Composition of Lactated Ringer's Solution
Lactated Ringer's (LR) solution contains sodium 130 mmol/L, chloride 109 mmol/L, potassium 4 mmol/L, calcium 1.4 mmol/L, and lactate 28 mmol/L, with an osmolarity of 273 mOsm/L. 1
Detailed Electrolyte Composition
The precise composition of LR solution includes:
- Sodium (Na+): 130 mmol/L 1
- Chloride (Cl-): 109 mmol/L 1
- Potassium (K+): 4 mmol/L 1
- Calcium (Ca2+): 1.4 mmol/L 1
- Lactate: 28 mmol/L (which serves as a bicarbonate precursor) 1
- Osmolarity: 273 mOsm/L 1
- pH: 6-7.5 1
Physiological Characteristics
LR solution has a Na+:Cl- ratio of 1.19:1, which more closely resembles plasma (1.28-1.45:1) compared to normal saline's 1:1 ratio. 1 This balanced electrolyte composition makes it physiologically more similar to plasma than 0.9% NaCl. 2
Tonicity Considerations
- LR is slightly hypotonic with an osmolarity of 273-277 mOsm/L compared to plasma (275-295 mOsm/L). 1, 2
- When measured by real osmolality rather than theoretical osmolality, LR demonstrates hypotonic characteristics. 2
- Some formulations may vary by manufacturer, with measured osmolality potentially differing from labeled values. 3
Clinical Implications of Composition
The lactate component (28 mmol/L) is metabolized in the liver to bicarbonate, providing a buffering effect. 1 Infusion of LR at resuscitation rates does not clinically increase serum lactate levels in hemodynamically stable patients. 4 Research shows that after a 30 mL/kg bolus, mean serum lactate increased by only 0.93 mmol/L, which was not significantly different from normal saline. 5
Key Contraindication Based on Composition
Due to its hypotonic nature (273 mOsm/L), LR solution is contraindicated in patients with severe traumatic brain injury or head trauma, as it can worsen cerebral edema. 1, 2 In these patients, 0.9% saline (308 mOsm/L) is the preferred isotonic crystalloid. 1, 2
The potassium content (4 mmol/L) is similar to normal plasma concentration and does not pose a hyperkalemia risk in most clinical scenarios, except in rhabdomyolysis or crush syndrome where it should be avoided. 2