Neonatal Care

Physiologic Third Spacing

• Physiologic third spacing may occur in the first 48 hours of life and typically resolves by days 7-10, as recommended by the American Academy of Pediatrics for postnatal ultrasound evaluation of urinary tract dilation to be performed after 48 hours of life 1
• Third spacing refers to the abnormal shifting of fluid from the intravascular space into interstitial or potential body spaces, resulting in decreased effective circulating volume, hypotension, tissue hypoperfusion, and organ dysfunction, and is treated with intensive fluid resuscitation with crystalloids to restore intravascular volume while addressing the underlying cause of the fluid shift, as recommended by the Kidney International guidelines 2
• Causes of third spacing include acute mesenteric ischemia, which results in fluid shifts into the intestinal wall and peritoneal cavity, and post-obstructive pulmonary edema, following relief of airway obstruction, which can cause significant fluid accumulation in the lungs, according to the World Journal of Emergency Surgery and Anaesthesia journal guidelines 3, 4

Diagnosis and Monitoring

• Effective monitoring for third space fluid shifts should include vital signs, urine output, daily weights, intake and output measurements, and electrolytes and renal function, as recommended by general medical guidelines 3
• Monitoring should be individualized based on factors such as scale of fluid loss, environmental conditions, time course of third spacing, and patient demographics, including careful titration in elderly and children 2

Treatment and Management

• Initial fluid management involves administering crystalloids, typically isotonic saline or balanced solutions, to restore intravascular volume, with the goal of improving hemodynamic parameters such as blood pressure, heart rate, and capillary refill, as recommended by the Kidney International guidelines 2
• The use of crystalloids is preferred over other types of fluids, and the choice of crystalloid should be based on the patient's underlying condition and laboratory values, with consideration of the potential risks and benefits of each type of fluid 2
• Patients with evidence of fluid overload after initial resuscitation may require loop diuretics, such as furosemide, which can be administered as boluses or continuous infusion, with consideration of the potential benefits and risks of each approach, including the risk of electrolyte imbalances and renal injury 2
• Consideration should be given to adding spironolactone for enhanced diuresis in appropriate patients with edema, although the evidence for this approach is limited, and the potential risks and benefits should be carefully weighed, including the risk of electrolyte imbalances and other complications 2
• Adjust fluid management based on renal function, and consider lower doses of diuretics in renal impairment, with careful monitoring of the patient's response to therapy, including the use of laboratory values and clinical parameters to guide adjustments, and consideration of the strength of evidence for each intervention, including the use of loop diuretics and continuous infusion 2

Fluid Management Considerations

• Avoid using potassium-containing fluids like Lactated Ringer's solution, and starch-based fluids due to increased risk of AKI, and consider using bicarbonate-containing fluids to alkalinize urine, although the evidence for benefit over standard crystalloids is limited, and the potential risks and benefits should be carefully weighed, including the risk of electrolyte imbalances and other complications 2
• Judicious fluid resuscitation is essential to maintain organ perfusion and prevent further complications, according to general medical principles 4