Hyponatremia

So your day is going along pretty well and you are checking off labs that were drawn on your patients yesterday and you come across Jane's labs showing a sodium level of 125. Normal sodium concentation is 135 to 145. What do you do?
1). Call Jane and ask her to come back to the clinic today.
2). Tell Jane to go directly to the ER.
3). Tell Jane to get a salt lick and come back next week.
4). Nothing, ignore it and hope it will go away.

Low levels of SODIUM in the blood = HYPOnatremia
Worry more if it's below 120.

The first thing I would do is ask Jane to come back to the clinic. If that is not possible, try to do a phone interview to decide if it's urgent that she go to ER or come in. Document the conversation either way.

Let's assume Jane is the ideal patient and comes right on over to the office. Look at her: how does she appear? Is she the same Jane you saw last week/last month? Is her mouth dry? Is her skin dry with poor turgor? Is her blood pressure low? Check it lying and standing, does it drop (20 points)? Does her heart rate go up (more than 20 points) when she stands up? Is she having any new symptoms? Has she been having headaches, nausea, vomiting, confusion? Hopefully if she's having seizures or coma you would have heard about it by now (?) but you never know. If Jane looks pretty normal, this is probably not an acute change in her sodium and it has occurred slowly over time.

If Jane has no reason to be dehydrated, ask her if she has been drinking excess fluids. I mean EXCESS, as in several liters a day. Does she have any swelling? Does she have crackles in her lungs with deep breath? Does she appear short of breath as she talks to you? Has she been having trouble breathing when she lies flat? Has her urine been very dilute/clear? Or has it been very concentrated and voiding small amounts or not at all?

At some point you will decide whether this can be treated at home or in the hospital. If in-patient treatment is not necessary, consider nephrology referral as they are great at helping us sort through these causes and treatments. In the hospital, referral will depend on level of comfort and response of the patient to treatment.

 Hyponatremia from whatever cause has only one physiological cause: Water Intake must have been greater than Water Excretion.

Here I will review three types of hyponatremia - from low volume, volume overload, or normal volume (if you are already sleepy you might want to skip this part and come back later).

Low volume:

• Causes include; vomiting or diarrhea or excessive use of laxatives, excess use of diuretics; osmotic diuresis (due to hyperglycemia in untreated diabetes mellitus)
  "3rd Space"
• S/S: Look at other lab data that indicates low volume status - hemoconcentration: increased albumin, BUN, and if severe, increased CRE, decreased urine sodium (the Urine Na is often Low (i.e. below 20 mEq/L) except when the patient is taking a diuretic)
• Urine output is low - why? Because decreased volume increases ADH release (your body says "wo! I need to save water!") so renin is increased and angiotensin II levels, which causes increased reabsorption (water retention). Therefore, total amount of dilute urine that can be generated is low.
• Treatment: isotonic saline (Normal Saline); discontinue any diuretics/laxatives
  Increasing fluids will increase the volume and ADH will be turned off and sodium CONCENTRATION will normalize. This needs to be a slow process, replacing too fast causes

High Volume

• Causes: CHF, SIADH (often caused by cancer), Psychogenic Polydipsia
• S/S: hypertension, SOB, orthopnea, rales on exam, edema (although we can retain 3 liters of extra fluid before edematous), increased LFTS from liver congestion, JVD.
•  Diagnostic clues: decreased albumin, hypoxia on ABGs, peripheral vascular congestion on CXR
• SIADH explained: (same as infused ADH): Remember, this is ANTI-diuretic, so it's doing the opposite of a diuretic ; Urine Na is often high (over 20) unless patient is on diuretics. SIADH is sometimes associated with certain types of cancers, but that's another lecture.
• May not have edema because you can retain up to 3 L of saline without getting edema. 
• Why? ADH is increased, which means the body holds water, the retained H2O dilutes the total body water - a portion of this is the intravascular volume, hence serum Na is decreased (diluted) and the volume increases.
  The increased intravascular volume and suppressed angiotensin II and decreases aldosterone secretion. Therefore less Na is reabsorbed distally, therefore you pee out more sodium and urine sodium will be high
• Treatment: fluid restriction, lasix, no 3% sodium unless critical symptoms, better to try demeclocycline to block the action of ADH in the kidney.
   

 Normal Volume:

• Causes: One rare cause is Psychogenic Polydipsia where water intake is greater than the kidney's ability to excrete dilute urine (about 20 Liters /day).
• Common Cause include decreased "Effective" Plasma Volume where there is arterial underfilling. This is seen in Heart Failure (low output), Cirrhosis(low proteins) and Nephrotic Syndrome (protein loss). Such patients often have edema. Other causes include hypothyroidism, hypopituitarism and reduced glucocorticoid activity as in Addison's disease (you'll have to look these up because I don't have time right now).
• Decreased Effective Volume also increases ADH release, which increases renin, and angiotensin II levels, which in turn causes increased reabsorption of water (aka water retention). Therefore, UOP is low.
• S/S: body weight likely to be same, no orthostatic changes, urine sodium is often low , decreased UOP
• Treatment  Water Restriction

Summary: Restrict fluids to 1 liter daily unless Jane has low volume, in that case she will need to have IV normal saline to replace fluids that were lost and discontinue any diuretics or laxatives.

For those who work in ER or Critical Care, he's a great link as well:
http://emcrit.org/podcasts/hyponatremia/
Please leave comments, I know this is incomplete in many ways, and too much information for some of you, but hopefully there are some PEARLS you can use in your practice.