Clinical impact of recruitment maneuvers in patients with acute respiratory distress syndrome

In patients with acute respiratory distress syndrome (ARDS), recruitment maneuvers have been proposed as an adjunct to mechanical ventilation to open up atelectasis and to keep these alveoli open by the application of adequate high levels of positive end-expiratory pressure (PEEP). Though several studies reported that the responsiveness to recruitment maneuvers resulted in a marked improvement of oxygenation with a concomitant decrease in airway pressure and/or inspiratory fraction of oxygen, the performance of recruitment maneuvers still remains a matter of dispute, especially in patients ventilated with a lung protective ventilation strategy. In this review we discuss the pathophysiological background, factors affecting the responsiveness to recruitment maneuvers and their clinical impact in the light of recently published studies. Successful recruitment depends on several factors like the applied recruitment pressure, the level of PEEP set before and after the recruitment maneuver, the stage and the underlying disease of the ARDS, chest wall mechanics and the transpulmonary pressure as well as the positioning of the patient. Regarding the current literature, recruitment maneuvers may be considered as a rescue therapy in the early stage of severe hypoxemic lung failure, if a lung protective ventilation strategy and other additive adjuncts like prone positioning or the application of inhaled vasodilators failed to induce adequate gas exchange.     

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.     

Diagnostic studies in patients with acute respiratory distress syndrome

Acute respiratory distress syndrome (ARDS) is a clinical-radiological diagnosis. Clinical diagnosis comprises severe hypoxemia assessed by arterial oxygen tension/fraction of inspired oxygen ratio of less than 200 and bilateral infiltrate on a chest radiograph in the absence of left atrial hypertension. The sensitivity and specificity of the clinical diagnosis vary based on the underlying etiology for ARDS. Except for presence of bilateral infiltrate on chest radiograph and severe hypoxemia on arterial blood gas, most diagnostic studies are used to exclude mimics of ARDS and potentially modify treatment. Computerized tomography of the chest is helpful in understanding the extent of the disease and is more sensitive in identifying pneumomediastinum and pneumothoraces seen frequently in patients with ARDS, which can be missed on a chest radiograph, especially if they are small in size. Measurements of alveolar dead space ventilation fraction can be helpful in determining the prognosis in individuals with ARDS. Bronchoalveolar lavage, transbronchial lung biopsy, and open lung biopsies can be safely performed in patients with ARDS. Bronchoalveolar lavage fluid in patients with ARDS shows neutrophil predominance with increased edema fluid to serum protein ratio. Diffuse alveolar damage, a pathognomic of ARDS, is seen on histopathology on transbronchial lung biopsy or open lung biopsy. Most common complications of these procedures include transient hypoxemia, respiratory acidosis, and pneumothorax with occasional persistent air leak. The potential risk of diagnostic studies should be balanced against the possible foreseeable benefits of the diagnostic studies.     

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     

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.     

Advances in the management of acute respiratory distress syndrome: protective ventilation

The approach to mechanical ventilation has been revolutionized by new insights into the pathogenesis of respiratory failure in acute respiratory distress syndrome (ARDS). Concepts such as low-volume ventilation, permissive hypercapnia, inverse ratio ventilation, best and intrinsic positive end-expiratory pressure, airway shear, pressure volume curves, inflection points, and prone positioning have radically transformed thinking about ventilator management. Since 1966, more than 8000 ARDS-related publications have appeared. Studies highlighting the experimental basis for innovations in mechanical ventilation are presented. Selected clinical series that exemplify the use of these new strategies are reviewed, to demonstrate how key experimental and clinical research has altered our understanding about what works, and why. Mismanagement of mechanical ventilation causes lung injury and increases mortality. The strategy of protective ventilation has provided the first substantial reduction of mortality in the history of ARDS.     

