The use of sodium-chloride difference and chloride-sodium ratio in the evaluation of metabolic acidosis in critically ill patients
Abstract
We read the study of Kurt et al. [4] and we believe that sodium chloride difference (Diff(NaCl)) and Cl Na ratio cannot be considered as an alternative method for assessment of unmeasured anions or tissue acids (TA). Significant correlation between Cl Na ratio and TA is not an unexpected result because metabolic acidosis (MAC) is generally caused either by loss of bicarbonate (insufficient renal synthesis of HCO3 compensated by an increase of Cl) or by retention of acids (chlorides remain unchanged), frequently by both.
The correlation is a weak evidence that one method can replace another. The confidence interval is not specified but at first glance it is apparent that variability is too high (Fig. 1e).
Cl Na ratio cannot be reliably used as a bedside method as it cannot exclude the accumulation of TA in individual case. Cl Na ratio indicates only approximately whether MAC with unchanged Cl is associated with retention of acids and MAC with hyperchloremia with insufficient synthesis of bicarbonate.