A not-so-basic case of metabolic alkalosis: an analysis featuring Leendert Paul and emphasizing Occam’s razor

A patient had the onset of a severe degree of metabolic alkalosis associated with a very large daily loss of diarrheal fluid. Because the expected acid-base disorder in this setting is metabolic acidosis, factors that could result in the markedly increased concentration of bicarbonate (HCO₃⁻) in plasma (P₃) were sought. In our approach, there is an emphasis on electroneutrality, mass balance, a quantitative analysis, and the application of basic concepts in physiology at the bedside. We suggest that there were 3 major factors that could explain why the P₃ was so high. First, a severe degree of extracellular fluid volume contraction was probably the most important factor that raised her P₃. Second, there may have been an unusual way to have an electroneutral addition of HCO₃⁻ and removal of chloride ions from her extracellular fluid compartment. Third, the diarrheal fluid could have contained little HCO₃⁻ because of a down-regulated intestinal secretion of HCO₃⁻. This analysis challenges the traditional pathophysiology of metabolic alkalosis.