3055 — Preoperative Hematocrit is Not Predictive of CNS Events in Elderly Patients after Major Non-Cardiac Surgery

Wu W (Providence VAMC), Schifftner T (Denver VAMC), Henderson W (Denver VAMC), EAton CB (Memorial Hospital of RI), Poses RM (Brown University), Uttley G (QCMetrix, Inc.), Sharma SC (Providence VAMC), Vezeridis M (Providence VAMC), Khuri SF (Boston VAMC), Friedmann P (Providence VAMC)

Objectives:
Elderly patients are at risk for both abnormal hematocrit values and perioperative Central Nervous System (CNS) events with non-cardiac surgery. Our previous work suggests that even mild degrees of preoperative anemia or polycythemia confer increased risk for 30-day postoperative cardiac events and mortality. Although the CNS is at least as susceptible to the effects of hypoxia as the myocardium, whether preoperative anemia or polycythemia confers similar risk for stroke or coma is not well-understood. We studied the relationship between preoperative anemia and polycythemia, and postoperative CNS events in elderly veterans undergoing non-cardiac surgery using the VA National Surgical Quality Improvement Program (NSQIP database).

Methods:
We conducted a retrospective study of 310,311 veterans 65 years or older who underwent major non-cardiac surgery between 1997 and 2004 in 132 Veterans’ Affairs Medical Centers across the United States. Based on preoperative hematocrit levels, we stratified patients into the following categories: < 18.0%, 18.0-20.9%, 21.0-23.9%, 24.0-26.9%, 27.0-29.9%, 30.0-32.9%, 33.0-35.9%, 36.0-38.9%, 39.0-41.9%, 42.0-44.9%, 45.0-47.9%, 48.0-50.9%, 51.0-53.9%, and =54.0%; and determined their rates of postoperative stroke or coma. We then estimated the independent predictive value of each hematocrit category for risk of 30-day postoperative study events comparing to the hematocrit category with the lowest 30-day study events rates.

Results:
The 30-day postoperative rate of stroke or coma was 0.54%. The hematocrit category of 45.0-47.9% had the lowest event rates (0.38%), with progressive increase in event rates above 47.9% and below 45.0%, with higher rates at both extremes of the hematocrit spectrum (1.8% for patients with hematocrit values below 20.9% and 1.0% for hematocrit values above 50.9%). However, after adjustment for demographic and clinical confounding factors, preoperative hematocrit categories were not predictive of postoperative CNS event rates (p=0.21).

Implications:
Preoperative anemia or polycythemia does not confer a significant risk for postoperative CNS events in elderly veterans undergoing major non-cardiac surgery.

Impacts:
Strategies to optimize preoperative hematocrit values such as hematocrit testing and blood transfusions are unlikely to improve elderly patients’ perioperative risk of stroke or coma.