A 28-year-old man has noticed an increase in urine output and periods of insatiable thirst. The patient's arterial blood gas results are as follows with an FIO2 of 0.21:
pH 7.24
PaCO2 20 torr
PaO2 112 torr
HCO3 8 mEq/L
BE -18 mEq/L
SaO2 97%

Which of the following is the most likely explanation?
A) diabetic ketoacidosis
B) hyperventilation
C) ventilatory failure
D) excessive diuretic therapy