**3. Individual risk factors**

At least 80% of all passengers (regardless of gender) have at least one identifiable risk factor for VTE (especially PE).

Air travel alone increases the risk of VTE by 1.8 (flight time 8–12 h) to 2.8 times (>12 h), factor V Leiden mutation by 13.6 times, and oral contraceptives even up

**155**

*Vein Thrombosis Risk in Women and Travel DOI: http://dx.doi.org/10.5772/intechopen.92229*

The predisposing factors to VTE are mainly:

• Pregnancy and the first month after giving birth.

• Individual or family history of VTE.

• Presence of varicose veins.

VTE increased by 10 times.

**3.1 Risk factors in association to flights**

**3.2 Factors that may affect passengers traveling by plane**

do not significantly increase the risk for air travelers.

Already in 2003, Martinelli et al. referred to the increase in VTE risk on long-haul flights (>8 h) in connection with congenital and acquired thrombophilia (risk increase by 16 times) and oral contraceptives (risk increase by 14 times). According to a recent calculation model by Kuipers et al. based on data from a previous cohort study including employees from international companies, the estimated absolute risk for symptomatic VTE in women after long-distance flights (>4 h) and oral contraceptive use was 1/259 flights and with hormone replacement therapy 1/405

• Oral estrogen-containing contraceptives: increased risk of VTE up to 20 times.

Women with thrombophilia that had surgery or trauma within the last 3 months,

and risk of

taking oral contraceptives or being under hormone replacement therapy.

• Height >1.90 or <1.60 m increased risk of VTE by 4–5 times [17–19].

• Obese patients with body mass index (BMI) greater than 30 kg/m<sup>2</sup>

Travel participation can expose passengers to a variety of risk factors that may have impact on their health. Health professionals can obtain information from the International Maritime Health Association and Aerospace Medical Association website (www.imha.net and www.asma.org), respectively.

At a normal altitude of 36,000–40,000 feet, the cabin pressure equals that of 6000–8000 feet at sea level and is therefore at low levels resulting in a decrease in oxygen supply [20–22]. This is not dangerous for healthy people unless there are cardiopulmonary problems and hematological disorders, for example, sickle cell anemia. These problems are particularly pronounced when the airplane rises (because of the reduction in air pressure in the cabin, outflow from the middle ear and nasal cavities) and also during the cathode of the plane where there is an increase in air pressure in the cabin, inlet air, and the middle ear to balance the pressures. The reduced air humidity in the flight cabin of 10–20% (optimally

to 40 times; BMI > 30 kg/m2

flights [2, 8, 17, 19].

• Recent surgery.

• Cancer diseases.

• Obesity.

*3.2.1 Cabin pressure*

### *Vein Thrombosis Risk in Women and Travel DOI: http://dx.doi.org/10.5772/intechopen.92229*

*Tourism*

travel [9, 10].

**2. Epidemiology**

necessary [13].

duration [13–16].

**3. Individual risk factors**

able risk factor for VTE (especially PE).

of venous thrombosis is an exclusive phenomenon of all travel-related thromboses, which play a role in clot formation. Stasis during the journey, the pressure of the "narrow" seat on the vessels, dehydration, and maybe reduced oxygen saturation are some of the factors that symptoms of venous thrombosis or pulmonary embolism do not always appear immediately. They may occur up to 8 weeks after the

Regardless of whether it is a trip by car, train, bus, or plane, travel thrombosis (for flight travel also named "economy class syndrome") will manifest up to 4 weeks after traveling according to the British Committee for Standards in Hematology up to 6 weeks after long-haul flights [9, 10]. It is estimated that 5–15% of all proven venous thromboembolism (VTE) occur in connection with long-haul flights [11, 12]. The risk is highest in the first week and then decreases continuously; the majority (approx. 60–75%) of all travel thrombosis are asymptomatic/low-symptom thrombosis exclusively located in the lower limbs, which is perceived as "unpleasant leg

The clinical relevance of these asymptomatic thromboses is questionable, but they may be the origin for the manifestation of deep vein thrombosis. So far, there is no prospective, controlled study with a sufficient number of cases (adequate statistical power) that proves an evidence-based association between air travel and the risk of venous thromboembolism (VTE). In order to demonstrate a significantly increased risk, a study including around 1 million passengers (+ controls) would be

The risk for VTE mainly depends on the flight duration, the number of flights within 3–4 weeks, and risk factors of each individual predisposing to VTE. According to meta-analyses from case-control studies, long-haul flights increase the risk of VTE by two to four times within the first 4 weeks. For every 2 h of extended flight time, the VTE risk may increase by 26%. The risk of VTE is not increased in healthy passengers without risk factors and a flight duration of less than 3–4 h. It should be taken into account in this context that the basic risk for VTE in healthy women under 35 years without hormone intake is 1–2/10,000/ years and increases fourfold after the age of 40 [13–16]. Young women (<30 years) are up to three times more likely to experience VTE than young men. An observational study from France analyzed 116 pulmonary embolisms (PE) over a period of 13 years, which occurred immediately after landing. With approximately the same gender distribution of passengers, 78% of all PE affected women [13–16]. Overall, the incidence of PE was 0.61/1,000,000 female passengers (0.2/1,000,000 male passengers). With a flight distance of more than 10,000 km, this risk rises to 7.2/1,000,000 female passengers. According to another study to 4.8/1,000,000 female passengers with a flight duration over 12 h, the total rate of VTE in healthy women without oral contraceptives is estimated 1/5000 regardless of the flight

At least 80% of all passengers (regardless of gender) have at least one identifi-

Air travel alone increases the risk of VTE by 1.8 (flight time 8–12 h) to 2.8 times (>12 h), factor V Leiden mutation by 13.6 times, and oral contraceptives even up

swelling/edema" due to long sitting with the legs hanging down [11, 12].

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to 40 times; BMI > 30 kg/m<sup>2</sup> do not significantly increase the risk for air travelers. Already in 2003, Martinelli et al. referred to the increase in VTE risk on long-haul flights (>8 h) in connection with congenital and acquired thrombophilia (risk increase by 16 times) and oral contraceptives (risk increase by 14 times). According to a recent calculation model by Kuipers et al. based on data from a previous cohort study including employees from international companies, the estimated absolute risk for symptomatic VTE in women after long-distance flights (>4 h) and oral contraceptive use was 1/259 flights and with hormone replacement therapy 1/405 flights [2, 8, 17, 19].

The predisposing factors to VTE are mainly:


Women with thrombophilia that had surgery or trauma within the last 3 months, taking oral contraceptives or being under hormone replacement therapy.

