Sodium Disorders Flashcards
What equation can be used to estimate serum osmolality?
[Na]x2 + [Glucose]/18 + [BUN]/2.8
What is normal sodium serum concentration?
135-145 mEq/L
What are the symptoms of sodium concentration below 125 mEq? 120-115? <115?
120-125: Nausea/malaise
115-120: Headache/lethargy
<115: Seizures, obtundation, coma
What is the main pathophysiological effect of hyponatremia?
Decreased extracellular osmolality results in brain cell swelling
What are the symptoms of hypernatremia?
Lethargy, weakness, irritability, twitching, seizures, coma, death
What is the key pathophysiological finding to hypernatremia?
Shrinkage of brain cells, leading to rupture of cerebral vasculature due to decreased volume
What are the nonosmotic stimuli to increasing levels of ADH?
Baroreceptors (hypovolemia)
Pain (post-operative for instance)
Esophageal stimuli
Various medications
If ADH is present, is serum osmolality increased or decreased?
decreased
If plasma osmolality is high, is urine osmolality supposed to be high or low?
high
If urine sodium is high, what does the body think about the body’s volume status?
Body thinks serum volume is expanded, wants to get rid of excess sodium
What level of urine osmolality usually means ADH is involved in the system?
> 100 mOsm/L
Given osmoles taken in per day and amount of urine osmolality, how can you calculate amount liquid excreted per day?
(Osm/day)/(urine osmolarity in Osm/day)
In the nephron, what percentage of sodium is reabsorbed by each of the tubules?
Proximal tubule: 65%
LOH: 25-35%
Distal tubule: 5%
Collecting duct: 4% (dependent upon aldosterone, ANP)
If the urine sodium concentration is <10 meq/L, then what is the body sensing the circulating volume to be?
low circulating volume
leads to increased water and sodium resorption
If the urine sodium concentration is >10 mEq/L, then what does the body think is going on?
Increased volume of ECV
Kidney unable to retain Na
Na is leaving with something else (as an obligate cation)
What is pseudohyponatremia with regular osmolality usually due to?
Hyperlipidemia, hyperproteinemia
What is pseudohyponatremia with elevated osmolality due to?
Increased Glucose levels
Increased mannitol levels
When evaluating Hyponatremia in the clinic, what steps should you follow?
Check serum osmolality (True or pseudo hyponatremia?)
Check urine osmolality (Is ADH acting?)
Check urine Na osmolality (What do kidneys think of ECV?)
Check H&P
What are primary and secondary causes of hyponatremia with Uosm <100?
- Increased water consumption
- Alcohol
- Tea and toast syndrome
How do you treat primary polydipsia?
Let the kidneys do their thang
If you have hyponatremia with Uosm >100, and UNa is <10 with volume depletion, what is the cause?
Normal kidney response to add fluid back into the depleted ECV.
From: Burns, diuretics, GI losses (vomiting, diarrhea), cortisol deficiency
If you have hyponatremia with Uosm >100, and UNa <10 with expanded volume but ECV depletion, what is likely the cause?
Kidney is confused because of edema (CHF, cirrhosis, nephrosis)
If you have hyponatremia with Uosm >100, and UNa >10 with depleted volume, what is likely the cause?
Salt-wasting (kidney is failing)
Causes:
Diuretics (early), renal diseases, adrenal insufficiency, hypokalemia/metabolic alkylosis after vomiting, hypothyroidism
If you have hyponatremia with Uosm >100, and UNa >10 with expanded volume, what is likely the cause?
Brain or kidney confused (inappropriate ADH secretion)
What are some causes of inappropriate ADH secretion?
Tumor Pulmonary process Drugs (oxytocin, cytoxan, tegretol, chlorpropramide) Esophageal process Pain Neuropsychiatric disorders
What should you give patients with volume depleted hyponatremia?
Normal saline
What should you give patients with volume expanded hyponatremia?
Nothing. Restrict free water intake.
What should you give patients with hyponatremia causing neurologic symptoms?
Hypertonic saline
What is the oral ADH antagonist?
Tolvaptan
What is the IV ADH antagonist?
Conivaptan
What drug can cause Nephrogenic diabetes insipidus after long term use?
Lithium
