A 23-year-old man is brought to the emergency department by his roommate due to progressive weakness and confusion. The roommate says that the patient has been "drinking water all of the time and using the bathroom constantly" since he got sick with a cold 2 days ago. Temperature is 37.8 C (100 F), blood pressure is 96/58 mm Hg, and pulse is 112/min. Physical examination shows dry mucous membranes and his urine has a strong, fruity odor. Laboratory results are as follows: Based on the current laboratory findings, which of the following is most likely occurring in this patient?

Question

A 23-year-old man is brought to the emergency department by his roommate due to progressive weakness and confusion.  The roommate says that the patient has been "drinking water all of the time and using the bathroom constantly" since he got sick with a cold 2 days ago.  Temperature is 37.8 C (100 F), blood pressure is 96/58 mm Hg, and pulse is 112/min.  Physical examination shows dry mucous membranes and his urine has a strong, fruity odor.  Laboratory results are as follows:  Based on the current laboratory findings, which of the following is most likely occurring in this patient?

Quizplus · Accepted Answer

11ec160b_3ac4_5742_9249_6f3569c5ef6f_MD0001_00 The combination of acute-onset polyuria, polydipsia, volume depletion, and a fruity odor to the urine or breath is suggestive of diabetic ketoacidosis, which in this patient was most likely precipitated by a viral infection. The laboratory findings of hyperglycemia and anion gap metabolic acidosis confirm the diagnosis. The high anion gap is due to the presence of unmeasured anionic ketoacids (eg, beta-hydroxybutyrate, acetoacetate). Patients with metabolic acidosis usually develop a compensatory respiratory alkalosis by hyperventilating (eg, Kussmaul respirations), which helps mitigate the acidemia by causing a drop in the PaCO₂. However, if the PaCO₂ persists above the expected compensatory range (given by Winter formula, where PaCO₂ = [1.5 * HCO₃⁻] + 8 ± 2), it indicates a superimposed respiratory acidosis that is interfering with normal respiratory compensation. This patient's serum HCO₃⁻ of 14 mEq/L should be compensated by a PaCO₂ in the range of 27-31 mm Hg. However, his PaCO₂ is higher than expected, indicating that he has a mixed acid-base disturbance consisting of metabolic and respiratory acidoses. Severe diabetic ketoacidosis can cause pulmonary edema, respiratory fatigue, and decreased mental status, which may lead to hypoventilation and subsequent hypercarbic respiratory failure. (Choice A) Acute adrenal insufficiency is characterized by mineralocorticoid deficiency, which can result in hypotension, hyperkalemia, and mild hyperchloremic acidosis. This patient's laboratory findings are not consistent with acute adrenal insufficiency. (Choice B) Ketoacidosis results in a low serum pH that causes much of the serum bicarbonate (HCO₃⁻) to be converted into carbonic acid (H₂CO₃), reducing the amount of bicarbonate filtered by the kidney. In addition, acidosis increases renal tubular H⁺ secretion, which promotes bicarbonate reuptake and further reduces renal bicarbonate loss. (Choice C) This patient's volume depletion and resulting hypotension reduce renal perfusion pressure, leading to increased renin release by the renal juxtaglomerular cells. (Choice D) Acute tubular necrosis is characterized by progressively increasing serum creatinine with epithelial cell casts and muddy brown granular casts seen on urinalysis. Acute tubular necrosis is unlikely in this patient with normal serum creatinine. Educational objective: Normally, metabolic acidosis is partially compensated for by respiratory alkalosis. When the steady-state PaCO₂ persists above the range given by the Winter formula (PaCO₂ = [1.5 * HCO₃⁻] + 8 ± 2), the patient has a superimposed respiratory acidosis (respiratory failure). __________ References: Respiratory failure in diabetic ketoacidosis. (http://www.ncbi.nlm.nih.gov/pubmed/26240698)

A 23-Year-Old Man Is Brought to the Emergency Department by His