Balanced fluid bolus: Should we prefer balanced crystalloids over "normal" saline?

A fluid bolus is administered to correct hypoperfusion, hypotension, and metabolic acidosis for resuscitation at birth or in the neonatal intensive care unit (NICU). However, there is a lack of evidence-based support for any particular fluid choice. The most used intravenous fluid is 0.9% sodium chloride or "normal saline" (NS). There is a growing body of evidence that NS is associated with hyperchloremic metabolic acidosis and acute kidney injury. Balanced crystalloid solutions such as lactated Ringer's solution and solutions with a more physiological composition similar to plasma may offer some advantages compared to NS based on adult literature. Here we discuss indications and challenges with the use of balanced crystalloids and propose a practical approach to fluid choice in the NICU. Further research is needed to better understand indications for and optimal fluid therapy to correct hypoperfusion and metabolic acidosis in neonates.