Association between intraoperative electroencephalographic suppression and postoperative mortality

Advances in awareness monitoring technologies

PURPOSE OF REVIEW

Initial studies suggested that the use of processed electroencephalogram technology could significantly decrease the incidence of unintended intraoperative awareness events during general anesthesia. Subsequent work has cast doubts on these findings. This review will examine the current state of awareness monitoring.

RECENT FINDINGS

Recently published randomized controlled trials examining the use of the bispectral index during general anesthesia have not been able to show superiority over other forms of monitoring depth of anesthesia, such as end-tidal anesthetic-agent concentration. Additionally, there is current interest in utilizing the unprocessed electroencephalogram to ascertain depth of anesthesia and recent studies have demonstrated its use in preventing postoperative delirium.

SUMMARY

Although awareness monitors such as the bispectral index monitor may have benefit in patients in whom volatile anesthetic agents must be minimized - such as in hemodynamically unstable patients, or patients undergoing total intravenous anesthesia - these monitors do not appear to be useful for all patients.

Protocol for the Electroencephalography Guidance of Anesthesia to Alleviate Geriatric Syndromes (ENGAGES) study: a pragmatic, randomised clinical trial

INTRODUCTION

Postoperative delirium, arbitrarily defined as occurring within 5 days of surgery, affects up to 50% of patients older than 60 after a major operation. This geriatric syndrome is associated with longer intensive care unit and hospital stay, readmission, persistent cognitive deterioration and mortality. No effective preventive methods have been identified, but preliminary evidence suggests that EEG monitoring during general anaesthesia, by facilitating reduced anaesthetic exposure and EEG suppression, might decrease incident postoperative delirium. This study hypothesises that EEG-guidance of anaesthetic administration prevents postoperative delirium and downstream sequelae, including falls and decreased quality of life.

METHODS AND ANALYSIS

This is a 1232 patient, block-randomised, double-blinded, comparative effectiveness trial. Patients older than 60, undergoing volatile agent-based general anaesthesia for major surgery, are eligible. Patients are randomised to 1 of 2 anaesthetic approaches. One group receives general anaesthesia with clinicians blinded to EEG monitoring. The other group receives EEG-guidance of anaesthetic agent administration. The outcomes of postoperative delirium (≤5 days), falls at 1 and 12 months and health-related quality of life at 1 and 12 months will be compared between groups. Postoperative delirium is assessed with the confusion assessment method, falls with ProFaNE consensus questions and quality of life with the Veteran's RAND 12-item Health Survey. The intention-to-treat principle will be followed for all analyses. Differences between groups will be presented with 95% CIs and will be considered statistically significant at a two-sided p<0.05.

ETHICS AND DISSEMINATION

Electroencephalography Guidance of Anesthesia to Alleviate Geriatric Syndromes (ENGAGES) is approved by the ethics board at Washington University. Recruitment began in January 2015. Dissemination plans include presentations at scientific conferences, scientific publications, internet-based educational materials and mass media.

TRIAL REGISTRATION NUMBER

NCT02241655; Pre-results.

Care of elderly patients: a prospective audit of the prevalence of hypotension and the use of BIS intraoperatively in 25 hospitals in London

BACKGROUND

Anaesthesia is frequently complicated by intraoperative hypotension (IOH) in the elderly, and this is associated with adverse outcome. The definition of IOH is controversial, and although management guidelines for IOH in the elderly exist, the frequency of IOH and typical clinically applied treatment thresholds are largely unknown in the UK.

METHODS

We audited frequency of intraoperative blood pressure against national guidelines in elderly patients undergoing surgery. Depth of anaesthesia (DOA) monitoring was also audited due to the association between low DOA values and IOH with increased mortality (as part of "double" and "triple low" phenomena) and because it is a suggested management strategy to reduce IOH.

RESULTS

Twenty-five hospitals submitted data on 481 patients. Hypotension varied depending on the definition, but affected 400 patients (83.3 %) using the AAGBI standard. Furthermore, 2.9, 13.5, and 24.6 % had mean arterial blood pressures <50, <60, and <70 mmHg for 20 min, respectively, and 136 (28.4 %) had systolic blood pressure decrease by 20 % for 20 min. DOA monitors were used for 45 (9.4 %) patients.

CONCLUSIONS

IOH is common and use of DOA monitors is less than implied by guidelines. Improved management of IOH may be a simple intervention with real potential to reduce morbidity in this vulnerable group.

Intraoperative Electroencephalogram Suppression Predicts Postoperative Delirium

BACKGROUND

Postoperative delirium is a common complication associated with increased morbidity and mortality, longer hospital stays, and greater health care expenditures. Intraoperative electroencephalogram (EEG) slowing has been associated previously with postoperative delirium, but the relationship between intraoperative EEG suppression and postoperative delirium has not been investigated.

