Eduovisual
Renal & Urinary
Hypernatremia: workup and free water replacement
— Severe: Na >160 mEq/L; mortality climbs sharply above this threshold, particularly in elderly inpatients
— Acute (<48 h) vs chronic (≥48 h) — distinction drives correction rate
— Sustained hypernatremia requires impaired thirst access or impaired AVP response; an awake, ambulatory patient with intact thirst rarely develops it
— Pure water loss: insensible losses, fever, central or nephrogenic diabetes insipidus (DI)
— Hypotonic fluid loss: osmotic diuresis (hyperglycemia, mannitol, high-protein tube feeds), GI losses, diuretics, post-ATN diuresis
— Sodium gain (rare): hypertonic saline, NaHCO₃ in codes, salt poisoning, hyperaldosteronism, improperly mixed dialysate or infant formula
— Hospitalized elderly with restricted access to water, dementia, stroke, intubation, or restraint
— ICU patients on tube feeds, lactulose, loop diuretics, or osmotic diuresis from hyperglycemia
— Postoperative neurosurgery (central DI), lithium users (nephrogenic DI), sickle cell disease, post-obstructive diuresis
— Infants and patients with hypodipsia from hypothalamic lesions
Board pearl: A normal-mentation outpatient with hypernatremia almost always has a thirst or access defect — screen for hypothalamic disease, dementia, or institutional neglect rather than chasing renal causes alone.
— Acute (hours): lethargy, irritability, twitching, seizures, coma, intracranial/subarachnoid hemorrhage from bridging vein tearing
— Chronic (days): weakness, anorexia, gait instability, confusion, low-grade encephalopathy
— Thirst: Present and unmet (access problem) vs absent (hypodipsia, hypothalamic lesion) — a critical fork
— Urine output and character: Polyuria + dilute urine → suspect DI; polyuria + glucosuria/mannitol → osmotic
— Fluid losses: Diarrhea (especially osmotic/lactulose), vomiting, NG suction, burns, sweating, fever
— Medications: Lithium, demeclocycline, foscarnet, amphotericin, loop diuretics, mannitol, tolvaptan, IV bicarbonate or hypertonic saline
— Diet/feeding: Tube feeds without adequate free-water flushes; infant formula errors; recent salt ingestion
— Neuro/endocrine: Head trauma, pituitary surgery, sarcoidosis, histiocytosis, craniopharyngioma
— Functional status: Bedbound, dementia, restraints, NPO orders, swallowing dysfunction
— Nocturia and preference for ice water suggest central DI
Key distinction: Polyuria with hypotonic urine (Uosm <300) suggests DI or primary polydipsia; polyuria with isotonic/hypertonic urine points to osmotic diuresis. Never lump them — the workup and treatment diverge immediately.
— Hypovolemic hypernatremia: Tachycardia, orthostasis, dry axillae and mucosa, flat neck veins, oliguria with concentrated urine (if renal response intact). Cause: hypotonic fluid loss exceeding free water replacement.
— Euvolemic hypernatremia: Stable vitals, near-normal exam, often polyuric. Cause: pure water loss, classically DI.
— Hypervolemic hypernatremia: Edema, elevated JVP, pulmonary crackles, hypertension. Cause: iatrogenic Na load (hypertonic saline, bicarbonate codes) or mineralocorticoid excess.
— Altered mental status, hyperreflexia, myoclonus, focal deficits, seizures
— In infants: high-pitched cry, doughy skin texture (classic for hypertonic dehydration), bulging or sunken fontanelle depending on cause
— Document baseline GCS; track q2–4h during correction to detect overshoot cerebral edema
— Visual field defect → pituitary mass causing central DI
— Bitemporal hemianopia + amenorrhea/galactorrhea → sellar lesion
— Goiter, skin/hair changes → consider associated endocrinopathies
— Lithium tremor, nephrogenic DI stigmata
— Bladder scan post-void if obstruction/post-obstructive diuresis suspected
— Capillary glucose at the bedside — hyperglycemia frequently coexists and confounds calculations
Board pearl: Doughy, tenting skin in a febrile infant with sunken eyes and irritability = hypertonic dehydration until proven otherwise; lab confirmation should not delay graded rehydration.
