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Discussion

Fluids & Electrolytes

I posted this on pathophysiology/electrolyte and fluids sticky but nobody responded, so I hope this time somebody can help me :imbar I find those questions hard to "make sense"...:uhoh3:

so i have a few questions here:

1) hypotonic dehydration (electrolyte loss exceeds water loss) might be caused by chronic illness, excessive fluid replacement (hypotonic), renal failure & chronic malnutrition. i don't have problem understanding the last 3 causes, but what kinda chronic illness can cause hypotonic dehydration? my guess would be colon cancer (cause it will have lesser absorption of electrolytes?). I can't think bout other chronic illnesses that lead to electrolyte loss. can it be liver dz/cancer because of altered in metabolism?

2) assessment for hypertonic dehydration (water loss exceeds electrolyte loss) are hyperactive deep tendon reflexes and pitting edema. i have no clue how hyperactive DTR r/t hypertonic dehydration. less water in the body makes reflex more active, but how? or maybe because of too much electrolytes (compares to water) makes nerve impulse travels faster?

3) "fluid volume excess causes visual disturbances, skeletal muscle weakness, and paresthesias" again, does this have to do with the nerve impulse distribution to those parts of the body?

4) can someone explain how hyperglycemia and CHF causes hyponatremia? It's stated that both dz cause "dilution of serum sodium"...how does too much glucose in the body cause removal of sodium? as for CHF, does kidneys retain water and sodium to compensate with decrease cardiac output?

as i was searching for answers, i found this cool chart from wikipedia about hyponatremia, so hope this help other students too. --> http://en.wikipedia.org/wiki/Image:H...mia_Causes.png

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Hey, Tori. Sorry you didn't get any responses to your post. Let me try to help.

1. Chronic illnesses that can cause hypotonic alterations include cirrhosis, CHF, renal failure, certain types of cancer, and SIADH. Other potential contributors are Diabetes Mellitus, hyperlipidemia, and hyperproteinemia (all of these lead to hypertonic hyponatremia---proteins and lipids displace water, thus decreasing sodium concentration, and hyperglycemia draws water from the ICF to the ECF by changing ECF osmolality and the concentration of sodium is also decreased). Everything in this list leads to water imbalance, which either results from excess free water or hyponatremia.

2. The relationship between hypertonic dehydration and hyperreflexia is directly related to the hypernatremia. The brain is very sensitive to sodium imbalances. Increased (or decreased) serum Na+ can (and in many cases, does) affect neurologic status because the fluid shift is messing with the brain cells. The neuro changes can include weakness, confusion, lethargy, or even seizures.

3. What's confusing you in this case is that they are using the language "fluid volume excess". Most people would read this as Hypervolemia, but it is not because in the case of hypervolemia fluid osmolality is not changed. The symptoms they are describing here are related to water intoxication, which is different from hypervolemia. The symptoms develop from a complication of hyponatremia together with increased ICP. Both these conditions have a direct effect on neuro function---including visual disturbances and muscle weakness.

4. Review #1 above again for the how hyperglycemia causes hyponatremia. Remember that water follows sodium. Hyperglycemia increases ECF osmolality so the fluids shift to the ECF compartment, which causes dilution of all the electrolytes, including sodium. Yes, in CHF, the patient will have decreased cardiac output which activates the renin-angiotensin mechanism, which causes retention of water and sodium. But there is also a thing known as arginine vasopressin that increases free water resorption in the renal tubules, which further increases blood volume and results in hemodilution---ergo hyponatremia. Also important to remember that CHF patients take a lot of diuretics as a part of home care, and use of loop diuretics waste sodium, too. Physicians always prescribe potassium replacement but few are concerned about sodium replacement because they presume that the patient will have adequate daily intake from the diet.

Hope this info was helpful. :)

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T'hanks NurseGuyFL!

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