Table 1. Summary of the main descriptive characteristics of the studies reviewed.

Author (year)	Study location	Details of sample	Method
Scurr et al. (2001)17	London, UK	231 passengers (89 men and 142 women), aged over 50 years, with no history of thromboembolic problems who intended to travel in economy class for at least 8 h in 6 weeks.	Random allocation of passengers into two groups: one group wore class I below-the-knee GCS (20-30 mmHg according to the German Hohenstein compression standard) and the other group did not.
		31 were excluded because of health problems, changes to travel plans, or inability to fulfill commitments.	Flow duration was measured by color or pulsed Doppler ultrasound. Duplex USG was used to assess deep veins before and after the journey by a technician blind to which group the volunteer had been randomized into. Presence of current venous disease or prior thrombosis was assessed by B mode imaging and color flow mapping and veins were assessed with B mode imaging. Blood samples were analyzed for two specific common genetic mutations that predispose to venous thromboembolism, factor V Leiden (FVL) and prothrombin G20210A (PGM), using the PCR technique. A sensitive D-dimer assay was used to screen for recent development of thrombosis.
			In the first 30 volunteers, USG examinations were performed 2 weeks before the journey and again within 2 days of the start of the first flight to provide a control for the interval during which occurrence of spontaneous DVT could be assessed in this population.
Belcaro et al. (2002)18	Italy, ITA	657 passengers of both sexes with moderate DVT risk.	PART I (7-8 h flights): 372 participants randomized into two groups: control group with no prophylaxis and treatment group wearing specially designed GCS (Flight Socks, Scholl producing 14-17 mmHg of pressure at the ankle). High risk criteria: previous episodes of DVT or superficial venous thrombosis, coagulation disorders, severe obesity, limited mobility caused by bone or joint problems, oncological disease during the preceding 2 years, cardiovascular disease, or large varicose veins. Individuals with height exceeding 190 cm and/or weight exceeding 90 kg were excluded. USG scanning protocol (before and after the flight): Sonosite 7.5 to 13 MHz scanners with high resolution linear probes were used to examine the venous system while compressing the major veins (popliteal, femoral). Suggestions for passengers were given to both groups (perform mild exercises, such as walking; drink water and avoid salty foods; avoid excessive baggage that restricts legroom). Edema assessment was based on the edema tests, ankle circumference, and discomfort score.
		PART I: GCS group: 101 men and 78 women, mean age of 49.0+7.0 years. Control group: 98 men and 81 women, mean age of 48.4+7.3 years.	PART II (11-12 h flights): 285 participants randomized into two groups: a control group with no prophylaxis and a treatment group wearing below-the-knee GCS (Flight Socks, Scholl, UK, producing 14-17 mmHg of pressure at the ankle). The same procedures and criteria were adopted as had been used in part I.
		PART II: GCS group: 89 men and 53 women, mean age of 48.0+8.0 years. Control group: 87 men and 56 women, mean age of 47.0+8.0 years.
Cesarone et al. (2003)19	Italy, ITA	284 low-medium risk passengers of both sexes in parts I and II.	PART I (7-8 h flights): 144 participants randomized into two groups: the control group had no prophylaxis and the treatment group wore GCS (Kendall, Travel Socks, Tyco Healthcare, Mansfield, United States) producing 20-30 mmHg of pressure at the ankle, with pressure reducing at the mid-calf. Suggestions for passengers were given to both groups (perform mild exercises, such as walking; drink water and avoid salty foods; avoid excessive baggage that restricts legroom). Ultrasound scanning protocol (before and after the flight): Sonosite 7.5 to 13 MHz scanners with high resolution linear probes (Sonosite, Bothell, United States) were used to examine the venous system while compressing the major veins (popliteal, femoral, tibial). Edema was assessed using a score proposed by Valentino and Irvine, based on a combination of data on ankle circumference (cm) and volume (mL) combined with subjective assessments of edema and discomfort.
		PART I: GCS group: mean age of 46+8.0 years, 37 men and 35 women. Control group: mean age of 47.0+5.0 years, 38 men and 34 women.	PART II (11-12 h flights): 132 participants randomized into two groups: the control group had no prophylaxis and the treatment group wore Kendall below-the-knee GCS. 30 participants with edema-related microangiopathy (10 with diabetes, 10 with chronic venous insufficiency and venous hypertension, and 10 on antihypertensive treatment with ACE inhibitors for hypertension) were included to evaluate the effects of GCS during the flights. The same procedures and criteria were adopted as had been used in part I.
		PART II: GCS group: mean age of 47.0+5.0 years, 34 men and 30 women. Control group: mean age of 46.9+4.0 years, 34 men and 32 women.
Cesarone et al. (2003)20	London, UK	PART I: 266 individuals at low-medium risk of DVT, with 55 excluded for non-medical problems related to their journeys.	PART I (7-8 h flights): 211 participants randomized into two groups: the control group had no prophylaxis and the treatment group wore below-the-knee GCS (Traveno, Sigvaris, Brazil), producing 12-18 mmHg of pressure at the ankle. Criteria for risk of DVT: previous episodes of DVT or superficial thrombosis, coagulation disorders, severe obesity, limited mobility caused by bone or joint problems, oncological disease during the preceding 2 years, cardiovascular disease, or large varicose veins. Individuals with height exceeding 190 cm and/or weight exceeding 90 kg were excluded. Ultrasound digitalization protocol (before and after the flights): Sonosite 7.5 to 13 MHz scanners with high resolution linear probes were used to examine the venous system while compressing the major veins (popliteal, femoral). Suggestions for passengers were given to both groups (perform mild exercises, such as walking; drink water and avoid salty foods; avoid excessive baggage that restricts legroom). Edema was assessed based on the edema test, ankle circumference, edema and discomfort score. The combined edema score was developed based on assessment of parametric data, such as the edema test, change in ankle circumference (cm), volume measurements (in mL or percentage volume), combined with subjective assessment of edema and discomfort (from 0 to 10) defined directly by participants before and after the flights.
