Modification of a Large Marine Mammal Restraint Cage to Control Body Temperature
Several research protocols for Steller sea lions (Eumetopias jubatus) at the Alaska SeaLife
Center require periodic long-term (2-3 hr) isoflurane anesthesia (Aerrane, Fort Dodge Animal Health, Fort Dodge, IA 50501
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.
1. Bowen TE, RF Bellamy. 1988. Emergency war surgery. Wash. D.C., U.S. Government
2. Kreeger TJ. 1999. Chemical restraint and immobilization of wild canids, In:Fowler ME, RE
Miller (eds.). Zoo and Wild Animal Medicine, 4th ed. W.B. Saunders Co., Philadelphia, Pennsylvania. Pp. 429-435.
3. Knochel JP. 1985. Disorders due to heat and cold. In: Wyngaarden, J.B. and L.H. Smith
(eds.). Cecil Textbook of Medicine. W. B. Saunders Co., Philadelphia, Pennsylvania. Pp. 845-848.
4. Williams TM, RW Davis, JM McBain, PA Tuomi, RK Wilson, CR McCormick, S Donoghue. 1995.
Diagnosing and treating common clinical disorders of oiled sea otters. In: Williams, T.M. and R.W. Davis (eds.).
Emergency Care and Rehabilitation of Oiled Sea Otters. UAA Press, Fairbanks, Alaska. Pp. 59-94.