Cardiff and Vale uLHB Paediatric Intensive Care Unit

The body mainly consists of fluid, the percentage of which will decrease in the first few years of life (i.e. 80% in a newborn which decreases to 60% after 1 year). Hence why the fluid requirement is depending on a patient age and weight.

The basic fluid requirement consists of insensible loss (evaporation via skin (2/3) & breathing (1/3)) + water losses (mainly urine).

There are different ways of calculating the daily fluid requirement. Rule 1 is the most used way of doing so (approved by the APLS guidelines). The second way is calculating the insensible and ongoing losses (rule 2), which may be helpful in patients with SIADH etc.

In both cases one has to adjust fluid intake for ongoing losses (i.e. diarrhoea, gastric aspirates, etc)

Body Surface Area = sq. root of (body weight (kg) x length (cm))/ 3600 or use the UKSCG chart (on hydrocortisone monograph in the bedside folder)

There are different factors that have their influence on the insensible loss as shown in the next table.

These increased insensible losses are electrolyte free.

In consideration of TPN prescribing

Consider whether total fluid requirement is to include drugs or whether volume from drugs/infusions is to be allowed in addition
If total fluid includes drugs you will need to calculate the volume left over once daily drugs/infusions have been given and prescribe the TPN to this volume. In this way the patient will get all of their nutrients
Consider the effect any potential increases in drugs/infusions throughout the day may have on the volume available for TPN. Consider prescribing a lesser amount of TPN in view of the possibility of the necessity of increasing drugs throughout the day.
NB Stability of the TPN may affect the minimum volume that can be made. The pharmacist will advise you if this is a problem.

Electrolyte requirement

These standard suggested electrolyte requirements can also be found on the back of the yellow or white TPN charts

In consideration of TPN prescribing

Consider electrolyte boluses given and drug changes made in the 24hr prior.
e.g. if patient was having large furosemide infusions the day before (+ high Potassium intake), but that is discontinued, you should adjust the TPN accordingly.

Remember: Be cautious with electrolytes added to TPN over the weekend because if the electrolytes become unsuitable (e.g. too much potassium), the only option would be to discontinue or reduce the TPN. (It's easier to put less in the TPN and top up with electrolyte infusions if needed)

Proteins (vaminolact)= 4kCal/gram (= 0.26kCal/ml)
Carbohydrates (Glucose)= 4kCal/gram (10% = 0.4kCal/ml) (= 100g/L =0.1g/ml)
Fat (intralipid 20%)= 9kCal/gram (=1.8kCal/ml), (= 0.2g/ml)

Standard suggested Nitrogen/ Glucose and Lipid requirements can be found on the back of the yellow or white TPN charts.

Considerations for TPN prescribing

If there is growth failure, there will be a difference between the actual and expected weight. In these circumstances, the mid-point between these two should be used to estimate nutritional requirements.
To promote adequate growth and body composition 200-250 kcal are required per gram of Nitrogen.
If energy needs are not fully met, then the amino acids will be used as energy instead of being available for essential functions and growth.
Although glucose intolerance is uncommon in infants, glucose should be introduced gradually.
If Glucose intolerance does occur then a slight reduction in infusion rate should be attempted as an initial measure. Occasionally it may be necessary to give insulin.
Glucose intolerance should be regarded as an early sigh of sepsis in a previously stable patient.
Rebound hypoglycaemia can occur occasionally if a high glucose rate is abruptly stopped. A stepwise reduction of glucose concentration reduces this risk.
Lipid not always! The administration of lipids to individuals with sepsis, jaundice, thrombocytopenia is much debated in the literature. For specific advice call pharmacy (number above)
Lipid will need to be administered separately (can go pheripherally)
Lipid runs over 20 hrs. (which allows clearance of the lipid emulsion from the plasma avoiding lipid accumulation and avoiding interference with haematological tests)
Other ingredients of TPN are vitamins and trace elements and these will be added to the TPN automatically.

Example 1
Patient: BW 32 kg, Length 130 cm, Urine output 2 ml/kg/h
According to Rule 1: 10x100 + 10x50 + 12x20 = 1740 ml/day
According to Rule 2: BSA = 1.07 m2 => 1.07x300 + 1.07x100 + 1.07x1440 = 1969 ml/day.
However in ITU setting urine output is measured; 1.07x300 + 1.07x100 + 2x32x24 = 1964 ml/day.

Example 2
Patient: BW 32 kg, fluid allowance 80%
Drugs: Noradrenaline 0.7ml/hr, Midazolam 1ml/hr, Morphine 1ml/hr, Total oral drugs (antibiotics etc) 150ml/day
Total daily fluid allowance=(10x100 + 10x50 + 12x20) x 0.8 = 1740 x 0.8 = 1392 ml/day
Total drugs= 0.7x24 + 1x24 + 1x24 + 150 = 214.8 ml/day
Total maximum TPN volume = 1392 – 214.8 = 1177.2 ml/day
So prescribe TPN volume of 1000m/day (the rest of the fluid allowance will have to be prescribed separately on the chart as Dextrose or1/2-1/2 or Normal Saline), so that there is room to increase Noradrenaline and add in other inotropes/drugs as necessary.

Example 3

Patient: BW 32 kg
Fluid allowance: 80%
Drugs: Noradrenaline 0.7ml/hr, Midazolam 1ml/hr, Morphine 1ml/hr, Total oral drugs (antibiotics etc) 150ml/day

Total daily fluid allowance= (10x100 + 10x50 + 12x20) x 0.8 = 1740 x 0.8 = 1392 ml/day
Total drugs = 0.7x24 + 1x24 + 1x24 + 150 = 214.8 ml/day
Total maximum TPN volume = 1392 – 214.8 = 1177.2 ml/day
So prescribe TPN volume of 1000m/day (see above in fluid requirement section for further explanation) & Dextrose5%-NaCl0.45% for 177.2ml/day (= 4.8ml/hr)

TPN Prescription chart (day 1):

So prescribe on PICU daily fluid chart: