Approach to Hyponatremia

Question 1

hyponatremia is usually due to failure of kidneys to :

Answer 1

excrete free water

Question 2

the ADH system reacts to __ concentration. the RAS system responds to ____

Answer 2

the water hormone system (ADH system) reacts to Na concentrations. The Na+/RAS system does not respond to Na+ concentration– it responds to water/cardiac output pressure on the afferent arteriole baro receptors.

Question 4

4 components of abnormal renal handling that can cause hyponatremia

Answer 4

1. inadequate GFR; water can’t even be filtered to be excreted
2. impaired desalination in the ascending LOH. water usually gets pulled into the tubules, diluting the filtrate. but in this case, water stays.
3. antidiuresis; water can’t be excreted
4. too few osmoles; there sjust not enough solute, causing low sodium in and of itself but also can’t draw out enough water in the collecting duct

Question 5

methods that may cause impaired desalination

Answer 5

loop diuretics, thiazide diruetcs, Gitelmans’

Question 6

why might ADH be produced?

Answer 6

Why is ADH being produced?

1. Reduced affective blood volume. The hypothalamus has a receptor for angiotensin II that can override osmolality signal. Angiotensin II activation causes ADH release, and thus water retained. Can cause person to be tachycardic, low URINE sodium concentration.
2. Is the biochemical info doesn’t suggest blood volume abnormality, it might be SIADH.

Question 7

explain how angiotensin II can override an osmolality signal

Answer 7

angiotensin II (part of RAS system) can override Na+ concentration (ADH activity). If ADH is not being released, angiotensin can still work in the hypothalamus to promote ADH release if the RAS axis detectsredcued Na+ delivery to the distal tubule

Question 8

Peri-Operative, medication-related, malignancy-related CNS causes, pulmonary causes, and hormone deficiency causes of SIADH

Answer 8

Question 9

Fill in this table

Answer 9

Question 10

Answer 10

Serum sodium concentration is reduced (should be 135-145). Osmolality is low too.
• Too much water.
• Is there inadequate GFR <25? – NO, it’s 95.
• Desalination? – could be an inhereted tubular disorder, or are they taking diuretics? NO.
• Antidiuresis? Less than 100? NO, it’s higher than 100 (600), therefore her problem is caused by ADH production. Her antidiuresis is causing retention of water and subsequent hyponatrremia.
• Look at urine sodium– low <20 because of RAS activation? No. Clinically and biochemically, this person does not have feature of reduced blood volume.
• Therefore this is appropriate ADH release.

They came in a few days ago with CAP pneumonia– leading to release of ADH, which could result hyponatremia

This is overall hyponatremia due to SIADH secondary to community acquire pneumonia– we really gotta ask GFR first!