Routine prone positioning in patients with severe ARDS: feasibility and impact on prognosis

Effects of transthoracic echocardiography on the prognosis of patients with acute respiratory distress syndrome: a propensity score matched analysis of the MIMIC-III database

Background

Acute respiratory distress syndrome (ARDS) has high mortality and is mainly related to the circulatory failure.Therefore, real-time monitoring of cardiac function and structural changes has important clinical significance.Transthoracic echocardiography (TTE) is a simple and noninvasive real-time cardiac examination which is widely used in intensive care unit (ICU) patients.The purpose of this study was to analyze the effect of TTE on the prognosis of ICU patients with ARDS.

Methods

The data of ARDS patients were retrieved from the MIMIC-III v1.4 database and patients were divided into the TTE group and non-TTE group. The baseline data were compared between the two groups. The effect of TTE on the prognosis of ARDS patients was analyzed through multivariate logistic analysis and the propensity score (PS). The primary outcome was the 28-d mortality rate. The secondary outcomes included pulmonary artery catheter (PAC) and Pulse index continuous cardiac output (PiCCO) administration, the ventilator-free and vasopressor-free days and total intravenous infusion volume on days 1, 2 and 3 of the mechanical ventilation. To illuminate the effect of echocardiography on the outcomes of ARDS patients,a sensitivity analysis was conducted by excluding those patients receiving either PiCCO or PAC. We also performed a subgroup analysis to assess the impact of TTE timing on the prognosis of patients with ARDS.

Results

A total of 1,346 ARDS patients were enrolled, including 519 (38.6%) cases in the TTE group and 827 (61.4%) cases in the non-TTE group. In the multivariate logistic regression, the 28-day mortality of patients in the TTE group was greatly improved (OR 0.71, 95%CI 0.55–0.92, P = 0.008). More patients in the TTE group received PAC (2% vs. 10%, P < 0.001) and the length of ICU stay in the TTE group was significantly shorter than that in the non-TTE group (17d vs.14d, P = 0.0001). The infusion volume in the TTE group was significantly less than that of the non-TTE group (6.2L vs.5.5L on day 1, P = 0.0012). Importantly, the patients in the TTE group were weaned ventilators earlier than those in the non-TTE group (ventilator-free days within 28 d: 21 d vs. 19.8 d, respectively, P = 0.071). The Kaplan–Meier survival curves showed that TTE patients had significant lower 28-day mortality than non-TTE patients (log-rank = 0.004). Subgroup analysis showed that TTE after hemodynamic disorders can not improve prognosis (OR 1.02, 95%CI 0.79–1.34, P = 0.844).

Conclusion

TTE was associated with improved 28-day outcomes in patients with ARDS.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12890-022-02028-5.

Application of prone position in hypoxaemic patients supported by veno-venous ECMO

INTRODUCTION

Veno-Venous Extracorporeal Membrane Oxygenation (VV-ECMO) is an advanced respiratory care therapy allowing replacement of pulmonary gas exchange. Despite VV-ECMO support, some patients may remain hypoxaemic. A possible therapeutic procedure for these patients is the application of prone positioning.

OBJECTIVE

The primary aim of the present study was to investigate modification of the PaO₂/FiO₂ ratio, in VV-ECMO patients with refractory hypoxaemia. The secondary aim was to evaluate the safety and feasibility of prone positioning for patients with severe Adult Respiratory Distress Syndrome supported by ECMO.

METHODS

We retrospectively reviewed the electronic records and charts of all patients supported by VV-ECMO who experienced at least one pronation. Complications related with prone positioning were also recorded. First PaO₂/FiO₂ ratio was analysed during four different time steps: before pronation, one hour after pronation, at the end of pronation and one hour after returning to supine.

