ICU Delirium: Little Attributable Mortality after Adjustment
Clinical question: Does delirium contribute to chance of death?
Background: Delirium is a well-recognized predictor of mortality. Prior observational studies have estimated a risk of death two to four times higher in ICU patients with delirium compared with those who do not experience delirium. The degree to which this association reflects a causal relationship is debated.
Study design: Prospective cohort study; used logistic regression and competing risks survival analyses along with a marginal structural model analysis to adjust for both baseline characteristics and severity of illness developing during ICU stay.
Setting: Single ICU in the Netherlands.
Synopsis: Regression analysis of 1,112 ICU patients confirmed the strong association between delirium and mortality; however, additional analysis, adjusting for the severity of illness as it progressed during the ICU stay, attenuated the relationship to nonsignificance. This suggests that both delirium and mortality were being driven by the common underlying illness.
In post hoc analysis, only persistent delirium was associated with a small increase in mortality. Although this observational study can neither prove nor disprove causation, the adjustment for changing severity of illness during the ICU stay was more sophisticated than prior studies. This study suggests that delirium and mortality are likely companions on the road of critical illness but that one may not directly cause the other.
Bottom line: Delirium in the ICU likely does not cause death, but its presence portends increased risk of mortality.
Citations: Klouwenberg PM, Zaal IJ, Spitoni C, et al. The attributable mortality of delirium in critically ill patients: prospective cohort study. BMJ. 2014;349:g6652. Inouye SK, Westendorp RGJ, Saczynski JS. Delirium in elderly people. Lancet. 2014;383(9920):911-922.
