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 (P_xO₂), the carbon dioxide tension (P_xCO₂) and carbon monoxide tension (P_xCO). 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.

Oxygen tension

P_aO₂ — Partial pressure of oxygen at sea level (765 mmHg) in arterial blood is between 75 mmHg and 100 mmHg.

P_vO₂ — Oxygen tension in venous blood at sea level is between 30 mmHg and 40 mmHg.

Carbon dioxide tension

Carbon dioxide is a by-product of food metabolism and in high amounts has toxic effects including: dyspnea, acidosis and altered consciousness.

P_aCO₂ — Partial pressure of carbon dioxide at sea level (765 mmHg) in arterial blood is between 35 mmHg and 45 mmHg.

Blood gas

A blood gas test is a blood test that measures blood gas tension values as indicators of ventilation, respiration, and oxygenation. The source of the blood is reflected in the name of each test; arterial blood gases come from arteries, venous blood gases come from veins and capillary blood gases come from capillaries.

Values measured

Purposes for testing

Abnormal results

Abnormal results may be due to a wide range of diseases, including poisoning and trauma as well as lung, kidney, or metabolic diseases. Head or neck injuries or other injuries that affect breathing can also lead to abnormal results.

References

Arterial blood gas

An arterial blood gas (ABG) test is a blood gas test of blood from an artery; it is thus a blood test that measures the amounts of certain gases (such as oxygen and carbon dioxide) dissolved in arterial blood. An ABG test involves puncturing an artery with a thin needle and syringe and drawing a small volume of blood. The most common puncture site is the radial artery at the wrist, but sometimes the femoral artery in the groin or other sites are used. The blood can also be drawn from an arterial catheter. An ABG test measures the blood gas tension values of arterial oxygen tension (PaO₂), arterial carbon dioxide tension (PaCO₂), and acidity (pH). In addition, arterial oxygen saturation (SaO₂) can be determined. Such information is vital when caring for patients with critical illness or respiratory disease. Therefore, the ABG test is one of the most common tests performed on patients in intensive care units (ICUs). In other levels of care, pulse oximetry plus transcutaneous carbon dioxide measurement is an alternative method of obtaining similar information less invasively.