In their multivariable case-control study in patients undergoing major orthopedic arthroplasty operations (reconstructive hip or knee surgery, emergent or elective) Mantilla and coworkers evaluated the association between preoperative anemia (Hb < 12 g/dl in females and < 13 g/dl in males) and myocardial infarction (MI) or death within 30 days post surgery. During the 20-year study period (1987-2006), 391 cases of death (n = 228) or nonfatal MI (n = 163) after major orthopedic arthroplasty were identified at the Mayo Clinic, Rochester, USA. For each patient included in the event (case) cohort one control patient (1:1 matching design) was identified having not experienced death/MI and was matched according to sex, age, date and type of surgery.
Preoperatively 39% of cases and 32% of control patients were anemic. After adjusting for other perioperative risk factors, preoperative anemia was not a significant risk factor for death/MI, neither was the intraoperative transfusion of RBCs. A post hoc analysis detected no significant interaction of preoperative anemia and the need for perioperative transfusion for predicting death/MI.
One major advantage of the present study over others having reported a statistically significant impact of preoperative anemia on outcome (e.g., Wu et al., JAMA 2007; Beattie et al., Anesthesiology 2009) is the higher homogeneity of the patient collective investigated concerning, for example, age and surgical procedure. A major disadvantage is the fact that only 6% (event) and 4% (control) of patients had preoperative Hb concentrations < 10 g/dl, i.e. overall preoperative anemia was mild. Moreover no details of the transfusion practice applied can be provided.
The present study provides important data for clinicians treating orthopedic patients undergoing hip or knee surgery. Moreover, the manuscript nicely reviews the literature dealing with the impact of anemia and transfusion on morbidity and mortality in surgical patients.
– Oliver Habler