		PART II: 200 low-medium risk individuals, with 35 excluded for non-medical reasons.	PART II (11-12 h flights): the remaining 165 participants were randomized into two groups: the control group had no prophylaxis and the treatment group wore below-the-knee Traveno GCS. The same procedures and criteria were adopted as had been used in part I.
Belcaro et al. (2003)14	Italy, ITA	300 individuals at high risk of DVT were contacted and pre-included; 76 were later excluded on the basis of a variety of considerations and the remainder were randomized into two groups (GCS, n = 110, vs. controls, n = 114) to assess prophylaxis with below-the-knee GCS.	Subjects were randomized into two groups to assess prophylaxis with specific GCS during flights lasting 11 h 30 min-12 h. The control group had no prophylaxis. The treatment group wore specially designed GCS (Scholl, UK), producing 14-17 mmHg of pressure at the ankle. Subjects were instructed to put on the GCS before leaving for the airport (3-4 h before the flight). The following were considered high risk for DVT or SVT: coagulation disorders, severe obesity or limited mobility caused by bone or joint problems, oncological disease during the preceding 2 years, cardiovascular disease and large varicose veins. Individuals with height exceeding 190 cm and/or weight exceeding 90 kg were excluded. Sonosite 7.5 to 13 MHz scanners with high resolution linear probes were used to examine the venous system while compressing the major veins (popliteal, femoral, and tibial). D-dimer and fibrinogen tests were conducted before flights (within 12 h) and repeated within 4 h of the end of the flight (Dade Dimertest, latex test, Behring, Germany). Digitalization was performed 90 min before flights and soon after flights (within 90 min). Patients were given suggestions for light exercise (stand up and move legs for 5 to 10 min every hour), avoid baggage between seats, and drink 100 to 150 mL of water regularly every hour. Statistical analysis was conducted using nonparametric tests and analysis of variance, considering subjects who completed the protocol as free from events. The incidence of thrombotic events (DVT, superficial thrombosis) was calculated and compared considering individuals and using intention-to-treat analysis.
			Exclusion criteria were clinical disease requiring treatment, severe bone or joint problems or limited mobility, uncontrolled diabetes, hypertension, obesity, recent thrombosis, and thrombi detected in pre-flight examination.
Hagan et al. (2008)21	Sydney, AUS	50 volunteers (22 pilots and 28 passengers); mean age: 24 to 71 years. GCS group: 26 participants (18 men and 6 women) on outward flight; 24 participants (17 men and 6 women) on return flight.	Twenty-six of the 50 participants wore GCS on the outward flight (group 1; 18 men and 6 women) and the other 24 wore GCS on the return flight (group 2; 17 men and 6 women). At the end of the study, 47 participants (24 in group 1 and 23 in group 2) comprised the study sample.
			Participants were assigned at random to wear low ankle pressure GCS for both outward and return flights. Random allocation was conducted by giving participants sealed envelopes containing instructions according to a computer-generated randomization sequence. The participants wore their normal clothing during the control flight (when GCS were not worn). Both groups were given exercise suggestions.
			The primary outcome was the difference in change in ankle circumference (measured before the flight and after landing) between the control group (without GCS) and treatment group (wearing GCS). Secondary outcomes included pain, discomfort, and feelings of edema in the legs, energy levels, alertness and concentration capacity, each classified one-dimensionally. The scale used was an 11-point numerical classification (NRS).
Charles et al. (2011)13	Wellington, NZL	20 adult participants (13 women), aged 18 to 65 years.	Participants underwent anthropometry (weight, height, and body mass index) and leg measurements to guarantee that the correct size compression stocking would be provided. Which leg the stocking would be worn on was also randomized. Participants were requested to avoid any type of strenuous physical exercise, such as running, rowing, or cycling 24 h before the USG examination. Mild to moderate physical activity such as walking or swimming was considered acceptable.
			USG was used to measure venous blood flow in the popliteal vein. Sonography of the popliteal fossa was used to position the ultrasound probe (USG Aplio XG) and blood flow was measured in the popliteal vein 0, 30, 60, and 120 minutes after the stocking had been put on. The primary outcome variable was maximum systolic velocity in the popliteal vein. Pre-planned secondary result variables were mean flow velocity, total flow volume, and cross-sectional vein area.
Olsen et al. (2019)22	Copenhague, DK	34 participants with mean age of 31 years (range: 25-54 years).	Controlled randomized study with a paired design, in which each participant was randomized to wear a compression stocking on just one leg. The stockings were below-the-knee length and compression class II, corresponding to 23 to 32 mmHg of pressure at the ankle. The study recruited adult men and women aged 18 to 60 years and excluded people with any type of condition that would demand GCS during flights or who had symptomatic arterial insufficiency in the lower limbs.
			Primary outcome: changes in differences in ankle circumference and leg circumference and subtraction of the circumference of the leg wearing the compression stocking, before and after the flight. Secondary outcomes were changes in differences in calf circumference before and after flights and pain and discomfort between legs with and without GCS. Pain and discomfort were also assessed.

GCS = graduated compression stockings; DVT = deep venous thrombosis; SVT = superficial venous thrombosis; PCR = polymerase chain reaction; ACE = angiotensin-converting enzyme; NRS = numerical rating scale; USG = ultrasonography.