RESULTS

A total of 45 prone positioning manoeuvers were performed in 14 VV-ECMO patients from November 2009 to November 2014. The median duration of prone positioning cycles was 8 hours (IQR 6-10). No accidental dislodgement of intravascular lines, endotracheal tubes, chest tubes or a decrease in ECMO blood flow was observed. During the first prone positioning for each patient, the median PaO₂/FiO₂ ratio recorded was 123 (IQR 82-135), 152 (93-185), 149 (90-186) and 113 (74-182), during PRE-supine step, 1 h-prone positioning step, END-prone positioning step, and POST-supine step respectively.

CONCLUSIONS

The application of prone positioning during VV-ECMO has shown to be a safe and reliable technique when performed in a recognised ECMO centre with the appropriately trained staff and standard procedures.

Acute respiratory distress syndrome: the heart side of the moon

PURPOSE OF REVIEW

Circulatory failure is a frequent complication during acute respiratory distress syndrome (ARDS) and is associated with a poor outcome. This review aims at clarifying the mechanisms of circulatory failure during ARDS.

RECENT FINDINGS

For the past decades, the right ventricle (RV) has gained a crucial interest since many authors confirmed the high incidence of acute cor pulmonale during ARDS and showed a potential role of the acute cor pulmonale in the poor outcome of ARDS patients. The most important recent progress demonstrated in ARDS ventilatory strategy is represented by the prone position, which has a huge beneficial effect on RV afterload. This review will focus on the mechanisms responsible for the RV dysfunction/failure during ARDS and on the strategy, which allows improving the right ventricular function.

SUMMARY

The RV has a pivotal role in the circulatory failure of ARDS patients. The ventilatory strategy during ARDS has to pay a peculiar attention to the RV to rigorously control its afterload.

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

PURPOSE

The 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).

METHODS

In 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.

RESULTS

Association 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%.

DISCUSSION

Our 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.

[Critically ill pediatric hemato-oncology patient: What we do is what we should do?]

OBJECTIVE

Primary objective, to describe the management and monitorization of critically ill pediatric hemato-oncology patient (CIPHO) in the Spanish pediatric intensive care units (PICU). Secondary objective, through a literature review, to identify possible areas of improvement.

MATERIAL AND METHODS

Observational transversal descriptive study. An anonymous web-based survey was sent to 324 Spanish pediatric intensivists from April 2011 to May 2011. None of them were pediatric residents.

RESULTS

The survey was answered by 105 intensivists, 59/105 always agreed their treatment with the oncologist. In case of hemodynamic instability, non-invasive blood pressure monitoring is always done by 85/105 and almost always optimized by intra-arterial measuring (85/105) and central venous pressure (70/105). If respiratory failure the use of non-invasive ventilation (NIPPV) is always (36/105) or frequently (60/105) established prior to conventional mechanical ventilation. To replace or withdraw non-invasive ventilation only 44/96 of the respondents to this question use a clinical protocol. Before the instauration of conventional mechanical ventilation the oncological prognosis is considered by 72/105. In case of acute oliguric renal failure the renal replacement techniques are widely used (74/105). The withdrawal of sustaining life support is frequently discussed (75/103) and agreed with the oncologist (91/103) and caregivers (81/103).

CONCLUSIONS

In our study, despite there is not a defined standard-of-care, the respondents showed similar therapeutics and monitorization choices. The use of NIPPV as first respiratory assistance is extended. Prospective, observational and multicenter studies should be developed to establish the results of this management in this population.

Prone position for acute respiratory failure in adults

BACKGROUND

Acute hypoxaemia de novo or on a background of chronic hypoxaemia is a common reason for admission to intensive care and for provision of mechanical ventilation. Various refinements of mechanical ventilation or adjuncts are employed to improve patient outcomes. Mortality from acute respiratory distress syndrome, one of the main contributors to the need for mechanical ventilation for hypoxaemia, remains approximately 40%. Ventilation in the prone position may improve lung mechanics and gas exchange and could improve outcomes.

