Delirium on the intensive care unit

Over the past few years the interest in delirium in patients on the intensive care unit has gathered pace, seemingly exponentially. Given that delirium is common, particularly in ventilated patients, a recurring question is, “does delirium increase mortality directly or is it an epiphenomenon?” In a linked paper (doi:10.1136/bmj.g6652) Klein Klouwenberg and colleagues try to answer this question.1 In their prospective cohort study the authors used sophisticated statistical modelling to show that delirium probably does not increase mortality directly, overturning findings from a large body of previous observational research.2 3

Dealing with clinical situations that change over time (such as severity of illness) is one of the key challenges when exploring associations between delirium and death in critically ill patients. Traditional analysis methods may result in incorrect estimates if the main exposure (delirium) influences important covariates such as treatment decisions or clinical complications during follow-up, and also if the main exposure itself (severity of delirium) changes over time.4 Both these problems occur in cohort studies linking delirium with mortality on the intensive care …