RESPIRATORY ACIDOSIS is the abnormal physiologic state which occurs when the blood level of dissolved CO2, and consequently of carbonic acid, is elevated. The term respiratory acidosis will be used to apply even to those conditions in which the blood is not abnormally acid in reaction, following a clinical usage of the term. Nevertheless it should be clear that the major problem in hypercapnic states lies in the elevation of CO2 tension in blood and tissues, rather than in the varying degree of acidosis of the blood.
Respiratory acidosis is unique in that the acid (as dissolved CO)2 penetrates cells and cerebrospinal fluid rapidly, rather than with the slower movement characteristic of ions. Consequently intracellular acidosis occurs more rapidly.
Alveolar ventilation and CO2 production determine the alveolar and therefore arterial and tissue levels of Pco2. The following equation expresses this relationship in simplified form.
where Vco2 is the CO2 output