OBJECTIVES

The objectives of this review are (1) to ascertain whether prone ventilation offers a mortality advantage when compared with traditional supine or semi recumbent ventilation in patients with severe acute respiratory failure requiring conventional invasive artificial ventilation, and (2) to supplement previous systematic reviews on prone ventilation for hypoxaemic respiratory failure in an adult population.

SEARCH METHODS

We searched the Cochrane Central Register of Controlled Trials (CENTRAL; 2014, Issue 1), Ovid MEDLINE (1950 to 31 January 2014), EMBASE (1980 to 31 January 2014), the Cumulative Index to Nursing and Allied Health Literature (CINAHL) (1982 to 31 January 2014) and Latin American Caribbean Health Sciences Literature (LILACS) (1992 to 31 January 2014) in Ovid MEDLINE for eligible randomized controlled trials. We also searched for studies by handsearching reference lists of relevant articles, by contacting colleagues and by handsearching published proceedings of relevant journals. We applied no language constraints, and we reran the searches in CENTRAL, MEDLINE, EMBASE, CINAHL and LILACS in June 2015. We added five new studies of potential interest to the list of "Studies awaiting classification" and will incorporate them into formal review findings during the review update.

SELECTION CRITERIA

We included randomized controlled trials (RCTs) that examined the effects of prone position versus supine/semi recumbent position during conventional mechanical ventilation in adult participants with acute hypoxaemia.

DATA COLLECTION AND ANALYSIS

Two review authors independently reviewed all trials identified by the search and assessed them for suitability, methods and quality. Two review authors extracted data, and three review authors reviewed the data extracted. We analysed data using Review Manager software and pooled included studies to determine the risk ratio (RR) for mortality and the risk ratio or mean difference (MD) for secondary outcomes; we also performed subgroup analyses and sensitivity analyses.

MAIN RESULTS

We identified nine relevant RCTs, which enrolled a total of 2165 participants (10 publications). All recruited participants suffered from disorders of lung function causing moderate to severe hypoxaemia and requiring mechanical ventilation, so they were fairly comparable, given the heterogeneity of specific disease diagnoses in intensive care. Risk of bias, although acceptable in the view of the review authors, was inevitable: Blinding of participants and carers to treatment allocation was not possible (face-up vs face-down).Primary analyses of short- and longer-term mortality pooled from six trials demonstrated an RR of 0.84 to 0.86 in favour of the prone position (PP), but findings were not statistically significant: In the short term, mortality for those ventilated prone was 33.4% (363/1086) and supine 38.3% (395/1031). This resulted in an RR of 0.84 (95% confidence interval (CI) 0.69 to 1.02) marginally in favour of PP. For longer-term mortality, results showed 41.7% (462/1107) for prone and 47.1% (490/1041) for supine positions, with an RR of 0.86 (95% CI 0.72 to 1.03). The quality of the evidence for both outcomes was rated as low as a result of important potential bias and serious inconsistency.Subgroup analyses for mortality identified three groups consistently favouring PP: those recruited within 48 hours of meeting entry criteria (five trials; 1024 participants showed an RR of 0.75 (95% CI 0.59 to 94)); those treated in the PP for 16 or more hours per day (five trials; 1005 participants showed an RR of 0.77 (95% CI 0.61 to 0.99)); and participants with more severe hypoxaemia at trial entry (six trials; 1108 participants showed an RR of 0.77 (95% CI 0.65 to 0.92)). The quality of the evidence for these outcomes was rated as moderate as a result of potentially important bias.Prone positioning appeared to influence adverse effects: Pressure sores (three trials; 366 participants) with an RR of 1.37 (95% CI 1.05 to 1.79) and tracheal tube obstruction with an RR of 1.78 (95% CI 1.22 to 2.60) were increased with prone ventilation. Reporting of arrhythmias was reduced with PP, with an RR of 0.64 (95% CI 0.47 to 0.87).

