Comparison of pulmonary function in isoflurane anaesthetized ventilated sheep (Ovis aries) following administration of intravenous xylazine versus medetomidine

Abstract

Alpha2 receptor agonists (alpha2-agonists) are useful sedative and analgesic agents in sheep, but have adverse pulmonary effects, which are reportedly similar between different alpha2-agonists. This randomized crossover study compared pulmonary function after intravenous administration of an alpha2-agonist, either xylazine or an equipotent dose of medetomidine in 34 female sheep anaesthetized twice. Pulmonary function was assessed using spirometry, volumetric capnography, arterial blood gas analysis 1 min prior to, and 5 and 10 min after administration of the allocated alpha 2 agonist drug. Pulmonary structural changes were subsequently assessed using computed tomography (CT). Tachypnoea or hypoxaemia prompted reversal with atipamezole and exclusion of data. Data were analysed for a fixed effect of drug using a mixed effect linear model with significance set at p < 0.05. Ten sheep administered xylazine required atipamezole while none of sheep receiving medetomidine did. Xylazine produced significantly higher respiratory frequency, airway pressures, airway resistance and arterial carbon dioxide (CO2), and lower dynamic compliance, tidal volume, CO2 elimination and end tidal CO2 tension and arterial oxygen tension than medetomidine. This was associated with a significantly lower % of aerated tissue and higher % poorly and non-aerated tissue in CT images of sheep receiving xylazine versus medetomidine. In conclusion, xylazine administration produced marked decreases in pulmonary function, in ventilated isoflurane anaesthetized sheep, when compared to an equipotent dose of medetomidine when administered as an intravenous bolus supporting the use of medetomidine when alpha2-agonists are required.

Breath-by-breath assessment of acute pulmonary edema using electrical impedance tomography, spirometry and volumetric capnography in a sheep (Ovis Aries) model

“…However, the changes observed, including decreased Cdyn and increased Raw, PIP and PEF are not specific as they are consistent with changes in both lung tissue and airways. As lung edema is associated with changes in airway diameter, respiratory mechanics changes cannot be considered sufficiently specific for bed side monitoring of developing lung edema ( 2 , 19 ). The use of an inspiratory pause and evaluation of static compliance might have allowed a distinction between airway and parenchymal changes using spirometry ( 8 ).…”

Surgical decompression of a paraspinal abscess in a 4‐month‐old lamb—Providing perioperative anaesthesia and analgesia within the remits of UK legislation for food‐producing animals

“…Xylazine has been attributed to anaesthetic deaths and impaired pulmonary function likely secondary to pulmonary oedema. [31][32][33] Similarly, as with all alpha-2 adrenergic receptor agonists in sheep, detomidine can cause clinically significant hypoxaemia 34,35 ; therefore, the lamb was preoxygenated and maintained with 100% oxygen. Infusion of detomidine may also result in bradycardia and hypoventilation 35 ; we did not observe bradycardia, and the sheep was ventilated throughout the anaesthetic period so any effects on ventilation cannot be confirmed.…”

“…There is no current evidence to suggest an analgesic effect of detomidine in sheep, but xylazine may have contributed to analgesia 29,30 and could have been prescribed according to the cascade. Xylazine has been attributed to anaesthetic deaths and impaired pulmonary function likely secondary to pulmonary oedema 31–33 . Similarly, as with all alpha‐2 adrenergic receptor agonists in sheep, detomidine can cause clinically significant hypoxaemia 34,35 ; therefore, the lamb was preoxygenated and maintained with 100% oxygen.…”