One of the most inexpensive monitoring devices in any animal clinic or hospital is the trusty thermometer. It can give us valuable information in just a few seconds. There are three common types of thermometers found in general practice: rectal, esophageal and tympanic. I am sure we are all familiar with telling clients over the phone that if they wish to try and take their pets temperature, the normal range is 100.5 to 102.5, use an infant rectal thermometer and lube well. Any deviation above or below this range should be of concern. Oh, and, proceed cautiously!
An animal’s first response to cold conditions is to decrease their exposed surface area usually by curling up in a little ball. If they continue to be chilled the body responds with piloerection and peripheral vasoconstriction. As the body continues to lose heat the animal will begin to shiver and increase its metabolic rate. Below 94ºF they lose the ability to shiver and you’ll see a decrease in heart rate (and thus a decreased cardiac output) and a decrease in blood pressure. IM and SQ administered drugs will be absorbed more slowly due to the decrease in perfusion and increased vasoconstriction. Orally administered drugs will also have a slower absorption rate due to a decrease in gut motility. The body is trying to conserve heat by drawing the blood to the organs it needs to sustain life (central nervous system, cardiovascular and kidneys) so digestive duties are not a priority.
So what is causing the hypothermia? Either the body has a decrease in heat production (trauma, cachexia, anesthesia, heart disease, immobility, impaired central thermoregulation or an endocrine disorder) or there is an increase in heat loss (environmental exposure, trauma, burn injury, immobility, anesthesia/surgery, pharmaceuticals).
On physical exam a hypothermic patient may have a dull mentation, bradycardia, possibly even an arrthymia, slow and shallow respirations, and weak to nonpalpable pulses. If the pet’s temperature is greater than 96ºF passive warming is often, but not always, enough. This entails placing them in a warm environment, covering them with a blanket and always placing insulation between the cage floor and the animal. A sheet of newspaper or a thin towel is not sufficient insulation on the floor of a cage.
If the pet’s temperature is less than 96ºF they will require active warming i.e. Bair Hugger®, recirculating warm water mats, hot water bottles, IV fluid warmers and the like. Just remember that even though you warmed the bag of IV fluids, by the time it travels down the line and reaches the pet it has invariably cooled back down to room temperature. This is especially true in small animals with slow drip rates. Instead of microwaving your bag of IV fluids to scalding in the hopes of preserving heat, try wrapping the IV fluid line around a hot water bottle close to, but never touching, the animal. Remember we want the fluids warmed, not hot.
With heat support it is very important to recheck a temperature every 30 minutes (active rewarming) to hourly until normothermic. Often times a pet’s temperature will continue to decrease with initial rewarming efforts as all that cold blood in the periphery is getting circulated into the warmer core blood. As perfusion increases so does the body temperature.
A simple thermometer and attentive monitoring is very important for our hypothermic patients. The return of the purr to a kitty or the wag of the doggy tail is a good indicator of success in increasing the comfort of our patient. So keep those thermometers close by and use them often.
What other ideas do you have for keeping patients warm both in surgery and in your treatment area?