Assessment of thermal response, cardiorespiratory parameters and post-operative analgesia in dogs undergoing ovariohysterectomy with different combinations of epidural analgesia and isoflurane

This study aimed to evaluate the thermal response of the eyelids and lacrimal gland of the left eye (LETG) through infrared thermography (IRT), cardiorespiratory parameters, and their association with nociception and pain in bitches undergoing elective ovariohysterectomy (OVH) anesthetized with isoflurane and epidural analgesia. Twenty-one healthy bitches of different breeds were randomized into three groups receiving epidural blocks: GL (n=7), lidocaine (2 mg Kg-1); GLF (n=7), lidocaine (2 mg Kg-1) and fentanyl (3 µg Kg-1); and GLM (n=7), lidocaine (2 mg Kg-1) with morphine (0.1 mg Kg-1). IRT and cardiorespiratory parameters were evaluated at baseline (Ebasal), thirty minutes before anesthetic premedication, and at different surgical events: first incision (EInc), ligature and section of the left (ELoV), and right (ERoV) ovarian pedicle, ligature, and re-section of the cervix (EUt), and skin suture (ESut). The assessment of acute pain in the immediate post-operative period was registered at E1h, E2h, and E3h using IRT, the Dynamic Interactive Visual Analogic Scale (DIVAS), and the University of Melbourne Pain Scale (UMPS) scales. The results showed a statistically significant decrease in the lower eyelid surface temperature (LELT) during EInc for GL (32.9°C ± 0.62), in comparison to GLF (34.2°C ± 0.62) and GLM (35.3°C ± 0.62) (P = 0.006). Regarding LETG, a significant increase (P = 0.03) in the IRT of Ebasal (36.8°C ± 0.63) and EInc (36.1°C ± 0.63) for GLM was observed in comparison to the thermographic values for both perioperative events and groups. The GLM showed a significant decrease in IRT values of ERoV at E3h in the upper and lower eyelids (P = 0.03 and P = 0.01, respectively). A progressive and significant reduction of the IRT values of LETG was also recorded in GLM, with differences in ERoV (35.2 °C ± 0.63) (P = 0.02) and E3h (35.3 °C ± 0.63) (P = 0.01). The cardiovascular parameters (SAP, DAP, and MAP) did not differ between treatments, but in GL, there was a significant difference (P = 0.01) during EInc and ESut, compared to Ebasal. In the body temperature, EInc and ESut gradually decreased in all treatment groups (P = 0.01). In conclusion, hemodynamic and cardiorespiratory stability was associated with IRT readings and the absence of nociception. Changes in superficial temperature in the immediate post-operative period were lessened using isoflurane and epidural analgesia of lidocaine alone or in combination with pure opioids. These findings were clinically validated to the DIVAS and UMPS acute pain assessment scales.