Background: ICU delirium duration has been associated with increased costs, however, it is unclear if this relationship is independent of time-varying changes in illness. In addition, delirium is associated with early mortality, and it is unclear the extent to which costs are impacted by this relationship. 

Methods: Using data from a prospective study of critically ill patients (BRAIN-ICU) we estimated the association between acute brain dysfunction (ABD = delirium or coma) and costs. This was done by fitting a three-part model (Basu et al.). The estimate of mean cost is obtained as the sum of conditional predictions from the following three models: a) a time-varying Cox model to estimate the hazard of death each day, b.) a Poisson model with a log link as a function of daily mental status to obtain the expected cost for intervals where patients died, and c) a Poisson model with a log link as a function of daily mental status to obtain the expected cost for intervals where patients survived. The estimates of the models were combined for all patients and over all days to calculate the mean cost over a 30-day length of stay and the incremental effect of delirium, divided into resource intensity and mortality. Covariates included baseline factors (age, insurance, cognitive impairment, comorbidities, APACHE-II score) and time varying factors (SOFA score, mechanical ventilation, and severe sepsis).  

Results: Among 517 patients with cost data, twenty-eight were excluded for persistent coma (N=489). The mean age of patients was 57 (SD = 15) and 5% were uninsured.  Mean Apache-II score was 25 (SD = 8) indicating a high illness severity. Sixty-five patients died within 30 days (13%). The output of the combined three-part model demonstrated a mean expected 30-day cost for patients experiencing ABD of $238,726 compared to $105,779 for a patient without ABD. The total incremental cost increase attributable to ABD was $39,835 (95% CI $11,537 to $59,515). The incremental cost attributable to intensity of resources versus mortality was $57,573 ($31,254 to $74,522) versus $-17,738 ($-19,682 to $-12,859), respectively.

Conclusions: Delirium and coma are associated with substantial costs after accounting for time-varying illness severity.  Costs of acute brain dysfunction the ICU are likely underestimated in light of the mortality effect on overall incremental costs.