Abstract
Objective
In ungulates, α2-adrenergic agonists can decrease oxygenation possibly through alteration of pulmonary
perfusion. Sodium nitroprusside can decrease pulmonary vascular resistance (PVR) and
increase cardiac output () through vasodilation. The objective was to determine if sodium nitroprusside would
improve pulmonary perfusion and attenuate the increased alveolar–arterial (a–a) gradient resulting from medetomidine–azaperone–alfaxalone (MAA) administration.
Study design
Prospective, randomized, crossover study with a 2 week rest period.
Animals
A group of eight adult female captive white-tailed deer (Odocoileus virginianus).
Methods
Deer were administered MAA intramuscularly (IM), and auricular artery and pulmonary
artery balloon catheters were placed. Deer spontaneously breathed air. Saline or sodium
nitroprusside (0.07 mg kg–1) were administered IM 40 minutes after MAA injection. Heart rate (HR), mean arterial
pressure (MAP), mean pulmonary arterial pressure (MPAP), pulmonary artery occlusion
pressure (PAOP), right atrial pressure (RAP), , arterial pH, PaCO2 and PaO2 were obtained immediately before nitroprusside injection (baseline) and 5, 10 and
15 minutes afterwards. Mixed venous blood samples were obtained at baseline and at
5 minutes. Systemic vascular resistance (SVR), PVR, intrapulmonary shunt fraction
(), a–a gradient, oxygen delivery (O2) and oxygen extraction ratio (O2ER) were calculated. Statistical analysis was performed with repeated measures analysis
of variance with correction factors. A p value < 0.05 was considered significant.
Results
With nitroprusside, MAP, MPAP, PAOP, RAP, SVR and O2ER significantly decreased and HR, and O2 increased compared with baseline and between treatments. There was a significant
decrease in PVR and a–a gradient and increase in PaO2 compared with baseline and saline treatment. Changes were not sustained.
Conclusions and clinical relevance
Nitroprusside temporarily changed hemodynamic variables, increased PaO2 and decreased a–a gradient. Nitroprusside possibly led to better pulmonary perfusion of ventilated
alveoli. However, IM nitroprusside at this dose is not recommended because of severe
systemic hypotension and short action.
Keywords
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Article info
Publication history
Published online: November 06, 2020
Accepted:
October 28,
2020
Received:
July 29,
2020
Identification
Copyright
© 2020 Published by Elsevier Ltd on behalf of Association of Veterinary Anaesthetists and American College of Veterinary Anesthesia and Analgesia.
