Mechanical ventilation in the management of acute respiratory distress syndrome

The occurrence of acute respiratory distress syndrome (ARDS), is now common in intensive care units throughout the world. The diagnosis of ARDS is based on a definition that includes bilateral pulmonary infiltrates on chest radiographs, impaired oxygenation, and the absence of clinical evidence of elevated left atrial pressure. ARDS is the clinical result of a group of diverse processes, which range from physical or chemical injury, to extensive activation of innate inflammatory response. All these processes damage the integrity of the alveolar-capillary barrier causing increased alveolar-capillary permeability and an influx of protein-rich fluid into the alveolar space. This alveolar flooding results in hypoxemia, inactivated surfactant, intrapulmonary shunt, and impaired alveolar ventilation. The treatment of acute respiratory distress syndrome is largely supportive in nature, keeping patients alive while allowing their lungs to heal, and minimizing further pulmonary insult. In 1994 the National Heart, Lung, and Blood Institute (NHLBI) established the ARDS Network for the conduct of clinical trials. This is a network, supported by the National Institutes of Health, that provided the infrastructure for well-designed, multicenter, randomized trials of therapies for ARDS. The first study from this group in 2001 produced landmark data demonstrating mortality improvements in ARDS with particular mechanical ventilation strategies. Specifically, low tidal volume mechanical ventilation was demonstrated to reduce mortality by 22%. Other strategies such as high positive end expiratory pressure and prone positioning have not been shown to reduce mortality. Clinicians who are involved in the care of patients with ARDS should have a basic understanding of mechanical ventilation and the evidence guiding the mechanical ventilation strategies of these patients. Until further evidence is published, providers should adopt the use of a volume and pressure limited approach to mechanical ventilation.     

Gas embolism during protective ventilation for acute respiratory distress syndrome

A 34-year-old woman with toxic coma developed inhalation pneumonia complicated by the acute respiratory distress syndrome. Marked parenchymal destruction and recurrent pneumothorax occurred despite protective ventilation. Altered consciousness persisted after sedative withdrawal, and the patient subsequently died. Computed tomography revealed multiple cerebral, renal and splenic infarcts. The only identified cause of systemic embolism was multiple gas embolisms. We discuss the physiopathological mechanisms, and the diagnostic and therapeutic management of such patients.     

Mechanical ventilation in acute respiratory distress syndrome

The acute respiratory distress syndrome occurs commonly in critical care. There is an increasing volume of clinical and experimental evidence that poor ventilatory technique that is injurious to the lungs can propagate the systemic inflammatory response and adversely affect mortality. Many ventilatory techniques have been hypothesized to 'protect' the lungs during mechanical ventilation, including tidal volume limitation, high positive end-expiratory pressure, pressure-controlled inverse ratio ventilation, and prone positioning. Experimental techniques include liquid ventilation, surfactant administration and extracorporeal gas exchange. Despite excellent rationale for their use, few techniques, apart from tidal volume limitation, have been shown to improve survival in randomized controlled trials.     

Mechanical ventilation and acute respiratory distress syndrome

Acute respiratory distress syndrome continues to be a high-mortality condition. The role of mechanical ventilation remains primarily a supportive modality. Recent research has elucidated the adverse impact of traditional ventilation strategies on development of the disease and, ultimately, mortality. The institution of low tidal volume ventilation has been the only intervention that has resulted in definitive improvement in survival. Animal and human investigations that culminated in the Acute Respiratory Distress Syndrome Network low tidal volume study are reviewed. Current controversies in the application of mechanical ventilation including the use of positive end-expiratory pressure, recruitment maneuvers, and high frequency oscillatory ventilation are also addressed.     

