Zannin Emanuela, Dellaca Raffaele L, Kostic Peter, Pompilio Pasquale P, Larsson Anders, Pedotti Antonio, Hedenstierna Goran, Frykholm Peter
Crit Care. 2012 Nov 7;16(6):R217. doi: 10.1186/cc11858.
It is well established that during mechanical ventilation of patients with acute respiratory distress syndrome cyclic recruitment/derecruitment and overdistension are potentially injurious for lung tissues. We evaluated whether the forced oscillation technique (FOT) could be used to guide the ventilator settings in order to minimize cyclic lung recruitment/derecruitment and cyclic mechanical stress in an experimental model of acute lung injury.
We studied six pigs in which lung injury was induced by bronchoalveolar lavage. The animals were ventilated with a tidal volume of 6 ml/kg. Forced oscillations at 5 Hz were superimposed on the ventilation waveform. Pressure and flow were measured at the tip and at the inlet of the endotracheal tube respectively. Respiratory system reactance (Xrs) was computed from the pressure and flow signals and expressed in terms of oscillatory elastance (EX5). Positive end-expiratory pressure (PEEP) was increased from 0 to 24 cm H2O in steps of 4 cm H2O and subsequently decreased from 24 to 0 in steps of 2 cm H2O. At each PEEP step CT scans and EX5 were assessed at end-expiration and end-inspiration.
During deflation the relationship between both end-expiratory and end-inspiratory EX5 and PEEP was a U-shaped curve with minimum values at PEEP = 13.4 ± 1.0 cm H2O (mean ± SD) and 13.0 ± 1.0 cm H2O respectively. EX5 was always higher at end-inspiration than at end-expiration, the difference between the average curves being minimal at 12 cm H2O. At this PEEP level, CT did not show any substantial sign of intra-tidal recruitment/derecruitment or expiratory lung collapse.
Using FOT it was possible to measure EX5 both at end-expiration and at end-inspiration. The optimal PEEP strategy based on end-expiratory EX5 minimized intra-tidal recruitment/derecruitment as assessed by CT, and the concurrent attenuation of intra-tidal variations of EX5 suggests that it may also minimize tidal mechanical stress.
众所周知，在急性呼吸窘迫综合征患者机械通气期间，周期性肺复张/萎陷和过度扩张对肺组织具有潜在损害。我们评估了强迫振荡技术（FOT）是否可用于指导呼吸机设置，以在急性肺损伤实验模型中使周期性肺复张/萎陷和周期性机械应力最小化。
我们研究了6只通过支气管肺泡灌洗诱导肺损伤的猪。动物以6 ml/kg的潮气量进行通气。在通气波形上叠加5 Hz的强迫振荡。分别在气管内导管尖端和入口处测量压力和流量。根据压力和流量信号计算呼吸系统电抗（Xrs），并以振荡弹性（EX5）表示。呼气末正压（PEEP）从0逐步增加至24 cm H₂O，步长为4 cm H₂O，随后从24逐步降至0，步长为2 cm H₂O。在每个PEEP水平，在呼气末和吸气末评估CT扫描和EX5。
在呼气过程中，呼气末和吸气末EX5与PEEP之间的关系均为U形曲线，分别在PEEP = 13.4 ± 1.0 cm H₂O（均值 ± 标准差）和13.0 ± 1.0 cm H₂O时取最小值。吸气末的EX5始终高于呼气末，平均曲线之间的差异在12 cm H₂O时最小。在此PEEP水平，CT未显示任何明显的潮气量内肺复张/萎陷或呼气期肺萎陷迹象。
使用FOT能够在呼气末和吸气末测量EX5。基于呼气末EX5的最佳PEEP策略可使CT评估的潮气量内肺复张/萎陷最小化，并且EX5潮气量内变化的同时减弱表明它也可能使潮气量机械应力最小化。
