Intravenous Fluids



Notes

  • Whenever possible the enteral route should be used for fluids
  • These guidelines only apply to children (beyond the newborn period) who cannot receive enteral fluids
  • The safe use of IV fluid therapy in children requires accurate prescribing of fluid and careful monitoring
  • Always check orders that you have written, and ensure that you double check on orders written by other staff when you take over the child's care
  • Iincorrectly prescribed or administered fluids are potentially very dangerous. More adverse events are described from fluid administration than for any other individual drug. If you have any doubt about a child's fluid orders - ask a senior doctor
  • There is often confusion about the difference between oral and IV fluid requirements for young infants. The water requirement is identical for both routes of administration. The relatively low energy density of milk means that infants need 150-200mls/kg/day to obtain adequate nutrition. That is why they pass more dilute urine than older children

Well children with normal hydration

How much fluid?

Pt weight mls/day mls/hour
3 to 10kg 100 x wt 4 x wt
10 - 20kg 1000 plus  50 x (wt-10) 40 plus  2 x (wt-10)
>20kg 1500 plus  20 x (wt-20) 60 plus  1 x (wt-20)

Well children with normal hydration but no oral intake require an amount of fluid that is often termed "maintenance".

Maintenance fluid is that volume of daily fluid intake which replaces the insensible losses (from breathing, through the skin, and in the stool), and at the same time allows excretion of the daily production of excess solute load (urea, creatinine, electrolytes etc) in a volume of urine that is of an osmolarity similar to plasma.

A child’s maintenance fluid requirement decreases proportionately with increasing age (and weight). The following calculations approximate the maintenance fluid requirement of well children according to weight in kg.

You might recognise these as the "100, 50, 20" and "4,2,1" rules of thumb. They are not quite equivalent because there are 24 and not 25 hours in a day, but for practical purposes either calculation is fine.

The following calculator or table may be used to estimate maintenance fluid requirements.

Wt (kg) 4 6 8 10 12 14 16 20 30 40 50 60 70
ml/hr 16 24 32 40 44 48 52 60 70 80 90 100 100

100mls/hour (2500mls/day) is the normal maximum amount.


Which Fluid?

The recommended fluid as maintenance for well children with normal hydration is:0.45% NaCl with 5% Glucose + 20mmol KCl / litre

Do not use this solution:

  • If the serum potassium is elevated
  • For volume resuscitation
  • If the serum sodium is low
  • For replacement of fluid deficit in dehydrated children

Unwell children (± abnormal hydration)

How much Fluid?

Firstly administer an Initial bolus of fluid to correct hypovolaemia ; Then Maintenance plus Deficit plus Ongoing losses

Hypovolaemia.

Give boluses of 10-20ml/kg of normal (0.9%) saline, which may be repeated.

Do not include this fluid volume in any subsequent calculations

Unwell children (± abnormal hydration) require maintenance fluids. They may also need extra to replace fluid deficit due to dehydration, and possibly more fluid to replace abnormal ongoing losses (eg from drain sites).

Maintenance

  • Less if in a basal state (ie very inactive lying in bed). -25%
  • Less in children on mechanical ventilation with humidified gases. -25%
  • More in children with fever. +10 to 20%
  • Less in children with excessive secretion of Antidiuretic Hormone (ADH)
eg pneumonia, meningitis Varies (-20 to 40%)
  • More if unable to concentrate urine (eg some renal diseases, Diabetes insipidus) Varies

Deficit

A child's water deficit in mls can be calculated following an estimation of the degree of dehydration expressed as % of body weight. (e.g. a 10kg child who is 5% dehydrated has a water deficit of 500mls)
Precise calculation of water deficit due to dehydration using clinical signs is usually inaccurate. The best method relies on the difference between the current body weight and the immediate pre-morbid weight. Unfortunately the latter is often unavailable.
Clinical signs of dehydration give only an approximation of the deficit.
In mild-moderate dehydration the useful clinical signs include:
• Cool pale peripheries with prolonged capillary return time.
• Decreased skin turgor
• Deep (acidotic) breathing
• Increased thirst

Other signs including irritability/lethargy, sunken eyes, dry mucus membranes, and sunken fontanelle are commonly mentioned but have not been shown to be useful in mild-moderate dehydration. They may appear in more severe cases.
Clinically the child may be placed in one of three categories:

Mild/No dehydration (<4%)

- No clinical signs

Moderate dehydration (4-6%)

- Some physical signs

Severe dehydration (>7%)

- Multiple physical signs present and child may also have acidosis and hypotension

The deficit is replaced over a time period that varies according to the child's condition.
Replacement may be rapid in most cases of gastroenteritis (although usually this is best achieved by oral or nasogastric fluids), but should be slower in diabetic ketoacidosis and meningitis, and much slower in states of hypernatraemia (aim to rehydrate over 48 hours, the serum sodium should not fall by >1mmol/litre/hour).

Ongoing losses (eg from drains)

These are best measured and replaced - calculations may be based on each previous hour, or each 4 hour period depending on the situation. Normal (0.9%) saline may be sufficient, or 5% albumin may be used if sufficient protein is being lost to lower the serum albumin. See Burns guideline for additional losses from burns.

Which Fluid? (in the unwell child)

0.18% NaCl with 4% glucose with KCl 20mmol/L is NOT the appropriate initial fluid for unwell children.

Three good fluid solutions for sick children include:

  • 0.9% Saline is suitable for initial volume resuscitation in hypovolaemia and ongoing fluid therapy in older children with normal blood glucose
  • 0.9% Saline with 5% Glucose or 0.45% Saline with 5% are suitable for ongoing fluid therapy in infants, or older children with low blood glucose
  • Which you use is a matter of individual circumstances, the patient's age, serum sodium and glucose
  • If in doubt, you will not go far wrong if you use 0.45% Saline with 5% Glucose with potassium chloride 20mmol/L in most circumstances

Monitoring

  • All children on IV fluids should be weighed prior to the commencement of therapy, 6 - 8 hours after the infusion is commenced, and then at least daily. Ensure you request this on the treatment orders
  • All children on IV fluids should have serum electrolytes and glucose checked before commencing the infusion (typically when the IV is placed) and again within 24 hours if IV therapy is to continue
  • For sick children, check the electrolytes and glucose 4-6 hours after commencing, and then according to results and the clinical situation but at least daily
  • Pay particular attention to the serum sodium on measures of electrolytes.
    • If <135mmol/L (or falling significantly on repeat measures)
    • If >145mmol/L (or rising significantly on repeat measures)

Special Fluids

Outside the newborn period, do not use these fluids apart from exceptional circumstances and check the serum sodium regularly

10% Dextrose

  • Used in ICU for patients under 12 months (with 0.45% saline).
  • Sometimes used by infusion in neonates and children with metabolic disorders.
  • Check blood glucose regularly

15-20% Dextrose

  • Very occasionally used by infusion in children with metabolic disorders.
  • Check blood glucose regularly

25% and 50% Dextrose

  • Only used by bolus, or low volume (1-2mls/hour) infusion to correct hypoglycaemia
  • Should not be used outside of ICU & NNU, except for some metabolic patients.
  • Check with consultant before prescribing.
  • Check blood glucose frequently

Newborns

Newborn infants (especially those born pre-term) have greatly increased water loss via the skin. See Guideline on Neonatal Fluid Requirements.

There is often confusion about the difference between oral and IV fluid requirements for young infants. The water requirement is identical for both routes of administration.The relatively low energy density of milk means that infants need 150-200mls/kg/day to obtain adequate nutrition. That is why they pass more dilute urine than older children.


Content by Prof. Ronán O' Sullivan. Last review Dr ÍOS 16/06/21.