Non-compliance with the AOA VTE prevention clinical guidelines was not significantly associated with the risk of VTE. We reported higher levels of non-compliant prophylaxis for people assessed as being at high VTE risk (27.0%) and high bleeding risk (100%), compared to those at routine risk (9.2%) (using AOA criteria). All people considered at high bleeding risk received chemical prophylaxis, despite this not being recommended for this group.
Adherence to AOA VTE prevention clinical guideline recommendations does not appear to reduce the risk of VTE after THA and TKA. These findings are consistent with the US Surgical Care Improvement Project (SCIP), which reported a higher rate of PE in those who received care compliant with the VTE process measures (doctor ordered VTE prophylaxis, and the patient received VTE prophylaxis at the right time) 14,15. This program uses process of care elements that are also very broad and may mask any differential outcome associated with different types of chemoprophylaxis 16. Compliance with AOA recommended VTE chemical prophylaxis is flexible and surgeons are given discretion to use aspirin (100-300mg), low molecular weight heparins or DOACs for people at routine VTE risk, although in this study aspirin was also used for people assessed as high VTE risk 5.
While nonsignificant, we reported a trend towards a reduction in risk associated with non-compliant VTE prophylaxis. This contrasts with our previous analysis demonstrating noncompliance with the NHMRC VTE guideline was significantly associated with increased risk of VTE 17. The main difference in the recommended prophylaxis is that aspirin is considered compliant for AOA VTE prevention clinical guidelines, but was not considered compliant for NHMRC VTE prevention clinical guideline 5,7. The use of aspirin remains controversial although it is now recommended in several VTE clinical guidelines when used as part of a comprehensive VTE prophylaxis program. VTE, SSI and bleeding outcomes for aspirin prophylaxis have been shown to be no different to potent anticoagulants 18–20. However other studies have reported aspirin is associated with an increased incidence of DVT and wound complications, but a lower risk of bleeding 21–23. There has been a call for high quality RCT to confirm the efficacy and safety profile of aspirin, and several are now underway 1,18,24,25.
This study has several limitations. The AOA guidelines target PE rather than DVT 26; we included symptomatic DVT as both are associated with higher costs, lower patient satisfaction and are a target for Australian hospital accreditation 27,28. Calculation of patient risk was constrained by the available data; alternative criteria for compliance may yield different results. We may not have accounted for all the variation in prophylactic regimens. We did not assess the quality of the AOA VTE prevention clinical guidelines as the lack of peer-reviewed evidence regarding the methods or impact of the AOA VTE clinical guidelines precluded formal assessment. Research has demonstrated variable quality and issues with implementing other VTE clinical guidelines 9,29, even though the patient and system benefits of increasing compliance 14,30 can only be realised if the guidelines are of the highest quality 8,9. Finally, our sample included a higher rate of THA and surgery performed in public hospitals than national registry data and the findings may not be generalisable to other populations 5.
A key strength of this study lies in the comprehensive prospective clinical data to assess risk stratified VTE prophylaxis and compliance with the AOA VTE prevention clinical guidelines. Patient appropriate variations were considered in assessing compliance 31,32. It is unclear whether the use of aspirin was associated with the increased VTE events we saw with people who experienced VTE while taking prophylaxis. Other potential factors are the AOA VTE prevention clinical guidelines recommendations are too broad to impact risk or a consequence of the varying recommendations between different guidelines or other factors 28,33. Further research is recommended to explore factors influencing individualised risk assessment and prophylaxis, and the association with economic and patient reported outcomes 27.