Key result
Recalculating ABG bicarbonate using the Henderson-Hasselbach equation resolves serum TCO2 discrepancies caused by human error.
Why the study?
Large differences between serum total carbon dioxide and blood gas bicarbonate concentrations can complicate the diagnosis of acid-base disorders and their sources are unclear.
Case Report (n=1)
No
Recalculation of blood gas HCO3- should be the first step when encountering large discrepancies between serum TCO2 and blood gas HCO3- to rule out human calculation error.
Calculation error may explain isolated TCO2-HCO3 discrepancies; case report leaves open need for systematic verification protocols.
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 (-).
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Kim et al. (2015) conducted a case report in Severe carbon dioxide retention and profound acidemia (n=1). Recalculation of blood gas HCO3- using the Henderson-Hasselbach equation with a pK' of 6.1 vs. Automated blood gas apparatus HCO3- calculation was evaluated on Resolution of the discrepancy between measured serum TCO2 and calculated blood gas HCO3-. Recalculation of arterial blood gas bicarbonate using the Henderson-Hasselbach equation with a pK' of 6.1 resolved the large discrepancy with measured serum total carbon dioxide, identifying human error as the source.
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