Notice that the CO2 and the HCO3 are on opposite sides of normal. The value that is on the same side as the pH is the cause of the pH abnormality. The value on the opposite side from the pH is attempting to compensate for the abnormality. The pH of 7.66 is alkalotic and the CO2 of 15 is the cause. The HCO3 of 17 is acidotic because the kidneys are dumping HCO3 to try to compensate for the alkalosis. If the HCO3 were normal the pH would be even more alkalotic. The kidneys have partially compensated for the alkalosis : A PARTIALLY COMPENSATED RESPIRATORY ALKALOSIS