Newly Published
Perioperative Medicine  |   February 2020
Preoperative Cognitive Abnormality, Intraoperative Electroencephalogram Suppression, and Postoperative Delirium: A Mediation Analysis
Author Notes
  • From the Department of Anesthesiology (B.A.F., C.R.K., A.B., A.M.M., T.P.B., J.O., D.P., H.R.M., T.S.W., M.S.A), and the Division of Biostatistics (N.L.), Washington University School of Medicine, St. Louis, Missouri; and the Department of Mathematics and Statistics, Washington University in St. Louis, St. Louis, Missouri (N.L.).
  • Department of Anesthesiology, Washington University School of Medicine, St. Louis, Missouri
  • Department of Anesthesiology, Washington University School of Medicine, St. Louis, Missouri
  • Department of Anesthesiology, Washington University School of Medicine, St. Louis, Missouri
  • Department of Anesthesiology, Washington University School of Medicine, St. Louis, Missouri
  • Department of Anesthesiology, Washington University School of Medicine, St. Louis, Missouri
  • Department of Anesthesiology, Washington University School of Medicine, St. Louis, Missouri
  • Department of Anesthesiology, Washington University School of Medicine, St. Louis, Missouri
  • Department of Anesthesiology, Washington University School of Medicine, St. Louis, Missouri
  • Department of Anesthesiology, Washington University School of Medicine, St. Louis, Missouri
  • Department of Anesthesiology, Washington University School of Medicine, St. Louis, Missouri
  • Department of Anesthesiology, Washington University School of Medicine, St. Louis, Missouri
  • Department of Anesthesiology, Washington University School of Medicine, St. Louis, Missouri
  • Department of Anesthesiology, Washington University School of Medicine, St. Louis, Missouri
  • Department of Anesthesiology, Washington University School of Medicine, St. Louis, Missouri
  • Department of Anesthesiology, Washington University School of Medicine, St. Louis, Missouri
  • Department of Anesthesiology, Washington University School of Medicine, St. Louis, Missouri
  • Department of Anesthesiology, Washington University School of Medicine, St. Louis, Missouri
  • Department of Anesthesiology, Washington University School of Medicine, St. Louis, Missouri
  • Department of Anesthesiology, Washington University School of Medicine, St. Louis, Missouri
  • Department of Anesthesiology, Washington University School of Medicine, St. Louis, Missouri
  • Department of Anesthesiology, Washington University School of Medicine, St. Louis, Missouri
  • Department of Anesthesiology, Washington University School of Medicine, St. Louis, Missouri
  • Department of Anesthesiology, Washington University School of Medicine, St. Louis, Missouri
  • Department of Anesthesiology, Washington University School of Medicine, St. Louis, Missouri
  • Department of Anesthesiology, University of Manitoba, Winnipeg, Canada
  • Department of Medicine, Beth Israel-Deaconess Medical Center, Boston, Massachusetts
  • Department of Medicine, Beth Israel-Deaconess Medical Center, Boston, Massachusetts
  • Department of Medicine, Beth Israel-Deaconess Medical Center, Boston, Massachusetts
  • Department of Medicine, Beth Israel-Deaconess Medical Center, Boston, Massachusetts
  • Department of Occupational Therapy, Washington University School of Medicine, St. Louis, Missouri
  • Department of Occupational Therapy, Washington University School of Medicine, St. Louis, Missouri
  • Department of Psychiatry, Washington University School of Medicine, St. Louis, Missouri
  • Department of Surgery, Washington University School of Medicine, St. Louis, Missouri
  • Department of Surgery, Washington University School of Medicine, St. Louis, Missouri
  • Supplemental Digital Content is available for this article. Direct URL citations appear in the printed text and are available in both the HTML and PDF versions of this article. Links to the digital files are provided in the HTML text of this article on the Journal’s Web site (www.anesthesiology.org).
    Supplemental Digital Content is available for this article. Direct URL citations appear in the printed text and are available in both the HTML and PDF versions of this article. Links to the digital files are provided in the HTML text of this article on the Journal’s Web site (www.anesthesiology.org).×
  • This work was presented as an abstract/poster at the Association of University Anesthesiologists and International Anesthesia Research Society annual meeting in Montreal, Canada, May 16–20, 2019.
    This work was presented as an abstract/poster at the Association of University Anesthesiologists and International Anesthesia Research Society annual meeting in Montreal, Canada, May 16–20, 2019.×
  • *Members of the ENGAGES Research Group are listed in the appendix.
    Members of the ENGAGES Research Group are listed in the appendix.×
  • Submitted for publication May 22, 2019. Accepted for publication January 8, 2020.
    Submitted for publication May 22, 2019. Accepted for publication January 8, 2020.×
  • Correspondence: Address correspondence to Dr. Fritz: 660 S Euclid Ave, Box 8054, St. Louis, Missouri 63110. bafritz@wustl.edu. Information on purchasing reprints may be found at www.anesthesiology.org or on the masthead page at the beginning of this issue. Anesthesiology’s articles are made freely accessible to all readers, for personal use only, 6 months from the cover date of the issue.
Article Information
Perioperative Medicine / Central and Peripheral Nervous Systems
Perioperative Medicine   |   February 2020
Preoperative Cognitive Abnormality, Intraoperative Electroencephalogram Suppression, and Postoperative Delirium: A Mediation Analysis
Anesthesiology Newly Published on February 5, 2020. doi:https://doi.org/10.1097/ALN.0000000000003181
Anesthesiology Newly Published on February 5, 2020. doi:https://doi.org/10.1097/ALN.0000000000003181
Abstract

