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LONG CASE FOR MD EMERGENCY MEDICINE EXAMINATION

Diagnosis: HYPONATREMIA (Symptomatic/Acute Severe)

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PRESENTING SCENARIO / PATIENT INTRODUCTION

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1. CHIEF COMPLAINTS / PRESENTING COMPLAINTS

1. Nausea and vomiting - 5 days duration
2. Generalized weakness and lethargy - 4 days duration
3. Headache - 3 days duration
4. Progressive confusion and disorientation - 3 days (worsening over last 24 hours)
5. One generalized tonic-clonic seizure - 45 minutes ago, lasted approximately 2 minutes, post-ictal state currently

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2. HISTORY OF PRESENTING ILLNESS

• Mrs. Rajan, 58 years, known case of small cell lung cancer on cyclophosphamide-based chemotherapy, presented to the ED at 2:15 AM.
• 5 days prior: onset of nausea, anorexia, and vomiting (2-3 episodes/day)
• 4 days prior: progressive fatigue, myalgia, and weakness in all four limbs
• 3 days prior: persistent headache (bifrontal, pressure-type, 6/10 on VAS), progressive confusion - she was unable to recognize her neighbors
• 24 hours prior: markedly worsened disorientation; could not recognize time or place; became drowsy intermittently
• 45 minutes before arrival: witnessed generalized tonic-clonic seizure lasting ~2 minutes, followed by post-ictal confusion
• She has been drinking significantly more water than usual (estimated ~4-5 liters/day) over the past week due to nausea
• No fever, no neck stiffness, no ear pain, no recent head trauma, no prior seizure history
• Urine output reportedly decreased over the last 48 hours (dark-colored, scant)
• Last chemotherapy cycle: 10 days ago

• Small cell carcinoma of the lung (Stage IIIA) - diagnosed 4 months ago
• No known diabetes, hypertension, or renal disease
• No prior seizure disorder

• Cyclophosphamide (chemotherapy - known cause of SIADH)
• Ondansetron (antiemetic - serotonergic mechanism, mild SIADH risk)
• No diuretics, no NSAIDs, no SSRIs

• No fever, no cough change, no chest pain, no dyspnea
• No polyuria, no polydipsia prior to this episode
• No skin hyperpigmentation, no weight loss beyond cancer-related

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3. PRIMARY SURVEY (ABCDE APPROACH)

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4. DIFFERENTIAL DIAGNOSIS

PRIMARY DIAGNOSIS:

• Known small cell lung carcinoma (paraneoplastic SIADH - #1 cause)
• Cyclophosphamide therapy (causes SIADH)
• Euvolemic state: no edema, no ascites
• Clinical triad: confusion + seizure + hyponatremia history

DIFFERENTIAL DIAGNOSES:

• History of drinking 4-5 L/day
• Differentiating feature: Urine sodium <20 mEq/L (dilute urine)
• Urine osmolality would be very low (<100 mOsm/kg)

• Can cause hyponatremia + hyponatremia + confusion
• Consider: fatigue, nausea, hypotension, hyponatremia + hyperkalemia
• Differentiating: check serum potassium (hyperkalemia) and cortisol

• Causes euvolemic hyponatremia
• Differentiating: TSH markedly elevated; bradycardia; coarse hair; delayed reflexes

• Vomiting-induced sodium loss
• Differentiating: hypovolemic picture (low urine sodium), non-resolution on fluid restriction

• Altered consciousness, seizures, headache
• Differentiating: fever, meningismus, CSF pleocytosis
• Can cause SIADH secondarily - not excluded until LP done when safe

• Known malignancy, seizures, confusion
• Differentiating: No focal neurological deficits mentioned, but CT head mandatory to exclude

• Can present with altered consciousness
• Differentiating: EEG required; seizures not ongoing here

• Due to hyperlipidemia or hyperproteinemia (myeloma, macroglobulinemia)
• Osmolality gap would be absent; triglycerides/protein elevated
• Less likely here

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5. SECONDARY SURVEY (SAMPLE + HEAD-TO-TOE EXAMINATION)

SAMPLE History (expanded):

Physical Examination (Head-to-Toe):

• HR: 100/min, BP: 100/64 mmHg (supine), 88/58 mmHg (sitting) - orthostatic drop present
• RR: 18/min, SpO2: 97% (on O2), Temperature: 37.1°C, GCS: 9/15

• GCS: E2V3M4 = 9/15
• Pupils: 4mm bilateral, sluggishly reactive to light (symmetric)
• No papilloedema visualized (fundoscopy)
• No focal motor/sensory deficit detectable in current state
• Deep tendon reflexes: diminished bilaterally
• Plantar response: bilateral extensor (suggesting intracranial process or post-ictal Todd's paresis)
• No neck stiffness (meningism absent)
• Kernig's and Brudzinski's sign: negative