AUTHORS' CONCLUSIONS

We found no convincing evidence of benefit nor harm from universal application of PP in adults with hypoxaemia mechanically ventilated in intensive care units (ICUs). Three subgroups (early implementation of PP, prolonged adoption of PP and severe hypoxaemia at study entry) suggested that prone positioning may confer a statistically significant mortality advantage. Additional adequately powered studies would be required to confirm or refute these possibilities of subgroup benefit but are unlikely, given results of the most recent study and recommendations derived from several published subgroup analyses. Meta-analysis of individual patient data could be useful for further data exploration in this regard. Complications such as tracheal obstruction are increased with use of prone ventilation. Long-term mortality data (12 months and beyond), as well as functional, neuro-psychological and quality of life data, are required if future studies are to better inform the role of PP in the management of hypoxaemic respiratory failure in the ICU.

High-volume hemofiltration and prone ventilation in subarachnoid hemorrhage complicated by severe acute respiratory distress syndrome and refractory septic shock

We report the successful treatment of two patients with aneurismal subarachnoid hemorrhage complicated by severe respiratory failure and refractory septic shock using simultaneous prone position ventilation and high-volume hemofiltration. These rescue therapies allowed the patients to overcome the critical situation without associated complications and with no detrimental effects on the intracranial and cerebral perfusion pressures. Prone position ventilation is now an accepted therapy for severe acute respiratory distress syndrome, and high-volume hemofiltration is a non-conventional hemodynamic support that has several potential mechanisms for improving septic shock. In this manuscript, we briefly review these therapies and the related evidence. When other conventional treatments are insufficient for providing safe limits of oxygenation and perfusion as part of basic neuroprotective care in subarachnoid hemorrhage patients, these rescue therapies should be considered on a case-by-case basis by an experienced critical care team.

Effects on lung stress of position and different doses of perfluorocarbon in a model of ARDS

We determined whether the combination of low dose partial liquid ventilation (PLV) with perfluorocarbons (PFC) and prone positioning improved lung function while inducing minimal stress. Eighteen pigs with acute lung injury were assigned to conventional mechanical ventilation (CMV) or PLV (5 or 10 ml/kg of PFC). Positive end-expiratory pressure (PEEP) trials in supine and prone positions were performed. Data were analyzed by a multivariate polynomial regression model. The interplay between PLV and position depended on the PEEP level. In supine PLV dampened the stress induced by increased PEEP during the trial. The PFC dose of 5 ml/kg was more effective than the dose 10 ml/kg. This effect was not observed in prone. Oxygenation was significantly higher in prone than in supine position mainly at lower levels of PEEP. In conclusion, MV settings should take both gas exchange and stress/strain into account. When protective CMV fails, rescue strategies combining prone positioning and PLV with optimal PEEP should improve gas exchange with minimal stress.

The acute respiratory distress syndrome: incidence and mortality, has it changed?

PURPOSE OF REVIEW

The purpose of this review is to examine and discuss the incidence and outcome of patients with the acute respiratory distress syndrome (ARDS). This is a challenging task, as there is no specific clinical sign or diagnostic test that accurately identifies and adequately defines this syndrome.

RECENT FINDINGS

This review will focus on published epidemiological studies reporting population-based incidence of ARDS, as defined by the American-European Consensus Conference criteria. In addition, the current outcome figures for ARDS patients reported in observational and randomized controlled trials will be reviewed. The focus will be on studies published since 2000, when the ARDSnet study on protective mechanical ventilation was published, although particular emphasis will be on those articles published in the last 24 months.

SUMMARY

On the basis of current evidence, and despite the order of magnitude of reported European and USA incidence figures, it seems that the incidence and overall mortality of ARDS has not changed substantially since the original ARDSnet study. The current mortality of adult ARDS is still greater than 40%.

Enteral Nutrition in Patients Receiving Mechanical Ventilation in a Prone Position

BACKGROUND

Patients treated with mechanical ventilation in the prone position (PP) could have an increased risk for feeding intolerance. However, the available evidence supporting this hypothesis is limited and contradictory.

