title: Discrepancy between Measured Serum Total Carbon Dioxide Content and Bicarbonate Concentration Calculated from Arterial Blood Gases.
abstract: Large differences between the concentrations of serum total carbon dioxide (TCO2) and blood gas bicarbonate (HCO3 (-)) were observed in two consecutive simultaneously drawn sets of samples of serum and arterial blood gases in a patient who presented with severe carbon dioxide retention and profound acidemia. These differences could not be explained by the effect of the high partial pressure of carbon dioxide on TCO2, by variations in the dissociation constant of the carbonic acid/bicarbonate system or by faults caused by the algorithms of the blood gas apparatus that calculate HCO3 (-). A recalculation using the Henderson-Hasselbach equation revealed arterial blood gas HCO3 (-) values close to the corresponding serum TCO2 values and clarified the diagnosis of the acid-base disorder, which had been placed in doubt by the large differences between the reported TCO2 and HCO3 (-) values. Human error in the calculation of HCO3 (-) was identified as the source of these differences. Recalculation of blood gas HCO3 (-) should be the first step in identifying the source of large differences between serum TCO2 and blood gas HCO3 (-).
authors.affiliation: Medicine Service, Sandoval County Regional Medical Center, Rio Rancho, New Mexico ; Department of Medicine, University of New Mexico School of Medicine.
authors.forename: Youngho
authors.initials: Y
authors.lastname: Kim
authors.affiliation: Pathology Service, Raymond G. Murphy VA Medical Center, Albuquerque, New Mexico.
authors.forename: Larry
authors.initials: L
authors.lastname: Massie
authors.affiliation: Raymond G. Murphy VA Medical Center, Albuquerque, New Mexico.
authors.forename: Glen H
authors.initials: GH
authors.lastname: Murata
authors.affiliation: University of New Mexico School of Medicine.
authors.forename: Antonios H
authors.initials: AH
authors.lastname: Tzamaloukas
keywords: acid-base status; acidemia; bicarbonate concentration; carbonic acid/bicarbonate pk'; hypercapnia; metabolic acidosis; respiratory acidosis; total co2 concentration
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