[Base excess] and [strong ion difference] during O2-CO2 exchange

Area of Science:

• Physiology
• Biochemistry
• Medical Diagnostics

Background:

• Detecting tissue metabolic acid production or uptake is crucial for understanding physiological states like endotoxemia, exercise, and shock.
• Traditional methods like whole blood base excess (BE) have limitations in accuracy, particularly with venous blood due to hypercarbia and hemoglobin dilution.
• The strong ion difference (SID) offers an alternative acid-base analysis approach, but its application in assessing arteriovenous differences requires further investigation.

Purpose of the Study:

• To test the hypothesis that arteriovenous strong ion difference (a-v [SID]p) can be used to detect metabolic acid uptake or production by tissues.
• To evaluate the relationship between a-v [SID]p and changes in oxygenated hemoglobin ([HbO2]) during simulated O2-CO2 exchange.
• To assess the potential of a-v [SID]p as a tool for examining arteriovenous differences in metabolic acid, building upon base excess concepts.

Main Methods:

• A computer simulation of O2-CO2 exchange was performed using the Siggaard-Andersen base excess (BE) equations.
• The study assumed that a change in BE is equivalent to a change in SID.
• The simulation analyzed the linear relationship between a-v [SID]p and decreasing [HbO2] during equimolar O2-CO2 exchange.

Main Results:

• Arteriovenous [SID]p decreased linearly with decreasing [HbO2] during simulated equimolar O2-CO2 exchange (delta mEq [SID]p.l-1 per delta gHbO2.dl-1 = 0.6, r2 = 1.0).
• Erythrocyte BE ([BE]e) and SID ([SID]e) decreased commensurately, maintaining a constant whole blood BE ([BE]WB).
• These observed changes were consistent with ion exchanges between erythrocytes and plasma, governed by the Gibbs-Donnan equilibrium.

Conclusions:

• Arteriovenous [SID]p shows potential for examining arteriovenous differences in metabolic acid, aligning with base excess (BE) concepts.
• The findings suggest that a-v [SID]p can be a viable alternative for assessing acid-base status in situations where traditional BE measurements may be less accurate.
• Further research is warranted to validate the use of a-v [SID]p in clinical settings for identifying organs responsible for metabolic acid changes.