110 External validity of thromboprophylaxis guidelines in hip fracture patients: a retrospective analysis

Abstract

Objectives Major orthopedic surgeries are recognized risk factors for thrombo-embolic events. Thromboprophylaxis following orthopedic surgery is widely recommended. Yet randomized controlled trials (RCT) evaluating efficacy and safety of thromboprophylaxis in the population with traumatic hip fracture have enrolled a selected group of patients. Patients with traumatic hip fracture often present with multiple comorbidities making them likely to be underrepresented in thromboprophylaxis studies. We hypothesize that randomized controlled trials in support of the CHEST guidelines for thromboprophylaxis following hip surgery for traumatic fracture have a low external validity. We designed a study to measure the prevalence of exclusion criteria from thromboprophylaxis trials in the population that underwent surgery for a traumatic hip fracture at the Centre Hospitalier de l’Université de Montréal (CHUM). We also aimed to quantify the number of transfusions received, number of bleeding events and deaths according to the presence or not of exclusion criteria to randomized controlled trials. Method We identified all original studies supporting the CHEST thromboprophylaxis guidelines for patients suffering a traumatic hip fracture (n=3). We extracted all inclusion and exclusion criteria reported by authors. Then, we conducted a retrospective cohort study on a random selection of all was patients who underwent an urgent traumatic hip fracture surgery at the CHUM from January 1 st 2012 to December 31 2016 Patients (n=250) were randomly selected from the medical archives list (50 patients/year). Data was collected through chart review of the electronic medical charts. For each participant, data on the presence of exclusion criteria, number of transfusions received post-operatively during hospital stay, significant bleeding events, thrombotic events and death were extracted. We used appropriate descriptive statistics, binomial exact confidence intervals and kruskall wallis and fisher’s exact tests to analyze results. Analysis was done using Stata 13. Results We included 250 patients, (172 (68.8%) women, mean age 78.7 SD (13.1)yo). Overall, 164 (66% 95%CI [59% to 71%]) subjects presented at least one exclusion criteria for one of the 3 RCT, and 57 (23%) [95% CI 18% to 29%] presented an exclusion criterion to all trials. No thrombotic event was reported (0%, 95% CI [0% to 1.4%]. There were 114 (46%, 95% CI [39% to 52%]) patients receiving at least one transfusion during the postoperative period. The median number (IQR) of transfusions according to the number of exclusion criteria were: no criteria, 0 (0–1) transfusion; 1 criterion, 0 (0–2); 2 criteria, 0 (0–2); 3 or more criteria, 2 (0–4) (p=0,011). The same trend was observed with significant bleeding events (p<0.001) and mortality (p=0.001), with an increasing proportion of patients experiencing these complications when presenting more exclusion criteria. Conclusions Our results suggest that patients who would have been excluded from the randomized controlled trials supporting the actual thromboprophylaxis guidelines present with more bleeding complications and a higher transfusion need in the postoperative period. There is a trend showing a relation between the number of exclusion criteria and the frequency of bleeding adverse events. This demonstrates that the population excluded from trial may be at higher bleeding risk, therefore, the risk-benefit ratio demonstrated in trials does not apply to this population. Whether thromboprophylaxis may be of benefit to these patients is unknown.