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Do Blood Transfusions Improve Outcomes Related to Mechanical Ventilation?^*

Paul C. Hébert, MD, MHSc; Morris A. Blajchman, MD; Deborah J. Cook, MD, FCCP, MSc(Epid); Elizabeth Yetisir, MSc; George Wells, MSc, PhD; John Marshall, MD; Irwin Schweitzer, MSc and the Transfusion Requirements in Critical Care Investigators for the Canadian Critical Care Trials Group

^* From the Critical Care Programs (Dr. Hébert) and the Clinical Epidemiology Unit (Dr. Wells, Mr. Schweitzer, Ms. Yetisir), University of Ottawa, Ottawa, Ontario; the University of Toronto (Dr. Marshall), Toronto, Ontario; and the Departments of Pathology (Dr. Blajchman) and Medicine and Epidemiology (Dr. Cook), McMaster University, Hamilton, Ontario, Canada. A list of other study investigators is given in the ^Appendix.

Correspondence to: Paul C. Hébert, MD, MHSc(Epid), Department of Medicine, Ottawa Hospital, General Site, 501 Smyth Rd, Box 201, Ottawa, Ontario K1H 8L6, Canada; e-mail: phebert{at}ottawahospital.on.ca

Background: Correcting the decrease in oxygen delivery from anemia using allogeneic RBC transfusions has been hypothesized to help with increased oxygen demands during weaning from mechanical ventilation. However, it is also possible that transfusions hinder the process because RBCs may not be able to adequately increase oxygen delivery. In this study, we determined whether a liberal RBC transfusion strategy improved outcomes related to mechanical ventilation.

Methods: Seven hundred thirteen patients receiving mechanical ventilation, representing a subgroup of patients from a larger trial, were randomized to either a restrictive transfusion strategy, receiving allogeneic RBC transfusions at a hemoglobin concentration of 7.0 g/dL (and maintained between 7.0 g/dL and to 9.0 g/dL), or to a liberal transfusion strategy, receiving RBCs at 10.0 g/dL (and maintained between 10.0 g/dL and 12.0 g/dL). The larger trial was designed to evaluate transfusion practice rather than weaning per se.

Results: Baseline characteristics in the restrictive-strategy group (n = 357) and the liberal-strategy group (n = 356) were comparable. The average durations of mechanical ventilation were 8.3 ± 8.1 days and 8.3 ± 8.1 days (95% confidence interval [CI] around difference, - 0.79 to 1.68; p = 0.48), while ventilator-free days were 17.5 ± 10.9 days and 16.1 ± 11.4 days (95% CI around difference, - 3.07 to 0.21; p = 0.09) in the restrictive-strategy group vs the liberal-strategy group, respectively. Eighty-two percent of the patients in the restrictive-strategy group were considered successfully weaned and extubated for at least 24 h, compared to 78% for the liberal-strategy group (p = 0.19). The relative risk (RR) of extubation success in the restrictive-strategy group compared to the liberal-strategy group, adjusted for the confounding effects of age, APACHE (acute physiology and chronic health evaluation) II score, and comorbid illness, was 1.07 (95% CI, 0.96 to 1.26; p = 0.43). The adjusted RR of extubation success associated with restrictive transfusion in the 219 patients who received mechanical ventilation for > 7 days was 1.1 (95% CI, 0.84 to 1.45; p = 0.47).

Conclusion: In this study, there was no evidence that a liberal RBC transfusion strategy decreased the duration of mechanical ventilation in a heterogeneous population of critically ill patients.

Key Words: critical care • mechanical ventilation • oxygen delivery • RBC transfusion • transfusion trigger • weaning

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