Brandly Jerrianne E, Midon Monica, Douglas Hope F, Hopster Klaus
Department of Clinical Studies, New Bolton Center, University of Pennsylvania School of Veterinary Medicine, Kennett Square, PA, United States.
Front Vet Sci. 2023 Apr 14;10:1135452. doi: 10.3389/fvets.2023.1135452. eCollection 2023.
Equine peri-anesthetic mortality is higher than that for other commonly anesthetized veterinary species. Unique equine pulmonary pathophysiologic aspects are believed to contribute to this mortality due to impairment of gas exchange and subsequent hypoxemia. No consistently reliable solution for the treatment of peri-anesthetic gas exchange impairment is available. Flow-controlled expiration (FLEX) is a ventilatory mode that linearizes gas flow throughout the expiratory phase, reducing the rate of lung emptying and alveolar collapse. FLEX has been shown to improve gas exchange and pulmonary mechanics in anesthetized horses. This study further evaluated FLEX ventilation in anesthetized horses positioned in dorsal recumbency, hypothesizing that after alveolar recruitment, horses ventilated using FLEX would require a lower positive end-expiratory pressure (PEEP) to prevent alveolar closure than horses conventionally ventilated.
Twelve adult horses were used in this prospective, randomized study. Horses were assigned either to conventional volume-controlled ventilation (VCV) or to FLEX. Following induction of general anesthesia, horses were placed in dorsal recumbency mechanically ventilated for a total of approximately 6.5 hours. Thirty-minutes after starting ventilation with VCV or FLEX, a PEEP-titration alveolar recruitment maneuver was performed at the end of which the PEEP was reduced in decrements of 3 cmHO until the alveolar closure pressure was determined. The PEEP was then increased to the previous level and maintained for additional three hours. During this time, the mean arterial blood pressure, pulmonary arterial pressure, central venous blood pressure, cardiac output (CO), dynamic respiratory system compliance and arterial blood gas values were measured.
The alveolar closure pressure was significantly lower (6.5 ± 1.2 vs 11.0 ± 1.5 cmHO) and significantly less PEEP was required to prevent alveolar closure (9.5 ± 1.2 vs 14.0 ± 1.5 cmHO) for horses ventilated using FLEX compared with VCV. The CO was significantly higher in the horses ventilated with FLEX (37.5 ± 4 vs 30 ± 6 l/min).
We concluded that FLEX ventilation was associated with a lower PEEP requirement due to a more homogenous distribution of ventilation in the lungs during expiration. This lower PEEP requirement led to more stable and improved cardiovascular conditions in horses ventilated with FLEX.
马的围麻醉期死亡率高于其他常用麻醉的兽医物种。独特的马肺病理生理方面被认为是导致这种死亡率的原因，因为气体交换受损及随后的低氧血症。目前尚无始终可靠的治疗围麻醉期气体交换受损的方法。流量控制呼气（FLEX）是一种通气模式，可使整个呼气阶段的气流线性化，降低肺排空率和肺泡塌陷率。FLEX已被证明可改善麻醉马匹的气体交换和肺力学。本研究进一步评估了仰卧位麻醉马匹的FLEX通气，假设在肺泡复张后，使用FLEX通气的马匹比传统通气的马匹需要更低的呼气末正压（PEEP）来防止肺泡闭合。
本前瞻性随机研究使用了12匹成年马。马匹被分配至传统容量控制通气（VCV）或FLEX组。全身麻醉诱导后，将马匹置于仰卧位进行机械通气，共约6.5小时。在开始VCV或FLEX通气30分钟后，进行一次PEEP滴定肺泡复张操作，操作结束时，将PEEP以3 cmH₂O的递减幅度降低，直至确定肺泡闭合压。然后将PEEP增加到先前水平并维持额外3小时。在此期间，测量平均动脉血压、肺动脉压、中心静脉血压、心输出量（CO）、动态呼吸系统顺应性和动脉血气值。
与VCV相比，使用FLEX通气马匹的肺泡闭合压显著更低（6.5±1.2 vs 11.0±1.5 cmH₂O），且防止肺泡闭合所需的PEEP显著更少（9.5±1.2 vs 14.0±1.5 cmH₂O）。FLEX通气马匹的CO显著更高（37.5±4 vs 30±6 l/min）。
我们得出结论，FLEX通气与更低的PEEP需求相关，这是由于呼气期间肺内通气分布更均匀。这种更低的PEEP需求使FLEX通气的马匹心血管状况更稳定且有所改善。
