Ringer's Lactate vs Normal Saline for Postoperative Complications
Balanced crystalloids like Ringer's lactate should be preferentially used over normal saline for perioperative fluid management, as saline increases the risk of hyperchloremic acidosis, acute kidney injury, and may require greater transfusion volumes, though the absolute differences in major complications are small.
Key Evidence from Guidelines
The most recent and authoritative guidelines strongly favor balanced crystalloids over normal saline for surgical patients:
Renal and Metabolic Outcomes
The 2023 ERAS Society guidelines for emergency laparotomy recommend limiting 0.9% saline use, citing evidence that saline-induced hyperchloremic metabolic acidosis negatively impacts perioperative electrolyte management, end-organ function, and survival 1.
Saline administration is associated with decreased kidney perfusion, reduced urine output, increased vasopressor requirements, and acute kidney injury (AKI) compared to balanced crystalloids 1.
The landmark SMART trial (15,802 ICU patients, ~21% from operating rooms) demonstrated that patients receiving 0.9% saline had significantly higher rates of major adverse kidney events within 30 days (15.4% vs 14.3%) compared to balanced crystalloids 1.
Fluid Requirements and Blood Loss
In hemorrhagic shock models, normal saline requires significantly greater volume for resuscitation (256 mL/kg vs 126 mL/kg for lactated Ringer's) and is associated with greater urine output, hyperchloremic acidosis, and dilutional coagulopathy 2.
Patients receiving saline during aortic surgery required more bicarbonate therapy and significantly more blood product transfusions compared to lactated Ringer's patients 3.
Acid-Base Balance
Saline consistently produces hyperchloremic metabolic acidosis with elevated chloride levels (119 vs 105 mEq/L) and lower pH (7.28 vs 7.45) compared to lactated Ringer's 2.
The 2022 LMIC ERAS guidelines explicitly state that 0.9% saline should be avoided due to salt and fluid overload risk, recommending balanced crystalloids like Ringer's lactate for intraoperative use 1.
Important Caveats and Special Populations
Neurosurgical Patients
In traumatic brain injury, 0.9% saline is recommended as first-line therapy over hypotonic solutions like Ringer's lactate, which should be avoided to minimize fluid shift into damaged cerebral tissue 1.
The 2024 perioperative fluid management guidelines provide a strong recommendation against hypotonic solutions in neurosurgical patients (moderate quality evidence) 1.
Trauma and Hemorrhagic Shock
The 2023 European trauma guidelines recommend that hypotonic solutions such as Ringer's lactate be avoided in patients with severe head trauma (Grade 1B recommendation) 1.
For trauma patients without severe head injury, balanced electrolyte solutions are favored, though if saline is used, it should be limited to a maximum of 1-1.5 L 1.
Clinical Significance
The SOLAR Trial Perspective
The 2020 SOLAR trial (8,616 elective orthopedic and colorectal surgery patients) found no clinically meaningful difference in the composite outcome of mortality and major complications between lactated Ringer's (5.8%) and normal saline (6.1%) 4.
However, absolute differences were less than 0.5%, and the trial concluded that clinicians can reasonably use either solution intraoperatively in elective surgery 4.
Reconciling the Evidence
Despite the SOLAR trial's neutral findings, the preponderance of guideline evidence and mechanistic studies support lactated Ringer's because:
Metabolic derangements from saline are consistent and measurable, even when they don't always translate to differences in major complications in well-controlled elective surgery 1, 3, 2.
In higher-risk scenarios (emergency surgery, hemorrhagic shock, prolonged procedures), the disadvantages of saline become more clinically apparent 1, 2.
The lack of benefit from saline combined with documented harms (hyperchloremia, acidosis, increased transfusion needs) makes balanced crystalloids the safer default choice 1, 3.
Practical Algorithm
For most surgical patients:
- Use balanced crystalloids (Ringer's lactate or Plasmalyte) as first-line perioperative fluid 1
- Target near-zero to mildly positive fluid balance (0-2 L postoperatively) 1
- Avoid routine use of 0.9% saline, especially volumes >1-1.5 L 1
For neurosurgical/severe TBI patients:
- Use 0.9% saline as first-line fluid 1
- Avoid hypotonic solutions including Ringer's lactate 1
- Consider buffered isotonic solutions (Plasmalyte) to avoid hyperchloremic acidosis while maintaining osmolarity 1
For hemorrhagic shock without head injury: