Free nephrology board questions: Electrolyte Disorders

A 28-year-old woman with type 1 diabetes has 2 days of nausea, vomiting, and abdominal pain. She has missed some insulin doses and cannot tolerate oral intake. Heart rate is 118/min and BP 92/58 mm Hg; she has deep, rapid respirations, dry mucous membranes, and capillary refill of 4 seconds. Na 132, K 4.3, Cl 88, total CO₂ 14 mEq/L; BUN 32 mg/dL; creatinine 1.43 mg/dL; glucose 574 mg/dL. Arterial pH 7.35, PaCO₂ 28 mm Hg. Which acid-base disorder best explains these findings?

A 35-year-old woman presents to the hospital with 2 days of worsening nausea, vomiting, and abdominal pain. Her past medical history is significant for type 1 diabetes and hypothyroidism. She reports running out of her home insulin several days ago, and a review of systems is positive for polyuria and increased thirst. On arrival, BP is 94/52 mm Hg, heart rate is 134/min, and respiratory rate is 24/min. On physical examination, she appears somewhat lethargic, with dry mucus membranes and a 2/6 systolic murmur best heard over the left upper sternal border. The rest of her physical examination is unremarkable. Based on her initial laboratory results, she is initiated on an IV insulin drip and potassium-containing IV fluids for management of diabetic ketoacidosis (DKA). Several hours later, she reports improving nausea and abdominal pain, and she is able to eat crackers. Laboratory data (initial; five hours later; reference range): Serum: sodium 132 mEq/L; 138 (136–145); potassium 4.8 mEq/L; 4.5 (3.5–5.0); chloride 98 mEq/L; 106 (98–106); total CO₂ 14 mEq/L; 22 (23–28); creatinine 1.4 mg/dL; 1.1 (0.5–1.1); glucose 384 mg/dL; 235 (70–99, fasting); albumin 3.6 g/dL; 3.3 (3.5–5.5); β-hydroxybutyrate 6.2 mmol/L; 0.4 (<0.5); lactate 2.0 mmol/L; 1.8 (0.7-2.1). Venous blood gas: pH 7.22; 7.30 (7.32–7.41); pCO₂ 32 mm Hg; 42 (42–53); pO₂ 42 mm Hg; 44 (35–42). Urinalysis: pH 6.0; 5.5 (4.5–8.0); specific gravity 1.023; 1.012 (1.005–1.025); glucose 4+; 2+ (negative); ketones small; large (negative); protein 2+; 1+ (negative). Which ONE of the following is the MOST appropriate next step in management?

A 71-year-old man presents to the emergency department after a fall. His wife notes that he has become progressively more confused during the past 2 weeks, and his gait has become unsteady. On examination, BP is 112/70 mm Hg, with heart rate of 82/min without postural change. There are no demonstrable injuries related to the fall. Heart and lungs are normal, and there is no edema. Neurologic exam reveals confusion, decreased coordination, and inability to stand or walk independently. Laboratory data: serum sodium 117 mEq/L (reference 136–145); potassium 3.8 mEq/L (3.5–5.0); chloride 88 mEq/L (98–106); total CO₂ 24 mEq/L (23–28); BUN 12 mg/dL (8–20); creatinine 0.8 mg/dL (0.7–1.3); glucose 91 mg/dL (70–99, fasting); osmolality 253 mOsm/kg H₂O (275–295). Urine: sodium 52 mEq/L (varies with intake); creatinine 98 mg/dL (varies with intake); osmolality 493 mOsm/kg H₂O (varies with intake). Which ONE of the following is the next BEST STEP in management?

A 55-year-old woman with metastatic colorectal cancer is treated with cetuximab (anti-EGFR monoclonal antibody). After 6 cycles, she presents with muscle cramps, tremors, and ECG changes (prolonged QTc, wide QRS). Labs: magnesium 0.5 mg/dL (normal 1.6–2.6), potassium 2.8 mEq/L, calcium 7.8 mg/dL. What is the mechanism of hypomagnesemia in this patient and the MOST appropriate management?

A 60-year-old man with primary biliary cholangitis and obstructive jaundice is found on routine labs to have a serum sodium of 128 mEq/L. He is asymptomatic and euvolemic, with normal blood pressure and no neurologic symptoms. Serum glucose is 90 mg/dL, BUN is 14 mg/dL, and total cholesterol is markedly elevated at 620 mg/dL. Measured serum osmolality is 290 mOsm/kg. Which of the following diagnoses BEST fits these findings?

A 57-year-old woman undergoes a hysteroscopy complicated by uterine perforation and extravasation of irrigant solution. She has a successful surgical repair and is then extubated in the post-anesthesia care unit. Her pain is treated with IV morphine. She has incisional pain and mild nausea. On physical examination, BP is 124/72 mm Hg, heart rate is 92/min, respiratory rate is 14/min, and temperature is 37.6°C. She is no acute distress. There is an expected degree of tenderness at the site of the surgical incision. There is no edema. Laboratory data (1 day preoperative, 1 hour postoperative; reference): sodium 137, 121 mEq/L (136–145); creatinine 0.8, 0.7 mg/dL (0.5–1.1); glucose 86, 75 mg/dL (70–99, fasting); osmolality 289, 282 mOsm/kg H₂O (275–295). Which ONE of the following is the MOST appropriate treatment?

A 57-year-old man with diabetes and bipolar disorder treated for many years with lithium has 5 years of polyuria and polydipsia, worse over the past 3 months; he drinks 6 L daily. Medications are metformin and lithium. After a 12-hour fast (time 0), fasting continues for 6 more hours, with desmopressin given at 0, 2, and 4 hours. Values at 0, 2, 4, and 6 hours: serum sodium 148, 153, 155, 156 mEq/L; serum glucose 245, 204, 185, 201 mg/dL; urine sodium <30 mEq/L throughout; urine osmolality 90, 95, 97, 99 mOsm/kg H₂O. What is the most likely cause of his symptoms?

A previously healthy 27-year-old man is brought in after being found down in a nightclub bathroom. He was well earlier and had at least a few mixed drinks interspersed with glasses of water. BP is 145/88 mm Hg and temperature 38°C; he is confused and diaphoretic. Serum sodium 120 mEq/L, creatine kinase 4300 U/L, serum osmolality 265 mOsm/kg H₂O. Urine osmolality is 457 mOsm/kg H₂O and urine sodium 58 mg/dL. Which substance most likely explains his laboratory abnormalities?

A 65-year-old man is in the ICU with septic shock from pneumonia on norepinephrine. He was intubated on day 1 and ventilated with tidal volume 12 mL/kg ideal body weight and PEEP 5 cm H₂O. On day 2, chest radiograph shows progressive bilateral opacities, and settings are changed to tidal volume 6 mL/kg, PEEP 20 cm H₂O, and FiO₂ 60%. One hour later, plateau pressure is 28 cm H₂O and hemodynamics are stable on low-dose norepinephrine. Arterial blood gas: pH 7.32, PaCO₂ 50 mm Hg, PaO₂ 80 mm Hg, bicarbonate 25 mEq/L. What is the most appropriate next step?

A 67-year-old man with hypertension and COPD on 2 L/min home oxygen presents with progressive lethargy and altered mental status 1 week after an upper respiratory infection. BP is 145/78 mm Hg, oxygen saturation 86% on 6 L/min, with diffuse bilateral wheezing. He is treated for a COPD exacerbation and started on BiPAP for hypercarbia, and his mental status improves over 48 hours. Arterial blood gas on admission and now: pH 7.27 and 7.55; PaCO₂ 81 and 40 mm Hg; bicarbonate 36 and 34 mEq/L. What is the most appropriate treatment for his current acid-base abnormality?

A 58-year-old man with a past medical history of chronic myeloid leukemia presents to the hospital for new-onset weakness. He denies nausea and vomiting but reports poor oral intake for the last 3 days. Three weeks ago, he saw his primary care physician, and his laboratory studies were unchanged from his baseline. Repeat laboratory data: WBC count 310,000/µL (reference 4000–11,000); blasts 25% (0%); serum potassium 2.8 mEq/L (3.5–5.0); total CO₂ 26 mEq/L (23–28); creatinine 1.3 mg/dL (baseline) (0.7–1.3); uric acid 6.5 mg/dL (3.0–7.0); magnesium 2 mEq/L (1.6–2.6); phosphorus 3.5 mg/dL (3.0–4.5). Which ONE of the following is the most likely cause of his abnormal potassium value?

