Why is normal saline (NS) preferred over Ringer's lactate in patients with chronic kidney disease (CKD)?

Normal Saline is Preferred Over Ringer's Lactate in Chronic Kidney Disease

Normal saline (0.9% NaCl) is preferred over Ringer's lactate in patients with chronic kidney disease primarily due to the absence of potassium in normal saline, which reduces the risk of hyperkalemia in these already vulnerable patients. 1

Rationale for Normal Saline in CKD

Potassium Content Considerations

• Normal saline contains no potassium (0 mmol/L), while Ringer's lactate contains 4 mmol/L of potassium 2
• Patients with CKD often have impaired potassium excretion, making them susceptible to hyperkalemia
• Even though the potassium content in Ringer's lactate is relatively low, in severe CKD it may contribute to potassium accumulation

Acid-Base Considerations

• While normal saline can cause hyperchloremic metabolic acidosis with large volume administration, this is generally considered a lesser concern than the risk of hyperkalemia in CKD patients
• KDIGO guidelines specifically recommend isotonic crystalloids for expansion of intravascular volume in patients at risk for AKI or with AKI 1

Evidence Supporting This Practice

The KDIGO guidelines state that "in the absence of hemorrhagic shock, we suggest using isotonic crystalloids rather than colloids as initial management for expansion of intravascular volume in patients at risk for AKI or with AKI" 1. While this doesn't specifically compare normal saline to Ringer's lactate, it establishes isotonic crystalloids like normal saline as appropriate.

A 2023 study comparing normal saline versus balanced crystalloids in patients with prerenal AKI and pre-existing CKD found that while Ringer's lactate showed a better profile in acid-base balance improvement, there was "no significant difference in short or long term kidney function" between the two fluids 3. This suggests that while there may be some acid-base advantages to Ringer's lactate, these don't translate to meaningful differences in kidney outcomes.

Another study from 2021 noted that the beneficial effects of Lactated Ringer's compared to saline were "small and non-significant in those with chronic kidney disease" 4, further supporting that any theoretical advantages of Ringer's lactate may not be clinically significant in CKD patients.

Special Considerations

Hyperkalemia Risk

• The risk of hyperkalemia is particularly concerning in advanced CKD (stages 4-5)
• A 2005 study in renal transplant patients found that 19% of patients receiving normal saline developed hyperkalemia (K+ >6 mEq/L) requiring treatment, compared to 0% in the Ringer's lactate group 5
• However, this was in the specific context of renal transplantation, where different physiological factors are at play

Recent Evidence on Ringer's Lactate in Reduced Kidney Function

• A 2022 study specifically examining Lactated Ringer's solution and risk of hyperkalemia in patients with reduced kidney function found that "LR use was not independently associated with the development of hyperkalemia in patients with reduced kidney function" 6
• Only 5% of patients with eGFR <30 ml/min/1.73m² developed de-novo hyperkalemia following LR use, and there was no significant correlation between the amount of LR administered and hyperkalemia development 6

Practical Approach to Fluid Selection in CKD

1. For most CKD patients requiring fluid resuscitation:

   • Normal saline remains the preferred initial choice, especially in emergency situations
   • This is particularly true for patients with severe CKD (stages 4-5) or those with baseline hyperkalemia

2. Consider Ringer's lactate in specific scenarios:

   • CKD patients with metabolic acidosis who need large volume resuscitation
   • Patients with normal potassium levels and less severe CKD (stages 1-3)
   • When monitoring of electrolytes and acid-base status can be performed frequently

3. Monitor closely regardless of fluid choice:

   • Serum potassium levels
   • Acid-base status
   • Fluid balance and signs of volume overload
   • Renal function parameters

Conclusion

While recent evidence suggests that the risk of hyperkalemia with Ringer's lactate in CKD patients may be lower than traditionally thought, normal saline remains the preferred choice in clinical practice for CKD patients due to its lack of potassium content and established safety profile in this population. The theoretical advantages of balanced crystalloids like Ringer's lactate must be weighed against the potential risks in this vulnerable population.