Objective:

The triple low state [low mean arterial pressure, low bispectral index (BIS) and a low minimum alveolar concentration (MAC)] fraction of anaesthetic during surgery) has been a controversial subject of interest in clinical practise. Previous retrospective studies have produced different conclusions on the association between a triple low state and postoperative 30-day mortality. This study was a systematic review of previous studies on the effects of the triple low state on postoperative 30-day mortality and a meta-analysis with a sample size larger than that of previous studies.

Methods:

After searching for relevant articles in the PubMed database as on 27 March 2017, we included studies that compared postoperative 30-day mortality between triple low and non-triple low groups. The identified articles were subjected to an initial screening using keywords ‘low bispectral index’, ‘intraoperative hypotension’ and ‘low minimum alveolar concentration’ according to the PRISMA Flow diagram (2009). After a full-text review, appropriate studies were finally included in our meta-analysis. All statistical analyses were performed using the R programme 3.3.2 and meta packages.

Results:

Three retrospective cohort studies were included in the meta-analysis. The total number of subjects in the triple low and non-triple low groups was 29,402 and 17,428, respectively; the sample size was 46,830. We derived a hazard ratio (HR) of 1.09 [95% confidence interval (CI), 1.07–1.11)] for the fixed effect model and of 1.30 (95% CI, 1.04–1.07) for the random effect model. In the analysis of heterogeneity among the three studies, I2=95% was obtained (P<0.01). Thus, the values obtained from the random effect model were used; HR was 1.30 for the triple low group, indicating a 30% increase in the overall 30-day mortality.

Conclusion:

The present study demonstrated that patients exposed to the triple low state exhibit higher 30-day mortality rates than those not exposed to the triple low state.

Keywords: Hypotension, bispectral index, anaesthesia