Table 2.

Risk levels categorized prior to operation^4,5)

	Level	Presentation
1st	Low risk	No risk factor and surgery with heparin
2nd	Moderate risk	Surgery without heparin for malignant or benign lung disease
3rd	High risk	With previous venous thromboembolism or thrombophilia
4th	Very high risk	With preoperative detected venous thromboembolism