How to ventilate patients with acute lung injury and acute respiratory distress syndrome

PURPOSE OF REVIEW: The purpose of this paper is to review the mechanisms of ventilator-induced lung injury as a basis for providing the less damaging mechanical ventilation in patients with acute respiratory failure. RECENT FINDINGS: In normal lungs, high tidal volume causes an immediate gene upregulation and downregulation. Although the importance of alveolar inflammatory reaction is well known, recent findings suggest the potential role of airway distension in causing ventilator-induced lung injury. The initial activation has been shown to occur in the airways, accounting for the damages induced by high peak flow. The healthier lung regions are more exposed to the injury, since they may be subjected to strain. Challenge with endotoxin enhances in a synergistic manner the pulmonary inflammation induced by mechanical ventilation. However, mechanical strain and endotoxin seem to trigger lung inflammation through two different pathways. Despite convincing experimental and clinical evidences of lung injury, the clinical implementation of low tidal volume ventilation is still limited and has not yet become part of standard clinical practice. Setting positive end-expiratory pressure remains an open problem because the ALVEOLI study did not provide any exhaustive answers, likely because of methodologic problems and, unphysiologic design. SUMMARY: Gentle lung ventilation must be standard practice. Because stress and strain are the triggers of ventilator-induced lung injury, their clinical equivalents should be measured (transpulmonary pressure and the ratio between tidal volume and end-expiratory lung volume). For a rational application of positive end-expiratory pressure, the potential for recruitment in any single patient should be estimated.     

CT在油酸致兔急性呼吸窘迫综合征早期诊断中的应用

目的 通过CT测定油酸性急性呼吸窘迫综合征(ARDS)兔病程中不同病变区域肺容积的变化,探讨CT早期诊断ARDS的价值.方法 健康成年大耳白兔20只,随机(随机数字法)分为对照组和油酸组,每组10只.于江苏大学附属人民医院CT室,采用静脉注射油酸法(0.1 mL/kg)制作ARDS模型.动态监测动脉血气,于造模前(T_o)、200 mmHg＜氧合指数(OI)≤300 mmHg(T_1)、OI≤200mmHg(T_2)三个时点对所有实验兔行胸部X线、CT检查,同时应用CT机载软件测定实验兔不同病变肺区百分比.观察并评价实验过程中不同病变区域肺容积的动态变化情况,比较肺容积的改变与OI的动态变化的相关性以及同一时点胸部X线片、CT的影像学表现.同时观察实验兔肺湿千重比及病理改变.数据采用两样本均数比较的t检验及重复测量数据的方差分析,两参数间的相关性分析采用等级相关分析法.结果 (1)T_1,T_2时点油酸组兔不通气肺区百分比[T_1(19.30±2.34)%,T_2(26.47±1.89)%]、通气不良肺区百分比[T_1(28.08±2.70)%,T_2(37.40±1.78)%]明显高于对照组(P＜0.01),通气正常肺区[T_1(47.38±3.19)%,T_2(30.82 4±3.25)%]显著低于对照组[T_1(79.12±1.25)%,T_2(78.24±1.84)%](P＜0.01),油酸组不通气、通气不良、通气正常肺区百分比不同时点比较差异具有统计学意义(P＜0.01),通气过度肺区百分比无明显变化(P＞0.05);(2)油酸组兔不同时点不通气、通气不良肺区百分比与氧合指数均呈负相关(-0.745～-0 636)(P＜0.05),通气正常肺区百分比与氧合指数呈正相关(0.742～0.842)(P＜0.05);(3)油酸组兔同时点胸部影像学表现CT较X线胸片早且显著;(4)油酸组免肺组织干/温质量比(W/D)明显高于对照组(分别为6.25±0.32,4.89±0.30),差异有统计学意义(P＜0.01).结论 油酸所致ARDS兔肺部影像学表现CT较X线胸片早且显著,同时通过CT测定模型兔肺容积的变化,可量化病情程度,有助于ARDS的早期诊断.     

Pumpless extracorporeal interventional lung assist in patients with acute respiratory distress syndrome: a prospective pilot study

Introduction  

Pumpless interventional lung assist (iLA) is used in patients with acute respiratory distress syndrome (ARDS) aimed at improving extracorporeal gas exchange with a membrane integrated in a passive arteriovenous shunt. In previous studies, feasibility and safety of the iLA system was demonstrated, but no survival benefit was observed. In the present pilot study we tested the hypothesis that timely initiation of iLA using clear algorithms and an improved cannulation technique will positively influence complication rates and management of lung protective ventilation.     