— Repeat BMP to exclude lab error, especially if clinically discordant
— Correct for hyperglycemia: add ~1.6 mEq/L to measured Na for every 100 mg/dL glucose above 100 (or 2.4 by some formulas) — though in hypernatremia, the hyperglycemia is itself often the driver
— Serum osmolality: Should be elevated (>295 mOsm/kg) and roughly = 2[Na] + glucose/18 + BUN/2.8
— Urine osmolality (Uosm): The single most discriminating test
— Urine sodium and urine specific gravity
— BUN/Cr, glucose, calcium, potassium
— Capillary or serum glucose to identify osmotic diuresis from hyperglycemia
— Uosm >700–800 mOsm/kg: Appropriate renal response → extrarenal water loss (insensible, GI) or inadequate intake. Kidney is doing its job.
— Uosm 300–700: Partial concentrating defect — osmotic diuresis, loop diuretic effect, partial DI
— Uosm <300 (especially <Posm): Frank DI — central or nephrogenic
— Daily urine osmoles = Uosm × 24-h urine volume
— >1000 mOsm/day → osmotic diuresis (glucose, urea from high-protein tube feeds, mannitol, post-obstructive)
— <800 mOsm/day with dilute urine → water diuresis (DI)
— Urine glucose, urine urea, fractional excretion of urea
— Lithium level if on lithium
— Calcium (hypercalcemia causes nephrogenic DI); potassium (hypokalemia does too)
Board pearl: A hypernatremic patient making >3 L/day of urine with Uosm <300 has DI until proven otherwise; the next test is the water deprivation test with desmopressin challenge, not more random electrolytes.
Key distinction: High Uosm + hypernatremia = the kidneys are innocent; look at intake and extrarenal losses.
— Indication: polyuria + dilute urine without obvious cause; only perform when patient is safe to dehydrate (close monitoring, frequent weights, hourly Na)
— Withhold fluids; measure Uosm, Posm, Na, and weight hourly
— Stop if weight loss >3–5%, Posm >295–300, or Na >145–150
— Then administer desmopressin (DDAVP) 2–4 µg SC and recheck Uosm at 1–2 h
— Uosm rises >50% (often >100%) after DDAVP → Central DI (kidney can respond; the problem was lack of AVP)
— Uosm rises <50% (usually <10%) after DDAVP → Nephrogenic DI (kidney unresponsive)
— Uosm rises appropriately during dehydration alone (>700) → Primary polydipsia (rare cause of hypernatremia but classic for hyponatremia/normonatremia with polyuria)
— Baseline or hypertonic saline–stimulated copeptin distinguishes central DI from primary polydipsia more reliably than the classic water deprivation test and is increasingly the preferred test in tertiary centers
— MRI brain with pituitary protocol for confirmed central DI — look for absent posterior pituitary "bright spot," stalk thickening (sarcoid, LCH, germinoma, lymphocytic hypophysitis), or sellar mass
— Anterior pituitary function panel (TSH/T4, cortisol/ACTH, prolactin, LH/FSH, IGF-1) — central DI often coexists with panhypopituitarism
— Renal ultrasound if obstructive uropathy with post-obstructive diuresis
— Lithium level and duration; serum Ca, K; review meds (demeclocycline, foscarnet, cidofovir, amphotericin); rule out sickle cell, amyloid, Sjögren
Step 3 management: Don't run a water deprivation test on a frail hypernatremic inpatient — they're already volume-deplete. Give DDAVP empirically and watch Uosm rise as a therapeutic trial in central DI when the clinical picture fits.