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6. INVESTIGATIONS IN THE EMERGENCY DEPARTMENT

IMMEDIATE / STAT (within 15 minutes):

URGENT (within 30-60 minutes):

IMAGING AND SPECIAL INVESTIGATIONS:

INTERPRETATION FRAMEWORK (Hyponatremia Workup):

Serum Na+ < 135 mEq/L
        |
   Serum Osmolality
     /        \
  <270           Normal/High
(Hypotonic)    (Pseudo/Hypertonic HN)
     |
 Assess Volume Status
  /     |     \
Hypo   Eu    Hyper
(depleted) (normal) (overloaded)
    |          |         |
GI loss    SIADH*    CHF / Cirrhosis
Diuretics  Hypothyroid  Renal Failure
Burns      Polydipsia
           *Urine Na >20 + Urine Osm >100 + Normal BUN + Low Uric Acid

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7. INTERVENTIONS AND TREATMENT IN THE EMERGENCY DEPARTMENT

IMMEDIATE RESUSCITATION (0-15 minutes):

1. Airway protection: Keep patient in lateral decubitus (recovery position); suction available; low threshold for definitive airway (intubation) if GCS falls below 8
2. Oxygen: 6-8 L/min via face mask; target SpO2 >96%
3. IV Access: Two large-bore IV cannulas (14-16G); bilateral antecubital fossa
4. Cardiac Monitor + Continuous SpO2
5. 12-lead ECG
6. Point-of-care blood glucose (done - 76 mg/dL)
7. Anti-seizure management: Lorazepam 0.1 mg/kg IV (or diazepam 0.15 mg/kg IV) - for acute seizure control; however, treating the underlying hyponatremia is the definitive therapy

SPECIFIC TREATMENT - HYPERTONIC SALINE (3% NaCl):

Change in serum Na+ = (Infusate Na+ - Serum Na+) / (Total body water + 1) TBW (female) = 0.5 × body weight (kg)

• TBW = 0.5 × 55 = 27.5 L
• Change per liter of 3% NaCl = (513 - 112) / (27.5 + 1) = 401 / 28.5 = 14 mEq/L per liter
• To raise by 6 mEq/L: need ~430 mL of 3% NaCl (given as 100 mL boluses with monitoring)

• Maximum correction: 10-12 mEq/L in first 24 hours
• Maximum correction: 18 mEq/L in first 48 hours
• Exceeding these rates risks Osmotic Demyelinating Syndrome (ODS) - previously called central pontine myelinolysis - causing flaccid paralysis, dysarthria, dysphagia, and hypotension

MONITORING DURING TREATMENT:

CHRONIC/UNDERLYING CAUSE MANAGEMENT:

WHAT NOT TO DO:

• Do NOT use hypotonic fluids (D5W, 0.45% NaCl) - will worsen hyponatremia
• Do NOT correct sodium faster than 12 mEq/L in 24 hours - risk of ODS
• Do NOT give IV free water
• Do NOT use phenytoin for hyponatremic seizures - ineffective as monotherapy for metabolic seizures; treat the electrolyte disturbance

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8. DISPOSITION

IMMEDIATE DISPOSITION DECISION:

Criteria for ICU Admission (ALL met in this patient):

ICU Handover Points (SBAR Format):

1. Continue 3% NaCl infusion with sodium correction target: +6 mEq/L in first 2 hours; +10-12 mEq/L total in 24 hours
2. Serum Na+ every 2 hours initially
3. Fluid restriction to 500 mL/day after acute phase
4. Oncology input for cyclophosphamide hold
5. Neurology consult re: anti-epileptic therapy
6. CT brain review with radiology; consider MRI brain if Na+ correction does not improve neurology
7. Repeat CT / MRI in 48-72 hours if clinical deterioration (to detect ODS)

Consults Required:

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SUMMARY TABLE

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EXAMINER'S VIVA TOPICS (Anticipated Questions):

