LONFLIT 4 ‐ Kendall 2

Methods	Trial design: randomised controlled trial (parallel). Country principal investigators: Italy, UK, Australia. Where trial conducted: UK. Date of trial: May to July 2002. Multi‐centre: yes. Funder: multiple sources. Blinding: outcome assessor not blinded. Lost to follow‐up: 0/66 (stocking) 2/68 (control); dropouts due to low compliance or flight connection problems.
Participants	Inclusion criteria: low‐ to medium‐risk participants. Participants were recruited through flight shops. Exclusion criteria: high‐risk participants defined as those with previous episodes of DVT, coagulation disorders, severe obesity, limited mobility due to bone or joint problems, neoplastic disease within the previous 2 years, large varicose veins or participants taller than 190 cm and heavier than 90 kg. No. randomised: 134 No. analysed: 132 Age (years): mean 47 (stocking), 46.9 (control). Sex: 34 M, 30 F (stocking), 34 M, 32 F (control) ‐ based on number analysed.
Interventions	Stocking Group Type of stocking: below‐knee Kendall travel sock with 20 to 30 mmHg of pressure at the ankle. Stockings were put on 2 to 3 hours before the flight. No. randomised: 66 No. analysed: 66 Length of flight: 11 to 12 hours. Type of seat: Economy, seat pitch 31 inches. Route and time of flight: London to Phoenix. Additional interventions: suggestions were given to participants i.e. mild exercise, walking, drinking water and avoiding salty food and excessive baggage restricting leg motion. Control Group Type of control: no intervention No. randomised: 68 No. analysed: 66 Length of flight: 11 to 12 hours Type of seat: Economy, seat pitch 31 ins Route and time of flight: London to Phoenix Additional interventions: the same advice as the stocking group was given.
Outcomes	Outcomes assessed: incidence of DVT, SVT and oedema score. DVT diagnosed by: pre‐ and post‐flight ultrasound scanning using Sonosite scanners with a 7.5 to 13 MHz, high‐resolution probe (Sonosite, Bothell, WA, USA). This was done by compressing the major veins (femoral, popliteal and tibial). Site of DVT: none developed. Site of SVT: not mentioned. Other investigations performed: oedema test (ankle circumference, volume, swelling, discomfort). Additional complications reported: increased oedema in the control group.
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Risk of bias
Bias	Authors' judgement	Support for judgement
Random sequence generation (selection bias)	Unclear risk	States randomised but no further details
Allocation concealment (selection bias)	Unclear risk	Not reported
Blinding of participants and personnel (performance bias) All outcomes	High risk	Not reported but not possible
Blinding of outcome assessment (detection bias) All outcomes	Unclear risk	Not reported. Oedema scale described but variation possible, parametric and non‐parametric
Incomplete outcome data (attrition bias) All outcomes	Low risk	All accounted for, dropouts reported
Selective reporting (reporting bias)	Low risk	All expected outcomes reported
Other bias	Low risk	No evidence of other bias