Updated: 4/3/2020

Electrolyte Disturbances

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  • A 56-year-old man is brought to the emergency department by his son due to mild confusion and shortness of breath. Prior to symptom develop he needed to sleep on a recliner due to feeling short of breath while supine. Medical history is significant for chronic obstructive pulmonary disease and a prior myocardial infarction requiring coronary artery bypass grafting. On physical exam, the patient is altered but able to follow commands. There is jugular venous distension, an S3 heart sound, and 2+ lower extremity pitting edema. Laboratory testing is significant for a brain natriuretic peptide 950 pg/mL and serum sodium of 130 mmol/L. (Hyponatremia secondary to congestive heart failure)
Potassium
 
Electrolyte Disturbances
Hyponatremia Hypernatremia
  • Definition
    • serum sodium of < 135 mmol/L
  • Etiology
    • pseudohyponatremia
      • hyperglycemia
      • hyperlipidemia
    • hypervolemic hyponatremia
      • congestive heart failure
      • nephrotic syndrome
      • cirrhosis
      • renal insufficiency
    • hypovolemic hyponatremia
      • vomiting and diarrhea 
      • burns
      • sweating
      • cystic fibrosis
      • diuretic use (e.g., thiazides)
      • angiotensin converting enzyme (ACE) inhibitor
      • adrenal insufficiency
    • euvolemic hyponatremia 
      • psychogenic polydipsia
      • hypothyroidism
      • syndrome of inappropriate anti-diuretic hormone (SIADH)
      • diuretic use
      • ACE inhibitors
  • Presentation
    • stupor
    • coma
    • seizures 
    • nausea
    • malaise
  • Studies
    • assess volume status
    • serum electrolyte and urine studies
  • Treatment
    • address underlying cause
    • asymptomatic
      • free water restriction 
    • moderate hyponatremia
      • IV normal saline
        • loop diuretics may be added
    • severe hyponatremia
      • hypertonic (3%) saline
  • Complications
    • rapid correction of hyponatremia can lead to osmotic demyelination syndrome 
  • Definition
    • serum sodium of > 145 mmol/L
  • Etiology
    • insensible losses (e.g., sweating)
    • osmotic diarrhea
    • osmotic diuresis
      • e.g., diabetic ketoacidosis
    • poor fluid intake
    • diuretic use
    • osmotic diuresis
    • vomiting and diarrhea
    • central and nephrogenic diabetes insipidus
    • hypertonic sodium gain
  • Presentation
    • stupor
    • coma
    • seizure
  • Studies
    • assess volume status
    • serum electrolyte and urine studies
  • Treatment
    • address underlying cause 
    • intravenous (IV) 5% dextrose in water (D5W) 
    • isotonic fluids when hypovolemic 
  • Complications
    • rapid corrrection of hypernatremia can lead to cerebral edema and herniation (from organic osmolytes causing osmotic shifting of fluid into the brain) 
Hypokalemia Hyperkalemia
  • Defintion
    • serum potassium of < 3.5 mEq/L
  • Etiology
    • ↑ insulin
    • hyperglycemia
      • this stimulates endogenous insulin secretion from the pancreas in normal conditions
    • β2-adrenergic agonists
    • alkalosis
      • consider contraction alkalosis when low volume state, high pH, and hypokalemia (treat with fluids) 
    • hyposmolality
    • diarrhea 
    • dehydration
      • secondary to activation of the RAA system causing K and H wasting 
  • Presentation
    • muscle and cardiac dysfunction
      • muscular symptoms
        • abdominal cramping
        • muscle weakness and cramping
      • cardiac symptoms
        • palpitations
    • parasthesias
    • nausea and vomiting
  • Studies
    • electrocardiogram (ECG) findings
      • U waves
      • T wave flattening
  • Treatment
    • address underlying cause
    • potassium repletion
      • remember to not use dextrose-containing fluids as this will stimulate insulin release and shift potassium within the cell
        • this worsens the hypokalemia
    • replace magnesium in magnesium deficiency
  • Definition
    • serum potassium of > 5-5.5 mEq/L
  • Etiology
    • insulin deficiency
    • β2-adrenergic antagonists
    • acidosis
      • cells attempt to buffer excess hydrogen ions to shift these ions into the cells
        • in exchange for this intracellular uptake of hydrogen, potassium is transferred out the cell
          • this attempts to achieve electroneutrality
    • digitalis
      • secondary to dose-dependent Na+/K+ -ATPase pump inhibition
    • cell lysis (e.g., rhabdomyolysis)
    • exercise
    • hyperosmolarity
    • succinylcholine
    • TMP-SMX 
    • ACE inhibitors 
  • Presentation
    • muscle and cardiac dysfunction
      • muscular symptoms
        • myalgias
        • muscle paralysis
        • chest pain
      • cardiac symptoms
        • arrhythmias and palpitations
    • nausea and vomiting
    • parasthesias
  • Studies
    • ECG findings
      • peaked T waves and wide QRS  
  • Treatment 
    • address underlying cause
    • IV calcium gluconate  
      • has no effect on potassium levels but stabilizes the myocardium
    • shifting potassium within cells 
      • insulin plus glucose
      • β2-adrenergic agonists
    • lowering body potassium
