Peter A. Stewart

Who was Peter A. Stewart?

Peter Arthur Robert Stewart was a Canadian physiologist who introduced an alternate approach to understanding acid base physiology.

He outlined his model in a paper in 1978, explained it his 1981 book, How to Understand Acid-Base. The book was unavailable for many years, then made available on-line and finally reprinted in 2009, with additional chapters on current applications in clinical medicine.

The Stewart approach models the complex chemical equilibrium system known as acid-base balance. Stewart introduced the term "strong ion difference" or [SID] to mean the concentration of strongly dissociating cations minus the concentration of strongly dissociating anions. He characterised this, the total weak acid concentration and the partial pressure of CO₂ as independent variables and formulated a quartic equation relating [H⁺] to these three independent variables. The quartic equation was solved numerically by computer and has never been validated by titration or phsyiological experiments. The model ignores intracellular and extravascular compartments.