Third space losses vary according to the surgery being done and the age of the child.

For a minor surgical procedure or superficial surgery they may only be
1 ml/kg/h.

For major abdominal surgery they may be 15-20 ml/kg/h.

The younger the child, the higher the relative proportion of losses because of the large extracellular fluid volume in young infants compared to older children.

Third space losses are difficult to measure and are often replaced empirically according to the surgery being done. For this reason, the child’s medical state should be monitored continuously, for haemodynamic stability.

For superficial surgery or neurosurgery    1-2 ml/kg/h
For moderate surgery - thoracotomy       4 ml/kg/h
For more major trauma – laparotomy       8 ml/kg/h