Pressure support compared with controlled mechanical ventilation in experimental lung injury

It has been suggested that, in acute lung injury (ALI), spontaneous breathing activity may increase oxygenation because of an improvement of ventilation-perfusion distribution. Pressure support ventilation (PSV) is one of the assisted spontaneous breathing modes often used in critical care medicine. We sought to determine the prolonged effects of PSV on gas exchange in experimental ALI. We hypothesized that PSV may increase oxygenation because of an improvement in ventilation-perfusion distribution. Thus, ALI was induced in 20 pigs by using repetitive lung lavage. Thereafter, the animals were randomized to receive either PSV with a pressure level set to achieve a tidal volume >4 mL/kg and a respiratory rate <40 min(-1) (n = 10) or controlled mechanical ventilation (CMV) with a tidal volume of 10 mL/kg and a respiratory rate of 20 min(-1) (n = 10). Positive end-expiratory pressure was set at 10 cm H(2)O in both groups. Blood gas analyses and determination of ventilation-perfusion (.V(A)/.Q) distribution were performed at the onset of ALI and after 2, 4, 8, and 12 h. The main result was an improvement of oxygenation because of a decrease of pulmonary shunt and an increase of areas with normal .V(A)/.Q ratios during PSV (P < 0.005). However, during CMV, a more pronounced reduction of shunt was observed compared with PSV (P < 0.005). We conclude that, in this model of ALI, PSV improves gas exchange because of a reduction of .V(A)/.Q inequality. However, improvements in .V(A)/.Q distribution may be more effective with CMV than with PSV. IMPLICATIONS: Assisted spontaneous breathing may have beneficial effects on gas exchange in acute lung injury. We tested this hypothesis for pressure support ventilation in an animal model of acute lung injury. Our results demonstrate that pressure support does not necessarily provide better gas exchange than controlled mechanical ventilation.     

Spontaneous breathing during high-frequency oscillatory ventilation improves regional lung characteristics in experimental lung injury

Background: Maintenance of spontaneous breathing is advocated in mechanical ventilation. This study evaluates the effect of spontaneous breathing on regional lung characteristics during high‐frequency oscillatory (HFO) ventilation in an animal model of mild lung injury. Methods: Lung injury was induced by lavage with normal saline in eight pigs (weight range 47–64 kg). HFO ventilation was applied, in runs of 30 min on paralyzed animals or on spontaneous breathing animals with a continuous fresh gas flow (CF) or a custom‐made demand flow (DF) system. Electrical impedance tomography (EIT) was used to assess lung aeration and ventilation and the occurrence of hyperinflation. Results: End expiratory lung volume (EELV) decreased in all different HFO modalities. HFO, with spontaneous breathing maintained, showed preservation in lung volume in the dependent lung regions compared with paralyzed conditions. Comparing DF with paralyzed conditions, the center of ventilation was located at 50% and 51% (median, left and right lung) from anterior to posterior and at 45% and 46% respectively, P<0.05. Polynomial coefficients using a continuous flow were ?0.02 (range ?0.35 to 0.32) and ?0.01 (?0.17 to 0.23) for CF and DF, respectively, P=0.01. Conclusions: This animal study demonstrates that spontaneous breathing during HFO ventilation preserves lung volume, and when combined with DF, improves ventilation of the dependent lung areas. No significant hyperinflation occurred on account of spontaneous breathing. These results underline the importance of maintaining spontaneous breathing during HFO ventilation and support efforts to optimize HFO ventilators to facilitate patients' spontaneous breathing.     

