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.