Respiratory Acid-base Disturbances

Abstract

The hydrogen ion concentration of plasma at any moment is a function of the ratio between the partial pressure of carbon dioxide and the bicarbonate concentration. Therefore, the only way a change in plasma acidity can occur is through a change in the partial pressure of carbon dioxide (\( {P_{{C{O_2}}}} \)) or bicarbonate concentration. Primary changes in the \(\left( {{P_{c{o_2}}}} \right)\) are the hallmark of respiratory acid-base disturbances. When \(\left( {{P_{c{o_2}}}} \right)\) is above normal the disorder is called respiratory acidosis and when below normal is denoted as respiratory alkalosis. Under normal conditions these disturbances give rise to physiologic responses that lead to changes in the plasma bicarbonate concentration; primary hypocapnia is followed by a secondary decreaspe in bicarbonate, whereas primary hypercapnia is followed by a secondary rise in plasma bicarbonate (\(\left( {{P_{c{o_3}}}} \right)\)). Thus, the degree to which plasma acidity is altered in response to primary changes in the partial pressure of CO2 is a reflection not only of the initiating change, but also of the secondary change in the plasma bicarbonate concentration (1–4).