Evaluation of intramuscular sodium nitroprusside injection to improve oxygenation in white-tailed deer (Odocoileus virginianus) anesthetized with medetomidine-alfaxalone-azaperone.

Objective: In ungulates, α ₂ -adrenergic agonists can decrease oxygenation possibly through alteration of pulmonary perfusion. Sodium nitroprusside can decrease pulmonary vascular resistance (PVR) and increase cardiac output (Q˙ _t ) 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), Q˙ _t , arterial pH, PaCO ₂ and PaO ₂ 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 (Q˙ _s /Q˙ _t ), a-a gradient, oxygen delivery (D˙O ₂ ) and oxygen extraction ratio (O ₂ ER) 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 O ₂ ER significantly decreased and HR, Q˙ _t and D˙O ₂ increased compared with baseline and between treatments. There was a significant decrease in PVR and a-a gradient and increase in PaO ₂ compared with baseline and saline treatment. Changes were not sustained.
Conclusions and Clinical Relevance: Nitroprusside temporarily changed hemodynamic variables, increased PaO ₂ 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.
(Copyright © 2020. Published by Elsevier Ltd.)