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Created January 1, 2016, last updated about 3 years ago.
Collection: 67, Score: 2191, Trend score: 0, Read count: 2505, Articles count: 6, Created: 2016-01-01 02:49:20 UTC. Updated: 2021-11-03 22:48:51 UTC.Notes
There has been some observational evidence that a greater depth of anesthesia, as measured by BIS, may be associated with an increase in post-operative mortality. In particular the association of the "triple low state" (low BIS, low volatile-ET, low MAP) with post-operative mortality is worrying.
Completion of the Balanced Anaesthesia Study Group’s large RCT looking at this issue however brings us as close to a final word as we may expect. Short et al. (2019) showed no difference in 1-year mortality for older patients undergoing major surgery, whether they received a deep (BIS target 35) or light (BIS target 50) general anaesthetic.
It is likely that earlier observational studies were showing the consequences of intraoperative hypotension resulting from anaesthetic depth, rather than anaesthetic depth itself.
Daniel Jolley
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Collected Articles
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Randomized Controlled Trial Multicenter Study Observational Study
Association between intraoperative electroencephalographic suppression and postoperative mortality.
Low bispectral index values frequently reflect EEG suppression and have been associated with postoperative mortality. This study investigated whether intraoperative EEG suppression was an independent predictor of 90 day postoperative mortality and explored risk factors for EEG suppression. ⋯ NCT00281489 and NCT00682825.
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Randomized Controlled Trial Observational Study
Concurrence of Intraoperative Hypotension, Low Minimum Alveolar Concentration, and Low Bispectral Index Is Associated with Postoperative Death.
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. ⋯ 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.
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Anesthesia and analgesia · May 2014
Randomized Controlled Trial Multicenter StudyA pilot study for a prospective, randomized, double-blind trial of the influence of anesthetic depth on long-term outcome.
Greater depth of anaesthesia may be associated with a higher incidence of wound infection, mortality and composite risk of complications.
pearl -
Review Meta Analysis
Relation between bispectral index measurements of anesthetic depth and postoperative mortality: a meta-analysis of observational studies.
The association between anesthesia depth and mortality is still controversial. There are a number of narrative reviews on this topic that affirm this association, but their conclusions were based only on qualitative analyses. The aim of this meta-analysis of observational studies was to examine the potential association between depth of anesthesia as a low bispectral index (BIS) and mortality using appropriate quantitative methods. ⋯ Existing observational studies support a significant association between depth of anesthesia (as measured by BIS) and long-term mortality (≥ one year), although it was without statistical significance at 30 days. Larger prospective, randomized trials are necessary to establish a definitive conclusion about whether this association represents true causality or is an epiphenomenon.
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Randomized Controlled Trial Multicenter Study
Anaesthetic depth and complications after major surgery: an international, randomised controlled trial.
What’s all the fuss?
Significant observational evidence suggested an association between mortality and deep anaesthesia, in particular a 2017 meta-analysis. However it has been suspected that anaesthetic depth may merely be a surrogate marker for intraoperative hypotension, a well-established risk factor for post-operative mortality and morbidity.
With this large RCT, the Balanced Anaesthesia Study Group has shown that deep general anaesthesia is not associated with an increase 1-year mortality.
What did they do?
The researchers conducted an ambitious, large (6,644 patients), multi-center, randomised controlled trial. Patients aged ≥60 years undergoing major surgery (expected ≥2h surgery and ≥2d hospital stay) were randomised to receive volatile general anaesthesia targeting BIS 50 or BIS 35.
To minimise intra-operative blood pressure as a confounder, anaesthetists were required to specify a target MAP before BIS-group allocation.
They found...
Not only was there no mortality difference between the BIS 50 and BIS 35 groups, there were also no major or moderate morbidity differences, or difference in recovery or length of stay. BIS targets were adequately achieved, though not perfect, and MAP was clinically similar for both groups.
Context is everything
This is about as high-quality as a large, modern study looking at longer-term outcomes can get. It is widely applicable to most populations and common general anaesthetic scenarios, except for a few important caveats:
- Very few ASA 4 (5%) patients were enrolled.
- Only volatile-maintenance anaesthesia was studied not propofol/TIVA.
- We can draw no conclusion regarding the consequences of extreme-depth (ie. BIS << 35).
- The actual depth difference between the BIS-35 and BIS-50 groups was not as much as perhaps ideal: mean BIS 39 vs 47 respectively...
Final thought
...there was (only) one case of awareness in the light-depth BIS 50 group, despite 39% of patients receiving volatile < 0.7 MAC.
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Meta Analysis
Processed Electroencephalogram Monitoring and Postoperative Delirium: A Systematic Review and Meta-analysis.
Use of processed-EEG monitoring to guide anaesthesia depth is associated with a 38% odds reduction of developing postoperative delirium.
pearl
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