METHODS

In this observational cohort study, 727 adult patients who received general anesthesia with planned intensive care unit admission were included. Duration of intraoperative EEG suppression was recorded from a frontal EEG channel (FP1 to F7). Delirium was assessed twice daily on postoperative days 1 through 5 with the Confusion Assessment Method for the intensive care unit. Thirty days after surgery, quality of life, functional independence, and cognitive ability were measured using the Veterans RAND 12-item survey, the Barthel index, and the PROMIS Applied Cognition-Abilities-Short Form 4a survey.

RESULTS

Postoperative delirium was observed in 162 (26%) of 619 patients assessed. When we compared patients with no EEG suppression with those divided into quartiles based on duration of EEG suppression, patients with more suppression were more likely to experience delirium (χ(4) = 25, P < 0.0001). This effect remained significant after we adjusted for potential confounders (odds ratio for log(EEG suppression) 1.22 [99% confidence interval, 1.06-1.40, P = 0.0002] per 1-minute increase in suppression). EEG suppression may have been associated with reduced functional independence (Spearman partial correlation coefficient -0.15, P = 0.02) but not with changes in quality of life or cognitive ability. Predictors of EEG suppression included greater end-tidal volatile anesthetic concentration and lower intraoperative opioid dose.

CONCLUSIONS

EEG suppression is an independent risk factor for postoperative delirium. Future studies should investigate whether anesthesia titration to minimize EEG suppression decreases the incidence of postoperative delirium. This is a substudy of the Systematic Assessment and Targeted Improvement of Services Following Yearlong Surgical Outcomes Surveys (SATISFY-SOS) surgical outcomes registry (NCT02032030).

Rationale and Design of the Balanced Anesthesia Study: A Prospective Randomized Clinical Trial of Two Levels of Anesthetic Depth on Patient Outcome After Major Surgery

BACKGROUND

An association between relatively deep anesthesia, as guided by the bispectral index (BIS), and increased postoperative mortality has been demonstrated in 6 of 8 published observational studies, but association does not necessarily mean causality. Small clinical trials of anesthetic depth have demonstrated increased delirium and postoperative cognitive dysfunction in patients who were relatively deeply anesthetized, but have been inadequately powered to study mortality. A large-scale randomized study is required to determine whether causality exists.

METHODS

The primary hypothesis of our study is that "light" anesthesia, defined as a BIS target of 50, will reduce all-cause mortality within 1 year of surgery in comparison with "deep" anesthesia, defined as a BIS target of 35, in patients aged ≥60 years presenting for major surgery under general anesthesia. The trial is an international multicenter, randomized, parallel-group, double-blind (patients and investigators) prospective, intention-to-treat, safety and efficacy study. The relative reduction in mortality in the light anesthesia group is expected to be 20%, giving an absolute risk reduction from 10% to 8%. Power analysis using a = 0.049 and b = 0.2 indicates that 3250 patients are required in each group.

RESULTS

The study is underway, and 1325 patients have been recruited in 40 centers in 5 countries. It is anticipated that the study will be completed in 3 years.

CONCLUSIONS

This randomized controlled trial should definitively answer the question of whether titrating anesthetic depth makes a difference to patient outcome in a vulnerable patient group.

Concurrence of Intraoperative Hypotension, Low Minimum Alveolar Concentration, and Low Bispectral Index Is Associated with Postoperative Death

BACKGROUND

An intraoperative concurrence of mean arterial pressure less than 75 mmHg, minimum alveolar concentration less than 0.8, and bispectral index less than 45 has been termed a "triple low" state. An association between triple low and postoperative mortality has been reported but was not replicated in a subsequent study. The authors pooled existing data from clinical trials to further evaluate the purported association in an observational study.

METHODS

This retrospective observational study included 13,198 patients from three clinical trials: B-Unaware, BAG-RECALL, and Michigan Awareness Control Study. Patients with greater than 15 not necessarily consecutive minutes of triple low were propensity matched to controls with similar characteristics and comorbidities. A multivariable Cox proportional hazards model was used to evaluate the association between triple low duration and postoperative mortality.

RESULTS

Thirty-day mortality was 0.8% overall, 1.9% in the triple low cohort, and 0.4% in the nontriple low cohort (odds ratio, 5.16; 95% CI, 4.21 to 6.34). After matching and adjusting for comorbidities, cumulative duration of triple low was significantly associated with an increased risk of mortality at 30 days (hazard ratio, 1.09; 95% CI, 1.07 to 1.11, per 15 min) and 90 days (hazard ratio, 1.09; 95% CI, 1.08 to 1.11, per 15 min).

CONCLUSION

There is a weak independent association between the triple low state and postoperative mortality, and the propensity-matched analysis does not suggest that this is an epiphenomenon.