The following calculations may be used to estimate fluid requirements for infants and children. Other reflections of volume status, including clinical exam, blood pressure, heart rate, urine output, central venous pressure, pulse pressure variation, straight leg raise, noninvasive cardiac output monitoring, fluid challenge, and osmolarity, may guide further adjustments.

1. Maintenance fluid requirements
   1. Administer 4 mL/kg/h for the first 10 kg of body weight (100 mL/kg/d), 2 mL/kg/h for the second 10 kg (50 mL/kg/d), and then add 1 mL/kg/h for more than 20 kg (25 mL/kg/d). For example, maintenance fluids for a 25-kg child would be ([4 mL/kg × 10 kg] + [2 mL/kg × 10 kg] + [1 mL/kg × 5 kg]) = 65 mL/h.
   2. The usual solution for replacement of fluid deficits and ongoing losses in the healthy child is lactated Ringer solution. A second solution of 5% dextrose is frequently used in the perioperative period for premature infants, septic neonates, infants of diabetic mothers, and those receiving total parenteral nutrition. These patients should have their blood glucose levels measured periodically.
2. Estimated blood volume (EBV) and blood losses
   1. EBV is 95 mL/kg in premature neonates, 80 to 90 mL/kg in full-term neonates, 75 to 80 mL/kg in infants up to 1 year old, and 70 mL/kg thereafter.
   2. Acceptable blood loss (ABL). ABL can be estimated with a simple formula. This should be used with caution if fluid redistribution/equilibration has not occurred.

      ABL = EBV × (Hct_initial − Hct_acceptable)/Hct_initial

   3. General guidelines are as follows:
      1. If the amount of the blood loss is less than one-third of the ABL, it can be replaced with lactated Ringer solution.
      2. If the amount of blood loss is greater than ABL, replace with packed red blood cells (leukoreduced, CMV negative, and irradiated). Fresh frozen plasma and platelet transfusions should be guided by the results of coagulation tests, estimates of the present and anticipated blood losses, and adequacy of clot formation in the wound.
      3. For infants and young children, blood loss should be measured using small suction containers and by weighing sponges. Because it is sometimes difficult to measure small-volume blood losses precisely in young children, monitoring of hemoglobin and hematocrit will help avoid unnecessary transfusions and also alert the anesthetist to the need for blood transfusion.
      4. The “acceptable hemoglobin and hematocrit” is no longer considered to be 10 g/dL and 30%. Each patient is evaluated with regard to the need for red blood cell transfusion. A healthy child with normal cardiac function can compensate for acute anemia by increasing cardiac output. A premature infant, a debilitated child, a child with sepsis, a child receiving chemotherapy, or one facing massive surgery may require a higher hemoglobin.
3. Estimated fluid deficit = (maintenance fluid per hour) × hours since the last oral intake. The entire estimated fluid deficit replaced during all major cases; the first half is administered during the first hour, and the remaining deficit is infused over the next 1 to 2 hours.
4. Third-space losses may require up to an additional 10 mL/kg/h of lactated Ringer solution or normal saline if there is extensive exposure of the intestine or a significant ileus.