Factitious Changes in Binding of Oxygen to Hemoglobin When Based on Extracellular pH in the Presence of Certain Blood Additives Like Radiographic Contrast Media

Construction of oxygen-hemoglobin dissociation curves based on extracellular pH and using blood tonometered with 5% CO2, is misleading under certain experimental conditions. These include the presence in blood of poorly penetrating non-ionic molecules like sucrose or poorly penetrating anionic compounds like radiographic contrast materials. False conclusions regarding the position of the oxygen-hemoglobin dissociation curve can result because of the disturbance of the normal pH gradient between plasma and red cell induced by such chemicals.