急性呼吸窘迫综合征家兔肺不同区域有效血流灌注变化及肺保护性通气对其的影响

目的 通过观察家兔急性呼吸窘迫综合征(ARDS)模型肺不同区域有效血流灌注变化及肺保护性通气对其的影响,探讨ARDS所致严重低氧血症的发生机制。方法 采用静脉注射油酸的方法建立家兔ARDS模型,应用PIM-Ⅱ激光多普勒血流灌注扫描仪观察不同肺通气模式[(大潮气、小潮气 外源性呼气末正压(PEEP)、大潮气 俯卧位、俯卧位 小潮气 PEEP]下肺不同区域(肺上区、肺下区腹侧和肺下区背侧)局部有效血流灌注及动脉血气指标的变化。结果 家兔静脉注射油酸后,(1)肺不同区域氧合指数明显下降,应用肺保护性通气(小潮气 PEEP,俯卧位 小潮气 PEEP)后氧合指数明显改善;(2)肺不同区域局部有效血流灌注均有不同程度的下降,以肺下区背侧最为明显,肺下区腹侧次之,肺上区变化最小,应用肺保护性通气后,小潮气 PEEP对改善肺下区背侧胸膜下肺局部有效血流灌注的效果不如俯卧位 小潮气 PEEP。结论小潮气 PEEP、俯卧位 小潮气 PEEP均可良好改善肺局部有效血流灌注,其中俯卧位 小潮气 PEEP效果尤为明显;右-左分流导致的肺内分流可能是ARDS发生严重进行性低氧血症的主要原因之一。     

Lung recruitment maneuvers in acute respiratory distress syndrome

In the experimental setting, repeated derecruitments of the lungs of ARDS models accentuate lung injury during mechanical ventilation, whereas open lung concept strategies can attenuate the injury. In the clinical setting, recruitment manuevers that use a continuous positive airway pressure of 40 cmH2O for 40 secs improve oxygenation in patients with early ARDS who do not have an impairment in the chest wall. High intermittent positive end-expiratory pressure (PEEP), intermitent sighs, or high-pressure controlled ventilation improves short-term oxygenation in ARDS patients. Both conventional and electrical impedance thoracictomography studies at the clinical setting indicate that high PEEP associated with low levels of pressure control ventilation recruit the collapsed portions of the ARDS lungs and that adequate PEEP levels are necessary to keep the ARDS lungs opened allowing a more homogenous ventilation. High PEEP/low tidal volume ventilation was seen to reduce inflammatory mediators in both bronchoalveolar lavage and plasma, compared to low PEEP/high tidal volume ventilation, after 36 hours of mechanical ventilation in ARDS patients. Recruitment maneuvers that used continuous positive airway pressure levels of 35-40 cmH2O for 40 secs, with PEEP set at 2 cmH2O above the lower inflection point of the pressure-volume curve, and tidal volume < 6 mL/kg were associated with a 28-day intensive care unit survival rate of 62%. This contrasted with a survival rate of only 29% with conventional ventilation (defined as the lowest PEEP for acceptable oxygenation without hemodynamic impairment with a tidal volume of 12 mL/kg), without recruitment manuevers (number needed to treat = 3; p < 0.001). In the near future, thoracic computed tomography associated with high-performance monitoring of regional ventilation may be used at the bedside to determine the optimal mechanical ventilation of the ARDS keeping an opened lung with a homogenous ventilation.     

Treatment of ARDS

Improved understanding of the pathogenesis of acute lung injury (ALI)/ARDS has led to important advances in the treatment of ALI/ARDS, particularly in the area of ventilator-associated lung injury. Standard supportive care for ALI/ARDS should now include a protective ventilatory strategy with low tidal volume ventilation by the protocol developed by the National Institutes of Health ARDS Network. Further refinements of the protocol for mechanical ventilation will occur as current and future clinical trials are completed. In addition, novel modes of mechanical ventilation are being studied and may augment standard therapy in the future. Although results of anti-inflammatory strategies have been disappointing in clinical trials, further trials are underway to test the efficacy of late corticosteroids and other approaches to modulation of inflammation in ALI/ARDS.     