肺内源性与外源性急性呼吸窘迫综合征模型猪的肺复张性比较

目的应用分层电阻抗成像技术（EIT）比较肺内源性急性呼吸窘迫综合征（ARDSp）和肺外源性急性呼吸窘迫综合征（ARDSexp）模型猪的肺复张性。 方法健康巴马猪16只,随机分为ARDSp组和ARDSexp组,每组各8只。采用盐酸气管吸入的方法复制ARDSp模型,油酸静脉滴注的方法复制ARDSexp模型。模型复制成功后,采用肺保护性通气策略进行机械通气并进行一次肺复张,之后保持其他呼吸机参数不变,分别在高低呼气末正压（PEEP）25 cmH₂O和5 cmH₂O水平下通气1 h,通气结束后进行吸气末和呼气末暂停,记录高低PEEP水平间的复张容积、每个PEEP水平下的氧合情况及血流动力学参数。 结果ARDSexp组和ARDSp组模型的复张容积为分别为（1572.8±314.9）ml和（1089.9±224.2）ml,差异有统计学意义（P=0.003）。升高PEEP能够改善ARDSexp的氧合指数,由（214.3±128.6）mmHg提高到（447.5±96.0）mmHg,差异有统计学意义（P=0.004）,而ARDSp高低PEEP水平间氧合指数变化不显著,差异无统计学意义［（173.6±112.0）mmHg vs （178.4±128.2）mmHg,P=0.943］。 结论ARDSexp和ARDSp模型猪的复张性不同,相比ARDSp,ARDSexp的复张性更好。高PEEP水平可能能够改善ARDSexp的氧合,而对ARDSp的效应相对不显著。     

Acute lung injury/acute respiratory distress syndrome pathophysiology: what we have learned from computed tomography scanning

PURPOSE OF REVIEW: Although many years have passed since its first application in acute respiratory distress syndrome, computed tomography remains widely employed for research and clinical purposes. Here, we review recent findings derived from computed tomography scanning during acute respiratory distress syndrome, particularly concerning setting positive end-expiratory pressure and mechanisms of ventilator-induced lung injury. RECENT FINDINGS: Several studies have provided evidence for the validity of monitoring dynamic mechanics of the respiratory system to estimate the balance between beneficial (i.e. reduction of alveolar derecruitment) and harmful (i.e. lung hyperinflation) effects, consequent to positive end-expiratory pressure increase. The combination of different respiratory variables to estimate lung recruitment has become a more accepted approach. Computed tomography scanning has provided important evidence of lung hyperinflation even after the use of low tidal volume in a specific category of patients. Alternative techniques, such as electrical impedance tomography and lung ultrasound, appear as promising tools potentially available at the bedside. SUMMARY: As far as setting positive end-expiratory pressure is concerned, further randomized clinical studies are warranted to verify the pathophysiologic findings recently observed with computed tomography scanning. Similarly, the safety of the widespread use of low tidal volume should be brought into question, possibly pointing out a category of patients who may benefit from alternative techniques of respiratory support.     

电阻抗成像技术监测急性呼吸窘迫综合征患者呼气末正压滴定时局部机械能的临床应用

目的观察急性呼吸窘迫综合征（ARDS）患者呼气末正压（PEEP）滴定过程中的潮气分布和局部机械能。 方法对2018年11月至2019年2月北京协和医院收入的10例接受有创机械通气的ARDS患者进行PEEP滴定（15~0 cmH₂O，1 cmH₂O=0.098 kPa），该过程中使用电阻抗成像（EIT）技术监测肺内从腹侧到背侧人为划分的4个"感兴趣区（ROI）"（ROI 1~2区代表非重力依赖区，ROI 3~4区代表重力依赖区）的局部潮气比例，并计算局部机械能大小。采用单因素方差分析比较不同PEEP水平下ROI 1~4区通气分布及机械能的差异。 结果（1）随着PEEP从15 cmH₂O递减至0 cmH₂O，重力依赖区潮气比例下降，非重力依赖区潮气比例增加，且差异均有统计学意义（F=5.611、5.587，P均<0.001），潮气由重力依赖区向非重力依赖区分布。（2）随着PEEP从15 cmH₂O递减至0 cmH₂O，总机械能降低，且差异有统计学意义（F=19.601，P<0.001）；而局部机械能在ROI 2~4区降低，且差异均有统计学意义（F=4.130，P=0.003；F=30.690，P<0.001；F=16.744，P<0.005），但在ROI 1区差异无统计学意义（F=0.460，P=0.804）。 结论借助EIT技术能够监测ARDS患者PEEP滴定过程中的局部机械能。PEEP递减过程中，总体机械能降低，但局部机械能存在增加的可能性。局部机械能在PEEP设置中可能提供有用的信息。     

