Arterial blood gas is a test that can be done to determine the amount of oxygen, carbon dioxide and bicarbonate in the blood, as well as the pH of the blood.
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2 Sample collection 3 Blood gas machines 4 Normal values and interpretation |
Brief theory
Arterial blood is taken with a syringe or out of an arterial line. The sealed syringe is taken to a blood gas machine. The machine aspirates this blood from the syringe and measures the partial pressures of oxygen and carbon dioxide, the bicarbonate concentration and pH. It may also measure other information such as glucose or lactate levels, and haemoglobin saturation.
The results are received quickly (usually within five minutes of putting the sample through) and can be interpreted. They determine the acid-base status of the person (whether they're acidotic or alkalotic), the cause (respiratory due to increased/decreased CO2, or metabolic such as ketoacidosis), and whether or not there's been any compensation by the body.
Other results can determine oxygen saturation, blood sugar status, and other metabolites in the blood.
Lactate levels are often included on blood gas machines in neonatal wards; infants often have elevated lactic acid.
(acid/alk, resp/meta, comp/non-comp, CO, CN-, venous)Sample collection
Syringes used for blood gas sampling contain heparin to keep the blood from becoming coagulated. The blood sample must be promptly transported chilled with ice to a blood gas machine.Blood gas machines
(mix blood, ion-selective electrodes, additional tests, physical description of machines ?history)Normal values and interpretation
In most people, arterial oxygen is at about 95 mmHg, carbon dioxide is about 40 mmHg, normal pH ranges from 7.35 to 7.45, and HCO3- about 24 mmol/L.
