Comparison of Different Ventilatory Modalities and Inspired Oxygen Fractions in the Common Rabbit (Oryctolagus cuniculus): A Randomized Clinical Trial

Abstract: This randomized clinical trial aimed to evaluate the effects of two inspired oxygen fractions (FiO₂: 40% and 60%) combined with different ventilatory modalities—spontaneous ventilation (SV, T0), volume-controlled ventilation (VCV, T1), and pressure-controlled ventilation (PCV, T2)—on cardiopulmonary and metabolic parameters in anesthetized rabbits. Sixteen healthy male New Zealand White rabbits were randomly assigned to two groups (G0.4 and G0.6). Animals were premedicated with ketamine (15 mg/kg), midazolam (2 mg/kg), and morphine (2 mg/kg), and general anesthesia was induced via face mask with isoflurane at 4.0%, diluted in oxygen at either 40% or 60%, according to group allocation. Physiological variables, blood gas analyses, and indirect calorimetry data were collected at multiple time points. Regarding blood gas variables, arterial oxygen partial pressure (PaO₂) increased progressively with higher inspired oxygen fractions, showing statistically significant differences between groups at T0, T1, and T2 (p =0.003, 0.001, and 0.001, respectively), while oxygenation indices remained within clinically acceptable ranges. Controlled ventilation was associated with improved oxygenation efficiency in both FiO₂ groups. Oxygen consumption (VO₂) and carbon dioxide production (VCO₂) progressively declined throughout anesthesia, whereas the respiratory quotient (RQ) range of approximately 0.8-0.9, indicating reduced metabolic demand and preserved substrate utilization. No clinically relevant differences were observed in heart rate, mean arterial pressure, or arterial carbon dioxide pressure (PaCO₂) between groups. These findings indicate that both 40% and 60% FiO₂ are safe and effective when combined with appropriate ventilatory strategies in healthy anesthetized rabbits, supporting individualized oxygen titration based on ventilation mode and physiological monitoring.