Pathophysiology of Electrolyte Imbalances

Question 1

What is the normal plasma phosphate level?

Answer 1

3.0-4.5 mg/dL

Question 2

What is the clinical presentation of hypernatremia?

Answer 2

Neurologic symptoms, volume depletion, urine Na+ <20, low urine osmolality

Question 3

What is the clinical presentation of euvolemic hyponatremia?

Answer 3

Neurologic symtoms, urine Na+ >20, high urine osmolality, elevated ADH

Question 4

A water deprivation test may be used to diagnose diabetes insipidus. What indicates a positive test?

Answer 4

Increased urine volume despite water deprivation is indicative of diabetes insipidus

Question 5

Diabetes inspidius is characterized by polyuria. With what electrolyte abnormality is the condition most associated?

Answer 5

Hypernatremia

Question 6

What is the treatment for hypovolemic hyponatremia?

Answer 6

Isotonic fluid (0.9% saline)

Question 7

Elevated plasma osmolality with a normal osmolar gap is suggestive of what disorders?

Answer 7

Hypernatremia, hyperglycemia, or hyperuricemia

Question 8

What is the most common cause of pseudohyponatremia?

Answer 8

Elevated cholesterol, also elevated plasma proteins or immunoglobulins

Question 9

True/False. Patients with hypovolemic hyponatremia often present with neurologic symptoms.

Answer 9

False - they most commonly present with dehydration and urine Na+ <20

Question 10

Elevated plasma osmolality with a high osmolar gap is indicative of what issue?

Answer 10

The presence of unmeasured osmotically active solutes, such as ethanol, ethylene glycol, methanol, alcohol, ketones, lactic acid, mannitol

Question 11

What is the normal plasma calcium level?

Answer 11

8.5-10.5 mg/dL

Question 12

What is the physiologic cause of euvolemic hyponatremia?

Answer 12

Inappropriate ADH release

Question 13

What is the single most accurate test to diagnose euvolemic hyponatremia?

Answer 13

Elevated serum ADH

Question 14

What ion concentrations are highest in the plasma?

Answer 14

Na+ & Cl-

Question 15

What is the normal serum range of sodium?

Answer 15

135-145 mEq/L

Question 16

What is the most common cause of hypernatremia?

Answer 16

Reduced water intake

Question 17

What are the likely ADH levels in patients with diabetes inspidius?

Answer 17

Central - low ADH

Nephrogenic - normal or high ADH

Question 18

What lab findings are typical in patients with hypernatremia?

Answer 18

High serum osmolality, low urine osmolality, low urine specific gravity

Question 19

Reduction in cardiac output, circulating volume, or organ perfusion is associated with what electrolyte abnormality?

Answer 19

Hypervolemic hyponatremia

Question 20

What symptoms are associated with hypocalcemia?

Answer 20

Muscle tetany, confusion, irritability, prolonged QT, CHF

Question 21

Mild cases of hypercalcemia are often asymptomatic. What symptoms are associated with severe cases?

Answer 21

Neuropsychiatric symptoms, GI symptoms, nephrogenic DI, CV symptomes

Question 22

How can central and nephrogenic diabetes insipidus be differentiated via lab testing?

Answer 22

Administration of exogenous ADH. A positive response indicates cDI and a negative response indicated nDI

Question 23

What is the equation to calculate ECF osmolality?

Answer 23

2(Na+) + (glucose/18) + (BUN/2.8)

Question 24

Symptoms of hyperphosphatemia resemble that of what other electrolyte abnormality?

Answer 24

Hypocalcemia - neuromuscular excitability

Question 25

True/False. A patient identified as having hyponatremia should be treated to return Na+ levels to normal as quickly as possible.

Answer 25

False - in patients with chronic hyponatremia, rapid correct can cause osmotic demyelination syndrome

Question 26

There are two types of diabetes insipidus, central and nephrogenic. What is the difference?

Answer 26

Central - deficiency of ADH

Nephrogenic - renal resistance to ADH

Question 27

What is the clinical presentation of hypervolemic hyponatremia?

Answer 27

Edema, ascites, urine Na+ <20, no neurologic symptoms