1. Restore hemodynamics with isotonic saline if hypovolemic and unstable
2. Calculate the free water deficit
3. Correct slowly to avoid cerebral edema
4. Replace ongoing losses in addition to the deficit
— FWD (L) = TBW × ([Na]measured / [Na]desired − 1)
— TBW ≈ 0.6 × weight (kg) in men, 0.5 in women, 0.45 in elderly women, 0.6–0.7 in children
— Example: 70-kg man, Na 160, target 140 → FWD = 42 × (160/140 − 1) = 6 L
— Chronic hypernatremia (≥48 h or unknown): lower Na by no more than 10 mEq/L per 24 h (≈0.5 mEq/L/h)
— Acute hypernatremia (<48 h, well documented): can correct faster — 1 mEq/L/h is acceptable
— Aim for goal Na ~145 over 48–72 h, not immediately
— D5W: pure free water; for euvolemic patients with pure water deficit
— 0.45% NaCl (½NS): half free water, half isotonic — for hypovolemic hypernatremia (gives volume + free water)
— 0.9% NaCl: for shock first; remember 1 L of NS is roughly isotonic and won't lower Na much
— Enteral free water via NG/PEG is preferred when feasible — safer, cheaper, harder to overshoot
— ΔNa per L infused = (Nainfusate − Naserum) / (TBW + 1)
— Use to plan rate; recheck Na q4–6h and adjust
CCS pearl: Order Na q4–6h during active correction, daily weights, strict I/Os, and re-check the free water deficit calculation as the Na drops — the math changes as TBW and Na evolve.
Board pearl: Overshooting correction in chronic hypernatremia causes cerebral edema, seizures, and herniation — the dreaded inverse of osmotic demyelination.
— Desmopressin (DDAVP) is first-line: 0.05–0.2 mg PO BID, 10–40 µg intranasal daily-BID, or 1–2 µg SC/IV BID
— Titrate to allow one daily "breakthrough" diuresis to prevent water intoxication and iatrogenic hyponatremia
— Counsel on water intake matching thirst, not arbitrary volumes
— Avoid in pregnancy planning? — actually safe in pregnancy and used for gestational DI (vasopressinase-mediated)
— Remove offending agent first (lithium, demeclocycline, etc.); correct hypercalcemia and hypokalemia
— Low-solute diet: reduce sodium and protein intake to lower obligate water excretion
— Thiazide diuretic (hydrochlorothiazide 25 mg/day) — paradoxically reduces polyuria by inducing mild volume depletion and increased proximal water reabsorption
— Amiloride (5–10 mg/day) — particularly useful in lithium-induced NDI; blocks ENaC and prevents lithium uptake in collecting duct
— NSAIDs (indomethacin) reduce prostaglandin-mediated AVP antagonism; use cautiously due to renal/GI risks
— Carbamazepine and chlorpropamide enhance residual AVP effect (rarely used now)
— 70 kg, Na 162, BP 90/60: bolus 1–2 L 0.9% NS until perfused, then switch to D5W or ½NS at a rate calculated to lower Na ≤10 mEq/L over 24 h
— Add maintenance free water for ongoing insensible losses (~30–40 mL/kg/day) and measured GI/urine losses
— If patient can take PO/enteral water, use that route preferentially
— D5W contains 50 g glucose/L; rapid infusion in diabetics produces hyperglycemia → osmotic diuresis → worsening hypernatremia. Monitor glucose and add insulin or switch to ½NS if needed.
Step 3 management: In lithium-induced NDI, don't reflexively stop lithium — coordinate with psychiatry and trial amiloride first; abrupt lithium discontinuation can precipitate manic relapse.
— 65 kg woman, Na 168, chronic. TBW = 0.5 × 65 = 32.5 L
— FWD = 32.5 × (168/140 − 1) = 6.5 L
— Goal Na drop in 24 h = 10 → roughly 25% of deficit = 1.6 L on day 1
— Plus insensible loss ~1 L/day, plus urine output
— Initial D5W rate: ~100–125 mL/h, recheck Na in 6 h, adjust
— D5W (Na 0): ΔNa = (0 − 168)/(32.5 + 1) = −5.0 mEq/L per liter
— ½NS (Na 77): ΔNa = (77 − 168)/(33.5) = −2.7 mEq/L per liter
— Confirms D5W lowers Na nearly twice as fast as ½NS
— Loop diuretic + D5W replacement of urine output; furosemide drives off Na with hypotonic urine
— Hemodialysis for severe salt overload, especially with renal failure or refractory hypernatremia >180
— Use low-Na dialysate cautiously; aim to lower Na ≤10 mEq/L per session
— Post-pituitary surgery: classic triple-phase response — DI → SIADH (days 5–10) → permanent DI
— Treat each phase distinctly; do not continue scheduled DDAVP into the SIADH phase
— Monitor Na q6h for 10–14 days post-op
— Add free-water flushes (e.g., 250 mL q4–6h) titrated to maintain Na 135–145
— High-protein formulas generate large urea solute load → osmotic diuresis
CCS pearl: On a CCS hypernatremia case, the high-yield order set is: D5W or ½NS infusion, BMP q4–6h, strict I/Os, daily weights, hold offending drugs, treat underlying cause (DDAVP, stop lithium, glucose control), and consult endocrine/nephrology when indicated.
