Prescribing fluids in paediatrics is simple but there is a system to it that you will need to learn if you have not worked in paediatrics before. This article breaks it down for you with examples of IV fluid prescribing. Please see this separate article for fluids and feeds in neonates.

The important thing to remember is that children are not just small adults. Maintenance fluids and fluid boluses need to be calculated correctly rather than squeezing in 1L over 10 minutes.

Background

• This article applies to prescribing IV fluids for children 1 month-18 years of age and is only relevant in the case of children who cannot take fluids or food enterally.
  • There could be any number of reasons for this but some examples are: they have severe D&V and aren’t keeping fluids down, or because they are pre or post-op, or have presented very unwell and need fluid resuscitation.
• Wherever possible we should aim for enteral fluids in children and avoid cannulation and IV fluids unless necessary
• The objective of IV fluid therapy is to provide water, sugar and electrolytes to meet physiological losses (this includes insensible losses and urine/vomiting/stool)
• The preferred type of IV fluid in paediatrics is either 0.9% saline + 5% dextrose or plasma-lyte 148 + 5% dextrose. This is hospital dependent and you should be told about which fluid to prescribe at your induction (or I’m sure the nurses will tell you!)

How much fluid?

Maintenance Fluids

In 1957, Malcolm Holliday and William Segar published an article in the Journal of Paediatrics, which claimed to be a simple scheme that could be easily remembered to calculate fluid requirements.

Holliday and Segar documented that there was a direct linear relationship between physiologic water needs (insensible and urinary losses) and energy metabolism, meaning that the average needs for water in ml equates to energy expenditure in calories (1ml of water is required to metabolise 1kcal)

Holliday and Segar found the relationship between energy expenditure and weight to be Non-Linear and they used their findings to create a graph plotting caloric requirements versus weight. The curve on this graph can be split into 3 linear sections corresponding to the following weight categories: 0-10kg, 10-20kg, and 20-70kg. [1] It is worth mentioning this formula was designed for well, euvolaemic children, which does not represent the popluation of children who require IV fluids. Our population and their demographics has also changed significantly since this study in 1957.

They then concluded that fluid requirement is as follows:

• 100ml/kg/day for the first 10kg
• 50ml/kg/day for the second 10kg
• 20ml/kg/day for every kg after [1]

This has been simplified by anaesthetic teams to be the 4-2-1 rule:

• 4ml/kg/hr for the first 10kg
• 2ml/kg/hr for the second 10kg
• 1ml/kg/hr for every kg after

This is generally the best way to calculate IV fluid requirements for paediatric patients. However it is not one size fits all. If a patient has presented with a traumatic brain injury or has a condition that puts them at risk of fluid retention (e.g. heart failure, renal failure, hepatic failure) you should consider prescribing 60% maintenance fluids to prevent fluid overload.

In any child on IV fluids they should be reassessed at least each day to review the need for these fluids and their fluid balance and electrolytes.

Fluids Boluses

IV fluid boluses should be considered for critically unwell children with signs of hypovalaemia / haemodynamic compromise. This would include prolonged capillary refill time, tachycardia, hypotension, cool peripheries, sunken eyes, metabolic acidosis, raised lactate, poor urine output.

They should be given in aliquots of 10ml/kg, with further assessment of fluid and haemodynamic status after each bolus. After each bolus is given you should also be assessing for fluid overload by palpating for a liver edge and auscultating for pulmonary oedema

Once a volume of 30-40ml/kg has been given and the child is still unstable you should be thinking about HDU/PICU level care, inotropes, and speaking to your local transport team if you are in a DGH.

The FEAST study published in 2011 was undertaken across centers in Uganda, Kenya and Tanzania, and randomly allocated children presenting with severe infection and impaired perfusion to groups receiving albumin bolus, saline bolus or no bolus. Boluses were given in 20-40ml/kg aliquots. The children who received no bolus had significantly better outcomes and reduced mortality compared to the two bolus group. [2] Since this data was published the APLS guidelines have altered to reflect these results and the need for more research in this area and now recommend the 10ml/kg boluses as above compared to the previous recommendation of 20ml/kg.

Which type of fluid to use?

Crystalloids vs. colloids. Balanced vs. non-balanced. Istonic vs. hypotonic.

Crystalloids – aqueous solutions composed of water and small solutes such as electrolytes and glucose. Crystalloids can be hypo or iso tonic. The tonicity describes the osmolality of the fluid, i.e. the ability to alter movement across the cell membrane.

