Objective

To compare F-shunt and oxygen content indices in sheep ventilated with a positive end-expiratory pressure (PEEP) of 5 cmH₂O alone or preceded by a stepwise alveolar recruitment manoeuvre (ARM).

Study design

Randomized crossover design.

Animals

A total of six nonpregnant Brogna ewes weighing 34–47 kg, undergoing thoracolumbar magnetic resonance scan.

Methods

In medetomidine-sedated sheep, anaesthesia was induced with propofol and maintained with isoflurane 1.1% ± 0.1% and an inspired oxygen fraction (FiO₂) of 0.4. Animals were placed in left lateral recumbency and, after 10 minutes of spontaneous breathing, mechanically ventilated with 5 cmH₂O of PEEP with (group ARM) or without (group PEEP) a stepwise recruitment manoeuvre. Maintaining a fixed driving pressure of 15 cmH₂O, PEEP was increased from 0 to 20 cmH₂O every 3 minutes in 5 cmH₂O increments. In each sheep, arterial blood samples were collected to measure arterial gases and to calculate F-shunt, PaO₂/alveolar oxygen partial pressure (PAO₂) and PaO₂/FIO₂ during spontaneous breathing before mechanical ventilation (T₀), after 20 minutes of ventilation (T₂₀) and during spontaneous breathing at extubation (T_ext).

Results

Both ventilatory strategies improved the arterial oxygen content although four animals in group PEEP showed oxygen content compatible with hypoxia compared with group ARM. F-shunt values were not statistically different at any time point in sheep that underwent only PEEP ventilation while they decreased at T₂₀ and T_ext compared with T₀ in group ARM. At extubation F-shunt was statistically lower in sheep that underwent an ARM. Mechanical ventilation improved PaO₂/PAO₂ and PaO₂/FIO₂ but they did not differ between groups.

Conclusions

and clinical relevance The stepwise ARM evaluated in this study improved oxygenation indices and decreased F-shunt. This effect was maintained at extubation compared with sheep that were ventilated with only PEEP 5 cmH₂O.

中文翻译：

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比较两种通气策略在麻醉羊中改善动脉血氧张力和含量的功效。

目的

为了比较单独使用呼气末正压（PEEP）5 cmH ₂ O或先进行逐步肺泡募集操作（ARM）通风的绵羊的F分流和氧含量指标。

学习规划

随机交叉设计。

动物

总共六只体重34-47 kg的Brogna母羊接受了胸腰椎磁共振扫描。

方法

在美托咪定镇静的绵羊中，用异丙酚诱导麻醉，并维持1.1％±0.1％的异氟烷​​和0.4的吸入氧分率（F i O ₂）。将动物置于左侧卧位，并在自发呼吸10分钟后，用5 cmH ₂ O的PEEP进行机械通气，使用（ARM组）或不使用（PEEP组）逐步募集动作。保持15 CMH一个固定驱动压力₂ O，PEEP从0增加至20 CMH ₂每3分钟○在5个CMH _2个ö增量。在每只绵羊中，采集动脉血样本以测量动脉气体并计算F分流，PaO ₂ /肺泡氧分压（PAO ₂）和PaO ₂ / FIO ₂在机械通气前的自发呼吸（T ₀），通气20分钟后（T ₂₀）和拔管时的自发呼吸（T _ext）。

结果

两种通气策略均改善了动脉血氧含量，尽管与ARM组相比，PEEP组的四只动物表现出的氧含量与低氧相容。仅进行PEEP通风的绵羊的F分流值在任何时间均无统计学差异，而在ARM组，在T ₂₀和T _ext与F ₀相比，F分流值降低。拔管后，经过ARM手术的绵羊的F分流在统计学上较低。机械通气改善了PaO ₂ / PAO ₂和PaO ₂ / FIO _2，但两组之间无差异。

结论

与临床相关性在这项研究中评估的逐步ARM改善了氧合指数并降低了F分流。与仅使用PEEP 5 cmH ₂ O进行通风的绵羊相比，拔管时可以保持这种效果。