OBJECTIVE

To examine the feasibility and efficacy of enteral nutrition (EN) support and its associated complications in patients receiving mechanical ventilation in PP.

METHODS

Prospective observational study including 34 mechanically ventilated intensive care patients who were turned to the prone position over a 3-year period. End points related to efficacy and safety of EN support were studied.

RESULTS

In total, more than 1200 patients were admitted to the intensive care unit over a period of 3 years. Of these, 34 received mechanical ventilation in PP. The mean days under EN were 24.7 ± 12.3. Mean days under EN in the supine position were significantly higher than in PP (21.1 vs 3.6; P < .001), but there were no significant differences in gastric residual volume adjusted per day of EN (126.6 vs 189.2; P = .054) as well as diet volume ratio (94.1% vs 92.8%; P = .21). No significant differences in high gastric residual events per day of EN (0.06 vs 0.09; P = .39), vomiting per day of EN (0.016 vs 0.03; P = .53), or diet regurgitation per day of EN (0 vs 0.04; P = .051) were found.

CONCLUSIONS

EN in critically ill patients with severe hypoxemia receiving mechanical ventilation in PP is feasible, safe, and not associated with an increased risk of gastrointestinal complications. Larger studies are needed to confirm these findings.

Effects of prone positioning on lung protection in patients with acute respiratory distress syndrome

RATIONALE

Positive end-expiratory pressure (PEEP) and prone positioning may induce lung recruitment and affect alveolar dynamics in acute respiratory distress syndrome (ARDS). Whether there is interdependence between the effects of PEEP and prone positioning on these variables is unknown.

OBJECTIVES

To determine the effects of high PEEP and prone positioning on lung recruitment, cyclic recruitment/derecruitment, and tidal hyperinflation and how these effects are influenced by lung recruitability.

METHODS

Mechanically ventilated patients (Vt 6 ml/kg ideal body weight) underwent whole-lung computed tomography (CT) during breath-holding sessions at airway pressures of 5, 15, and 45 cm H2O and Cine-CTs on a fixed thoracic transverse slice at PEEP 5 and 15 cm H2O. CT images were repeated in supine and prone positioning. A recruitment maneuver at 45 cm H2O was performed before each PEEP change. Lung recruitability was defined as the difference in percentage of nonaerated tissue between 5 and 45 cm H2O. Cyclic recruitment/de-recruitment and tidal hyperinflation were determined as tidal changes in percentage of nonaerated and hyperinflated tissue, respectively.

MEASUREMENTS AND MAIN RESULTS

Twenty-four patients with ARDS were included. Increasing PEEP from 5 to 15 cm H2O decreased nonaerated tissue (501 ± 201 to 322 ± 132 grams; P < 0.001) and increased tidal-hyperinflation (0.41 ± 0.26 to 0.57 ± 0.30%; P = 0.004) in supine. Prone positioning further decreased nonaerated tissue (322 ± 132 to 290 ± 141 grams; P = 0.028) and reduced tidal hyperinflation observed at PEEP 15 in supine patients (0.57 ± 0.30 to 0.41 ± 0.22%). Cyclic recruitment/de-recruitment only decreased when high PEEP and prone positioning were applied together (4.1 ± 1.9 to 2.9 ± 0.9%; P = 0.003), particularly in patients with high lung recruitability.

CONCLUSIONS

Prone positioning enhances lung recruitment and decreases alveolar instability and hyperinflation observed at high PEEP in patients with ARDS.

Combination of positioning therapy and venovenous extracorporeal membrane oxygenation in ARDS patients

Positioning therapy may improve lung recruitment and oxygenation and is part of the standard care in severe acute respiratory distress syndrome (ARDS). Venovenous extracorporeal membrane oxygenation (vvECMO) is a rescue strategy that may ensure sufficient gas exchange in ARDS patients failing conventional therapy. The aim of this case series was to describe the feasibility and pitfalls of combining positioning therapy and vvECMO in patients with severe ARDS.