• Hypo-tonic crystalloids have an osmolality lower than that of normal plasma and which means it expands the extracellular volume, reudces the osmolality in the extracellular compartment and then causes fluid to move intracellular include. These fluids include: 0.45% saline, 5% dextrose
• Iso-tonic crystalloids have an osmolality and Na concentration similar to plasma and therefore do not cause big fluid shifts, and they maintain extracellular fluid volume. These fluids include: 0.9% saline, Hartmanns, plasma-lyte 148
• Hypertonic crystalloids have an osmolality much higher than that of normal plasma and causes redistribution of fluid from intracellular to the extracellular compartment. These include hypertonic saline and mannitol. This is mainly reserved for patients with raised intracranial pressure
• Balanced crystalloids have an electrolyte concentration similar to plasma such as plasma-lyte.
• Non-balanced crystalloids have non physiological concentrations of solutes, such as 0.9% saline which contains high concentrations of sodium and chloride but no other electrolytes which would normally be found in plasma [3]

Colloids – contain large molecular weight particles such as starches and proteins, which are suspended in a crystalloid solution. Colloids can be natural or synthetic

• Natural colloids include whole blood, plasma and human albumin solution
• Synthetic colloids include gelatins, strarches and dextrans and are rarely used in paediatrics. [3]

The type of IV fluid you use will vary depending on which hospital you are working in and what is available. Generally speaking, the closer the composition of IV fluid is to the composition of plasma, the better it will be at maintaining normal electrolyte values and staying in the circulatory system. So, let’s review these compositions:

As you can see, Hartmann’s and Plasma-Lyte 148 most closely resemble the solute concentration of plasma, and therefore are more likely to stay in the circulatory system for longer, and less likely to cause electrolyte imbalance.

The preferred fluid for boluses and maintenance fluids in paediatrics would be Plasma-lyte 148 + Plasma-lyte 148 5% dextrose but some hospitals are still using 0.9% saline + 0.9% saline + 5% dextrose due to cost.

Repeated boluses with 0.9% saline followed by maintenance fluids of saline can cause hyperchloraemic acidosis as chloride is a negative anion. When giving 0.9% saline as maintenance fluid you also need to be mindful of your serum potassium levels and may need to add potassium to your fluids.

A recent meta-analysis reviewed the evidence behind volumes and types of IV fluids prescribed in paediatrics. They concluded that some evidence in the literature shows a shorter length of hospital stay associated with prescribing balanced isotonic fluids (Plasma-lyte) over non-balanced (0.9% saline), however more research is needed in this area. [4]

There is currently a study taking place across USA, Canada, Australia and New Zealand (PREDICT) to review the efficacy of 0.9% saline vs balanced crystalloid solutions for initial fluid management in the treatment of septic shock which may give us more insight into this topic. [5]

Examples

(1) A 4 year old presents to your paediatric assessment unit with 48 hours history of diarrhoea and vomiting. She is tachycardic with HR 160, she has cool peripheries with CRT 3 seconds and her BP is in the normal range for her age. She weighs 16kg

Select the management from the options below and scroll down for the correct answer

[A] Fluid bolus of 380ml, then start IV fluids at 60ml/hr. Reassess after 2 hours of IV fluids

[B] Fluid bolus of 160ml, then reassess and consider the need for a second bolus. Once cardiovascular status has improved start maintenance IV fluids at 54ml/hr

[C] Fluid bolus of 200ml, then reassess and consider discharging if improved HR and perfusion.

[D] No need for fluid bolus, start IV maintenance fluids at 54ml/hr

(2) A 18 month old is referred by a GP for tonsillitis and reduced oral intake. When you review the child he has a cup of juice in his hands and has had ice lollies throughout the day. He is tachycardic with HR 180 and he has a fever of 38.8. You are unable to get a BP as he screams and kicks when the cuff inflates. He has had 2 wet nappies today. He is hot centrally and cool peripherally with a normal capillary refill time. He weighs 10kg

Select the management from the options below and scroll down for the correct answer

[A] Fluid bolus of 100ml, reassess and consider the need for a second bolus. Once cardiovascular status has improved start maintenance fluids at 42ml/hr

[B] No need for fluid bolus, start IV maintenance fluids at 42ml/hr

[C] No need for IV fluids, give the child some calpol or neurofen and observe to ensure his HR comes down as his fever resolves. Offer a fluid challenge of dioralyte or yoghurts and ice lollies.

