What is the preferred fluid for resuscitation in hypovolemia or hemorrhagic shock in pregnancy, Lactated Ringer's (LR) solution or Normal Saline (NS)?

Lactated Ringer's Solution is Preferred Over Normal Saline for Hemorrhagic Shock in Pregnancy

Lactated Ringer's (LR) solution should be used as the first-line crystalloid for resuscitation in pregnant women with hypovolemia or hemorrhagic shock, rather than normal saline (NS). 1

Primary Recommendation

The Surviving Sepsis Campaign guidelines, endorsed by the American College of Obstetricians and Gynecologists and the Society for Maternal-Fetal Medicine, specifically recommend balanced crystalloid solutions like lactated Ringer's for resuscitation in pregnant and postpartum women. 1 This recommendation is based on LR's lower risk of hyperchloremic metabolic acidosis and renal vasoconstriction compared to NS. 1

Evidence Supporting Lactated Ringer's Superiority

Reduced Fluid Requirements and Better Outcomes

• LR requires significantly less volume for effective resuscitation. In hemorrhagic shock models, animals resuscitated with LR required only 125.7 mL/kg compared to 256.3 mL/kg with NS to achieve the same hemodynamic endpoints. 2
• LR prevents dilutional coagulopathy better than NS. Resuscitation with NS resulted in significantly lower fibrinogen levels (99 mg/dL vs. 123 mg/dL with LR), which is particularly concerning in obstetric hemorrhage where coagulopathy is already a major risk. 2

Avoidance of Hyperchloremic Acidosis

• NS causes hyperchloremic metabolic acidosis (chloride 119 mEq/L vs. 105 mEq/L with LR; pH 7.28 vs. 7.45 with LR), which can worsen clinical outcomes and complicate assessment of tissue perfusion. 2
• Balanced crystalloids consistently maintain better acid-base balance across multiple studies, avoiding the deleterious effects of high-volume chloride-rich solutions on renal function and survival. 3

Survival Advantage

• In massive hemorrhage models, LR demonstrated 100% survival compared to only 50% with NS when used for resuscitation. 4
• Animals resuscitated with NS were significantly more acidotic (pH 7.14 vs. 7.39 with LR) and had worse mortality outcomes. 4

Clinical Application in Pregnancy

Initial Resuscitation Protocol

• Administer an initial fluid bolus of 1-2 L of lactated Ringer's solution as recommended by the Surviving Sepsis Campaign. 1
• Consider escalating to 30 mL/kg within the first 3 hours for patients in shock or those with inadequate response to initial bolus. 1
• Target mean arterial pressure of 65 mm Hg, though this threshold has not been specifically validated in pregnant patients. 1

Volume Considerations Specific to Pregnancy

• Pregnant women require careful fluid management due to lower colloid oncotic pressure and higher risk of pulmonary edema, even when using the preferred balanced crystalloid. 1
• The Society for Maternal-Fetal Medicine recommends tailoring fluid volume to the patient's condition rather than automatically administering the full 30 mL/kg, given pregnancy-related physiological changes. 1

Critical Monitoring Parameters

• Assess hemodynamic response after each bolus: heart rate, blood pressure, skin perfusion, capillary refill time, and mental status. 5
• Monitor urine output with target >0.5 mL/kg/hr. 5
• Regular assessment of acid-base status through arterial or venous blood gases, particularly monitoring chloride levels and renal function. 1
• Fluid balance monitoring to avoid volume overload, especially critical given pregnancy-related increased risk of pulmonary edema. 1

Common Pitfalls to Avoid

Misinterpretation of Lactate Levels

• Elevated lactate with LR does not indicate worsening shock. Resuscitation with LR results in elevation of lactate levels that is NOT associated with acidosis, unlike the acidosis seen with NS. 2
• This is a metabolic byproduct of the lactate in the solution being converted to bicarbonate, not a sign of tissue hypoperfusion. 2

Avoiding Outdated Alternatives

• Do not use hypertonic saline solutions (3% or 7.5%) as first-line treatment, as they have no beneficial effect on mortality in hemorrhagic shock. 3
• Avoid synthetic colloids due to lack of superiority over crystalloids, significantly higher cost, and potential for adverse effects. 3, 5

Strength of Evidence

While the 2022 critical care guidelines acknowledge that present-day data do not suffice to justify a GRADE 1 recommendation for a specific crystalloid in hemorrhagic shock generally, they clearly state that the potentially deleterious effects on renal function and survival of high-volume chloride-rich solutions should orient first-line treatment choices toward balanced solutions. 3 The pregnancy-specific guidelines from major obstetric societies provide more definitive recommendations favoring LR. 1