1. What is the maximum safe rate of sodium correction and why? - 10-12 mEq/L per 24 hours; faster rates cause osmotic demyelination. High-risk patients (alcoholics, malnourished, geriatric) - some recommend even slower, max 8 mEq/L/24 hours.
2. What is ODS and how does it manifest? - Osmotic Demyelinating Syndrome (central pontine myelinolysis); appears 2-6 days after rapid correction; features: dysarthria, dysphagia, quadriparesis, locked-in syndrome; MRI shows pontine demyelination.
3. How do you differentiate SIADH from cerebral salt wasting (CSW)? - Both cause hyponatremia with high urine sodium. In CSW, the patient is hypovolemic (volume depleted); in SIADH, the patient is euvolemic or mildly hypervolemic. Treatment is opposite: CSW requires IV saline replacement; SIADH requires fluid restriction. This distinction is critical.
4. What is the diagnostic criteria for SIADH (Schwartz-Bartter criteria)?
   • Serum Na+ < 135 mEq/L
   • Serum osmolality < 280 mOsm/kg
   • Urine osmolality > 100 mOsm/kg (inappropriately concentrated)
   • Urine Na+ > 20 mEq/L (with normal salt intake)
   • Euvolemia (no edema, no ascites, no dehydration)
   • Normal thyroid and adrenal function
5. What is the role of Vaptans in hyponatremia? - Tolvaptan (oral, V2 antagonist) and Conivaptan (IV, V1a/V2 antagonist) promote aquaresis (free water excretion without sodium loss). Used for chronic SIADH. NOT recommended in severe acute symptomatic hyponatremia as sole therapy or in liver disease.

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• ROSEN's Emergency Medicine: Concepts and Clinical Practice, Chapter 114 (Hyponatremia), pp. 2432-2590
• Harrison's Principles of Internal Medicine, 22nd Edition (2025), Chapter 36: Clinical Features of Hyponatremia, pp. 392+
• Bradley and Daroff's Neurology in Clinical Practice, Chapter 84: Hyponatremia Without Water Loss, pp. 1791-1792

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LONG CASE FOR MD EMERGENCY MEDICINE EXAMINATION

Diagnosis: HYPONATREMIA - Thiazide Diuretic-Induced (Hypovolemic Hyponatremia)

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PRESENTING SCENARIO / PATIENT INTRODUCTION

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1. CHIEF COMPLAINTS / PRESENTING COMPLAINTS

1. Generalized weakness and fatigue - 4 days
2. Nausea and vomiting (3-4 episodes/day) - 4 days
3. Dizziness on standing - 3 days
4. Headache (diffuse, pressure-type) - 2 days
5. Confusion and disorientation - since morning (4-5 hours)
6. Brief episode of unresponsiveness / possible syncope - 2 hours ago

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2. HISTORY OF PRESENTING ILLNESS

• 4 days prior: onset of generalized malaise, fatigue, anorexia, and nausea with 3-4 episodes of vomiting daily. Unable to tolerate oral food but was drinking excess water (~3-4 L/day) to manage the dry sensation
• 3 days prior: dizziness on standing (orthostatic), near-fall twice while going to the toilet; mild muscle cramps in both calves
• 2 days prior: persistent bifrontal headache; mild leg swelling not present; decreased urine output noticed by family
• This morning (4-5 hours ago): became progressively confused, unable to recognize the date or address; found sitting blankly; one episode of unresponsiveness lasting ~30 seconds with post-event drowsiness (possible brief seizure vs. syncopal episode - unclear)
• No fever, no neck stiffness, no ear pain, no chest pain or breathlessness
• No prior similar episodes
• Key trigger: Hydrochlorothiazide started 3 weeks ago + increased water intake + ongoing vomiting
• No diarrhea, no blood in stools, no melena
• Urine output: decreased, concentrated for past 2 days

• Hypertension (8 years) - on Amlodipine 5 mg
• No diabetes mellitus, no renal disease, no cardiac disease, no malignancy
• No prior hospitalizations for electrolyte disturbance

• Hydrochlorothiazide (HCTZ) 25 mg/day - started 3 weeks ago (primary culprit)
• Amlodipine 5 mg OD (longstanding)
• No NSAIDs, no SSRIs, no steroids, no other diuretics
• (Note: NSAID use independently increases risk of thiazide-induced hyponatremia)

• No polyuria, no polydipsia prior to this episode
• No weight loss, no skin pigmentation changes
• No cold intolerance, no constipation (thyroid symptoms)
• No palpitations, no ankle swelling (cardiac symptoms)
• Menstrual history: Post-menopausal for 15 years

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3. PRIMARY SURVEY (ABCDE APPROACH)

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4. DIFFERENTIAL DIAGNOSIS

PRIMARY DIAGNOSIS:

• Classic triad present: Elderly female + HCTZ started 3 weeks ago + confusion + hypovolemia
• Thiazide block NaCl transport in cortical diluting segment → natriuresis + volume depletion → ADH stimulation → impaired free water excretion → hyponatremia
• Mean serum sodium in thiazide hyponatremia: ~116 mEq/L (often severe)
• Hyponatremia usually develops within 14 days but can occur up to 2 years after initiation
• 56-70% of cases are women; risk is 3.9× higher in patients over 70 years
• Low BMI is an independent risk factor (smaller total body water volume)

