Discrepancy between Measured Serum Total Carbon Dioxide Content and Bicarbonate Concentration Calculated from Arterial Blood Gases

摘要

Large differences between the concentrations of serum total carbon dioxide (TCOsub2/sub) and blood gas bicarbonate (HCOsub3/subsup-/sup) 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 TCOsub2/sub, 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 HCOsub3/subsup-/sup. A recalculation using the Henderson-Hasselbach equation revealed arterial blood gas HCOsub3/subsup-/sup values close to the corresponding serum TCOsub2 /subvalues and clarified the diagnosis of the acid-base disorder, which had been placed in doubt by the large differences between the reported TCOsub2/sub and HCOsub3/subsup-/sup values.?Human error in the calculation of HCOsub3/subsup-/sup was identified as the source of these differences. Recalculation of blood gas HCOsub3/subsup-/sup should be the first step in identifying the source of large differences between serum TCOsub2/sub and blood gas HCOsub3/subsup-/sup.