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

Abstract

IntroductionMetabolic acidosis is the most frequent acid–base disorder in the intensive care unit. The optimal analysis of the underlying mechanisms is unknown.AimTo compare the conventional approach with the physicochemical approach in quantifying complicated metabolic acidosis in patients in the intensive care unitPatients and methodsWe 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 HCO3-, 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.ResultsMost 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 (r2 = 0.934), with a bias of 1.86 and a precision of 0.96.ConclusionMultiple 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.

A Physicochemical Acid-Base Approach for Managing Diabetic Ketoacidosis

“…However, we should keep in mind that AG is the sum of dissociated, non-volatile weak acids (albumin and phosphate), lactate and unmeasured anions. Therefore, to quantify unmeasured anions properly, the AG should be adjusted for weak acids (mainly albumin) and lactate should be subtracted 11. For this reason, we believe that AG, SIG or even the Cl − /Na + ratio should be used to determine the moment of DKA resolution as opposed to using pH or bicarbonate.…”

Comparative Study between Traditional Approach and Physico-Chemical Approach in Acid Base Disorders Interpretation in Critically Ill Patients

“…High anion gap acidosis (13%) was detected in cases of normal SIG. there was also moderate correlation between the ALAG and SIG (r = 0.51) where other studies found higher correlation between them [13,14,24]. Fencl et al [13] had already demonstrated that BE fails as a measure of metabolic acidosis when there is a change in the plasma concentration of the non-bicarbonate buffers, an almost universal disorder in critically ill patients.…”

“…there was also moderate correlation between the ALAG and SIG (r = 0.51) where other studies found higher correlation between them [13,14,24]. Fencl et al [13] had already demonstrated that BE fails as a measure of metabolic acidosis when there is a change in the plasma concentration of the non-bicarbonate buffers, an almost universal disorder in critically ill patients. Kellum [20,22,23] considered that both methods yield virtually identical results, despite a different conceptual approach to underlying mechanisms.…”

Use of Sodium-Chloride Difference and Corrected Anion Gap as Surrogates of Stewart Variables in Critically Ill Patients

“…Second, no quantitative assessment of the secondary responses to primary changes in acid-base status is offered by the physicochemical approach [28]. Nevertheless, several studies [15], [16], [17], [29] have demonstrated that the Stewart's approach to acid-base disturbances allows the differentiation between tissue acidosis and hyperchloremic acidosis, and then results in identification of more patients with major acid-base disorders than the traditional evaluation.…”

“…Nevertheless, the Stewart's approach is a time-consuming method and unsuitable at the bedside. Previous studies [16], [17] have shown that strong ion gap (SIG) could be substituted by the anion gap corrected for albumin and lactate (AG corr ). Furthermore, recently, Nagaoka et al [18] suggested that the difference between sodium and chloride concentrations ([Na + ] – [Cl − ]) could be used as a surrogate of SID.…”