Relation between pH and ionized calcium in vitro and in vivo in man

Abstract

We investigated the in vitro and in vivo relation between pH and ionized calcium during acute respiratory pH changes. The in vitro slope ΔlgcCa²⁺/ΔpH determined in 20 healthy volunteers after equilibration at two different pCO₂ values was -0.22 ± 0.04 (mean ± 2 SD) for whole blood and -0.24 ± 0.04 (mean ± SD) for serum. The in vivo slope ΔlgcCa²⁺/ΔpH during acute respiratory changes in 10 healthy volunteers was -0.17 ± 0.04 (mean ± 2 SD) for capillary blood.

A mathematical formula which describes the relation between pH and ionized calcium is presented.

Key words:

• acid-base imbalance
• bicarbonate
• blood
• carbon dioxide
• hyperventilation
• ionized calcium
• ion-selective electrodes
• lactate
• water