USMLE Prep - Medical Reference Library

Hypernatremia — Free Water Correction

System: Nephrology • Reviewed: Aug 31, 2025 • Step 1Step 2Step 3

Synopsis:

Treat dehydration and hyperosmolality by calculating free water deficit and replacing slowly; correct underlying cause and monitor sodium closely.

Key Points

  • Stabilize ABCs; begin targeted evaluation without delaying life-saving therapy.
  • Use system-specific risk tools to guide testing and disposition.
  • Order high-yield tests first; escalate imaging when indicated.
  • Start evidence-based initial therapy and reassess frequently.

Algorithm

  1. Primary survey and vitals; IV access and monitors.
  2. Focused history/physical; identify red flags and likely etiologies.
  3. Order system-appropriate labs and imaging (see Investigations).
  4. Initiate guideline-based empiric therapy (see Pharmacology).
  5. Reassess response; arrange consultation and definitive management.

Clinical Synopsis & Reasoning

For Hypernatremia Correction Adult, frame the differential by acuity and pathophysiology, then align diagnostics to the leading hypotheses. Prioritize stabilization while obtaining high‑yield studies such as BMP (Renal/electrolytes), UA ± culture (Hematuria/proteinuria/infection), Renal ultrasound (selected) (Obstruction). Incorporate bedside imaging and targeted labs to define severity and identify complications; synthesize results with clinical trajectory to refine the working diagnosis and disposition needs.


Treatment Strategy & Disposition

Initiate disease‑directed therapy alongside supportive care, titrating to objective response. Pharmacologic options commonly include IV Fluids, Electrolyte repletion. Use validated frameworks (e.g., Helpful Calculations) to guide escalation and site of care. Address precipitating factors, de‑escalate empiric therapies with data, and arrange follow‑up for monitoring and risk‑factor modification; admit patients with instability, high risk of deterioration, or needs for close monitoring.


Epidemiology / Risk Factors

  • CKD/AKI, nephrotoxins; obstruction

Investigations

TestRole / RationaleTypical FindingsNotes
BMPRenal/electrolytesAKI/lyte changes
UA ± cultureHematuria/proteinuria/infectionFindings vary
Renal ultrasound (selected)ObstructionHydronephrosis

Helpful Calculations

FormulaUse
TBW = 0.6 × weight (men) or 0.5 (women)Total body water estimate
Deficit = TBW × ((Na/140) − 1)Free water deficit

Pharmacology

MedicationMechanismOnsetRole in TherapyLimitations
Hypotonic fluids (D5W, 0.45%)Free water replacementHoursGradual correctionCerebral edema if too rapid
Desmopressin (central DI)V2 agonistHoursDI casesHyponatremia

Prognosis / Complications

  • Reversibility by cause; electrolyte/volume complications

Patient Education / Counseling

  • Explain red flags and when to seek emergent care.
  • Reinforce medication adherence and follow-up plan.

Notes

Avoid overly rapid correction that can cause cerebral edema, especially in chronic elevations. In diabetes insipidus, add desmopressin for central or thiazide/NSAID strategy for nephrogenic when appropriate.


References

  1. KDIGO Acute Disorders of Sodium Guidance — Link
  2. Endocrine Society Resources — Sodium Disorders — Link