Classification of Lactated Ringer's Solution
Lactated Ringer's (LR) solution is a slightly hypotonic, balanced crystalloid with an osmolarity of approximately 273-277 mOsm/L, which is below the isotonic range of 280-310 mOsm/L. 1
Tonicity Classification
LR is hypotonic when measured by real osmolarity rather than theoretical osmolarity, distinguishing it from truly isotonic solutions like 0.9% normal saline (308 mOsm/L). 1
The hypotonic nature of LR becomes clinically significant in specific patient populations, particularly those with acute brain injury where even slight hypotonicity can worsen cerebral edema. 2, 1
In contrast, normal saline with an osmolarity of 308 mOsm/L is considered isotonic and remains the preferred crystalloid for patients with traumatic brain injury. 1
Electrolyte Composition
LR is classified as a balanced crystalloid due to its electrolyte composition that more closely resembles plasma compared to normal saline. 1
The solution contains sodium (130 mmol/L), potassium (4 mmol/L), chloride (108 mmol/L), calcium (0.9 mmol/L), and lactate (27.6 mmol/L). 1
The balanced Na+:Cl- ratio prevents the hyperchloremic metabolic acidosis associated with large volumes of normal saline. 1, 3
Critical Clinical Distinction
The most important clinical implication is that LR should be avoided in patients with severe head trauma or traumatic brain injury due to its hypotonic nature, which can increase cerebral edema and intracranial pressure. 2, 1
A multicentre study comparing pre-hospital use of LR to isotonic solutions in traumatic brain injury patients demonstrated higher mortality in the LR group (HR 1.78,95% CI 1.04-3.04, p=0.035). 2
For brain-injured patients, 0.9% saline is the recommended isotonic crystalloid of choice. 1
Appropriate Clinical Applications
Despite being hypotonic, LR is recommended as first-line fluid therapy for most other clinical scenarios including general trauma resuscitation (without severe TBI), burns, diabetic ketoacidosis, and general fluid resuscitation. 1, 3
Large randomized trials (SMART trial with 15,802 patients and SALT trial with 974 patients) demonstrated that balanced crystalloids like LR result in lower incidence of major adverse kidney events (14.3% vs 15.4%), reduced 30-day mortality, and decreased vasopressor requirements compared to normal saline. 3
LR is specifically recommended as the first-line balanced fluid resuscitation solution for burns victims due to its electrolyte composition closely matching plasma. 1
Additional Contraindications
- LR should also be avoided in suspected or proven rhabdomyolysis or crush syndrome due to its potassium content (4 mmol/L), which poses additional risk when potassium levels may increase markedly following reperfusion of crushed tissue. 1
Lactate Content Considerations
The lactate in LR (27.6 mmol/L) does not significantly increase serum lactate levels in healthy individuals receiving rapid infusions, so clinicians should not disregard elevated lactate concentrations in patients receiving LR resuscitation. 4, 5
In healthy volunteers receiving 30 mL/kg of LR, mean serum lactate increased by only 0.93 mmol/L, with no statistically significant difference compared to normal saline. 5