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Chapter 23. Renal, Infectious, Electrolytes, and Other General Critical Care Questions

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A patient presents after a several-day history of abdominal pain and diarrhea, accompanied by minimal food and fluid intake due to feeling “unwell.” Initial laboratory evaluation reveals the following. What is the acid-base abnormality in this patient?

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pH 7.30
PCO2 30 mm Hg
HCO3 16 mmol/L
Anion gap 17 mmol/L

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A. Anion gap metabolic acidosis

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B. Anion gap metabolic acidosis and respiratory acidosis

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C. Normal anion gap metabolic acidosis and respiratory acidosis

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D. Anion gap metabolic acidosis and metabolic alkalosis

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E. Anion gap metabolic acidosis and normal anion gap metabolic acidosis

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E. This patient presents with a serum pH of 7.30, indicative of acidemia. Lab values of bicarbonate (HCO3; 16 mmol/L) and partial pressure of carbon dioxide (PCO2; 30 mm Hg) reveal a metabolic acidosis with adequate respiratory compensation. The elevated anion gap at 17 mmol/L further describes the presence of an anion gap metabolic acidosis, potentially due to lactic acidosis or ketosis in the setting of poor oral intake. Examination of the “gap-gap” ratio, however, reveals the following:

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Thus, the gap-gap ratio is <1, signaling a greater decrease in HCO3 than increase in anion gap. This signals the co-existence of a normal anion gap (hyperchloremic) metabolic acidosis in this patient, likely due to the patient’s preceding history of diarrhea.

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A patient is admitted to the intensive care unit (ICU) after being found down next to several empty pill bottles. She is unarousable to voice and noxious stimuli, with significant metabolic disarray noted on laboratory evaluation. After conversing with her parents, you suspect that the patient has ingested large amounts of aspirin. You would expect her labs to reflect which of the following?

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A. Anion gap metabolic acidosis

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B. Normal anion gap metabolic acidosis

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C. Anion gap metabolic acidosis and respiratory alkalosis

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D. Anion gap metabolic acidosis and respiratory acidosis

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E. Normal anion gap metabolic acidosis and metabolic alkalosis

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C. Aspirin, or acetylsalicylic acid, is a salicylate. Ingestion of high amounts of salicylates (>150 mg/kg) triggers both a primary metabolic acidosis and a primary respiratory alkalosis, resulting in a mixed acid-base disorder with normal pH. Salicylic acid uncouples oxidative phosphorylation within mitochondria, spurring lactic acid production via anaerobic metabolism to create an anion gap metabolic acidosis. Salicylic acid also acts directly ...

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