Protective ventilation strategy in the acute respiratory distress syndrome

Acute lung injury (ALI) and acute respiratory distress syndrome (ARDS) contribute to progressive hypoxemia in critically ill patients. It has been proved that conventional mechanical ventilation with physiological respiratory volume contributes to further lung damage. In this respect, application of protective ventilatory strategy--pulmonary ventilation with limited volume and pressure can avoid mentioned consequences. The aim of this paper is to discuss mechanims by which elements contained in protective mechanical ventilation of patients with ALI/ARDS prevent further progrssive lung injury, to argue the effects of positive end--expiratory pressure and present insturctions for its application.     

Protective ventilation of patients with acute respiratory distress syndrome

Editor—We read with interest the review article by Moloneyand Griffiths¹ on protective ventilation of patients with acuterespiratory distress syndrome (ARDS). Recent insights into pulmonarymechanics have led to a re-evaluation of the role of positiveend-expiratory pressure (PEEP) in ventilated ARDS patients.We felt that the authors did not highlight this issue correctly.In their review, the     

Protective ventilation of patients with acute respiratory distress syndrome

The majority of patients with acute respiratory distress syndrome(ARDS) require mechanical ventilation. This support providestime for the lungs to heal, but the adverse effects of mechanicalventilation significantly influence patient outcome. Traditionally,these were ascribed to mechanical effects, such as haemodynamiccompromise from decreased venous return or gross air leaks inducedby large transpulmonary pressures. More recently, however, theARDS Network study has established the clinical importance oflowering the tidal volume to limit overdistension of the lungwhen ventilating patients with ARDS. This study suggests thatventilator-associated lung injury (VALI) caused by overdistensionof the lung contributes to the mortality of patients with ARDS.Moreover, the results from clinical and basic research haverevealed more subtle types of VALI, including upregulation ofthe inflammatory response in the injured and overdistended lung.This not only damages the lung, but the overflow of inflammatorymediators into the systemic circulation may explain why mostpatients who die with ARDS succumb to multi-organ failure ratherthan respiratory failure. The results of these studies, thepresent understanding of the pathophysiology of VALI, and protectiveventilatory strategies are reviewed. Br J Anaesth 2004; 92: 261–70     

An approach to ventilation in acute respiratory distress syndrome.

Appropriate management of patients with acute respiratory distress syndrome (ARDS) represents a challenge for physicians working in the critical care environment. Significant advances have been made in understanding the pathophysiology of ARDS. There is also an increasing appreciation of the role of ventilator-induced lung injury (VILI). VILI is most likely related to several different aspects of ventilator management: barotrauma due to high peak airway pressures, lung overdistension or volutrauma due to high transpulmonary pressures, alveolar membrane damage due to insufficient positive end expiratory pressure levels and oxygen-related cell toxicity. Various lung protective strategies have been suggested to minimize the damage caused by conventional modes of ventilation. These include the use of pressure- and volume-limited ventilation, the use of the prone position in the management of ARDS, and extracorporeal methods of oxygen delivery and carbon dioxide removal. Although the death rate resulting from ARDS has been declining over the past 10 years, there is no evidence that any specific treatment or change in approach to ventilation is the cause of this improved survival.     

Mechanical ventilation in acute respiratory distress syndrome. New Trends

Adult Respiratory Distress Syndrome (ARDS) is characterized by an inflammatory process affecting endothelial and epithelial lung tissue, with occurrence of hypoxemia, bilateral X-ray infiltrates, in absence of cardiogenic edema. The introduction of Computerized Tomography brought some improvements in understanding the ARDS lung, leading to a pulmonary model made up of three zones: 1) normally inflated, 2) recruitable and 3) consolidated. It has now been well established that mechanical ventilation of ARDS lung presents some iatrogenic effects that may affect mortality. Several mechanisms are considered responsible of ventilator-associated lung injury (VALI): high inspired oxygen fraction, high inspiratory plateau pressure and large tidal volume, and intratidal collapse and reinflation of alveolar units. In these years, different ventilatory strategies in the treatment of ARDS patients have been suggested to decrease and to prevent VALI. The most important one seems to be the application of an appropriate value of tidal volume and positive end-expiratory pressure (PEEP). Several randomized studies, which compared low versus high tidal volumes, have recently been finished. Despite some differences, it seems that a ventilatory management limiting inspiratory plateau pressure to 35 cmH2O or lower may be useful to reduce VALI and mortality, also in association with a PEEP level sufficient to decrease the end-expiratory collapse. Another useful ventilatory tool for improving gas exchange and decreasing VALI in ARDS patients is likely the prone positioning, even if further studies are necessary to understand how this maneuver may really affect mortality. Another therapeutic instrument for improving oxygenation in ARDS patients is the inhalation of NO. Unfortunately, this pharmacological agent does not seem to affect the outcome of these patients.     

