Assessing the Severity of Dehydration in Calves With Diarrhea
TAKE HOME MESSAGE
- The extent of eyeball recession into the orbit ("sunken eyes") is the best indicator of dehydration in calves with diarrhea.
- Skin pliability (as assessed by skin tent duration) in the neck region is the second best indicator of dehydration in calves with diarrhea.
- Intravenous fluids should be administered to dehydrated calves
when the eyes are recessed > 1/6" (4 mm) into the skull or the neck
skin tent duration is > 6 seconds. If the calf is less dehydrated
than this, administration of appropriate volumes of oral electrolyte
fluids should be sufficient to correct dehydration, and intravenous
fluids are not needed.
Neonatal diarrhea is a major source of economic loss to the cattle industry, being the leading cause of death in dairy and beef calves. Financial losses occur not only from mortality, but also from the cost of medication and labor needed to treat sick calves. One of the major goals of treatment is correction of dehydration, through administration of oral electrolyte solutions and/or intravenous fluids.
Dehydration in calves with diarrhea is accompanied by a large decrease in extracellular fluid volume and a smaller increase in intracellular fluid volume. During diarrhea there is increased intestinal loss of sodium, potassium, chloride, and bicarbonate, with a concurrent decrease in plasma sodium concentration, resulting in hypoosmotic extracellular (plasma and interstitial) fluid. Extracellular hypoosmolality causes free water to move from the extracellular to intracellular space, thereby increasing intracellular fluid volume. Because water loss is from the extracellular space, clinical estimation of extracellular fluid volume is a valuable and commonly used method to guide fluid therapy in dehydrated calves with diarrhea. Empirical guidelines have been widely used to evaluate hydration status in calves; however, experimental data to support the accuracy of these guidelines, or other similar guidelines, are unavailable.
Treatment of dehydrated calves requires rapid replacement of the existing fluid deficit and provision of additional fluid for ongoing fluid loss. An important determinant of treatment success is therefore an accurate assessment of the fluid deficit. This is usually derived by estimating the severity of dehydration in each calf. The extent of dehydration can be assessed by examining the eye position in the orbit, skin pliability, mucous membrane moistness and color, and capillary refill time, serial measurement of hematocrit, hemoglobin, and plasma protein concentration, determining mean central venous pressure, and measuring the temperature of the extremities. These reflect plasma and/or interstitial fluid volume. A decrease in interstitial volume is indicated by eyeball recession into the orbit, decreased skin pliability (prolonged skin tent duration) and dry mucous membranes. Because it was unknown which factors were of greatest clinical utility in evaluating hydration status, the major purpose of this study was to determine and compare the accuracy of factors suspected to be useful in evaluating hydration status in neonatal calves. A second goal was to develop guidelines for assessing degree of dehydration that were based on experimental data rather than empiric observation.
MATERIALS AND METHODS
Dehydration and diarrhea were induced in 15 neonatal male dairy calves by administration of diuretic agents (furosemide, spironolactone, hydrochlorothiazide) and sucrose solution. Linear regression was used to examine the relationship between potentially useful factors for evaluating hydration status (extent of eyeball recession into orbit; skin tent duration on neck, thorax, upper eyelid, lower eyelid; heart rate; mean central venous pressure; fetlock temperature; rectal-fetlock temperature difference; hematocrit, hemoglobin concentration, plasma protein concentration) and degree of dehydration, as determined by change in body weight.
RESULTS AND DISCUSSION
The administration of sucrose and three diuretic agents resulted in profuse watery diarrhea, moderate dehydration and an average weight loss of 3.9 kg, equivalent to 10 percent of initial body weight, in 24 hours. At 48 hours the average body weight loss was 5.4 kg, corresponding to 14 percent dehydration. Calves had clinical evidence of severe dehydration at that time, as measured by eyeball recession into orbit (mean 7.7 mm = 1/3"), prolonged neck and thoracic skin tent duration (> 6 seconds for all calves), and increased rectal-fetlock temperature difference (12-14oC).
The best predictors of degree of dehydration were extent of eyeball recession into orbit, skin pliability on neck and thorax, and plasma protein concentration.
The findings of this study indicate that clinical assessment of dehydration in neonatal calves is best done utilizing extent of eyeball recession into the orbit and skin pliability in the lateral neck region. Eye position and skin pliability have been widely used to guide assessment of hydration status. Because the position of the eye within the orbit is dependent on body fat stores as well as hydration status, and dehydration in the study reported here was acute rather than chronic, eye position may not be an accurate indicator of hydration status in calves with chronic diarrhea. We therefore suggest that in calves with cachexia or chronic diarrhea, skin pliability in the neck region would be the most reliable indicator of hydration status.
Skin pliability in calves has been most commonly assessed by evaluating skin tent duration in the eyelid or lateral neck region. The results of the study reported here suggest that eyelid skin pliability is inferior to neck and thoracic skin pliability for evaluating hydration status in dehydrated calves. Skin pliability reflects the elastic properties of skin and subcutaneous tissue, and is therefore dependent upon interstitial volume and fat in the skin and subcutaneous tissue, location on the body, position of the animal (e.g. standing, recumbent), and age, with old animals having reduced skin pliability because of a primary decrease in tissue elasticity.