What is the best fluid choice between Lactated Ringer's (LR) solution and 0.45 Normal saline for patients with impaired renal function or at risk for kidney injury?

Lactated Ringer's Solution is Superior for Renal Protection

For patients with impaired renal function or at risk for kidney injury, Lactated Ringer's (LR) solution is the preferred crystalloid over 0.45% normal saline, as balanced crystalloids like LR reduce major adverse kidney events, acute kidney injury, and mortality compared to saline-based solutions. 1

Why Lactated Ringer's Protects the Kidneys

Mechanism of Renal Benefit:

• High chloride loads in normal saline cause renal afferent arteriolar vasoconstriction, directly reducing glomerular filtration rate, whereas LR's balanced electrolyte composition avoids these deleterious hemodynamic effects 1
• LR reduces the risk of hyperchloremic metabolic acidosis, which itself impairs renal function and worsens outcomes 1
• The SMART trial (n=15,802 critically ill patients) demonstrated that balanced crystalloids resulted in lower rates of major adverse kidney events compared to saline 1
• A large retrospective cohort (n=10,249) showed higher percentages of LR were associated with reduced mortality and less acute kidney injury, with effects most pronounced in patients receiving larger fluid volumes (>7L) 2

Evidence Hierarchy Supporting LR

Guideline Recommendations:

• KDIGO guidelines recommend isotonic crystalloids for volume expansion in patients at risk for or with established AKI, with emerging evidence favoring balanced solutions like LR 1
• European guidelines and ERAS guidelines for emergency laparotomy suggest balanced crystalloids result in improved patient outcomes 1
• The SALT trial demonstrated lower 30-day in-hospital mortality and lower incidence of renal replacement therapy with balanced crystalloids versus saline 1

Clinical Trial Data:

• In prerenal AKI with pre-existing CKD stage III-V, LR showed better acid-base balance improvement compared to normal saline, though short-term kidney function recovery was similar 3
• In critically ill patients, higher percentages of LR (75% vs 25%) reduced mortality odds ratio to 0.50 (95% CI 0.32-0.79) in those receiving >7L of fluid 2

Critical Contraindication: Traumatic Brain Injury

Avoid LR in severe head trauma:

• LR has an osmolarity of 273-277 mOsm/L, making it hypotonic compared to plasma (275-295 mOsm/L), which can worsen cerebral edema and increase intracranial pressure 1, 4
• In patients with traumatic brain injury, use 0.9% normal saline (not 0.45% saline) as it is isotonic 1, 4

Why 0.45% Normal Saline is Not Appropriate

0.45% saline is hypotonic and not recommended for renal protection:

• The evidence base compares LR to 0.9% (isotonic) normal saline, not 0.45% saline 1, 5
• Hypotonic solutions like 0.45% saline would theoretically pose similar risks to LR regarding cerebral edema but lack LR's balanced electrolyte composition 4
• For fluid resuscitation and renal protection, isotonic crystalloids are required—either LR or 0.9% saline 1

Practical Algorithm for Fluid Selection

Step 1: Assess for contraindications to LR:

• Severe traumatic brain injury or increased intracranial pressure → Use 0.9% normal saline instead 1, 4
• Suspected or proven crush syndrome/rhabdomyolysis → Use 0.9% normal saline due to potassium content concerns 1

Step 2: If no contraindications exist:

• Use LR as first-line crystalloid for patients with or at risk for AKI 1
• LR is appropriate even in mild-to-moderate hyperkalemia or renal dysfunction (potassium content of 4 mmol/L is not a contraindication) 1
• LR can be used safely in liver disease 1

Step 3: Limit normal saline if used:

• If 0.9% normal saline must be used, limit to maximum 1-1.5L to minimize chloride load and hyperchloremic acidosis 1, 5

Common Pitfalls to Avoid

• Do not avoid LR due to potassium content (4 mmol/L) in patients with mild-moderate hyperkalemia or CKD—this is physiologic and not contraindicated except in crush syndrome 1
• Do not use 0.45% saline for resuscitation or renal protection—it is hypotonic and not supported by evidence for these indications 1, 4
• Do not use large volumes of 0.9% saline (>5L) as this is associated with increased mortality and major adverse kidney events 5
• Do not confuse LR's slight hypotonicity as a general contraindication—it is only contraindicated in severe TBI, not in renal patients 1, 4