Interpret the ABG: pH 7.38, PO2 90, PCO2 58, HCO3- 22. Which disturbance best fits this ABG?

• A. Uncompensated respiratory acidosis
• B. Partially compensated respiratory acidosis
• C. Compensated respiratory acidosis
• D. Mixed disturbance

Answer: (C)

The key idea is recognizing compensation in a respiratory disorder by looking at the pH in relation to the elevated CO2. Here, the PCO2 is high (58 mmHg), which points to a respiratory acidosis as the primary problem. Yet the pH sits in the normal range (7.38), meaning the body has adjusted metabolically to counter the acidosis. When the acid-base disturbance is a respiratory issue but the pH is maintained within normal limits thanks to renal (metabolic) compensation, we call it a compensated respiratory acidosis. The bicarbonate level being within the normal range doesn’t negate the compensation, because the important clue is the normal pH despite the high CO2, indicating the metabolic system has adjusted to balance the acid load. If the pH remained acidemic, it would suggest incomplete (partially compensated) or uncompensated acidosis, and if two opposing disturbances were present, a mixed disturbance would typically push the pH outside the normal range.