a riskDeep vein thrombosis and pulmonary embolism

A clot forms in a deep vein, usually in the leg, and part of it travels to the lung. Surgery raises the risk and long-haul flight raises it, and a patient who has both in the same fortnight carries both. The CDC states that air travel and surgery independently increase the risk, and that travel after surgery increases it further because it requires sitting still for long periods in a hypercoagulable state.

The travel half of the risk has been measured, and it is smaller than the coverage of it suggests. A 2022 systematic review found 18 studies addressing the question and concluded that the association between venous thromboembolism and length of travel is real but mild to moderate, with odds ratios between 1.1 and 4. It identified a dose-response relationship — a 26% higher risk for every two hours of air travel after the first four — and rated the quality of evidence for both travel length and for thromboprophylaxis as low. Graduated compression stockings were the one measure shown to work.

The surgical half is larger and is procedure-specific; it is carried on the records for the operations themselves.

Inference — the combination is what has no published figure. Nobody has measured the rate of venous thromboembolism in patients who had major surgery and then flew home inside two weeks, because no registry follows a patient across that border. The 2026 Birmingham series of UK patients readmitted after cosmetic surgery abroad records venous thromboembolism among the complications seen, without a denominator to put it over.

Prophylaxis after major surgery is compression, early mobilisation and, for higher-risk operations, an anticoagulant for a defined period after discharge. That last one is where a cross-border episode strains: the drug is prescribed in one country, dispensed for a fixed number of days, and the patient goes home to a system that has no record of when the course started. Presentation is a swollen painful calf, or sudden breathlessness and chest pain, and it is usually to an emergency department with no note of the operation.

As of 16 September 2026 the measured figure this site carries is the 26% increase in risk per two hours of flying beyond four, from the 2022 review, with its own authors' rating of low evidence quality. The combined surgical-plus-flight figure is not measured.