Disorders of Salt and Water Balance

Question 1

Hyponatriemia

Answer 1

• Low plasma sodium concentration

- Induces fluid movement into cells

Question 2

Hypernatriemia

Answer 2

• High plasma sodium concentration

- Induces fluid movement out of cells

Question 3

Hypovolemia

Answer 3

ECF volume contraction

Question 4

Hypervolemia

Answer 4

ECF volume expansion

Question 5

Hyponatriemia

-In virtually all patients, hyponatriemia results from?

Answer 5

the intake (oral or intravenous) and subsequent retention of water

Question 6

What happens in a normal individual when they have water load?

Answer 6

The water will be rapidly excreted as the dilutional fall in serum osmolality suppresses the release of ADH thereby allowing excretion of the excess water in a dilute urine

Question 7

What happens in patients who develop hyponetriemia?

Answer 7

They typically have an impairment in renal water excretion, most often due to an inability to suppress ADH secretion

Question 8

Hyponatriemia

-Exception?

Answer 8

Patients with primary polydipsia
-drink such large quantities of fluid that they overwhelm the excretory capacity of the kidney even though ADH release is appropriately suppressed

Question 9

Causes of hyponatriemia

-Pseudohyponatriemia?

Answer 9

• Hyperproteinemia
• Hyperproteinemia
• Hyperlipidemia
• Hypercholesterolemia
• Unmeasured osmol

Question 10

Causes of hyponatriemia

• Hyperproteinemia, hyperproteinemia, hyperlipidemia
  
  • Lead to?

Answer 10

Errors in lab measurement of Na

Question 11

Causes of hyponatriemia

-Hyperglycemia and unmeasured osmol?

Answer 11

-Water is pulled via osmotic gradient into vasculature with resulting dilutional hyponatriemia

Question 12

True hyponatriemia

-Dilute urine and low ADH?

Answer 12

• Reset osmostat (e.g. pregnancy)

- Psychogenic polydipsia

Question 13

True hyponatriemia

-Concentrated urine, high ADH?

Answer 13

• Decreased ECV (e.g. CHF, cirrhosis)
• SIADH (syndrome of inappropriate ADH)
• Cortisol deficiency
• Hypothyroidism

Question 14

Hyponatriemia

Answer 14

• Usually indicates hypotonicity of ECF
• Cell swelling due to water movement into cells
• Can cause neurological problems with rapid onset
• Not due to loss of sodium but excess volume relative to amount of sodium in ECF

Question 15

True hyponatriemia

-Plasma Na concentration and osmolality?

Answer 15

Both are below normal

Question 16

Diabetes insipidus

• Patient has excess dilute urine-Give them ADH
  
  • If there is no change?
  • If the problem is corrected?

Answer 16

If there is no change-nephrogenic DI

If the problem is corrected-Central or neurogenic DI

Question 17

Hypernatriemia

Answer 17

• Always associated with hypertonicity

- Usually due to unreplaced water loss, not Na gain (unless hypertonic saline is administered)

Question 18

Hypernatriemia

• Extrarenal water loss
  
  • Symptoms?

Answer 18

• Excessive sweating, fever, diarrhea, vomiting

- Low urine output, high circulating ADH

Question 19

Hypernatriemia

-Renal water loss

Answer 19

• ADH mechanism for retaining water isn’t working

- Central or nephrogenic DI

Question 20

ADH MOA?

Answer 20

Increases permeability (reabsorption) of late DT, CD via V2 receptors and insertion of aquaporin channels

Question 21

Signs of hypovolemia?

Answer 21

• Orthostatic hypotension
• Orthostatic tachycardia
• Loss of skin turgor
• Dry mucous membranes