Effect of Anaesthesia Depth on Postoperative Delirium and Postoperative Cognitive Dysfunction in High-Risk Patients: A Systematic Review and Meta-Analysis

Abstract

Postoperative delirium (POD) and postoperative cognitive dysfunction (POCD) pose increased morbidity and mortality, especially to elderly patients. The effect of anesthesia is debatable. The databases of PubMed, EMBASE, Google Scholar, Cochrane Library and Web of Science were searched from inception until 24 February 2022 to identify randomized-controlled trials (RCTs) studying the effect of depth of anesthesia on POD and POCD primarily. Data on length of hospital stay and mortality were also extracted. Trial sequential analysis was also performed. Seventeen studies were eligible for systematic review and 15 studies of 5392 patients were eligible for meta-analysis. High bispectral index (BIS) favored a reduction in POD and POCD at three months. We found no significant difference between High BIS and Low BIS for mini-mental state exam (MMSE) score and POCD on day 7. However, this did not translate to a significant difference in length of stay and mortality. The data was also underpowered and heterogeneous. Future RCTs should focus on high-risk patients. A standardized methodology of reporting postoperative delirium and cognitive dysfunction is needed to improve comparisons across trials.

Keywords: bispectral index monitoring; depth of anesthesia; elderly population; postoperative cognitive dysfunction; postoperative delirium.

Conflict of interest statement

The authors have declared that no competing interests exist.

Copyright © 2022, Ling et al.

Figures

Figure 1. Study flow diagram (PRISMA flow chart)

Figure 2. Risk of Bias Summary

“+”: low risk of bias; “?”: unclear risk of bias; “-”: high risk of bias.

Figure 3. Risk of Bias Graph

Figure 4. Forest Plot of Postoperative Delirium (POD).

BIS: bispectral index; CI: confidence interval. Brown [21], Chan [22], Evered [13], Kunst [9], Radtke [25], Sieber [27], Sieber [28], Wildes [11], Zhou [31].

Figure 5. Funnel Plot of Postoperative Delirium (POD)

Figure 6. Forest Plot of MMSE on postoperative day three.

MMSE: mini-mental state examination; BIS: bispectral index; CI: confidence interval. Chen [23], Evered [13], Kunst [9], Sadek [26], Sieber [27], Sieber [28], Wong [30].

Figure 7. Funnel Plot of MMSE on postoperative day three.

MMSE: mini-mental state examination

Figure 8. Forest Plot of POCD on postoperative day seven.

BIS: bispectral index; CI: confidence interval; POCD: postoperative cognitive dysfunction. Chan [22], Chen [23], Hou [24], Quan [10], Radtke [25], Valentin [19].

Figure 9. Funnel Plot of POCD on postoperative day seven.

POCD: postoperative cognitive dysfunction.

Figure 10. Forest plot of POCD at three months.

BIS: bispectral index; CI: confidence interval; POCD: postoperative cognitive dysfunction. Chan [22], Hou [24], Quan [10], Radtke [25], Valentin [19].

Figure 11. Funnel Plot of POCD at three months.

POCD: postoperative cognitive dysfunction.

Figure 12. Forest Plot of Mortality.

BIS: bispectral index; CI: confidence interval. Brown [21], Chan [22], Quan [10], Radtke [25], Sieber [27], Wildes [11].

Figure 13. Funnel Plot of Mortality.

Figure 14. Forest plot of Length of Stay.

BIS: bispectral index; CI: confidence interval. Brown [21], Chan [22], Kunst [9], Quan [10], Radtke [25], Sieber [27], Sieber [28], Wildes [11].

Figure 15. Funnel Plot of Length of Stay.

Figure 16. Trial Sequential Analysis for Post Operative Delirium.

Y-axis: the cumulative Z-Score; Horizontal green dotted lines: conventional boundaries (upper for benefit, Z-score = 1.96, lower for harm, Z-score = −1.96, two-sided P = 0.05); Sloping red full lines with black square fill icons: trial sequential monitoring boundaries calculated accordingly; Blue full line with black square fill icons: Z-curve; Vertical red full line: required information size calculated accordingly.

Figure 17. Trial Sequential Analysis for Postoperative Cognitive Dysfunction at three months.

Y-axis: the cumulative Z-Score; Horizontal green dotted lines: conventional boundaries (upper for benefit, Z-score = 1.96, lower for harm, Z-score = −1.96, two-sided P = 0.05); Sloping red full lines with black square fill icons: trial sequential monitoring boundaries calculated accordingly; Blue full line with black square fill icons: Z-curve; Vertical red full line: required information size calculated accordingly.