When conducting surgery with anesthesia on small animals in a clinical setting, special care must be taken to maintain the animal’s body temperature at its optimum level. Adequate body temperature is important not only for the comfort of the animal and physiological well-being, but to minimize risks from anesthesia and encourage recovery from the surgery.
Because of their smaller body size, rodents have a greater surface-to-body weight ratio, so they tend to lose heat rapidly. Mice and rats are especially prone to losing body heat through the tail, ears, and feet, which can significantly decrease the core and surface body temperature of the animal. Placing an animal under anesthesia increases these qualities.
When exposed to anesthesia during surgery, animals frequently become hypothermic due to the inhalation of cold gases, having body cavities exposed to the open air, and the inability of an animal’s body to use normal mechanisms and behaviors to regulate its own heat.
If an animal enters hypothermia during surgery, the results can be catastrophic. Hypothermia depresses all physiological functions, including respiration and cardiac function, and can lead to death.
In a study by E. Dardai and James E. Heavner, it was determined that maintaining a constant temperature minimizes the cardiovascular and respiratory disturbances in laboratory animals.
The study compared the respiratory and cardiovascular effects of three different types of anesthesia—halothane, isoflurane, and enflurane—on temperature controlled and uncontrolled rats. The study found that arterial pressure, heart rate and respiratory rate were depressed significantly in rats whose body temperature was not controlled.
Avoiding hypothermia is also important post-surgery. Hypothermia slows metabolism, which means the animal’s body can take longer to excrete anesthetic drugs, leading to an extended anesthesia period and increasing the risk of complications. When an animal is warm, body metabolism increases, enabling the body to more quickly eliminate anesthetics and toxins, which leads to a faster recovery.
Hyperthermia, while also problematic, is less common. It can occur in rodents with a genetic predisposition or when excessive heat sources are present during surgery, and can lead to dehydration, muscle rigidity, high fever, seizures, and cardiopulmonary failure.
To maintain optimal body temperature, the temperature of the animals should be monitored frequently using a thermometer during surgical procedures and recovery. Other methods of maintaining the right temperature include:
- Increasing the temperature of the surgical room/procedure room
- Placing a thermal blanket (such as a recirculating warm water or infrared heating pad) between the animal and heat-absorbing surfaces
- Minimizing organ exposure from body cavities during surgery
- Placing the animal on a warming blanket or in a temperature supported cage
- Administering warmed subcutaneous or intraperitoneal fluids intra- and/or postoperatively
- Using bedding during post-surgical recovery to provide thermal insulation
