[Base Excess] vs [Strong ION Difference]

Blood [base excess] ([BE]) is defined as the change in [strong acid] or [strong base] needed to restore pH to normal at normal PCO2. Some believe that [BE] is unhelpful because [BE] may be elevated with a “normal” [strong ion difference] ([SID]), where a strong ion is one that is always dissociated in physiological solution, and where [SID] = [strong cations] — [strong anions]. Using a computer simulation, the hypothesis was tested that [SID] = [SID Excess] ([SIDEx]), where [SIDEx] is the change in [SID] needed to restore pH to normal at normal PCO2. The most current version of the plasma [SID] ([SID]p) equation was used as a template, and an [SIDEx] formula, of the Siggaard-Andersen form, derived: \({\left[ {{\text{SIDEx}}} \right]_p} = {\left[ {HC{O_3}^ - } \right]_P} - 24.72 + \left( {p{H_p} - 7.4} \right) \times \left( {1.159 \times {{\left[ {{\text{alb}}} \right]}_p} \times + 0.423 \times {{\left[ {Pi} \right]}_p}} \right)\). [SID] was compared to [SIDEx] over the physiologic range of plasma buffering, and it was found that [SIDEx] varied by ~ 15 mM at any given [SID], thereby faulting the hypothesis. It is concluded that [SID] can be “normal” with an elevated [SIDEx], the latter being an expression of the [BE] concept, and a more helpful quantity in physiology.