A 75-year-old woman with a history of hypertension and diabetes is brought to the emergency department after being found confused at home. She was in her usual state of health the previous day. She is unable to provide any history, but her children report that since her husband passed away 2 weeks ago, she has hardly eaten while consuming an increased amount of alcohol. Medications include chlorthalidone and metformin. On arrival, BP is 92/60 mm Hg and heart rate is 104/min. Skin turgor is poor. She is lethargic but answers simple questions, and there are no focal neurologic deficits. She receives 0.9% saline 2 L and potassium chloride 60 mEq over the next few hours, and urine output increases from 20 to 300 mL/h. Mental status remains unchanged. Laboratory data (on arrival, 6 hours later; reference): sodium 110, 121 mEq/L (136–145); potassium 2.9, 3.4 mEq/L (3.5–5.0); chloride 78, 93 mEq/L (98–106); glucose 154, 102 mg/dL (70–99, fasting); BUN 38, 18 mg/dL (8–20); creatinine 1.3, 0.9 mg/dL (0.5–1.1); serum osmolality 240, 263 mOsm/kg H₂O (275–295); urine sodium 11 mEq/L on arrival (varies); urine osmolality 190 mOsm/kg H₂O on arrival (varies). Which of the following is the next BEST STEP in management?

A 63-year-old man with a history of CKD stage 3, type 2 diabetes mellitus, and congestive heart failure with preserved ejection fraction presents to the emergency department with a 3-day history of nausea, vomiting, and malaise. He receives most of his care at another health system and is unable to provide a current medication list. Physical examination reveals a BP of 121/71 mm Hg, heart rate of 92/min, respiratory rate of 26/min, and temperature of 37.3°C. His abdomen is soft and nontender, and the remainder of the examination is normal. Laboratory data: sodium 136 mEq/L (reference 136–145); potassium 3.6 mEq/L (3.5–5.0); chloride 99 mEq/L (98–106); total CO₂ 12 mEq/L (23–28); glucose 161 mg/dL (70–99, fasting); creatinine 2.0 mg/dL (baseline) (0.7–1.3); lipase 33 IU/mL (10–140); lactic acid 0.6 mmol/L (0.7–2.1). Urinalysis reveals 3+ ketones and 2+ glucose but is otherwise normal. Which ONE of the following medications is MOST LIKELY to be the cause of this patient's clinical presentation?

A 57-year-old man with CKD stage 3b, and GERD is admitted for elective right knee arthroplasty. He has had several days of constipation. Surgery is uncomplicated (minimum BP 92/68 mm Hg). Postoperative potassium is 6.1 mEq/L, treated with insulin, dextrose, and two doses of sodium polystyrene sulfonate. Hospital medications include cefazolin, insulin, famotidine, oxycodone, and prophylactic heparin. On day 3 he develops severe lower abdominal pain, decreased bowel sounds, and BP 95/40 mm Hg. Hemoglobin falls from 9.2 to 7.5 g/dL; lactate is normal. Abdominal x-ray shows free air under the diaphragm. What is the most likely diagnosis?

A 25-year-old woman with a medical history of asthma and hypothyroidism presents to the emergency department with 1 week of progressive wheezing and shortness of breath. Her current medications include a fluticasone/salmeterol inhaler and levothyroxine sodium, and she reports using an albuterol metered-dose inhaler every 1–2 hours without relief. On examination, her BP is 110/62 mm Hg, heart rate is 100/min, respiratory rate is 24/min, her oxygen saturation is 89% while breathing supplemental oxygen at 2 L/min, and body mass index (BMI) is 22 kg/m². She appears in respiratory distress, with diffuse wheezing in all lung fields. She has reduced muscle strength in her legs bilaterally. She is treated with albuterol nebulizers, methylprednisolone, and 2 L of normal saline IV. Laboratory data: serum sodium 139 mEq/L (reference 136–145); potassium 2.8 mEq/L (3.5–5.0); chloride 112 mEq/L (98–106); total CO₂ 20 mEq/L (23–28); BUN 16 mg/dL (8–20); creatinine 0.8 mg/dL (0.5–1.1); glucose 95 mg/dL (70–99, fasting); thyroid-stimulating hormone 3.5 µU/mL (0.5–4.0); free thyroxine 1.0 ng/dL (0.8–1.8). Arterial blood gas: arterial pH 7.35 (7.38–7.44); PaCO₂ 38 mm Hg (38–42). Urine, spot: sodium 18 mEq/L (varies); potassium 10 mEq/L (varies); chloride 28 mEq/L (varies); creatinine 85 mg/dL (varies). A urinalysis reveals a pH of 5.0, with negative blood and protein. Which ONE of the following is the MOST likely cause of this patient’s hypokalemia?