Dr. Elizabeth Sheffield
Dr Emma Bellenger
DR DAVID MCCREARY
Case of the day:
You’re on night shift and your short stay resident is concerned that their 3 year-old patient has pyelonephritis. They have been vomiting continuously despite 4 mg of ondansetron. Bedside urine confirms leukocytes, nitrates, blood and ketones. On exam, the child is alert but miserable, flushed, with dry oral mucosa. They have a RR 30, SBP 100, HR 150, & CRT 2 seconds centrally. On your assessment, the child is unwell, but not shocked, so you ask the resident to commence IV benzylpenicillin 60 mg/kg and IV gentamicin 7.5 mg/kg and IV fluids.
The resident hasn’t had much paediatric experience and asks you to instruct them how best to tackle ongoing rehydration.
Why does it matter?
- I.V. fluid is a drug (ie. it has associated benefits, side effects, indications, contraindications and complications).
- It’s true what they say: kids have brains like a sponge… excessive or incorrect fluid administration (and subsequent hyponatramia) can lead to cerebral oedema, seizures and death.
- It is an evolving area of medical research and as such there can be a lack of consistency in the guidelines across states, hospitals and sometimes departments.
- The ACEM Part 2 exam is typically riddled with paediatric fluid calculation MCQs… which is why it’s good to nail down a quick strategy to answering questions that won’t cause you too much of a headache during the exam when you’re already under pressure.
Our strategy for fluid replacement can be summarised as follows:
- Treat shock.
- Replace deficit in addition to ongoing maintenance fluids over 24 to 48 hours.
- Account for ongoing losses.
🤓 We’re focusing on IV hydration in this post, but remember enteral fluids via NGT are often preferred. For more on NG fluids check out the RCH guideline here.
Generally, IV fluids are required for patients who:
- are NBM (e.g. pre-surgery)
- are failing an oral fluid challenge and won’t will not tolerate an NG tube
- have significant dehydration or shock which needs urgent correction
Which conditions should be excluded from the the standard fluid calculations?
- Diabetic Ketoacidosis
- Haemorrhage or significant trauma
- Known or suspected inborn errors of metabolism
- Renal failure
- Liver failure
- Pyloric stenosis
- Oncology Hyperhydration
- Premature children < 1 week corrected age
These conditions require specialist advice and often have their own guidelines or will involve discussion with a paediatrician.
Isotonic vs hypotonic fluids?
Avoid Hypotonic fluids such as 0.45% sodium chloride or straight 5-10% glucose without additives.
Prescribe isotonic fluids such 0.9% sodium chloride, Hartmann’s or Plasma-lyte 148 – to which we typically add 5-10% glucose.
Isotonic fluids – what’s the difference and why do we care?
It’s all about balance. Let’s compare our plasma to what’s going on in these fluids…
The main difference you should note is our serum chloride of 103 mmol/l vs the 154 mmol/l of chloride you’re getting with 0.9% saline.
Excess chloride can cause subsequent development of hyperchloraemic metabolic acidosis, which may reduce renal perfusion and cause acute kidney injury. The studies in this area are not robust enough to be conclusive at this stage. With evidence as it sits now, all 3 are acceptable fluids to administer and in ED we’re unlikely to be keeping patients long enough to give large volumes of fluid compared to in intensive care or on the paediatric ward, so our initial choice of fluid therapy has so far not been weighted to one or the other.
Which fluid do we choose for deficit replacement and maintenance therapy?
In contrast to our adult patients, with these kids we always need some glucose in the mix. The question as to whether that is 5% or 10% (or more) is a bit murky depending on how young the patient is. For exam purposes:
For children < 4 weeks corrected age: the fluid of choice is an isotonic (e.g. 0.9% chloride) + 10% glucose, +/-20 mmol/L potassium chloride
For children > 4 weeks corrected age: the suggested choice is 0.9% + 5% glucose (although Plasmalyte-148 + 5% glucose, or Hartmann’s + 5% glucose are accepted alternatives in some institutions and interchanging these can be a trick on exams).
What’s with the sugar?
Infants and children have a higher consumption of glucose per kilogram than adults. Neonates have even higher requirements still and are at greater risk of becoming hypoglycaemic, hence the requirement for 10% glucose.
Do we add potassium?
In the ED, generally not, unless the patient is hypokalaemic on their UEC.
