Disorders of Sodium Concentration Flashcards
What is the equation for plasma [Na+]?
Blood (plasma or serum) [Na+] = Total body sodium/Total body water
What happens with water excess without a change in total body sodium content?
Hyponatremia
What happens with water deficit without a change in total body sodium content?
Hypernatremia
What happens to ADH levels with increased water intake?
ADH will decrease due to the decrease in [Na+]
What is ADH a.k.a.?
AVP
What are the actions of ADH?
ADH acts on the distal tubule collecting duct to increase water reabsorption and thus decrease renal water excretion. In the presence of substantial amounts of ADH the urine will be concentrated.
What is the main mechanism controlling ADH release?
A small (1‐2%) increase in effective osmolality ([Na+] + [glucose]) will increase ADH release.
What is a second mechanism controlling ADH release?
A large (10%) decrease in blood volume or blood pressure will also increase ADH release and can override the effect of osmolality.
What would increased TBW with normal TBNa+ cause? What is an example of this?
Hyponatremia.
SIADH
What would decreased TBW with greatly decreased TBNa+ cause? What is an example of this?
Hyponatremia
Diuretic drug with water intake
What would greatly increased TBW with increased TBNa+ cause? What is an example of this?
Hyponatremia
Congestive Heart Failure
What is the pathogenesis of hyponatremia?
Hyponatremia almost always indicates impaired renal water excretion.
Beer Drinker’s Potomania
Consumption of solely large amounts of beer which is poor in solutes, making the production of dilute urine difficult with low solutes leading to hyponatremia
What 3 factors does the ability of the kidney to excrete water depend upon?
(1) Filtration of solute by the glomeruli
(2) Delivery of solute to distal (diluting) nephron sites
(3) Reabsorption of solute (but not water) at diluting nephron sites
Hypovolemic Hyponatremia
- decrease in TBNa+
What are some causes of hypovolemic hyponatremia?
– Renal Na+ losses – diuretics, primary adrenal insufficiency (Addison’s disease), salt‐wasting nephropathies
– Extrarenal Na+ losses – diarrhea, vomiting, excessive sweating
What are clinical findings of Hypovolemic Hyponatremia?
(flat neck veins, decreased skin turgor, orthostatic hypotension)
Euvolemic Hyponatremia
- normal TBNa+
What are some causes of Euvolemic Hyponatremia?
– SIADH – most commonly due to (1) tumor (2) pulmonary disease (3) central nervous system disease
– “Beer drinker’s potomania”
Hypervolemic Hyponatremia
- increased TBNa+
What are some causes of Hypervolemic Hyponatremia?
– CHF
– Liver cirrhosis
– Renal failure
What are some clinical findings of Hypervolemic Hyponatremia?
(edema)
What does low UNa+ suggest?
It suggests extrarenal loss of Na+ or edematous disorder
What does normal UNa+ suggest?
It suggests renal loss of Na+ or excess ADH in the absence of renal sodium avidity, as in SIADH.
Hypovolemic hyponatremia Treatment
Physiologic Saline
Hypervolemic hyponatremia Treatment
Fluid restriction and diuretics.
Euvolemic hyponatremia Treatment (symptomatic)
Hypertonic saline with or without diuretics.
What happens with decreased TBW with normal TBNa+? What are examples?
Hypernatremia.
1) patients with decreased thirst or inability to drink water; 2) diabetes insipidus (DI), in which ADH release is impaired or absent
What happens with greatly decreased TBW with decreased TBNa+? What are examples?
Hypernatremia.
Diuretics without concomitant water ingestion.
What happens with normal TBW with increased TBNa+? What are examples?
Hypernatremia.
Administration of hypertonic saline.
Hypovolemic hypernatremia
- decrease in TBNa+
Examples of hypovolemic hypernatremia
– Renal Na+ losses – diuretics (with inadequate water intake), osmotic or post‐obstructive diuresis, tubular injury
– Extrarenal Na+ losses – sweating, diarrhea, vomiting (with inadequate water intake).
Euvolemic hypernatremia
- decrease in TBH2O
Examples of euvolemic hypernatremia
– Central diabetes insipidus (trauma, idiopathic, tumor)
– Nephrogenic diabetes insipidus (congenital, drugs,
hypercalcemia, tubular disease)
– Decreased thirst, water intake (“nursing home syndrome”)
Hypervolemic hypernatremia
- increase in TBNa+
Examples of hypervolemic hypernatremia
– Hypertonic fluid administration
– Mineralocorticoid excess states
– Salt poisoning
Hypovolemic hypernatremia Treatment
Hypotonic fluids
Euvolemic hypernatremia Treatment
Water administration
Hypervolemic hypernatremia Treatment
If severe, it may require both water administration plus either diuretics or dialysis to remove the excess sodium.
A 60 year old man with known lung cancer presents with fatigue and cough. On exam his vital signs are normal. He is not orthostatic. His jugular veins are visible but not distended, skin turgor is normal, and he has no edema. He is alert and oriented and answers questions appropriately. Chest X‐ray shows a R lower lobe infiltrate. Serum electrolytes (in mmol/L) are: Na 114, K4, Cl 80 CO2 24. The BUN and Cr are 6 and 0.6 mg/dL, respectively. Urine chemistries (in mmol/L) are: Na 70 K 30 Cl 50 osm 500.
What is the most likely diagnosis?
A. Beer drinker’s syndrome
B. Psychogenic polydipsia
C. Addison’s disease
D. SIADH
D. SIADH
Euvolemic Hyponatremia
A 60 year old man with known lung cancer presents with fatigue and cough. On exam his vital signs are normal. He is not orthostatic. His jugular veins are visible but not distended, skin turgor is normal, and he has no edema. He is alert and oriented and answers questions appropriately. Chest X‐ray shows a R lower lobe infiltrate. Serum electrolytes (in mmol/L) are: Na 114, K4, Cl 80 CO2 24. The BUN and Cr are 6 and 0.6 mg/dL, respectively. Urine chemistries (in mmol/L) are: Na 70 K 30 Cl 50 osm 500.
How do you treat the hyponatremia?
A. Isotonic saline
B. Hypertonic saline
C. Tolvaptan
D. Fluid restriction
D. Fluid restriction
An 85‐year‐old woman with Alzheimer’s dementia is admitted from a nursing home for obtundation. On examination she has hypotension (BP 80/50 mmHg), flat neck veins, clear chest, and no edema. Chest X‐ray is clear. Serum electrolytes (in mmol/L) are: Na 164,K 4,Cl 130 CO2 24. The BUN and Cr are 16 and 1.2 mg/dL, respectively. Urine chemistries (in mmol/L) are: Na 20 K 30 Cl 15 osm 500.
What is your diagnosis? A. Dehydration B. Volume depletion C. Both D. Neither
C. Both
Hypovolemic Hypernatremia
An 85‐year‐old woman with Alzheimer’s dementia is admitted from a nursing home for obtundation. On examination she has hypotension (BP 80/50 mmHg), flat neck veins, clear chest, and no edema. Chest X‐ray is clear. Serum electrolytes (in mmol/L) are: Na 164,K 4,Cl 130 CO2 24. The BUN and Cr are 16 and 1.2 mg/dL, respectively. Urine chemistries (in mmol/L) are: Na 20 K 30 Cl 15 osm 500.
How do you initially treat this patient?
A. Isotonic saline
B. Hypotonic saline
C. Dextrose in water
D. Oral water replacement
A. Isotonic saline
Volume depletion more important then after the BP
is raised, it should be change to hypotonic saline
