Frequency and prevention of symptomless deep-vein thrombosis in long-haul flights: a randomised trial. Prevention of edema, flight microangiopathy and venous thrombosis in long flights with elastic stockings. A randomized trial: The LONFLIT 4 Concorde Edema-SSL Study. The LONFLIT4--Concorde Deep Venous Thrombosis and Edema Study: prevention with travel stockings. The LONFLIT4-Concorde--Sigvaris Traveno Stockings in Long Flights (EcoTraS) Study: a randomized trial. Randomized trial of graded compression stockings for prevention of deep-vein thrombosis after acute stroke.
The true frequency of deep-vein thrombosis (DVT) during long-haul air travel is unknown. We sought to determine the frequency of DVT in the lower limb during long-haul economy-class air travel and the efficacy of graduated elastic compression stockings in its prevention.
                We recruited 89 male and 142 female passengers over 50 years of age with no history of thromboembolic problems. Passengers were randomly allocated to one of two groups: one group wore class-I below-knee graduated elastic compression stockings, the other group did not. All the passengers made journeys lasting more than 8 h per flight (median total duration 24 h), returning to the UK within 6 weeks. Duplex ultrasonography was used to assess the deep veins before and after travel. Blood samples were analysed for two specific common gene mutations, factor V Leiden (FVL) and prothrombin G20210A (PGM), which predispose to venous thromboembolism. Asensitive D-dimer assay was used to screen for the development of recent thrombosis.
                12/116 passengers (10%; 95% CI 4.8-16.0%) developed symptomless DVT in the calf (five men, seven women). None of these passengers wore elastic compression stockings, and two were heterozygous for FVL. Four further patients who wore elastic compression stockings, had varicose veins and developed superficial thrombophlebitis. One of these passengers was heterozygous for both FVL and PGM. None of the passengers who wore class-I compression stockings developed DVT (95% CI 0-3.2%).
                We conclude that symptomless DVT might occur in up to 10% of long-haul airline travellers. Wearing of elastic compression stockings during long-haul air travel is associated with a reduction in symptomless DVT. The LONFLIT1/2 studies have established that in high-risk subjects after long (> 10 hours) flights the incidence of deep venous thrombosis (DVT) is between 4% and 6%. The LONFLIT4 study has been planned to evaluate the control of edema and DVT in low-medium-risk subjects. The aim of this study was to evaluate edema and its control with specific flight stockings, in long-haul flights. In the first part of the study 400 subjects at low-medium risk for DVT were contacted; 28 were excluded for several nonmedical problems; 372 were randomized into 2 groups to evaluate prophylaxis with stockings in 7-8-hour flights; the control group had no prophylaxis. Below-knee, Scholl, Flight Socks, producing 14-17 mm Hg of pressure at the ankle, were used in the treatment group. The occurrence of DVT was evaluated with high-resolution ultrasound scanning (femoral, popliteal, and tibial veins). Edema was assessed with a composite score based on parametric and nonparametric measurements. Part II: In this part of the study 285 subjects at low-medium risk for DVT were included and randomized into 2 groups to evaluate edema prophylaxis in 11-12-hour flights; the controls had no prophylaxis while the prevention group had below-knee, Scholl, Flight Socks (comparable to part I).
