Former smoking, but not active smoking, is associated with delirium in postoperative ICU patients: a matched case-control study

Maria Angeliki Komninou; Simon Egli; Aurelio Rossi; Jutta Ernst; Michael Krauthammer; Reto A Schuepbach; Marcos Delgado; Jan Bartussek

doi:10.3389/fpsyt.2024.1347071

Former smoking, but not active smoking, is associated with delirium in postoperative ICU patients: a matched case-control study

Front Psychiatry. 2024 Mar 14:15:1347071. doi: 10.3389/fpsyt.2024.1347071. eCollection 2024.

Authors

Maria Angeliki Komninou¹, Simon Egli¹, Aurelio Rossi¹, Jutta Ernst², Michael Krauthammer³, Reto A Schuepbach¹, Marcos Delgado^{1

4}, Jan Bartussek^{1

3}

Affiliations

¹ Institute of Intensive Care Medicine, University Hospital Zurich & University of Zurich, Zurich, Switzerland.
² Center of Clinical Nursing Sciences, University Hospital Zurich, Zurich, Switzerland.
³ Department for Quantitative Biomedicine, University of Zurich, Zurich, Switzerland.
⁴ Department of Anesthesia and Intensive Care Medicine, Tiefenau Hospital, Insel Group. University of Bern, Bern, Switzerland.

Abstract

Objective: To examine the relationship between current and former smoking and the occurrence of delirium in surgical Intensive Care Unit (ICU) patients.

Methods: We conducted a single center, case-control study involving 244 delirious and 251 non-delirious patients that were admitted to our ICU between 2018 and 2022. Using propensity score analysis, we obtained 115 pairs of delirious and non-delirious patients matched for age and Simplified Acute Physiology Score II (SAPS II). Both groups of patients were further stratified into non-smokers, active smokers and former smokers, and logistic regression was performed to further investigate potential confounders.

Results: Our study revealed a significant association between former smoking and the incidence of delirium in ICU patients, both in unmatched (adjusted odds ratio (OR): 1.82, 95% confidence interval (CI): 1.17-2.83) and matched cohorts (OR: 3.0, CI: 1.53-5.89). Active smoking did not demonstrate a significant difference in delirium incidence compared to non-smokers (unmatched OR = 0.98, CI: 0.62-1.53, matched OR = 1.05, CI: 0.55-2.0). Logistic regression analysis of the matched group confirmed former smoking as an independent risk factor for delirium, irrespective of other variables like surgical history (p = 0.010). Notably, also respiratory and vascular surgeries were associated with increased odds of delirium (respiratory: OR: 4.13, CI: 1.73-9.83; vascular: OR: 2.18, CI: 1.03-4.59). Medication analysis showed that while Ketamine and Midazolam usage did not significantly correlate with delirium, Morphine use was linked to a decreased likelihood (OR: 0.27, 95% CI: 0.13-0.55).

Discussion: Nicotine's complex neuropharmacological impact on the brain is still not fully understood, especially its short-term and long-term implications for critically ill patients. Although our retrospective study cannot establish causality, our findings suggest that smoking may induce structural changes in the brain, potentially heightening the risk of postoperative delirium. Intriguingly, this effect seems to be obscured in active smokers, potentially due to the recognized neuroprotective properties of nicotine. Our results motivate future prospective studies, the results of which hold the potential to substantially impact risk assessment procedures for surgeries.

Keywords: ICU delirium; case-control studies; critical care medicine; nicotine; postoperative delirium (POD); risk factors; smoking; withdrawal.

Grants and funding

The author(s) declare financial support was received for the research, authorship, and/or publication of this article. The study was supported by unrestricted funds to RAS, an innovation grant of the USZ (INOV00125) to JB and a grant of the Swiss National Science Foundation (SNF 201184) to MK.