Original Article
Predictors and Outcomes of Cardiac Surgery-Associated Delirium. A Single Centre Retrospective Cohort Study

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Background

The predictors and independent outcome association of delirium after cardiac surgery are important and yet poorly characterised.

Methods

We performed a retrospective observational study of cardiac surgery patients between January 2009 and March 2016. We defined delirium using ICD-10 diagnostic codes. Multivariable analysis was conducted to find independent associations between baseline variables, delirium, and key clinical outcomes.

Results

We studied 2,447 study patients (28.7% female, median age was 66 [IQR 57–74] years). Delirium was coded for in 12.9% of patients overall, and in 22.9% of those aged >75 years. Increasing age, Charlson co-morbidity index, admission not from home, peripheral vascular disease, respiratory disease, preoperative atrial fibrillation, duration of cardiopulmonary bypass and nature of surgery were all independent predictors of delirium. Delirium was independently and strongly associated with increased risk of reintubation (OR 8.18 [95% CI 5.24–12.78]), tracheostomy (OR 10.44 [95% CI 5.91–18.45]), and increased length of stay by 113.7 [95% CI 99.7–127.7] ICU hours and 6.95 [95% CI 5.94–7.95] hospital days, but not 30-day mortality (OR 0.78 [95% CI 0.38–1.59]; p = 0.5).

Conclusions

Delirium is common in cardiac surgery patients and increases with age. Delirium was the strongest predictor of reintubation, need for tracheostomy, and prolongation of intensive care unit (ICU) and hospital length of stay. Delirium prevention and attenuation are a priority in cardiac surgery patients.

Introduction

Cardiac surgery is the most common major surgery in the developed world. Improved surgical techniques, anaesthesia and postoperative care mean that its mortality is low [1]. However, as more complex cardiac surgery is applied to older and frailer patients, the focus of investigation and care is increasingly shifting to decreasing its medical complications. Among these, cardiac surgery-associated delirium (CSAD) appears to be growing in incidence [2]. CSAD may be associated with increased duration of mechanical ventilation, as well as prolonged intensive care and hospital length of stay, as summarised in a recent review [3].

However, despite such clinical studies, it remains unknown whether delirium causes, or is a consequence of such complications, or occurs in parallel with their development [4], [5], [6]. This uncertainty stems from the fact that studies of CSAD have often not adjusted for potential key confounders [7], and none have examined the independent association between CSAD and key medical complications such as reintubation or need for tracheostomy in detail.

Accordingly, we undertook an analysis of cardiac surgical procedures conducted over more than 6 years in a single centre to identify the independent predictors of CSAD and its independent association with key clinical outcomes. Specifically, we aimed to assess whether the occurrence of delirium was independently associated with several pre-defined postoperative complications, including reintubation, need for tracheostomy, and prolongation of intensive care unit (ICU) and in-hospital length of stay.

Section snippets

Ethics Approval

Ethics approval was obtained to conduct the study (LNR/16/Austin/239) and the need for informed patient consent was waived.

Details of Operative and Postoperative Care

All surgical procedures were overseen by a consultant cardiac surgeon. A balanced anaesthesia technique consisting of fentanyl, a propofol infusion and a volatile anaesthesia were typically used. Cardiopulmonary bypass was employed in almost all cases. Postoperative care occurred in the ICU under the direction of an ICU consultant in consultation with the treating cardiac

Details of the Cohort

Between 1 January 2009 and 31 March 2016, we identified 2,447 cardiac surgery patients (Table 1). Coronary risk factors were common: 316 (12.9%) had a previous history of myocardial infarction, 1,516 (62.0%) had a history of smoking, and 382 (15.6%) were current smokers. Diabetes was present in 766 (31.3%), and hyperlipidaemia and hypertension were present in 1,785 (73.0%) and 1,927 (78.7%) of patients, respectively.

Baseline Associations With the Development of CSAD

A total of 316 (12.9%) of patients were ICD-10 coded for postoperative

Key Findings

We conducted a large retrospective observational study of cardiac surgery patients to describe the incidence, risk factors for and outcome associations of CSAD in the Australian setting. We found several important pre and perioperative risk factors for delirium. Moreover, we found that CSAD was the cardiac surgery associated complication with the strongest independent association with need for re-intubation and tracheostomy. Finally, the development of delirium was independently associated with

Conclusions

Delirium affects one in eight patients undergoing cardiac surgery and one in three patients over 85 years of age, can be predicted with an acceptable degree of accuracy and is a key risk factor for reintubation, need for tracheostomy, and prolonged of ICU and hospital length of stay. As specific risk factors for delirium were identified in this study, it is now possible to target preventive interventions in high risk groups. Our findings require confirmation in a prospective multi-centre study.

Acknowledgement of Contribution

All authors contributed significantly to the paper.

A/Prof Jones takes full responsibility for the integrity of the work.

Design: DJ, GM, SS, and RB.

Database extract: RR and MS.

Drafting and revision of manuscript: all.

Data analysis: DJ and JM.

None of the authors have a conflict of interest in relation to this work.

There is no external financial support declared.

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