Blood gas analysis


In a blood gas analysis (short: BGA) the concentrations of certain gases in the blood are measured. These gases, which include oxygen (O2) and carbon dioxide (CO2), have a certain partial pressure (pO2 and pCO2) in the blood, which should normally be stable and thus maintain the vitality of the organism. In addition, other parameters are determined, such as the current oxygen saturation in the blood, the acid-base balance using bicarbonate (current or standard bicarbonate (aHCO3 or SBC or StHCO3)) and base deviation (BE= base excess) as well as the pH value of the blood.

The bicarbonate value and the base excess are not measured directly, but calculated and always refer to standardized values in the blood (temperature: 37°, pCO2: 40mmHg, fully saturated blood). Furthermore, the haemoglobin value, lactate values or blood sugar values can be determined during a blood gas analysis. In special cases, e.g. if smoke poisoning or similar is suspected.

the BGA can also be used to determine the concentration of carbon monoxide or nitrogen. You will find general information under: Blood analysisBlood gas analysis is part of standard clinical diagnostics in intensive care units and is performed daily (or several times a day). Particularly in the case of severe respiratory diseases, it can quickly provide information about an increasing deterioration and the necessary measures can be taken quickly. Blood gas analysis is also carried out regularly when monitoring anaesthesia.

Physiological backgrounds

There should always be a constant concentration of hydrogen ions in the blood and thus a stable pH value of 7.36 – 7.44. For this purpose, the body has several buffer systems through which excess hydrogen ions can be excreted or, in the event of a deficiency, hydrogen ions can also be retained. The most important buffer system is the bicarbonate balance, which can absorb hydrogen ions and then decompose via carbonic acid to water and carbon dioxide (which is exhaled).

In case of a lack of hydrogen ions, however, the carbon dioxide constantly produced in the body during cell respiration can also be coupled to water with the help of enzymes or spontaneously and then react via the back reaction to bicarbonate and a hydrogen ion. Other important buffer systems are the haemoglobin buffer, the phosphate buffer and the protein buffer. The regulation of the pH value in the blood therefore involves the buffer system itself, but also the exhalation of carbon dioxide via the lungs and the excretion of hydrogen ions via the kidneys.

In this regulatory circuit there are therefore many starting points that can cause the system to shake if it loses its normal function. For example, there are metabolic (metabolic) disorders in which an imbalance of hydrogen ions exists due to a malfunction in the buffer systems. On the other hand, there are respiration-related (respiratory) disorders, in which there is an increased or reduced exhalation of carbon dioxide. Of course there can also be a fault in both systems, here we speak of a mixed disorder.