DIFFERENTIAL DIAGNOSES:

• Causes hyponatremia + hypotension + confusion
• Distinguished by: hyperkalemia, hyperpigmentation, serum cortisol low, elevated ACTH
• Can co-exist with thiazide use; do not miss this

• Euvolemic hyponatremia - not hypovolemic
• Causes: hypothyroidism, carcinoma, CNS disease, drugs
• Distinguished by: urine Na+ >20 mEq/L + euvolemia + normal adrenal/thyroid function

• Hypovolemic hyponatremia from severe vomiting with free water replacement
• HCTZ effect dominant here; GI loss is a co-contributor
• Urine Na+ <20 mEq/L (if diuretic has worn off)

• Euvolemic hyponatremia, usually mild
• Distinguished by: bradycardia, periorbital puffiness, constipation, markedly elevated TSH
• Hyponatremia only occurs with TSH >50 mIU/L typically

• Hypervolemic hyponatremia
• Distinguished by: elevated JVP, bilateral crepts, pedal edema, cardiomegaly on CXR
• Not present here (flat JVP, no edema)

• Euvolemic, very dilute urine (Uosm <100 mOsm/kg)
• Distinguished by: urine very dilute; psychiatric history
• Patient's water intake is a reaction to thiazide-induced nausea, not primary polydipsia

• POCT glucose 68 mg/dL - borderline; correct and recheck
• Distinguished by: rapid response to glucose administration

• Elderly hypertensive: always exclude
• Distinguished by: CT brain; no focal deficits apparent
• Must do CT head regardless

• Confusion + possible seizure
• Distinguished by: afebrile here; no neck stiffness; no photophobia
• LP only if CT head is clear and clinical suspicion rises

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5. SECONDARY SURVEY (SAMPLE + HEAD-TO-TOE EXAMINATION)

SAMPLE History (Structured):

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Head-to-Toe Physical Examination:

• GCS: 11/15 (E3V3M5)
• Pupils: 4mm bilateral, equally reactive to light
• No papilledema on fundoscopy
• No focal motor deficit (UL: 5/5 bilaterally; LL: 5/5 bilaterally)
• No sensory deficit
• Deep tendon reflexes: symmetrically reduced (hyporeflexia consistent with hyponatremia + hypokalemia)
• Plantar response: flexor bilaterally (normal)
• No cerebellar signs
• No neck stiffness; Kernig's negative; Brudzinski's negative
• Orientation: Disoriented to time and place; responds to name; cannot recall current date or location

HYPOVOLEMIC - Dry mucosa, flat JVP, decreased skin turgor, tachycardia, orthostatic hypotension, dark urine, dry axillae, sunken eyes

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6. INVESTIGATIONS IN THE EMERGENCY DEPARTMENT

IMMEDIATE / STAT (within 15 minutes):

URGENT (within 30-60 minutes):

IMAGING AND SPECIAL INVESTIGATIONS:

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DIAGNOSTIC INTERPRETATION (Thiazide vs. SIADH):

Key Pitfall: Because thiazide diuretics are still active, urine Na+ may be misleadingly >20 mEq/L even in a hypovolemic patient, mimicking SIADH. The uric acid and BUN:Cr ratio are more reliable distinguishing markers. - Brenner & Rector's The Kidney

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7. INTERVENTIONS AND TREATMENT IN THE EMERGENCY DEPARTMENT

STEP 1 - IMMEDIATE RESUSCITATION (0-15 min):

1. Airway: Maintain with positioning; low threshold for intubation if GCS falls to <8
2. Oxygen: 2-4 L/min nasal cannula; upgrade to face mask if SpO2 drops
3. IV Access: Two large-bore cannulas (16G); send bloods simultaneously
4. Cardiac Monitor + Continuous SpO2 + BP monitoring
5. 12-lead ECG: Urgently assess for hypokalemia-induced arrhythmia (flat T, U waves, prolonged QT)
6. POCT Glucose: 68 mg/dL → Give 25% Dextrose 50 mL IV bolus; recheck in 15 minutes
7. Urinary catheter: Insert to monitor hourly urine output (altered GCS)

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STEP 2 - STOP THE CULPRIT:

STOP HYDROCHLOROTHIAZIDE IMMEDIATELY - The single most important intervention. Thiazides should never be restarted - rechallenge almost universally causes recurrence of hyponatremia. Thiazide effects on urinary dilution can persist for up to 1 month after stopping.

