Respiratory and hemodynamic effects of 2 protocols of low-dose infusion of dexmedetomidine in dogs under isoflurane anesthesia

Abstract

The aim of this study was to evaluate the respiratory and hemodynamic effects of a low-dose dexmedetomidine infusion [1 μg/kg body weight (BW) per hour], with or without a loading dose (1 μg/kg BW), in dogs under isoflurane anesthesia. Thirty dogs were premedicated with methadone [0.3 mg/kg BW intramuscular (IM)], induced with propofol intravenous (IV) and maintained with isoflurane (1.3% to 1.4%) under mechanical ventilation. Animals were randomly assigned to 3 intravenous (IV) treatments (n = 10): 1 μg/kg BW dexmedetomidine, followed by 1 μg/kg BW per hour (group BI); or saline solution bolus, followed by either an infusion of 1 μg/kg BW per hour dexmedetomidine (group I) or saline solution (group C). The infusions were interrupted after 30 minutes. Respiratory system static compliance (Cstat) and respiratory system resistance (Rrs), partial pressure of oxygen/fractional inspired oxygen ratio (PaO2/FIO2), intrapulmonary shunt (Fshunt), and cardiac output (CO) were determined 5 minutes before the bolus (BASELINE), at the end of the bolus (BOLUS), and at 15 (T15), 30 (T30), and 45 minutes (T45) intervals. In group BI, Cstat and PaO2/FiO2 were higher at T15 and T30 than at BASELINE in the same group and than group C at the same times. In group I, the same parameters at T30 were higher than at BASELINE and than group C at the same time. In group BI, Rrs and Fshunt were lower than at BASELINE and than group C at the same time. In group I, the same parameters at T30 were lower than at BASELINE and those of group C at the same time. Cardiac output (CO) at T30 was higher in groups BI and I than in group C. The results of this study showed that low-dose dexmedetomidine infusion improves oxygenation and respiratory system mechanics and has a stabilizing hemodynamic effect in dogs anesthetized with isoflurane and mechanically ventilated.

Conflict of interest statement

Conflict of interest statement The authors do not have any conflict of interest to declare.

Copyright and/or publishing rights held by the Canadian Veterinary Medical Association.

Figures

Figure 1

Mean ± SD values of respiratory system static compliance (Cstat, mL/cmH2O/kg) in 30 dogs undergoing ovariectomy under isoflurane general anesthesia. In group BI (n = 10, solid line), dogs received a bolus [1 μg/kg body weight (BW) per hour, IV], followed by a continuous rate infusion (CRI) of dexmedetomidine (1 μg/kg BW per hour, IV). In group I (n = 10, dashed line), dogs received a bolus of Ringer’s lactate solution IV, followed by a CRI of dexmedetomidine (1 μg/kg BW per hour, IV). In group C (n = 10, dotted line), dogs received a bolus and a CRI of Ringer’s lactate solution IV. The drug infusion started after the induction and was interrupted 30 min later (T30). The data were registered before the beginning of the infusion (BASELINE), at the end of bolus (BOLUS), and at 15 (T15), 30 (T30), and 45 (T45) min after the beginning of the infusion. * P < 0.05 compared to group C at the same study time; #P < 0.05 compared to group I at the same study time; aP < 0.05 compared to BASELINE in the same group.

Figure 2

Mean ± SD values of total resistance of the respiratory system (Rrs, cmH2O/L/s) in 30 dogs undergoing ovariectomy under isoflurane general anesthesia. In group BI (n = 10, solid line), dogs received a bolus [1 μg/kg body weight (BW,) IV], followed by a continuous rate infusion (CRI) of dexmedetomidine (1 μg/kg BW per hour, IV). In group I (n = 10, dashed line), dogs received a bolus of Ringer’s lactate solution IV, followed by a CRI of dexmedetomidine (1 μg/kg BW per hour, IV). In group C (n = 10, dotted line), dogs received a bolus and a CRI of Ringer’s lactate solution IV. The drug infusion started after the induction and was interrupted 30 min later (T30). The data were registered before the beginning of the infusion (BASELINE), at the end of bolus (BOLUS), and at 15 (T15), 30 (T30), and 45 (T45) min after the beginning of the infusion. * P < 0.05 compared to group C at the same study time; aP < 0.05 compared to BASELINE in the same group.

Figure 3

Mean ± SD values of arterial oxygen partial pressure/fractional inspired oxygen ratio (PaO2/FiO2) in 30 dogs undergoing ovariectomy under isoflurane general anesthesia. In group BI (n = 10, solid line), dogs received a bolus [1 μg/kg body weight (BW), IV], followed by a continuous rate infusion (CRI) of dexmedetomidine (1 μg/kg BW per hour, IV). In group I (n = 10, dashed line), dogs received a bolus of Ringer’s lactate solution IV, followed by a CRI of dexmedetomidine (1 μg/kg BW per hour, IV). In group C (n = 10, dotted line), dogs received a bolus and a CRI of Ringer’s lactate solution IV. The drug infusion started after the induction and was interrupted 30 min later (T30). The data were registered before the beginning of the infusion (BASELINE), at the end of bolus (BOLUS), and at 15 (T15), 30 (T30), and 45 (T45) min after the beginning of the infusion. * P < 0.05 compared to group C at the same study time; #P < 0.05 compared to group I at the same study time; aP < 0.05 compared to BASELINE in the same group.

Figure 4

Mean ± SD values of estimated intrapulmonary shunt (Fshunt) in 30 dogs undergoing ovariectomy under isoflurane general anesthesia. In group BI (n = 10, solid line), dogs received a bolus [1 μg/kg body weight (BW), IV], followed by a continuous rate infusion (CRI) of dexmedetomidine (1 μg/kg BW per hour, IV). In group I (n = 10, dashed line), dogs received a bolus of Ringer’s lactate solution IV, followed by a CRI of dexmedetomidine (1 μg/kg BW per hour, IV). In group C (n = 10, dotted line), dogs received a bolus and a CRI of Ringer’s lactate solution IV. The drug infusion started after the induction and was interrupted 30 min later (T30). The data were registered before the beginning of the infusion (BASELINE), at the end of bolus (BOLUS), and at 15 (T15), 30 (T30), and 45 (T45) min after the beginning of the infusion. * P < 0.05 compared to group C at the same study time; #P < 0.05 compared to group I at the same study time; aP < 0.05 compared to BASELINE in the same group.

Figure 5

Mean ± SD values of cardiac index (CI) in 30 dogs undergoing ovariectomy under isoflurane general anesthesia. In group BI (n = 10, solid line), dogs received a bolus [1 μg/kg body weight (BW), IV], followed by a continuous rate infusion (CRI) of dexmedetomidine (1 μg/kg BW per hour, IV). In group I (n = 10, dashed line), dogs received a bolus of Ringer’s lactate solution IV, followed by a CRI of dexmedetomidine (1 μg/kg BW per hour, IV). In group C (n = 10, dotted line), dogs received a bolus and a CRI of Ringer’s lactate solution IV. The drug infusion started after the induction and was interrupted 30 min later (T30). The data were registered before the beginning of the infusion (BASELINE), at the end of bolus (BOLUS), and at 15 (T15), 30 (T30), and 45 (T45) min after the beginning of the infusion. * P < 0.05 compared to group C at the same study time; aP < 0.05 compared to BASELINE in the same group; bP < 0.05 compared to BOLUS in the same group.