                Part 1: DVT evaluation. Of the 184 included subjects in the stockings group and 188 in the control group, 358 (96.2%) completed the study. Dropouts were due to compliance or connection problems. Age/sex distributions were comparable in the groups. Stockings Group: of 179 subjects (mean age 49; SD 7; M:F = 101:78), none had DVT or superficial thromboses. Control Group: of 179 subjects (mean age 48.4; SD 7.3; M:F = 98:81), 4 (2.2%) had a DVT. There were also 2 superficial thromboses. In total, 3.35% (6) subjects had a thrombotic event. The difference (p<0.002) is significant. Intention-to-treat analysis detects 15 failures in the control group (9 lost + 6 thromboses) out of 188 subjects (7.9%) versus 5 subjects (2.7%) in the stockings group (p <0.05). All thrombotic events were observed in passengers sitting in nonaisle seats. The tolerability of the stockings was very good and there were no complaints or side effects. Thrombotic events were asymptomatic. No difference was observed in the distribution of events between men and women. The 3 women who had a thrombotic event were taking low-dose, oral contraceptives. Edema evaluation: The level of edema at inclusion was comparable in the 2 groups. After the flight there was a score of 6.7 (3.1) in controls; in the stockings group the score was 2.9 times lower (p<0.05). The control of edema with stockings was clear considering both parametric (circumference, volume) and nonparametric (analogue scale lines) data. Part II: DVT evaluation. Of the 285 included subjects, 271 (95%) completed the study. Dropouts were due to low compliance or connection problems. Age/sex distributions were comparable in the groups. Stockings Group: of 142 subjects (mean age 48; SD 8; M:F = 89:53), none had DVT or superficial thromboses. Control Group: of 143 subjects (mean age 47; SD 8; M:F = 87:56), 3 had a popliteal DVT and 3 a superficial thrombosis. In total, 4.2% (6) subjects had a thrombotic event. The difference (p<0.02) between groups is significant. Intention-to-treat analysis detects 14 failures in the control group (8 lost + 6 thromboses = 9.7%) versus 6 (all lost = 4.2% in the stockings group) (p<0.05). Four of 6 events (3 DVT + 1 SVT) were observed in non-aisle seats. The tolerability of the stockings was very good. No difference was observed in the distribution of events between men and women. Edema evaluation: The level of edema at inclusion was comparable in the 2 groups. After the flight there was a score of 8.08 (2.9) in controls while in the stockings group the score was 2.56 (1.5) (p < 0.005). In conclusion. Scholl Flight Socks are very effective in controlling edema. Also this type of compression is effective in significantly reducing the incidence of DVT and thrombotic events in low-medium-risk subjects, in long-haul flights.
                Considering these observations, Flight Socks are effective in controlling edema and in reducing the incidence of DVT in low-medium-risk subjects, in long-haul flights (7-11 hours). The LONFLIT1+2 studies have established that in high risk subjects after long flights (> 10 hours) the incidence of deep venous thrombosis (DVT) is between 4% and 6%. The LONFLIT4 study was designed to evaluate the control of edema and DVT in low-medium risk subjects. The aim of this study was to evaluate edema and its control with specific stockings (ankle pressure between 20 and 30 mm Hg) in long-haul flights. The first part of the study included flights lasting 7-8 hours and the second part included flights lasting 11-12 hours. Ultrasound scans were used to assess thrombosis before and after the flights and a composite edema score was used to evaluate edema and swelling. A group of patients with microangiopathy associated to edema (diabetes, venous hypertension, anti-hypertensive treatment) were also included to evaluate the preventive effects of stockings during flight. Part I: DVT evaluation: Of the 74 subjects in the stocking group and 76 in the control group (150), 144 completed the study. Dropouts were due to low compliance or traveling and connection problems. Age and gender distribution were comparable in the 3 groups as was risk factor distribution. In this part of the study there were no DVTs. Edema Evaluation: The level of edema at inclusion was comparable in the two groups of subjects. After the flight there was an average score of 6.9 (1) in the control group. In the stocking group, the score was on average 2.3 (1), three times lower than in the control group (p < 0.05). Part II: DVT evaluation: Of the 66 included subjects in the stocking group and 68 in the control group (134), 132 completed the study. Dropouts were due to low compliance or connection problems. Age and gender distribution were comparable in the two groups. In the stocking group no DVT was observed. In the control group, 2 subjects had a popliteal DVT and 2 subjects had superficial venous thrombosis (SVT); in total 4 subjects (6%) in the control group had a thrombotic event; the incidence of DVT was 3%. The difference (p < 0.02) is significant.
                The composite edema score at inclusion was comparable in the two groups. After the flight there was a score of 7.94 (2) in the control group, while in the treatment group the score was 3.3 (1.2).
                In all these subjects, the level of edema was very high in the control group and significantly lower in the compression stocking group. Stockings are effective in controlling edema during flights even in subjects with microangiopathy and edema. Compression was well tolerated in normal subjects and in patients.
