140 mmol/L of sodium versus 77 mmol/L of sodium in maintenance intravenous fluid therapy for children in hospital (PIMS): a randomised controlled double-blind trial

This single-centre study of children requiring maintenance IV hydration for ≥6 hours found isotonic fluid (containing 140 mmol/L sodium) was associated with a lower risk of hyponatraemia than hypotonic fluid (77 mmol/L sodium; 4% v 11%), with no increase in adverse effects.

The results of this study are in line with the findings of previous meta-analyses in this area, suggesting that isotonic fluid is safer than hypotonic fluid in terms of risk of hyponatraemia. The patient group recruited was heterogeneous which allows the findings to be more broadly applied to all settings in which paediatric patients receive IV fluids.

The authors of an accompanying Comment article note that critics have argued against the use of isotonic fluids for maintenance, saying hospital-acquired hyponatraemia is more due to raised antidiuretic hormone concentrations secondary to poorly corrected hypovolaemia than to the hypotonic fluid itself. Concerns have also been raised about hypernatraemia; yet this study and the two recent meta-analyses show no such increased risk with maintenance isotonic fluid. Although there are some clinical scenarios in which clinicians should consider use of hypotonic fluid as a maintenance fluid, the authors argue that this should now be the exception and not the rule.