Contradictory findings on one-year mortality following ICU delirium

In contrast to prior studies (Table 1), Wolters and colleagues [1] reported no significant association between delirium and 1-year survival among Dutch ICU survivors. The authors attributed this finding to a novel adjustment of their Cox survival model for the sum of patients’ Sequential Organ Failure Assessment (SOFA) scores (obtained three times daily). Hence, we wish to enquire about the results of their multivariable model if re-run without SOFA adjustment: is the adjusted hazard ratio for delirium statistically significant? This contradictory result also could be attributable to other issues, rather than this unique adjustment that combined SOFA score and length of stay, as described below. The study’s 1-year mortality was 18%, with 59% of survivors discharged home. In contrast, 1-year mortality in a prior US study was 41% [2], raising the question of whether Dutch ICU survivors are healthier than those in some prior studies? Perhaps delirium is more strongly associated with mortality in frail ICU survivors. The Dutch study also reported that delirium was associated with increased cognitive impairment without impaired quality of life. Consequently, we wonder if care for cognitively impaired individuals is better in the Netherlands, hence conferring less risk of mortality to ICU survivors with cognitive impairment. Finally, what were the results of testing the proportional hazards assumption in the Cox model? If the association between delirium and mortality is time-dependent [3], with the hazard greatest shortly after discharge, as per a prior Dutch study [4], a single hazard ratio over 1 year could attenuate this measure and violate the proportional hazards assumption.