Successful treatment of a critically ill patient with acute respiratory distress syndrome from COVID-19 using mechanical ventilation strategy with low levels of positive end-expiratory pressure: A CARE-compliant case report

Introduction:Acute respiratory distress syndrome (ARDS) secondary to COVID-19 is different from the ARDS caused by other infections. Conventional mechanical ventilation strategies using high levels of PEEP may not be beneficial and can even be harmful to patient with ARDS from COVID-19. So the ventilation strategies should be adjusted in order to improve the pulmonary ventilation function and oxygenation status, and outcomes of the patient.Patient concerns:Herein, we present a 76-year-old male patient with ARDS secondary to COVID-19. We describe our experience with mechanical ventilation strategy and the changes in respiratory mechanics in the patient during treatment.Diagnosis:The patient had tested positive for coronavirus (COVID-19) in nucleic acid test. Chest CT showed multiple ground glass shadows in both lungs.Interventions:The patient received mechanical ventilation with low tidal volume and low PEEP.Outcomes:After treatment, the patients condition, as well as oxygenation status was improved, and he tested negative for the coronavirus several times.Conclusion:This case demonstrated that the low tidal volume with low levels of PEEP ventilation strategy may be more suitable for ARDS from COVID-19.     

Is permissive hypercapnia a beneficial strategy for pediatric acute lung injury?

It is clear that mechanical ventilation strategies influence the course of lung disease, and the choice of a ventilation strategy that avoids volutrauma and atelectrauma is firmly based on experimental literature and clinical experience. The application of a lung-protective strategy with reduced tidal volumes, effective lung recruitment, adequate PEEP to minimize alveolar collapse during expiration, and permissive hypercapnia has been shown to be advantageous in adult patients who have ARDS, although it has not been systematically studied in children. A significant body of literature confirms the beneficial effects of hypercapnic acidemia in the setting of acute lung injury. As a corollary, experimental evidence indicates that buffering hypercapnic acidosis abrogates its protective effects. The use of permissive hypercapnia as part of a lung-protective strategy in children should be accepted and perhaps even desired, provided it does not result in significant hemodynamic instability. This acceptance should be tempered with the recognition that a low-stretch, reduced-tidal volume strategy without hypercapnia has also been shown to improve outcomes in adults who have ARDS and that HFOV can generally provide lung-protective ventilation without necessarily inducing hypercapnia. Thus, a synthesis of the available clinical and research data strongly supports a graded approach to managing patients who have acute lung injury requiring intubation. The highest priority should be a mechanical ventilation strategy that limits the tidal volume, with the allowance of hypercapnia to a degree that does not compromise hemodynamic status.     

Ventilatory strategies in patients with sepsis and respiratory failure

Patients with sepsis may require mechanical ventilation due to the acute respiratory distress syndrome (ARDS). It has become increasingly accepted that mechanical ventilation can contribute to lung injury in these patients. The modern concept of ventilator-induced lung injury is described in the context of alveolar over-distention (volutrauma), alveolar de-recruitment (atelectrauma), and biochemical injury and inflammation to the lung parenchyma (biotrauma). To avoid over-distention lung injury, the tidal volume should be set at 6 mL/kg predicted body weight and plateau pressure should be limited to 30 cm H₂O. This has been shown to afford a survival benefit. Although setting positive end-expiratory pressure (PEEP) to zero is likely harmful during mechanical ventilation of patients with ARDS, evidence is lacking for a survival benefit if a high PEEP level is set compared with a modest level of PEEP. Although adjunctive measures such as recruitment maneuvers, prone position, and inhaled nitric oxide may improve oxygenation, evidence is lacking that these measures improve survival.     

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??Abstract??Ventilation with low tidal volume (Vt)normalized to ideal body weight (IBW) has become a doctrine for the ventilation of patients with ARDS since the end of last century and mortality of ARDS has decreased to some extent.However??it is still highly debatable about how to choose a suitable tidal volume.Recently??with better insights into ARDS’ pathophysiological changes and its respiratory mechanics??especially with the more popular use of EIT??critical ultra sound and lung stress and strain??it is feasible to choose tidal volume individually according to the lung compliance of ARDS patients.     

Effect of surfactant on ventilation-induced mediator release in isolated perfused mouse lungs

The human acute respiratory distress syndrome (ARDS) is a severe pulmonary complication with high mortality rates. To support their vital functions, patients suffering from ARDS are mechanically ventilated. Recently it was shown that low tidal volume ventilation reduces mortality and pro-inflammatory mediator release in these patients, suggesting biotrauma as a side effect of mechanical ventilation. Because the application of exogenous surfactant has been proposed as a treatment for ARDS, we investigated the effect of surfactant on ventilation-induced release of tumor necrosis factor (TNF), interleukin-6 (IL-6) and 6-keto-PGF(1 alpha) (the stable metabolite of prostacyclin) in isolated perfused mouse lungs ventilated with high end-inspiratory pressures. Instillation of 100mg/kg surfactant into the lungs was well tolerated and improved tidal volume, pulmonary compliance and alveolar expansion. Exogenous surfactant increased the ventilation-induced liberation of TNF and IL-6 into the perfusate, but had no effect on the release of 6-keto-PGF(1 alpha). The surfactant preparation used reduced baseline TNF production by murine alveolar macrophages, indicating that the exaggeration of ventilation-induced TNF release cannot be explained by a direct effect of surfactant on these cells. We hypothesize that ventilation-induced mediator release is explained by stretching of lung cells, which is reinforced by surfactant. The findings that in this model of ventilation-induced lung injury exogenous surfactant at the same time improved lung functions and enhanced mediator release suggest that surfactant treatment may prevent barotrauma and augment biotrauma.     

Mechanical ventilation in ARDS: a state-of-the-art review

Mechanical ventilation is an essential component of the care of patients with ARDS, and a large number of randomized controlled clinical trials have now been conducted evaluating the efficacy and safety of various methods of mechanical ventilation for the treatment of ARDS. Low tidal volume ventilation (相似文献   

Effects of short-term pressure-controlled ventilation on gas exchange,airway pressures,and gas distribution in patients with acute lung injury/ARDS: comparison with volume-controlled ventilation

STUDY OBJECTIVES: The potential clinical benefits of pressure-controlled ventilation (PCV) over volume-controlled ventilation (VCV) in patients with acute lung injury (ALI) or ARDS still remain debated. We compared PCV with VCV in patients with ALI/ARDS with respect to the following physiologic end points: (1) gas exchange and airway pressures, and (2) CT scan intrapulmonary gas distribution at end-expiration. DESIGN: Prospective, observational study. SETTING: A multidisciplinary ICU in a nonuniversity, acute-care hospital. PATIENTS: Ten patients with ALI or ARDS (9 men and 1 woman; age range, 17 to 80 years). INTERVENTIONS: Sequential ventilation in PCV and VCV with a constant inspiratory/expiratory ratio, tidal volume, respiratory rate, and total positive end-expiratory pressure; measurement of gas exchange and airway pressures; and achievement of CT sections at lung base, hilum, and apex for the quantitative analysis of lung densities and of aerated vs nonaerated zones. RESULTS: PaO(2), PaCO(2), and PaO(2)/fraction of inspired oxygen ratio levels did not differ between PCV and VCV. Peak airway pressure (Ppeak) was significantly lower in PCV compared with VCV (26 +/- 2 cm H(2)O vs 31 +/- 2 cm H(2)O; p < 0.001; mean +/- SEM). The surface areas of the nonaerated zones as well as the total areas at each section level were unchanged in PCV compared with VCV, except at the apex level, where there was a significantly greater nonaerated area in VCV (11 +/- 2 cm(2) vs 9 +/- 2 cm(2); p < 0.05). The total mean CT number of each lung (20 lungs from 10 patients) was similar in the two modes, as were the density values at the basal and apical levels; the hilum mean CT number was - 442 +/- 28 Hounsfield units (HU) in VCV and - 430 +/- 26 HU in PCV (p < 0.005). CONCLUSIONS: These data show that PCV allows the generation of lower Ppeaks through the precise titration of the lung distending pressure, and might be applied to avoid regional overdistension by means of a more homogeneous gas distribution.     

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??Abstract??Mechanical ventilation is still one of the main treatment measures of acute respiratory distress syndrome (ARDS).From the traditional high tidal volume ventilation (10 ~ 15 mL/kg) to the current use of lung protective ventilation strategies??low tidal volume ventilation (VT)??positive end-expiratory pressure (PEEP)??airway pressure release ventilation (APRV)??bilevel positive airway pressure(BIPAP)??considerable progress has been made.In addition to the well-known conventional mechanical ventilation modes and methods??there are many non-standard mechanical ventilation modes and methods??such as prone position ventilation??neurally adjusted ventilatory assist (NAVA)??extracorporeal membrane oxygenation (ECMO)??high-frequency ventilation and etc.All these measures produce unique effects on the treatment of ARDS.     

肺复张手法与单纯小潮气量机械通气治疗急性呼吸窘迫综合征

目的观察肺复张手法对急性呼吸窘迫综合征（ARDS）患者的治疗作用,并与小潮气量辅助／控制通气方式比较。方法20例ARDS患者,平均年龄（58±8）岁。分为两组：（1）试验组10例：采用肺复张手法机械通气;（2）对照组10例：采用小潮气量辅助／控制通气（潮气量设为6ml／kg,体重为标准体重）。分别观察两组患者上机后0、48和72h的氧合指数、中心静脉压、镇静药物的用量以及28d的病死率和并发症等。结果试验组与对照组比较,氧合指数48h分别为（297±15）及（211±12）cmH20,72h为（305±18）及（247±16）cmH2O;带机时间缩短为（15±2）及（21±2）d;48h中心静脉压分别为（14．1±0．5）及（19．2±1．0）cmH2O,72h分别为（11．3±0．8）及（17．1±1．1）cmH2O。28d病死率和并发症的发生率两组比较差异无统计学意义（P〉0．05）。结论肺复张手法比单纯小潮气量容量控制／辅助通气具有改善氧合迅速、带机时间短、血流动力学稳定及所用镇静药物少等优点。     

Extracorporeal lung assist in severe respiratory failure and ARDS. Current situation and clinical applications

Despite improvements in ventilation support techniques, lung protection strategies, and the application of new support treatment, acute respiratory distress syndrome continues to have a high mortality rate. Many strategies and treatments for this syndrome have been investigated over the last few year. However, the only therapeutic measure that has systematically shown to be able to improve survival is that of low volume lung protective ventilation. Thus, using a low tidal volume prevents added lung damage by the same mechanical ventilation that is essential for life support. In this context, the use of extracorporeal lung assist systems is considered an exceptional use rescue treatment in extreme cases. On the other hand, it could be a potentially useful complementary method for an ultra-protective ventilation strategy, that is, by using even lower tidal volumes. The currently available extracorporeal lung assist systems are described in this article, including high flow systems such as traditional extracorporeal membrane oxygenation, CO₂ removal systems (interventional lung assist or iLA, with or without associated centrifugal pumps), and the new low flow and less invasive systems under development. The aim of this review is to update the latest available clinical and experimental data, the indications for these devices in adult respiratory distress syndrome (ARDS), and their potential indications in other clinical situations, such as the bridge to lung transplantation, multiple organ dysfunction syndrome, or COPD.     

Reducing acute respiratory distress syndrome occurrence using mechanical ventilation

The standard treatment for acute respiratory distress syndrome (ARDS) is supportive in the form of low tidal volume ventilation applied after significant lung injury has already developed. Nevertheless, ARDS mortality remains unacceptably high (> 40%). Indeed, once ARDS is established it becomes refractory to treatment, and therefore avoidance is key. However, preventive techniques and therapeutics to reduce the incidence of ARDS in patients at high-risk have not been validated clinically. This review discusses the current data suggesting that preemptive application of the properly adjusted mechanical breath can block progressive acute lung injury and significantly reduce the occurrence of ARDS.     

Best compliance during a decremental, but not incremental, positive end-expiratory pressure trial is related to open-lung positive end-expiratory pressure: a mathematical model of acute respiratory distress syndrome lungs

A mathematical model of the acute respiratory distress syndrome (ARDS) lung, incorporating simulated gravitational superimposed pressure and alveolar opening and closing pressures, was used to study the mean tidal pressure-volume (PV) slope ("effective compliance") during incremental and decremental positive end-expiratory pressure (PEEP) trials with constant tidal volume (VT) "ventilation." During incremental PEEP, the PEEP giving maximum mean tidal PV slope did not coincide with "open lung PEEP" (minimum PEEP preventing end expiratory collapse of 97.5% of alveoli inflated at end-inspiration), and it varied greatly with varying VT and "lung mechanics." Incremental PEEP with a low VT tests recruitment by the peak pressure, not prevention of collapse by PEEP. During decremental PEEP with a low VT, maximum mean tidal PV slope occurred with PEEP 2-3.5 cm H2O below open-lung PEEP, unless closing pressure was high. High VT, high "specific compliance," and high opening pressures caused slightly greater underestimation of open-lung PEEP. Maximum mean tidal PV slope was always higher (e.g., 93.7 versus 16.69 ml/cm H2O), and the variation in PV slope with PEEP was greater, during decremental PEEP. The maximum PV slope during a decremental PEEP trial with a low VT may be a useful method to determine open-lung PEEP in ARDS, and should be studied clinically.     

The effect of hypopnea on low-pressure pulmonary edema

The effects of the mechanical factors involved in ventilation on pulmonary edema are only partially understood. To clarify the effect of ventilation on the adult respiratory distress syndrome (ARDS), we examined the effect of reducing rate and tidal volume on oleic acid-induced low-pressure pulmonary edema in dogs, hypothesizing that hypopnea would reduce lung edema. We placed the experimental animals on venous-venous extracorporeal membrane oxygenation (ECMO) for CO2 clearance and oxygenation 1 h after the injury. This allowed reduction of the ventilatory rate from 17.2 +/- 4.8 to 3.3 +/- 0.8 breaths/min and tidal volume from 20 to 16 ml/kg, effectively resting the injured lung. After 5 h of hypopnea there was no reduction in edema by gravimetric or extravascular thermal volume measurements. The ECMO-facilitated hypopnea reduced airway pressure and pulmonary artery pressure while improving arterial oxygen saturation but increased venous admixture. These results suggest that there may be a supportive role for ECMO-assisted hypopnea, but there was no direct beneficial effect of hypopnea on edema.     

机械通气在急性呼吸窘迫综合征中的应用进展

在治疗急性呼吸窘迫综合征的各种手段中,呼吸机机械通气是至关重要的.各种机械通气方式及参数的设置对于改善患者预后极为重要.从现有的研究资料来看,小潮气量机械通气(<6 ml/kg预计体质量,并使平台压小于30 cm H_2O)能减少死亡率,是急性呼吸窘迫综合征治疗的标准疗法.而个体化的呼气末正压通气也是一个有前途的值得研究的方向.其他一些方法例如俯卧位通气、肺复张等不能作为常规的一线治疗,而只能作为严重情况下低氧血症的挽救治疗.另外本文也就机械通气在2009年甲型H1N1流感所致急性呼吸窘迫综合征的治疗方面做了简单综述.     

Clinicians' approaches to mechanical ventilation in acute lung injury and ARDS.

STUDY OBJECTIVES: To examine clinicians' approaches to mechanical ventilation in patients with acute lung injury (ALI; PaO(2)/fraction of inspired oxygen [FIO(2)] 35 cm H(2)O in 26% of patients. Seventy-eight percent of patients with ARDS received 相似文献   

改良的保护性肺通气策略对婴幼儿体外循环术后急性呼吸窘迫综合征的疗效

目的:探讨改良“保护性肺通气策略”的可行性,并评价其对婴幼儿体外循环术后急性呼吸窘迫综合征(ARDS)的治疗效果。方法:对17例先天性心脏病术后合并ARDS的婴幼儿采用新的通气模式:(1)低潮气量(6～8ml/kg);(2)高PEEP(6～12cmH_2O);(3)限制气道峰压(<30～35cmH_2O);(4)高呼吸频率(25～40次/分钟);(5)适当允许高碳酸血症(PaCO_2≤60mmHg)。同时注重液体限制、体位疗法等辅助措施,并在部分危重患儿及时应用外源性肺表面活性物质和(或)一氧化氮。结果:术后平均应用呼吸机时间12.73天。与以往同类病例的治疗结果相比,本组患儿无死亡,并发症发生率降低,无明显后遗症,近远期随访均满意。结论:在改良的保护性肺机械通气的基础上,辅以液体限制、外源性肺表面活性物质、一氧化氮等综合治疗手段,可以明显提高体外循环术后ARDS的治疗效果。