[Base excess] vs [strong ion difference]. Which is more helpful?

Area of Science:

• Physiology
• Biochemistry
• Medical Diagnostics

Background:

• The traditional base excess (BE) metric for metabolic acid-base disturbances is criticized for inadequacy in complex cases.
• The strong ion difference (SID) method is proposed as an alternative, but its relationship with BE in certain conditions remains unclear.
• Hypoproteinemia has been observed with normal SID but elevated BE, posing a diagnostic challenge.

Purpose of the Study:

• To test the hypothesis that strong ion difference (SID) equals strong ion difference excess (SIDEx) under normal physiological conditions.
• To develop and validate a SIDEx formula analogous to the Siggaard-Andersen BE equation.
• To compare SID and SIDEx across physiological ranges of plasma albumin, phosphate, and pH.

Main Methods:

• Computer simulation was employed to test the hypothesis.
• A novel SIDEx formula was derived based on the plasma SID equation: SIDEx = [HCO3-] - 24.72 + (pH - 7.4) * (1.159 * [alb] + 0.423 * [Pi]).
• SID and SIDEx were compared across physiological variations in plasma albumin, phosphate, and pH.

Main Results:

• The hypothesis that SID equals SIDEx was refuted.
• SIDEx demonstrated a variation of approximately 15 mM at any given SID.
• A normal SID was observed concurrently with an elevated SIDEx.

Conclusions:

• Strong ion difference (SID) can appear normal even when strong ion difference excess (SIDEx) is elevated.
• SIDEx is a more accurate physiological reflection of base excess (BE) than SID alone.
• SIDEx provides a more helpful quantity for understanding complex acid-base disturbances in physiology.