The pharmacokinetics of cisatracurium in patients with acute respiratory distress syndrome

Continuous neuromuscular blockade is often necessary in patients being treated for acute respiratory distress syndrome (ARDS) to optimize oxygenation. In this study, neuromuscular blockade (no response to two responses at the train-of-four stimulation at the orbicularis oculi muscle) was achieved in six patients with ARDS by a continuous infusion of cisatracurium. The plasma concentration of cisatracurium during the infusion averaged 1.00 (0.25-1.45) microg/mL, expressed as median (range). The clearance and half-life were 6.5 (3.3-7.6) mL. min(-1). kg(-1) and 25 (16-48) min, respectively. The laudanosine plasma concentrations were 0.70 (0.12-1.20) microg/mL. The pharmacokinetic variables of cisatracurium are similar to those of patients without organ failure undergoing elective surgery. Plasma laudanosine levels always remained well less that those associated with seizure activity in animal models. Long-term infusion of cisatracurium was not associated with any side effects. Cisatracurium is a suitable muscle relaxant when deep and continuous levels of muscle relaxation are required in patients treated for ARDS. IMPLICATIONS: We studied the pharmacokinetics of cisatracurium in six patients treated for respiratory distress syndrome by continuous muscle relaxation. A deep degree of neuromuscular blockade corresponding to abolition of two responses at the orbicularis oculi to train-of-four stimulation was obtained in all patients. The pharmacokinetic variables observed in these severely ill patients were similar to those of anesthetized patients. No accumulation of laudanosine was seen. Cisatracurium appears to be suitable when continuous muscle relaxation is required in critically ill patients.     

急性呼吸窘迫综合征病人肺泡表面活性物质的变化

目的　研究患急性呼吸窘迫综合征 (ARDS)时病人肺泡表面活性物质的变化。方法　应用薄层色谱法测定ARDS早期病人 ( 5例 )和晚期病人 ( 5例 )肺泡灌洗液中肺泡表面活性物质 ,并和正常对照组 ( 5例 )作比较。结果　肺泡表面活性物质的含量在对照组、早期组、晚期组分别为6 7 6± 7 2、44 0± 7 3、31 3± 6 5 μg/ml肺灌洗液 ,呈递减改变。肺泡表面活性物质主要活性成份磷脂酰胆碱、磷脂酰甘油和二磷脂酰甘油的百分比在ARDS早期升高 ,分别达 5 6 2 %± 2 8%、9 2 %±1 5 %和 2 9%± 0 7%。在ARDS晚期 ,上述三种活性成份分别降至 39 7%± 5 2 %、5 6 %± 0 7%和 2 6 %± 0 6 %。结论　ARDS病人随着病情的进展加重 ,其肺泡表面活性物质的含量和主要活性成份逐渐减少。提示若使用外源性肺泡表面活性物质防治ARDS ,不仅要在数量上补足 ,而且需要恢复活性成份的比例 ,才有可能获得理想的疗效     

分化综合征合并急性呼吸窘迫综合征患者的护理

对6例分化综合征合并急性呼吸窘迫综合征患者转重症医学科抢救治疗,均给予经口气管插管、呼吸机辅助呼吸,采取肺保护性通气策略,3例好转,3例死亡。紧急配合各项抢救措施到位,严密观察生命体征及白血病相关颅内并发症的发生,做好机械通气的管理及感染预防等是有效救治的基础。     

Airway pressure release ventilation as a primary ventilatory mode in acute respiratory distress syndrome

BACKGROUND: Airway pressure release ventilation (APRV) is a ventilatory mode, which allows unsupported spontaneous breathing at any phase of the ventilatory cycle. Airway pressure release ventilation as compared with pressure support (PS), another partial ventilatory mode, has been shown to improve gas exchange and cardiac output. We hypothesized whether the use of APRV with maintained unsupported spontaneous breathing as an initial mode of ventilatory support promotes faster recovery from respiratory failure in patients with acute respiratory distress syndrome (ARDS) than PS combined with synchronized intermittent ventilation (SIMV-group). METHODS: In a randomized trial 58 patients were randomized to receive either APRV or SIMV after a predefined stabilization period. Both groups shared common physiological targets, and uniform principles of general care were followed. RESULTS: Inspiratory pressure was significantly lower in the APRV-group (25.9 +/- 0.6 vs. 28.6 +/- 0.7 cmH2O) within the first week of the study (P = 0.007). PEEP-levels and physiological variables (PaO2/FiO2-ratio, PaCO2, pH, minute ventilation, mean arterial pressure, cardiac output) were comparable between the groups. At day 28, the number of ventilator-free days was similar (13.4 +/- 1.7 in the APRV-group and 12.2 +/- 1.5 in the SIMV-group), as was the mortality (17% and 18%, respectively). CONCLUSION: We conclude that when used as a primary ventilatory mode in patients with ARDS, APRV did not differ from SIMV with PS in clinically relevant outcome.     

