 100 CFU are associated with major bacterial pathogen detection. This threshold for surface hygiene can be used to ensure compliance with ICU environmental cleaning protocols and to guide quality improvement initiatives.

The impact of spinal versus general anesthesia on the variability of surgical times: a systematic review and meta-analysis.

BACKGROUND: With spinal anesthesia, when cases are taking longer than usual, there may be behavioural tendencies for surgical teams to work more quickly. We conducted a systematic review with meta-analysis to examine standard deviations of surgical times for single-dose spinal anesthetics versus general anesthesia. We compared ratios of mean surgical times as a secondary endpoint. METHODS: We included randomized trials of humans where general or spinal anesthesia was used for one category of surgical procedure (e.g., hip arthroplasty) and the article reported the means and standard deviations of operative durations. We used statistical methods suitable for surgical times following log-normal distributions. We used generalized confidence intervals to calculate point estimates of ratios and standard errors for each study, followed by pooling among studies using DerSimonian and Laird random-effects meta-analysis with Knapp-Hartung adjustment. RESULTS: Among the 77 included studies, 96% were of high quality for our endpoint (i.e., had a low risk of bias), as no (0%) study focused on comparing variability of surgical times and none had surgical time as the primary endpoint. Spinal anesthesia was associated with 6.6% smaller standard deviations than general anesthesia (95% confidence interval, 15.8% smaller to 1.9% larger, P = 0.13). By meta-regression, there was no significant association of the ratios of standard deviations with study quality (P = 0.39), year of publication (P = 0.76), or categories of procedures (all five P ≥ 0.28). Spinal anesthesia was associated with 1.1% smaller means than general anesthesia (95% confidence interval, 3.7% smaller to 1.5% larger, P = 0.42). There were no significant associations between the ratios of means and study quality (P = 0.47), year of publication (P = 0.95), or categories of procedures (all five, P ≥ 0.63). CONCLUSIONS: The results of this systematic review and meta-analysis show with high confidence that the effect of choosing spinal anesthesia on variability in surgical time, if present, is sufficiently small to have no substantive direct economic effect. The same conclusion applies to mean surgical time. Therefore, although anesthetic choice has a clinical (biological) impact and affects anesthesia times, the direct effects on surgical times and workflow are minimal at most. Anesthetic choice does not influence operating theatre productivity via changes to surgical times. The impact of spinal anesthetic effects is limited to nonoperative times (e.g., reducing anesthesia-controlled times by using a block room before the patient enters the operating room). STUDY REGISTRATION: PROSPERO ( CRD42023461952 ); first submitted 8 September 2023.

RéSUMé: CONTEXTE: Lors de l'utilisation de rachianesthésie, si les cas prennent plus de temps que d'habitude, les équipes chirurgicales pourraient avoir tendance à travailler plus rapidement. Nous avons réalisé une revue systématique avec méta-analyse pour examiner les écarts types des temps chirurgicaux pour les rachianesthésies en dose unique par rapport à l'anesthésie générale. Nous avons comparé les rapports des durées chirurgicales moyennes comme critère d'évaluation secondaire. MéTHODE: Nous avons inclus des études randomisées chez l'humain dans lesquelles l'anesthésie générale ou rachidienne avait été utilisée pour une catégorie d'intervention chirurgicale (par exemple, l'arthroplastie de la hanche) et pour lesquelles les moyennes et les écarts types des durées opératoires étaient rapportés. Nous avons utilisé des méthodes statistiques adaptées aux temps chirurgicaux suivant des distributions log-normales. Nous avons utilisé des intervalles de confiance généralisés pour calculer des estimations ponctuelles des ratios et des erreurs-types pour chaque étude, suivis d'un regroupement entre les études à l'aide d'une méta-analyse à effets aléatoires de DerSimonian et Laird avec ajustement de Knapp-Hartung. RéSULTATS: Parmi les 77 études incluses, 96 % étaient de haute qualité pour notre critère d'évaluation (c'est-à-dire qu'elles présentaient un faible risque de biais), car aucune étude (0 %) ne s'est concentrée sur la comparaison de la variabilité des temps chirurgicaux et aucune n'avait le temps chirurgical comme critère d'évaluation principal. La rachianesthésie était associée à des écarts types inférieurs de 6,6 % à ceux de l'anesthésie générale (intervalle de confiance à 95 %, 15,8 % plus petit à 1,9 % plus grand, P = 0,13). Par métarégression, il n'y avait pas d'association significative entre les ratios des écarts types et la qualité de l'étude (P = 0,39), l'année de publication (P = 0,76), ou des catégories de procédures (les cinq P ≥ 0,28). La rachianesthésie était associée à des moyennes inférieures de 1,1 % à celles de l'anesthésie générale (intervalle de confiance à 95 %, 3,7 % plus petit à 1,5 % plus grand, P = 0,42). Il n'y a pas eu d'association significative entre les ratios des moyennes et la qualité des études (P = 0,47), l'année de publication (P = 0,95), ou les catégories de procédures (toutes les cinq, P ≥ 0,63). CONCLUSION: Les résultats de cette revue systématique et de cette méta-analyse montrent avec un degré de confiance élevé que l'effet du choix de la rachianesthésie sur la variabilité du temps chirurgical, le cas échéant, est suffisamment faible pour n'avoir aucun effet économique direct substantiel. La même conclusion s'applique au temps chirurgical moyen. Par conséquent, bien que le choix de l'anesthésie ait un impact clinique (biologique) et affecte les temps d'anesthésie, les effets directs sur les temps chirurgicaux et le flux de travail sont tout au plus minimes. Le choix du type d'anesthésie n'influence pas la productivité de la salle d'opération en modifiant les temps chirurgicaux. L'impact des effets de la rachianesthésie est limité aux périodes non opératoires (p. ex., réduire les temps de contrôle de l'anesthésie en utilisant une salle de bloc avant que le patient ou la patiente n'entre en salle d'opération). ENREGISTREMENT DE L'éTUDE: PROSPERO ( CRD42023461952 ); première soumission le 8 septembre 2023.

