April 5, 2016 - Hyponatremia

Question 1

Maximal Renal Free Water Excretion

Answer 1

1. Freely filtered from blood
2. PCT reabsorption (60-70%)
3. Desalination of water in ALH
4. Variable reabsorption in CD (ADH-dependent)
5. Excretion with osmoles

Question 2

Causes of Hyonatremia

Answer 2

1. Reduced filtration
2. Increased PCT reabsorption
3. Impaired desalination
4. Antidiuresis
5. Water intake too high for osmoles

Question 3

Reduced Filtration

Answer 3

A cause for hyponatremia.

Low GFR (especially <25)

Examples are acute kidney injury and chronic kidney disease.

Question 4

Increased PCT Reabsorption

Answer 4

A cause for hyponatremia.

Urine Na low (especially <20 )

Example is reduced effective arterial blood volume (EABV)

Question 5

Impaired Desalination

Answer 5

A cause for hyponatremia.

Usually on diuretics.

Question 6

Antidiuresis

Answer 6

A cause for hyponatremia.

ADH is putting in lots of AQP2 channels which is concentrating the urine. As a result, urine osmolality is >100.

Examples are reduced EABV and SIADH

Question 7

Syndrome of Inappropriate ADH (SIADH)

Answer 7

Normally ADH is produced when either the serum concentration of sodium is high, or in response to volume depletion.

SIADH is when ADH is secreted at times when it is not appropriate. This results in dilutional hyponatremia in which the plasma sodium levels are lowered and the total body fluid is increased.

Can be seen in cancer, neurological problems, lung conditions, and drugs.

Question 8

Water Intake Too High for Osmoles

Answer 8

A cause for hyponatremia.

Urine osmolality is < 100

Examples are primary polydipsia or eating disorders.

Question 9

Treatment of Hyponatremia

Answer 9

Treat the underyling cause

Restrict free water intake

+ give salt

+ inhibit action of ADH

Question 10

Treatment Goals for Hyponatremia

Answer 10

If acute and symptomatic –> Rapid increase until symptoms resolve

If chronic and mild –> Increase [Na] < 10 in 24 hours

If acute on chronic –> Rapid Rx to treat symptoms and then chronic target

If overly rapid correction –> Rapid reversal of correction

Question 11

Sodium Math

Answer 11

To increase a 60kg female patient’s sodium from 122 to 130…

Females are 50% water weight, so we are dealing with 30L of water.

30L x 8 mmol/L = 240 mmol ovr the next 24 hours

Question 12

Normal vs. Hypertonic Saline

Answer 12

Normal Saline = 154 mmol/L

Hypertonic Saline = 513 mmol/L