This is the foundational equation linking blood pH, bicarbonate, and CO₂, underlying how every arterial blood gas is interpreted for acid-base status.
Normal pH.
Mild acidemia or alkalemia.
Moderate derangement.
Severe acidemia or alkalemia.
pH is driven by the ratio of bicarbonate to dissolved carbon dioxide.
Rarely — ABG machines report pH directly. But understanding the relationship is essential for recognizing when values don't make sense together, since a mismatch signals a lab or sampling error.
That blood pH is set by the ratio of bicarbonate (the metabolic/base component) to dissolved CO₂ (the respiratory/acid component). Raising bicarbonate or lowering CO₂ raises pH, and vice versa.
About 7.35–7.45. Below 7.35 is acidemia; above 7.45 is alkalemia.
It's the dissociation constant of the carbonic acid/bicarbonate buffer system, the dominant buffer this equation describes.