Evaluating acid-base disorders

Abstract

Sir, In their review of acid-base disturbances in cholera, Zalunardo et al. illustrate the limitations of the conventional approach when dealing with complex clinical situations.1 The patient with cholera was thought to have both contraction metabolic alkalosis and metabolic acidosis from bicarbonate losses in diarrhoea, with the combination leading to a relatively normal arterial pH, PCO2, and plasma bicarbonate concentration. A different approach to these issues was introduced by Stewart2,,3 and supported by Fencl4 and Kellum,5 among others. In this development, acid-base disorders can be considered to arise from alterations in three independent variables: the plasma strong ion difference (SID), the plasma concentration of weak acids (in most situations the plasma concentration of albumin and phosphate), and the arterial partial pressure of carbon dioxide (PCO2). From the data provided, an alternative explanation for the clinical problem presented would be that the relatively normal pH, PCO2, and plasma bicarbonate concentration result from a combination of metabolic alkalosis resulting from an elevated SID, offset by a metabolic acidosis from the markedly increased plasma protein concentration. While the marked reduction in ECF helps to explain the acid-base abnormalities identified, …