Relationship between postoperative anemia and cardiac morbidity in high- risk vascular patients in the intensive care unit

Objective: To determine if postoperative anemia is associated with postoperative myocardial ischemia and morbid cardiac events. Design: Case control study. Setting: Postanesthesia care unit and surgical intensive care unit. Patients: A total of 27 high-risk patients undergoing infra-inguinal arterial bypass procedures. Interventions: None. Measurements and Main Results: After informed consent, patients were continuously monitored by ambulatory electrocardiographic recorders from the evening before surgery up to 80 hrs during the postoperative period. Myocardial ischemia was defined as ≥1 mm of horizontal or downsloping ST depression of ≥2 mm ST segment elevation persisting for at least 60 secs on the ambulatory electrocardiogram. Morbid cardiac events were defined as: cardiac death, myocardial infarction, unstable angina, and ischemic pulmonary edema. Using a receiver operating characteristic curve, a hematocrit of 28% was determined to be the best threshold hematocrit value below which morbid cardiac events were most likely to occur. Statistical significance between hematocrit and cardiac outcome was determined by Fisher's exact test where appropriate. Thirteen of 27 patients had a hematocrit <28%. Of these 13 patients, ten demonstrated postoperative myocardial ischemia and six sustained a morbid cardiac event. Of 14 patients with a hematocrit ≥28%, two displayed myocardial ischemia and none sustained a morbid cardiac event. A hematocrit of <28% was significantly associated with myocardial ischemia (p = .001) and morbid cardiac events (p = .0058). No significant differences in baseline heart rate and heart rate at the onset of myocardial ischemia were noted between the anemic and nonanemic patients. Conclusions: This study suggests that postoperative anemia may play a role in postoperative myocardial ischemia and cardiac morbidity.