You need some calculations for the total base amount of fluid to be given:
- Bolus (if required): 10-20ml/kg x 2-3 doses
- Deficit (if required): weight (kg) x % deficit x 10
- Maintenance: 4:2:1 rule (see below)
- Any ongoing losses
Maintenance: the 4:2:1 rule
This is a weight-based calculation for determining the general IV fluid maintenance requirement for a paediatric patient per hour.
For example – if we take our 3 year old, 14 kg patient above:
First 10 kg at 4 mls/kg/hr = 40 mls
Next 4 kg at 2 mls/kg/hr = 8 mls
… So, the total IV fluid maintenance rate is 48 mls/hr
What about the newborns?
In the first week of life, use an algorithmic rather than weight-based guide to maintenance fluid requirements:
Day 1: 60 ml/kg/day
Day 2: 90 ml/kg/day
Day 3: 120 ml/kg/day
Day 4-7: 150 ml/kg/day
☝️ Note these are per day so divide by 24 for the hourly rate
After the first week (adjusted) you can use the weight-based 4:2:1 rule to guide your starting doses.
Keep in mind there isn’t a one-sized-fits all formula for human fluid requirements. Some patients may have requirements more or less than this to maintain desired clinical end-points.
When do we use 2⁄3 maintenance?
Antidiuretic hormone (ADH) is frequently released in our unwell kids – in particular those with meningitis or pneumonia. This release of ADH means that full maintenance is often unnecessary and thus we should consider starting the maintenance fluid aspect of our calculations at a reduced (2/3rd of total calculated based on 4:2:1 rule) dose, and reassess and increase as required.
Who needs even less – ½ maintenance?
50% maintenance should be considered for:
- patients with suspected meningitis, encephalitis or head injury
- intubated and cannot tolerate enteral feeding
- hyponatraemia, discuss these patients with specialist team (PICU, endocrine)
- in whom hyponatraemia or respiratory distress worsens despite on 70% rate
- children with inborn errors of metabolism
- children on dialysis or post renal transplant (reference 1)
Thirsty for more?
We can’t really discuss IV fluids for kids without a discussion of the FEAST trial. This RCT conducted in Africa examined boluses of saline vs albumin vs no bolus. They concluded that there was increased mortality in patients receiving an IV bolus.
This was in a population of children with a high incidence of Malaria and severe anaemia, however, and probably isn’t directly applicable to an Australian paediatric population.
🤓 There’s a bit more to it than just ‘fluids are bad’, however, so drop-down for more information if you’re interested
P: Children 60d – 12y with (all three of):
- severe febrile illness
- impaired consciousness and/or respiratory distress
- impaired perfusion
Key exclusions: gastroenteritis, non-infectious causes
I: Two groups:
- Without severe hypotension: 20ml/kg normal saline or 5% albumin
- With severe hypotension: 40ml/kg normal saline or 5% albumin
- Severe hypotension = BP<50 (<12 months), <60 (1-5 yrs), <70 (>5 yrs)
🤨 Halfway protocol change alert! Increased to 40ml/kg and 60ml/kg when preliminary results were showing no difference
C: No bolus
O: Mortality at 48 hours
48 hr mortality significantly worse in bolus groups vs control: 6% (Albumin) vs 10.5% (Saline) vs 7.3% control
- RR of death saline vs control: 1.44 [95%CI 1.09-1.9, p=0.01]
In the resource-limited setting, fluid bolus significantly increased mortality of children with severe febrile illness and impaired perfusion.
🤓 Editor’s Thoughts:
This study has a couple of weaknesses preventing generalisability or application to our paediatric population and it certainly hasn’t changed my practice:
- As we mention above there was a high incidence of malaria and severe anaemia in this population. Fluid boluses without transfusion may cause more haemodilution in already anaemic patients.
- The protocol change midway is concerning. Particularly when you see the volume of boluses being tested which have then gone to show increased mortality. I don’t think any of us would be using 60ml/kg boluses in our usual practice, even for severe hypotension.
- The trial was performed in a resource limited setting with no access to PICUs.
Some clinical practice points:
- Don’t forget to factor in the fluid given with medications (antibiotics etc.). Adjust maintenance rate accordingly.
- Fluid balance should be totalled at least every 6-12 hours, this includes in the ED, particularly in times of access block.
- Unwell children should have electrolytes and glucose measured 4-6 hours after commencement of IV fluids.
- Consider whether your patient needs full, 2⁄3 or ½ maintenance
- Serial weights are the best measure of acute changes in fluid status. Weights should be “bare weight” on babies.
- Beware sodium. If it’s <135, >145 or changes >0.5 – escalate to your senior or a specialist.
