Prospective Repeated-Measures Study of Popliteal Vein Diameter During the First 48 Hours After Commercial Air Travel to Bogota for a Plastic Surgery Intervention

Inclusion Criteria: * Age 18 to 65 years. * International commercial flight to Bogota with total airborne time of at least 4 hours. * Preflight baseline ultrasound obtained within 24 hours before departure using the standardized protocol. * Arrival ultrasound completed within 2 hours after reaching the study site and before surgery or intravenous fluid therapy. * Availability for 24-hour and 48-hour examinations. * Written informed consent. Exclusion Criteria: * Known current deep venous thrombosis or pulmonary embolism. * Therapeutic anticoagulation at enrollment. * Major lower-extremity venous surgery, active leg infection, or condition preventing popliteal ultrasound. * Surgery, prolonged immobilization, or substantial intravenous fluid administration before completion of the 48-hour measurement. * Pregnancy. * Nondiagnostic baseline examination or inability to reproduce the landmark.