Surface Cleaning with a Microfiber Cloth and Water followed by Ultraviolet-C Light Exposure Achieves Non-Inferior Disinfection of a Pathogenic Staphylococcus aureus Strain versus Use of Germicidal Wipes.

BACKGROUND: We hypothesized that ultraviolet-C (UV-C) irradiation (Surfacide, Waukesha, WI) following use of microfiber cloths (Sanny Shop LLC, Longmont, CO) soaked in water would be noninferior to surface disinfection wipes containing a quaternary ammonium compound and alcohol (PDI Healthcare, Woodcliff Lake, NJ) for the pathogenic Staphylococcus aureus (S. aureus) sequence type 5 (ST5). METHODS: This was a randomized laboratory study of disinfection approaches for S. aureus ST5. A total of 270 polycarbonate slides loaded with ST5 were prepared for the standard surface disinfection group (N=18) and water-soaked microfiber cloths and UV-C treatment group (N=144), along with positive and negative microbiological controls. RESULTS: All 18 samples of S. aureus ST5 bacteria treated with standard chemical wipes showed complete disinfection (colony forming units (CFU) = 0). All 144 treatments with water-soaked microfiber wipes followed by UV-C exposure showed complete disinfection (CFU =0) regardless of soiling, height from the floor, or orientation to the emitters. The upper 95% exact one-sided confidence limit for any CFU >0 was 2.1%. DISCUSSION: These data affirm our hypothesis that surface wiping with a damp cloth followed by triangular UV-C irradiation delivery is noninferior to surface disinfection for S. aureus ST5 using germicidal wipes, even when UV-C is compromised by height from the floor and orientation to the emitters and surface disinfection is targeted. CONCLUSION: Removing bioburden with chemical-free microfiber cloths followed by triangular UV-C delivery is a noninferior strategy to targeted surface disinfection with chemical disinfecting wipes for the pathogenic S. aureus ST5 strain in the laboratory setting.

Since the COVID-19 pandemic, approximately 90% of elective anesthetics have been ambulatory: A retrospective analysis of statewide data in Florida from 2010 through 2022.

