Body mass index, risk of allogeneic red blood cell transfusion, and mortality in elderly patients undergoing hip fracture surgery.

Abstract

Despite improvements in preoperative and postoperative treatment, hip fracture surgery may lead to blood transfusion. Little is known about the impact of body mass index on transfusion risk and subsequent mortality. Opposite overweight and obese patients, underweight patients had increased risk of transfusion and death within 1year of surgery. Despite improvements in preoperative and postoperative treatment of hip fracture patients, hip fracture surgery may lead to blood loss. We examined the risk of red blood cell transfusion (as an indirect measure of blood loss) and subsequent mortality by body mass index level in patients aged 65 and over undergoing hip fracture surgery. This is a population-based cohort study using medical databases. We included all patients who underwent surgery for hip fracture during 2005-2013. We calculated the cumulative risk of red blood cell transfusion within 7days of surgery treating death as a competing risk and, among transfused patients, short- (8-30days postsurgery) and long-term mortality (31-365days postsurgery). Among 56,420 patients, 47.7% received at least one red blood cell transfusion within 7days of surgery. In patients with normal weight, the risk was 48.8% compared with 57.0% in underweight patients (adjusted RR = 1.11; CI 1.08-1.15), 42.1% in overweight patients (adjusted RR = 0.89; CI 0.86-0.91), and 42.2% in obese patients (adjusted RR = 0.87; CI 0.84-0.91). Among transfused patients, adjusted HRs for short-term mortality were 1.52 (CI 1.34-1.71), 0.70 (CI 0.61-0.80), and 0.58 (CI 0.43-0.77) for underweight, overweight, and obese patients, respectively, compared with normal-weight patients. The corresponding adjusted HRs for long-term mortality were 1.45 (CI 1.33-1.57), 0.80 (CI 0.74-0.86), and 0.58 (CI 0.50-0.69). Similar association between BMI and mortality was observed also among non-transfused patients. Underweight patients had a higher risk of red blood cell transfusion and death in the first year of surgery than normal-weight patients, even when controlling for age and comorbidity. Opposite findings were seen for overweight and obese patients.