Bench-to-bedside review: Fundamental principles of acid-base physiology

Table 1 Classification of acid–base disorders

Stewart variables/constants	Classification	Acidosis	Alkalosis
PCO₂	Respiratory	↑	↓
[SID⁺]	Metabolic
Chloride excess/deficit		↓	↑
Strong ion gap		↑
[A_TOT]^a	Modulator
Extracellular
Albumin		↑	↓
Phosphate		↑	↓
Intracellular^b
Hgb		↑	↓
DPG		↑	↓
Rate constants	Modulator
(K_a, K'_w, K'₁, K₃, and SCO₂)
Temperature^c		↓	↑

^aChanges in [A_TOT] modulate and do not necessarily cause acid–base disorders. ^bResult in negligible changes in pH. ^cMay be clinically significant in hypothermia. [A_TOT], total concentration of weak acids; DPG, 2,3-diphosphoglycerate; Hgb, hemoglobin; PCO₂, partial CO₂ tension; SCO₂, CO₂ solubility; SID⁺, strong ion difference.

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