In postoperative surgical patients, should hypertensive individuals receive 1 pint of 0.45% sodium chloride with isotonic maintenance fluids (e.g., Ringer’s lactate) while normotensive individuals receive 1 pint of 0.9% sodium chloride with isotonic maintenance fluids?

Postoperative Fluid Management: Blood Pressure-Based Strategy

Do not differentiate fluid tonicity based on preoperative blood pressure status; instead, use balanced isotonic crystalloids (Ringer's Lactate or Plasmalyte) as the standard maintenance and resuscitation fluid for all postoperative surgical patients, regardless of whether they are hypertensive or normotensive. 1, 2, 3

Why the Proposed Strategy is Flawed

The rationale of giving hypotonic saline (0.45% NS) to hypertensive patients is physiologically unsound and contradicts current evidence:

• 0.45% sodium chloride is not endorsed for routine adult perioperative maintenance or resuscitation by any major guideline and should be avoided in standard surgical care. 3
• Hypotonic solutions carry significant risk of hyponatremia without providing any benefit for blood pressure management in the postoperative period. 3
• Surgery-induced stress hormones (ACTH, ADH, aldosterone) cause sodium retention regardless of baseline blood pressure, making hypotonic fluid administration potentially dangerous as it can worsen hyponatremia while failing to address the underlying volume status. 4

Evidence-Based Fluid Strategy for All Postoperative Patients

First-Line Fluid Choice

Balanced crystalloids (Ringer's Lactate or Plasmalyte) should be used as the default maintenance and resuscitation fluid for all surgical patients, with the following evidence:

• Balanced crystalloids reduce mortality (OR 0.84,95% CI 0.74-0.95) and major adverse kidney events compared to normal saline in critically ill and surgical patients. 3
• In kidney transplant recipients—a population at high risk for hyperkalemia—Ringer's Lactate resulted in less hyperkalemia (0% vs 19%, p=0.05) and less metabolic acidosis (0% vs 31%, p=0.004) compared to normal saline, demonstrating safety even in vulnerable populations. 5
• The potassium content in Ringer's Lactate (4 mmol/L) does not create clinically significant hyperkalemia risk because it matches normal plasma concentration and cannot create excess when the patient's level is normal or low. 2

Volume Considerations

Aim for a mildly positive fluid balance (+1-2 L) by the end of surgery to protect kidney function while avoiding excessive administration:

• Intraoperative rates of 1-2 mL/kg/h minimize postoperative lung injury risk while maintaining adequate perfusion. 4
• Excessive fluid administration leads to organ dysfunction, pulmonary complications, gut edema, and poor wound healing, so volumes should be titrated to objective endpoints. 4
• In major surgery with anastomoses, administration of <1.5 liters may be detrimental, as evidenced by three anastomotic leakages in a restrictive fluid group. 6

Critical Exceptions to Balanced Crystalloid Use

Traumatic Brain Injury or Severe Head Trauma

Use 0.9% normal saline (not 0.45% saline) as the isotonic crystalloid of choice in patients with severe TBI or increased intracranial pressure:

• Ringer's Lactate is hypotonic (273-277 mOsm/L vs plasma 275-295 mOsm/L) when measured by real osmolality and can worsen cerebral edema. 2
• Normal saline (308 mOsm/L) is truly isotonic and prevents fluid shifts that increase intracranial pressure. 2, 3
• For severe head trauma with focal signs, hypertonic saline (3% or 7.5%) boluses may be indicated for osmotic effect, but never hypotonic solutions. 3

Rhabdomyolysis or Crush Syndrome

Avoid Ringer's Lactate in suspected or proven rhabdomyolysis/crush syndrome due to the potassium content (4 mmol/L), which poses additional risk when potassium levels increase markedly following reperfusion. 2

Why Normal Saline Should Be Limited

When normal saline must be used (e.g., TBI), limit administration to 1-1.5 L maximum to minimize chloride-related complications:

• Large volumes of normal saline (>5 L) cause hyperchloremic metabolic acidosis, renal vasoconstriction, and increased 30-day mortality through supraphysiologic chloride concentration (154 mmol/L). 3
• Hyperchloremia develops in 20% of surgical patients receiving normal saline and is associated with increased mortality. 2
• Normal saline increases major adverse kidney events and vasopressor requirements compared to balanced solutions. 3

Practical Algorithm for Postoperative Fluid Selection

1. Assess for contraindications to balanced crystalloids:

   • Severe TBI or increased ICP? → Use 0.9% saline (limit to 1-1.5 L if possible) 2, 3
   • Rhabdomyolysis or crush syndrome? → Use potassium-free crystalloid 2
   • Severe hyperkalemia (>6.5 mmol/L)? → Use potassium-free crystalloid until resolved 2

2. For all other patients (including hypertensive and normotensive):

   • Use Ringer's Lactate or Plasmalyte as first-line fluid 1, 3, 4
   • Target mildly positive balance (+1-2 L) by end of surgery 4
   • Administer at 1-2 mL/kg/h intraoperatively 4

3. Monitor and titrate to endpoints:

   • Mean arterial pressure ≥65 mmHg 3
   • Urine output ≥0.5 mL/kg/h 3
   • Avoid fluid overload (pulmonary edema, organ dysfunction) 4

Common Pitfalls to Avoid

• Never use 0.45% saline for routine postoperative maintenance in adults, regardless of blood pressure status. 3
• Do not assume hypertensive patients need less sodium—they need appropriate volume resuscitation with isotonic fluids. 1, 4
• Do not fear the potassium in Ringer's Lactate unless specific contraindications exist (rhabdomyolysis, severe hyperkalemia >6.5 mmol/L). 2, 5
• Avoid synthetic colloids (hydroxyethyl starch, gelatins) as they increase renal failure risk (RR 1.34,95% CI 1.0-1.8) without mortality benefit. 1
• Do not routinely use albumin as it provides no mortality advantage and is substantially more expensive. 1