Respostas fisiológicas e sedativas em Phrynops geoffroanus (SCHWEIGGER, 1812): comparação de dois protocoloas anestésicos com Dexmedetomidina e Cetamina

Abstract

Anesthesia in chelonians presents specific challenges due to the absence of a diaphragm, the restriction of the coelomic cavity by the carapace, and the ability to tolerate prolonged apnea, factors that can compromise the effectiveness of inhalational anesthetics. Therefore, injectable protocols have been extensively investigated for safety and efficacy. The Geoffroy's sidenecked turtle (Phrynops geoffroanus) is a semi-aquatic and diurnal species, widely distributed in South America, recognized as an environmental bioindicator and adaptable to urbanized and hypoxic environments. As reptile metabolism is temperature-dependent, the animals were kept at 28 °C (within the recommended range of 24–32 °C) to ensure adequate physiological and pharmacokinetic stability. This study evaluated the intramuscular combination of dexmedetomidine and ketamine, with reversal by atipamezole, in 25 adult P. geoffroanus. The animals were divided into two groups: HG (dexmedetomidine 0.1 mg/kg + ketamine 10 mg/kg; n = 13) and LG (dexmedetomidine 0.05 mg/kg + ketamine 10 mg/kg; n = 12). Heart rate (HR), respiratory rate (RR), cloacal temperature (CT), behavioral reflexes, and venous blood gases were evaluated at baseline, during chemical restraint, and during recovery. There were no significant differences between the groups at the same time points for HR, RR, and CT, indicating physiological stability at both doses. However, compared to baseline, there were significant reductions in HR and RR, more evident in the HG group. In this group, respiratory rate decreased from 39 ± 13 (12–64) to 7 ± 12 (0–42) breaths/min between 35–45 minutes, returning to 36 ± 10 (17–56) 15 minutes after atipamezole administration. The HG group showed deeper sedation, with significant reductions in head and limb tone, righting and eyelid reflexes, spontaneous movements, and mandibular tone, while the LG group showed mild to moderate sedation. The cloacal reflex did not differ between groups. After reversal, all reflexes gradually returned without excitation, and physiological parameters approached baseline. Blood gas analysis revealed mild alkalinization, with increased pH, reduced pCO₂, and stable bicarbonate, without clinical repercussions. The protocol demonstrated rapid onset, dosedependent sedation, effective reversal, and safe recovery, making it suitable for clinical, experimental, and field use with P. geoffroanus.