The use of prone ventilation in acute lung injury and acute respiratory distress syndrome

Prone positioning has been suggested since 1974 as a ventilatory strategy to improve oxygenation and pulmonary mechanics in patients with acute lung injury and acute respiratory distress syndrome. Although this mode of ventilation can improve gas exchange, the optimal role of the prone position is uncertain. The aim of this article is to examine the evidence in support of this mode of ventilation in adult patients with acute lung injury and acute respiratory distress syndrome. Limitations of the currently available evidence upon which the recommendations are made must be recognized. With these limitations in mind, however, the available evidence has been considered and conclusions presented. Considerable clinical experience confirms that prone ventilation can improve oxygenation in the majority of patients. It is difficult to predict which patients will respond. There are few contraindications and with experienced staff it can be achieved safely. Most patients should therefore be considered for a trial of prone positioning. Prolonged and repeated prone ventilation may be more effective. Whether the improvement in physiological parameters translates into improved clinical outcomes is less certain and well-designed randomized controlled trials will be required to address this issue.     

Combining partial liquid ventilation and prone position in experimental acute lung injury.

BACKGROUND: Partial liquid ventilation (PLV) and prone position can improve arterial oxygen tension (PaO2) in acute lung injury (ALI). The authors evaluated additive effects of these techniques in a saline lung lavage model of ALI. METHODS: ALI was induced in 20 medium-sized pigs (29.2+/-2.5 kg body weight). Gas exchange and hemodynamic parameters were determined in both supine and prone position in all animals. Thereafter, one group was assigned to PLV with two sequential doses of 15 ml/kg of perfluorocarbon (n = 10); the second group was assigned to gaseous ventilation (n = 10). Gas-exchange and hemodynamic parameters were determined at corresponding time points in both groups in prone and supine position. RESULTS: In the PLV group, positioning the animals prone resulted in an increase of PaO2 prior to PLV and during PLV with both doses of perfluorocarbon when compared to ALI. PLV in supine position was only effective if 30 ml/kg of perfluorocarbon was applied. In the gaseous ventilation group, PaO2 increased reproducibly compared with ALI when the animals were turned prone. A significant additive improvement of arterial oxygenation was observed during combined therapy with 30 ml/kg of perfluorocarbon and prone position in the PLV group compared with either therapy alone. CONCLUSIONS: The authors conclude that combining PLV with prone position exerts additive effects on pulmonary gas exchange in a saline lung lavage model of ALI in medium-sized pigs.     

Short-term cardiorespiratory effects of proportional assist and pressure-support ventilation in patients with acute lung injury/acute respiratory distress syndrome

BACKGROUND: Recent data indicate that assisted modes of mechanical ventilation improve pulmonary gas exchange in patients with acute lung injury (ALI)/acute respiratory distress syndrome (ARDS). Proportional assist ventilation (PAV) is a new mode of support that amplifies the ventilatory output of the patient effort and improves patient-ventilator synchrony. It is not known whether this mode may be used in patients with ALI/ARDS. The aim of this study was to compare the effects of PAV and pressure-support ventilation on breathing pattern, hemodynamics, and gas exchange in a homogenous group of patients with ALI/ARDS due to sepsis. METHODS: Twelve mechanically ventilated patients with ALI/ARDS (mean ratio of partial pressure of arterial oxygen to fractional concentration of oxygen 190 +/- 49 mmHg) were prospectively studied. Patients received pressure-support ventilation and PAV in random order for 30 min while maintaining mean airway pressure constant. With both modes, the level of applied positive end-expiratory pressure (7.1 +/- 2.1 cm H2O) was kept unchanged throughout. At the end of each study period, cardiorespiratory data were obtained, and dead space to tidal volume ratio was measured. RESULTS: With both modes, none of the patients exhibited clinical signs of distress. With PAV, breathing frequency and cardiac index were slightly but significantly higher than the corresponding values with pressure-support ventilation (24.5 +/- 6.9 vs. 21.4 +/- 6.9 breaths/min and 4.4 +/- 1.6 vs. 4.1 +/- 1.3 l . min . m, respectively). None of the other parameters differ significantly between modes. CONCLUSIONS: In patients with ALI/ARDS due to sepsis, PAV and pressure-support ventilation both have clinically comparable short-term effects on gas exchange and hemodynamics.     