[D] Discharge home with safety net advice

(3) A 6 year old is referred from ED with known chronic kidney disease stage 3, presenting unwell with vomiting, pyrexia, tachycardia and reduced urine output with offensive smelling, cloudy urine. Her temperature is 38, her HR is 150 and her BP is in the normal range for her age group. She has cool peripheries and a CRT of 3-4 seconds. She weighs 20kg.

Select the management from the options below and scroll down for the correct answer

[A] Fluid bolus of 200ml, reassess and consider the need for a second bolus. Once cardiovascular status has improved start maintenance fluids at 63ml/hr

[B] Fluid bolus of 400ml, reassess and consider the need for inotropes. Then start maintenance fluids at 70ml/hr

[C] No fluid bolus, start IV maintenance fluids at 40ml/hr

[D] Fluid bolus of 200ml, reassess and consider the need for a second bolus. Once cardiovascular status has improved start maintenance fluids at 38ml/hr, monitor urine output closely, liaise with your local paediatric renal team.

Answers

(1) [B] is the correct answer. This is a child who is clearly dehydrated and unable to tolerate oral fluids therefore IV fluids are the best option. Her bolus would be 10ml/kg = 160ml. This can be repeated until her cardiovascular status has improved, e.g. HR has come down, perfusion improved. Then you would start maintenance fluids at 54ml/hr ((10ml/kg for first 10 kg = 10X10 = 1000) + (50ml/kg for next 10kg = 50 X 6 = 300 = 1300ml) / 24 = 54ml/hr)

(2) [C] is the correct answer. This child should be monitored as he is tachycardic with his fever and has had some reduced input / output but he is tolerating some oral fluids and food so does not need IV fluids. The best option will be to offer him some diorlayte / apple juice / yoghurts or ice lollies and observe him to make sure his observations normalise when his temperature resolved.

(3) [D] is the correct answer. This child has a background of renal problems and therefore will be fluid restricted due to her risk of fluid overload. She should still receive the same management for fluid boluses as she is compromised but once her perfusion improves and HR comes down she should be started on 60% maintenance fluids to reduce the risk of overloading her. 60% Maintenance fluids = ((10X10kg for first 10kg = 1000) +(10 X 50kg for next 10kg = 500)) = (1500ml X 0.6) / 24 = 38ml/hr Her paediatric renal team should also be informed of her admission and may well make changes to your IV fluids plan. They will want daily weights and closely monitored fluid balance.

Conclusion

• IV fluid prescriptions are different in paediatrics to adults.
• When a child presents unwell think carefully about whether they need cannulating and IV fluids or whether you could offer oral fluids and observe for a period of time.
• Fluid boluses should be prescribed and given in aliquots of 10ml/kg and you should reassess your patient after every fluid bolus. Once you have reached a volume of 40ml/kg you should be calling for help
• Maintenance fluids should be calculated using the Holliday-Segar formula, but consider reducing this if there is a background of heart failure, renal failure, hepatic failure or raised intracranial pressure.
• The preffer type of IV fluids for use in paediatrics is a balanced isotonic solution, e.g. Plasma-lyte 148, with 5% dextrose. However there is insufficient evidence to suggest this is far superior to 0.9% saline.
• Children on IV fluids should be reassessed at least every 24 hours to evaluate the need for IV fluids, review fluid balance and they should have daily U&Es.

Bibliography

1. Holliday MA, Segar WE, “The Maintenance Need for Water in Parenteral Fluid Therapy”, Paediatrics, pp823-832, 1957
2. Maitland K et al. “Mortality after Fluid Bolus in African Children with Severe Infection”, New England Journal of Medicine pp2483-2495, 2011
3. Rudloff E, Hopper K, “Crystalloid and Colloid Compositions and Their Impact”, Frontiers, 2021
4. Brossier DW et al, “ESPNIC clinical practice guidelines: intravenous maintenance fluid therapy in acute and critically ill children- a systematic review and meta-analysis” Intensive Care Medicine pp1691-1708, 2022
5. Weiss SL et al. “PRagMatic Pediatric Trial of Balanced vs nOrmaL Saline FlUid in Sepsis: study protocol for the PRoMPT BOLUS randomized interventional trial”, Trials pp776, 2021

Written and edited by Dr Bex Evans, paediatric registrar