Risk of Post-Discharge Venous Thromboembolism and Associated Mortality in General Surgery: A Population-Based Cohort Study Using Linked Hospital and Primary Care Data in England

BACKGROUND Trends towards day case surgery and enhanced recovery mean that postoperative venous thromboembolism (VTE) may increasingly arise after hospital discharge. However, hospital data alone are unable to capture adverse events that occur outside of the hospital setting. The National Institute for Health and Care Excellence has suggested the use of primary care data to quantify hospital care-related VTE. Data in surgical patients using these resources is lacking. The aim of this study was to measure VTE risk and associated mortality in general surgery using linked primary care and hospital databases, to improve our understanding of harm from VTE that arises beyond hospital stay. METHODS This was a longitudinal cohort study using nationally linked primary care (Clinical Practice Research Datalink, CPRD), hospital administrative (Hospital Episodes Statistics, HES), population statistics (Office of National Statistics, ONS) and National Cancer Intelligence Network databases. Routinely collected information was used to quantify 90-day in-hospital VTE, 90-day post-discharge VTE and 90-day mortality in adults undergoing one of twelve general surgical procedures between 1st April 1997 and 31st March 2012. The earliest postoperative recording of deep vein thrombosis or pulmonary embolism in CPRD, HES and ONS was counted in each patient. Covariates from multiple datasets were combined to derive detailed prediction models for VTE and mortality. Limitation included the capture of VTE presenting to healthcare only and the lack of information on adherence to pharmacological thromboprophylaxis as there was no data linkage to hospital pharmacy records. RESULTS There were 981 VTE events captured within 90 days of surgery in 168005 procedures (23.7/1000 patient-years). Overall, primary care data increased the detection of postoperative VTE by a factor of 1.38 (981/710) when compared with using HES and ONS only. Total VTE rates ranged between 3.2/1000 patient-years in haemorrhoidectomy to 118.3/1000 patient-years in esophagogastric resection. Predictors of VTE included emergency surgery (OR = 1.91 95%CI 1.60-2.28, p<0.001), age (OR = 1.02 95%CI 1.02-1.03, p<0.001), body mass index (OR = 1.03 95%CI 1.01-1.04, p<0.001), previous VTE (OR = 8.07 95%CI 6.61-9.83, p<0.001), length of stay (OR = 1.00 95%CI 1.00-1.00, p = 0.007) and cancer stages II (OR = 1.38 95%CI 1.03-1.87, p = 0.033), III (OR = 1.50 95%CI 1.11-2.01, p = 0.008) and IV (OR = 1.63 95%CI 1.03-2.59, p = 0.038). Major organ resections had the greatest odds of VTE when adjusted for other risk factors including length of hospital stay. Post-discharge VTE accounted for 64.8% (636/981) of all recorded VTE. In-hospital VTE (165.4/1000 patient-years) was recorded more frequently than post-discharge VTE (16.2/1000 patient-years). Both in-hospital (OR = 2.07 95%CI 1.51-2.85, p<0.001) and post-discharge (OR = 4.03 95%CI 2.95-5.51, p<0.001) VTE independently predicted 90-day mortality. In patients who died and VTE was recorded on HES or CPRD (n = 56), VTE was one of the causes of death in 37.5% (21/56) of cases. CONCLUSIONS A large proportion of postoperative VTE was detected in primary care. Evaluation of linked databases was a useful way of measuring postoperative VTE at population level. These resources identified a significant association between post-discharge VTE and mortality in general surgery.