Low-dose chest computed tomography for quantitative and visual anatomical analysis in patients with acute respiratory distress syndrome

Purpose

Chest computed tomography (CT) is a fundamental tool for the characterization of acute respiratory distress syndrome (ARDS). Its frequent use is, however, hindered by the associated radiation exposure. The aim of the present study was to evaluate, in patients with ARDS, the accuracy of quantitative and visual anatomical lung analysis performed on low-dose CT. We hypothesized that low-dose CT would provide accurate quantitative and visual anatomical results.

Methods

Chest CT was performed in 45 ARDS patients in static conditions at set airway pressures of 45 and 15 or 45 and 5 cmH₂O. During each pause, two consecutive scans were obtained at two different tube current–time products (mAs). In 24 patients 110 mAs was coupled with 60 mAs; in 21 patients 110 was coupled with 30 mAs. All other CT parameters were kept unaltered. Quantitative and visual anatomical results obtained at different mAs were compared via Bland–Altman analysis.

Results

Good agreements were observed between 110 and 60 mAs and between 110 and 30 mAs both for quantitative and visual anatomical results (all biases below 1.5 %). Estimated mean effective dose at 110, 60, and 30 mAs corresponded to 5.3 ± 1.6, 2.8 ± 0.8, and 1.4 ± 0.3 mSv, respectively.

Conclusions

In patients with ARDS a reduction of mAs up to 30 (70 % effective dose reduction) can be achieved without significant effect on quantitative and visual anatomical results. Low-dose chest CT, with related quantitative and visual anatomical analysis, could be a valuable tool to characterize and potentially monitor lung disease in patients with ARDS.     

A prospective survey of early 12-h prone positioning effects in patients with the acute respiratory distress syndrome

OBJECTIVES: To evaluate of the oxygenation effects of 12-h prone positioning (PP) in ARDS patients and to assess the safety of such a procedure. DESIGN AND SETTING: Prospective observational study in a medical intensive care unit (12 beds) of a university hospital. PATIENTS:51 consecutive ARDS patients. INTERVENTION: PP for at least 12 h daily until recovery or death. MEASUREMENTS AND RESULTS: Arterial blood gases were collected before and during PP and 1 h after return to supine. Turning adverse events, cutaneous bedsores, and enteral nutrition intolerance were specifically monitored and collected daily by a referring physician. In total 224 PP sessions were performed. Oxygenation improved 1 h after the turn and continued improving over the 12-h period (4). The beneficial effect persisted 1 h after return to supine (01). We considered 96% patients responders: 45% as early responders and 53% persistent responders (persistent benefit after return to supine). Four significant adverse events occurred during the 448 turning maneuvers (0.9%). Stage III ulceration and stage IV necrosis cutaneous bedsores occurred in ten patients (20%). Enteral nutrition intolerance was reported in 25% but without inability to meet patient's caloric requirement. CONCLUSIONS: Twelve-hour PP is a safe procedure and allows a continuous oxygenation improvement throughout the entire session.     

Computerised tomography scan imaging in acute respiratory distress syndrome

Computerised tomography (CT) is being used with increasing frequency in acute respiratory distress syndrome (ARDS) patients. This brief review will discuss some of the clinical insights that a CT scan can offer. A large number of CT scan studies have provided new insights into the pathophysiology of ARDS and of mechanical ventilation, and are particularly focused on the recruitment-derecruitment phenomenon. To this end, newer fast CT scan technology promises a dynamic, rather than a static view of lung ventilation.     

Adrenal insufficiency in early phase of pediatric acute lung injury/acute respiratory distress syndrome

