Le Brigand 1981.

Methods	Quasi‐randomised, single‐centre study
Participants	Patients (n = 2420) of 21 to 70 years old undergoing thoracic surgery
Interventions	‐ Group A: UFH 5000 IU subcutaneous starting 2 hours and 30 minutes before surgery and then twice daily ‐ Group B: UFH 5000 IU subcutaneous starting 24 to 72 hours after surgery then twice daily ‐ Control: no UFH because of contraindication or minor surgical procedures UFH doses were increased after the 4th day to maintain a difference in partial thromboplastin time between participant and control between 7 and 14 seconds. UFH was continued until discharge or for 15 to 21 days UFH doses were increased postoperatively to therapeutic levels in case of clinically suspected VTE
Outcomes	Fatal and non fatal PE. The authors did not report if all suspected cases of PE and/or DVT underwent objective test confirmation
Notes	—
Risk of bias
Bias	Authors' judgement	Support for judgement
Random sequence generation (selection bias)	High risk	This was a quasi‐randomised trial in which participants were allocated to study treatment according to the time of operation. However, the time of surgery was influenced by the presence or absence of contraindications and the type of surgical procedure (minor versus major)
Allocation concealment (selection bias)	High risk	The allocation was not concealed but planned and thus predictable
Blinding of participants and personnel (performance bias) All outcomes	High risk	It is not explicitly reported whether personnel or participants were blinded but, given the type of interventions considered, it is likely that the study was open
Blinding of outcome assessment (detection bias) All outcomes	Unclear risk	It is not explicitly reported whether outcome assessment was blinded
Incomplete outcome data (attrition bias) All outcomes	Low risk	All included participants were considered in the analysis
Selective reporting (reporting bias)	Unclear risk	Outcomes are not clearly specified in the report and no protocol is available
Other bias	High risk	Participants in the study treatment groups had a different prognosis before the surgical procedure and, accordingly, could have a different risk of VTE. Clinically suspected cases of PE were followed up clinically but it is not reported if they all underwent an objective test for PE