A previously healthy female collegiate athlete is admitted to the medical intensive care unit shortly after collapsing at the finish line of a summer half-marathon. Emergency medical personnel found her lethargic and disoriented. On arrival, her temperature is 39.4 °C (102.9 °F), blood pressure is 88/54 mm Hg, heart rate is 132/min, and respiratory rate is 26/min. Physical examination reveals dry mucous membranes and diffuse muscle tenderness, but lungs are clear to auscultation.
Initial laboratory studies demonstrate the following:
| Laboratory Test | Result |
|---|---|
| Sodium | 138 mEq/L |
| Potassium | 6.2 mEq/L |
| Chloride | 102 mEq/L |
| Bicarbonate | 12 mEq/L |
| Blood urea nitrogen | 58 mg/dL |
| Creatinine | 3.2 mg/dL |
Arterial blood gas (on room air):
| Parameter | Result |
|---|---|
| pH | 7.12 |
| 38 mm Hg | |
| 85 mm Hg |
Which of the following best describes this patient's current acid-base disturbance?
- High anion gap metabolic acidosis and respiratory acidosisCevap
- BHigh anion gap metabolic acidosis with appropriate respiratory compensation
- CHigh anion gap metabolic acidosis and respiratory alkalosis
- DNormal anion gap metabolic acidosis and respiratory acidosis
- EMixed high and normal anion gap metabolic acidosis
Cevap
High anion gap metabolic acidosis and respiratory acidosis
This patient presents with a severe acute kidney injury, likely due to exertional heat stroke and rhabdomyolysis, resulting in an acid-base disturbance. Stepwise analysis is required. First, the anion gap is mEq/L, confirming a primary high anion gap metabolic acidosis (HAGMA). Next, respiratory compensation is evaluated using Winter's formula: . For a bicarbonate of 12 mEq/L, the expected is 24-28 mm Hg. The patient's actual is 38 mm Hg. Because the actual is significantly higher than the expected range, she has a concomitant respiratory acidosis. This often occurs when patients develop respiratory muscle fatigue from the work of breathing associated with severe metabolic acidosis (Kussmaul respirations) or from altered mental status.
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Anahtar Kavram
In patients with a primary metabolic acidosis, adequate respiratory compensation must be confirmed via Winter's formula; an actual pCO2 higher than the expected value indicates a concomitant respiratory acidosis.