INTRODUCTION: Adequate adrenal function is essential to survive critical illness. Several recent articles have reported the significant effect of adrenal insufficiency (AI) in patients with sepsis. However, the prevalence of AI in pediatric acute lung injury (ALI)/acute respiratory distress syndrome (ARDS) is so far still scanty. Thus, we elected to study its prevalence and its clinical outcome. METHODS: This is a cross-sectional observational study. We enrolled eligible infants and children aged between 1 month and 15 years who were admitted to our tertiary pediatric intensive care unit from February 1, 2005, to December 31, 2005, with ALI or ARDS diagnosed by the American-European Consensus criteria. A short corticotropin stimulation test (250 microg) was done within 24 hours of enrollment, and all clinical data were also recorded. Cortisol levels were measured at baseline, 30 minutes, and 60 minutes posttest. Adrenal insufficiency was defined as a baseline cortisol level of less than 15.1 microg/dL or an increment of cortisol level of less than 9 microg/dL after the adrenocorticotropic hormone stimulation test. RESULTS: Of 507 patients admitted to the pediatric intensive care unit, there were 20 diagnosed with ALI/ARDS. Of 20 children, 16 met the inclusion criteria and had none of the exclusion criteria. Of 16, there were 9 (56%) with ARDS, and 7 (44%) of 12 had ALI. The prevalence of AI was observed in 37.5% (6/16), diagnosed by baseline level criteria in 25% (4/16) and by incremental criteria in 12.5% (2/16). The Baseline level of the adrenocorticotropic hormone was 7.8 +/- 5 (nmol/L). The median age in the AI group was 2 months. Of 6 children, 5 (83.3%) were in the ARDS group. Pediatric Risk of Mortality III score was significantly higher in the AI group compared with that in the non-AI (P < .05). Initial Pao(2)/fraction of inspired oxygen ratio tended to be lower in the AI group (123.2 +/- 62.2) compared with that in the non-AI group (183.8 +/- 79.1), although not statistically significant (P = .1). The mortality was also not statistically different between the AI (1/6, 16.7%) and the non-AI groups (1/10, 10%). CONCLUSIONS: Our study demonstrated that the prevalence of AI was common in pediatric ALI/ARDS. These results would be an initial step to further study the impact of AI on clinical outcomes of these children in a larger scale.     

无创正压通气治疗急性呼吸窘迫综合征的前瞻性队列研究

目的 观察和评价无创正压通气(NPPV)对急性呼吸窘迫综合征(ARDS)的疗效和安全性.方法 采用前瞻性队列研究,分析2004年1月-2007年12月北京朝阳医院呼吸重症监护病房(RICU)使用NPPV治疗ARDS患者的临床资料.结果 ①31例患者纳入本研究,其中男23例,女8例;年龄20～76岁,平均(49±17)岁;NPPV前急性生理学与慢性健康状况评分系统Ⅰ(APACHE Ⅰ)评分(14±8)分,氧合指数(PaO2/FiO2)(123±32)mm Hg(1 mm Hg=0.133 kPa).②NPPV成功率为74.2%(23/31),非肺部感染所致ARDS的成功率显著高于肺部感染所致ARDS(100%比60%,P=0.017).③与NPPV前相比,成功组NPPV治疗后2 h及24 h的心率(HR)、呼吸频率(RR)及PaO2/FiO2均有显著改善(P均<0.01),而失败组上述指标不但无显著改善,尚伴有动脉血二氧化碳分压(PaCO2)逐渐升高(P<0.05).患者均无NPPV相关的严重并发症.结论 对于无NPPV禁忌的ARDS患者,NPPV可作为一线呼吸支持手段;但对于在短期应用NPPV后生命体征及动脉血气无显著改善者,尤其是肺部感染诱发ARDS时应及早改为有创通气.     

Acute lung injury and the acute respiratory distress syndrome in Ireland: a prospective audit of epidemiology and management

Introduction  

The aim of this study was to describe the epidemiology and management of acute lung injury (ALI) and the acute respiratory distress syndrome (ARDS) in Ireland.     

Prevalence of pulmonary hypertension associated with severe acute respiratory distress syndrome: Predictive value of computed tomography

Objective To evaluate the prevalence of pulmonary hypertension associated with severe acute respiratory distress syndrome (ARDS) and to asses the value of pulmonary artery trunk diameter (PAT) to predict pulmonary hypertension. Design Prospective studySetting University teaching hospital and ARDS referral center.Patients 103 patients with ARDS, who received both right heart catheterization and chest computed tomography.Interventions None.Measurements and results 95 patients (92.2%) with ARDS had pulmonary artery hypertension, 16 of them (16.8%) mild, 72 (75.8%) moderate, and 7 (7.4%) severe, as assessed by right heart catheterization. Of the patients with moderate and severe pulmonary hypertension, 43 had a pulmonary artery trunk diameter ≥ 29 mm yielding a sensitivity of 0.54 and a specificity of 0.63. Pulmonary artery trunk diameter correlated significantly but weakly with mean pulmonary artery pressure (r = 0.34, p = 0.0004). The positive predictive value was 0.83, and the negative predictive value was 0.28. The diagnosis of pulmonary hypertension by PAT diameter measurements was incorrect in 43.7% of patients with ARDS.Conclusions Pulmonary artery hypertension has a high prevalence in patients with severe ARDS. Measurement of PAT diameter on admission CT scan is an unreliable tool for identification of ARDS patients with pulmonary hypertension.Electronic supplementary material The electronic reference of this article is . The online full-text version of this article includes electronic supplementary material. This material is available to authorised users and can be accessed by means of the ESM button beneath the abstract or in the structured full-text article. To cite or link to this article you can use the above reference.     

