Clinical Aspects of Hyponatremia Flashcards
What type of patients are linked with volume status issues
Hospitalized and elderly patients as well as patients with CHF and GI disturbances, burns, and sweating
Medications that can cue us in to volume issues in our patients
Thiazides, nicotine, NSAIDs, morphine
Lab findings for hyponatremia
plasma osmolality (usually reduced <100mOsmol/L if max dilute urine)
Urine sodium (fractional excretion of sodium U(Na)/P(Na)/U(Cr)/P(Cr))
Acid/base and Potassium status
Remember, hyponatremia is not a disease, it is a ___ ___.
Remember, hyponatremia is not a disease, it is an “electrolyte sign”
Measurement of serum osmolarity to rule out _____.
Measurement of serum osmolarity to rule out pseudohyponatremia
What volumes are affected by hypovolemic hyponatremia
Effective art. volume depletion
True volume depletion (TBNa>TBW)
Hormone levels associated with hypovolemic Hyponatremia
ADH Level elevated
Hypoaldosterone (inc. vascular reactivity and Na+ reabsorption)
We associate these things with hypovolemic hyponatremia
Thiazide diuretics
GI losses (vomit, diarrhea)
Sweating
Burns
What is Euvolemic Hyponatremia?
Euvolemic Hyponatremia (volume looks okay but hyponatremic→ compulsive water drinkers)
Hormones associated with euvolemic hyponatremia
Increased ADH activity
We associate these with euvolemic hyponatremia
Other clinical: pulmonary lesions, pain, CNS lesions, nonpituitary sources: tumor, granulomatous disease, exogenous administration
Volume shifts with euvolemic hyponatremia
effective art. volume normal (initially elevated)
We often refer to euvolemic hyponatremia as a syndrome of inappropriate ADH secretion. What causes this?
syndrome of inappropriate ADH secretion
drugs: nicotine, morphine, clofibrate, SSRIs, vincristine, cyclophosphamide
These drugs elevate the activity of ADH
Drugs: tolbutamide, chlorpropamide, methylxanthines, NSAIDs (ecstasy?)
This hyponatremic volume issue is known as a diagnosis of exclusion
Euvolemic
Hormones related to hypervolemic hyponatremia
ADH level elevated
Volume findings for hypervolemic hyponatremia
Effective art. volume depletion
We associate these clinical findings with hypervolemic hyponatremia
Edematous states: CHF, Cirrhosis, nephrotic syndrome, pregnancy
Compare total body sodium and volumes between the three subtypes.
Hypovolemic: decreased total body sodium accompanied by a decrease in the normal amounts of body water
Euvolemic: increased total body water with normal total body sodium.
Hypervolumic (like the movie Supersize Me): increase in both total body water and total body sodium, with the increase in TBW exceeding that of sodium.
The physiology of Hypovolemic
ADH is physiologically secreted in response to low effective arterial volume and perfusion pressure. Tubular filtrate delivery distally is limited, due to GFR reduction, increased proximal Na reabsorption due to sluggish intra-tubular flow, and TGF. The result is that both H20 and Na excretion are reduced, but relatively more water is retained due to ADH effect.
Physiology of euvolemia
There is either inappropriate ADH secretion, ADH sensitivity, or another situation which limits the ability to maximally dilute the urine. Patients often have a relatively normal to high urinary sodium excretion once they have achieved steady state.
Physiology of hypervolemia
Effective arterial volume is perceived (by brain and kidneys) to be low, and although there is overall water and Na overload, the kidney behaves as if the total organism were hypovolemic. ADH is inappropriately active.
Hypovolemic causes
renal losses: diuretics (thiazides), cerebral salt wasting, salt wasting nephropathy, mineralocorticoid insufficiency, bicarbonaturia, glycosuria, ketonuria
extrarenal losses: GI (vomiting, diarrhea), third spacing, sweat (endurance exercise)
Causes of Euvolemic issues
SIADH
tumor-related ADH-like peptides
Pituitary disorders (several patterns exist), drugs, pain, lung disorders, thyroid/adrenal insufficiency OR
decreased solute intake and subsequent decreased excretion (beer potamia, low protein diet)
Conditions of hypervolemic states
Edematous states: CHF, cirrhosis, nephrotic syndrome, renal failure (water is outside of vascular space so baroreceptors think that you’re hypovolemic)
*Remember, ___ is controlled by volume status and this supercedes ____ sensitivity.
*Remember, ADH is controlled by volume status and this supercedes tonicity sensitivity.
How do we treat the different types of volume changes?
Hypovolemic
IV normal saline
Brisk water diuresis
Euvolemic
Treatment of underlying cause
Hypervolemic
ACE inhibitors
When do we want to concentrate the urine vs. dilute it?
Maximum diluting capacity is 50-100 mOsm/Kg. In hyponatremia, it is appropriate to maximally dilute the urine unless there is some other physiologic or pathophysiologic process active.
Maximum concentrating capacity is 900-1400 mOsm/Kg.
In hypernatremia, it is appropriate to maximally concentrate the urine–unless some other process (physiologic or pathophysiologic process) is active. The elderly should not get more than 500-700 mOsm/Kg
Use of hypertonic saline is for the treatment of ________ in order to:
Use of hypertonic saline is for the treatment of acute symptomatic hyponatremia to alleviate symptoms only
Issue with using hypertonic saline in a hyponatremic patient.
Known to be highly unpredictable due to rapid changes in the physiology; should be monitored every 2-4 hrs.