Compare conditions

Put any two — or three — conditions side by side, adult or pediatric, to spot the look-alike differences fast, row by row.

Hyponatremia

—

In one line

·Low sodium (Hyponatremia) means too much water diluting the blood, not too little sodium—the kidney either kept water it should have dumped, or the body lost salt faster than water.

—

Normal physiology

·Your kidneys balance water and sodium every minute by listening to a hormone called ADH (antidiuretic hormone, made by the posterior pituitary gland at the base of your brain). ADH reads the salt concentration in your blood (osmolality). When blood gets too salty (high osmolality), ADH rises, and the kidneys hold onto water by putting water channels (aquaporin-2) into the collecting ducts so water gets pulled back into the blood instead of leaving as pee. When blood gets too watery (low osmolality), ADH drops, the water channels disappear, and the kidneys dump water as dilute urine. This feedback loop keeps sodium between 135 and 145 milliequivalents per liter. Keep this picture in your head: ADH up → water stays in, ADH down → water leaves. Every weird finding in low sodium (hyponatremia) is a break in this loop.

—

What goes wrong

·Low sodium (Hyponatremia) happens when the kidney keeps water it should dump, or when the body loses sodium faster than water, or when someone drinks huge amounts of plain water the kidney cannot keep up with.

—

Hallmark signs

·Headache
·Nausea and vomiting
·Confusion or trouble thinking clearly
·Muscle cramps or weakness
·Seizures (sudden shaking or blackout spells)
·Lethargy or extreme sleepiness
·Coma (unresponsive, cannot be woken)
·Dry skin and low blood pressure (hypovolemic signs)

—

Red flags · escalate now

·Seizures or sudden shaking spells
·Coma or cannot be woken up
·Sodium below 120 mEq/L or dropped more than 10 mEq/L in 24 hours
·Severe confusion or inability to speak clearly
·Trouble breathing or very slow heart rate

—

Workup

·Serum sodium and serum osmolality
·Urine osmolality
·Urine sodium
·Thyroid-stimulating hormone (TSH) and free T4
·Morning cortisol or ACTH stimulation test
·Chest X-ray or CT chest
·Medication review
·BUN (blood urea nitrogen) and creatinine

—

Treatment

·3% hypertonic saline 100 mL IV bolus over 10 minutes, repeat every 10 minutes up to 3 doses if severe symptoms (seizures, coma, severe confusion)
·Fluid restriction to 500–1000 mL per day if SIADH is the cause
·Stop the offending drug: thiazide diuretics, SSRIs, NSAIDs, carbamazepine, or other medications that raise ADH or cause sodium loss
·Normal saline (0.9% NaCl) IV if the patient is volume-depleted (dry skin, low blood pressure, urine sodium <20 mEq/L)
·Treat the underlying disease: levothyroxine if hypothyroid (TSH >10, low free T4), hydrocortisone 50–100 mg IV if adrenal insufficiency, treat cancer or infection if SIADH from those
·Raise sodium no faster than 6–8 mEq/L in 24 hours (or 4–6 mEq/L in the first 24 hours if high risk: chronic low sodium (hyponatremia), alcoholism, malnutrition, liver disease). Give desmopressin (DDAVP) 1–2 µg IV and free water by mouth or IV if sodium rises too fast
·Vasopressin receptor antagonists (vaptans: tolvaptan, conivaptan) if severe SIADH or heart failure with low sodium (hyponatremia) not responding to fluid restriction

—

NCLEX trap

·Fast correction of low sodium (hyponatremia) causes osmotic demyelination syndrome (the brain's insulation strips away), which can leave the patient locked-in — awake but paralyzed and unable to speak. Raise sodium no faster than 8 mEq in 24 hours for chronic low sodium. If the patient has seizures or coma from acute low sodium, you can raise it 4–6 mEq in the first hour only, then slow down.
·Low sodium (Hyponatremia) usually means the body kept too much water, not that it lost sodium. SIADH (a condition where ADH, the body's water-holding hormone, stays too high), heart failure, and cirrhosis all cause low sodium by making the kidneys hold water when they should dump it. The water dilutes the sodium that is already there.
·Chronic low sodium (hyponatremia) without symptoms is dangerous if you correct it too fast. The brain has adjusted over days by dumping organic osmolytes (tiny particles inside brain cells that balance water). Fast correction pulls water out of brain cells too quickly and strips their insulation. This causes osmotic demyelination even if the patient seemed fine before.
·Different low sodium (hyponatremia) patients need different fixes based on what broke upstream. SIADH needs fluid restriction because the kidneys are holding too much water. Low volume from vomiting needs normal saline to replace lost salt and water. Too much free water intake (like marathon runners drinking only water) needs fluid restriction. Do not give the same fix to everyone.
·If serum osmolality is low but urine osmolality is high and concentrated, the kidneys are working fine — ADH (antidiuretic hormone, the signal that tells kidneys to hold water) is too high when it should be low. This pattern is SIADH or another ADH problem, not kidney failure. The kidneys are following the wrong signal.
·You need the speed of the drop (acute or chronic), the patient's body fluid status (dry, normal, or puffy), urine osmolality, urine sodium, and serum osmolality to find what broke upstream and caused low sodium (hyponatremia). One number tells you sodium is low but not why it is low or how to fix it.

—

Install Maldek by Hill as an app — studies work even offline