神经电活动辅助通气模式和压力支持通气模式对急性呼吸窘迫综合征患者肺内气体分布影响的比较

目的比较神经电活动辅助通气(NAVA)模式和压力支持通气(PSV)模式对急性呼吸窘迫综合征(ARDS)患者肺内气体分布的影响。方法本研究纳入18例符合标准的ARDS机械通气患者,男11例,女7例,采用单盲随机自对照的研究方法,同一患者以随机先后顺序应用NAVA和PSV模式分别通气30min,在通气0、30min时观察气体交换、血流动力学指标,对呼吸参数、人机同步性以及电阻抗断层摄影监测的肺气体分布均进行持续监测分析。结果与PSV比较,两种模式下HR、MAP、PIP及PEEP差异无统计学意义;NAVA模式改善ARDS患者氧合指数(P0.05),减少人机不同步事件的发生(P0.05),增加重力依赖区ROI 3、4区通气,减少非重力依赖区ROI 1、2区通气(P0.05)。结论与PSV比较,NAVA可以改善ARDS患者气体交换和人机同步性,改善肺内气体分布不均一性。     

急性肺损伤/急性呼吸窘迫综合征液体治疗策略

背景 高通透性肺水肿是急性肺损伤/急性呼吸窘迫综合征(acute lung injury/acute respiratory distress syndrome,ALI/ARDS)的基本病理生理特征,其程度与ALI/ARDS的预后密切相关.目的 对ALI/ARDS患者合理的液体管理,有助于改善ALI/ARDS患者的肺水肿,降低该病病死率.内容 回顾了ALI/ARDS液体治疗策略探索过程中存在争议的问题(如限制性或开放性的液体治疗策略及治疗液体种类的选择),总结了该领域近年来的研究进展(如ALI/ARDS病程不同阶段的差异化治疗及液体治疗的监测指标).趋向 今后将进一步探索该病在不同的病理生理状态下特异性的液体治疗方法,寻求高效敏感的监测指标,指导液体治疗策略的选择和调整.     

Hemodynamic variability caused by pressure-volume plotting and alveolar recruitment maneuvers in patients with adult respiratory distress syndrome

OBJECTIVES: The plotting of pressure-volume curves and the performance of alveolar recruitment maneuvers are common practices in the care of patients with adult respiratory distress syndrome (ARDS), even though potentially harmful hemodynamic effects are associated with sustaining a high intrathoracic pressure. Our aim was to analyze hemodynamic and ventilatory changes related to these 2 maneuvers and to assess the short-term effectiveness of recruitment. PATIENTS AND METHODS: The patients had ARDS and were being monitored with a catheter connected to a PiCCO system. All measurements were taken in sinus rhythm and with adequate vascular filling. Values recorded during plotting of the quasistatic pressure-volume curve and the recruitment maneuver (sustained airway pressure of 40 cm H2O) were the cardiac index, mean arterial pressure, heart rate, systolic volume index, and oxygen saturation (SpO2). Blood gas measurements were recorded before the maneuvers and 15 minutes afterwards. RESULTS: All parameters decreased significantly in the 14 patients studied. The mean (SD) maximum decreases, from which all patients recovered within 2 minutes, were as follows: cardiac index, 26% (16%); mean arterial pressure, 6% (6%); heart rate, 4% (5%), systolic volume index, 21% (15%); and SpO2, 3% (3%). Significant increases in PaO2 (7% [6%]) and the ratio of PaO2 to the fraction of inspired oxygen were recorded after the recruitment maneuver (P=.016 and P=.014, respectively), but the changes were not clinically significant. CONCLUSIONS: The hemodynamic disturbances associated with the alveolar recruitment maneuver based on sustaining a high end-expiratory pressure and the minor improvement in oxygenation achieved as a result suggest that the routine use of that maneuver in ARDS patients is of questionable value.