A 72-yrs-old male with diabetes mellitus is evaluated in the emergency room because of lethargy, disorientation, and rapid breathing. Initial chemistries on venous blood demonstrate high glucose at 380 mg/dL and a pH of 7.22. Recalling the normal bicarbonate (22 to 28 mM) and Pco2 (33 to 45 mmHg) values, which of the following additional test results would be consistent with the man’s pH and breathing pattern?
|A||A bicarbonate of 50 mM and Pco2 of 10 mmHg|
|B||A bicarbonate of 15 mM and Pco2 of 30 mmHg|
|C||A bicarbonate of 15 mM and Pco2 of 60 mmHg|
|D||None of the above|
a. The man is acidotic as defined by the pH lower than the normal 7.4. His hyperventilation with Kussmaul respirations can be interpreted as compensation by the lungs to blow off CO2 lower Pco2 increase [HCO3-] / [CO2] ratio, and raise pH.
b. The correct answer therefore includes a low Pco2 eliminating choices c through e. Using the Henderson-Hasselbalch equation indicates that the pH minus the pK for carbonic acid (7.3 — 6.1 = 1.2) equals log  / [0.03 x 30 mmHg] or log [15/0.9].
c. These values correspond to those in choice b. The man has compensated his metabolic acidosis (caused by the accumulation of ketone bodies such as acetoacetic acid) by increasing his respiratory rate and volume.