A blood gas test or blood gas analysis tests blood to measure blood gas tension values and blood pH. It also measures the level and

base excess In physiology, base excess and base deficit refer to an excess or deficit, respectively, in the amount of base present in the blood. The value is usually reported as a concentration in units of mEq/L (mmol/L), with positive numbers indicating an ...

bicarbonate In inorganic chemistry, bicarbonate (IUPAC-recommended nomenclature: hydrogencarbonate) is an intermediate form in the deprotonation of carbonic acid. It is a polyatomic anion with the chemical formula . Bicarbonate serves a crucial bioche ...

. The source of the

blood Blood is a body fluid in the circulatory system of humans and other vertebrates that delivers necessary substances such as nutrients and oxygen to the cells, and transports metabolic waste products away from those same cells. Blood is com ...

is reflected in the name of each test;

arterial blood Arterial blood is the oxygenated blood in the circulatory system found in the pulmonary vein, the left chambers of the heart, and in the artery, arteries. It is bright red in color, while venous blood is dark red in color (but looks purple through ...

gases come from

arteries An artery () is a blood vessel in humans and most other animals that takes oxygenated blood away from the heart in the systemic circulation to one or more parts of the body. Exceptions that carry deoxygenated blood are the pulmonary arteries in ...

venous blood Venous blood is deoxygenated blood which travels from the peripheral blood vessels, through the venous system into the right atrium of the heart. Deoxygenated blood is then pumped by the right ventricle to the lungs via the pulmonary artery whi ...

gases come from veins and capillary blood gases come from

capillaries A capillary is a small blood vessel, from 5 to 10 micrometres in diameter, and is part of the microcirculation system. Capillaries are microvessels and the smallest blood vessels in the body. They are composed of only the tunica intima (the in ...

. The blood gas tension levels of

partial pressure In a mixture of gases, each constituent gas has a partial pressure which is the notional pressure of that constituent gas as if it alone occupied the entire volume of the original mixture at the same temperature. The total pressure of an ideal g ...

s can be used as indicators of ventilation, respiration and oxygenation. Analysis of paired arterial and venous specimens can give insights into the aetiology of acidosis in the newborn.

Values measured

Blood samples for testing are taken from arterial blood by a radial artery puncture, and from venous blood by

venipuncture In medicine, venipuncture or venepuncture is the process of obtaining intravenous access for the purpose of venous Sampling (medicine)#blood, blood sampling (also called ''phlebotomy'') or intravenous therapy. In healthcare, this procedure is p ...

. Samples of capillary blood are taken using a lancet and

capillary action Capillary action (sometimes called capillarity, capillary motion, capillary rise, capillary effect, or wicking) is the process of a liquid flowing in a narrow space without the assistance of external forces like Gravitation, gravity. The effe ...

. Capillary samples from the earlobe or the fingertip can be used to predict blood pH and the arterial partial pressure of carbon dioxide in the blood. Samples from the earlobe are seen to be a more appropriate site for the prediction of the arterial partial pressure of oxygen. Blood gas tests also measure the levels of

and standard bicarbonate,

oxygen saturation Oxygen saturation (symbol SO2) is a relative measure of the concentration of oxygen that is Dissolution (chemistry), dissolved or carried in a given medium as a proportion of the maximal concentration that can be dissolved in that medium at the g ...

, and pH. Typically, an arterial blood gas test is used more often than venous blood gas tests.

Clinical significance

Blood gas tests can be used in the

diagnosis Diagnosis (: diagnoses) is the identification of the nature and cause of a certain phenomenon. Diagnosis is used in a lot of different academic discipline, disciplines, with variations in the use of logic, analytics, and experience, to determine " ...

of a number of acidosis conditions such as lactic,

metabolic Metabolism (, from ''metabolē'', "change") is the set of life-sustaining chemical reactions in organisms. The three main functions of metabolism are: the conversion of the energy in food to energy available to run cellular processes; the ...

, and

respiratory acidosis The respiratory system (also respiratory apparatus, ventilatory system) is a biological system consisting of specific organs and structures used for gas exchange in animals and plants. The anatomy and physiology that make this happen varies gr ...

, diabetic ketoacidosis, and also of respiratory alkalosis. Particularly, umbilical cord blood gas analysis can give an indication of preceding fetal hypoxic stress. In combination with other clinical information, normal paired arterial and venous cord blood gas results can usually provide a robust defence against a suggestion that an infant had an intrapartum hypoxic-ischaemic event. Abnormal results may be due to a wide range of diseases, including poisoning and trauma as well as lung, kidney, or metabolic diseases. Drug overdose and uncontrolled diabetes may be determined from abnormal results. Head, neck or injuries that affect breathing can also lead to abnormal results.

References

External links

Blood Gas Interpretation
- Simplified process for blood gas interpretation. {{Respiratory system procedures Respiratory therapy Mechanical ventilation Pulmonology