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STEP 3 - FLUID RESUSCITATION (for Hypovolemic Hyponatremia):

Important Warning - Overcorrection Risk with Saline in Thiazide Hyponatremia: Once volume is restored, ADH falls abruptly → a sudden large water diuresis may occur → serum Na+ can rise very rapidly, exceeding safe limits. This is a recognized specific danger in thiazide hyponatremia. - Symptom to Diagnosis, 4th Ed.

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SODIUM CORRECTION TARGETS (MANDATORY):

This patient's hyponatremia has been developing for ~3 weeks (chronic). Therefore, the more conservative target of 8 mEq/L per 24 hours applies, with risk of Osmotic Demyelinating Syndrome (ODS) from overcorrection.

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STEP 4 - POTASSIUM AND MAGNESIUM REPLACEMENT:

Critical Note: Potassium correction is not just adjunctive - it directly contributes to sodium correction. Intracellular K+ and Na+ are exchangeable; replacing K+ moves K+ into cells and displaces Na+ to extracellular space, raising serum Na+. Potassium correction adds to the effective Na+ correction rate and must be factored in to avoid overcorrection. - Rosen's EM

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STEP 5 - IF SEIZURE OCCURS:

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MONITORING PROTOCOL:

If serum Na+ rises faster than 1 mEq/L/hour or urine output suddenly surges (diuresis > 200 mL/hr) → STOP all saline immediately → consider D5W infusion to slow the correction rate → this is the ODS prevention protocol.

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TREATMENT SUMMARY TABLE:

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WHAT NOT TO DO:

• Do NOT give hypotonic fluids (D5W or 0.45% NaCl) as initial treatment - will worsen hyponatremia
• Do NOT correct Na+ faster than 8-12 mEq/L in 24 hours - ODS risk
• Do NOT restart HCTZ - rechallenge invariably causes recurrence
• Do NOT use furosemide in a hypovolemic patient - will deepen volume depletion
• Do NOT use Vaptans in hypovolemic hyponatremia - V2 receptor antagonists cause aquaresis and further volume loss, worsening hypotension
• Do NOT ignore the potassium correction rate when calculating total sodium correction

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8. DISPOSITION

IMMEDIATE DISPOSITION DECISION:

Criteria for Admission Level:

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ICU HANDOVER - SBAR FORMAT:

1. HCTZ stopped (confirmed)
2. 0.9% NS resuscitation ongoing (500 mL bolus given; Na+ correction target: 8 mEq/L in 24 hours - chronic hyponatremia)
3. Close monitoring: serum Na+ every 2 hours; stop saline if Na+ rises >1 mEq/L/hour
4. IV KCl replacement in progress; cardiac monitoring continuous
5. CT brain result review; neurology consult if seizure recurs
6. Nephrology consult for hyponatremia management guidance
7. Endocrinology consult: cortisol and TFTs pending to exclude adrenal/thyroid cause

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CONSULTS REQUIRED:

ANTIHYPERTENSIVE MANAGEMENT NOTE:

• Continue Amlodipine 5-10 mg
• Add ACE inhibitor (Ramipril/Enalapril) or ARB
• Beta-blocker if additional indication
• Avoid all thiazide and thiazide-like diuretics permanently in this patient

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SUMMARY TABLE

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EXAMINER'S VIVA TOPICS (Anticipated Questions):

• Thiazide: hypovolemic (flat JVP, orthostatic hypotension, dry mucosa, high BUN:Cr ratio, elevated uric acid, hypokalemia)
• SIADH: euvolemic, normal BUN:Cr, low uric acid (hypouricemia), normokalemia
• Urine Na+ is unreliable as sole marker because active thiazide action can maintain high urine Na+ even in hypovolemia

• Stop all sodium-containing infusions immediately
• Administer D5W infusion to re-lower serum Na+
• Consider DDAVP (desmopressin) 2-4 mcg IV or SC to reduce free water excretion and prevent further Na+ rise
• Seek Nephrology input urgently
• Monitor Na+ every 1-2 hours
• The goal is to bring the 24-hour correction back within 8-12 mEq/L

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• ROSEN's Emergency Medicine: Concepts and Clinical Practice - Chapter 114 (Hyponatremia), Management section
• Brenner and Rector's The Kidney, 2-Volume Set - Hyponatremia with ECF Volume Depletion, Diuretic-Induced Hyponatremia
• National Kidney Foundation Primer on Kidney Diseases, 8e - Hyponatremia, Thiazide Complications
• Symptom to Diagnosis: An Evidence-Based Guide, 4th Ed. - Chapter 24: Diuretic-Induced Hyponatremia
• Frameworks for Internal Medicine - Renal Causes of Hypovolemic Hyponatremia