Hyponatremia

Today we discussed hyponatremia and its management:

Some take home points - rapid correction of hyponatremia is often not required unless it is clear that the patient is acutely symptomatic from their hyponatremia - if you do need to give hypertonic saline (often in marathon runners, ecstasy overdose, etc.) it is often given as 3%NS with a 100cc bolus, then reassessment for further doses. The patient should be in a monitored setting and have frequent repeat electrolytes sent.

Consulting nephrology is never a bad idea for these patients.

We also discussed "BEER POTOMANIA" (apparently potomania is: An intense and persistent desire to drink alcohol to excess).

Malnourished patients (low-protein, high water intake diets) often do noy have enough solute excretion to deal with their water intake . Beer and other primary carbohydrates meals have little solute, however their CHO content suppresses endogenous protein catabolism/urea production.

Example:
Normal subject - 600 mosm/day of solute intake (and output). If they are hyponatremic and make a maximally dilute urine of 60 mosm/L (assume the kidneys cannot make a more dilute urine), their solute load allows a maximum of 10L of urine/day i.e. - their free H2O intake would have to exceed 10L for them to get more hyponatremic.

In malnourished patients - their solute intake/output can be 240 mosm/day. Therefore with a maximally dilute urine of 60 mosm/L (the kidneys cant make it more dilute) then their maximum urine output will be 4L/day. If their intake of fluid is >4L (>11 beers)/ day they will worsen their hyponatremia.

Other tips:
When seeing hyponatremia in the ER:

First rule out acute hyponatremia that needs acute correction.

Recheck the lytes if they were done several hours previously- the patient has possibly received intravenous fluids in the ER that may have significantly altered the sodium concentration - especially if the stimulus (often ECF volume depletion) for ADH secretion has been removed. Following the urine output may help to identify this (although recording can be an issue outside of the ICU) as a brisk, dilute diuresis can be bad sign.

Further tips from a nephrologist who attends on GIM are posted here, as well as an article about the use of DDAVP to prevent overly rapid sodium correction.