Between plain normal saline (PNSS) and Lactated Ringer's, which is preferred when Plasma‑Lyte is unavailable?

Lactated Ringer's is preferred over normal saline when Plasma-Lyte is unavailable.

Choose Lactated Ringer's (LR) as your first-line crystalloid over plain normal saline (PNSS/0.9% NaCl) for fluid resuscitation in critically ill patients. The most recent high-quality guidelines and research consistently demonstrate that balanced crystalloids like LR reduce adverse renal events and may improve mortality compared to normal saline 1.

Why Lactated Ringer's Over Normal Saline

Guideline-Based Recommendation

The 2022 international guidelines for critically ill patients provide a GRADE 2+ recommendation (strong agreement) to use balanced crystalloids rather than 0.9% NaCl as first-line fluid therapy to reduce mortality and adverse renal events 1. While this is not the highest grade of recommendation (GRADE 1), the strong agreement reflects clinical consensus based on accumulating evidence of harm from high-volume chloride-rich solutions.

Key Evidence Supporting Lactated Ringer's

The SMART study (15,802 ICU patients) demonstrated that balanced crystalloids (including Lactated Ringer's) reduced major adverse kidney events (MAKE 30: death, doubling of creatinine, or renal replacement therapy within 30 days) compared to normal saline 2. This represents the largest and most robust randomized trial directly comparing these fluids.

Most recent 2025 data from the CLOVERS trial secondary analysis showed that initial fluid resuscitation with LR versus NS in sepsis-induced hypotension resulted in:

• Lower mortality: 12.2% vs 15.9% (adjusted HR 0.71,95% CI 0.51-0.99, p=0.043) 3
• More hospital-free days: 16.6 vs 15.4 days (p=0.009) 3
• Better acid-base balance with less hyperchloremia 3

The Problem with Normal Saline

Normal saline causes hyperchloremic metabolic acidosis when given in moderate to large volumes 1, 4. Observational studies have linked this to:

• Increased mortality in patients receiving >5000 mL of chloride-rich solutions 1
• Postoperative hyperchloremia associated with increased mortality after high-risk hemorrhagic surgery 1
• Inflammation, hypotension, and acute kidney injury in preclinical models 4

Clinical Algorithm for Fluid Selection

First Choice: Lactated Ringer's

Use LR for:

• Sepsis and septic shock 3
• Hemorrhagic shock and trauma (unless contraindicated) 1
• General ICU resuscitation 2
• Diabetic ketoacidosis (faster resolution of high anion gap metabolic acidosis) 5
• Perioperative fluid management in most surgeries 1

When to Use Normal Saline Instead

Specific contraindications to Lactated Ringer's:

1. Traumatic brain injury (TBI): Use 0.9% saline as first-line 6. The 2024 perioperative guidelines recommend normal saline for TBI patients (weak recommendation, moderate quality evidence) because hypotonic solutions can worsen cerebral edema. While LR is technically isotonic, the concern about lactate metabolism and slight hypotonicity relative to plasma has led to preference for NS in neurosurgical patients.

2. Severe hepatic insufficiency: LR may not produce alkalinizing effects due to impaired lactate metabolism 7. Normal saline is safer when lactate clearance is severely compromised.

3. Hypercalcemia or conditions predisposing to it: LR contains calcium and should be used cautiously in severe renal impairment with hypercalcemia, sarcoidosis, or calcium nephrolithiasis 7.

4. Neonates ≤28 days receiving ceftriaxone: Absolute contraindication due to risk of fatal ceftriaxone-calcium precipitation 7. Must use NS or wait appropriate time between administrations.

5. Hyperkalemia: LR contains 4 mEq/L potassium; use NS in severe hyperkalemia or with potassium-sparing drugs 7.

6. Type 2 diabetes with severe hyperglycemia: Lactate is a gluconeogenesis substrate; consider NS if concerned about worsening hyperglycemia 7, though the 2025 DKA study actually showed faster resolution with LR 5.

Important Caveats and Pitfalls

The Nuanced Reality

Not all studies show benefit: The 2025 FLUID trial (hospital-wide crossover study) found no significant difference in 90-day death or readmission between LR and NS (20.3% vs 21.4%, p=0.35) 8. However, this was a pragmatic hospital-wide study with heterogeneous patient populations, which may have diluted treatment effects seen in more targeted critically ill populations.

Volume Matters

The benefits of balanced crystalloids become more apparent with larger volumes (>5000 mL) 1. For small-volume resuscitation (<2000 mL), the clinical difference may be minimal, though LR still avoids unnecessary chloride load and maintains better acid-base balance 1.

Don't Mix with Ceftriaxone

Critical drug interaction: Never administer LR through the same line as ceftriaxone in any patient, and absolutely contraindicated in neonates ≤28 days even with separate lines 7. Flush lines thoroughly between medications if sequential use is necessary in older patients.

Neonatal Considerations

Use LR with particular caution in neonates and infants <6 months 7. While emerging evidence suggests balanced crystalloids may reduce hyperchloremic acidosis and AKI in neonates 9, safety data remain limited in this population.

Practical Implementation

Default to Lactated Ringer's for fluid resuscitation unless one of the specific contraindications above applies. This approach aligns with the 2022 guideline recommendation that "potentially deleterious effects on renal function and survival of high-volume chloride-rich solutions should in most cases orient first-line treatment choices toward balanced solutions" 1.

When Plasma-Lyte is unavailable, LR is the next best balanced crystalloid option and superior to normal saline for most clinical scenarios based on mortality, renal outcomes, and acid-base balance 1, 2, 3.