Effect of Anemia on Mortality in Mechanically Ventilated Patients With Chronic Obstructive Pulmonary Disease

Rationale: The effect of anemia on patients with chronic obstructive pulmonary disease (COPD) requiring invasive mechanical ventilation for acute respiratory failure is unknown. Objectives: To examine the association between anemia (hemoglobin <12 g/dL) and 90-day and overall mortality in patients with COPD having acute respiratory failure requiring invasive mechanical ventilation. Methods: Retrospective study of patients admitted to a quaternary referral medical intensive care unit (ICU) between October 2007 and December 2012 with a diagnosis of COPD and requiring invasive mechanical ventilation for acute respiratory failure of any cause. Results: We identified 1107 patients with COPD who required invasive mechanical ventilation for acute respiratory failure. Mean age was 64.2 12.7 years; 563 (50.9%) were females. The mean Acute Physiology and Chronic Health Evaluation III score at ICU admission was 80.5 +/- 29.3. The median duration of mechanical ventilation was 35.7 hours (interquartile range: 20.0-54.0). In all, 885 (79.9%) patients were anemic (Hb < 12g/dL) on ICU admission, and 312 patients (28.2%) received blood transfusion during their ICU stay. A total of 351 inhospital deaths were recorded, the majority (n = 320) occurring in the ICU. The 90-day mortality, though lower in the nonanemic patients compared to the patients with anemia, was not statistically significant (35.6% vs 44.9%; hazard ratio [HR] [95% confidence interval; CI] = 1.16 [0.91 -1.48], P = .22). The overall mortality was lower in the nonanemic patients compared to patients with anemia (HR [95% CI] = 0.68 [0.55-0.83], P < .001). There was a 5% decrease in risk of death for every unit increase in hemoglobin (P = .01). There was no difference in terms of both 90-day and overall mortality in patients who received blood transfusions compared to patients who did not receive any transfusion. Conclusions: Critically ill patients with COPD requiring invasive mechanical ventilation for acute respiratory failure without anemia on admission had a better overall survival when compared to those with anemia. No difference was noted in the 90-day mortality. Further studies are needed to determine the impact of the trajectory of hemoglobin on mortality.