Peter Arthur Robert Stewart (1921–1993) was a Canadian physiologist who introduced an alternate approach to understanding acid–base physiology.

[2] 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 impact of the Stewart analysis has been slow in coming but there has been a recent resurgence in interest, particularly as this approach provides explanations for several areas which are otherwise difficult to understand (e.g., dilutional acidosis, acid–base disorders related to changes in plasma albumin concentration).

[4] Ole Siggaard-Andersen, author of the textbook, the Acid–Base Status of the Blood, wrote, "the Stewart approach is absurd and anachronistic.

This naturally yielded an equation that phrased [H+] in terms of [SID], ATOT and PCO₂, but people take it as support for the characterisation of variables as dependent and independent.