PRACTICAL TASK ONE: INFUSION RATE DETERMINATION

INTRODUCTION
Dehydration may affect an animal by varying degrees, and therefore the volume of fluid to be transfused over an established time period must be accurately predetermined. It is essential for the veterinary nurse to be aware of the clinical signs associated with the degrees of dehydration in order to be able to adjust the fluid volume accordingly.

METHOD

1. Work out the fluid requirement for maintenance.
   • 50mls/kg/24 hrs
   Maintenance requirements include both sensible losses and insensible (inevitable) losses such as panting and cutaneous losses.
2. Calculate fluid deficits according to the degree of dehydration.
   Either -
   • Body weight in kg x percentage dehydration x 10 (this gives the volume of fluid required to replace deficits in mls)

   or

   • Body weight in kg x (percentage dehydration divided by 100)

   
   This gives the volume of fluid required to replace deficits in litres
   
   Fluid deficits may also be calculated from a good history provided by the patient's owner.

   •  
     • Days of illness x (50 x body weight) PLUS
     • Days of illness + (4 x bodyweight x number of occurrences of vomiting and/or diarrhoea)

   This method gives the fluid loss in mls; divide by 1000 to convert to litres if preferred.
   It is estimated that approximately 4mls/kg of fluid is lost in each episode of vomiting or diarrhoea.
   
   Weight loss may also aid with the calculation of fluid deficits.

   •  
     • A 1kg weight loss is equivalent to the loss of 1000mls (1litre) of fluid.

   This method is not as accurate as those previously described.

3. Replace ongoing abnormal losses.
   • 4 x body weight in kg x number of occurrences of vomiting and/or diarrhoea since admission.
   This gives the total ongoing abnormal losses in mls; to convert to litres divide the total by 1000.
4. Add together maintenance requirements, fluid deficit and abnormal losses.
   This gives the total amount of fluid to be infused over 24 hours.
5. Assess the time period for infusion.
   • Acute losses should be replaced rapidly with half of the total fluid calculated to be given in the first 2 hours and the rest over the next 12-24 hours.
     (Total fluid volume divided by 2) divided by 2 again to give volume per hour
   • Chronic losses can be replaced more slowly over two 12 hour periods.
     Total fluid volume divided by 2.
   This gives the amount required in each 12 hour period.
6. Work out the infusion rate.
   

   i) Convert the number of hours in your set time period to minutes.

   ii) Divide the total fluid volume (in mls) by the number of minutes in the given time period.

   iii) Multiply the drop rate per minute of the giving set by the figure arrived at in ii).

   This gives the amount of drips per minute to be given during your first designated time period; count the drops falling into the giving set reservoir and adjust the rate as necessary.
   If a syringe driver is used, the fluid volume and infusion rate are entered allowing precise timed delivery of the fluids.
   
   IMPORTANT NOTES
   SHOCK RATE FLUID THERAPY IS GIVEN AT A FASTER RATE (60-80mls per hour; max rate 90mls/hr)
   
   PYREXIA INCREASES FLUID REQUIREMENTS BY 3 mls/Kg/°C INCREASE ABOVE NORMAL

PRACTICAL TASK TWO: INFUSION RATE EXAMPLES

INTRODUCTION
It is essential to be proficient at infusion rate calculations in practice.

QUESTION
A 4kg cat is presented suffering 6% dehydration from chronic losses. There has been no vomiting or diarrhoea and the cat's temperature is normal. The giving set to be used for fluid administration delivers fluid at a rate of 20 drops per ml. Work out the fluids required over a 12 hour period and show the rate of infusion in drips per minute.

ANSWER
Maintenance requirements
Weight of animal
4 x 50 = 200mls (per 24 hours)

Deficits
4 x 6 x 10 = 240mls (per 24 hours)

Ongoing losses
None

Total fluids required over 24 hours
200 + 240 = 440mls

Total fluids required over 12 hours
440 divided by 2 = 220mls

Minutes in 12 hour time period
60 x 12 = 720mins

Volume of fluid required per minute
220 divided by 720 = 0.31ml/min

Drip rate per minute
20 x 0.31 = 6.2 drips/min (This figure is usually rounded up to the nearest 10; so 6 drips/min)

This figure is usually rounded up to the nearest 10, so 6 drips/min.