What is the best maintenance fluid for post-operative abdominal surgery?

Postoperative Maintenance Fluid for Abdominal Surgery

For postoperative maintenance fluid after abdominal surgery, use hypotonic crystalloid with 70-100 mmol/day of sodium and up to 1 mmol/kg/day of potassium, and discontinue intravenous fluids by postoperative day 1 while encouraging early oral intake. 1

Immediate Postoperative Fluid Strategy

Discontinue IV fluids as early as possible:

• Intravenous fluids should be discontinued at latest during postoperative day 1 1
• Patients should be encouraged to drink when fully recovered from anesthesia 1
• Offer oral diet within 4 hours after abdominal/pelvic surgery 1

When IV Fluids Must Continue Postoperatively

If IV fluids need to be continued beyond day 1, use the following approach:

Maintenance Fluid Composition

• Use hypotonic crystalloid with 70-100 mmol/day of sodium and up to 1 mmol/kg/day of potassium 1
• This differs from intraoperative management where balanced crystalloids (like Ringer's lactate) are preferred 1

Replacement of Ongoing Losses

• Any ongoing losses from diarrhea or vomiting must be replaced with balanced crystalloid solution (e.g., Ringer's lactate) 1
• Avoid 0.9% saline for both maintenance and replacement due to risk of salt and fluid overload 1, 2

Target Fluid Balance

Aim for near-zero fluid balance postoperatively:

• The ERAS Society provides a strong recommendation (high evidence) for near-zero fluid balance 1
• By end of surgery, target a mildly positive balance of 1-2 liters to protect kidney function 1, 3, 2
• Postoperatively, avoid both fluid overload and dehydration 2

Critical Pitfalls to Avoid

Do not use 0.9% saline routinely:

• Normal saline causes hyperchloremic metabolic acidosis, renal vasoconstriction, and increased risk of acute kidney injury 1, 3, 2
• The SMART trial demonstrated significantly higher major adverse kidney events with 0.9% saline compared to balanced crystalloids 1

Do not trigger fluid therapy based on oliguria alone:

• Low urine output is a normal physiological response during surgery and anesthesia 1
• Oliguria should not be managed in isolation but rather investigated to establish the cause before administering additional fluid therapy 1

Avoid synthetic colloids and albumin:

• Strong recommendation against routine use of albumin or synthetic colloids for postoperative fluid administration 1, 2
• These offer no mortality benefit and carry potential risks 1, 2

Special Considerations for Different Patient Populations

Patients with lower fluid tolerance require more conservative management:

• Those with congestive heart failure, chronic kidney disease, and acute/chronic lung disease have higher risk of fluid accumulation 1, 2
• These patients are at greater risk of organ dysfunction from fluid overload 1, 2

High-risk surgical patients:

• A restrictive strategy during oxygen delivery optimization reduces major complications by 52% compared to conventional liberal fluid administration 4
• Goal-directed therapy may be considered for high-risk patients, though the primary focus postoperatively should be early transition to oral intake 3

Evidence Quality and Nuances

The ERAS Society guidelines provide high-quality evidence with strong recommendations for near-zero fluid balance and early discontinuation of IV fluids 1. This represents the most authoritative guidance available, published in 2022 in the World Journal of Emergency Surgery.

The British Journal of Anaesthesia 2024 consensus from the Perioperative Quality Initiative reinforces avoiding 0.9% saline and synthetic colloids, with 98% and 90% expert agreement respectively 1, 2. A large multicenter RCT of 3000 patients demonstrated that stringently restrictive fluid regimens resulted in significantly higher acute kidney injury rates compared to modestly liberal regimens, supporting the 1-2 liter positive balance target by end of surgery 1, 2.

The key distinction is that intraoperative fluids differ from postoperative maintenance fluids: intraoperatively use balanced crystalloids like Ringer's lactate, but postoperatively switch to hypotonic crystalloid for maintenance if IV fluids cannot be discontinued 1.