If you have the time and want to test yourself, try out these examples:
Example One: A 2 week-old child born 40+3 is being admitted for suspected meningitis. He is lethargic, and rejecting breast and bottle feeding. His SBP is 70, HR 160 and RR 40, Cap refil is < 2 seconds, and he is peripherally warm. His fonatelle and eyes are sunken. Review of the Maternal Child Health record states a recent pre-morbid weight of 5000g. Bare weight in the department today is 4750g
Example One: Drop-down for the answer
- Shocked or not?
- Nope, no fluid bolus required.
- What is the deficit?
- In teeny chippers (newborn) bare weights can be relied upon to determine fluid deficit accurately.
- Based on the above weights, we have a deficit of 5% (which correlates clinically).
- Thus, deficit = (pre-morbid weight – current weight)kg x 1000 mls
- = (5 – 4.75) x 1000 = 250mls
- If replacing fluid over 48 hours:
- Thus, rate of replacement of existing deficit per hour would be: = 250mls/48 = 2mls/hour
- What is the maintenance?
- Using the 4:2:1 rule: 20mls/hour.
- Adjusting to 2/3 maintenance = 13.3mls/hour
- Rate of admin to account for maintenance fluid plus replacement of deficit over 48 hours would be: 13.3 + 5.2 = 5mls/hour.
- Ongoing losses?
- Record losses over the space of an hour and then account for those losses over the next hour.
- If child vomits once in one hour, we would presume a 5ml loss and replace this over the next hour (adjusting the rate to 23.5mls/hour for one hour before reverting back to 18.5mls.hour)
Example Two: A 7 year-old child is being admitted with suspected appendicitis. She is haemodynamically stable, with nil concern of shock or perforation. Initially assessment did not reveal any dehydration. Due to access block, she has remained in your department for the past several hours. Maintenance fluid were started 4 hours ago and during this time she has vomited 2 cups of fluid totalling 100mls. She weighs 20kg.
Example Two: Drop-Down for the Answer
- Shocked or not?
- What is the maintenance rate?
- Calculated according to 4:2:1 rule is 60mls/hour
- How does the rate change given the ongoing losses?
- Given the loss of 100mls over the past 4 hours, we would increase the rate to replace this over the next 4 hours (ie by 25mls/ hour)
- Thus rate for the next 4 hours will be 60 mls/hour of 5% dextrose saline plus an additional infusion of normal saline at 25mls/hour.
Example Three (our 14kg child from the case): Back to our 3 year-old, 14 kg child above. An hour or so later (having been unattended during this time) the nurses alert you she is now in met call criteria with RR of 42, HR 175, and a SBP of 65.
Example Three: Drop-Down for the answer
- Shocked or not?
- Yes, fluid bolus of 20mls/kg indicated.
- Second bolus can be considered if shock persists.
- What is the remaining deficit?
Following treatment and correction of shock (which is a > 10% deficit), it can be assumed that the child now has moderate dehydration, which estimated to be 5% (or 50mls/kg)
- Thus deficit = 14 x 50mls= 700mls
- Replacing deficit over 48 hours provides a rate of 14.5mls/hour
- What is the maintenance rate?
- Using 4:2:1 rule: 48mls/hour
- What is the total ongoing rate?
- 5mls/hour over the next 48 hours, whilst monitoring and adjusting for ongoing losses. (whilst monitoring and accounting for ongoing losses)
Great job, you aced it!
- The Starships Hospital guidelines on I.V. fluid administration
- The Nice guidelines on I.V. fluid therapy
- The RCH guidelines of I.V. fluid therapy
- The Queensland Children’s Hospital guidelines on I.V. fluid therapy
- Don’t Forget the Bubbles summary on the evolution in practice regarding I.V. fluid administration in Children.
- The FEAST Trial – Maitland K, Kiguli S, Opoka RO, Engoru C, Olupot-Olupot P, Akech SO, et al. Mortality after Fluid Bolus in African Children with Severe Infection. New England Journal of Medicine. 2011 Jun 30;364(26):2483–95. DOI: 10.1056/NEJMoa1101549
- The Bottom Line review of the FEAST trial
Senior Registrar, Alfred Health
Dr. Elizabeth Sheffield (BSc (Hons), MA, MA (Hons), MBChB) is a critical care and airway enthusiast from Washington, D.C., working at The Alfred Hospital in Melbourne, Australia. Lover of medical education, SIM, rural medicine and critically ill airway management in the ED, plus exploring the outdoors with her beautiful family and frequently wet dog.