Risk Factors for Delirium After On-pump Cardiac Surgery

A Systematic Review

Alex NC Gosselt; Arjen JC Slooter; Pascal RQ Boere; Irene J Zaal


Crit Care. 2015;19(346) 

In This Article

Abstract and Introduction


Introduction: As evidence-based effective treatment protocols for delirium after cardiac surgery are lacking, efforts should be made to identify risk factors for preventive interventions. Moreover, knowledge of these risk factors could increase validity of etiological studies in which adjustments need to be made for confounding variables. This review aims to systematically identify risk factors for delirium after cardiac surgery and to grade the evidence supporting these associations.

Method: A prior registered systematic review was performed using EMBASE, CINAHL, MEDLINE and Cochrane from 1990 till January 2015 (http://www.crd.york.ac.uk/PROSPERO/display_record.asp?ID=CRD42014007371). All studies evaluating patients for delirium after cardiac surgery with cardiopulmonary bypass (CPB) using either randomization or multivariable data analyses were included. Data was extracted and quality was scored in duplicate. Heterogeneity impaired pooling of the data; instead a semi-quantitative approach was used in which the strength of the evidence was graded based on the number of investigations, the quality of studies, and the consistency of the association reported across studies.

Results: In total 1462 unique references were screened and 34 were included in this review, of which 16 (47 %) were graded as high quality. A strong level of evidence for an association with the occurrence of postoperative delirium was found for age, previous psychiatric conditions, cerebrovascular disease, pre-existent cognitive impairment, type of surgery, peri-operative blood product transfusion, administration of risperidone, postoperative atrial fibrillation and mechanical ventilation time. Postoperative oxygen saturation and renal insufficiency were supported by a moderate level of evidence, and there is no evidence that gender, education, CPB duration, pre-existent cardiac disease or heart failure are risk factors.

Conclusion: Of many potential risk factors for delirium after cardiac surgery, for only 11 there is a strong or moderate level of evidence. These risk factors should be taken in consideration when designing future delirium prevention strategies trials or when controlling for confounding in future etiological studies.


Postoperative delirium is a frequent condition after cardiac surgery, with reported frequency between 3 %[1] and 31 %.[2–7] Postoperative delirium is associated with short-term and long-term morbidity and mortality,[8–11] and consequent raised health care costs.[12,13]

To date, well-established treatment options for postoperative delirium are lacking.[14–17] This emphasizes the importance of applying prophylactic strategies to decrease the burden of delirium after cardiac surgery. Knowledge as to whether there is supporting or conflicting evidence for an association between different predisposing and precipitating factors and delirium, will provide guidance to clinicians on opportunities for prevention. Moreover, knowledge about risk factors will inform researchers about the key variables that should be incorporated in future multivariable models for the analysis of postoperative delirium.

Earlier systematic reviews on this topic have limited validity as they included heterogeneous study populations within limited search strings and time-windows and because they applied quantitative measures to identify strong risk factors without taking the quality of the studies into account.[18,19] The aim of this study was to systematically review the literature on potential risk factors for delirium after cardiac surgery in which cardiopulmonary bypass (CPB) was performed.