A comparison of rectal versus fetlock temperatures in dorsally recumbent horses during general anesthesia

Abstract

Objective: To investigate the effect of isoflurane anesthesia on thermoregulation and peripheral heat loss in dorsally recumbent horses.

Study design: Prospective, clinical study.

Animals: Seven adult horses (2.6 ± 1.5 years old, 455 ± 70.2 kg).

Methods: Horses underwent elective surgical procedures in dorsal recumbency under general anesthesia (GA) maintained with isoflurane in oxygen. Rectal (T_R), intranasal (T_N) and fetlock surface temperatures (T_F) were measured every 10 minutes for the first 80 minutes following induction of GA. Room temperature (T_RO) was monitored during the study. Statistical analysis to determine differences between temperature measurement sites and techniques (T_R, T_N and T_F), and differences over time were completed using a mixed-effects model with Tukey's multiple comparison or Dunnett's multiple comparison testing where appropriate. Significance was set at p < 0.05.

Results: Following induction of anesthesia, T_F was significantly increased compared with baseline (0 minutes) from 40 to 80 minutes (p < 0.01). No significant differences were detected in T_R and T_N at any time point compared with baseline (p > 0.05). T_F was significantly lower than T_N (p < 0.02) at all time points and T_R from times 0 to 70 minutes (p < 0.04). There were no significant differences between T_R and T_N at any time (p > 0.05).

Conclusions: In horses undergoing isoflurane GA, T_F increased, indicating peripheral heat loss likely because of vasodilation, whereas T_R showed a clinically relevant decrease over time. These findings are suggestive of body heat redistribution during GA in horses in dorsal recumbency. Thermographic imaging of the peripheral limbs in combination with T_R and T_N monitoring allowed for recognition of peripheral heat redistribution in anesthetized horses.

Clinical relevance: Anesthetized horses experience peripheral heat loss through their extremities as a result of vasodilation. Mitigating peripheral heat loss may improve thermoregulation and reduce hypothermic complications in anesthetized horses.

Keywords: horse anesthesia; peripheral temperature; rectal temperature; temperature gradient; thermographic imaging; thermoregulation.