Key distinction: Free water deficit corrects existing hypernatremia; you must separately replace ongoing losses (urine, insensible, GI) or you'll never catch up.
— Age-related decline in thirst perception and AVP responsiveness
— Reduced TBW (≈45–50% body weight) → smaller deficits produce higher Na
— Polypharmacy: loop diuretics, lithium, SGLT2 inhibitors (glucosuria → osmotic diuresis), laxatives
— Functional dependency for water access — assisted-living and SNF residents have hypernatremia prevalence up to 30% during illness
— Use TBW of 0.45 (women) or 0.5 (men) in FWD calculation — overestimating TBW underestimates risk of overshoot
— Correct more slowly: 8 mEq/L/24 h is a safer cap
— Re-check Na q4h, not q6–8h, especially during the first day
— Beware coexisting dementia masking neuro deterioration during correction
— Impaired urinary concentration → predisposed to both DI-like polyuria and inability to excrete free water loads
— Free water replacement with D5W is fine, but watch for volume overload and hyperglycemia
— Severe hypernatremia in HD patients: adjust dialysate sodium downward gradually (1–2 mEq per session) — sudden drops cause disequilibrium and cerebral edema
— Hypernatremia is uncommon but devastating; often from lactulose-induced osmotic diarrhea
— Aggressive D5W with simultaneous lactulose dose adjustment; avoid worsening hepatic encephalopathy from rapid osmolar shifts
— Avoid 0.45% NaCl in tense ascites — sodium load worsens fluid overload
— Loop diuretic–driven hypernatremia is common; replace with enteral free water rather than IV crystalloid to avoid volume overload
— Reassess diuretic dose and dietary sodium
Step 3 management: In a nursing home patient with Na 158 and dry mucosa, the highest-yield intervention is scheduled oral or NG free water plus a thirst/hydration care plan — IV therapy is a bridge, not the solution.
Board pearl: Elderly + tube feeds + loop diuretic + UTI is the modal Step 3 vignette for hospital-acquired hypernatremia.
— Gestational DI: placental vasopressinase degrades endogenous AVP, typically late 2nd/3rd trimester; resolves postpartum
— Treat with desmopressin (DDAVP) — resistant to vasopressinase and safe in pregnancy (category B-equivalent)
— Distinguish from unmasking of preexisting subclinical central DI
— Preeclampsia–HELLP can produce transient DI via hepatic dysfunction reducing vasopressinase clearance? — actually the opposite, hepatic dysfunction increases vasopressinase activity
— Hypertonic dehydration in infants from diarrhea, inadequate breastfeeding, or improperly mixed formula (too much powder)
— Doughy skin, irritability, high-pitched cry, fever, hyperglycemia
— Rehydrate over 48–72 h, not 24 h — children are especially prone to cerebral edema
— Use isotonic saline bolus for shock (20 mL/kg), then transition to ½NS or ⅓NS + D5
— Target Na decline ≤0.5 mEq/L/h, ≤10–12 mEq/L per 24 h
— Seizures during correction → not always overshoot; can be hypocalcemia (often coexists)
— Intentional (Munchausen by proxy) or accidental (homemade rehydration with table salt) — mandatory reporting if abuse suspected
— Na often >180; treat with cautious D5W and consider hemodialysis
— Anticipate central DI after pituitary surgery, TBI, brain death evaluation
— Hourly urine output; if >300 mL/h for 2 h with dilute urine → start DDAVP
Key distinction: Gestational DI responds to DDAVP but not to native AVP/vasopressin (which is destroyed by vasopressinase); choosing AVP over DDAVP in pregnancy is a classic distractor.
Board pearl: Infant with Na 165 after a week of bottle-fed gastroenteritis → rehydrate over 48–72 h with isotonic-leaning fluids, monitor calcium and glucose, and watch for cerebral edema during correction.
