Should the duration of surgery and the volume of normal saline (0.9% NaCl) be limited?

Yes, Both Duration of Surgery and Volume of Normal Saline Should Be Limited

You should limit the volume of normal saline (0.9% NaCl) during surgery, targeting moderately restrictive fluid administration of approximately 6-7 mL/kg/hr, and avoid both liberal (>10 mL/kg/hr) and severely restrictive (<4 mL/kg/hr) fluid volumes, as both extremes are associated with increased mortality, morbidity, and costs. 1, 2

The Critical Evidence on Fluid Volume

The most compelling data comes from a large hospital registry study of 92,094 surgical patients that demonstrated a U-shaped relationship between intraoperative fluid volume and 30-day mortality 2. This means both too much and too little fluid kills patients:

• Liberal fluid volumes (highest quintile, typically >10 mL/kg/hr) were significantly associated with:

  • Respiratory complications (pulmonary edema, reintubation, pneumonia, respiratory failure)
  • Increased mortality
  • Higher costs and longer hospital stays

• Severely restrictive volumes (lowest quintile, typically <4 mL/kg/hr) were associated with:

  • Acute kidney injury
  • Increased mortality

• Optimal "moderately restrictive" volumes (second quintile, ~6-7 mL/kg/hr or approximately 1 liter for a 3-hour case) were consistently associated with the best outcomes—representing volumes approximately 40% less than traditional textbook estimates 2

Why Normal Saline Specifically Should Be Limited

The 2024 PeriOperative Quality Initiative guidelines strongly recommend buffered crystalloid solutions over 0.9% saline in the perioperative period 1. The evidence is clear:

Dose-Response Toxicity of Normal Saline

Large volumes of 0.9% saline cause:

• Hyperchloremic metabolic acidosis
• Renal vasoconstriction and acute kidney injury (AKI)
• Increased 30-day mortality (demonstrated in 22,851 patients where hyperchloremia was present in ~20% and associated with increased mortality) 1

Key Studies Supporting Buffered Solutions

• The SALT trial (974 critically ill patients): Patients receiving large volumes of 0.9% saline had higher rates of major adverse kidney events (MAKE: death, need for dialysis, persistent renal dysfunction) compared to buffered fluids 1

• A trial in 15,802 critically ill patients demonstrated buffered crystalloids were associated with lower risk of MAKE than 0.9% saline 1

• A registry study of >30,000 patients undergoing major abdominal surgery showed fewer complications with buffered crystalloids versus 0.9% saline 1

Important Caveat About Volume

Two large RCTs including 19,136 patients found no difference between saline and buffered solutions, BUT patients only received small amounts of study fluid (median 1900 mL) 1, 3. This suggests a dose-response relationship—small volumes of saline may be tolerable, but larger volumes are harmful.

Practical Algorithm for Fluid Management

Choose Your Fluid Type:

1. First-line: Buffered crystalloids (Ringer's Lactate, Plasma-Lyte) for all perioperative patients 1
2. Exception: Traumatic brain injury - Use 0.9% saline (unclear if benefit is from salt load or tonicity) 1
3. Avoid synthetic colloids - Associated with increased risk in critically ill patients 1

Target Your Fluid Volume:

1. Aim for 6-7 mL/kg/hr (moderately restrictive) 2
2. Avoid >10 mL/kg/hr (liberal—causes respiratory complications, fluid overload) 2
3. Avoid <4 mL/kg/hr (severely restrictive—causes AKI) 2
4. For a 70 kg patient in a 3-hour case: Target approximately 1000-1200 mL total

Monitor for Complications:

Signs you've given too much fluid:

• Tissue edema
• Respiratory failure
• Worsening congestive heart failure
• Ileus 1

Signs you've given too little:

• Hypoperfusion
• Acute kidney injury
• Hypotension 1

Special Populations

High-Risk Patients

Patients with cardiac or renal comorbidities have lower fluid tolerance and are at higher risk of fluid accumulation. They require even more careful titration to maintain the "green zone" of intravascular euvolemia 1.

Minor Surgery

For minor noncardiac surgery, the guidelines recommend a mildly positive fluid balance at approximately 2 mL/kg/hr to reduce postoperative nausea and vomiting (PONV) 1.

Common Pitfalls to Avoid

1. Don't follow outdated textbook formulas that recommend 10-15 mL/kg/hr—these volumes are associated with worse outcomes 2

2. Don't assume "more is better" for hemodynamic optimization—fluid overload causes organ dysfunction 1

3. Don't use 0.9% saline as your default crystalloid—switch to buffered solutions as your institutional standard 1

4. Don't ignore the duration-volume relationship—longer surgeries with continuous liberal fluid rates compound the toxic effects 1, 2

The evidence overwhelmingly supports a paradigm shift toward moderately restrictive fluid volumes using buffered crystalloids rather than normal saline for most surgical patients.