title: Venous thrombosis after long-haul flights.
abstract: BACKGROUND
  The risk for venous thromboembolism after long-haul flights represents a controversial issue. The aim of our study was to assess the incidence of venous thrombosis associated with long-haul flights in a prospective, controlled cohort study.
  
  
  METHODS
  We included 964 passengers returning from long-haul flights (flight duration, > or =8 hours) and 1213 nontraveling control subjects. We excluded participants who were being treated with anticoagulant drugs or who used compression stockings. Main outcome measures were the incidence of ultrasonographically diagnosed thrombosis in the calf muscle and deep veins, symptomatic pulmonary embolism, and death.
  
  
  RESULTS
  We diagnosed venous thrombotic events in 27 passengers (2.8%) and 12 controls (1.0%) (risk ratio [RR], 2.83; 95% confidence interval [CI], 1.46-5.49). Of these, 20 passengers (2.1%) and 10 controls (0.8%) presented with isolated calf muscle venous thrombosis (RR, 2.52; 95% CI, 1.20-5.26), whereas 7 passengers (0.7%) and 2 controls (0.2%) presented with deep venous thrombosis (RR, 4.40; 95% CI, 1.04-18.62). Symptomatic pulmonary embolism was diagnosed in 1 passenger with deep venous thrombosis (P =.44). All of these individuals had normal findings at baseline ultrasonography. Passengers with isolated calf muscle venous thrombosis or deep venous thrombosis had at least 1 risk factor for venous thrombosis (>45 years of age or elevated body mass index in 21 of 27 passengers). The follow-up after 4 weeks revealed no further venous thromboembolic event.
  
  
  CONCLUSIONS
  Long-haul flights of 8 hours and longer double the risk for isolated calf muscle venous thrombosis. This translates into an increased risk for deep venous thrombosis as well. In our study, flight-associated thrombosis occurred exclusively in passengers with well-established risk factors for venous thrombosis.
authors.affiliation: Division of Vascular Medicine, Department of Internal Medicine III, University of Dresden Medical School, Germany. tho_schwartz@hotmail.com
authors.forename: Thomas
authors.initials: T
authors.lastname: Schwarz
authors.forename: Gabriele
authors.initials: G
authors.lastname: Siegert
authors.forename: Wolfram
authors.initials: W
authors.lastname: Oettler
authors.forename: Kai
authors.initials: K
authors.lastname: Halbritter
authors.forename: Jan
authors.initials: J
authors.lastname: Beyer
authors.forename: Roswitha
authors.initials: R
authors.lastname: Frommhold
authors.forename: Siegmund
authors.initials: S
authors.lastname: Gehrisch
authors.forename: Florian
authors.initials: F
authors.lastname: Lenz
authors.forename: Eberhard
authors.initials: E
authors.lastname: Kuhlisch
authors.forename: Hans-Egbert
authors.initials: HE
authors.lastname: Schroeder
authors.forename: Sebastian M
authors.initials: SM
authors.lastname: Schellong
mesh_terms: D000293:Adolescent; D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D000401:Aircraft; D016022:Case-Control Studies; D005260:Female; D006801:Humans; D015994:Incidence; D008297:Male; D008875:Middle Aged; D018482:Muscle, Skeletal / Q000098:blood supply; D011446:Prospective Studies; D011655:Pulmonary Embolism / Q000453:epidemiology* / Q000209:etiology; D012107:Research Design; D012307:Risk Factors; D015983:Selection Bias; D013577:Syndrome; D014195:Travel; D020246:Venous Thrombosis / Q000453:epidemiology* / Q000209:etiology