Matsuda Kenichi, Sawada Shigeki, Bartlett Robert H, Hirschl Ronald B
Department of Surgery, University of Michigan, Ann Arbor, USA.
Crit Care Med. 2003 Jul;31(7):2034-40. doi: 10.1097/01.CCM.0000075353.38441.45.
To investigate the settings necessary to achieve maximum gas exchange and pulmonary function while minimizing effects on cardiovascular hemodynamics during total liquid ventilation with a pressure-limited, time-cycled ventilator in a rat model.
Prospective, randomized controlled animal study.
A university research laboratory.
Male Sprague-Dawley rats (n = 48).
All animals had a tracheostomy tube designed for total liquid ventilation placed under anesthesia. The carotid artery was cannulated for blood pressure monitoring and for assessing blood gas data.
Forty 492 +/- 33 g rats were assigned to one of four inspiratory/expiratory ratio groups (inspiratory/expiratory ratio of 1:2, 1:2.5, 1:3, and 1:4). Total liquid ventilation was performed with a pressure-limited, time-cycled total liquid ventilator. Outcome measures were evaluated as a function of respiratory rate and included tidal volume, maximal alveolar ventilation, inspiratory and expiratory mean arterial pressures, the difference of mean arterial pressure between the inspiratory and expiratory phase, static end-inspiratory/expiratory pressures, Paco(2), Pao(2), tidal volume + approximate expiratory reserve volume, and lung volume-induced suppression of mean arterial pressure. Maximal alveolar ventilation increased and decreased in parabolic fashion as a function of respiratory rate and was maximal at rates of 4.3-6.8 breaths/min and high inspiratory/expiratory ratios that corroborated with optimal levels of Pao(2) and Paco(2). Lung overdistention occurred at high respiratory rates and high inspiratory/expiratory ratios. Deleterious effects were observed on the difference of mean arterial pressure between the inspiratory and expiratory phase during total liquid ventilation at low respiratory rates, apparently due to increased tidal volume, and on suppression of mean arterial pressure at high inspiratory/expiratory ratios and high respiratory rate apparently due to "auto-positive end-expiratory pressure." These effects were minimized in this model at respiratory rates >/=5.7 and </=6.8 breaths/min and inspiratory/expiratory ratios </=1:2.5. These settings were successfully tested in eight additional animals.
These data demonstrate the feasibility of performing total liquid ventilation in rodents. A balance must be identified where gas exchange is optimal yet hemodynamics are least affected. In the specific system studied, an inspiratory/expiratory ratio of 1:2.5 and respiratory rate of 6.8 breaths/min appeared to provide optimal gas exchange while minimizing the effects on hemodynamics.
在大鼠模型中，研究使用压力限制、时间切换通气机进行全液体通气时，为实现最大气体交换和肺功能同时最小化对心血管血流动力学影响所需的设置。
前瞻性、随机对照动物研究。
大学研究实验室。
雄性斯普拉格 - 道利大鼠（n = 48）。
所有动物在麻醉下放置专为全液体通气设计的气管造口管。将颈动脉插管用于监测血压和评估血气数据。
40只体重492±33克的大鼠被分配到四个吸气/呼气比组之一（吸气/呼气比为1:2、1:2.5、1:3和1:4）。使用压力限制、时间切换的全液体通气机进行全液体通气。将结果指标作为呼吸频率的函数进行评估，包括潮气量、最大肺泡通气量、吸气和呼气平均动脉压、吸气相和呼气相之间的平均动脉压差值、静态吸气末/呼气末压力、动脉血二氧化碳分压（Paco₂）、动脉血氧分压（Pao₂）、潮气量 + 近似呼气储备量以及肺容积引起的平均动脉压抑制。最大肺泡通气量随着呼吸频率呈抛物线状增加和减少，在呼吸频率为4.3 - 6.8次/分钟且吸气/呼气比高时达到最大值，此时动脉血氧分压（Pao₂）和动脉血二氧化碳分压（Paco₂）处于最佳水平。在高呼吸频率和高吸气/呼气比时发生肺过度扩张。在低呼吸频率下全液体通气期间，观察到吸气相和呼气相之间的平均动脉压差值有不良影响，显然是由于潮气量增加所致；在高吸气/呼气比和高呼吸频率下，观察到平均动脉压受到抑制，显然是由于“自动呼气末正压”。在本模型中，当呼吸频率≥5.7且≤6.8次/分钟以及吸气/呼气比≤1:2.5时，这些影响最小化。这些设置在另外8只动物中成功进行了测试。
这些数据证明了在啮齿动物中进行全液体通气的可行性。必须找到一个平衡点，使气体交换最佳而血流动力学受影响最小。在所研究的特定系统中，吸气/呼气比为1:2.5且呼吸频率为6.8次/分钟似乎能提供最佳气体交换，同时最小化对血流动力学的影响。
