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To determine whether moderate hypothermia during anesthesia significantly affects the serum concentration of transdermally delivered fentanyl and whether halothane or isoflurane affect these concentrations. Randomized cross-over experimental trial. Six mature, healthy Beagles (three males, three females) weighing 10.6 ± 0.43 kg. A 50-µg hour−1 fentanyl patch was applied 36 hours prior to anesthesia. Anesthesia was induced at time 0 ( t = 0). Each dog received four treatments: isoflurane + normothermia (ISO-NORM), isoflurane + hypothermia (ISO-HYPO), halothane + normothermia (HAL-NORM), and halothane + hypothermia (HAL-HYPO). Dogs were intubated and maintained at 1.5 times MAC. Animals in the hypothermia treatments were cooled to 35 °C during anesthesia. Serum fentanyl analysis was performed at −36, −24, −12, 0, 0.5, 1, 1.5, 2, 2.5, 3, 3.5, 4, 4.5, 5, 6, 7, 8, 9, 10, 18, and 26 hours. Direct arterial blood pressures and arterial blood gases were monitored. The mean body temperatures (±SEM) during the anesthetic period for the four treatments were: ISO-NORM = 37.7 ± 0.07 °C, ISO-HYPO = 35.8 ± 0.1 °C, HAL-NORM = 37.7 ± 0.06 °C, and HAL-HYPO = 35.8 ± 0.13 °C. The mean (±SEM) serum fentanyl concentrations (SFC) for both hypothermia treatments were significantly lower than baseline concentrations at t = 1 hour and persisted for the duration of anesthesia for the ISO-HYPO treatment but only from t = 1 to 2 hours for the HAL-HYPO treatment. Serum fentanyl concentrations returned to baseline within one hour of the end of anesthesia, regardless of body temperature. There were no significant differences between treatments for systolic or diastolic blood pressure but mean blood pressures were higher during normothermia versus hypothermia during the last hour of anesthesia. Hypothermia during inhalation anesthesia produced a significant reduction in SFC using transdermal administration and was more protracted with isoflurane than halothane anesthesia. While significant reductions in SFC occurred, the SFC were still within the range believed to confer analgesia. [ABSTRACT FROM AUTHOR]

Extracorporeal shock wave therapy is becoming increasingly used in equine practice to treat musculoskeletal disorders. Although the exact effects of extracorporeal shock waves on tissues still need to be elucidated, transient cutaneous analgesia has been observed within treated areas in humans and horses. The purpose of this study was to determine the onset, magnitude, and duration of cutaneous analgesia after non-focused extracorporeal shock wave (ESW) application by comparing the limb withdrawal reflex latency (LWRL) in treated and untreated areas on the metacarpus of horses, using a focused light source. A single treatment with non-focused ESW was applied to 3 areas over the dorsal aspect of one metacarpus in 12 horses. The LWRL was measured to assess cutaneous sensation in treated and untreated control areas of the treated metacarpus and in an untreated area on the opposite metacarpus, before and at various time points after ESW application. Most treated and control areas revealed a significant decrease in LWRL over time compared with baseline values. Although the results of our study do not suggest cutaneous analgesia after ESW application to the equine metacarpus, we advise cautious use of this treatment modality for horses in training or before competition until further research is done.