What is the best fluid to administer to a pregnant patient?

Best Fluid for Pregnant Patients

Balanced crystalloid solutions, specifically lactated Ringer's solution, should be used as the first-line fluid for pregnant patients requiring resuscitation, as recommended by the Surviving Sepsis Campaign and supported by the American College of Obstetricians and Gynecologists. 1, 2, 3

Primary Recommendation

• Lactated Ringer's solution is the preferred crystalloid for fluid resuscitation in pregnant patients due to its lower risk of hyperchloremic metabolic acidosis, renal vasoconstriction, and acute kidney injury compared to normal saline 1, 2, 3
• The Surviving Sepsis Campaign explicitly recommends balanced crystalloids instead of normal saline for resuscitation in patients with sepsis or septic shock, including pregnant women 1
• The Society for Maternal-Fetal Medicine supports this recommendation, noting that balanced crystalloids have near-physiological electrolyte concentrations and lower chloride content 2

Evidence Supporting Lactated Ringer's Over Normal Saline

Maternal Outcomes

• Normal saline causes hyperchloremic metabolic acidosis, renal vasoconstriction, increased cytokine secretion, and increased risk of acute kidney injury—all particularly concerning in pregnant women 1, 2, 3
• In a randomized trial of 500 parturients undergoing urgent cesarean delivery, 38% of women receiving normal saline developed acidosis compared to 29% receiving lactated Ringer's (relative risk 1.29, P=0.04) 4
• Specifically, 32% of women receiving normal saline experienced a drop in venous pH below 7.32 postoperatively, compared with only 19% receiving lactated Ringer's (relative risk 1.65, P=0.003) 4

Fetal Outcomes

• Lactated Ringer's solution results in minimal changes in fetal electrolytes and acid-base balance, whereas normal saline significantly alters fetal plasma electrolyte concentrations and blood pH 5
• In ovine fetal studies, normal saline amnioinfusion increased fetal plasma sodium and chloride concentrations by 2-3 mEq/L and decreased fetal arterial pH by 0.015 units, while lactated Ringer's caused only modest changes 5

Clinical Application Algorithm

Initial Resuscitation

• Start with 1-2 L bolus of lactated Ringer's solution as the initial fluid resuscitation 1, 2, 3
• Target mean arterial pressure of 65 mm Hg (though this threshold has not been specifically validated in pregnant patients) 2, 3

Escalation for Septic Shock

• Consider escalating to 30 mL/kg within the first 3 hours for patients in septic shock or those with inadequate response to initial bolus 1, 2, 3
• If initial fluid bolus of less than 30 mL/kg is given, CMS requires documentation of clinical reason and specific amount ordered 1

Volume Considerations Specific to Pregnancy

• Tailor fluid volume to the patient's condition rather than automatically administering the full 30 mL/kg, given pregnancy-related physiological changes 1, 2, 3
• Pregnant women have lower colloid oncotic pressure and higher risk of pulmonary edema, making careful fluid management essential even when using balanced crystalloids 1, 2, 3

Critical Monitoring Parameters

Hemodynamic Assessment

• Assess hemodynamic response after each bolus: heart rate, blood pressure, skin perfusion, capillary refill time, and mental status 3
• Monitor urine output with target >0.5 mL/kg/hr 3

Laboratory Monitoring

• Regular assessment of acid-base status through arterial or venous blood gases 2, 3
• Monitor serum electrolytes, particularly chloride levels 2, 3
• Assess renal function and urine output 2, 3

Volume Status

• Fluid balance monitoring to avoid volume overload is especially critical given pregnancy-related increased risk of pulmonary edema 2, 3, 6
• Perform volume status and tissue perfusion assessment within 6 hours of septic shock presentation if hypotension persists after fluid administration or if initial lactate level is ≥4 mmol/L 1

Important Caveats and Pitfalls

Avoid These Alternatives

• Do not use 5% dextrose solutions as they are associated with neonatal hyponatremia (33.3% vs 13.3% with normal saline, P=0.03) and higher incidence of neonatal hyperbilirubinemia 7
• Avoid synthetic colloids (hydroxyethyl starch, gelatin) due to lack of superiority over crystalloids, significantly higher cost, and potential adverse effects including mild hypocoagulable state 1, 3, 8
• 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

Special Considerations for Pre-eclampsia

• Women with pre-eclampsia handle crystalloid fluid differently: they have smaller central body fluid space expansion (2940 mL vs 4240 mL in controls) and higher clearance constants for both distribution and elimination 9
• Lactated Ringer's solution is both distributed and eliminated faster in women with pre-eclampsia than in matched pregnant controls 9

Lack of Pregnancy-Specific Data

• No specific recommendation can be issued concerning the choice of fluid therapy for volume resuscitation of women during the peripartum period based on pregnancy-specific mortality data 1
• By default, the solution chosen should be the one recommended according to the context in the general population, which is balanced crystalloids 1