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 (${\dot{Q}}_{\mathrm{t}}$) 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), ${\dot{Q}}_{\mathrm{t}}$, 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 (${\dot{Q}}_{\mathrm{s}}/{\dot{Q}}_{\mathrm{t}}$), a–a gradient, oxygen delivery ($\dot{\text{D}}$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, ${\dot{Q}}_{\mathrm{t}}$ and $\dot{\text{D}}$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.

中文翻译：

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肌内硝普钠注射液改善美托咪定-阿法沙酮-阿扎哌酮麻醉白尾鹿（Odocoileus virginianus）氧合的评价

客观的

在有蹄类动物中，α _{2 -}肾上腺素能激动剂可能通过改变肺灌注来降低氧合。硝普钠可以降低肺血管阻力（PVR），增加心输出量。${\dot{问}}_{\mathrm{吨}}$) 通过血管舒张。目的是确定硝普钠是否会改善肺灌注并减弱因美托咪定-氮杂哌酮-阿法沙酮 (MAA) 给药引起的肺泡-动脉 ( a - a) 梯度增加。

学习规划

具有 2 周休息期的前瞻性、随机、交叉研究。

动物

一群八只成年雌性圈养白尾鹿（Odocoileus virginianus）。

方法

对鹿进行肌肉注射（IM）MAA，并放置耳动脉和肺动脉球囊导管。鹿自发地呼吸空气。MAA 注射后 40 分钟肌肉注射生理盐水或硝普钠 (0.07 mg kg ^–1 )。心率（HR）、平均动脉压（MAP）、平均肺动脉压（MPAP）、肺动脉闭塞压（PAOP）、右心房压（RAP）、${\dot{问}}_{\mathrm{吨}}$在硝普钠注射前（基线）和注射后 5、10 和 15 分钟立即获得动脉 pH 值、PaCO ₂和 PaO ₂。在基线和 5 分钟时获得混合静脉血样本。全身血管阻力（SVR）、PVR、肺内分流分数（${\dot{问}}_{\mathrm{秒}}/{\dot{问}}_{\mathrm{吨}}$), a -a 梯度, 氧气输送 ($\dot{\text{D}}$计算O ₂ )和氧提取率(O ₂ ER)。统计分析采用重复测量方差分析和校正因子进行。甲p值<0.05被认为显著。

结果

使用硝普钠，MAP、MPAP、PAOP、RAP、SVR 和 O ₂ ER 显着降低，HR、${\dot{问}}_{\mathrm{吨}}$ 和 $\dot{\text{D}}$与基线和治疗之间相比，O ₂增加。与基线和生理盐水治疗相比，PVR 和a- a 梯度显着降低，而PaO ₂显着增加。变化没有持续。

结论和临床相关性

硝普钠暂时改变了血液动力学变量，增加了 PaO ₂并降低了a -a 梯度。硝普钠可能导致通气肺泡更好的肺灌注。然而，由于严重的全身性低血压和作用时间短，不推荐使用此剂量的硝普钠肌肉注射。