Editor’s Perspective:

What We Already Know about This Topic:

  • Postoperative delirium is common in older surgical patients

  • Intraoperative electroencephalogram suppression has been associated with postoperative delirium

  • Patients with preoperative cognitive impairment have an increased risk of developing postoperative delirium

What This Article Tells Us That Is New:

  • The indirect effect of intraoperative electroencephalogram suppression on the development of postoperative delirium among patients with preexisting cognitive impairment is probably small but nonzero

  • Approximately 28 cognitively impaired patients would need to be kept out of electroencephalogram suppression to avoid 1 case of postoperative delirium

Background: Postoperative delirium is a common complication that hinders recovery after surgery. Intraoperative electroencephalogram suppression has been linked to postoperative delirium, but it is unknown if this relationship is causal or if electroencephalogram suppression is merely a marker of underlying cognitive abnormalities. The hypothesis of this study was that intraoperative electroencephalogram suppression mediates a nonzero portion of the effect between preoperative abnormal cognition and postoperative delirium.

Methods: This is a prespecified secondary analysis of the Electroencephalography Guidance of Anesthesia to Alleviate Geriatric Syndromes (ENGAGES) randomized trial, which enrolled patients age 60 yr or older undergoing surgery with general anesthesia at a single academic medical center between January 2015 and May 2018. Patients were randomized to electroencephalogram-guided anesthesia or usual care. Preoperative abnormal cognition was defined as a composite of previous delirium, Short Blessed Test cognitive score greater than 4 points, or Eight Item Interview to Differentiate Aging and Dementia score greater than 1 point. Duration of intraoperative electroencephalogram suppression was defined as number of minutes with suppression ratio greater than 1%. Postoperative delirium was detected via Confusion Assessment Method or chart review on postoperative days 1 to 5.

Results: Among 1,113 patients, 430 patients showed evidence of preoperative abnormal cognition. These patients had an increased incidence of postoperative delirium (151 of 430 [35%] vs.123 of 683 [18%], P < 0.001). Of this 17.2% total effect size (99.5% CI, 9.3 to 25.1%), an absolute 2.4% (99.5% CI, 0.6 to 4.8%) was an indirect effect mediated by electroencephalogram suppression, while an absolute 14.8% (99.5% CI, 7.2 to 22.5%) was a direct effect of preoperative abnormal cognition. Randomization to electroencephalogram-guided anesthesia did not change the mediated effect size (P = 0.078 for moderation).

Conclusions: A small portion of the total effect of preoperative abnormal cognition on postoperative delirium was mediated by electroencephalogram suppression. Study precision was too low to determine if the intervention changed the mediated effect.