If you’re preparing for the United States Medical Licensing Examination® (USMLE®) Step 3 exam, you might want to know which questions are most often missed by test-prep takers.

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Check out this example from Kaplan Medical, and read an expert explanation of the answer. Also check out all posts in this series.

This month’s stumper

An 18-year-old man with type I diabetes mellitus is brought to the emergency department by a friend after being found comatose. There is a known history of noncompliance with medications, however, there is no known history of drug use.

Vital signs are: temperature 37 °C (98.6 °F), blood pressure 80/65 mm Hg, pulse 110 beats a minute, and respirations 17 per minute. Oxygen saturation obtained while the patient is receiving supplemental oxygen of 2 L a minute via nasal cannula is 98%. The patient is comatose and is taking rapid, shallow breaths. Deep tendon reflexes are hypoactive. An intravenous line has been placed in the field. A fingerstick glucose is 430 mg/dL. An arterial blood gas, basic chemistry panel, and toxicology screen has been sent to the laboratory.

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What is the next step in the management of this patient?

A. A chest x-ray

B. An endotracheal intubation.

C. An intravenous fluid replacement with insulin.

D. Methadone.

E. A pulmonary artery catheter insertion.












The correct answer is C.

Kaplan Medical explains why

This patient is suffering from diabetic ketoacidosis caused by a severe deficiency of insulin. Clinical symptoms include coma, rapid and shallow breathing, high serum glucose levels, and metabolic acidosis. The immediate management of this patient includes intravenous fluid replacement and insulin infusion. When laboratory results return, electrolyte imbalances must also be corrected.

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Why the other answers are wrong

Choice A: A chest x-ray would be complementary to a complete the evaluation of any comatose patient. In this patient with a picture of diabetic ketoacidosis, a chest x-ray would be a secondary concern. The first priority is intravenous fluid replacement and insulin therapy.

Choice B: Endotracheal intubation is not necessary at this point as the patient has a normal oxygen saturation. Adequacy of respiration will need to be reassessed when the arterial blood gas results are available. The first priority is intravenous fluid replacement and insulin therapy.

Choice D: Methadone is used to treat heroin dependency.

Choice E: A pulmonary artery catheter is not yet necessary as the patient is at the present time hemodynamically stable. The first priority is intravenous fluid replacement and insulin therapy.

For more prep questions on USMLE Steps 1, 2 and 3, view other posts in this series.

The AMA selected Kaplan as a preferred provider to support you in reaching your goal of passing the USMLE® or COMLEX-USA®. AMA members can save 30% on access to additional study resources, such as Kaplan’s Qbank and High-yield courses. Learn more.

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