Clinical Significance

Blood Gases

It is important for the enzyme and electrolyte systems to maintain the correct pH of the blood. The pH of blood is regulated chemically by buffers, by the lungs via excretion of CO₂, and by the kidneys by excretion of acid or reabsorption of base. The most important pH buffer in the blood is the carbonic acid-bicarbonate system. In order to evaluate the system, pH and pCO₂ are measured.

pH
Used for the evaluation of the acid-base balance. Acidity or basicity is a sign of a disorder that can be of either respiratory or metabolic origin.

pCO₂
CO₂ is the waste product from metabolism and is excreted through the lungs. CO₂ readily diffuses from the lung capillaries to the alveoli to be exhaled. pCO₂ is used for evaluation of ventilation and the acid-base statusm, as it is a measure of the ability of the lungs to excrete carbon dioxide. pCO₂ therefore gives an indication of how well the lungs are functioning. pCO₂ is an important parameter for the evaluation of artificial/assisted ventilation therapy.

pO₂
Used for a general evaluation of oxygen uptake in the lungs. Oxygen is carried to tissues as oxyhemoglobin in red blood cells. A small amount in dissolved in the plasma and is measured as pO₂. A low pO₂ indicates either poor perfusion across the alveolar walls or poor ventilation.

sO₂
sO₂ is a measure of the degree to which Hb is carrying oxygen, i.e. the percentage of hemoglobin which binds O₂ compared to the amount which potentially could carry O₂. sO₂ can be used to evaluate whether the oxygen uptake in the lungs is optimal and sufficient.