Prescribing fluids with electrolytes – how to do it

Prescribing Fluids

• What to give?
• Start with 10% dextrose
• How much to give?
• Babies considered at risk of HIE or having HIE give 40ml/kg/day iv
• Other babies
• start at 60ml/kg/day on day 1
• 90ml/kg on day 2,
• 120ml/kg on day 3
• 150ml/kg from day 4 onwards.
• Then calculate the rate in ml/hr
• Simple: divide the calculated amount in ml/kg/day by 24 to give an hourly rate! 

 Prescribing electrolytes with your fluids

• On day 1 you generally do not add electrolytes
• Electrolytes (Sodium and Potassium) are usually prescribed from day 2 onwards with reference to daily U+Es
• Assuming normal U+Es prescribe both Sodium Chloride and Potassium Chloride at 2mmol/kg/day as additives to dextrose (or whatever your local protocol says)
• Consult your senior if you have any queries regarding prescription in relation to the latest U+Es.  Beware of omitting Sodium supplementation in hypernatraemia – it is most likely due to dehydration rather than excess sodium.

When prescribing electrolytes with your fluids bear in mind that when you calculate electrolyte requirements based on the baby weight in mmol/kg/day this amount relates to your baby’s fluid requirement for the day.  For example a 3kg baby on 90ml/kg/day of 10% dextrose on day 2 of life with Sodium and Potassium additives at 2mmol/kg/day needs 6 mmol of Sodium and 6mmol of Potassium in 270ml of 10% dextrose over 24 hours.

But since we are putting our additives into a 500ml bag of dextrose rather than the baby’s exact fluid requirement (270ml), we need to adjust the amount of electrolytes to ensure that baby gets the correct amount of electrolytes per day. (In this case 500/270x6 = 11.1mmol of Sodium and Potassium for your 500ml bag)

The simplest formula for calculating the amount of Sodium or Potassium to add to a 500ml bag of dextrose is as follows:

No. of mmols to add to bag =          Volume of bag (always 500ml)    x   mmol/kg/day requirement

                                                             Fluid requirement in ml/kg

Worked example – sodium chloride

Baby on 120 ml/kg/day.  Normal U+Es

Additive: Sodium Chloride at 2mmol/kg/day

mmols of sodium  to add to 500ml bag =  (500/120)  x 2 = 8.3 mmol Sodium Chloride

                                                                               

Follow the same steps to add Potassium Chloride