A retrospective cohort of nine patients is described. The patients received 20 (15–86) hours (median, 25th and 75th percentile) of positioning therapy while being treated with vvECMO. The initial PaO2/FiO2 index was 64 (51–67) mmHg and the arterial carbon dioxide tension was 60 (50–71) mmHg. Positioning therapy included 135 degrees prone, prone positioning and continuous lateral rotational therapy. During the first three days, the oxygenation index improved from 47 (41–47) to 12 (11–14) cmH2O/mmHg. The lung compliance improved from 20 (17–28) to 42 (27–43) ml/cmH2O. Complications related to positioning therapy were facial oedema (n=9); complications related to vvECMO were entrance of air (n=1) and pump failure (n=1). However, investigation of root causes revealed no association with the positioning therapy and had no documented effect on the outcome.

The reported cases suggest that positioning therapy can be performed safely in ARDS patients treated with vvECMO, providing appropriate precautions are in place and a very experienced team is present.

Feasibility and effectiveness of prone position in morbidly obese patients with ARDS: a case-control clinical study

BACKGROUND

Obese patients are at risk for developing atelectasis and ARDS. Prone position (PP) may reduce atelectasis, and it improves oxygenation and outcome in severe hypoxemic patients with ARDS, but little is known about its effect in obese patients with ARDS.

METHODS

Morbidly obese patients (BMI ≥ 35 kg/m²) with ARDS (Pao₂/FIo₂ ratio ≤ 200 mm Hg) were matched to nonobese (BMI < 30 kg/m²) patients with ARDS in a case-control clinical study. The primary end points were safety and complications of PP; the secondary end points were the effect on oxygenation (Pao₂/FIo₂ ratio at the end of PP), length of mechanical ventilation and ICU stay, nosocomial infections, and mortality.

RESULTS

Between January 2005 and December 2009, 149 patients were admitted for ARDS. Thirty-three obese patients were matched with 33 nonobese patients. Median (25th-75th percentile) PP duration was 9 h (6-11 h) in obese patients and 8 h (7-12 h) in nonobese patients (P = .28). We collected 51 complications: 25 in obese and 26 in nonobese patients. The number of patients with at least one complication was similar across groups (n = 10, 30%). Pao₂/FIo₂ ratio increased significantly more in obese patients (from 118 ± 43 mm Hg to 222 ± 84 mm Hg) than in nonobese patients (from 113 ± 43 mm Hg to 174 ± 80 mm Hg; P = .03). Length of mechanical ventilation, ICU stay, and nosocomial infections did not differ significantly, but mortality at 90 days was significantly lower in obese patients (27% vs 48%, P < .05).

CONCLUSIONS

PP seems safe in obese patients and may improve oxygenation more than in nonobese patients. Obese patients could be a subgroup of patients with ARDS who may benefit the most of PP.

Acute respiratory distress syndrome: current concepts and future directions

Acute respiratory distress syndrome is one of the leading causes of death in critically ill patients. Recent advances in supportive care have led to a moderate improvement in mortality. In particular, a much lower mortality rate than expected was evident in the severest category of patients (requiring extracorporeal membrane oxygenation) in Australia during the recent H1N1 pandemic. Though improvements in supportive care may have provided some benefit, there remains an absence of effective biological agents that are necessary to achieve further incremental reduction in mortality. This article will review the evidence available for current treatment strategies and discuss future research directions that may eventually improve outcomes in this important global disease.

Prone positioning in severe acute respiratory distress syndrome

BACKGROUND

Previous trials involving patients with the acute respiratory distress syndrome (ARDS) have failed to show a beneficial effect of prone positioning during mechanical ventilatory support on outcomes. We evaluated the effect of early application of prone positioning on outcomes in patients with severe ARDS.