— CNS: lethargy, seizures, coma, intracranial/subdural/subarachnoid hemorrhage from venous sinus and bridging vein tearing as the brain shrinks
— Rhabdomyolysis from severe hypertonicity and immobility
— Hyperglycemia from impaired insulin secretion in hypertonic states
— Venous thromboembolism: hypertonic states are prothrombotic
— Cerebral edema from overly rapid correction in chronic hypernatremia — the brain has accumulated idiogenic osmoles (taurine, myoinositol, glutamate) over hours-days; rapid free water shifts back in cause swelling
— Presents as new-onset seizures, declining GCS, papilledema during therapy
— Treatment of overshoot: stop free water, consider 3% saline bolus (e.g., 100 mL over 10 min) to re-raise Na 2–3 mEq/L, mannitol, head-of-bed elevation, ICU transfer
— DDAVP overuse → iatrogenic SIADH-like hyponatremia, especially in post-pituitary patients during triple-phase response
— Thiazides for NDI → hypokalemia, hyperuricemia, glucose intolerance
— D5W in diabetics → worsening hyperglycemia and osmotic diuresis, paradoxically perpetuating hypernatremia
— NSAIDs for NDI → AKI, GI bleeding, especially in elderly
— Hospital-acquired hypernatremia has mortality 40–60% in some ICU series — largely a marker of underlying severity but also reflects preventable iatrogenesis
— Severe community-acquired hypernatremia in elderly carries similar mortality
— Persistent neurocognitive deficits after severe episodes in infants and elderly
— Permanent DI after pituitary insult; chronic polyuria/nocturia affecting QoL
Step 3 management: If Na drops faster than 10–12 mEq/L in 24 h in a chronic case, slow or stop free water and consider isotonic or hypertonic re-correction to bring Na back up — treat overshoot like you would overcorrected hyponatremia.
Board pearl: New seizure during hypernatremia treatment ≠ hypernatremia worsening; it usually means cerebral edema from overcorrection — recheck Na immediately.
— Na >160 mEq/L with altered mental status, seizures, or hemodynamic instability
— Acute hypernatremia from salt poisoning or hypertonic infusions
— Requirement for hypertonic saline correction of overshoot
— Post-neurosurgical DI with hourly fluid balance demands
— Severe nephrogenic DI with urine output >500 mL/h
— ESRD or advanced CKD with hypernatremia (dialysate management)
— Nephrogenic DI workup and chronic management
— Hemodialysis for salt poisoning or refractory severe hypernatremia
— Complex acid-base + electrolyte derangements
— Confirmed or suspected central DI (especially post-op, post-trauma)
— Multiple pituitary axis deficiencies
— Gestational DI
— DDAVP titration in complicated cases (triple-phase response, partial DI)
— Pituitary mass on MRI in newly diagnosed central DI
— Hemorrhagic complications from severe hypertonicity
— Status epilepticus during correction
— Stable Na 145–155 with identified reversible cause, intact mentation, oral intake → general floor
— Na 155–165 needing IV correction or with comorbidities → telemetry/step-down
— Na >165 or symptomatic → ICU or step-down with q4h labs
— Always explicitly hand off the correction rate target, current Na, fluid type/rate, and time of next BMP — this is a high-litigation transition
— Use closed-loop communication and EHR-based correction calculators when available
CCS pearl: A CCS case asking about Na 172 with confusion → transfer to ICU, start D5W via central line if needed, BMP q2–4h initially, consult nephrology and endocrine in parallel — don't sequentialize when the patient is decompensating.
Key distinction: ICU triage in hypernatremia is driven by rate of change and mental status, not the absolute number alone — a chronic Na of 158 in an alert patient may be a floor admission.