      • sodium polystyrene sulfonate
        • this is a cation exchange resin
    • dialysis
      • used in patients unresponsive to medical therapy
Hypocalcemia Hypercalemia
  • Definition
    • serum total calcium < 8.4 mg/dL
      • decreased albumin can cause a decreased total calcium but a normal free calcium (thus the patient is asymptomatic) 
    • ionized fraction of calcium < 4.4 mg/dL 
  • Etiology
    • renal failure
    • hypoparathyroidism
    • vitamin D deficiency
    • hypomagnesemia
      • inhibits PTH release
    • pancreatitis
    • alkalemia
  • Presentation
    • seizures
    • tetany
    • Chvostek sign
      • ipsilateral facial muscle contraction caused by tapping the facial nerve
    • Trousseau sign
      • carpopedal spasms by inflating the sphygmomanometer above systolic blood pressure
  • Studies
    • QTc prolongation
  • Treatment
    • address underlying cause
    • asymptomatic or patients with chronic hypocalcemia
      • oral calcium replacement therapy such as
        • calcium citrate
        • calcium carbonate
      • vitamin D supplementation
      • thiazides for patients with hypoparathyroidism
    • symptomatic patients
      • IV calcium gluconate
        • first-line
    • chronic renal failure
      • phosphate binders
      • oral calcium replacement
      • calcitriol
  • Definition
    • serum total calcium > 10.5 mg/dL
    • ionized fraction of calcium > 5.6 mg/dL
  • Etiology
    • hyperparathyroidism
    • humoral hypercalcemia of malignancy
      • higher calcium with more symptomatic patients (typically > 12.0 mg/dL) 
      • secondary to parathyroid hormone-related peptide (PTHrP)
      • associated with squamous cell cancer and solid tumors involving the
        • lung
        • esophageus
        • skin
        • cervix
        • breast
        • kidney
    • vitamin D overdose
    • granulomatous diseases like
      • sarcoidosis
    • thiazide diuretics
    • lithium
    • calcium-containing antacids
    • familial hypocalciuric hypercalcemia 
    • immobilization
  • Presentation 
    • nephrolithiasis
    • polyuria
    • muscle weakness
    • bone pain
    • abdominal pain 
      • secondary to bowel hypomotility and constipation 
    • confusion
    • stupor
    • coma
    • mnemonic: stones (renal), bones (pain), groans (abdominal pain), thrones (↑ urinary frequency), and psychiatric overtones (altered mental status)
  • Studies
    • ECG
      • shortened QTc interval
  • Treatment
    • address underlying cause
    • IV isotonic normal saline
      • increases urinary calcium excretion
    • calcitonin
      • impairs bone resorption
      • increases urinary calcium excretion
    • bisphosphonates (e.g., zoledronic acid and pamidronate)  
      • has a delayed onset of action
      • impairs bone resorption
      • long term calcium control
    • loops diuretics
      • increases urinary calcium excretion
Hypomagnesemia Hypermagnesemia
  • Definition
    • typically serum magnesium < 1.8 mg/dL
  • Etiology
    • magnesium redistribution
      • refeeding syndrome
    • malnutrition
    • alcohol use disorder
    • anorexia nervosa
    • proton pump inhibitors
    • loop diuretics
    • digoxin
  • Presentation
    • tetany
    • torsades de pointes
    • hypokalemia
    • hypocalcemia
      • when significant (< 1.2 mg/dL)
  • Studies
    • ECG
      • U waves
      • T wave flattening
      • QT prolongation
      • widened QRS complexes
  • Treatment
    • magnesium repletion
      • asymptomatic
        • oral magnesium supplementation
      • severe or symptomatic hypomagnesemia
        • IV magnesium sulfate
  • Definition
    • typically serum magnesium > 2.6 mg/dL
  • Etiology
    • increased magnesium ingestion
      • magnesium cathartics
      • antacids
      • laxatives
      • dietary supplements
    • renal insufficiency
  • Presentation
    • ↓ deep tendon reflexes
    • bradycardia
    • cardiac arrest
    • hypocalcemia
  • Studies
    • ECG
      • PR, QRS, and QT prolongation
      • heart block
  • Treatment
    • address underlying cause
    • IV isotonic saline
    • loop diuretics can be considered
Hypophosphatemia Hyperphosphatemia
  • Definition
    • serum phosphate < 2.5 mg/dL
  • Etiology
    • refeeding syndrome 
    • hungry bone syndrome
    • inadquate phosphate intake
    • hyperparathyroidism
    • phosphate binders
  • Presentation
    • weakness
    • muscle and bone pain
    • osteomalacia
    • rickets
  • Treatment
    • address underlying cause
    • mild hypophosphatemia
      • increase dietary phosphate intake
    • moderate hypophosphatemia
      • oral phosphate replacement therapy
        • IV phosphate replacement in patients who are on a ventilator
    • severe hypophosphatemia
      • IV phosphate replacement
  • Definition
    • serum phosphate > 4.5 mg/dL
  • Etiology
    • acute phosphate ingestion
    • hypoparathyroidism
    • vitamin D toxicity
    • renal failure
    • rhabdomyolysis
    • tumor lysis syndrome
  • Presentation
    • typically asymptomatic
  • Treatment
    • address underlying cause
    • dietary modifications
    • phosphate binders
      • calcium carbonate or acetate
 
