Will changing maintenance intravenous fluid from 0.18% to 0.45% saline do more harm than good?

The recommended change in maintenance intravenous fluid in children from 0.18% to 0.45% saline might cause more children to develop hypernatraemia than it would prevent children from developing hyponatraemia, and thus could do more harm than good. There is no simple formula that will guarantee to prevent either hyponatraemia or hypernatraemia in all children, and it is impossible to decide on a safe fluid regimen merely by knowing the plasma sodium concentration and estimating the degree of dehydration, as is often done. Changing which fluid is used for routine maintenance therapy will not compensate for using a too-simple approach to fluid replacement. Instead, it is necessary to base the fluid regimen on an assessment of the child's physiology. A vital part of that assessment includes measuring the urinary volume, sodium and creatinine, and using them to calculate the fractional excretion of water and sodium. This enables fluid replacement to be decided using a logical approach in which plasma sodium measurements are just used for fine-tuning. Also, 0.18% saline provides a more physiological standard replacement than 0.45% saline, equivalent to normal oral intakes, and should remain the basic maintenance fluid.