— Central DI: trauma, pituitary surgery, sarcoidosis, Langerhans cell histiocytosis, germinoma, lymphocytic hypophysitis, idiopathic, autosomal dominant familial
— Nephrogenic DI: lithium (most common acquired), hypercalcemia, hypokalemia, demeclocycline, foscarnet, amphotericin, sickle cell, Sjögren, amyloid, X-linked AVPR2 mutation, AQP2 mutations
— Insensible losses: fever, burns, mechanical ventilation without humidification, hyperthyroidism
— GI: osmotic diarrhea (lactulose, sorbitol, malabsorption), severe vomiting, NG suction
— Renal: osmotic diuresis (hyperglycemia/DKA-HHS, mannitol, high-urea from tube feeds), loop diuretics, post-ATN diuresis, post-obstructive diuresis
— Cutaneous: burns, excessive sweating
— Third spacing in critical illness
— Hypertonic saline (3%) for ICP or hyponatremia overcorrection
— Sodium bicarbonate during codes
— Improperly prepared infant formula or homemade ORS
— Sea water ingestion
— Salt tablet overdose / Munchausen
— Primary hyperaldosteronism, Cushing syndrome (mild Na elevation only)
— Dialysate errors
— Hyperosmolar hyperglycemic state (HHS): hypernatremia + hyperglycemia + osmotic diuresis — the "perfect storm"
— Tube-feed hypernatremia: hypertonic feeds + inadequate flushes + osmotic diuresis from urea
Board pearl: Calculate urine osmoles/day to separate water diuresis (DI) from osmotic diuresis — both cause polyuria and hypernatremia but the workup and treatment diverge sharply.
Key distinction: Lithium and hypercalcemia are the two most testable acquired causes of nephrogenic DI — always ask about both in a polyuric hypernatremic patient.
— Spurious hypernatremia: sampling from a line running saline — repeat from a different site
— Translocational pseudohyponatremia inverse: in mannitol or radiocontrast, measured Na may drop while tonicity is high — assess osmolality, not just Na
— Primary polydipsia: psychiatric or hypothalamic; usually presents with hyponatremia or normal Na, not hypernatremia — but can mimic DI on water deprivation. Distinguished by copeptin and clinical context.
— Diuretic abuse
— Diabetes mellitus with glucosuria
— Stroke, meningitis, hepatic encephalopathy, hypoglycemia, drug intoxication can present similarly to hypernatremic encephalopathy. Always check a BMP and glucose first.
— Coexisting hypocalcemia (especially in infants), hypoglycemia, intracranial hemorrhage from brain shrinkage, alcohol withdrawal, structural lesion
— Cerebral edema from overcorrection (during therapy)
— Think HHS before DI: glucose >600, no/minimal ketones, severe dehydration, AMS, often elderly with T2DM
— Management differs: insulin + isotonic saline first, NOT D5W
— Adrenal insufficiency typically causes hyponatremia, not hypernatremia — but may coexist with panhypopituitarism + central DI, where Na can be variable
— Hyperthyroidism can produce mild hypernatremia via insensible losses
Step 3 management: Always reconcile the Na with glucose and osmolality. Hyperglycemia–driven hypernatremia in HHS gets isotonic saline first; pure DI gets D5W. Choosing the wrong starting fluid is a classic Step 3 distractor.
Board pearl: A patient with polyuria, polydipsia, normonatremia, and dilute urine is more likely to have primary polydipsia than DI — DI patients with intact thirst usually stay just above 140.
— Central DI: DDAVP (oral 0.1–0.2 mg BID-TID, intranasal 10–20 µg BID, or sublingual 60–120 µg BID); medical alert bracelet
— Lithium-induced NDI: continue lithium if psychiatrically essential + add amiloride 5–10 mg/day; consider switching mood stabilizer with psychiatry
— Other NDI: thiazide ± amiloride, low-salt low-protein diet, NSAIDs if renal function permits
— Drink to thirst, not to schedule, especially on DDAVP — over-drinking causes iatrogenic hyponatremia
— Skip one DDAVP dose weekly to allow a "water diuresis" and recalibrate thirst
— Recognize warning signs: headache, nausea, confusion (could be either hypo- or hypernatremia)
— Improve dementia care plans for nursing home patients: scheduled offered fluids, swallow evaluation, hypodermoclysis if needed
— Tube-feed protocols: standing free-water flushes, weekly BMP review
— Diabetes optimization to prevent glucosuria-driven hypernatremia
— Pituitary mass: oncology/neurosurgery follow-up
— Central DI: BMP at 1–2 weeks, then every 3–6 months once stable
— Lithium NDI: BMP, lithium level, Ca, TSH every 3–6 months
— Recurrent hypernatremia in elderly: outpatient follow-up within 1–2 weeks; engage caregivers and primary care
— Standard adult schedule; influenza and pneumococcal vaccines particularly important since febrile illness commonly precipitates hypernatremia in vulnerable patients
Step 3 management: Discharging a patient with central DI on DDAVP requires written instructions, a medical alert ID, a follow-up Na within 7–14 days, and a clear "what to do if sick" plan — illness with vomiting can rapidly tip them into either hypo- or hypernatremia.