Prone positioning ventilation for treatment of acute lung injury and acute respiratory distress syndrome

Patients who are diagnosed with acute lung injury/acute respiratory distress syndrome (ALI/ARDS) usually have ventilation-perfusion mismatch, severe decrease in lung capacity, and gas exchange abnormalities. Health care work-ers have implemented various strategies in an attempt to compensate for these pathological alterations. By rotating patients with ALI/ARDS between the supine and prone position, it is possible to achieve a significant improvement in PaO2/FiO2, decrease shunting and therefore improve oxy-genation without use of expensive, invasive and experimen-tal procedures.     

气道压力释放通气对急性肺损伤或急性呼吸窘迫综合征患者呼吸功能的影响

目的评价气道压力释放通气（APRV）对急性肺损伤（ALI）或急性呼吸窘迫综合征（ARDS）患者呼吸功能的影响。方法ALI患者42例、ARDS患者33例，随机分2组，APRV组（n=37）、同步间歇指令通气（SIMV）组（n=38）；两组均用SIMV加用呼气末正压通气30min后，APRV组采用APRV模式通气，SIMV组仍用初始参数，分别于APRV前（基础值）、APRV1、8、16、24h测定动脉血气、气道峰压（Ppeak）、气道平均压（Pmean）、中心静脉压（CVP）、氧合指数（PaO2／FiO2）、心率（HR），并记录芬太尼、咪达唑仑、多巴胺用量及尿量。结果与SIMV组比较，APRV组APRV1～24h各时点Ppeak、Pmean降低，APRV16、24h时动脉血PaCO2降低，PaO2／FiO2升高，APRV1—24h时CVP和HR降低，芬太尼用量和咪达唑仑用量明显减少，APRV8—24h各时点尿量升高，多巴胺用量减少（P〈0．05或0．01）。结论APRV用于ARDS或ALI患者的机械通气治疗，不仅能提供更好的通气，而且血液动力学平稳，减少镇静剂和麻醉药用量。     

New aspects of ventilation in acute lung injury

Recent recognition that artificial ventilation may cause damage to the acutely injured lung has caused renewed interest in ventilation techniques that minimise this potential harm. Many ventilation techniques have proved beneficial in small trials of very specific patient groups, but most have subsequently failed to translate into improved patient outcome in larger trials. An exception to this is 'protective ventilation' using reduced tidal volumes (to lower airway pressure) and increased PEEP (to reduce pulmonary collapse). Results of trials of protective ventilation have been encouraging, and the technique should now be adopted more widely. High frequency ventilation, inverse ratio ventilation, prone positioning and inhaled nitric oxide are all techniques that may be considered when, in spite of optimal artificial ventilation, the patient's gas exchange remains dangerously poor. Under these circumstances, the choice of technique is dependent on their availability, local expertise and individual patient needs.     

Clara细胞分泌蛋白对兔单肺通气肺损伤的保护作用

目的 观察Clara细胞分泌蛋白(CCSP)对兔单肺通气肺损伤的保护作用.方法 30只新西兰大白兔随机均分为三组:双肺通气3 h组(Ⅰ组);单肺通气2 h,随后双肺通气1 h组(Ⅱ组);单肺通气Clara细胞剥除组(Ⅲ组)(通气方法同Ⅱ组).观察支气管Clara细胞百分率、血清和肺泡灌洗液(BALF)中CCSP含量、BALF中白细胞计数及中性粒细胞比值、血清肿瘤坏死因子α(TNF-α)、白细胞介素(IL)-6、IL-8水平、肺组织湿/干比值和肺组织病理学检查.结果 Clara细胞百分率、CCSP含量Ⅰ组高于Ⅱ组(P<0.05),Ⅱ组高于Ⅲ组(P(0.01);BALF中白细胞计数、中性粒细胞比值和血清中TNF-α、IL-6、IL-8水平、肺湿/干比值Ⅰ组低于Ⅱ组(P<0.05),Ⅱ组低于Ⅲ组(P<0.01);病理学检查示肺损伤程度Ⅰ组轻于Ⅱ组,Ⅱ组轻于Ⅲ组.结论 Clara细胞分泌蛋白可减轻单肺通气所致肺损伤.     

