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Effects of opioids and anesthetic drugs on body temperature in cats


Lysa Posner, Department of Molecular and Biomedical Sciences, North Carolina State College of Veterinary Medicine, 4700 Hillsborough St, Raleigh, NC 27606, USA. E-mail:


Objective  To determine which class of opioid alone or in conjunction with other anesthetic drugs causes post-anesthetic hyperthermia in cats.

Study design  Prospective, randomized, crossover study.

Animals  Eight adult, healthy, cats (four spayed females and four castrated males weighing 3.8 ± 0.6 kg).

Methods  Each cat was instrumented with a wireless thermistor in the abdominal cavity. Temperature in all phases was recorded every 5 minutes for 5 hours. Population body temperature (PBT) was recorded for ∼8 days. Baseline body temperature is the final 24 hours of the PBT. All injectable drugs were given intramuscularly. The cats were administered drugs in four phases: 1) hydromorphone (H) 0.05, 0.1, or 0.2 mg kg−1; 2) morphine (M) (0.5 mg kg−1), buprenorphine (BUP) (0.02 mg kg−1), or butorphanol (BUT) (0.2 mg kg−1); 3) ketamine (K) (5 mg kg−1) or ketamine (5 mg kg−1) plus hydromorphone (0.1 mg kg−1) (KH); 4) isoflurane in oxygen for 1 hour. Fifteen minutes prior to inhalant anesthetic, cats received either no premed (I), hydromorphone (0.1 mg kg−1) (IH), or hydromorphone (0.1 mg kg−1) plus ketamine (5 mg kg−1) (IHK).

Results  Mean PBT for all unmedicated cats was 38.9 ± 0.6 °C (102.0 ± 1 °F). The temperature of cats administered all doses of hydromorphone increased from baseline (p < 0.03) All four opioids (H, M, BUP and BUT) studied increased body temperature compared with baseline (p < 0.005). A significant difference was observed between baseline temperature values and those in treatment KH (p < 0.03). Following recovery from anesthesia, temperature in treatments IH and IHK was different from baseline (p < 0.002).

Conclusions and clinical relevance  All of the opioids tested, alone or in combination with ketamine or isoflurane, caused an increase in body temperature. The increase seen was mild to moderate (<40.1 °C (104.2 °F) and self limiting.