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CHIEF COMPLAINT

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PATIENT Image not available.

Mr. L is a 42-year-old man with type 1 diabetes mellitus (DM) who complains of weakness, anorexia, abdominal pain, and vomiting. Laboratory studies demonstrate a HCO3 of 6 mEq/L.

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His very low HCO3 suggests a significant acid-base abnormality. In addition to evaluating his abdominal pain, exploring his acid-base disorder is critical.

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Image not available. What is the differential diagnosis of acid-base disorders? How would you frame the differential?

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CONSTRUCTING A DIFFERENTIAL DIAGNOSIS

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The differential diagnosis of acid-base disorders is extensive (Table 4-1) but can be easily organized into 4 distinct subsets by first determining whether the primary disorder is a (1) metabolic acidosis, (2) metabolic alkalosis, (3) respiratory acidosis, or (4) respiratory alkalosis. The key pivotal feature that allows the clinician to narrow the differential to 1 of these subsets is to first evaluate the pH and then the HCO3 and PaCO2.

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Table Graphic Jump Location
Table 4-1.Differential diagnosis of primary acid-base disorders.
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Step 1: Determine Whether the Primary Disorder is an Acidosis or Alkalosis by Reviewing the pH.

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  1. pH < 7.4 indicates the primary disorder is an acidosis.

  2. pH > 7.4 indicates the primary disorder is an alkalosis.

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Step 2: Determine Whether the Primary Acidosis or Alkalosis is Metabolic or Respiratory by Reviewing the ...

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