Experimental determination of net protein charge and Atot and Ka of nonvolatile buffers in canine plasma

Peter D. Constable, Henry R. Stämpfli

Research output: Contribution to journalArticlepeer-review


Acid-base abnormalities frequently are present in sick dogs. The mechanism for an acid-base disturbance can be determined with the simplified strong ion approach, which requires accurate values for the total concentration of plasma nonvolatile buffers (Atot) and the effective dissociation constant for plasma weak acids (Ka). The aims of this study were to experimentally determine Atot and Ka values for canine plasma. Plasma was harvested from 10 healthy dogs; the concentrations of quantitatively important strong ions (Na+, K+, Ca 2+, Mg2+, Cl-, L-lactate) and nonvolatile buffer ions (total protein, albumin, phosphate) were determined; and the plasma was tonometered with CO2 at 37°C. Strong ion difference (SID) was calculated from the measured strong ion concentrations, and nonlinear regression was used to estimate values for Atot and Ka, which were validated with data from an in vitro and in vivo study. Mean (±SD) values for canine plasma were Atot = (17.4 ± 8.6) mM (equivalent to 0.273 mmol/g of total protein or 0.469 mmol/g of albumin); Ka = (0.17 ± 0.11) × 10-7; pKa = 7.77. The calculated SID for normal canine plasma (pH = 7.40; PCO2 = 37 mm Hg; [total protein] = 64 g/L) was 27 mEq/L. The net protein charge for normal canine plasma was 0.25 mEq/g of total protein or 0.42 mEq/g of albumin. Application of the experimentally determined values for Atot, K a, and net protein charge should improve understanding of the mechanism for complex acid-base disturbances in dogs.

Original languageEnglish (US)
Pages (from-to)507-514
Number of pages8
JournalJournal of veterinary internal medicine
Issue number4
StatePublished - Jul 2005


  • Anion gap
  • Metabolic acidosis
  • Respiratory acidosis
  • Strong ion gap

ASJC Scopus subject areas

  • veterinary(all)


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