A patient in the CVICU is has the following hemodynamic valu…

A patient in the CVICU is has the following hemodynamic values:  BP 100/ 70 mmHg, PAP 38/20 mmHg, PCWP 14mmHg, and the SV02 is 70%.  Abg’s are drawn and reveal the following:  7.31, paC02 35mmHg, pa02 80mmHg on a 50% Venti Mask, HC03 20meq/Liter, Hb 12.0 g/dL.   Which of the following explains the patient’s low HC03?