Modification of a Large Marine Mammal Restraint Cage to Control Body Temperature During General Anesthesia
Several research protocols for Steller sea lions (Eumetopias jubatus) at the Alaska SeaLife Center require periodic long-term (2–3 hours) isoflurane anesthesia (Aerrane, Fort Dodge Animal Health, Fort Dodge, IA, USA). Despite the large body mass of these animals (150–380 kg), hypothermia was frequently observed during these anesthetic events, even when the procedures were conducted indoors.
Hypothermia is defined in most mammals as a core body temperature less than 35°C (95°F).3 It has been recognized as a common side effect of general anesthesia in man and animals. Severe hypothermia (core temperature less than 32°C or 90°F) is associated with reductions in heart rate, blood pressure, peripheral vascular resistance, cardiac output, and central venous pressure. These cardiovascular changes can result in long-term cellular damage, particularly in metabolically active tissue such as the liver and brain.4 Anesthetic recovery is slowed because of impaired drug metabolism.2 Prolonged hypothermia can result in metabolic acidosis and hyperkalemia leading to cardiac arrhythmias.1
Our facilities department added a simple grid of 3/8 inch soft copper tubing to the underside of the stainless-steel squeeze cage used to hold the animals. The grid was connected by means of flair fittings and adapters to standard brass hose couplings. Removable structural foam blocks were placed below the grid to insulate the area adjacent to the cage floor. Tap water is run through a garden hose into the system to warm the metal floor of the cage during anesthetic induction and continued through recovery. Body temperature drops have been consistently less severe and, in some cases, have even been reversed during these long procedures, preventing complications and improving recovery. If hyperthermia were encountered, cooling could be accomplished by running cold water through the same system.
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4. Williams TM, Davis RW, McBain JM, Tuomi PA, Wilson RK, McCormick CR, Donoghue S. Diagnosing and treating common clinical disorders of oiled sea otters. In: Williams TM, Davis RW, eds. Emergency Care and Rehabilitation of Oiled Sea Otters. Fairbanks, AK: UAA Press; 1995:59–94.