What is the acute respiratory distress syndrome?

It has been known for decades that shock and sepsis can cause a syndrome of acute respiratory failure with characteristics of non-cardiogenic pulmonary edema. Over the years, this syndrome has been given a number of names, including congestive atelectasis, traumatic wet lung, and shock lung. In 1967 the modern counterpart to this syndrome was described and subsequently called the "acute respiratory distress syndrome" (ARDS). This syndrome results from lung injury and inflammation. As with inflammation elsewhere, ARDS is accompanied by many cellular and molecular processes, some of them specific to the syndrome, others perpetuating the syndrome, and others inactivating the by-products of inflammation. Since no specific clinical sign or diagnostic test has yet been described that identifies ARDS, its diagnosis is based on a constellation of clinical, hemodynamic, and oxygenation criteria. Current ARDS treatment is mainly supportive, since these patients frequently have coexisting conditions. Although in 1994 a new standard ARDS definition was accepted, that definition failed to standardize the measurement of the oxygenation defect and does not recognize different severities of pulmonary dysfunction. Based on current evidence there is a need for a better definition and classification system that could help us to identify ARDS patients who would be most responsive to supportive therapies and those unlikely to benefit because of the severity of their disease process. This paper examines our current understanding of ARDS and discusses why the current definition may not be the most appropriate for research and clinical practice.     

Where are we with recruitment maneuvers in patients with acute lung injury and acute respiratory distress syndrome?

Reduction of tidal volume to limit plateau pressure currently is recommended for the ventilatory management of acute respiratory distress syndrome. However, sufficient evidence now exists to support the fact that excessive reduction in tidal volume may result in harmful alveolar derecruitment depending on the level at which positive end-expiratory pressure is set. The use of recruitment maneuvers has been proposed as an adjunctive lung-protective strategy to reverse low tidal volume-related derecruitment. Many questions remain regarding the basic physiologic principles of recruitment, and, therefore, the optimal way to perform recruitment maneuvers remains unknown. Moreover, apart from physiologic studies suggesting a potential benefit of recruitment maneuver in terms of recruitment and gas exchange, no data are yet available that demonstrate the ability of such a maneuver to improve outcome. In this article, we discuss the physiologic rules governing recruitment and derecruitment and review articles that provide new insights in the field of recruitment maneuver.     

Can lung ultrasonography predict prone positioning response in acute respiratory distress syndrome patients?

PurposeThe purpose was to assess whether lung ultrasonography (L-US) is a useful tool in prediction of prone positioning (PP) oxygenation response in patients with acute respiratory distress syndrome (ARDS).MethodsIn a prospective study, 19 ARDS patients were included for assessment of PP oxygenation response. The latter was assessed for at least 12 hours 6 different ultrasonography windows were performed on each hemithorax before prone (H0, H2, H12 before return to supine and at H14 (2 hours after return to supine). Patients were classified into 2 groups (responders / non responders) according their oxygenation response to PP. Ultrasonography videos were blindly evaluated by 3 expert clinicians to classify lung regions as “normal”, “moderate loss of aeration,” “severe loss of aeration,” or “lung consolidation.” Oxygenation parameters were collected at H0, H2, and H14.ResultsAssociation of each lung region aspect to PP oxygenation response was compared between the 2 groups. The normal aspect of the anterobasal regions was significantly associated with the oxygenation response (P = .0436), with a positive predictive value equal to or near 100%.DiscussionOur results demonstrated that a simple and short L-US examination could be a useful tool in prediction of PP oxygenation response in ARDS patients. A normal L-US pattern of both anterobasal lung regions in supine position may predict a significant Pao₂/Fio₂ ratio improvement.     

Why do pulse pressure variations fail to predict the response to fluids in acute respiratory distress syndrome patients ventilated with low tidal volume?

Respiratory-associated variations in stroke volume and pulse pressure are frequently used to predict the response to fluid administration. However, it has been demonstrated that low tidal volume ventilation may limit their use in patients with acute respiratory distress syndrome (ARDS). In this issue, a trial investigates the value of pulse pressure variation to predict fluid responsiveness in a large series of patients with ARDS ventilated according to current guidelines.     

Is a short trial of prone positioning sufficient to predict the improvement in oxygenation in patients with acute respiratory distress syndrome?

OBJECTIVE: To determine whether a 1-h trial of prone positioning is sufficient to identify responders. DESIGN: Prospective clinical cohort study in a medico-surgical ICU in a teaching hospital. PATIENTS: 49 patients with acute respiratory distress syndrome. INTERVENTIONS: A 6-h period of prone positioning. MEASUREMENTS AND RESULTS: Baseline measurements (blood gas analysis and respiratory parameters) were evaluated in supine position just prior to turning the patients prone. Measurements were then repeated 1 h after the beginning of prone positioning (PP1h) and at the end of the 6-h period of prone positioning (PP6h). The last measurements were performed 1 h after repositioning the patients supine. Prone position induced an increase in the PaO2/FIO2 ratio (p < 0.001). A response (increase in PaO2/FIO2 ratio of at least 20 % at PP1h and/or at PP6h) was observed in 37 of 49 patients (76%). Twenty-seven of these patients (73%) were responders at PP1h while 10 (27%) were responders only at PP6h- In all, two-thirds of the patients were considered persistent responders. However, whereas the PaO2/FIO2 ratio decreased significantly 1 h after repositioning the fast responders supine, the PaO2/ FIO2 ratio remained unchanged after repositioning slow responders. CONCLUSIONS: A short-term trial of prone positioning does not appear a sufficient method to identify patients who would benefit from the postural treatment.     

Is acute respiratory distress syndrome an iatrogenic disease?

In this month's issue of Critical Care, Determann and colleagues report the results of a randomized controlled trial comparing the effects of mechanical ventilation (MV) with two tidal volumes (6 versus 10 ml/kg predicted body weight) on cytokine levels in lung lavage fluid and plasma as a surrogate for early identification of acute lung injury (ALI) and/or acute respiratory distress syndrome (ARDS). The study was stopped early after an interim analysis - when 150 patients were enrolled - showing that the incidence of ALI/ARDS according to the current definition was 10.9% higher in the 10 ml/kg group, although duration of MV and mortality was similar in both groups. We examine these interesting results after providing a brief historical perspective and discuss the limitations and implications of the study.     

Glucocorticoid treatment in acute lung injury and acute respiratory distress syndrome

Experimental and clinical evidence show a strong association between dysregulated systemic inflammation and progression of acute respiratory distress syndrome (ARDS). This article reviews eight controlled studies evaluating corticosteroid treatment initiated before day 14 of ARDS. Available data provide a consistent strong level of evidence for improving outcomes. Treatment was also associated with a markedly reduced risk of death. This low-cost highly effective therapy is well-known, and has a low-risk profile when secondary prevention measures are implemented. The authors recommend prolonged methylprednisolone at 1 mg/kg/d initially in early ARDS, increasing to 2 mg/kg/d after 7 to 9 days of no improvement.