Board pearl: Amiloride is the drug of choice for lithium-induced NDI when lithium must continue — it blocks ENaC-mediated lithium entry into principal cells.
— Serum Na q2–4h for severe or symptomatic; q4–6h for moderate; q12h once stable
— Urine output and urine osmolality at least q6h in DI patients
— Daily weights, strict I/Os, glucose checks
— Mental status q2–4h during active correction; lower threshold for neuroimaging if status changes
— Drop Na by ≤10 mEq/L in any 24 h (≤8 in elderly, ≤12 in pediatrics over 24 h)
— Goal Na ~145 by 48–72 h
— Hourly urine output 0.5–1 mL/kg/h indicates adequate perfusion
— Central DI: endocrinology within 2–4 weeks of discharge; BMP and clinical assessment at each visit
— Nephrogenic DI: nephrology + primary care; review BMP, Ca, K, urine osmolality, lithium level if applicable
— Recurrent dehydration-driven hypernatremia: geriatric assessment, swallow evaluation, social work for care coordination
— Sick-day rules: double check fluid intake, weigh daily, contact provider if vomiting/diarrhea >24 h
— DDAVP-specific: symptoms of water intoxication (headache, nausea, lethargy) → skip next dose, check Na
— Caregivers of dementia patients: offer fluids every 1–2 hours during the day, track intake on a log, recognize early signs (dry mouth, decreased urine output, irritability)
— Speech-language pathology for dysphagia rehabilitation post-stroke
— PT/OT for fall risk that limits self-hydration
— Consider feeding tube only after thorough goals-of-care discussion in advanced dementia
CCS pearl: After resolution, schedule follow-up BMP at 1 week and 1 month, and reassess the precipitating factor — diuretic dose, tube-feed regimen, lithium level — because recurrence is high when the upstream cause isn't fixed.
Key distinction: Frequency of follow-up labs is driven by cause and chronicity, not just severity at presentation — a stable central DI patient needs lifelong but infrequent monitoring; a lithium NDI patient needs quarterly checks.
— Hospital-acquired hypernatremia is increasingly tracked as a nursing-sensitive indicator
— Root causes: missed free-water flushes on tube feeds, prolonged NPO without IV maintenance, restricted mobility limiting water access, overlooked rising Na trends
— Institutional response: standardized order sets, automated EHR alerts when Na trends upward, mandatory free-water orders with enteral feeds
— Water deprivation testing involves deliberately worsening hypertonicity — requires explicit informed consent with risks of seizure, hemodynamic instability, and need for emergent intervention
— DDAVP therapy consent: discuss risk of iatrogenic hyponatremia and need for follow-up
— Pediatric salt poisoning with no plausible accidental explanation → mandatory child protective services report and admission for safety
— Hypernatremia in nursing home residents with evidence of neglect → adult protective services referral
— Document objective findings (Na trend, intake records, exam) clearly
— In advanced dementia or end-stage illness, aggressive IV correction may not align with goals — discuss with surrogate decision-makers
— Subcutaneous hypodermoclysis can offer a less invasive, comfort-oriented approach for mild-moderate hypernatremia in hospice settings
— Avoid placing PEG tubes solely to prevent hypernatremia in advanced dementia — evidence does not support survival benefit
— Highest-risk handoffs: ICU → floor, hospital → SNF, ED → floor
— Mandatory elements in the handoff: current Na, correction goal, fluid type/rate, time of next lab, who is responsible for the next decision
— Closed-loop, read-back communication required for any patient with Na >155 or active correction
Step 3 management: A 92-year-old with end-stage dementia in a SNF presents with Na 158 from poor intake — the right next step often includes a family meeting on goals of care, hypodermoclysis or oral free water, and avoiding aggressive ICU-level intervention if it conflicts with stated wishes.
Board pearl: Salt poisoning in a child is abuse until proven otherwise — admit and report.
