Venous hemorrhage
Venous hemorrhage is a darker red, a steady and copious flow. The colour darkens still further from inordinate oxygen desaturation when blood loss is severe, or in respiratory depression or obstruction. Blood loss is particularly rapid when large veins are opened, e.g. common femoral or jugular. Venous bleeding can be under increased pressure as in asphyxia, or from ruptured varicose veins. Portal vein pressures are high enough to cause rapid blood loss, especially in portal hypertension with esophageal varices. Pulmonary artery hemorrhage is dark red (venous blood) at around 30 mmHg (4 kPa), whereas bleeding from the pulmonary veins is bright red (oxygenated).