Blood gas tension Blood gas tension Blood gas tension refers to the partial pressure of gases in blood. There are several significant purposes for measuring gas tension; the most common gas tensions measured are oxygen tension (PO), the carbon dioxide tension (PCO) and carbon monoxide tension (PCO). The subscript "x" in each symbol represents the source of the gas being measured; ""a"" meaning arterial, ""A"" being alveolar, ""v"" being venous, ""c"" being capillary. Blood gas tests (such as arterial blood gas tests) measure these partial pressures. PO – Partial pressure of oxygen at sea level (765 mmHg) in arterial blood is between 75
Arterial blood gas test in a glass syringe and immediately placed on ice. Standard blood tests can also be performed on arterial blood, such as measuring glucose, lactate, hemoglobins, dys-haemoglobins, bilirubin and electrolytes. Derived parameters include bicarbonate concentration, SaO2, and base excess. Bicarbonate concentration is calculated from the measured pH and PCO2 using the Henderson-Hasselbalch equation. SaO2 is derived from the measured PO2 and calculated based on the assumption that all measured hemoglobin is normal (oxy- or deoxy-) hemoglobin. The machine used for analysis aspirates this blood from the syringe and measures the pH and the partial pressures of oxygen and carbon dioxide. The