Anemia before coronary artery bypass surgery as additional risk factor increases the perioperative risk

A negative relationship between anemia before coronary artery bypass graft (CABG) surgery and the perioperative mortality has been shown. We tried to clarify whether anemia only expresses an increased perioperative risk or is a risk factor per se in a two-institution database.

In the years 2005 and 2006, 185 of 3,311 patients undergoing isolated first-time CABG surgery had anemia defined as hematocrit less than 33% or Hb≤11 g/dL. Preoperative and postoperative data of patients having anemia and patients having normal hematocrit were compared using χ2-tests or Fisher's exact tests regarding structural group differences. To determine factors influencing perioperative mortality, methods of logistic regression were used.

The 30-day mortality of anemic patients (12.9%) was significantly higher (p<0.001) than the mortality of nonanemic patients (2.2%). Patients having anemia, though, had a worse risk profile before surgery: high European System for Cardiac Operative Risk Evaluation values (median, 7 in anemic patients versus 4 in nonanemic patients), acute myocardial infarction (9.7% in anemic versus 2% in nonanemic patients), diabetes mellitus (45.4% in anemic versus 33.3% in nonanemic patients), and cardiogenic shock (5.4% in anemic versus 0.8% in nonanemic patients) were significantly more frequent in the anemic group. However, taking these risks in account, the logistic regression revealed preoperative anemia still to be a mortality-increasing factor in patients undergoing CABG surgery (odds ratio 3.727, confidence interval: 2.196 to 6.324). Furthermore, anemia was a risk factor for perioperative morbidity (major adverse cardiovascular events) after CABG surgery (odds ratio 2.199, confidence interval: 1.423 to 3.397).

In our patient group undergoing CABG surgery, preoperative anemia increased the mortality risk by 3.4, even when taking the higher perioperative risk of anemic patients into consideration.