Platelet-activating factor acetylhydrolase is increased in lung lavage fluid from patients with acute respiratory distress syndrome

OBJECTIVE: Platelet-activating factor (PAF) is a proinflammatory phospholipid that may contribute to inflammation in the acute respiratory distress syndrome (ARDS). PAF acetylhydrolase (PAF-AH) degrades PAF and regulates its biological activity. We characterized PAF-AH in bronchoalveolar lavage fluid from ARDS patients (n = 33, 22 survivors), patients at risk for ARDS (n = 6), and healthy controls (n = 6). DESIGN: Bronchoalveolar lavage was performed during acute (<96 hrs from onset), plateau (6 to 12 days), and late (> or = 14 days) phases of ARDS. PATIENTS: Intubated patients with ARDS or a risk factor for ARDS. MEASUREMENTS AND MAIN RESULTS: In ARDS, total bronchoalveolar lavage PAF-AH activity was markedly increased in the acute phase (87 +/- 89 mU/mL, n = 33) and then decreased in the plateau (23 +/- 14 mU/mL, n = 10) and late phases (19 +/- 14 mU/mL, n = 7) (p = .003). Total bronchoalveolar lavage PAF-AH activity during the acute phase of ARDS was also increased as compared with patients at risk for ARDS (16 +/- 13 mU/mL, n = 6) and healthy controls (3 +/- 3 mU/mL, n = 6) (p < .001). In contrast, plasma PAF-AH activities were the same in controls (3215 +/- 858 mU/mL, n = 6), in patients at risk for ARDS (3606 +/- 1607 mU/mL, n = 6), and during the acute phase of ARDS (3098 +/- 2395 mU/mL, n = 33) (p = .18). PAF-AH mRNA was present in alveolar macrophages in the acute phase of ARDS (five of six) and in at-risk patients (two of three) but not in healthy controls. CONCLUSIONS: PAF-AH activity is increased in bronchoalveolar lavage fluid from patients with ARDS. Likely sources include leakage of plasma PAF-AH into alveoli or release of PAF-AH from injured cells; however, the presence of PAF-AH mRNA in alveolar macrophages suggests that PAF-AH may be actively synthesized in the lungs of patients with ARDS. PAF-AH activity in the lungs of ARDS patients may regulate inflammation caused by PAF and related oxidized phospholipids generated in the inflammatory response.     

Pharmacotherapy of acute lung injury and the acute respiratory distress syndrome

Acute lung injury and the acute respiratory distress syndrome are common syndromes with a high mortality rate that affect both medical and surgical patients. Better understanding of the pathophysiology of acute lung injury and the acute respiratory distress syndrome and advances in supportive care and mechanical ventilation have led to improved clinical outcomes since the syndrome was first described in 1967. Although several promising pharmacological therapies, including surfactant, nitric oxide, glucocorticoids and lysofylline, have been studied in patients with acute lung injury and the acute respiratory distress syndrome, none of these pharmacological treatments reduced mortality. This article provides an overview of pharmacological therapies of acute lung injury and the acute respiratory distress syndrome tested in clinical trials and current recommendations for their use as well as a discussion of potential future pharmacological therapies including beta(2)-adrenergic agonist therapy, keratinocyte growth factor, and activated protein C.     

急性肺损伤/急性呼吸窘迫综合征的药物治疗

急性肺损伤(acute lung injury,ALI)/急性呼吸窘迫综合征(acute respiratory dysfunction syndrome,ARDS)是危重病医学的重要课题,死亡率很高.尽管一些药物治疗包括肺表面活性物质、一氧化氮、糖皮质激素以及利索茶碱已经在ALI/ARDS 患者中应用,但是没有一种药物可降低死亡率.本文综述了ALI/ARDS治疗药物的临床试验结果及其目前推荐应用的等级,同时也就一些有望在未来临床应用的药物,如β2-受体激动剂、角质化细胞生长因子以及活化蛋白-C 进行讨论.