FPC: salt/water imbalance Flashcards
What is salt balance?
Maintenance of ECFV; too much salt leads to volume overload, not enough leads to volume depletion.
Where do we find NaCl in the body?
Interstitial/intravascular spaces; very little intracellularly.
What is a normal serum sodium?
135-145.
What labs suggest ECFV depletion?
Low urinary sodium, low central venous pressure, low pulmonary artery wedge pressure, azotemia (high creatinine).
What labs suggest ECFV overload?
Alveolar congestion, pleural effusion, elevated central venous pressure, BNP, elevated pulmonary artery pressure.
What is one of the most important factors in assessing a renal patient?
ECFV status.
What leads to morbidity in ECFV depletion?
Hypotension, shock, vascular collapse.
What leads to morbidity in ECFV overload?
Pulmonary edema, hypoxia, respiratory failure.
What is water balance?
Maintenance of the ratio of total body salt mass to total body salt water.
Water balance disorders are categorized by…
Salt balance status.
What labs identify water balance disorders?
Serum sodium concentration and serum osmolality.
What defines hyponatremia?
Serum sodium less than 135.
What defines hypernatremia?
Serum sodium greater than 145.
In most cases of hyponatremia, what is serum osmolality like?
Low aka hypotonic!
What is a normal serum osmolality?
285.
What is a normal urine osmolality?
50.
What causes morbidity in hyponatremia?
Neurological issues; water shifts into the cells of the brain leading to swelling and herniation.
What is the one case where ICFV expansion is seen as opposed to ECFV?
Brain edema.
What is the pathophysiology of hyponatremia?
We can’t make maximally dilute urine; people normally are able to make dilute urine when there is extra fluid intake, but if they can’t they become hyponatremic.
What is necessary for production of dilute urine?
- Adequate glomerular filtration
- Healthy nephrons
- Delivery of fluid to distal nephron aka the diluting segment
- Suppression of ADH.
Describe osmolar regulation of ADH.
When plasma osmolality goes up, the body releases ADH. This allows us to reabsorb water from the nephron and re-balance our osmolality.
What is a non-osmolar regulation of ADH?
Volume depletion.
What are the categories of hypotonic hyponatremia?
- Low ECFV with water drinking (diarrhea, vomiting, excess diuretic)
- Normal ECFV (unregulated ADH)
- High ECFV (HF, kidney failure, liver failure).
How do we treat salt and water balance disorders?
Treat underlying disease!
