Effects of Lidocaine Alone Versus Lidocaine–Dexmedetomidine Infusion on Pulmonary Gas Exchange and Respiratory Mechanics During Isoflurane Anesthesia in Horses

Dexmedetomidine improves pulmonary function in dogs and humans, but evidence in horses is scarce. This study evaluated dexmedetomidine infusion on oxygenation and respiratory mechanics in anesthetized horses. Twenty horses undergoing elective surgery were included in a prospective, non-randomized, observational study. Horses received either lidocaine alone (1.3 mg/kg over 15 min, then 3 mg/kg/hour; LIDO) or combined with dexmedetomidine (1.75 μg/kg over 15 min, then 1.75 μg/kg/hour; DL). Respiratory mechanics, gas exchange, and cardiovascular variables were recorded at baseline, post-loading, and after 30, 60, and 90 min. Data were analyzed using mixed-effects linear models with horse as a random effect and time and treatment and their interaction as fixed effects (<i>p</i> ≤ 0.05). Peak inspiratory pressure increased over time with both treatments but was lower with DL at 90 min (-1.26 mmHg, <i>p</i> = 0.046). There was no evidence that arterial oxygen pressure or oxygenation ratio improved over time with DL (<i>p</i> > 0.75). Shunt fraction did not significantly change over time or between treatments (Wald χ² = 4.77, <i>p</i> = 0.85). Heart rate with DL decreased from baseline (<i>p</i> ≤ 0.001) but remained higher than LIDO overall (<i>p</i> = 0.001). Dexmedetomidine infusion showed no benefit on oxygenation or respiratory mechanics in anesthetized horses.