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.     

High frequency oscillatory ventilation in burn patients with the acute respiratory distress syndrome

BACKGROUND: High frequency oscillatory ventilation (HFOV) improves gas exchange while providing lung protective effects during the ventilation of patients with the acute respiratory distress syndrome (ARDS). The purpose of this study was to review our experience with HFOV in adult burn patients with oxygenation failure secondary to ARDS. METHODS: Retrospective cohort review of all burn patients treated with HFOV at a regional adult burn center. RESULTS: All values are reported as the mean +/- standard deviation (S.D.). HFOV was used on 28 occasions in 25 patients (age 44 +/- 16 years, %TBSA burns 40 +/- 15, and a 28% incidence of inhalation injury) who had severe oxygenation failure from ARDS (PaO2/FiO2 ratio 98 +/- 26, and oxygenation index (OI) (FiO2 x 100 x mean airway pressure/PaO2) 27 +/- 10) following 4.8 +/- 4.4 days of conventional mechanical ventilation (CMV). After switching from CMV to HFOV, there were significant improvements in the PaO(2)/FiO2 ratio within 1h and in the oxygenation index within 24 h. The duration of HFOV was 6.1 +/- 5.8 days. HFOV was continued during 26 surgeries for 14 patients where a mean of 18 +/- 9% TBSA burns were excised and closed. The only complications related to HFOV were three episodes of severe hypercapnia. In-hospital mortality was 32%. CONCLUSIONS: HFOV was safe, and was highly effective in correcting oxygenation failure associated with ARDS in burn patients, and can be successfully used as an intra-operative ventilation modality for burn patients.     

高频振荡通气在成年人急性呼吸窘迫综合征的临床应用

背景 高频振荡通气(high-frequency oscillatory ventilation,HFOV)作为一种新的通气模式,具有高频率、小潮气量、高平均气道压的特点,近年来被成功应用于成年人急性呼吸窘迫综合征(acute respiratory distress syndrome,ARDS)的治疗.研究表明,HFOV在改善氧合、减少呼吸机相关性肺损伤(ventilator associated lung injury,VILI)方面较常规机械通气(conventional mechanical ventilation,CMV)具有优势.但其对ARDS病死率的影响尚不明确. 目的 通过归纳HFOV在成年人ARDS中的临床应用揭示HFOV的优势和缺陷. 内容 HFOV能够高效改善氧合、减少VILI,但不能减少ARDS的病死率.HFOV技术的最适患者的筛选、最佳使用时机、最佳参数的设定以及与其他治疗手段联用等问题有待进一步探索. 趋向 HFOV应用于ARDS的治疗需要更加深入的研究和探索.     

Comparative study of pressure-control ventilation and volume-control ventilation in treating traumatic acute respiratory distress syndrome

echanicalventilationisthemosteffectivemethodintreatingtraumaticacuterespiratorydistresssyndrome (ARDS ) .Butcommonmechanicalventilationmaycausesomesideeffects ,suchas pressureinjuryanddecreaseofcardiacoutput.Inthisstudy ,4 0 patientssufferingfromtraumaticARDShospitalizedinourdepartmentfromJune 1996toDecember 2 0 0 2weretreatedwithpressure controlventilation (PCV ,n =2 0 )andvolume controlventilation (VCV ,n =2 0 ) ,respectively .METHODSClinicaldataAmongthe 4 0 patientswithtraumaticAR…