右美托咪定可减轻肺叶切除术中单肺通气所致肺损伤

目的探讨右美托咪定对肺叶切除术中单肺通气所致肺损伤的影响。方法选择2014年5月至2017年2月拟行肺叶切除术的肺癌患者64例,男38例,女26例,年龄42~75岁,ASAⅡ或Ⅲ级。根据不同治疗方式将患者分成两组,每组32例。麻醉诱导前20min,观察组泵注右美托咪定0.5μg·kg~(-1)·h~(-1),10min后改为0.2~0.5μg·kg~(-1)·h~(-1),对照组予以等容量生理盐水。检测麻醉诱导前10min(T_0)、单肺通气即刻(T_1)、单肺通气60min(T2)、单肺通气90min(T_3)、术后24h(T_4)的全血中性粒细胞(PMN)计数,血清髓过氧化物酶(MPO)、黄嘌呤氧化酶(XOD)活性,肺内分流率(Qs/Qt),以及T_0~T_3时血管内皮生长因子(VEGF)和一氧化氮(NO)浓度。结果与T_0时比较,T_2~T_4时两组PMN计数明显增多,MPO和XOD活性明显升高(P0.05),但观察组明显低于对照组(P0.05)。与T_0时比较,T_2、T_3时两组血清VEGF浓度明显升高,但T_3时观察组明显低于对照组(P0.05)。T_2、T_3时观察组血清NO浓度明显高于对照组(P0.05)。结论右美托咪定能减少患者肺部炎症反应,减轻单肺通气所致缺血-再灌注损伤,且降低了患者机体氧化应激程度,从而对肺起到保护作用。     

Comparative effects of vaporized perfluorohexane and partial liquid ventilation in oleic acid-induced lung injury

BACKGROUND: It is currently not known whether vaporized perfluorohexane is superior to partial liquid ventilation (PLV) for therapy of acute lung injury. In this study, the authors compared the effects of both therapies in oleic acid-induced lung injury. METHODS: Lung injury was induced in 30 anesthetized and mechanically ventilated pigs by means of central venous infusion of oleic acid. Animals were assigned to one of the following groups: (1) control or gas ventilation (GV), (2) 2.5% perfluorohexane vapor, (3) 5% perfluorohexane vapor, (4) 10% perfluorohexane vapor, or (5) PLV with perfluorooctane (30 ml/kg). Two hours after randomization, lungs were recruited and positive end-expiratory pressure was adjusted to obtain minimal elastance. Ventilation was continued during 4 additional hours, when animals were killed for lung histologic examination. RESULTS: Gas exchange and elastance were comparable among vaporized perfluorohexane, PLV, and GV before the open lung approach was used and improved in a similar fashion in all groups after positive end-expiratory pressure was adjusted to optimal elastance (P < 0.05). A similar behavior was observed in functional residual capacity (FRC) in animals treated with vaporized perfluorohexane and GV. Lung resistance improved after recruitment (P < 0.05), but values were higher in the 10% perfluorohexane and PLV groups as compared with GV (P < 0.05). Interestingly, positive end-expiratory pressure values required to obtain minimal elastance were lower with 5% perfluorohexane than with PLV and GV (P < 0.05). In addition, diffuse alveolar damage was significantly lower in the 5% and 10% perfluorohexane vapor groups as compared with PLV and GV (P < 0.05). CONCLUSIONS: Although the use of 5% vaporized perfluorohexane permitted the authors to reduce pressures needed to stabilize the lungs and was associated with better histologic findings than were PLV and GV, none of these perfluorocarbon therapies improved gas exchange or lung mechanics as compared with GV.     

机械通气肺损伤的基本机制

机械通气肺损伤发生机制复杂,临床表现多样,日益受到重视.其基本机制为对肺组织过度牵拉的机械因素和机械力学诱导的肺脏局部细胞因子和炎症介质的释放.不适当的机械通气除可造成气压损伤、容积损伤和肺不张损伤等机械性损伤外,其最后的共同途径可能是激活细胞内信号转导通路和加重炎症介质介导的肺局部炎症反应,即机械伤转化为生物伤.现就其发生机制、防治对策等方面的研究作一简要综述.     

