Electroretinography in Wild Canids (Lycalopex gymnocercus and Cerdocyon thous) - Anesthetic Quality of a Multimodal Protocol

Abstract

Background: Ophthalmic parameters and diseases affecting wild animals remain poorly investigated, and electroretinography (ERG) stands out as an objective and non-invasive tool for assessing retinal function. However, its application in wild mammals relies on the use of safe and effective anesthetic protocols. The aim of this study was to evaluate the duration and anesthetic quality of the protocol employed for ERG, as well as its potential interferences with the examination and possible complications for the patient.
Cases: Nine cases of wild canids housed at the Municipal Zoo of Cachoeira do Sul were reported, in which animals were sedated for electroretinography (ERG). The intended anesthetic protocol consisted of an intramuscular (IM) combination of ketamine (8 mg·kg-¹), dexmedetomidine (3 μg·kg-¹), and midazolam (0.5 mg·kg-¹). When anesthesia was deemed superficial, rescue was performed with intravenous administration of propofol (1 mg·kg-¹) over 1 min, followed by a continuous rate infusion (CRI) at 0.1–0.3 mg·kg-¹·h-¹, in order to maintain immobility without ocular globe rotation until completion of the procedure. Parameters monitored every 5 min included heart rate (HR), respiratory rate (ƒ), electrocardiogram (ECG), rectal temperature (TR°C), oxygen saturation of hemoglobin (SpO2), systolic arterial pressure (SAP), diastolic arterial pressure (DAP), mean arterial pressure (MAP), and sedation score. At the end of the procedure, dexmedetomidine and midazolam were antagonized with intravenous atipamezole (9 μg·kg-¹) and flumazenil (0.01 mg·kg-¹), respectively.
Discussion: In this study, the estimated body weight was close to the actual weight of the patients, preventing pharmacological underdosing or overdosing. Given the irascible behavior of the animals and the lack of facilities for general anesthesia, dissociative anesthesia was chosen. Fisher’s exact test revealed no significant association between whether the administered dose was higher or lower than estimated and sedation duration longer than 30 min. The mean propofol infusion rate required to maintain an adequate anesthetic plane was 0.23 mg·kg-¹·h-¹, and only 2 animals required ocular positioning adjustments after the onset of propofol infusion. Among the monitored parameters, only rectal temperature (°C) showed statistical significance, decreasing over time as a result of propofol administration. Electrocardiographic changes were observed in 4 animals; however, no interventions were necessary, as no concurrent alterations in oxygen saturation or arterial blood pressure were detected.
Keywords: ketamine, dexmedetomidine, electroretinography, ERG, wild canid, midazolam.