Water Intoxication

Speed is what hurts, not the number - Acute hypo-osmolality gives the brain no time to adapt, so a patient can seize at a sodium a chronically hyponatremic patient tolerates. Even mild symptoms in acute hyponatremia warrant prompt hypertonic saline.

Symptomatic acute hyponatremia - With sodium under 130 mEq/L and symptoms suggesting raised ICP, give 3% saline 100 mL over 10 minutes, repeated up to two more times (300 mL total) if symptoms persist. An alternative is two 150 mL boluses of 3% saline over 20 minutes each with a serum sodium drawn between them. The goal is a 4 to 6 mEq/L rise over a few hours, which is enough to stop symptoms and prevent herniation.

Asymptomatic acute hyponatremia - With sodium under 130 mEq/L and no symptoms, a 50 mL bolus of 3% saline stops the sodium falling further. Hold it if autocorrection is already underway: brisk urine output with dilute urine (osmolality under 200 mOsm/kg, specific gravity under 1.005, or urine sodium plus potassium less than half the serum sodium).

Not mannitol, not vaptans - Mannitol is nephrotoxic and can worsen hyponatremia, which makes the sodium harder to control. Vaptans act too slowly for acute hyponatremia. In severe symptomatic hyponatremia, 3% saline is the only rapid way to raise the sodium, and it is the one that improves neurologic symptoms and prognosis.

Correction rate ceiling - Overcorrection causes osmotic demyelination syndrome, classically when the sodium rises faster than 18 mEq/L over 48 hours or 10 to 12 mEq/L in 24 hours, with cases reported after rates as slow as 9 mEq/L in 24 hours. Because it is the change per day rather than per hour that drives demyelination, the first few hours can be aggressive. See the Hyponatremia entry for the full correction framework.

Irrigation absorption - TURP, transurethral resection of bladder tumor and hysteroscopic resection all use electrolyte-free irrigation. Patients absorb 20 to 30 mL per minute and up to 6 L in two hours. Keep resection time near an hour, hang the irrigation no higher than 30 cm above the table early and 15 cm late, and have the circulator calculate I&O. Draw electrolytes if the case runs past an hour or two.

Regional keeps the monitor awake - An awake patient under spinal is the best early detector of irrigation absorption, because mental status is the earliest sign. Under GETT that exam is gone, so watch the vitals: restlessness gives way to headache, tachypnea, bradycardia with hypertension, and a prolonged QRS, then pulmonary edema, hypoxia and coma.

Treating TURP syndrome - Ensure oxygenation and circulatory support, tell the surgeon and terminate the procedure, consider invasive monitors, and send electrolytes, glucose and an ABG with a 12-lead ECG. Mild symptoms with sodium under 120 mEq/L get furosemide and fluid restriction; severe symptoms with sodium under 115 mEq/L get 3% saline at no more than 100 mL/hr, stopped once the sodium passes 120 mEq/L. Midazolam or diazepam for seizures, intubate if needed.

Oxytocin infusions - Oxytocin cross-reacts at the vasopressin receptor, so a prolonged infusion causes water retention and hyponatremia. Track total free-water volume during long augmentation. Remember oxytocin also causes hypotension and potentiates ephedrine and phenylephrine.

Serum sodium is the parameter that drives treatment - Recheck it every couple of hours, since the sodium can keep falling after presentation as ingested or absorbed water is taken up and because volume expansion increases sodium excretion. A point-of-care sodium analyzer gives the trajectory fastest.

Altered mental status that looks like psychosis - The initial presentation can mimic psychosis, with a hostile delirious profile, delusions, hallucinations, confusion and disorientation. In a psychiatric patient on antipsychotics, send a serum sodium before writing a behavioral change off as disease.

Water intoxication is acute free-water excess that outruns renal excretion and drops plasma osmolality faster than the brain can adapt. Intracellular solute concentration exceeds that of the extracellular space, so the excess water diffuses into cells and swells them. The blood-brain barrier is impermeable to sodium but freely permeable to water, so the brain takes the hit: swollen neurons raise ICP and produce headache, confusion, lethargy and drowsiness, then bradycardia and hypertension as pressure climbs, and finally seizures, delirium, coma and death if uncorrected.

Three routes matter around the OR. Primary or psychogenic polydipsia, including water-drinking contests and alcohol intoxication. Absorption of electrolyte-free irrigation during transurethral and hysteroscopic resection. And oxytocin, which is structurally close enough to ADH to cross-react at the vasopressin receptor and drive water retention on a prolonged infusion.