 

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(M2.RL.17.4830) A 75-year-old man with coronary artery disease and mitral valve stenosis status-post coronary artery bypass graft and mitral bioprosthetic valve replacement is evaluated in the intensive care unit. His postsurgical course was complicated by ventilator-associated pneumonia and bilateral postoperative pleural effusions requiring chest tubes. He has been weaned from the ventilator and has had his chest tubes removed but has required frequent suctioning to minimize aspirations. He has been dependent on a percutaneous gastrostomy tube for enteral nutrition for the past four weeks. He is currently on aspirin, carvedilol, atorvastatin, ceftazidime, and pantoprazole. He has a history of prostate cancer status post radical prostatectomy. His temperature is 96°F (35.6°C), blood pressure is 95/55 mmHg, pulse is 50/min, and respirations are 20/min. On physical exam, he is not alert and oriented but responds with moans when stimulated. His laboratory data are listed below:

Serum:
Na+: 145 mEq/L
Cl-: 110 mEq/L
K+: 3.4 mEq/L
HCO3-: 26 mEq/L
BUN: 10 mg/dL
Glucose: 112 mg/dL
Creatinine: 1.4 mg/dL
Thyroid-stimulating hormone: 10 µU/mL
Ca2+: 11.1 mg/dL
PO4-: 1.0 mg/dL
AST: 6 U/L
ALT: 10 U/L
Albumin: 2.5 mg/dL
Lactate dehydrogenase: 200 U/L (140-280 U/L)
Haptoglobin: 150 mg/dL (30-200 mg/dL)
1,25-(OH)2 D3: 10 pg/mL (15-75 pg/mL)
Parathyroid hormone: 9 pg/mL (10-60 pg/mL)

Leukocyte count: 10,000 cells/mm^3 with normal differential
Hemoglobin: 9 g/dL
Hematocrit: 30 %
Platelet count: 165,000 /mm^3

His electrocardiogram and chest radiograph are shown in Figures A and B. What is the most likely cause of his hypercalcemia?
Tested Concept

QID: 109466
FIGURES:
1

Hemolytic anemia

2%

(1/62)

2

Euthyroid sick syndrome

15%

(9/62)

3

Immobilization

66%

(41/62)

4

Malignancy

13%

(8/62)

5

Primary hyperparathyroidism

5%

(3/62)

M 6 C

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(M2.RL.17.4799) A 62-year-old male with a history of chronic lymphocytic leukemia is admitted to the hospital for chemotherapy with fludarabine after transformation into prolymphocytic leukemia. Three days later, the nurse calls you because the patient is vomiting. The patient reports he is nauseous and he feels weak. On physical exam, he is ill-appearing, and you appreciate diffuse, bilateral lymphadenopathy, symmetrical muscle weakness, and bilateral areflexia. Labs are drawn and an electrocardiogram (EKG) is obtained, which is shown in Figure A. In addition to cardiac stabilization, which of the following is the best next step in management? Tested Concept

QID: 109340
FIGURES:
1

Albuterol

35%

(17/49)

2

Allopurinol

14%

(7/49)

3

Furosemide

8%

(4/49)

4

Rasburicase

22%

(11/49)

5

Sodium polystyrene sulfonate

20%

(10/49)

M 7 C

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(M2.RL.17.20) A 58-year-old man complains of ascending weakness, palpitations, and abdominal pain. He has a history of hypertension, type II diabetes mellitus, diabetic retinopathy, and end-stage renal disease requiring dialysis. He denies any recent infection. Physical examination is notable for decreased motor strength in both his upper and lower extremities, intact cranial nerves, as well as decreased bowel sounds. On further questioning, the patient shares that he has been depressed, as he feels he may not be able to see his grandchildren grow due to his complicated medical course. This caused him to miss two of his dialysis appointments. Which of the following will mostly likely be found on electrocardiography? Tested Concept

