Are lactated Ringer's (LR) solutions appropriate fluids for neonates?

Lactated Ringer's Solution for Neonatal Fluid Therapy

Isotonic saline (0.9% NaCl) is the first-choice fluid for resuscitation in neonates with hypovolemia, not lactated Ringer's solution. 1

Primary Recommendation for Neonatal Resuscitation

The Dutch Pediatric Society evidence-based guideline explicitly recommends isotonic saline as the first-choice fluid for resuscitation in neonates and children with hypovolemia, based on systematic review of randomized controlled trials and consideration of all available evidence. 1 This recommendation takes precedence over lactated Ringer's solution due to specific neonatal physiological considerations.

Critical Contraindication: Hypotonic Nature

Lactated Ringer's solution should be avoided in neonates, particularly those with neurological concerns, because it is hypotonic. 2, 3

• Lactated Ringer's has an osmolarity of 273-277 mOsm/L, making it hypotonic compared to plasma (275-295 mOsm/L). 3, 4
• When measured by real osmolarity rather than theoretical osmolarity, lactated Ringer's is definitively hypotonic and poses risk of cerebral edema. 3
• In neonates with any risk of intracranial pathology or head trauma, hypotonic solutions like lactated Ringer's are specifically contraindicated. 1, 2, 3

Specific Neonatal Concerns

Hypernatremia Risk

While there was historical concern that isotonic saline might cause hypernatremia in neonates due to diminished renal sodium clearance in the first week of life, evidence shows no significant difference in sodium concentrations or rates of intraventricular hemorrhage between colloid and crystalloid solutions in hypotensive premature infants. 1 However, a recent trial found that isotonic fluids (0.9% saline with 5% dextrose) caused significantly higher rates of hypernatremia compared to hypotonic fluids in neonates ≥34 weeks gestation (14 of 31 vs. 1 of 29 patients; p=0.0001). 5

Hyponatremia Risk

The same trial found no significant reduction in hyponatremia with isotonic versus hypotonic fluids at 24 hours (0 vs. 3 patients; p=0.106), challenging the assumption that isotonic fluids are superior for preventing hyponatremia in neonates. 5

Clinical Algorithm for Neonatal Fluid Selection

For neonatal hypovolemic shock or resuscitation:

• Use isotonic saline (0.9% NaCl) as first-line fluid. 1
• Administer up to 60 mL/kg during treatment of hypovolemic and septic shock. 1
• For rapid fluid resuscitation in septic shock, aim for >40 mL/kg in the first hour, which is associated with improved survival. 1

For neonatal maintenance fluids:

• The evidence is mixed regarding isotonic versus hypotonic solutions. 5
• If using isotonic maintenance fluids, monitor closely for hypernatremia. 5
• Add dextrose (typically D10%) at maintenance rate to prevent hypoglycemia, as neonates do not tolerate prolonged fasting. 1, 6

For neonates with persistent pulmonary hypertension:

• Crystalloid is the fluid of choice in neonates with hemoglobin >12 g/dL. 1
• Packed red blood cells should be transfused in newborns with hemoglobin <12 g/dL. 1

Why Not Lactated Ringer's in Neonates?

The combination of hypotonic nature and vulnerable neonatal physiology makes lactated Ringer's a suboptimal choice:

• Neonates have large insensible fluid losses and adaptive changes in renal function during the first days of life. 6
• The hypotonic nature of lactated Ringer's (273 mOsm/L) poses risk in a population with immature blood-brain barrier and risk of intraventricular hemorrhage. 1, 3, 4
• While lactated Ringer's does not falsely elevate lactate concentrations when properly administered, this is not the primary concern in neonates. 7

Common Pitfalls to Avoid

• Do not assume lactated Ringer's is interchangeable with normal saline in neonates – the tonicity difference matters in this vulnerable population. 2, 3
• Do not use lactated Ringer's in any neonate with suspected or confirmed intracranial pathology – the hypotonic nature can worsen cerebral edema. 1, 2, 3
• Do not rely solely on theoretical osmolarity – lactated Ringer's is hypotonic when measured by real osmolarity. 3
• Monitor electrolytes closely regardless of fluid choice – both isotonic and hypotonic solutions carry risks in neonates. 5

Special Circumstances

For neonatal septic shock with persistent hypovolemia:

• Fluid losses can continue for days due to diffuse capillary leak. 1
• Ongoing fluid replacement should be directed at clinical endpoints including perfusion and central venous pressure. 1
• Consider diuretics or continuous renal replacement therapy if the neonate becomes >10% fluid overloaded. 1