Physicochemical characterization of metabolic acidosis induced by normal saline resuscitation of patients with severe sepsis and septic shock.

OBJECTIVE The aim of this study was to characterize and quantify metabolic acidosis that was caused by initial volume expansion during the reanimation of patients with severe sepsis and septic shock. METHODS A blood sample was drawn for physicochemical characterization of the patient's acid-base equilibrium both before and after volume expansion using 30 mL/kg 0.9% saline solution. The diagnosis and quantification of metabolic acidosis were based on the standard base excess (SBE). RESULTS Eight patients with a mean age of 58 ± 13 years and mean APACHE II scores of 20 ± 4 were expanded using 2,000 ± 370 mL of 0.9% saline solution. Blood pH dropped from 7.404 ± 0.080 to 7.367 ± 0.086 (p=0.018), and PC O2 increased from 30 ± 5 to 32 ± 2 mmHg (p=0.215); SBE dropped from -4.4 ± 5.6 to -6.0 ± 5.7 mEq/L (p=0.039). The drop in SBE was associated with the acidifying power of two factors, namely, a significant increase in the strong ion gap (SIG) from 6.1 ± 3.4 to 7.7 ± 4.0 mEq/L (p = 0.134) and a non-significant drop in the apparent inorganic strong ion differences (SIDai) from 40 ± 5 to 38 ± 4 mEq/L (p = 0.318). Conversely, the serum albumin levels decreased from 3.1 ± 1.0 to 2.6 ± 0.8 mEq/L (p = 0.003) with an alkalinizing effect on SBE. Increased serum chloride levels from 103 ± 10 to 106 ± 7 mEq/L (p < 0.001) led to a drop in SIDai. CONCLUSION Initial resuscitation using 30 mL/kg of 0.9% saline solution for patients with severe sepsis and septic shock is associated with worsened metabolic acidosis, as measured by SBE. This worsened SBE can be ascribed to a serum increase in the levels of unmeasurable anions and chloride.