In this episode of Hospital Medicine Unplugged, we cut through inpatient hyponatremia—how to triage by symptoms and acuity, push 3% safely, prevent overcorrection, and fix the cause.
We open with the do-firsts: confirm it’s true hypotonic hyponatremia (check measured serum osmolality; correct Na for glucose), assess duration (<48 h vs >48 h), and stratify symptoms. Severe symptoms (seizure, coma, cardiorespiratory distress) or moderate symptoms with high-risk context (post-op, intracranial disease) → treat now. Place in a monitored setting; q2–4 h Na checks.
Hypertonic saline—how to do it without hurting anyone
• Give 3% NaCl 100–150 mL IV bolus, repeat up to 2–3 times aiming +4–6 mEq/L in 1–2 h and clinical improvement.
• Stop-lights: ≤10 mEq/L in 24 h (≤8 if high-risk: chronic, alcoholism, malnutrition, liver disease, hypokalemia); ≤18 mEq/L in 48 h.
• Bolus beats drips for speed and control; switch to slower correction once stabilized.
• Desmopressin (DDAVP) clamp: 2 mcg IV/SC q6–8 h proactively in high-risk chronic cases, or reactively at the first sign of rapid aquaresis.
• If you overshoot: relower with D5W and/or DDAVP; re-check Na q2 h until back on track.
Etiology playbook (hypotonic only)
• Hypovolemic (GI losses, diuretics, adrenal): 0.9% saline to restore volume → ADH shuts off → watch for brisk water diuresis (have DDAVP ready). Stop offending meds; check cortisol if unclear.
• Euvolemic (SIADH): start fluid restriction (500–1000 mL/day), remove triggers (SSRIs, carbamazepine, pulmonary/CNS insults). If refractory:
– Oral urea (effective, predictable, low ODS risk).
– Vaptan (tolvaptan) for carefully selected inpatient use with close Na checks (watch overcorrection, liver cautions).
– Salt tabs + loop diuretic are optional adjuncts when urine is highly concentrated.
• Hypervolemic (HF, cirrhosis, nephrosis): fluid ± Na restriction, optimize underlying disease, loop diuretics; consider vaptan if truly refractory (short course, monitored). In cirrhosis, albumin can help in select scenarios.
Severity & pace—what changes with chronicity
• Acute (<48 h) severe → you can correct faster initially (still obey 24/48 h caps).
• Chronic (>48 h) → go slow, set the 8 mEq/24 h guardrail in high-risk patients from the start.
Monitoring that prevents ODS
• During active correction: Na q2–4 h, strict I/O, frequent neuro checks; track urine osmolality/Na (early fall in Uosm = impending aquaresis).
• Pre-write orders for DDAVP PRN and D5W relowering; add potassium early if low (correcting K raises Na).
Math you’ll actually use (only if needed)
• 3% NaCl ≈ 513 mEq/L Na. One 100 mL bolus raises serum Na by ~1–2 mEq/L in many adults; verify with labs, not math.
• Avoid formula chasing; let measured Na drive the next step.
Common pitfalls (and fixes)
• Treating pseudohyponatremia or hypertonic hyponatremia as hypotonic → check measured osmolality first.
• Missing adrenal insufficiency → add AM cortisol if unclear etiology.
• Overcorrection after volume repletion or diuretic stop → anticipate with a DDAVP clamp.
• Chasing numbers instead of symptoms → target +4–6 mEq/L early for encephalopathy, then slow down.
We close with the system moves: a “Hyponatremia Bundle” that (1) hardwires osmolality/urine studies before therapy; (2) defaults to 3% bolus + guardrails with q2–4 h sodium checks; (3) includes DDAVP and D5W standing orders; (4) prompts SIADH second-line options (urea/vaptan) when fluid restriction fails; (5) flags high-risk for ODS to apply the 8-mEq/24-h cap; and (6) nudges endocrine/nephrology when etiology is unclear or correction is tricky.
Fast, guideline-driven, and bedside-ready—everything your team needs to rescue the brain, respect the caps, and fix the cause.