Anemia and end-organ dysfunction in critically ill medical and surgical ICU patients
Author list
Sarah Hemauer
Adam J. Kingeter
Xue Han
Matthew S. Shotwell
Pratik P. Pandharipande
Liza M. Weavind
Department of Anesthesiology and Biostatistics, Vanderbilt University Medical center,
Nashville, TN
Background: Anemia is associated with increased morbidity and mortality, however, transfusion
of packed red blood cell (PRBC) is also an independent predictor of worse clinical outcomes.
Recent data have supported the safety of restrictive transfusion strategies with a resultant
decrease in PRBC use and acceptance of anemia, yet little is known about the impact of this
anemia on the daily risk of individual organ dysfunctions in medical and surgical ICU patients.
Methods: We performed a post-hoc analysis of prospectively collected data from the BRAINICU observational cohort study of medical and surgical ICU patients admitted with respiratory
failure or shock. Baseline demographic data as well as detailed in-ICU and hospital data,
including daily hemoglobin levels, were collected in the study up to hospital day 30. Patients
were evaluated daily for brain dysfunction (delirium) using the CAM-ICU, for renal dysfunction
using the renal SOFA score (based on creatinine and urinary output) and for respiratory
dysfunction using the respiratory SOFA score (based on the PaO2/FiO2 ratio) or need for
mechanical ventilation. We also collected data on in-hospital mortality and calculated time to
death. The adjusted associations between the current day hemoglobin level and organ
dysfunction the following day were assessed using multinomial, ordinal (proportional odds) and
binary logistic regression. Cox proportional hazards regression with time-varying covariates was
used to assess the adjusted association between current day hemoglobin and time to death. In
each analysis, we adjusted for covariates including age, the APACHE II score, Charlson
comorbidity index, Framingham stroke risk profile, ICU day, ICU type (medical vs. surgical),
current sepsis, current organ dysfunction, and current lowest hemoglobin level. Statistical
significance was indicated for p-values less than 0.05, or for 95% confidence intervals that fail to
include the relevant null value.
Results: We enrolled 821 patients with a median (interquartile, IQR) age of 61 (51, 71),
APACHE II score of 21 (15, 26), and 30% had sepsis on enrollment. The hemoglobin level on a
given day was significantly associated with the respiratory SOFA score the following day, such
that for each increasing hemoglobin unit on the current day the odds of more severe respiratory
SOFA score the following day were decreased by 30.6% (95% CI: 16.0, 62.7). This protective
effect was significantly reduced in patients with greater current respiratory SOFA score (p-value
<0.001). There was no evidence of an association between current hemoglobin level and brain
dysfunction, renal dysfunction, or the odds of mechanical ventilation the following day, or time to
death.
Conclusion: In this study population, lower hemoglobin levels were not associated with daily
risk of development of brain or renal dysfunctions, or death. However, lower hemoglobin levels
were associated with more severe respiratory dysfunction the following day, especially in
patients who previously had a lower respiratory SOFA score implying less pulmonary
dysfunction.