Plasma bicarbonate and total carbon dioxide: terms to be employed with precision

Authors

Todd S. Ing, Department of Medicine, Stritch School of Medicine, Loyola University Chicago, Maywood, IL, USA.
Larry Massie, Department of Pathology, Raymond G. Murphy Veterans Affairs Medical Center, University of New Mexico School of Medicine, Albuquerque, NM, USA
Antonios H. Tzamaloukas, Research Service, Department of Medicine, Raymond G. Murphy Veterans Affairs Medical Center, University of New Mexico School of Medicine, Albuquerque, NM, USA
Susie Q. Lew, Department of Medicine, George Washington University, 2150 Pennsylvania Ave, NW, #3-438, District of Columbia, Washington, DC, 20037, USA. sqlew@gwu.edu

Document Type

Article

Publication Date

7-1-2021

Abstract

Total carbon dioxide (TCO₂) is the acid–base determinant included in a venous plasma basic metabolic panel. TCO₂ represents the sum of bicarbonate ion, dissolved CO₂ gas, carbonic acid, carbonate ion, and CO₂ combined with the amino group of plasma proteins to form carbamino compounds [1]. Bicarbonate concentration in arterial or venous blood gases is obtained by solving the Henderson-Hasselbalch equation for bicarbonate [1]. TCO₂ and bicarbonate have been used interchangeably in the past [2]. After institutional review board approval, we carried a physician survey addressing knowledge of this topic in two institutions (Table 1). Each question was asked after the response to the previous question was received. The answers were similar in the two institutions. Table 1 documents knowledge gaps of the topic of TCO₂ and bicarbonate in substantial number of physicians. This raises the question of whether this lack of knowledge affects adversely the diagnosis and management of acid–base disorders. Normally, bicarbonate and dissolved CO₂, both reported in mmol/L (dissolved CO₂=0.0306 x P_CO2—where P_CO2 is in mm Hg), account for 94%, and 5%, respectively of TCO₂ [1]. Using the terms bicarbonate and TCO₂ interchangeably would have no significant effects under these circumstances. However, there are conditions causing substantial differences between TCO₂ and bicarbonate.

Recommended Citation

Ing TS, Massie L, Tzamaloukas AH, Lew SQ. Plasma bicarbonate and total carbon dioxide: terms to be employed with precision. Int Urol Nephrol. 2021 Jul;53(7):1483-1484. doi: 10.1007/s11255-020-02734-1. Epub 2021 Jan 3. PMID: 33389503.