BACKGROUND: When the vast majority (e.g., ≈90%) of a specialty's elective (scheduled) care is ambulatory (i.e., length of stay 0 or 1 night), the administrative, clinical, and economic policy implications are profound. We examined the progressive shift of elective anesthetics in Florida from inpatient to ambulatory, from the first quarter of 2010 through the fourth quarter of 2022. We were particularly interested in the most recent data following the lifting of COVID-19 restrictions on elective surgery in the state. METHODS: This retrospective cohort study included major therapeutic and major diagnostic procedures with >0 American Society of Anesthesiologists base units in the state of Florida inpatient and ambulatory surgery databases. The last 8 quarters of these operating room anesthetic data corresponded to the end of restrictions on elective surgery in Florida due to the COVID-19 pandemic. Our goal was to determine whether the overall mean percentage of cases with 0- or 1-day lengths of stay has reached 90% since the lifting of pandemic restrictions. Numbers of cases over periods of at least four weeks tend to follow normal distributions. Therefore, we analyzed the N = 8 quarters of cases from 2021 to 2022 using Student's t-test. The study was performed when there were N = 8 quarters available from the Florida healthcare databases. RESULTS: There were overall 22,584,752 surgical cases studied. The percentages of elective anesthetics with length of stay ≤1-day increased progressively from 2010 through 2020. Among the eight successive quarters since the end of pandemic-related elective surgery restrictions, the percentage of elective cases with length of stay 0- or 1 day was stable, averaging 90% (95% two-sided confidence interval 89.4% to 90.3%). CONCLUSION: Since the COVID-19 pandemic, the mean quarterly percentage of elective surgery cases with anesthesia in Florida that were ambulatory has been reliably ≈90%. Implications include value in expecting overnight post-anesthesia care unit stay in ambulatory surgery centers and scheduling and sequencing cases based on post-anesthesia care unit capacity. Furthermore, because the vast majority (i.e., ≈90%) of cases would be excluded (i.e., not involve hospital admission for at least 2 midnights), there is a minimal role that risk-adjusted hospital length of stay and mortality can have in evaluating anesthesia department overall quality and economic effectiveness.

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 age­adjusted 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 p­values 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.

Few Anesthesia-Related Adverse Events in a Retrospective Cohort Study of Patients With Unanticipated Intensive Care Unit Admission After Ambulatory Procedures.

We evaluated whether a hospital-based anesthesia department can validly use automated intensive care unit (ICU) admission data after elective ambulatory procedures to assess the quality of anesthetic care. Among 13,656 patients, 25 (0.2%) had an unplanned hospital length of stay >1 night and ICU admission. On review, only 1 of the 25 cases (0.007%) had an anesthesia-related complication. The false-positive incidence of anesthetic complications was ≥96% for scheduled ambulatory cases with ICU admission. Therefore, fully automated computerized identification of all unexpected ICU admissions after ambulatory procedures without manual review is an unsuitable (invalid) metric of individual anesthesiologists' clinical performance.

Predictive Validity of Anesthesiologists' Quality of Clinical Supervision and Nurse Anesthetists' Work Habits Assessed by Their Associations With Operating Room Times.

BACKGROUND: At all Joint Commission-accredited hospitals, the anesthesia department chair must report quantitative assessments of anesthesiologists' and nurse anesthetists' (CRNAs') clinical performance at least annually. Most metrics lack evidence of usefulness, cost-effectiveness, reliability, or validity. Earlier studies showed that anesthesiologists' clinical supervision quality and CRNAs' work habits have content, convergent, discriminant, and construct validity. We evaluated predictive validity by testing for (expected) small but statistically significant associations between higher quality of supervision (work habits) and reduced probabilities of cases taking longer than estimated. METHODS: Supervision quality of each anesthesiologist was evaluated daily by assigned trainees using the 9-item de Oliveira Filho scale. The work habits of each CRNA were evaluated daily by assigned anesthesiologists using a 6-item scale. Both are scored binary, 1 if all items are rated the maximum, 0 otherwise. From 40,718 supervision evaluations and 53,722 work habit evaluations over 8 fiscal years, 16 mixed-effects logistic regression models were estimated, with raters as fixed effects and ratees (anesthesiologists or CRNAs) as random effects. Empirical Bayes means in the logit scale were obtained for 561 anesthesiologist-years and 605 CRNA-years. The binary-dependent variable was whether the case took longer than estimated from the historical mean time for combinations of scheduled procedures and surgeons. From 264,060 cases, 8 mixed-effects logistic regression models were fitted, 1 per fiscal year, using ratees as random effects. Predictive validity was tested by pairing the 8 one-year analyses of clinical supervision, and the 8 one-year analyses of work habits, by ratee, with the 8 one-year analyses of whether OR time was longer than estimated. Bivariate errors in variable linear least squares linear regressions minimized total variances. RESULTS: Among anesthesiologists, 8.2% (46/561) had below-average supervision quality, and 17.7% (99/561), above-average. Among CRNAs, 6.3% (38/605) had below-average work habits, and 10.9% (66/605) above-average. Increases in the logits of the quality of clinical supervision were associated with decreases in the logits of the probabilities of cases taking longer than estimated, unitless slope = -0.0361 (SE, 0.0053), P < .00001. Increases in the logits of CRNAs' work habits were associated with decreases in the logits of probabilities of cases taking longer than estimated, slope = -0.0238 (SE, 0.0054), P < .00001. CONCLUSIONS: Predictive validity was confirmed, providing further evidence for using supervision and work habits scales for ongoing professional practice evaluations. Specifically, OR times were briefer when anesthesiologists supervised residents more closely, and when CRNAs had better work habits.

