Regulation and Disorders of Salt and Water

Question 1

What is the cause of disorders of extracellular volume?

Answer 1

Alteration in SODIUM BALANCE

***Remember Sodium in the main determinant of ECFV)

Question 2

What effect does ADH have on urine sodium and osmolality?

Answer 2

• LOW urine sodium

* HIGH urine osmolality

Question 3

What is ECV?
• what does it tell you?
• How does it relate to ECFV?

Answer 3

ECV = Effective Circulating Volume

Relates to the FULLNESS and TENSION within the arterial tree (this is only 15% of total blood volume)

ECV relates the Extra Cellular Fluid Volume almost all the time with the exception of a few diseases (CHF, Liver Disease, Sepsis, Nephrotic Syndrome, Pregnancy, Anaphylaxis)

Question 4

What are the 2 most important disorders where ECV does not relate to Extra Cellular Fluid Volume?
• why do these two values not line up?

Answer 4

Heart Failure:
• Veins are distended (high ECFV)
• Arteries are Relatively Empty (Low ECV)

Liver Disease:
• Splanchic Ciruculation is Taking all the Blood (low ECFV)
• Renal Arteries don’t get blood flow (Low ECV)

Question 5

What is TRUE volume depletion?

• general cause?

Answer 5

Decreased:
•ECV and ECFV
•Low Total BODY Na+

Question 6

What occurs in TRUE volume depletion due to Extra Renal Losses?
•examples of causes.
• Labs?

Answer 6

Low Na+ and Low ECV and ECFV

Examples of Causes:
• Diarrhea, Burns

Labs:
• URINE should be HIGHLY CONCENTRATED
• URINE should also be SALT POOR

Question 7

What occurs in TRUE volume depletion due to Renal Losses?
• examples of causes.
• Labs?

Answer 7

Low Na+ and Low ECV and ECFV

Examples of Causes:
• Diuretics, reconvery phase of ATN

Labs:
• URINE will not be that concentrated
• URINE could also be salt rich

Question 8

What clinical features will you see in someone with TRUE volume depletion?

Answer 8

• Reduction in Blood Pressure
• Poor skin turgor
• ABSENCE OF DEPENDENT EDEMA
• Disproportionate increase in BUN relative to serum creatinine:Reduced Urine Na except in cases with renal losses of Na
• Decline in mental status and cool extremities

Question 9

When does volume expansion occur?

• common underlying disturbance?

Answer 9

• When salt and water intake exceeds renal and extrarenal losses.
• Common underlying disturbance - sodium and water retention by the kidney

Question 10

What are some common causes of volume excess?
• Primary and Secondary?
• Net Result of both of these diseases?

Answer 10

Primary:
• Chronic Kidney Disease
***Results in increased ECV

Secondary:
• Liver Disease and Heart Failure
***ECV is not increased despite increases in ECFV

Net Result:
• Starling Forces (increased capillary hydrostatic pressure, reduction in osmolarity) SHIFTS FLUID TO INTERSTITIAL SPACE

Question 11

What are some clinical features of Excessive Volume?

Answer 11

• Edema
• Elevated JVD
• Crackles, Ascites, Pleural Effusion

Question 12

What should your plasma osmolality be?

• what happens if you get above this range (in healthy individuals)?

Answer 12

280-290 mOsm/L

Above Range:
• Hypothalamic Receptors are Stimulated triggering… 1) Thirst 2) ADH release

Question 13

T or F: Sodium balance is regulated by both osmolality and volume.

Answer 13

FALSE, sodium balance is ONLY regulated by VOLUME STATUS

water balance is controlled by BOTH osmolarity and volume

Question 14

What value of plasma Na+ defines Hyponatremia (low plasma Na+)?

Answer 14

Less than 135 mEq/L

Question 15

How is serum sodium calculated?

• why is that important to Remember?

Answer 15

Serum Na is NOT the same as total body Na, SERUM SODIUM IS DEPENDENT ON VOLUME OF WATER in the body

Formula:
Serum Na Conc. = Amount of Na(TBNa) / (Volume of water (TBW))

Question 16

What is a hyperosmolar hyponatremia?

• what causes it?

Answer 16

• Low Sodium concentration due to other osmotically active molecules in the periphery

Causes:
• Mannitol
• Hyperglycemia

Question 17

What is the most common type of Hyponatremia?

Answer 17

Hypoosmolar Hyponatremia

Question 18

Is hypernatremia typically due to water loss or sodium gain?
• who is most susceptible?

Answer 18

Water Loss is the cause of Hypernatremia

Ppl with Primary Defects:
• Don’t make ADH
• Resistant to ADH

Ppl. with Secondary Defects:
• Diseases of Brain
• Paralyzed people

Question 19

Hypoosmolar Hyponatremia
• HYPOVOLUMERIC
• Lab Values
• Associated Diseases

Answer 19

Lab Values:
• Low TBW
• EVEN LOWER Na+

Associated Diseases: 
EXTRA renal Sodium Loss: 
• Vomiting 
• Burns
• Hemorrhage 

Renal Sodium Loss:
• Defective Renal Handling of Na
• Mineral Corticoid Deficiency
• Diuretic Therapy

Question 20

Hypoosmolar Hyponatremia
• EUVOLUMERIC
• Lab Values
• Associated Diseases

Answer 20

Lab Values:
• Low TBW
• Na+ is normal

Associated Diseases:
• Pulmonary disorders, CNS disorders and malignancy
• Pain/ nausea
• Glucocorticoid deficiency
•Hypothyroidism
• Drug-induced water retention
Vasopressin analogues or drugs that enhance vasopressin action i.e chlorpropamide, clofibrate, narcotics, antipsychotics, carbemezepine

Question 21

Hypoosmolar Hyponatremia
• HYPERVOLUMERIC
• Lab Values
• Associated Diseases

Answer 21

Lab Values:
• HIGH TBW
• Na+ increased but not enough

Associated Diseases: 
• Congestive heart failure
• Hepatic cirrhosis
• Nephrotic Syndrome
• Renal disease

Question 22

How can lab values help you to distinguish Renal Sodium Loss from Extrarenal Sodium Loss in hypovolemic hyponatremia?
• explain this finding

Answer 22

RENAL
Una will be GREATER than 20 mEq/L

Extra Renal
Una will be LESS THAN 20 mEq/L

Having a high Urinary concentration of Na+ implies that your kidney is not responding appropriately to the hypovolemic state. In most people you should resorb lots of Na+