You are asked to consult on a previously healthy 68-year-old woman who presented with malaise and one episode of hematuria. She visited her primary care doctor 5 days ago for a “bladder infection” and was prescribed trimethoprim-sulfamethoxazole, which she has been taking. She is alert and oriented, and her physical examination is within normal limits. Her vital signs are normal. Her laboratory data are unremarkable except for elevated eosinophils, creatinine of 3 mg/dL, and urea 41 mg/dL.
What would you expect to see in urine analysis?
Correct Answer: C
Acute interstitial nephritis (AIN) is a rare cause of AKI. Most patients present with nonspecific signs and symptoms of acute kidney failure. The classical triad of fever, rash, and eosinophilia occurs only in 10% of the population. Moreover, patients can be oliguric or nonoliguric, and hematuria can occur in 5% of them. The most common cause of AIN is drug-associated, such as trimethoprim-sulfamethoxazole that the patient has been taking. Other causes include infection, idiopathic, or associated with systemic autoimmune diseases. Laboratory results usually show an increase in creatinine level, eosinophilia or eosinophiluria, white blood cells or white blood cell casts in urine (question 1—choice C), and a variable degree of proteinuria.
Muddy brown cast is usually seen in acute tubular necrosis (ATN), which is associated with prolonged prerenal insult or nephrotoxin induced. Red blood cell cast is associated with acute glomerulonephritis, in which immunological mechanisms cause glomerular inflammation. These mechanisms could be infection-related, cancer, or exposure to drugs of toxins. Enveloplike, calcium oxalate crystals are seen in patients with ethylene glycol poisoning. As the patient is healthy and does not have any risk factors, and her examination is normal, ATN, acute glomerulonephritis, or ethylene glycol poisoning are very unlikely.
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What management should you pursue next?
Correct Answer: B
Treatment of AIN includes discontinuing the offending agent (question 2—choice B) or treating the underlying disease. In severe cases of biopsy- confirmed AIN, steroids can be administered. Answer A is incorrect because fomepizole is the treatment for ethylene glycol poisoning, not AIN. Her urea/creatinine ratio is less than 20, making prerenal cause unlikely, so fluid bolus would not be needed here. Also, CT scan with IV contrast would not be the best choice as there is no indication for this study, and IV contrast should be avoided in patients with AKI (answer D).
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Which of the electrolyte abnormalities is associated with advanced chronic kidney disease?
Correct Answer: A
Kidneys play an essential role in the body to maintain normal acid-base status and electrolyte levels. In addition, kidneys excrete acids in the form of ammonium chloride. As kidney disease progresses, patients lose the ability to effectively neutralize and excrete acids, leading to metabolic acidosis. As the glomerular filtration decreases, renal failure patients lose the ability to concentrate urine, which can lead to hyponatremia. Studies suggest that a decreased clearance of vasopressin also contributes to the development of dysnatremia. It is not uncommon for hyperkalemia, hyperphosphatemia, and hypermagnesemia to occur as the kidneys lose their ability to excrete these electrolytes.
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You are working as an intensivist in a rural hospital where the emergency physician calls you to evaluate a patient for intensive care unit (ICU) admission. When you come to the emergency department (ED), you see a disheveled, cachectic, old gentleman who was brought in by his neighbor for altered mental status. His neighbor reports that the patient has been complaining about back pain, and he was taking some “over-the-counter” (OTC) pain medication. You cannot elicit any history from the patient, and his physical examination is unremarkable. His laboratory data show:
His arterial blood gas shows pH 7.39 and pCO2 38.
What is the next test that you would order?
Because we cannot obtain any useful history from the patient, we need to look for clues from his physical examination and laboratory results. His anion gap (corrected for serum albumin) is 147 − 113 − 22 + 2.5(4 − 2) = 17, indicating a high-gap metabolic acidosis. Based on the Winter’s formula, his expected pCO2 should be 1.5 × 22 + 8 = 41 mm Hg. However, as his pCO2 is 38, he also has a respiratory alkalosis.
In the presence of a high-gap metabolic acidosis, we need to identify if there is a third process. The patient’s Δ gap = 17 – 12 = 5, and Δ bicarbonate = 24 – 22 = 2. As Δ gap > Δ bicarbonate, he also has a metabolic alkalosis.
The history of taking OTC medications and the combination of metabolic acidosis and respiratory alkalosis make aspirin toxicity high on the differential diagnosis. Aspirin could also cause altered mental status, confusion, and possible seizure at a toxic dose. Moreover, aspirin could cause GI upset, which could explain his metabolic alkalosis.
Although euglycemic diabetes ketoacidosis has been described in the literature, a normal glucose level makes diabetic ketoacidosis very unlikely. Similarly, alcohol intoxication is less likely to cause respiratory alkalosis, which makes it lower in the differential diagnosis. Because of its availability OTC and the potential combination with aspirin in some formulary, acetaminophen level should be checked; however, it would not be the best choice as it does not typically cause mixed metabolic acidosis and respiratory alkalosis. Moreover, acetaminophen overdose typically presents with gastrointestinal signs and symptoms.
What is the BEST next step of management?
In a patient with salicylate toxicity, the presence of altered mental status is an indication for emergent dialysis. Other indications for emergent dialysis are pulmonary edema, seizure, decreased renal function impairing salicylate elimination (consider when creatinine >2 mg/dL or 1.5 mg/dL for elderly or glomerular filtration rate <45 mL/min per 1.73 m2 ), severe volume overload, severe acidemia, and serum salicylate level >90 mg/dL. Urine alkalization is indicated in salicylate poisoning to enhance its elimination; however, the presence of altered mental status and AKI makes dialysis the best choice for this patient.
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