In our last exam tips post, we looked at the physiology of fluid and electrolyte balance in children. In this article, we will move on to look at the administration of routine maintenance fluids in children.
Indications for routine maintenance fluids in children
Regular maintenance fluid therapy becomes necessary when the current oral intake is inadequate for maintaining proper hydration. For example, in cases where the child is nil by mouth or cannot consume oral fluids for a substantial period for other reasons.
If the child can ingest some fluids orally but falls short of meeting their complete fluid requirements, a portion of full maintenance fluids may be administered, aligning with their oral intake.
Choice of routine maintenance fluids
In children over 28 days old, the first-line maintenance fluid is usually isotonic crystalloids plus 5% glucose, for example, 0.9% sodium chloride with 5% glucose.
In term neonates less than 28 days old, the fluid choice depends upon the clinical scenario. Initially, the use of isotonic crystalloids with 5-10% glucose is recommended. In the first few days of life, the sodium content of isotonic fluids (131-154 mmol/l) may be too high, and a glucose content of 5-10% may be too high. If there is a critical illness (e.g., infantile respiratory distress syndrome or meconium aspiration), expert advice will be necessary, and fluids with no or minimal sodium are often used initially.
Calculating fluid requirements
The current NICE guidelines advocate using the Holliday-Segar formula to estimate the daily maintenance fluid requirements for children. This formula approximates water and caloric losses utilising a patient’s body weight and provides a guideline for calculating the amount of fluid needed to sustain normal physiological functions.
The Holliday-Segar formula is as follows:
| Body Weight | Fluid requirements per day (ml/kg) | Fluid requirements per hour (ml/kg) |
|---|---|---|
| First 10 kg | 100 | 4 |
| Second 10 kg | 50 | 2 |
| For each additional kg of body weight | 20 | 1 |
The rationale behind the adjustments in the formula is that the metabolic rate and fluid requirements vary with body weight. The initial 100 ml/kg/day for the first 10 kg reflects the higher metabolic rate and fluid needs of smaller children.
It’s important to note that the Holliday-Segar formula is primarily used to estimate maintenance fluid requirements and doesn’t account for additional fluid needs related to ongoing losses, such as vomiting, diarrhoea, or fever.
Maintenance for term neonates is different and is calculated according to their age and weight:
- Birth to day 1: 50-60 ml/kg/day
- Day 2: 70-80 ml/kg/day
- Day 3: 80-100 ml/kg/day
- Day 4: 100-120 ml/kg/day
- Days 5-28: 120-150 ml/kg/day
Worked example 1:
Calculate the 24-hour maintenance fluids and hourly infusion rate for a 3-year-old child who weighs 14 kg:
Answer:
First 10 kg = 100 ml x 10 = 1000 ml
Next 5 kg = 50 ml x 4 = 200 ml
Total = 1200 ml
Infusion rate in ml/hour = 1200/24 = 50 ml/hour
Worked example 2:
Calculate the 24-hour maintenance fluids and hourly infusion rate for a 4-year-old child who weighs 35 kg:
Answer:
First 10 kg = 100 ml x 10 = 1000 ml
Next 10 kg = 50 ml x 10 = 500 ml
Final 20 kg = 20 ml x 15 = 300 ml
Total = 1800 ml
Infusion rate in ml/hour = 1800/24 = 75 ml/hour
References:
NICE Guideline: Intravenous fluid therapy in children and young people in hospital
Advanced Paediatric Life Support: A Practical Approach to Emergencies (7th Edition): Appendix B
Next: Paediatric Intravenous Fluid Prescribing – Dehydration and Shock
Header image used on licence from Shutterstock
Thank you to the joint editorial team of www.mrcemexamprep.net for this ‘Exam Tips’ blog post.
