Emergency medical responders transport a 54-year-old male to the emergency department after his neighbor found him unresponsive. The patient has a known history of severe chronic obstructive pulmonary disease and alcohol use disorder. On physical examination, he is obtunded and taking slow, shallow breaths.
Vital signs include:
Temperature: 36.5 °C (97.7 °F)
Blood pressure: 92/58 mmHg
Heart rate: 108/min
Respiratory rate: 8/min
Laboratory studies display the following results:
| Test | Value |
|---|---|
| Sodium | 142 mEq/L |
| Potassium | 4.5 mEq/L |
| Chloride | 100 mEq/L |
| Bicarbonate | 12 mEq/L |
| Blood urea nitrogen | 30 mg/dL |
| Creatinine | 1.8 mg/dL |
An arterial blood gas sample on room air shows:
| Test | Value |
|---|---|
| pH | 7.15 |
| 35 mmHg | |
| 60 mmHg |
Which of the following best describes this patient's acid-base disturbances?
- Elevated anion gap metabolic acidosis with a concurrent respiratory acidosisAnswer
- BFully compensated metabolic acidosis with elevated unmeasured anions
- CElevated anion gap metabolic acidosis with a concurrent respiratory alkalosis
- DHyperchloremic metabolic acidosis with a concurrent respiratory acidosis
- EFully compensated hyperchloremic metabolic acidosis
Answer
Elevated anion gap metabolic acidosis with a concurrent respiratory acidosis
The patient's presentation and lab results indicate a mixed acid-base disorder. First, the primary process is a metabolic acidosis, given the low pH and low bicarbonate. The anion gap is calculated as mEq/L. Since this is greater than the normal 8-12 mEq/L range, there is an elevated anion gap metabolic acidosis (likely due to lactic acidosis from hypoperfusion or alcoholic ketoacidosis). Next, Winter's formula must be applied to evaluate respiratory compensation: expected mmHg. Because the patient's actual (35 mmHg) is higher than the expected range of 24-28 mmHg, the patient is retaining . This relative hypoventilation (consistent with his obtunded state and history of COPD) indicates a concurrent primary respiratory acidosis.
Step-by-Step Solution
Key Concept
Evaluation of mixed acid-base disorders using the anion gap and Winter's formula.