Incremental Societal Costs of Perioperative Complications Following Adult Elective Inpatient Major Therapeutic Surgery in the State of Florida: A Seven-Year Retrospective Epidemiological Analysis.

Introduction There is an expanding role for anesthesiologists in the preoperative optimization and postoperative management of patients, often in the context of a so-called perioperative surgical home. Such efforts typically include enhanced recovery after surgery (ERAS) protocols and often an anesthesiologist-led team for perioperative management. Studies of the cost-effectiveness of such approaches have generally been conducted at single institutions, with most patients cared for by small numbers of surgeons. This limitation creates generalizability issues as to whether improvement was related mostly to organizational culture or the studied surgeons' practices (non-generalizable) versus the procedures (generalizable). We studied whether other organizations can rely on achieving similar benefits following the adoption of a studied process improvement strategy at a single institution. Methods All patients undergoing elective major therapeutic inpatient surgery discharged between October 2015 and June 2022 at non-federal hospitals in the state of Florida were included. For each discharge, the United States Medicare Severity Diagnosis-Related Group (MS-DRG) weighting factor (i.e., the multiplier for the hospital's base rate for admissions that determines reimbursement) and the Clinical Classification Software Refined (CCSR) code for the principal procedure were determined at admission and discharge from the state's inpatient healthcare database based on the diagnoses present at those time points. An increase in the weighting factor from admission to discharge represents societal costs from perioperative complications. Statewide, by hospital, and by surgeon, we calculated the total increase for each CCSR's weighting factor. Our primary hypothesis was that surgeon variability would be statistically greater than CCSR variability but that the incremental effect would be <5%. If CCSR and surgeon variability were comparable, this would be supportive of generalizability. In contrast, if there were a predominant effect related to the surgeon, results from one institution might not be applicable to others. Results Among the 1,482,344 discharges studied, the pooled (N=7 years) contributions to MS-DRG weighting factor increases from the upper 20% of surgeons were 2.8% more than from the upper 20% of CCSRs (95% CI 1.9%-3.9%, p=0.0006). Those CCSRs accounted for 85.5% (95% CI 79.4%-91.7%, p<0.0001) of the total increase in the MS-DRG weighting factor. The average contribution of the top two surgeons at each hospital to that hospital's increase in the weighting factor ranged among CCSRs from 68% to 97%. The median and 75th percentile of surgeons performing at least 10% of the total number of cases at each hospital was similar to those values for the contributions to the increases in the MS-DRG weighting factor, median 2.0 to 3.0, and 75th percentile 1.75 to 4.0. Conclusions Because variability among surgeons in their contributions to increases in the MS-DRG weighting factor only slightly exceeded the variability among CCSR surgical categories, perioperative surgical home and ERAS study research results involving single institutions and a small number of surgeons would likely be generalizable to other hospitals and healthcare systems. Funding agencies should not be hesitant to fund single-center perioperative surgical home studies and ERAS interventions based on concerns related to lack of generalizability.

Poor Concordance Between Intensive Care Unit Patients' and Family Members' Patient Dignity Inventory Scores Despite Communication of Dignity-Related Distress.

