Alerting thresholds for the prevention of intraoperative awareness with explicit recall: a secondary analysis of the Michigan Awareness Control Study.

BACKGROUND: Intraoperative awareness with explicit recall is a potentially devastating complication of surgery that has been attributed to low anaesthetic concentrations in the vast majority of cases. Past studies have proposed the determination of an adequate dose for general anaesthetics that could be used to alert providers of potentially insufficient anaesthesia. However, there have been no systematic analyses of appropriate thresholds to develop population-based alerting algorithms for preventing intraoperative awareness. OBJECTIVE: To identify a threshold for intraoperative alerting that could be applied for the prevention of awareness with explicit recall. DESIGN: Secondary analysis of a randomised controlled trial (Michigan Awareness Control Study). SETTING: Three hospitals at a tertiary care centre in the USA. PATIENTS: Unselected patients presenting for surgery under general anaesthesia. INTERVENTIONS: Alerts based on end-tidal anaesthetic concentration or bispectral index values. MAIN OUTCOME MEASURES: Using case and outcomes data from the primary study, end-tidal anaesthetic concentration and bispectral index values were analysed using Youden's index and c-statistics derived from a receiver operating characteristic curve to determine a specific alerting threshold for the prevention of awareness. RESULTS: No single population-based threshold that maximises sensitivity and specificity could be identified for the prevention of intraoperative awareness, using either anaesthetic concentration or bispectral index values. The c-statistic for anaesthetic concentration was 0.431 ±â€Š0.046, and 0.491 ±â€Š0.056 for bispectral index values. CONCLUSION: We could not derive a single population-based alerting threshold for the prevention of intraoperative awareness using either anaesthetic concentration or bispectral index values. These data indicate a need to move towards individualised alerting strategies in the prevention of intraoperative awareness. TRIAL REGISTRATION: Primary trial registration (Michigan Awareness Control Study) ClinicalTrials.gov identifier: NCT00689091.

Prevention of intraoperative awareness with explicit recall in an unselected surgical population: a randomized comparative effectiveness trial.

BACKGROUND: Intraoperative awareness with explicit recall occurs in approximately 0.15% of all surgical cases. Efficacy trials based on the Bispectral Index® (BIS) monitor (Covidien, Boulder, CO) and anesthetic concentrations have focused on high-risk patients, but there are no effectiveness data applicable to an unselected surgical population. METHODS: We conducted a randomized controlled trial of unselected surgical patients at three hospitals of a tertiary academic medical center. Surgical cases were randomized to alerting algorithms based on either BIS values or anesthetic concentrations. The primary outcome was the incidence of definite intraoperative awareness; prespecified secondary outcomes included postanesthetic recovery variables. RESULTS: The study was terminated because of futility. At interim analysis the incidence of definite awareness was 0.12% (11/9,376) (95% CI: 0.07-0.21%) in the anesthetic concentration group and 0.08% (8/9,460) (95% CI: 0.04-0.16%) in the BIS group (P = 0.48). There was no significant difference between the two groups in terms of meeting criteria for recovery room discharge or incidence of nausea and vomiting. By post hoc secondary analysis, the BIS protocol was associated with a 4.7-fold reduction in definite or possible awareness events compared with a cohort receiving no intervention (P = 0.001; 95% CI: 1.7-13.1). CONCLUSION: This negative trial could not detect a difference in the incidence of definite awareness or recovery variables between monitoring protocols based on either BIS values or anesthetic concentration. By post hoc analysis, a protocol based on BIS monitoring reduced the incidence of definite or possible intraoperative awareness compared with routine care.

A novel electronic algorithm for detecting potentially insufficient anesthesia: implications for the prevention of intraoperative awareness.

OBJECTIVE: A recent clinical trial compared a minimum alveolar concentration (MAC)-based protocol to an electroencephalography (EEG)-based protocol for the prevention of intraoperative awareness. One limitation of this study design is that MAC-based protocols are not sensitive to the use of intravenous agents, while EEG-based protocols are. Our objective was to develop a MAC alert that incorporates intravenous agents. METHODS: We developed an electronic algorithm and alerting system that calculates a total age-adjusted MAC value based on inhalational agents, but also incorporates intravenous agents. We retrospectively applied the algorithm to adult general anesthesia cases over a 1 year period to assess the frequency of alert triggers, using thresholds of <0.8, <0.7, <0.6, <0.5 and <0.4 age-adjusted MAC. We also electronically analyzed 12 cases of intraoperative awareness that occurred over a 4-year period for the frequency of alert triggers using the same thresholds. Finally, we calculated positive and negative likelihood ratios based on these analyses. RESULTS: Over a 1-year period we identified 15,091 cases without self-reported awareness that were valid for analysis. At all age-adjusted MAC thresholds, the incidence of triggered alerts was higher in the awareness cases. The threshold of<0.8 age-adjusted MAC was associated with the highest negative likelihood ratio; the<0.5 age-adjusted MAC was associated with the highest positive likelihood ratio. CONCLUSIONS: Our novel electronic alerting system incorporates both age-adjusted MAC and intravenous anesthesia, and triggers with a higher frequency in cases of awareness. These data suggest the potential for our system to alert clinicians to insufficient anesthesia.

A retrospective study of intraoperative awareness with methodological implications.

BACKGROUND: Awareness during general anesthesia is a problem receiving increased attention from physicians and patients. Large multicentered studies have established an accepted incidence of awareness during general anesthesia as approximately 1-2 per 1000 cases or 0.15%. More recent retrospective data, however, suggest that the actual incidence may be as low as 0.0068%. METHODS: To assess the incidence of awareness at our institution, we conducted a review of adult patients undergoing surgical procedures over a 3-year period. Information on awareness came from entries of "Intraoperative Awareness" captured during our standard evaluations on postoperative day one in our perioperative information system. Patients were not questioned specifically about awareness. RESULTS: We reviewed 116,478 charts; 65,061 patients received general anesthesia and 51,417 received other types of anesthesia. Of the patients receiving general anesthesia, 44,006 had complete postoperative documentation. The reported incidence of undesired intraoperative awareness in this population was 10/44,006 (1/4401 or 0.023%). Of the patients who received other anesthetic modalities, 22,885 had complete postoperative documentation. Undesired intraoperative awareness was reported in 7/22,885 patients who did not receive general anesthesia (1/3269 or 0.03%). The reported incidence of intraoperative awareness was not statistically different between the two groups (P = 0.54). Relative risk of intraoperative awareness during a general anesthetic compared with a nongeneral anesthetic was 0.74, with 95% confidence interval [0.28, 2.0]. CONCLUSION: Using a retrospective methodology, reports of intraoperative awareness are not statistically different in patients who received general anesthesia compared with those who did not. These results suggest that, despite success with other rare perioperative events, the resolution of retrospective database analyses may be too low to study intraoperative awareness.