We appreciate the accurate analysis of our work made by Gatz (Citation1). Actually, we used the formula that we described in method section, that was:
Formula 1: Effective SID = 1000 × 2.46 × 10−11 × PCO2/(10−pH) + [Albumin] ×(0.12 × [pH − 0.631]) + [Phosphate] × (0.309 × [pH – 0.469]); (Citation2)
Gatz (Citation1) objected to the use of this formula, instead of the following:
Formula 2: Effective SID = 1000 × 2.46 × 10−11 × PCO2/(10−pH) + [Albumin] × (0.123 × [pH – 0.631]) + [Phosphate] × (0.309 × [pH − 0.469]) (Citation3)
affirming that the use of value 0.12 instead of 0.123 in the formula, affected the final result of our study. (The different number between the two formulas is underlined and in cursive script).
We re-computed SIG with both formulas, using a standard PH value (7.40) and a standard PCO2 value (35 mmHg) for all patients, in order to nullify PH and PCO2 influence in both formulas.
The main finding was that SIG values were similar, using the first or the second formula.
Group 1 (Formula 1): 34.56 ± 7.76
Group 2 (Formula 2): 34.58 ± 7.76
P (t test): 0.989 (ns)
In our opinion, taking into account also these results, our finding that ‘the SIG approach does not seem to add further information in risk stratification’ appears to be related not to differences in formula computation (as inferred by Gatz), but to the ‘patients’. In our opinion, the mechanism(s) underlying cardiogenic shock following STEMI are peculiar, different from those accounting for septic shock. It is, therefore, not surprising that the SIG approach may hold a different clinical role in predicting outcomes.
Concluding, the unused third decimal number in our formula, differently from the original formula, did not change the main result of our study.
Declaration of interest: The authors report no conflict of interest. The authors alone are responsible for the content and writing of the paper.
References
- Gatz R. Strong ion gap in cardiogenic shock—the calculation seems wrong. Acute Card Care 2014;16:34.
- Attanà P, Lazzeri C, Chiostri M, Picariello C, Gensini GF, Valente S. Strong-ion gap approach in patients with cardiogenic shock following ST-elevation myocardial infarction. Acute Card Care 2013;15:58–62.
- Figge J, Mydosh T, Fencl V. Serum proteins and acid-base equilibria: A follow-up J Lab Clin Med. 1992;120:713–9.