Basic sciences review Acid-Base Balance: Part I. Physiology

Objective: To review the normal human acid-base physiology and the pathophysiology and management of acid-base disturbances in a two-part presentation. Data sources: Articles and published peer-review abstracts and a review of studies reported from 1990 to 2000 and identified through a MEDLINE search of the English language literature on acid-base balance. Summary of review: In a healthy individual the extracellular fluid pH change following addition of a metabolic acid or base, is modified initially by the body’s buffers. Subsequent respiratory compensation, by excretion or retention of CO2, modifies this change before metabolism of the organic acid or renal excretion of the acid or alkali returns the plasma bicarbonate to normal. A primary respiratory acid-base change is modified initially by cellular buffers, with renal compensatory mechanisms adjusting slowly to this change. However, correction of the respiratory pH disorder only occurs with correction of the primary disease process. Conclusions: In man the acid-base balance is maintained and regulated by the renal and respiratory systems, which modify the extracellular fluid pH by changing the bicarbonate pair (HCO3 and PCO2); all other body buffer systems adjust to the alterations in this pair. (Critical Care and Resuscitation 2001; 3: