ARDS患者如何进行通气支持治疗.doc

ARDS患者如何进行通气支持治疗 上一篇文章： 基底动脉尖综合征患者的临床及影像学表现 下一篇文章： 绵羊急性呼吸窘迫综合征开放肺压力安全性的实验研究| 收藏此文到365KEY| 收藏此文到YOUNOTE 属性:作者:急诊论坛来源:急诊论坛点击数:更新:2006-6-12文章录入：vancomycin责任编辑：vancomycin功能:文字:变小 变大 【繁】作者：PEEPman时间：2003-05-29 22:10:07 ARDS患者如何进行通气支持治疗 -最近，美国重症监护医学学会第31届国际教育和科学研讨会举办了一次有关急性呼吸窘迫综合征（ARDS）患者通气支持治疗的技术与方法的专家座谈会，与会专家就许多专题进行了广泛讨论。其中肺复张治疗、6 ml/kg小潮气量(VT)通气支持的必要性和高频振荡通气(HFOV)，引起了听众的极大兴趣。ARDS治疗中的肺复张巴西圣保罗大学的Amato 医师援引其所在医院完成的一项研究（研究结果已发表在新英格兰医学杂志上），该研究显示，采用限制吸气末肺过度牵张的保护性通气策略（肺复张是这一通气策略的重要措施），可显著降低ARDS患者病死率。胸部CT扫描发现，相当数量的肺组织得以复原。他指出，肺复张的目的并非专为改善肺氧合，而是为减少通气机造成的肺损伤（VILI）。PaO2只是复张和降低VILI危险的指标。但有关肺复张的运用还有很多未解决的问题：（1）如何最好地进行肺复张，包括每次持续多长时间，采用多高的压力及其重复使用的频度；（2）胸壁顺应性通过气道压力对肺复张效果有重大影响。打开肺泡单位的主要压力是跨肺压，如果患者的胸壁非常僵硬，那么通气支持时所给的气道压力就不能使肺充分扩张，跨肺压也不会明显增高，肺泡单位不能充分开放；(3）全肺复张是否必要？这是一个颇有争论的问题，临床发现，全肺复张实际上有可能进一步加重肺损伤；（4）目前需要采用严格方法，研究肺复张对病人预后的影响。ARDSNet研究者目前正进行一项临床研究，比较高呼气末正压（PEEP）的疗效。在这一研究中，高PEEP组中最初纳入的数百例患者采用了肺复张，但由于长期观察证明，这一方法缺乏肯定的疗效，因此已被停用，这些数据尚未发表。值得注意的是，虽然在这项研究中，肺复张采用的压力升高至35 cmH2O，部分肥胖患者甚至采用了更高的压力值，但根据ARDS患者病变肺区复张情况看，这一压力水平仍相对较低。疗效差的另一种可能原因是，复张后使用的PEEP水平不够高。此外，肺复张也有副作用，包括低血压和气压伤。ARDSNet治疗方案在ARDS患者中的应用马里兰州约翰斯霍普金斯大学的Brower阐述了ARDS患者的治疗是否应严格完全按照ARDSNet方案进行。他公布了一些尚未发表的资料，这些资料显示，纳入ARDSNet临床研究时平台压在较低四分位数的患者中， VT为12 ml/kg组患者的平台压30 cmH2O，采用较低的VT 5 ml/kg或4 ml/kg（PBW）。3 如患者有呼吸窘迫或严重呼吸困难，只要Pplat医学院附属中大医院ICU 邱海波谭焰-顽固性低氧血症是急性呼吸窘迫综合征（ARDS）最突出的临床表现。机械通气是改善此症的重要治疗手段。传统的通气策略是采用较大的潮气量（1015ml/kg）促进萎陷的肺泡复张，维持正常的动脉血气，以最小的呼气末正压（PEEP）达到“足够”的动脉氧合，监测气道压力但不对其作严格限制，这种通气策略易导致肺泡过度膨胀，加重肺损伤。随着人们对ARDS病理生理特征的认识，近年来，有人提出了肺保护与肺复张通气策略，在改善患者氧合的同时，尽可能避免气压伤，对ARDS患者具有重要的意义。ARDS的病理生理特点肺容积明显降低是ARDS最重要的病理生理特征。严重的ARDS患者，仅2030肺泡能参与通气，因此，ARDS患者的肺又称“小肺”或“婴儿肺”。应用常规潮气量进行机械通气时，必然引起肺泡过度膨胀。此外，CT发现，ARDS患者的肺损伤分布具有不均一性。当应用常规水平的压力和潮气量通气支持时，病变严重的肺泡尚未开放，而相对正常的肺泡已被过度扩张，在塌陷肺泡和正常肺泡之间产生较大的剪切力，引起气压伤。ARDS的肺顺应性曲线（PV曲线）PV曲线反映了ARDS患者的肺力学特征。对选择最佳PEEP、设置潮气量和计算呼吸系统的顺应性具有重要意义。PV曲线的吸气支呈“S”形，有两个转折点，一个位于曲线左下方，称为低位转折点；另一个位于曲线右上方，称为高位转折点。低位转折点与高位转折点将曲线分为3个部分：(1)低位转折点以下部分反映部分塌陷肺泡开始复张时的压力；(2)低位转折点与高位转折点之间的部分几乎成直线，表明肺顺应性明显增加，高位转折点反映肺泡已达到最大限度的扩张；(3)高位转折点以上的部分：高位转折点的出现是肺泡过度膨胀的信号。为避免气压伤，机械通气治疗ARDS时，潮气量和气道压力应设置在低位转折点和高位转折点之间。ARDS的肺保护性通气策略在保证基本组织氧合的同时，保护肺组织以尽量减轻肺损伤是ARDS患者的通气目标。一些学者提出了肺保护性通气策略，即采用较小的潮气量、限制气道平台压及应用最佳PEEP水平进行通气支持的策略。1 允许性高碳酸血症（PHC）PHC是采用小潮气量（47 mlkg），允许动脉血二氧化碳分压一定程度增高（4080 mmHg）。为ARDS患者实施PHC时，血流动力学改变主要表现为心排出量和氧输送显著增加，体血管阻力显著降低，肺血管阻力降低或不变，肺动脉嵌顿压和中心静脉压增加或无明显改变。PHC的禁忌证有：颅内压增高、缺血性心脏病或严重的左心功能受损等。2 应用最佳PEEP如单纯应用PHC同样可导致呼吸机相关肺损伤。主要原因是ARDS患者呼气末大量塌陷的肺泡在吸气初突然开放产生的剪切力，以及正常肺泡和萎陷肺泡之间的剪切力损伤。为防止这种损伤，需要应用PEEP防止肺泡塌陷，使更多的肺泡维持在开放状态。PEEP通过呼气末肺泡内正压的支撑作用来防止肺泡塌陷，改善气体交换，其作用和效应与PEEP的水平密切相关。适当水平的PEEP可以消除塌陷肺泡反复复张产生的剪切力，减轻肺损伤，同时增加功能残气量，改善通气血流比例和肺顺应性，从而改善低氧血症。但过高水平的PEEP会导致肺泡过度膨胀，在PV曲线上出现高位转折点。因此，选择最佳的PEEP，使之既可防止呼气末肺泡萎陷，又能避免肺泡过度膨胀是十分必要的。临床上选择最佳PEEP常用的方法有静态PV曲线低位转折点法和氧输送法。3压力控制或压力支持通气使用压力控制通气易于人机同步，提供的吸气流量为减速波型，有利于气体交换和增加氧合，更重要的是可精确调节肺膨胀所需的压力和吸气时间，控制气道峰值压力，保证ARDS患者的气道压不会超过设定的吸气压力，避免高位转折点的出现。肺保护性通气策略的提出，反映了ARDS机械通气的重大变革。但它仍存在不可避免的局限性。如不利于改善患者的氧合，对于重度ARDS患者可能导致不良后果等。因此，在实施肺保护性通气策略时，有必要采用有效的方法促进塌陷肺泡复张，增加能参与通气的肺泡数目。ARDS的肺复张策略肺复张策略是一种使塌陷肺泡最大限度复张并保持其开放，以增加肺容积、改善肺氧合和肺顺应性的方法。它是肺保护性通气策略必要的补充。主要有以下几种：1、 叹息即为正常生理情况下的深呼吸，有利于促进塌陷的肺泡复张。对于ARDS患者，目前有学者间断地采用叹息，使气道平台压达到45 cmH2O。应用叹息后，患者的动脉血氧分压显著增加，二氧化碳分压和肺内分流率显著降低，呼气末肺容积增加。因此，叹息可有效促进塌陷肺泡复张，改善患者的低氧血症。但叹息不能改善患者的肺顺应性，其作用不持久，临床价值尚有争议。2、 间断应用高水平PEEP在容量控制通气时，间断应用高水平PEEP使气道平台压增加，也能促进肺泡复张。有学者在机械通气治疗ARDS患者时，每隔30 s应用高水平PEEP通气2次，可以增加患者的动脉血氧分压，降低肺内分流率。间断应用高水平PEEP虽然能使塌陷的肺泡复张，改善患者的氧合，但它与叹息相似，不能保持肺泡的稳定状态，同样作用不持久。3控制性肺膨胀（SI）是一种促使不张的肺泡复张和增加肺容积的新方法，由叹息发展而来。即在吸气开始时，给予足够压力（3045 cmH2O），让塌陷肺泡充分开放，并持续一定时间（2030 s），使病变程度不一的肺泡之间达到平衡，气道压力保持在SI的压力水平。SI结束后，恢复到SI应用前的通气模式，通过SI复张的塌陷肺泡，在相当时间内能够继续维持复张状态，SI导致的氧合改善也就能够维持较长时间。4俯卧位通气利用翻身床、翻身器或人工徒手操作，使患者在俯卧位进行机械通气。其治疗作用是改善ARDS患者的氧合。然而对血流动力学不稳定、颅内压增高、急性出血、脊柱损伤、骨科手术、近期腹部手术、妊娠等不宜采用俯卧位通气。作者：PEEPman时间：2006-03-10 22:04:04 Mechanical ventilation in ARDS: One size does not fit all - Editorial AJCCM Fri, 20 May 2005 ARMA was a government-sponsored, $41 million experiment involving 861 critically ill patients with severe lung injury-i.e., acute respiratory distress syndrome (ARDS). It has been at the center of continuing debate prompted by revelations that researchers at 14 of the nations major medical research institutions comprising the ARDS Network,* violated fundamental medical ethics principles. 1 2 Patients with ARDS almost always need to be supported with mechanical ventilation to help them breathe. During this kind of support, breaths, termed tidal volumes, are administered to patients with a ventilator to inflate the lung to deliver oxygen and remove carbon dioxide from the blood. However, lungs with ARDS are much stiffer than healthy lungs. In the 1980s emerging research strongly suggested that although necessary for survival, if tidal volumes with mechanical ventilation were too large, the high airway pressures they produced might themselves be harmful. In 1992, a survey of more than 1,000 physicians caring for patients with ARDS showed that most were aware that tidal volumes producing increased airway pressures might be harmful and that physicians adjusted their practice to account for this. 3 A consensus conference of physicians in 1993 warned of the need to reduce tidal volumes if airway pressures were high, and recommended that physicians reduce tidal volumes when necessary to ensure that airway pressures remained below a potentially harmful level. 4 NIH sponsored the ARMA study to investigate the benefits of reducing tidal volumes in ARDS patients. Between 1996 and 1999, the ARDS Network enrolled 861 patients out of an eligible pool of 3,448 patients. Patients who were enrolled in this experiment had been receiving oxygen at a tidal volume setting according to the judgment of their primary, critical care physician. They were withdrawn from that ventilation setting, and randomized to receive one of two tidal volume settings-either high (12 ml/kg) which was termed traditional or low (6 ml/kg). The experiment failed to include a comparison control group receiving the current best treatment-which included individualized ventilation settings determined by the condition of the individual patients lungs. Most of the patients enrolled in this randomized experiment were unable to Provide informed consent. Furthermore, the consent forms that had been approved by the institutional review boards (IRBs) at the participating hospitals ALL failed to comply with federal requirements of disclosure. See: urlhttp:/www.ahrp.org/ethical/CaromeARDS082802.php/url In fact, none of the consent forms informed patients or their families that they would be withdrawn from current best therapeutic treatment and randomly assigned to a fixed ventilation setting which might increase their risk of dying. Neither were they informed that an alternative to participating in the experiment was available at the same medical center. On July 29, 2002, AHRP filed a complaint with the federal Office of Human Research Protections about violations of informed consent. See: urlhttp:/www.ahrp.org/ethical/Koski0729.php/url After enrolling more than 860 patients the study was stopped because mortality was substantially higher in the high tidal volume group (12ml/kg, 41%) compared to the low tidal volume group (6ml/kg, 31%). The ARDS investigators concluded that the low tidal volume (6ml/kg) increased survival rate and recommended that it should be applied to all patients with ARDS. 1 Following publication of the trial in the New England Journal of Medicine, critical care physician-scientists at the NIH who analyzed the ARDS Network report raised concerns about the design of the experiment in the American Journal of Respiratory and Critical Care Medicine (AJRCCM). 5 This independent analysis raised the following concerns about the design of the trial: First, airway pressures associated with the 12 mg/kg tidal volume were significantly higher than what critical care physicians were routinely administering in standard practice to their patients at the time of the trial. Second, the trials failed to include a control group in which patients would be provided individualized ventilation settings-as is the practice in standard care, and is required under the Declaration of Helsinki ethical research standards. 6 Ethical research requires that: The benefits, risks, burdens and effectiveness of a new method should be tested against those of the best current prophylactic, diagnostic, and therapeutic methods. Other groups of investigators were also examining what routine ventilatory care was both before and during the ARDS trial. These studies showed that physicians varied tidal volumes based on how injured or stiff the lungs of patients were. A very sick patient with a very stiff lung would get a low tidal volume while a patient with a more pliant lung would receive a higher tidal volume. Randomizing patients to high or low tidal volumes without regard for their underlying level of lung injury was (and is) contrary to what was at the time-and continues to be-the best therapeutic method of care. Therefore, the significant findings of the ARDS Network experiment may relate largely to having increased mortality in patients with very stiff lungs who had their tidal volumes increased to 12ml/kg. Ultimately the ARDSNET trial is impossible to interpret and its recommendations that all patients with ARDS should get very low tidal volumes-should be rejected precisely because the trial failed to provide a randomly-selected control group of patients who received standard treatment. Mechanical ventilation in ARDS: One size does not fit all, an editorial by Katherine Deans, Peter Minneci, Xizhounog Cui, Steven Banks, Charles Natanson and P