METHODS

In this multicenter, prospective, randomized, controlled trial, we randomly assigned 466 patients with severe ARDS to undergo prone-positioning sessions of at least 16 hours or to be left in the supine position. Severe ARDS was defined as a ratio of the partial pressure of arterial oxygen to the fraction of inspired oxygen (FiO2) of less than 150 mm Hg, with an FiO2 of at least 0.6, a positive end-expiratory pressure of at least 5 cm of water, and a tidal volume close to 6 ml per kilogram of predicted body weight. The primary outcome was the proportion of patients who died from any cause within 28 days after inclusion.

RESULTS

A total of 237 patients were assigned to the prone group, and 229 patients were assigned to the supine group. The 28-day mortality was 16.0% in the prone group and 32.8% in the supine group (P<0.001). The hazard ratio for death with prone positioning was 0.39 (95% confidence interval [CI], 0.25 to 0.63). Unadjusted 90-day mortality was 23.6% in the prone group versus 41.0% in the supine group (P<0.001), with a hazard ratio of 0.44 (95% CI, 0.29 to 0.67). The incidence of complications did not differ significantly between the groups, except for the incidence of cardiac arrests, which was higher in the supine group.

CONCLUSIONS

In patients with severe ARDS, early application of prolonged prone-positioning sessions significantly decreased 28-day and 90-day mortality. (Funded by the Programme Hospitalier de Recherche Clinique National 2006 and 2010 of the French Ministry of Health; PROSEVA ClinicalTrials.gov number, NCT00527813.).

Clinical review: Acute respiratory distress syndrome - clinical ventilator management and adjunct therapy

Acute respiratory distress syndrome (ARDS) is a potentially devastating form of acute inflammatory lung injury with a high short-term mortality rate and significant long-term consequences among survivors. Supportive care, principally with mechanical ventilation, remains the cornerstone of therapy - although the goals of this support have changed in recent years - from maintaining normal physiological parameters to avoiding ventilator-induced lung injury while providing adequate gas exchange. In this article we discuss the current evidence base for ventilatory support and adjunctive therapies in patients with ARDS. Key components of such a strategy include avoiding lung overdistension by limiting tidal volumes and airway pressures, and the use of positive end-expiratory pressure with or without lung recruitment manoeuvres in patients with severe ARDS. Adjunctive therapies discussed include pharmacologic techniques (for example, vasodilators, diuretics, neuromuscular blockade) and nonpharmacologic techniques (for example, prone position, alternative modes of ventilation).

The ALIEN study: incidence and outcome of acute respiratory distress syndrome in the era of lung protective ventilation

PURPOSE

While our understanding of the pathogenesis and management of acute respiratory distress syndrome (ARDS) has improved over the past decade, estimates of its incidence have been controversial. The goal of this study was to examine ARDS incidence and outcome under current lung protective ventilatory support practices before and after the diagnosis of ARDS.

METHODS

This was a 1-year prospective, multicenter, observational study in 13 geographical areas of Spain (serving a population of 3.55 million at least 18 years of age) between November 2008 and October 2009. Subjects comprised all consecutive patients meeting American-European Consensus Criteria for ARDS. Data on ventilatory management, gas exchange, hemodynamics, and organ dysfunction were collected.

RESULTS

A total of 255 mechanically ventilated patients fulfilled the ARDS definition, representing an incidence of 7.2/100,000 population/year. Pneumonia and sepsis were the most common causes of ARDS. At the time of meeting ARDS criteria, mean PaO(2)/FiO(2) was 114 ± 40 mmHg, mean tidal volume was 7.2 ± 1.1 ml/kg predicted body weight, mean plateau pressure was 26 ± 5 cmH(2)O, and mean positive end-expiratory pressure (PEEP) was 9.3 ± 2.4 cmH(2)O. Overall ARDS intensive care unit (ICU) and hospital mortality was 42.7% (95%CI 37.7-47.8) and 47.8% (95%CI 42.8-53.0), respectively.