QID: 105386
1

Progressive PR prolongation, followed by a 'drop' in QRS

0%

(0/2)

2

S wave in lead I, Q wave in lead III, and inverted T wave in lead III

0%

(0/2)

3

ST-segment elevation in leads II, III, and aVF

0%

(0/2)

4

Peaked T-waves and shortened QT interval

100%

(2/2)

5

Diffuse PR segment depression and ST-segment deviations

0%

(0/2)

M 6 A

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(M2.RL.15.2) A 54-year-old man presents with 3 days of non-bloody and non-bilious emesis every time he eats or drinks. He has become progressively weaker and the emesis has not improved. He denies diarrhea, fever, or chills and thinks his symptoms may be related to a recent event that involved sampling many different foods. His temperature is 97.5°F (36.4°C), blood pressure is 133/82 mmHg, pulse is 105/min, respirations are 15/min, and oxygen saturation is 98% on room air. Physical exam is notable for a weak appearing man with dry mucous membranes. His abdomen is nontender. Which of the following laboratory changes would most likely be seen in this patient? Tested Concept

QID: 104276
1

Anion gap metabolic acidosis and hypokalemia

0%

(0/41)

2

Metabolic alkalosis and hyperkalemia

7%

(3/41)

3

Metabolic alkalosis and hypokalemia

2%

(1/41)

4

Non-anion gap metabolic acidosis and hypokalemia

12%

(5/41)

5

Respiratory acidosis and hyperkalemia

76%

(31/41)

M 6 E

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(M2.RL.14.30) A 19-year-old male with cystic fibrosis is evaluated in the clinic for regular health maintenance. He is compliant with his respiratory therapy, but states that he often "forgets" to take the medications before he eats. A panel of labs is drawn which reveals a moderate vitamin D deficiency. Which of the following electrolyte abnormalities might be seen as a consequence of vitamin D deficiency? Tested Concept

QID: 104304
1

Increased calcium and increased phosphate

0%

(0/77)

2

Increased calcium and decreased phosphate

4%

(3/77)

3

Decreased calcium and increased phosphate

35%

(27/77)

4

Decreased calcium and decreased phosphate

56%

(43/77)

5

Normal calcium and decreased phosphate

4%

(3/77)

M 6 E

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(M2.RL.14.3) A 64-year-old man presents for a routine physical. He states that he has felt abnormally weak during this time and has had trouble focusing in the setting of losing 5 pounds. The patient states he has a decreased appetite and also has not had a bowel movement in the past 5 days and feels uncomfortable. On review of system, he endorses abdominal pain. His temperature is 97.5°F (36.4°C), blood pressure is 132/83 mmHg, pulse is 115/min, respirations are 15/min, and oxygen saturation is 98% on room air. Physical exam is notable only for the patient being able to recall 1 of 3 objects. His cranial nerve exam is unremarkable and his gait is stable. Urinalysis is initially notable for a clear and voluminous sample with a low specific gravity. Which of the following tests is most likely abnormal in this patient? Tested Concept

QID: 104277
1

Calcium level

12%

(5/43)

2

Lead level

9%

(4/43)

3

Phosphate level

5%

(2/43)

4

Potassium level

60%

(26/43)

5

TSH level

12%

(5/43)

M 6 E

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(M2.RL.12.1) A 32-year-old man with a history of chronic alcoholism presents to the emergency department with vomiting and diarrhea for 1 week. He states he feels weak and has had poor oral intake during this time. The patient is a current smoker and has presented many times to the emergency department for alcohol intoxication. His temperature is 97.5°F (36.4°C), blood pressure is 102/62 mmHg, pulse is 135/min, respirations are 25/min, and oxygen saturation is 99% on room air. On physical exam, he is found to have orthostatic hypotension and dry mucus membranes. Laboratory studies are ordered as seen below.

Serum:
Na+: 139 mEq/L
Cl-: 101 mEq/L
K+: 3.9 mEq/L
HCO3-: 25 mEq/L
BUN: 20 mg/dL
Glucose: 99 mg/dL
Creatinine: 1.1 mg/dL
Ca2+: 9.8 mg/dL

The patient is given normal saline, oral potassium, dextrose, thiamine, and folic acid. The following day, the patient seems confused and complains of diffuse weakness and muscle/bone pain. An ECG and head CT are performed and are unremarkable. Which of the following is the most likely explanation for this patient's new symptoms?
Tested Concept

QID: 102617
1

Hypocalcemia

26%

(13/50)

2

Hypoglycemia

4%

(2/50)

3

Hypomagnesemia

12%

(6/50)

4

Hyponatremia

36%

(18/50)

5

Hypophosphatemia

20%

(10/50)

M 6 E

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