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

Abstract

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; chronic obstructive pulmonary disease; intensive care; mortality.

Figure 1

Survival curves according to hemoglobin levels at ICU admission for chronic obstructive pulmonary disease patients treated with mechanical ventilation [----Hb < 7.4 mmol/L (12.0 g/dL); — 7.4 mmol/L (12.0 g/dL) < Hb < 9.3 mmol/L (15.0 g/dL); Hgb > 9.3 mmol/L (15.0 g/dL)].