In which perioperative adult surgical patients is 0.45% sodium chloride indicated (e.g., postoperative hypernatremia, intra‑operative diabetes insipidus, iatrogenic hyperchloremic metabolic acidosis, or specific neurosurgical cases)?

When to Give 0.45% Normal Saline in Adult Perioperative Patients

In adult perioperative patients, 0.45% sodium chloride should generally be avoided in favor of balanced isotonic crystalloids, with the rare exception of specific neurosurgical cases involving central diabetes insipidus with concurrent salt wasting where hypertonic saline replacement may be needed.

Primary Recommendation: Avoid Hypotonic Solutions Perioperatively

Balanced isotonic crystalloids (Ringer's Lactate, Plasma-Lyte) are the preferred perioperative fluids for adult surgical patients, as they reduce mortality, major adverse kidney events, and prevent hyperchloremic metabolic acidosis compared to both 0.9% saline and hypotonic solutions. 1

• The European guidelines for critically ill patients recommend balanced crystalloids as first-line therapy, particularly when large volumes (5-10 L in first 24 hours) are required 2, 1
• Balanced solutions consistently demonstrate better acid-base balance compared to 0.9% NaCl 2
• The SMART trial showed balanced crystalloids reduce 30-day mortality (OR 0.84,95% CI 0.74-0.95) and major renal events 1

Why 0.45% Saline is Generally Contraindicated

Hypotonic solutions like 0.45% NaCl are not recommended for routine perioperative fluid management in adults because they lack evidence for improved outcomes and carry risk of hyponatremia.

• The pediatric literature demonstrates increased hyponatremia risk with hypotonic solutions (0.45% NaCl) compared to isotonic fluids 2
• No adult perioperative guidelines recommend 0.45% saline as a standard maintenance or resuscitation fluid 2, 1, 3
• Hypotonic fluids should be avoided in traumatic brain injury patients to prevent cerebral edema 1

Specific Clinical Scenario: Central Diabetes Insipidus with Salt Wasting

The only perioperative situation where hypotonic or hypertonic saline may be considered is in neurosurgical patients with central diabetes insipidus complicated by concurrent salt wasting, where fluid composition must match urinary losses.

Diagnostic Criteria

• Polyuria persisting despite adequate glucose control and fluid resuscitation 4, 5
• Low urine osmolality (<300 mOsm/kg) with elevated serum osmolality 4, 6
• Positive electrolyte-free water clearance 4, 6
• Response to desmopressin acetate confirming central diabetes insipidus 6

Management Approach

• When central diabetes insipidus coexists with salt wasting, the urine becomes hypertonic with high sodium concentration despite desmopressin treatment 4
• In this specific scenario, infused fluid should match the sodium concentration and volume of urine output to prevent further dysnatremia 4
• This may require hypertonic saline infusion (not 0.45% saline) when urine sodium concentration is elevated 4
• Alternatively, decrease urinary sodium concentration with loop diuretics or urea while replacing losses with isotonic solutions 4

Critical Pitfall

• Hypernatremia in postoperative neurosurgical patients is primarily due to positive sodium balance rather than water deficit alone 4
• Hyponatremia developing after desmopressin is primarily from negative sodium balance due to continued salt wasting, not water excess 4
• Central diabetes insipidus is uncommon in neurointensive care (only 8 of 75 hypernatremic patients in one series), with most hypernatremia from osmotherapy and diuretics 6

Management of Hyperchloremic Metabolic Acidosis

If hyperchloremic metabolic acidosis develops from 0.9% saline administration during surgery, switch immediately to balanced crystalloid solutions rather than using hypotonic saline.

• Rapid saline infusion at 30 mL/kg/h inevitably causes hyperchloremic acidosis during surgery 7
• Hyperchloremic acidosis from 0.9% saline is associated with increased 30-day mortality, renal vasoconstriction, and acute kidney injury 3
• Balanced crystalloid solutions like Plasma-Lyte prevent and treat hyperchloremic acidosis more effectively than diluting with hypotonic solutions 3
• Discontinuing normal saline and switching to balanced crystalloids resolves hyperchloremic acidosis 3

Practical Algorithm for Perioperative Fluid Selection

Standard Perioperative Care

1. Use balanced isotonic crystalloids (Ringer's Lactate or Plasma-Lyte) for all routine perioperative fluid therapy 1, 3
2. Limit 0.9% saline to maximum 1-1.5 L if it must be used 1
3. Avoid 0.45% saline entirely for routine maintenance or resuscitation 2, 1

Neurosurgical Patients with Polyuria

1. Measure urine and serum osmolality, electrolytes, and calculate electrolyte-free water clearance 4, 6
2. If central diabetes insipidus confirmed (low urine osmolality, positive EWC), administer desmopressin 4, 6
3. If polyuria persists with hypertonic urine after desmopressin, suspect concurrent salt wasting 4
4. Match replacement fluid sodium concentration to urine sodium concentration (may require hypertonic saline, not 0.45%) 4
5. Monitor serum sodium hourly and adjust fluid composition accordingly 4

Hemorrhagic Shock

• Use balanced crystalloids as first-line, especially when large volumes needed 2, 1
• Avoid synthetic colloids (hydroxyethyl starch, gelatins) due to renal failure risk 1
• In severe head trauma with focal signs, hypertonic saline (3% or 7.5%) bolus may be used for osmotic effect, not 0.45% saline 2