ABSTRACT
Acid-base homeostasis is defined by the pH of blood plasma and by the conditions of the acid-base pairs that determine it. Normally, arterial plasma pH is maintained between 7.35 and 7.45. Because blood plasma is an aqueous solution containing both volatile (carbon dioxide) and fixed acids, its pH will be determined by the net effects of all these components on the dissociation of water.1-3 The determinants of blood pH can be grouped into two broad categories, respiratory and metabolic. Respiratory acid-base disorders are disorders of carbon dioxide (CO2) tension, whereas metabolic acid-base disorders comprise all other conditions affecting the pH. This later category includes disorders of both weak acids (often referred to as buffers, although the term is imprecise) and strong acids and bases (including both organic and inorganic acids). The terms acidemia or alkalemia represent only blood hydrogen concentration and therefore the pH. The terms acidosis and alkalosis refer to the actual physiologic (or pathophysiologic) process.4 Acid-base disorders can be recognized by any of the following conditions:
1. an alteration in the pH of the arterial blood (pH <7.35 signifying an acidemia, whereas a pH >7.45 signifies an alkalemia)
2. an arterial partial pressure of CO2 (PaCO2) outside the normal range (35-45 mmHg). 3. a plasma bicarbonate concentration outside the normal range (22-26 mEq/L) 4. an arterial standard base excess (SBE) ≥5 or ≤−5 mEq/L.
