venous blood gas

venous blood gas

Etymology: L, venosus, full of veins; AS, blod + Gk, chaos, gas

the oxygen and carbon dioxide levels in venous blood. Venous blood gas is measured by various methods to assess the adequacy of oxygenation and ventilation and to determine the acid-base status. The oxygen tension of venous blood normally averages 40 mm Hg; the dissolved oxygen content, 0.1% by volume; the total oxygen content, 15.2%; and the oxygen saturation of venous hemoglobin, 75%. The carbon dioxide tension normally averages 46 mm Hg; the dissolved carbon dioxide content, 2.9% by volume; and the total carbon dioxide content, 50%. The normal average pH of venous plasma is 7.37. Venous blood gas in an extremity pertains chiefly to that limb. A sample from a central venous catheter is usually an incomplete mix of venous blood from various parts of the body; a sample of completely mixed venous blood may be obtained from the pulmonary artery for an accurate determination of venous blood gas.