Background: Delirium occurs frequently in the intensive care unit (ICU), but its pathophysiology is still unclear. Low levels of insulin-like growth factor 1 (IGF-1), a hormone with neuroprotective properties, have been associated with delirium in some non-ICU studies, but this relationship has not been examined in the ICU. We sought to test the hypothesis that low IGF-1 concentrations are associated with delirium during critical illness.

Methods: Mechanically ventilated medical ICU patients were prospectively enrolled, and blood was collected after enrollment for measurement of IGF-1 using radioimmunometric assay. Delirium and coma were identified daily using the Confusion Assessment Method for the ICU and the Richmond Agitation-Sedation Scale, respectively. The association between IGF-1 and delirium was evaluated with logistic regression. In addition, the association between IGF-1 and duration of normal mental state, measured as days alive without delirium or coma, was assessed using multiple linear regression.

Results: Among 110 patients, the median age was 65 years (IQR, 52–75) and APACHE II was 27 (IQR, 22 –32). IGF-1 levels were not a risk factor for delirium on the day after IGF-1 measurement (p = 0.97), at which time 65% of the assessable patients were delirious. No significant association was found between IGF-1 levels and duration of normal mental state (p = 0.23).

Conclusions: This pilot study, the first to investigate IGF-1 and delirium in critically ill patients, found no association between IGF-1 and delirium. Future studies including serial measurements of IGF-1 and IGF-1 binding proteins are needed to determine whether this hormone has a role in delirium during critical illness.