Review Question - QID 104288

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Arterial Blood Gases Introduction Interpretation QID: 104288 (M2.PL.17.14)

QID 104288 (Type "104288" in App Search)

A 19-year-old male college student with no significant medical history presents to the emergency department with altered mental status. His girlfriend said that he drank multiple shots of vodka and gin throughout the weekend and was found slumped on the couch with some vomit on his shirt. He is afebrile, with a blood pressure of 128/60 mmHg, pulse of 100/min, respirations at 25/min, and SpO2 of 95% on room air. His pupils are equal and reactive to light bilaterally. He exhibits no tremors or myoclonus. The remainder of the physical exam is unremarkable. His basic metabolic panel is displayed below:

Serum:
Na+: 138 mEq/L
Cl-: 90 mEq/L
K+: 4.0 mEq/L
HCO3-: 20 mEq/L
BUN: 30 mg/dL
Glucose: 100 mg/dL
Creatinine: 0.8 mg/dL

An arterial blood gas reveals the following:

pH: 7.32
pCO2: 34 mmHg
pO2: 89 mmHg

The girlfriend is concerned that the patient's breathing appears uncomfortable. How do you respond?

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His breathing is concerning for hepatic encephalopathy

10%

18/179

His breathing requires evaluation for a pulmonary embolism

6/179

His breathing suggests that he needs some fluids

59%

106/179

His breathing suggests that he has major depression disorder

6/179

You are not his healthcare proxy and I cannot speak to you

23%

41/179

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This young patient likely has alcoholic and starvation ketoacidosis with tachypnea suggesting a compensatory respiratory alkalosis. Given the widened anion gap in the setting of emesis, he would benefit from oral or intravenous fluids to improve his acid-base status more quickly.

With a prolonged drinking-vomiting binge, decreased food intake, and vomiting produces starvation ketoacidosis. Ketogenesis is intensified by a high plasma level of catecholamines (suggested by the tachycardia) arising from volume depletion and by a direct effect of alcohol. The clinical history is sufficient to explain the widened anion gap without actively searching for ketones in the patient's urine or blood. His tachypnea is due to respiratory alkalosis, through which the body seeks to maintain acid-base homeostasis.

Incorrect Answers:
Answer 1: There are no clinical findings to suggest decompensated cirrhosis causing portosystemic encephalopathy.

Answer 2: Pulmonary embolism is unlikely in the presence of a better explanation for the tachypnea and maintenance of the oxygen saturation on room air.

Answer 4: Tachypnea can be a manifestation of pain and anxiety but not necessarily depression.

Answer 5: The girlfriend is not the healthcare proxy, but that does not limit the physician's capacity to reassure the girlfriend in this setting.

Bullet Summary:
Look for tachypnea or deeper respirations as evidence of compensatory alkalosis for primary metabolic acidosis.

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