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Exotic mammal anesthesia (Proceedings)

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Aug 01, 2010

The biggest concern with all exotic animals under anesthesia is hypothermia. Other main concerns include airway access, intravenous access, pain management, and hemorrhage.

Their body mass to surface area ratio is so small that they become much colder than the average small animal patient. Warming devices include heating pads, warming disks (SnuggleSafes), warm bags of fluids, warm blankets, heating lamps, and forced air warmers (Bair Huggers).

Some exotic species are very difficult to intubate, and instead of spending time attempting to intubate, a mask is used to maintain inhalant anesthesia. The specific benefits of intubation are a reduction of waste gas exposure for employees, the ability to administer positive pressure ventilation, and less bulky equipment around the patient's face. Each patient should have the options considered and a decision made about attempting intubation or not.

Many exotic animals are so small that intravenous access is very difficult to accomplish and may not be possible in some cases. Depending on the procedure and the species, it may be beneficial or even necessary. IV access during a procedure is helpful for administration of fluids, antibiotics, analgesics, and CPR drugs. Keeping IV catheters in place as long as possible after a procedure is recommended for continued administration of fluids, or to reverse anesthetic drugs if necessary. If intravenous catheterization is not possible, intraosseous catheterization may be considered. Drugs and fluids can be administered intraosseously. Care should be given when administering large volumes through this route. Subcutaneous fluid administration is another option for animals in which we are unable to get an IV catheter.

Pain management is another consideration in these species. We are limited with how much knowledge we have of certain species, and sometimes it is very difficult to assess pain status because certain species are especially good at masking their pain. Consideration should be given to drugs that are able to be reversed.

Hemorrhage is much more significant with exotic animals due to their small blood volume. For more invasive procedures, blood volumes should be calculated for each patient. Blood loss should be replaced with crystalloids (lactated Ringer's solution) at approximately 2 – 3 times the volume lost or with colloids (hetastarch or Oxyglobin) one to one with the volume lost. In some cases the clinician may want to consider having another animal of the same species ready to donate blood if needed.

Sevoflurane is our inhalant anesthetic of choice for exotic animals because it allows for rapid changes in anesthetic depth. Isoflurane is also a safe choice for inhalant anesthetic in exotic animals and less expensive than sevoflurane. Use of sevoflurane is only possible with sevoflurane compatible vaporizers.

Monitoring of exotic animals can be more difficult than in most small animals. Due to their small size, many monitors are unable to give accurate measurements and readings. We generally try to monitor HR, RR, and temperature in all animals. Electrocardiogram (ECG) can be measured by attaching clips to the skin. However, some exotic animals have very friable skin so we use gauze to pad the ECG clips or even needles through the skin with ECG clips attached to the needles. Pulse oximeters are very helpful, however often they will not read, because the pressure of the probe compresses the blood flow through the tissue at that point. Small probes are available but can sometimes be hard to obtain. Blood pressure monitoring is definitely recommended when possible. Most exotic animals are too small to make this possible. Applying a Doppler to a foot or even attaching it near the patient's heart can serve as a good heart rate monitor. Temperature should be monitored even if just occasionally throughout a procedure to facilitate appropriate warming.

The recovery period for exotic animals is especially critical. Temperature, respiratory rate, and heart rate should be monitored throughout recovery until after extubation. If recovery is prolonged, a blood glucose level should be checked in order to supplement if necessary. All exotic animals should be offered food as soon as possible once awake (procedure allowing). Fluid administration may be required during this period. Reversal of certain anesthetic drugs may allow for a smoother and quicker recovery in some cases.