Changes in pulmonary blood flow during gaseous and partial liquid ventilation in experimental acute lung injury

BACKGROUND: It has been proposed that partial liquid ventilation (PLV) causes a compression of the pulmonary vasculature by the dense perfluorocarbons and a subsequent redistribution of pulmonary blood flow from dorsal to better-ventilated middle and ventral lung regions, thereby improving arterial oxygenation in situations of acute lung injury. METHODS: After induction of acute lung injury by repeated lung lavage with saline, 20 pigs were randomly assigned to partial liquid ventilation with two sequential doses of 15 ml/kg perfluorocarbon (PLV group, n = 10) or to continued gaseous ventilation (GV group, n = 10). Single-photon emission computed tomography was used to study regional pulmonary blood flow. Gas exchange, hemodynamics, and pulmonary blood flow were determined in both groups before and after the induction of acute lung injury and at corresponding time points 1 and 2 h after each instillation of perfluorocarbon in the PLV group. RESULTS: During partial liquid ventilation, there were no changes in pulmonary blood flow distribution when compared with values obtained after induction of acute lung injury in the PLV group or to the animals submitted to gaseous ventilation. Arterial oxygenation improved significantly in the PLV group after instillation of the second dose of perfluorocarbon. CONCLUSIONS: In the surfactant washout animal model of acute lung injury, redistribution of pulmonary blood flow does not seem to be a major factor for the observed increase of arterial oxygen tension during partial liquid ventilation.     

Small dose of exogenous surfactant combined with partial liquid ventilation in experimental acute lung injury: effects on gas exchange, haemodynamics, lung mechanics, and lung pathology

A combination of exogenous surfactant and partial liquid ventilation(PLV) with perfluorocarbons should enhance gas exchange, improverespiratory mechanics and reduce tissue damage of the lung inacute lung injury (ALI). We used a small dose of exogenous surfactantwith and without PLV in an experimental model of ALI and studiedthe effects on gas exchange, haemodynamics, lung mechanics,and lung pathology. ALI was induced by repeated lavages (Pa_O2/FI_O2less than 13 kPa) in 24 anaesthesized, tracheotomized and mechanicallyventilated (FI_O2 1.0) juvenile pigs. They were treated randomlywith either a single intratracheal dose of surfactant (50 mgkg^–1, Curosurf^®, Serono AG, München, Germany)(SURF-group, n=8), a single intratracheal dose of surfactant(50 mg kg^–1, Curosurf^®) followed by PLV with 30 mlkg^–1 of perfluorocarbon (PF 5080, 3M, Germany) (SURF-PLV-group,n=8) or no further intervention (controls, n=8). Pulmonary gasexchange, respiratory mechanics, and haemodynamics were measuredhourly for a 6 h period. In the SURF-group, the intrapulmonaryright-to-left shunt (Q^·S/Q^·T) decreased significantlyfrom mean 51 (SEM 5)% after lavage to 12 (2)%, and Pa_O2 increasedsignificantly from 8.1 (0.7) to 61.2 (4.7) kPa compared withcontrols and compared with the SURF-PLV-group (P<0.05). Inthe SURF-PLV-group, Q^·S/Q^·T decreased significantlyfrom 54 (3)% after induction of ALI to 26 (3)% and Pa_O2 increasedsignificantly from 7.2 (0.5) to 30.8 (5.0) kPa compared withcontrols (P<0.05). Static compliance of the respiratory system(C_RS), significantly improved in the SURF-PLV-group comparedwith controls (P<0.05). Upon histological examination, theSURF-group revealed the lowest total injury score compared withcontrols and the SURF-PLV-group (P<0.05). We conclude thatin this experimental model of ALI, treatment with a small doseof exogenous surfactant improves pulmonary gas exchange andreduces the lung injury more effectively than the combined treatmentof a small dose of exogenous surfactant and PLV. Br J Anaesth 2001; 87: 593–601