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 approximately 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 degrees C (102.0 +/- 1 degrees 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 degrees C (104.2 degrees F) and self limiting.