CONCLUSIONS

This is the first study to prospectively estimate the ARDS incidence during the routine application of lung protective ventilation. Our findings support previous estimates in Europe and are an order of magnitude lower than those reported in the USA and Australia. Despite use of lung protective ventilation, overall ICU and hospital mortality of ARDS patients is still higher than 40%.

Prone and ECMO - a contradiction per se?

Acute respiratory distress syndrome (ARDS) still represents a serious problem in clinical routine and is associated with a high mortality. Several concepts are known for special treatment, but, in some instances, the application of an extracorporeal membrane oxygenation (ECMO) is necessary for both the improvement of oxygenation and the elimination of carbon dioxide (CO(2)). One basic aspect in lung protective ventilation in this context is alveolar recruitment, which can be achieved by different approaches, such as "the open lung concept", according to Lachmann, or by additional kinetic therapy. The most exposed feature of this entity is 'prone', which may be quite challenging in patients requiring extracorporeal support or organ replacement therapy under ongoing critical illness. We report two outstanding cases of prone under conditions of a veno-venous ECMO therapy which improved significantly under this position. Furthermore, we reflect critically possible risk factors and adverse events of such procedures and afford a current view from the literature.

PaCO2 and alveolar dead space are more relevant than PaO2/FiO2 ratio in monitoring the respiratory response to prone position in ARDS patients: a physiological study

INTRODUCTION

Our aims in this study were to report changes in the ratio of alveolar dead space to tidal volume (VDalv/VT) in the prone position (PP) and to test whether changes in partial pressure of arterial CO2 (PaCO2) may be more relevant than changes in the ratio of partial pressure of arterial O2 to fraction of inspired O2 (PaO2/FiO2) in defining the respiratory response to PP. We also aimed to validate a recently proposed method of estimation of the physiological dead space (VDphysiol/VT) without measurement of expired CO2.

METHODS

Thirteen patients with a PaO2/FiO2 ratio < 100 mmHg were included in the study. Plateau pressure (Pplat), positive end-expiratory pressure (PEEP), blood gas analysis and expiratory CO2 were recorded with patients in the supine position and after 3, 6, 9, 12 and 15 hours in the PP. Responders to PP were defined after 15 hours of PP either by an increase in PaO2/FiO2 ratio > 20 mmHg or by a decrease in PaCO2 > 2 mmHg. Estimated and measured VDphysiol/VT ratios were compared.

RESULTS

PP induced a decrease in Pplat, PaCO2 and VDalv/VT ratio and increases in PaO2/FiO2 ratios and compliance of the respiratory system (Crs). Maximal changes were observed after six to nine hours. Changes in VDalv/VT were correlated with changes in Crs, but not with changes in PaO2/FiO2 ratios. When the response was defined by PaO2/FiO2 ratio, no significant differences in Pplat, PaCO2 or VDalv/VT alterations between responders (n = 7) and nonresponders (n = 6) were observed. When the response was defined by PaCO2, four patients were differently classified, and responders (n = 7) had a greater decrease in VDalv/VT ratio and in Pplat and a greater increase in PaO2/FiO2 ratio and in Crs than nonresponders (n = 6). Estimated VDphysiol/VT ratios significantly underestimated measured VDphysiol/VT ratios (concordance correlation coefficient 0.19 (interquartile ranges 0.091 to 0.28)), whereas changes during PP were more reliable (concordance correlation coefficient 0.51 (0.32 to 0.66)).

CONCLUSIONS

PP induced a decrease in VDalv/VT ratio and an improvement in respiratory mechanics. The respiratory response to PP appeared more relevant when PaCO2 rather than the PaO2/FiO2 ratio was used. Estimated VDphysiol/VT ratios systematically underestimated measured VDphysiol/VT ratios.