A young woman is found comatose, having taken an unknown number of sleeping pills an unknown time before. An arterial blood sample yields the following values: pH 6.90, HCO3- 13 meq/liter, and PaCO2 68 mmHg. This patient’s acid-base status is most accurately described as:
A. Metabolic Acidosis
B. Respiratory Acidosis
C. Simultaneous Respiratory and Metabolic Acidosis
D. Respiratory Acidosis with Complete Renal Compensation
Correct Answer: C. Simultaneous Respiratory and Metabolic Acidosis
Whenever the PCO2 and HCO3 are abnormal in opposite directions, ie, one above normal while the other is reduced, a mixed respiratory and metabolic acid-base disorder exists. When the PCO2 is elevated and the [HCO3-] reduced, respiratory acidosis and metabolic acidosis coexist.