                The Kendall Travel Socks (Tyco Healthcare, Mansfield, MA, USA) which provide 20-30 mm Hg pressure at the ankle, are effective in controlling edema and reducing the incidence of DVT in both low-medium-risk subjects and in patients with microangiopathy and edema in long-haul flights (7-11 hours). The LONFLIT1/2 studies have established that in high-risk subjects after long ( > 10 hours) flights the incidence of deep venous thrombosis (DVT) may be between 4% and 6%. The LONFLIT4 study was aimed at evaluating the control of edema and DVT prevention in low-medium-risk subjects. In this study prophylaxis of edema with specific travel stockings was evaluated in 2 separate studies involving flights lasting 7 hours and 10-12 hours. Part I. Subjects at low-medium risk for DVT were contacted; 55 subjects were excluded for several nonmedical, travel-related problems or inconvenient evaluation time; the remaining 211 were randomized into 2 groups to evaluate prophylaxis with elastic stockings in 7-8-hour, long-haul flights. The control group had no prophylaxis; the treatment group used below-knee, Sigvaris Traveno elastic stockings (Ganzoni, Switzerland, producing 12-18 mm Hg of pressure at the ankle). Color duplex scanning was used to evaluate the possible presence of DVT; edema/swelling were evaluated with a composite score including the presence of edema (with an edema tester), variations in ankle circumference and leg volumetry, subjective swelling, and discomfort (scale ranging from 0 to 10). Results: Of the 103 included subjects in the stockings group and 108 in the control group (total 211), 195 subjects completed the study. Dropouts (16) were due to low compliance or traveling and connection problems. Age, sex distribution, and risk factors distributions were comparable in the 2 groups. Stockings Group: Of 97 subjects none had DVT or superficial thromboses. Control Group: Of 98 subjects none had thrombosis. The level of edema at inclusion was comparable in the 2 groups of subjects. After flights there was an average score of 6.4 (1.3) in the control group, while in the stockings group the score was on average 2.4 (SD 1), 2.6 times lower than in the control group (p < 0.05). In the control group 83% of the subjects had an evident increase in ankle circumference and volume that was visible at inspection and associated with discomfort. The control of edema with stockings was clear, considering both parametric data (circumference and volume) and nonparametric (analogue scale lines) measurements. Part II. In this part of the study 200 subjects at low-medium risk for DVT were contacted; 35 subjects were excluded for several nonmedical, travel-related problems or inconvenient evaluation time; the remaining 165 were randomized into 2 groups to evaluate prevention in flights lasting between 11 and 12 hours. The control group had no prophylaxis; the treatment group used Traveno stockings. Of the 83 included subjects in the stockings group and 82 in the control group (total 165), 146 subjects completed the study. Dropouts were due to low compliance or connection problems. Age/sex distribution were comparable. Of 75 subjects completing the study in the stockings group and 71 in the control group, none had thrombosis. The average level of edema at inclusion was comparable in the 2 groups (1.1). After the flight there was a score of 8.9 (2) in controls; in the stockings group the score was 2.56 (1.3) (p < 0.05). The control of edema and swelling with stockings even after 11 hours of flight was clear, considering both parametric (circumference, volume) and nonparametric (analogue scale lines) measurements. The tolerability of the stockings was very good and there were no complaints or side effects. In conclusion Sigvaris Traveno stockings are very effective in controlling edema in long-haul flights. Graded compression stockings are commonly used to prevent deep-vein thrombosis (DVT) after stroke, but their efficacy in this setting has not been evaluated. Extrapolation of effectiveness from trials in patients undergoing elective surgery may be inappropriate. We undertook a randomized, controlled trial, with blinded data review, in a University hospital Acute Stroke Unit. Patients were allocated to graded compression stockings or to standard care alone. DVT incidence was determined at baseline and at day 7+/-2 by colour-flow Doppler ultrasound. Ninety-eight patients with acute, immobilizing stroke were randomized; 97 had full outcome data. One patient had clinically manifest DVT, and no patient had pulmonary thromboembolism. DVT was detected in 7/65 patients allocated stockings, and 7/32 controls (odds ratio 0.43, 95% CI 0.14-1.36); DVT involving femoral veins was detected in 3/65 and 2/32. In the first week after stroke, radiologically-detected DVT remains common, but is usually clinically silent. Proximal DVT is less common. Graded compression stockings produced a reduction in DVT incidence comparable to that in other patient groups, but the reduction was not statistically significant, and the magnitude of effect size requires confirmation. There is greater doubt over efficacy in early prevention of proximal DVT.
Airline passengers similar to those in this review can expect a substantial reduction in the incidence of symptomless DVT and leg oedema if they wear compression stockings. We cannot assess the effect of wearing stockings on death, pulmonary embolus or symptomatic DVT because no such events occurred in these trials. Randomized trials to assess these outcomes would need to include a very large number of people.