— Na ↑ = water ↓ in most cases — think "deficit," not "excess"
— Free water deficit (L) = TBW × ([Na]/140 − 1)
— Adrogué–Madias: ΔNa per L = (Nainf − Naserum)/(TBW + 1)
— Uosm >700: extrarenal losses or poor intake (kidneys appropriate)
— Uosm 300–700: partial DI, osmotic diuresis, loop diuretics
— Uosm <300: complete DI (central or nephrogenic)
— Uosm doubles → central DI
— Uosm unchanged → nephrogenic DI
Step 3 management: Always start hypernatremia management with three orders simultaneously — BMP, urine osmolality, and a calculated fluid plan written explicitly in the chart with goal Na and next lab time.
Board pearl: "Pee a lot, drink a lot, Na high, urine dilute" = DI; the fork is the DDAVP response.
— 84-year-old with dementia, fever, dry mucosa, Na 162, BUN 60, normal urine output but concentrated urine (Uosm 850)
— Answer: extrarenal water loss + poor intake; treat with enteral free water and ½NS, slow correction ≤8 mEq/L/24 h, address upstream care plan
— Bipolar patient on lithium 5 years, presents with polyuria 5 L/day, Na 150, Uosm 180, no rise after DDAVP
— Answer: lithium-induced nephrogenic DI → add amiloride, coordinate with psychiatry; do not abruptly stop lithium
— POD 2 after transsphenoidal resection: urine output 400 mL/h, urine specific gravity 1.001, Na 148 and rising
— Answer: central DI → start DDAVP, monitor for triple-phase response, expect possible SIADH around day 5–10
— Stroke patient on PEG with high-protein formula, Na 158, Uosm 720, urine output 2.5 L/day
— Answer: osmotic diuresis from urea load → increase free-water flushes, consider lower-protein formula
— Patient with Na 168 corrected to 150 in 12 h, now seizing
— Answer: cerebral edema from rapid correction → stop free water, consider 3% saline bolus to re-raise Na, ICU transfer
— Third-trimester woman with polyuria, Na 148, no response to AVP but responds to DDAVP
— Answer: gestational DI from placental vasopressinase
— T2DM, glucose 950, Na 152 (measured), AMS
— Answer: correct Na for glucose first (true Na higher); start 0.9% NS + insulin, not D5W
— Infant Na 178, witnessed homemade ORS, sibling history of unexplained illness
— Answer: child abuse evaluation, mandatory report, cautious D5W, consider HD
CCS pearl: Recognize the trigger phrase: "Uosm 850" = appropriate kidney; "Uosm 150" = DI. The single number reframes the whole differential.
Hypernatremia is a free-water deficit problem requiring you to (1) classify by volume status, (2) interpret urine osmolality, (3) calculate the free water deficit, and (4) correct slowly — ≤10 mEq/L per 24 hours — while replacing ongoing losses and fixing the upstream cause.
— Volume: hypovolemic (hypotonic loss), euvolemic (pure water loss/DI), hypervolemic (Na gain)
— Urine osmolality: >700 = kidneys fine, extrarenal; <300 = DI; in between = partial defect or osmotic
— Cause: DI subtype via DDAVP challenge; otherwise drug review, GI/insensible losses, iatrogenic Na load
— Hemodynamics first with 0.9% NS if unstable
— Free water deficit = TBW × ([Na]/140 − 1) plus ongoing losses
— D5W or ½NS, oral/NG free water preferred when feasible
— Cap correction at 10 mEq/L per 24 h (8 in elderly, 12 in pediatrics over 24 h with 48–72 h total horizon)
— DDAVP for central DI, amiloride/thiazide + low-solute diet for nephrogenic DI
— Overcorrection → cerebral edema → seizures → re-raise Na with 3% saline
— Iatrogenic hyponatremia from DDAVP misuse
— Underlying pituitary mass in new central DI → MRI + pituitary panel
— Audit inpatient flowsheets and tube-feed orders
— Plan transitions of care with explicit handoff of correction targets
— Recognize salt poisoning in children as mandatory-report abuse
— Align aggressive correction with goals of care in advanced illness
Board pearl: Hypernatremia management is a rate problem as much as a fluid problem — the right fluid at the wrong rate kills brains; the right rate with the wrong fluid fails to correct.