Why is normal saline (sodium chloride) not recommended for fluid resuscitation?

Why Normal Saline Is Not Recommended for Fluid Resuscitation

Normal saline (0.9% sodium chloride) should be avoided or limited in fluid resuscitation because it causes hyperchloremic metabolic acidosis, increases acute kidney injury risk, and leads to worse patient outcomes compared to balanced crystalloids. 1

Primary Mechanisms of Harm

Normal saline contains 154 mEq/L of chloride—significantly higher than the physiological plasma concentration of approximately 100-110 mEq/L. 2 This supraphysiologic chloride load produces several harmful effects:

• Hyperchloremic metabolic acidosis develops in a dose-dependent, reproducible manner when large volumes are administered 1, 2
• Renal vasoconstriction occurs due to elevated chloride levels, reducing kidney perfusion and urine output 1, 2
• Increased vasopressor requirements result from impaired end-organ perfusion 1
• Dilutional coagulopathy develops more frequently compared to balanced crystalloids 1

Evidence from High-Quality Trials

The SMART trial (2018, n=15,802 ICU patients) demonstrated that normal saline resulted in significantly higher rates of major adverse kidney events within 30 days (15.4% vs 14.3%) compared to balanced crystalloids. 1 While this trial had methodological limitations including single-center design, it represents the largest pragmatic comparison available.

The SALT trial showed patients receiving balanced crystalloids had lower 30-day in-hospital mortality and reduced incidence of renal replacement therapy compared to normal saline. 1

Guideline Recommendations Across Clinical Contexts

Emergency laparotomy patients: Balanced crystalloids should be used in preference to normal saline for resuscitation and maintaining intravascular volume (weak recommendation, low-quality evidence). 1

Trauma patients: Both 0.9% sodium chloride and balanced crystalloid solutions are acceptable for initial resuscitation, but if normal saline is used, it should be limited to a maximum of 1-1.5 L and avoided in severe acidosis with hyperchloremia. 1

Sepsis and septic shock: The Surviving Sepsis Campaign guidelines recommend balanced crystalloids (lactated Ringer's solution) instead of normal saline due to lower risk of hyperchloremic metabolic acidosis and renal complications. 3

Acute kidney injury prevention: KDIGO guidelines recommend crystalloids over colloids but do not distinguish between types of crystalloids, though the emerging evidence favors balanced solutions. 1

Special Clinical Scenarios Where Balanced Crystalloids Show Superior Outcomes

Diabetic ketoacidosis (DKA): Despite decades of normal saline use in DKA, recent evidence demonstrates balanced crystalloids lead to faster DKA resolution. 4, 5 In a subgroup analysis of the SMART and SALT-ED trials, balanced crystalloids resulted in median time to DKA resolution of 13.0 hours versus 16.9 hours with saline (adjusted HR 1.68,95% CI 1.18-2.38, P=0.004). 4 A 2025 study confirmed these findings with median resolution time of 13 hours with balanced fluids versus 17 hours with normal saline (P=0.02). 5

Hemorrhagic shock: Early studies showed patients receiving normal saline experienced higher incidence of hyperchloremic metabolic acidosis, electrolyte derangements, dilutional coagulopathy, and higher overall volume requirements compared to lactated Ringer's solution. 1

When Normal Saline May Still Be Used

Traumatic brain injury: Hypotonic solutions like Ringer's lactate should be avoided to minimize fluid shift into damaged cerebral tissue, making normal saline or balanced crystalloids with appropriate tonicity the preferred options. 1, 6 However, this does not mean normal saline is superior—it simply means hypotonic solutions are contraindicated.

Initial resuscitation when balanced crystalloids unavailable: If balanced crystalloids are not immediately available, normal saline can be used for initial boluses but should be transitioned to balanced solutions as soon as possible. 1, 7

Critical Caveats

• Volume limitations matter: When normal saline must be used, restrict to 1-1.5 L maximum to minimize chloride load 1
• Avoid in pre-existing acidosis: Normal saline is particularly harmful in patients with existing metabolic acidosis or hyperchloremia 1
• Monitor chloride and acid-base status: Regular assessment of serum chloride, arterial or venous blood gases, and renal function is essential when any crystalloid is used in large volumes 3
• Pregnancy considerations: Pregnant and postpartum women have lower colloid oncotic pressure and higher pulmonary edema risk, making the choice of balanced crystalloids even more important to avoid compounding metabolic derangements 3

Practical Algorithm for Fluid Selection

1. First-line choice: Use balanced crystalloids (lactated Ringer's or Plasma-Lyte) for all resuscitation needs 1, 3
2. If balanced crystalloids unavailable: Normal saline acceptable for initial 1-1.5 L, then switch 1
3. Severe traumatic brain injury: Avoid hypotonic solutions; use isotonic balanced crystalloids or normal saline 1, 6
4. Pre-existing hyperchloremia or severe acidosis: Absolutely avoid normal saline; use only balanced crystalloids 1
5. DKA management: Strongly prefer balanced crystalloids for faster resolution 4, 5

The weight of evidence from multiple guidelines and high-quality trials supports balanced crystalloids as the default choice for fluid resuscitation, with normal saline reserved only for specific circumstances or when balanced solutions are unavailable. 1, 3