Why is lactated Ringer's (LR) solution preferred over normal saline for fluid resuscitation?

Why Choose Lactated Ringer's Over Normal Saline

Lactated Ringer's solution should be the preferred first-line crystalloid for fluid resuscitation in most clinical scenarios because it reduces the risk of acute kidney injury, avoids hyperchloremic metabolic acidosis, and may reduce mortality compared to normal saline, with the critical exception of traumatic brain injury where normal saline is mandatory. 1

Key Clinical Advantages of Lactated Ringer's

Renal Protection

• A large randomized trial of 15,802 critically ill patients demonstrated that balanced crystalloids like lactated Ringer's resulted in significantly lower rates of major adverse kidney events (OR 0.91,95% CI 0.84-0.99) compared to normal saline. 2
• The SALT trial showed lower 30-day in-hospital mortality and reduced incidence of renal replacement therapy with balanced crystalloids versus saline. 1
• KDIGO guidelines recommend isotonic crystalloids for volume expansion in patients at risk for or with established AKI, with emerging evidence favoring balanced solutions. 1

Avoidance of Hyperchloremic Acidosis

• Normal saline contains 154 mmol/L of chloride (hyperchloremic compared to plasma), while lactated Ringer's has lower chloride content (108 mmol/L), reducing the risk of hyperchloremic metabolic acidosis. 1
• High chloride loads in normal saline cause renal afferent arteriolar vasoconstriction, reducing glomerular filtration rate, whereas lactated Ringer's balanced electrolyte composition avoids these deleterious effects. 1
• Hyperchloremic acidosis from saline can impair renal function and coagulation. 3

Mortality Benefits in Specific Populations

• In acute pancreatitis, lactated Ringer's as initial resuscitation fluid was associated with lower 1-year mortality compared to normal saline (adjusted OR 0.61,95% CI 0.50-0.76). 4
• European guidelines recommend balanced crystalloids over normal saline for initial trauma management (excluding severe TBI), with strength of evidence level 1A. 3

Critical Exception: Traumatic Brain Injury

In patients with severe traumatic brain injury or head trauma, normal saline MUST be used instead of lactated Ringer's. 1, 3, 5

Why This Exception Exists

• Lactated Ringer's has an osmolarity of 273-277 mOsm/L, making it hypotonic compared to plasma (275-295 mOsm/L). 3
• This hypotonic nature can worsen cerebral edema and increase intracranial pressure in TBI patients. 1, 3
• A study from the PROMMTT trial showed lactated Ringer's was associated with higher adjusted mortality in TBI patients (HR 1.78,95% CI 1.04-3.04, p=0.035) compared to normal saline. 5
• Normal saline has an osmolarity of 308 mOsm/L and is isotonic, making it the crystalloid of choice for brain-injured patients. 3

Additional Contraindications for Lactated Ringer's

• Rhabdomyolysis or crush syndrome: Avoid lactated Ringer's due to its potassium content (4 mmol/L), which poses additional risk when potassium levels may increase markedly following reperfusion of crushed limbs. 3

Practical Clinical Algorithm

Step 1: Assess for Contraindications

• If severe TBI or head trauma present: Use normal saline exclusively. 1, 3, 5
• If rhabdomyolysis or crush syndrome present: Use normal saline or potassium-free crystalloid. 3

Step 2: For All Other Patients

• Use lactated Ringer's as first-line fluid for resuscitation. 1
• If normal saline must be used, limit to 1-1.5 L maximum to minimize hyperchloremic acidosis risk. 1

Step 3: Specific Clinical Scenarios

• Trauma resuscitation (without severe TBI): Lactated Ringer's preferred. 3
• Burns ≥20% TBSA: Lactated Ringer's is the first-line balanced fluid (20 mL/kg in first hour). 3
• Acute pancreatitis: Lactated Ringer's preferred to reduce 1-year mortality. 4
• Septic shock: Balanced crystalloids like lactated Ringer's preferred. 1

Common Pitfalls to Avoid

• Do not avoid lactated Ringer's in mild-to-moderate hyperkalemia or renal dysfunction (except in rhabdomyolysis/crush syndrome). The 4 mmol/L potassium content is physiological and does not create clinically significant hyperkalemia risk in most patients. 3
• Do not use lactated Ringer's in TBI patients even if they have other injuries that would benefit from balanced crystalloids—the TBI contraindication takes precedence. 1, 3, 5
• Remember that both colloids and crystalloids are effective for fluid resuscitation, but crystalloids are recommended initially due to lower cost and similar outcomes. 2, 1

Nuance: Recent Hospital-Wide Trial

A 2025 crossover trial of hospital-wide lactated Ringer's versus normal saline in Ontario hospitals found no significant difference in the composite outcome of death or readmission within 90 days (20.3% vs 21.4%, adjusted difference -0.53 percentage points, p=0.35). 6 However, this trial was interrupted by COVID-19 with only 7 hospitals completing both periods, and the population included all hospitalized patients rather than focusing on acute resuscitation scenarios where the benefits of lactated Ringer's are most pronounced. The weight of evidence from larger, more focused trials in critically ill and resuscitation populations still supports lactated Ringer's as preferred. 2, 1, 4