Ionic composition of arterial and mixed venous plasma in the unanesthetized dog

The use of permanent catheters in the aorta and pulmonary artery permitted the establishment of normal values for hemoglobin concentration in blood and -or pH, PCO2, osmolality, and protein and electrolyte concentrations in the plasma of arterial and venous samples from unanesthetized, undisturbed dogs, and the comparison of the ionic composition of simultaneously taken arterial and venous samples. Arterial samples yielded the following mean values: CHb, 143 g liter-1; pHP, 7.427; PCO2, 32.5 mmHg; CPosmol, 295 mmol kg-1; CPpr, 73.1 g liter-1, CPNa+, 148.0; CPK+, 3.9; CPCa2+, 2.38; CPMg2+, 0.85; CPCl-, 116.0; CPHCO3-, 21.1; CPlact-, 1.4; CPphosph, 1.21; net cation equivalency, 16.4; and anion gap, 1.03 mmol liter-1 in eight male mongrel dogs with seven or eight samplings from each dog. The anion gap in arterial and venous plasma was small, indicating that the contribution of sulfate and organic acids to the ionic composition of dog plasma is quantitatively unimportant. In simultaneously taken arterial and venous samples the following significant arteriovenous differences were found: HP, +0.038; PCO2, -5.6 mmHg; CPosmol, -1.8 mmol kg-1; protein, -0.8 g liter-1; CPNa+, -1.0; CPK+, -0.1; CPCl-, +1.3; and CPHCO3-, -1.7 mmol liter-1. These differences are explained on the basis of the changes that occur in blood upon the addition of CO2 and the ensuing chloride and water shifts.