Coronary bypass surgery involves bypassing constricted arteries with venous grafts. Other less common symptoms include nausea, vomiting, pancreatitis, diabetes or recurrent venous thrombosis. Wet gangrene usually develops rapidly due to blockage of venous (mainly) or arterial blood flow. Administration of high percentage oxygen is recommended for both venous and arterial air embolism. Other risks include stroke and venous thromboembolism. Obesity has long been regarded as a risk factor for venous thrombosis. They may become acutely inflamed as a result of torsion (twisting) or venous thrombosis. Pleural effusion may also be noticed, which is due to pulmonary venous hypertension. Portal hypertension is defined as a hepatic venous pressure gradient. Occasionally they result from chronic venous insufficiency. There are three main types&colon; neurogenic, venous, and arterial. The clinical presentation of a venous air embolism may be silent. Short stature decreases the risk of venous insufficiency. It may be associated with pain and other signs of chronic venous insufficiency. Entry of air into venous circulation has the potential to cause a venous air embolism.