When ADH Is Off But Sodium Still Falls: Water Intoxication, Exercise Hyponatremia, and the Low Solute Trap

The Special Populations: Cirrhosis, Dialysis, and Everything You Need to Remember

The final episode of the hyponatremia series. Covers hypervolemic hyponatremia in cirrhosis — including the potassium-first approach — asymptomatic cirrhotic hyponatremia, and severe hyponatremia requiring emergent dialysis and why CVVH with modified replacement fluid is the only safe option. Closes with a rapid-fire review of all 12 clinical pearls from the series.

When ADH Is Off But Sodium Still Falls: Water Intoxication, Exercise Hyponatremia, and the Low Solute Trap

Every episode so far has been about ADH being on when it shouldn't be. Today we flip that entirely. This episode covers hyponatremia where ADH is suppressed, the urine is maximally dilute, and the kidneys are doing exactly what they're supposed to — but the patient is still hyponatremic. Either the water intake is overwhelming the kidneys' capacity, or there isn't enough solute to carry the water out. We work through four presentations: acute water intoxication from a college drinking contest, where the critical teaching point is that rapid correction is safe in acute hyponatremia (unlike chronic); exercise-associated hyponatremia in a marathon runner, including field treatment with hypertonic saline and why normal saline makes things worse; tea-and-toast hyponatremia, with the solute math that explains why a patient eating almost nothing can develop hyponatremia even with maximally dilute urine and normal ADH; and primary polydipsia, where the diagnosis is pure volume overwhelming a compromised excretory system. A three-question framework at the close ties the group together: is intake overwhelming capacity, is solute too low, or is excretory capacity compromised? Final episode of the hyponatremia series next: cirrhosis and dialysis — the special populations where the standard algorithm breaks down.

Salt Wasting: The Diagnosis That Looks Like SIADH But Requires the Opposite Treatment

Same low osmolality. Same concentrated urine. Same high urine sodium. A clinician scanning those results would call it SIADH without hesitating — and then reach for fluid restriction. In salt wasting, that's exactly the wrong move. This episode covers three salt wasting syndromes where the confusion with SIADH causes real harm. First, cerebral salt wasting after subarachnoid hemorrhage — how to distinguish it from SIADH using volume status, fractional excretion of phosphorus, and the saline challenge, which functions as both a diagnostic test and a therapeutic intervention. Second, cisplatin-induced renal salt wasting — a tubular toxicity that causes massive ongoing sodium losses (up to 400 mEq/day) in oncology patients, and why the combination of polyuria, hypovolemia, and a high urine sodium should never be attributed to SIADH. Third, vomiting-associated hyponatremia — why the urine sodium lies in the setting of metabolic alkalosis, why the urine chloride tells the truth, and how bicarbonaturia drags sodium into the urine even in a truly volume-depleted patient. The three-question framework at the close gives you a systematic way to work through any case where the urine sodium is high and SIADH is on your differential. Next episode: water intoxication, exercise-associated hyponatremia, and the low solute syndromes — where ADH is suppressed and the kidneys are doing everything right, but the patient is still hyponatremic.

How to Treat SIADH Without Making It Worse

Your patient has confirmed SIADH. Now what? This episode is all protocol — four clinical scenarios that cover every treatment situation you'll encounter, from the emergency department to the ICU to the outpatient clinic. We start with acute symptomatic hyponatremia: why the answer is a 100–150 mL bolus of 3% saline, not an infusion, and why normal saline can paradoxically worsen things through desalination. Then the scenario that keeps nephrologists up at night — the high-risk patient primed for overcorrection, where the proactive desmopressin clamp removes the variable you can't control. We cover what to do when overcorrection has already happened (act on the numbers, not the exam — osmotic demyelination doesn't show for days). Then subarachnoid hemorrhage, where fluid restriction is contraindicated and the standard rules don't apply. And finally, the outpatient patient with chronic SIADH who can't tolerate fluid restriction — why oral urea beats tolvaptan and salt tablets in most cases. Every scenario ends with a clear rule. The treatment algorithm at the close ties it all together. Next episode: salt wasting syndromes — the conditions that look exactly like SIADH on labs but require the opposite treatment.

The SIADH Trap: Diagnosis, Causes, and the Mimics That Will Fool You

You've checked the osmolality. It's low. The patient looks euvolemic, the urine is concentrated, the urine sodium is high. It looks like SIADH — and you're ready to make the diagnosis. Not so fast. SIADH is a diagnosis of exclusion. In this episode, we build a precise picture of what SIADH actually is — and why calling it a sodium problem instead of a water problem is the first mistake most people make. We go through the drug causes you need to know, including a detailed case of cyclophosphamide-induced SIADH in a patient with GPA where the bladder hydration protocol turns a drug side effect into a crisis. Then we go deep on the three mimics that wear SIADH's face. Adrenal insufficiency — the one you cannot afford to miss, with no hyperkalemia to tip you off in the secondary form. Hypothyroidism — the nuance of when it actually causes hyponatremia versus when a mildly elevated TSH is a red herring. And reset osmostat — the diagnosis that requires no treatment and where treating is futile. We close with the fracture data — why a sodium of 131 in your clinic patient is not something to watch and wait. Next episode: SIADH treatment — 3% saline bolus strategy, the desmopressin clamp, rescuing overcorrection, and subarachnoid hemorrhage where the rules change entirely.