Example fluid therapy calculations

VM 551
Cheryl R Dhein DVM MS

50 pound neutered male mixed breed dog
6 years old
history of vomiting for 4 days
5% dehydrated based on physical findings

Rehydration

50 lb X 0.05= 2.5 lb deficit
2.5 lb X 500ml/lb =1,250ml
GI loss "isotonic" (loss of H₂0 & electrolytes in similar proportions to ECF)
Fluid choice: like ECF = LRS
Recommended to replace 80% of the deficit in the first 24 hours (80% of 1,250 = 1,000ml)

Maintenance

renal ~ 15 ml/lb/day (12 -20 ml/lb/day)
50lb x 15ml/lb = 750ml/ day ("isotonic" loss, LRS)

insensible ~10 ml/lb/ 24 hours (10 - 15 ml/lb/day)
50 lb x 10 ml/lb= 500ml/ day (hypotonic loss, D5W)

Initial Calculations

First 24 hrs: 80% (1,250ml)(rehydration) + 750ml(renal) + 500ml(insensible) = 2,250ml
Divide by # hours available to deliver fluids (example 12 hours)
2,250ml ÷ 12 hours = 188 ml/hour

Ideally the fluid choices would be 1,000ml (LRS rehydration) + 750ml (LRS- renal) + 500ml (5% dextrose-insensible)
but... I will usually use only LRS the first day.

Recalculations based on ongoing losses

The patient vomits twice during the first 6 hours of fluid therapy an ~ volume of 300ml.
(GI losses "isotonic", replace with LRS)
Recalculate fluid rate to include ongoing losses
1/2 of fluids left to give (1,125ml) plus 300ml = 1,425 ÷ 6 hrs = 238 ml/hr

Several times daily, the patient is evaluated and fluid plan is adjusted based on your assessment of the patient.
Subsequent to the first day, a maintenance-type fluid is given.

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This page was last edited on November 27, 2002 by CRD
visits to this page since November 29, 1999