Conventional or physicochemical approach in intensive care unit patients with metabolic acidosis

INTRODUCTION: Metabolic acidosis is the most frequent acid–base disorder in the intensive care unit. The optimal analysis of the underlying mechanisms is unknown. AIM: To compare the conventional approach with the physicochemical approach in quantifying complicated metabolic acidosis in patients in the intensive care unit PATIENTS AND METHODS: We included 50 consecutive patients with a metabolic acidosis (standard base excess ≤ -5). We measured sodium, potassium, calcium, magnesium, chloride, lactate, creatinine, urea, phosphate, albumin, pH, and arterial carbon dioxide and oxygen tensions in every patient. We then calculated HCO(3)(-), the base excess, the anion gap, the albumin-corrected anion gap, the apparent strong ion difference, the effective strong ion difference and the strong ion gap. RESULTS: Most patients had multiple underlying mechanisms explaining the metabolic acidosis. Unmeasured strong anions were present in 98%, hyperchloremia was present in 80% and elevated lactate levels were present in 62% of patients. Calculation of the anion gap was not useful for the detection of hyperlactatemia. There was an excellent relation between the strong ion gap and the albumin-corrected and lactate-corrected anion gap (r(2 )= 0.934), with a bias of 1.86 and a precision of 0.96. CONCLUSION: Multiple underlying mechanisms are present in most intensive care unit patients with a metabolic acidosis. These mechanisms are reliably determined by measuring the lactate-corrected and albumin-corrected anion gap. Calculation of the more time-consuming strong ion gap according to Stewart is therefore unnecessary.