arterial blood gas

An arterial blood gas is a snapshot of how well the lungs and the body's chemistry are working, taken from a small sample of blood drawn from an artery rather than a vein. It is one of the most informative bedside tests in respiratory and critical care.

From that sample the analyzer reports the partial pressures of oxygen and carbon dioxide, the blood pH, and the bicarbonate level, among other values. Together these reveal how well oxygen is being taken up, how effectively carbon dioxide is being cleared, and whether the blood is too acidic or too alkaline, allowing the cause of an acid-base disturbance to be worked out.

Arterial sampling is used because arterial blood reflects what is leaving the lungs and reaching the tissues, unlike venous blood. The puncture is briefly painful and is usually taken from the wrist; pulse oximetry can track oxygen saturation non-invasively but cannot replace the carbon dioxide and pH information an arterial gas provides.