The effects of inhalation salbutamol administration on systemic and pulmonary hemodynamic, pulmonary mechanics and oxygen balance during general anaesthesia in the horse

Abstract

This research aimed to determine the effect of aerosolized salbutamol administration on systemic and pulmonary hemodynamic, pulmonary mechanics and oxygen balance in healthy horses during general anaesthesia. Six healthy Thoroughbreds (body weight range 471–587 kg) underwent two general anaesthesias in dorsal recumbency with and without aerosolized salbutamol administration in randomized order with a one month washout period. The anaesthesia was induced by 1.1 mg/kg of xylazine, 0.02 mg/kg of diazepam and 2.2 mg/kg of ketamine, maintained with isoflurane in oxygen and air and horses were mechanically ventilated. Measurement of arterial and pulmonary arterial blood pressures, cardiac output and arterial and mixed venous blood gas analysis was carried out. Spirometry was performed using a Horse-lite. After achieving a steady state, baseline (T₀) values of cardiac output, systemic and pulmonary arterial blood pressures, heart rate, dynamic compliance, airway resistance and arterial and mixed venous blood gas values and pH were recorded in both groups. In the S-group (salbutamol), 2 µg/kg of aerosolized salbutamol were administered synchronously with inspirium into the tracheal tube. In both groups data were recorded at 15, 30, 45 and 60 min (T₁₅, T₃₀, T₄₅, T₆₀) after the baseline. PaO₂/FiO₂ ratio, oxygen consumption (VO₂), oxygen delivery (DO₂), pulmonary shunt values were calculated. Data were tested for normality and compared within each group: T₀ value with T₁₅, T₃₀, T₄₅, T₆₀ values using Wilcoxon's test with Bonferoni correction (significance level 0.0125). For each time point, comparisons were made between the S- and C-groups (control) using Wilcoxon's test. In the S-group, there was a significant increase in values (mean ± SD) of cardiac output (l/min), T₀ (38 ± 7), a peak at T₁₅ (64 ± 25.5), significantly higher values persisted throughout the period of anaesthesia; heart rate (beats/min), T₀ (32 ± 2), T₁₅ (40 ± 6), T₃₀ (38 ± 5); DO₂ (l/min), T₀ (5.8 ± 0.8), a peak at T₁₅ (9.6 ± 3.2), significantly higher values persisted until the end of anaesthesia and VO₂ (l/min), T₀ (1.1 ± 0.5), T₃₀ (1.6 ± 0.7) and T₄₅ (1.8 ± 0.5). In the C-group, there was a significant decrease in values of PaO₂/FiO₂ ratio from T₀ (176 ± 67) to a minimum at T₆₀ (114 ± 36) and in DO₂ from T₀ (6 ± 2.3) to a minimum at T₆₀ (4.3 ± 1.2). A comparison of the S- and C-groups did not reveal any difference in the baseline data. Subsequently, significantly higher values of cardiac output, heart rate, DO₂, and the PaO₂/FiO₂ratio were found in the S-group compared to the C-group. Pulmonary arterial blood pressure was significantly lower in the S-group. Aerosolized salbutamol administration in healthy horses during general anaesthesia caused hemodynamic changes which resulted in an elevation of oxygen delivery. It can have a positive effect on arterial oxygenation, but the effect varies between individuals.