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Assessing Patient Hydration

Veterinary nurses are often the first member of the veterinary healthcare team to assess patients.

Total Body Water

Healthy animals maintain normal fluid balance in the body from food and water intake, which compensates for ongoing fluid losses. Sick animals are unable to correct fluid loss through oral intake, which may be exacerbated by vomiting, diarrhoea, and polyuria. When total fluid loss exceeds fluid intake, dehydration occurs.


Asking unbiased, open-ended questions is an important part of the history and evaluation of hydration status for example:

How much food and water does your pet normally eat and drink?

Explain any vomiting or diarrhea episodes.

Have you noticed any changes in your pets weight?

Physical Examination

To assess a patients hydration status, examine the following:

Tenting, which is a measure of how quickly the skin returns to normal after extension, should be tested to help determine interstitial volume. Gently pull the skin at the back of the neck and evaluate how long the skin takes to return to the patients body. A slow return to normal, indicates dehydration.

Mucous membranes (gums) should be assessed for moisture. Normal mucous membranes should be moist to the touch and shiny in appearance. Tacky mucous membranes have a sticky quality and are consistent with mild dehydration. Dry mucous membranes, which often develop a dull appearance, indicate a more significant level of dehydration.

Laboratory Tests

Packed cell volume (PCV) may be used to help assess hydration and can be simply and quickly measured with a centrifuged hematocrit tube. The blood sample separates the erythrocytes, buffy coat and plasma. The percentage of erythrocytes in the sample or PCV is measured with a simple chart. The tube is carefully broken, a drop of plasma placed on the refractometer glass plate, and the cover closed. The value is obtained by looking through the eyepiece and reading the g/dL scale corresponding to the level of the horizontal line created by the plasma.

Urine specific gravity (USG) can also help assess hydration. Because USG reflects the urine concentration, an increased USG is consistent with dehydration in patients with normal renal function. A patient with compromised renal function will be unable to properly concentrate its urine and will have inappropriately diluted urine even in the face of dehydration.


Veterinary nurses frequently work with patients suspected of dehydration and should be familiar with the signs, as well as the assessments and measurements that should be used to determine the degree of dehydration.

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