**6.5 What causes vein thrombosis and pulmonary embolism?**

Clots can be formed at various points, in the legs and in the thighs, with similar problems. All veins have valves every 10–12 cm, and some of them can form clots.

If the clot stays there, then the member has swelling and pain. Small fever may occur, and the member may be warmer. The most serious complication, however, is pulmonary embolism (PE), which occurs in 25% of cases with thrombosis. If the clot is detached, it is transported through the veins and eventually clamped to the lung. The condition can appear immediately or even 2 weeks after the long journey. The most common symptoms to suspect pulmonary embolism are sudden chest pain, dyspnea, dizziness, fever, hemoptysis, etc. Symptoms depend on the size of the plunger and the size of the vessel, the age of the person, if he or she is suffering from other diseases, etc. Immediate admission to the hospital is required for diagnosis and special treatment. In rare cases, a part of the clot can cause embolism in other organs, such as the brain.

People predisposed to thrombosis, as well as patients with previously mentioned illnesses, should be consulted by their physician prior to long journeys. In these individuals, it is recommended to inject antithrombotic (heparin) once 24 h before flight. It is also recommended to take aspirin before takeoff, except for pregnant women who are not allowed [5, 53–56].
