In humans the respiratory system and the circulatory system work hand in hand to supply the cells with oxygen and dispose of carbon dioxide. The gas exchange takes place in the lungs following a concentration gradient. O2 is taken up via the alveoli as its partial pressure in the venous blood is lower than in the alveolar air. This freshly oxygenated arterial blood will then supply the cells of the body with oxygen for cellular respiration. CO2, which is produced by the cells during this process, has to be removed from the body. It is transported to the lungs by the blood (venous) and following the concentration gradient diffuses out of the blood via the alveolar membrane. So in healthy individuals arterial blood has a high O2 and a low CO2 partial pressure.
In critically ill individuals or individuals with respiratory diseases these parameters often differ from the normal values. Thus it is important to be able to monitor these parameters and interpret them correctly.
Arterial blood gas (ABG) analysis is used to determine the partial pressure of oxygen and carbon dioxide in arterial blood as well as its pH. The pH of blood in a healthy individual is between 7.35 and 7.45. It is regulated by buffer systems in the blood, the one with the highest capacity being the bicarbonate buffer system.
Trained medical staff is able to interpret parameters in the results of an ABG analysis and relate them to different medical conditions.
For further reading see:
https://www.thoracic.org/professionals/clinical-resources/critical-care/clinical-education/abgs.php
