Strong ion gap in cardiogenic shock—the calculation seems wrong

Abstract

These formulae are erroneous and lead to predictably grossly wrong results. The authors find SIG values of mean –14 mEq/l in the non-survivors’ and –10 mEq/l in the survivors’ group. ‘ According to our data the SIG approach does not seem to add further information to usual parameters in acid-base evaluation or early risk stratification in cardiogenic shocks patients.’

Keywords::

• Strong ion gap
• cardiogenic shock
• heart failure
• metabolism
• shock

The recently published paper by Attanà et al. (1), while addressing a clinically relevant topic, in my opinion, does contain an error in its central calculations, namely those of the anionic charge of the weak acids, albumin and phosphate.

The formulae given by the authors in the methods section are:

anionic charge of albumin [albumin]*(0.12*(pH –0.631))

anionic charge of phosphate [phosphate]*(0.309* (pH –0.469))

The correct form of these formulae is:

anionic charge of albumin [albumin]*(0.123*pH –0.631)

anionic charge of phosphate [phosphate]*(0.309* pH–0.469) (2)

The formulae used by the authors lead to extremely high effective SID values, reflected in their highly negative results for SIG, with a mean –14 mEq/l in the non-survivors’ and −10 mEq/l in the survivors’ group.

Whether applying the correct formulae would have changed their main conclusion, ‘the SIG approach does not seem to add further information to usual parameters in acid-base evaluation or early risk stratification in cardiogenic shocks patients’ is doubtful, though, as long as these patients do not develop severe hepatic or renal failure.

Declaration of interest: The author reports no conflict of interest. The author alone is responsible for the content and writing of the paper.