RESEARCH
The attributable mortality of delirium in critically ill patients: prospective cohort study Peter M C Klein Klouwenberg,1 Irene J Zaal,1 Cristian Spitoni,2 David S Y Ong,1 Arendina W van der Kooi,1 Marc J M Bonten,3 Arjen J C Slooter,1 Olaf L Cremer1 1
Department of Intensive Care Medicine, University Medical Centre Utrecht, 3508 GA, Utrecht, Netherlands 2 Department of Mathematics, Utrecht University, Utrecht, Netherlands 3 Department of Medical Microbiology, University Medical Centre Utrecht, Utrecht, Netherlands Correspondence to: P Klein Klouwenberg p.m.c.kleinklouwenberg@ umcutrecht.nl Cite this as: BMJ 2014;349:g6652 doi: 10.1136/bmj.g6652
This is a summary of a paper that was published on thebmj.com as BMJ 2014;349:g6652
thebmj.com ЖЖPractice: Post-traumatic stress disorder after intensive care (BMJ 2013;346:f3232) ЖЖEditorial: Delirium in intensive care patients (BMJ 2012;344:e346) ЖЖResearch News: Daily interruptions to sedation for critically ill adults? (BMJ 2012;345:e7068)
STUDY QUESTION What is the mortality due to delirium in critically ill patients? SUMMARY ANSWER Delirium prolongs stay on an intensive care unit but does not cause death in critically ill patients. WHAT IS KNOWN AND WHAT THIS PAPER ADDS Numerous observational studies have suggested that delirium increases the risk of death in critically ill patients by up to threefold but failed to adjust for confounding caused by time varying disease severity and for competing events that occur during intensive care unit admissions. Our study suggests that delirium does not cause short term mortality in critically ill patients after correction for time dependent sources of confounding.
Participants and setting Consecutive adults admitted to a 32 bed mixed intensive care unit in the Netherlands for a minimum of 24 hours. Design, size, and duration Prospective cohort study of 1112 patients admitted between January 2011 and July 2013. Trained observers evaluated delirium daily using a validated protocol, which included a confusion assessment method for evaluation on the intensive care unit. The primary outcome of interest was mortality during admission to an intensive care unit. We used logistic regression and competing risks survival analyses to adjust for baseline variables, treating discharge from the intensive care unit as a competing risk for mortality. In addition, to adjust for confounding by evolution of disease severity before the onset of delirium, we performed a marginal structural model analysis. Main results and the role of chance Delirium was significantly associated with mortality in the multivariable logistic regression analysis (odds ratio 1.77, 95% confidence interval 1.15 to 2.72) and survival analysis (subdistribution hazard ratio 2.08, 95% confidence interval 1.40 to 3.09). However, the association disappeared after adjustment for time varying confounders in the marginal structural model (subdistribution hazard ratio 1.19, 95% confidence interval 0.75 to 1.89). Using this approach, only 7.2% (95% confidence interval −7.5% to 19.5%) of deaths in the intensive care unit were attributable to delirium, with an absolute mortality excess in patients with delirium of 0.9% (95% confidence interval −0.9% to 2.3%) by day 30. In post hoc analyses, however, delirium that persisted for two days or more remained
Cumulative incidence of observed and estimated mortality during stay on intensive care unit (ICU) Intensive care unit mortality (%)
ЖЖEDITORIAL by Page and Kurth
12 9 6 3 0 0
Observed ICU mortality Estimated ICU mortality without delirium 10
20
30
Day on intensive care unit
associated with a 2.0% (95% confidence interval 1.2% to 2.8%) absolute mortality increase. Furthermore, competing risk analysis showed that delirium of any duration was associated with a significantly reduced rate of discharge from the intensive care unit (cause specific hazard ratio 0.65, 95% confidence interval 0.55 to 0.76).
Bias, confounding, and other reasons for caution Since this is an observational study we cannot rule out residual confounding, even after accounting for a relatively large number of covariables. Furthermore, because the assessment of delirium in unresponsive patients is impossible and the statistical models that we used required a dichotomous classification of participants, we chose to recategorise patients who were comatose as delirious and patients who were sedated as non-delirious. In doing this, we cannot rule out the possibility of misclassification being introduced. Finally, delirium can be the first symptom of an impending complication, such as sepsis acquired in the intensive care unit. When this happens, any mortality due to this sepsis event may be falsely attributed to delirium. The true association between delirium and mortality may then be weaker than we report. Generalisability to other populations The results are generalisable to other critically ill patients, although the association between delirium and death may vary among centres using different strategies from ours for the prevention or treatment of delirium. Study funding/potential competing interests This work was supported by the Centre for Translational Molecular Medicine, project MARS (grant 04I-201). MB has received research funding from the Netherlands Organization of Scientific Research (NWO Vici 918.76.611). We have no competing interests.
the bmj | 6 December 2014
11
Copyright of BMJ: British Medical Journal is the property of BMJ Publishing Group and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use.
