Quantifying pH-induced changes in plasma strong ion difference during experimental acidosis: clinical implications...

Area of Science:

• Physiology
• Biochemistry
• Acid-Base Balance

Background:

• The strong ion difference (SID) is a key determinant of acid-base status.
• Changes in plasma SID are often assumed to directly correlate with whole blood base excess (BE).
• However, factors like albumin binding and transcellular ion shifts complicate this relationship.

Purpose of the Study:

• To investigate the relationship between plasma SID and whole blood BE under varying physiological conditions.
• To determine if an "expected" plasma SID (SIDexp) can be predicted based on albumin and hemoglobin charges.
• To test the hypothesis that only deviations from SIDexp reflect actual changes in BE.

Main Methods:

• Equilibration of whole blood from healthy subjects and septic patients with varying CO2 concentrations.
• In vitro induction of anemia in healthy subjects.
• Addition of lactic or hydrochloric acid to whole blood.
• Calculation and comparison of plasma SID, expected SID (SIDexp), and whole blood base excess (BE).

Main Results:

• Plasma SID changes were observed, but their agreement with SIDexp was strong, indicating predictable electrolyte redistribution.
• The agreement between changes in BE (ΔBE) and changes in total plasma SID (ΔSID) was weak, especially with varying CO2.
• Changes in the "non-carbonic" SID (ΔSIDwb), representing deviations from SIDexp, showed strong agreement with ΔBE.

Conclusions:

• Whole blood base excess (BE) reflects only those changes in plasma strong ion difference (SID) not attributable to predictable electrolyte redistribution.
• Albumin and hemoglobin charges are crucial for predicting expected SID shifts.
• This understanding allows for a more accurate interpretation of SID and BE during in vitro acidosis.