BACKGROUND: Promptly assessing and treating the distress of intensive care unit (ICU) patients may improve long-term psychological outcomes. One holistic approach to reduce patient distress is through dignity-centered care, traditionally used in palliative care. The 25-item Patient Dignity Inventory has construct validity and reliability for measuring dignity-related distress among ICU patients. Because family members often serve as ICU patients' surrogates and play an integral role in patients' dignity, we examined whether family members reliably recognized ICU patients' sources of distress. METHODS: Two single-center observational studies of adult ICU patients were performed from May to June 2022. Inclusion criteria were ICU length-of-stay >48 hours, awake and alert, intact cognition, and no delirium. Study #1 evaluated concordance between patient and family for dignity-related distress. Both completed the Patient Dignity Inventory independently. The next Study #2 measured how many distressing items that the patient reported discussing with family members. RESULTS: Study #1 of concordance had 33 patient-family dyads complete the Patient Dignity Inventory. The concordance correlation coefficient was small, 0.20 (99% confidence interval -0.21 to 0.55) and less than the inventory's test-retest reliability (r = .85). Study #2 examined sharing of Patient Dignity Inventory-related items between patients and family members. There were 12 of 19 patients who had severe distress based on an average Patient Dignity Inventory item score ≥1.92. The median patient shared multiple items of distress with their family (median 12, 99% 2-sided exact Hodges-Lehmann interval 4.0-17.5). CONCLUSIONS: Although ICU patients often report sharing sources of distress with their loved ones, family members cannot accurately or reliably assess the extent to which patients experience psychosocial, existential, and symptom-related distress during critical illness. Treatments of distress should not be delayed by the absence of family members.

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.

Lateness of Acetaminophen and Non-steroidal Anti-inflammatory Drug Administrations in a Retrospective Cohort of Medication Administration Records Among Patients After Cesarean Delivery.

INTRODUCTION: In an earlier study of patients after cesarean delivery, the concurrent versus alternating administration of acetaminophen and non-steroidal anti-inflammatory drugs was associated with a substantial reduction in total postoperative opioid use. This likely pharmacodynamic effect may differ if the times when nurses administer acetaminophen and non-steroidal anti-inflammatory drugs often differ substantively from when they are due. We examined the "lateness" of analgesic dose administration times, the positive difference if administered late, and the negative value if early. METHODS: The retrospective cohort study used all 67,900 medication administration records for scheduled (i.e., not "as needed") acetaminophen, ibuprofen, and ketorolac among all 3,163 cesarean delivery cases at the University of Iowa between January 2021 and December 2023. Barcode scanning at the patient's bedside was used right before each medication administration. RESULTS: There were 95% of doses administered over a 4.8-hour window, from 108 minutes early (97.5% one-sided upper confidence limit 105 minutes early) to 181 minutes late (97.5% one-sided lower limit 179 minutes late). Fewer than half of doses (46%, P <0.0001) were administered ±30 minutes of the due time. The intraclass correlation coefficient was approximately 0.11, showing that there were small systematic differences among patients. There likewise were small to no systematic differences in lateness based on concurrent administrations of acetaminophen and ibuprofen or ketorolac, time of the day that medications were due, weekday, year, or number of medications to be administered among all such patients within 15 minutes. DISCUSSION: Other hospitals should check the lateness of medication administration when that would change their ability to perform or apply the results of analgesic clinical trials (e.g., simultaneous versus alternating administration).

Generalized Confidence Intervals for Ratios of Standard Deviations Based on Log-Normal Distribution when Times Follow Weibull Distributions.

Modern anesthetic drugs ensure the efficacy of general anesthesia. Goals include reducing variability in surgical, tracheal extubation, post-anesthesia care unit, or intraoperative response recovery times. Generalized confidence intervals based on the log-normal distribution compare variability between groups, specifically ratios of standard deviations. The alternative statistical approaches, performing robust variance comparison tests, give P-values, not point estimates nor confidence intervals for the ratios of the standard deviations. We performed Monte-Carlo simulations to learn what happens to confidence intervals for ratios of standard deviations of anesthesia-associated times when analyses are based on the log-normal, but the true distributions are Weibull. We used simulation conditions comparable to meta-analyses of most randomized trials in anesthesia, n ≈ 25 and coefficients of variation ≈ 0.30 . The estimates of the ratios of standard deviations were positively biased, but slightly, the ratios being 0.11% to 0.33% greater than nominal. In contrast, the 95% confidence intervals were very wide (i.e., > 95% of P ≥ 0.05). Although substantive inferentially, the differences in the confidence limits were small from a clinical or managerial perspective, with a maximum absolute difference in ratios of 0.016. Thus, P < 0.05 is reliable, but investigators should plan for Type II errors at greater than nominal rates.