Assessing redox status in human plasma: experience in critically ill patients.

Clinical evaluation of metabolic acidosis has involved measurement of lactate (L), pyruvate (P), beta-hydroxybutyrate (BOHB), and acetoacetate (AcAc). We previously demonstrated that these metabolites are not at equilibrium in plasma. Their degree of disequilibrium is reflected in the ratio of apparent equilibrium constants (KLP/KBA) for the two redox couplets, L-P and BOHB-AcAc. The purpose of the study was to examine how well this ratio reflects disequilibrium in patients with metabolic acidosis. Measurements of the four metabolites were obtained in 23 critically ill patients. Disequilibrium was again observed, as manifested in an inconstant ratio (p less than .01). The ratio increased with clinical improvement. Patients were more likely to die during their ICU stay if the estimated ratio was low, particularly if metabolic acidosis was present. Patients with respiratory acidosis had both intermediate probabilities of death and intermediate ratios when compared to inpatient controls (ICU patients without acidosis). Our data indicate that changes in the L-P-BOHB-AcAc cycle reflect the degree of metabolic derangement in critically ill patients.