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Chart to Calculate Patient Daily Fluid Needs

If an animal patient will not, or cannot, consume and/or utilize its daily water needs, dehydration will result. Deficiencies in daily water needs are cumulative so, for instance, if a patient has a need for 1.5 liters per day and the patient has not consumed any water for 3 days, the total water deficit is: 1.5 L/day X 3 days = a total deficit of 4.5 L.

Daily water needs are based on many factors which begin with a baseline amount of water. The baseline daily water needs can be calculated based on body weight (in Kilograms) to the three quarter power (Kg 3/4 ) which is also “metabolic body size”. The results of these calculations can be converted to a chart format for ease of use. The following chart can be used to quickly and accurately determine baseline daily water needs in any patient weighing 1 to 1000 Kg.

How to use this chart

Weigh the animal patient, or better yet use a recent known weight before the onset of illness, in Kg (weight in pounds/2.2 = Kg). In the example shown, the patient weighs 15 Kg (33 Lb). On the horizontal axis of the chart create a vertical line up at the 15 Kg point until it reaches the slanted line. Then create a horizontal line from that point to the left until it reaches the vertical axis of the chart. Read the daily fluid needs on the vertical axis at this point. In the example the Baseline Daily Water need is 1370 ml.

Print and use this chart

You are welcome to print out and post for later use the chart and examples (in .pdf format) by selecting a chart or the chart example and selecting “Print”

It is important to keep in mind this is only a baseline of daily water needs. Many factors can alter this base calculation up or down. Kidney failure may decrease or increase daily water needs. Fever, hyperventilation, exertion, diarrhea, vomiting, severe damage to the skin (as in burns), sequestration (pooling) of water in body cavities or intestines are examples of conditions which may increase, sometimes dramatically, total daily water needs. The estimated or measured loss or retention of water needs to be estimated for a 24 hour period and the result added to or subtracted from the baseline water needs. Water needs should be recalculated and adjusted daily, or more often, if necessary.

Water needs can be met by administering water by stomach tube if the digestive tract is functioning sufficiently, by subcutaneous administration, enema into the rectum and large intestine, by intra-osseous infusion, or preferably by intravenous infusion.