The attributable mortality of delirium in critically ill patients: prospective cohort study Peter M C Klein Klouwenberg,1 Irene J Zaal,1 Cristian Spitoni,2 David S Y Ong,1 Arendina W van der Kooi,1 Marc J M Bonten,3 Arjen J C Slooter,1 Olaf L Cremer1 1
Department of Intensive Care Medicine, University Medical Centre Utrecht, 3508 GA, Utrecht, Netherlands 2 Department of Mathematics, Utrecht University, Utrecht, Netherlands 3 Department of Medical Microbiology, University Medical Centre Utrecht, Utrecht, Netherlands Correspondence to: P Klein Klouwenberg p.m.c.kleinklouwenberg@ umcutrecht.nl Cite this as: BMJ 2014;349:g6652 doi: 10.1136/bmj.g6652
This is a summary of a paper that was published on thebmj.com as BMJ 2014;349:g6652
thebmj.com ЖЖPractice: Post-traumatic stress disorder after intensive care (BMJ 2013;346:f3232) ЖЖEditorial: Delirium in intensive care patients (BMJ 2012;344:e346) ЖЖResearch News: Daily interruptions to sedation for critically ill adults? (BMJ 2012;345:e7068)
STUDY QUESTION What is the mortality due to delirium in critically ill patients? SUMMARY ANSWER Delirium prolongs stay on an intensive care unit but does not cause death in critically ill patients. WHAT IS KNOWN AND WHAT THIS PAPER ADDS Numerous observational studies have suggested that delirium increases the risk of death in critically ill patients by up to threefold but failed to adjust for confounding caused by time varying disease severity and for competing events that occur during intensive care unit admissions. Our study suggests that delirium does not cause short term mortality in critically ill patients after correction for time dependent sources of confounding.
Participants and setting Consecutive adults admitted to a 32 bed mixed intensive care unit in the Netherlands for a minimum of 24 hours. Design, size, and duration Prospective cohort study of 1112 patients admitted between January 2011 and July 2013. Trained observers evaluated delirium daily using a validated protocol, which included a confusion assessment method for evaluation on the intensive care unit. The primary outcome of interest was mortality during admission to an intensive care unit. We used logistic regression and competing risks survival analyses to adjust for baseline variables, treating discharge from the intensive care unit as a competing risk for mortality. In addition, to adjust for confounding by evolution of disease severity before the onset of delirium, we performed a marginal structural model analysis. Main results and the role of chance Delirium was significantly associated with mortality in the multivariable logistic regression analysis (odds ratio 1.77, 95% confidence interval 1.15 to 2.72) and survival analysis (subdistribution hazard ratio 2.08, 95% confidence interval 1.40 to 3.09). However, the association disappeared after adjustment for time varying confounders in the marginal structural model (subdistribution hazard ratio 1.19, 95% confidence interval 0.75 to 1.89). Using this approach, only 7.2% (95% confidence interval −7.5% to 19.5%) of deaths in the intensive care unit were attributable to delirium, with an absolute mortality excess in patients with delirium of 0.9% (95% confidence interval −0.9% to 2.3%) by day 30. In post hoc analyses, however, delirium that persisted for two days or more remained
Cumulative incidence of observed and estimated mortality during stay on intensive care unit (ICU) Intensive care unit mortality (%)
ЖЖEDITORIAL by Page and Kurth
12 9 6 3 0 0
Observed ICU mortality Estimated ICU mortality without delirium 10
20
30
Day on intensive care unit
associated with a 2.0% (95% confidence interval 1.2% to 2.8%) absolute mortality increase. Furthermore, competing risk analysis showed that delirium of any duration was associated with a significantly reduced rate of discharge from the intensive care unit (cause specific hazard ratio 0.65, 95% confidence interval 0.55 to 0.76).
Bias, confounding, and other reasons for caution Since this is an observational study we cannot rule out residual confounding, even after accounting for a relatively large number of covariables. Furthermore, because the assessment of delirium in unresponsive patients is impossible and the statistical models that we used required a dichotomous classification of participants, we chose to recategorise patients who were comatose as delirious and patients who were sedated as non-delirious. In doing this, we cannot rule out the possibility of misclassification being introduced. Finally, delirium can be the first symptom of an impending complication, such as sepsis acquired in the intensive care unit. When this happens, any mortality due to this sepsis event may be falsely attributed to delirium. The true association between delirium and mortality may then be weaker than we report. Generalisability to other populations The results are generalisable to other critically ill patients, although the association between delirium and death may vary among centres using different strategies from ours for the prevention or treatment of delirium. Study funding/potential competing interests This work was supported by the Centre for Translational Molecular Medicine, project MARS (grant 04I-201). MB has received research funding from the Netherlands Organization of Scientific Research (NWO Vici 918.76.611). We have no competing interests.
the bmj | 6 December 2014
11
Copyright of BMJ: British Medical Journal is the property of BMJ Publishing Group and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use.
