Anemia and 90-day mortality in COPD patients requiring invasive mechanical ventilation

Lone Rasmussen^1,2, Steffen Christensen^1,2, Poul Lenler-Petersen², Søren P Johnsen^1
1Department of Clinical Epidemiology, Aarhus University Hospital, Aarhus, Denmark; ²Department of Anaesthesiology and Intensive Care, Silkeborg Hospital, Silkeborg, Denmark

Background: There are data to suggest that anemia is associated with increased mortality in patients with chronic obstructive pulmonary disease (COPD). In contrast, critically ill patients with low hemoglobin levels (4.3–5.5 mmol/L, 7.0–9.0 g/dL) in general do not appear to have a worsened clinical outcome. The effects of anemia in critically ill patients with COPD remain to be clarified. We examined the association between anemia (hemoglobin < 7.4 mmol/L, <12.0 g/dL) and 90-day mortality in COPD patients with acute respiratory failure treated with invasive mechanical ventilation in a single-institution follow-up study.
Method: We identified all COPD patients at our institution (n = 222) admitted for the first time to the intensive care unit (ICU) requiring invasive mechanical ventilation in 1994–2004. Data on patient characteristics (eg, hemoglobin, pH, blood transfusions, and Charlson Comorbidity Index), and mortality were obtained from population-based clinical and administrative registries and medical records. We used Cox’s regression analysis to estimate mortality rate ratios (MRR) in COPD patients with and without anemia.
Results: A total of 42 (18%) COPD patients were anemic at time of initiating invasive mechanical ventilation. The overall 90-day mortality among anemic COPD patients was 57.1% versus 25% in nonanemic patients. The corresponding adjusted 90-day MRR was 2.6 (95% confidence interval 1.5–4.5). Restricting analyses to patients not treated with blood transfusions during their intensive care unit stay did not materially change the MRR.
Conclusion: We found anemia to be associated with increased mortality among COPD patients with acute respiratory failure requiring invasive mechanical ventilation.

Keywords: anemia, mortality, chronic obstructive pulmonary disease, intensive care