Postdischarge thromboprophylaxis and mortality risk after hip-or knee-replacement surgery

Abstract

Background: Patients undergoing hip or knee replacement are at high risk of developing a postoperative venous thromboembolism even after discharge from hospital. We sought to identify hospital and patient characteristics associated with receiving thromboprophylaxis after discharge and to compare the risk of short-term mortality among those who did or did not receive thromboprophylaxis.

Methods: We conducted a retrospective cohort study using system-wide hospital discharge summary records, physician billing information, medication reimbursement claims and demographic records. We included patients aged 65 years and older who received a hip or knee replacement and who were discharged home after surgery.

Results: In total we included 10 744 patients. Of these, 7058 patients who received a hip replacement and 3686 who received a knee replacement. The mean age was 75.4 (standard deviation [SD] 6.8) years and 38% of patients were men. In total, 2059 (19%) patients received thomboprophylaxis at discharge. Patients discharged from university teaching hospitals were less likely than those discharged from community hospitals to received thromboprophylaxis after discharge (odds ratio [OR] 0.89, 95% confidence interval [CI] 0.80-1.00). Patients were less likely to receive thromboprophylaxis after discharge if they had a longer hospital stay (15-30 days v. 1-7 days, OR 0.69, 95% CI 0.59-0.81). Patients were more likely to receive thromboprophylaxis if they had hip (v. knee) replacement, osteoarthritis, heart failure, atrial fibrillation or hypertension, higher (v. lower) income or if they were treated at medium-volume hospitals (69-116 hip and knee replacements per year). In total, 223 patients (2%) died in the 3-month period after discharge. The risk of short-term mortality was lower among those who received thromboprophylaxis after discharge (hazard ratio [HR] 0.34, 95% CI 0.20-0.57).

Interpretation: Fewer than 1 in 5 elderly patients discharged home after a hip-or knee-replacement surgery received postdischarge thromboprophylaxis. Those prescribed these medications had a lower risk of short-term mortality. The benefits of and barriers to thromboprophylaxis therapy after discharge in this population requires further study.

Figure 1: Selection of patients for inclusion in the study.

Figure 2: Crude and adjusted odds ratios for receiving thromboprophylaxis after discharge among patients aged 65 years and older who underwent hip or knee replacement surgery between January 1997 and December 2004. Note: OR = odds ratio, CI = confidence interval, SD = standard deviation. *Adjusted for all variables listed in Figure 2.

Figure 3: Kaplan–Meier survival curves for patients aged 65 years and older who did or did not receive thromboprophylaxis after discharge. A) Patients in hospital for 1–7 days after surgery, B) patients in hospital for 8–14 days after surgery and C) patients in hospital for 15–30 days after surgery.