What is the best fluid for hydration, lactated Ringer's (LR) or normal saline (NS), in a general patient population with no significant contraindications such as severe liver disease or hyperkalemia?

Lactated Ringer's Solution is Preferred Over Normal Saline for General Hydration

For general hydration in patients without severe liver disease, hyperkalemia, or traumatic brain injury, lactated Ringer's solution (or other balanced crystalloids) should be used preferentially over normal saline. This recommendation is based on consistent guideline consensus and recent high-quality evidence demonstrating improved mortality and reduced complications with balanced crystalloids 1, 2.

Guideline Recommendations

Primary Recommendation

• French Society of Anaesthesia guidelines (2022) recommend balanced crystalloids (such as Ringer's lactate) over 0.9% saline for critically ill patients, citing their ionic composition that more closely resembles normal plasma and reduces the risk of hyperchloremic acidosis 1.
• The ERAS Society (2022) explicitly states that 0.9% saline should be avoided due to the risk of salt and fluid overload, recommending balanced crystalloids like Ringer's lactate for intravenous fluid therapy 1.
• Multiple pediatric guidelines recommend isotonic solutions with either normal saline or balanced crystalloids as acceptable options, though balanced crystalloids are increasingly preferred 3, 4.

Specific Clinical Contexts

For sepsis-induced hypotension:

• The most recent high-quality evidence (2025) from the CLOVERS trial secondary analysis demonstrates that lactated Ringer's solution reduced mortality by 29% compared to normal saline (adjusted HR 0.71,95% CI 0.51-0.99, p=0.043) and increased hospital-free days by 1.6 days 2.
• An earlier study (2021) showed lactated Ringer's reduced mortality in sepsis patients (adjusted HR 0.59,95% CI 0.43-0.81), with particularly strong benefits in patients with chronic pulmonary disease 5.

For diabetic ketoacidosis:

• Recent evidence (2024) shows lactated Ringer's achieves faster resolution of high anion gap metabolic acidosis compared to normal saline (adjusted HR 1.325,95% CI 1.121-1.566, p<0.001) with no difference in complications 6.

For acute pancreatitis:

• Guidelines (2019) state that isotonic crystalloids are preferred, with weak evidence suggesting Ringer's lactate may have anti-inflammatory effects and better corrects potassium levels, though the evidence for superiority is not definitive 1.
• A 2023 systematic review found that aggressive hydration strategies (regardless of fluid type) may increase mortality threefold in non-severe pancreatitis, emphasizing the importance of fluid rate over fluid type 1.

Key Advantages of Lactated Ringer's

Metabolic Benefits

• Prevents hyperchloremic metabolic acidosis, a common complication of large-volume normal saline administration that can worsen outcomes 1, 6, 2.
• Maintains better acid-base balance with bicarbonate levels remaining more stable 1, 2.
• The lactate in LR (28 mmol/L) causes only a modest, clinically insignificant increase in serum lactate (mean 0.93 mmol/L) that does not interfere with lactate monitoring 7.

Renal Protection

• Some evidence suggests reduced transfusion requirements and potentially better renal outcomes with balanced solutions, though this is not universally demonstrated across all studies 1.

Electrolyte Composition

• Contains potassium (4 mmol/L), which is physiologic and does not cause hyperkalemia even in at-risk patients, including renal transplant recipients 1.
• The concern about potassium content is unfounded: it is physiologically impossible to create potassium excess using a fluid with potassium concentration lower than the patient's plasma level 1.

Critical Contraindications and Exceptions

When Normal Saline is Preferred

Traumatic brain injury:

• In patients with severe head trauma or TBI, normal saline should be used as first-line therapy 3, 8.
• A 2016 study demonstrated that pre-hospital lactated Ringer's was associated with increased mortality in TBI patients (HR 1.78,95% CI 1.04-3.04, p=0.035) compared to normal saline 8.
• The mechanism likely relates to the slightly hypotonic nature of LR (osmolarity 277 mOsm/L vs. 308 mOsm/L for NS), which may worsen cerebral edema 1.

Severe liver disease:

• While not an absolute contraindication, patients with moderate to severe liver disease show smaller benefits from lactated Ringer's, as the liver metabolizes lactate to bicarbonate 5.
• Guidelines specifically exclude cirrhosis patients from general fluid recommendations, suggesting individualized approaches 1.

Hyperkalemia:

• Though guidelines state the potassium content (4-5 mmol/L) is safe even in hyperkalemic patients, clinical caution is warranted in severe hyperkalemia (>6.5 mmol/L) until more definitive evidence exists 1.

Anaphylaxis:

• Normal saline is recommended for anaphylaxis, as lactated Ringer's might potentially contribute to metabolic acidosis in this specific context 4.

Practical Implementation Algorithm

1. Assess for absolute contraindications:

   • Severe head trauma/TBI → Use normal saline 3, 8
   • Anaphylaxis → Use normal saline 4

2. For all other patients requiring hydration:

   • Use lactated Ringer's or other balanced crystalloids (PlasmaLyte, Isofundine) as first-line 1, 3

3. Special considerations:

   • Sepsis/septic shock → Strongly prefer lactated Ringer's 2
   • DKA → Prefer lactated Ringer's for faster acidosis resolution 6
   • Burns → Use Ringer's lactate as first-line 4
   • Perioperative fluids → Use balanced crystalloids, avoid normal saline 1

4. Monitor for complications:

   • With normal saline: Watch for hyperchloremic acidosis (chloride >110 mmol/L), declining bicarbonate, and worsening base deficit 1, 2
   • With lactated Ringer's: Monitor serum lactate trends (expect modest transient increase that resolves) 7

Common Pitfalls to Avoid

• Do not avoid lactated Ringer's due to concerns about hyperkalemia in patients with normal to moderately elevated potassium; the evidence shows this is safe 1.
• Do not use lactated Ringer's in TBI patients despite its general superiority; this is the one clear exception where normal saline is preferred 8.
• Do not interpret rising lactate levels as worsening sepsis if the patient recently received large volumes of LR; expect a modest transient increase 7.
• Do not use hypotonic solutions (osmolarity <280 mOsm/L) for resuscitation or maintenance fluids in most patients 1, 4.