Tonicity of Lactated Ringer's Solution
Lactated Ringer's solution is hypotonic when measured by real osmolality (mosmol/kg) rather than theoretical osmolality (mosmol/L), and should be avoided in patients with severe head trauma. 1
Composition and Tonicity
- Lactated Ringer's solution has an osmolarity of approximately 273-277 mOsm/L, making it slightly hypotonic compared to plasma (which has an osmolarity of 275-295 mOsm/L) 1, 2
- It contains sodium (130 mmol/L), potassium (4 mmol/L), chloride (109 mmol/L), calcium (1.4 mmol/L), and lactate (28 mmol/L as buffer) 1, 2
- When considering real osmolality (mosmol/kg) rather than theoretical osmolality (mosmol/L), Lactated Ringer's is hypotonic and should be avoided in certain clinical scenarios 1
Clinical Implications of Tonicity
- Hypotonic solutions like Lactated Ringer's should be avoided in patients with severe head trauma due to the risk of increasing cerebral edema 1
- Guidelines specifically recommend against using Ringer's lactate (compound sodium lactate) in brain-injured patients as it is hypotonic when real osmolality is determined 1
- For brain-injured patients, 0.9% saline is the recommended crystalloid of choice as it is isotonic in terms of osmolality 1
Comparison to Other Solutions
- Normal saline (0.9% NaCl) has an osmolarity of 308 mOsm/L and is considered isotonic 1
- 5% glucose solutions have an osmolarity of 278 mOsm/L but are functionally hypotonic once the glucose is metabolized 1
- Balanced solutions like Lactated Ringer's have a Na+:Cl- ratio (1.19:1) that more closely resembles plasma (1.28-1.45:1) compared to normal saline (1:1) 1
Clinical Applications Based on Tonicity
- Despite being slightly hypotonic, Lactated Ringer's is recommended as a first-line balanced fluid resuscitation solution for burns victims due to its electrolyte composition 1
- For patients with sepsis-induced hypotension, Lactated Ringer's solution may be associated with improved survival compared to 0.9% saline 3
- In uncontrolled hemorrhagic shock, resuscitation with Lactated Ringer's requires significantly less volume than normal saline and is associated with less hyperchloremic acidosis 4
Important Considerations
- The infusion of Lactated Ringer's solution in normal adults does not significantly increase circulating lactate concentrations when given at standard resuscitation rates 5
- Lactated Ringer's has greater volume expansion efficiency compared to normal saline, with studies showing it can be 7-20 times more effective at expanding plasma volume per unit volume infused 6
- A 30 mL/kg bolus of Lactated Ringer's may cause a modest rise in serum lactate, but this is not significantly different from the effect of normal saline 7
Clinical Decision Making
- For most patients requiring fluid resuscitation without head trauma, Lactated Ringer's is an appropriate choice due to its balanced electrolyte composition 1
- For patients with traumatic brain injury or at risk for cerebral edema, 0.9% saline is preferred over Lactated Ringer's due to its isotonicity 1
- When monitoring patients receiving Lactated Ringer's, clinicians should not disregard increased lactate concentrations as they are unlikely to be caused by the solution itself 5