Daily Lowest Hemoglobin and Risk of Organ Dysfunctions in Critically Ill Patients

To determine the association between hemoglobin levels and the daily risk of individual organ dysfunctions in critically ill patients.

Post hoc analysis of prospectively collected data.

Vanderbilt University Medical Center and Saint Thomas Hospital Medical and Surgical ICUs.

Medical and surgical ICU patients admitted with respiratory failure or shock.

Baseline demographic data, and detailed in-ICU and hospital data, including daily lowest hemoglobin, were collected up to hospital day 30. We assessed patients daily for brain dysfunction (delirium, using Confusion Assessment Method for ICU), for renal and respiratory dysfunction (using the ordinal renal and respiratory Sequential Organ Failure Assessment score), and for ICU mortality. Associations between the lowest hemoglobin on a given day and organ dysfunctions the following day were assessed using multivariable regressions, adjusting for age, Acute Physiology and Chronic Health Evaluation II score, Charlson comorbidity index, Framingham Stroke Risk Profile, ICU day, ICU type, sepsis, and current organ dysfunction status. A sensitivity analysis further adjusted for daily transfusions and fluid balance in a subset of our patients.

We enrolled 821 patients with a median (interquartile range) age of 61 (51-71) years, Acute Physiology and Chronic Health Evaluation II score of 25 (19-31), and hemoglobin level of 10.0 (9.0-11.1) g/dL. There was no evidence of an association between lowest daily hemoglobin and brain dysfunction (p = 0.69 for delirium), renal dysfunction (p = 0.30), or ICU mortality (p = 0.95). The lowest hemoglobin on a given day was significantly associated with the respiratory Sequential Organ Failure Assessment score the following day; for each increasing hemoglobin unit, the odds of worsened respiratory Sequential Organ Failure Assessment score the following day were decreased by 36% (OR, 0.64; 95% CI, 0.53-0.77; p < 0.001). The sensitivity analysis including daily transfusions and fluid balance (in a subset of 518 patients) did not qualitatively change any of these associations.

In this study in ICU patients, lower hemoglobin was associated with a higher probability of worsening respiratory dysfunction scores the following day. There was no evidence of association between hemoglobin and brain or renal dysfunction, or ICU mortality. The possible differential effects of anemia on organ dysfunctions seen in this hypothesis-generating study will have to be studied in a larger prospective study before any alterations to present restrictive transfusion guidelines can be recommended.