Purpose: The recommended method for elucidating the effects of strong ions other than lactate on acid-base balance is to calculate the non-lactate strong ion difference (SIDnl). A relationship between HCO3 (-) and SIDnl in hyperchloremic patients has already been demonstrated; in the present study, the relationships between SIDnl, the apparent strong ion difference (SIDa), and mortality at intensive care unit (ICU) admission were investigated.
Methods: In our two-center study, 2691 patients admitted to the ICU were retrospectively evaluated, including 1069 critically ill patients. These patients were divided into three subgroups according to their SIDnl levels at admission to the ICU: low (<38 mmol L(-1)), normal (38-40 mmol L(-1)), and high (>40 mmol L(-1)). Patient age, gender, diagnosis, blood gas values, length of ICU stay, and mortality were recorded.
Results: The low-SIDnl group included 768 patients (71.8 %), the normal-SIDnl group consisted of 127 patients (11.9 %), and the high-SIDnl group contained 174 patients (16.3 %). There was no significant difference in lactate levels among the SIDnl groups (p = 0.635). In a multivariate logistic regression model, likelihood of mortality was increased 1.24-fold (1.20-1.28), 2.56-fold (1.61-4.08) and 2.55-fold (1.003-6.47) by APACHE II, lactate level ≥2mmol L(-) and low SIDnl (p < 0.001, p < 0.001, and p = 0.049, respectively).
Conclusions: SIDnl can be used to determine the effects of strong ions other than lactate on SIDa values and acid-base balance. Furthermore, a low SIDnl at ICU admission can be a prognostic indicator of mortality.
Keywords: Hyperchloremia; Lactate; Outcome; Strong ion difference.