Effect of alveolar recruitment maneuver in early acute respiratory distress syndrome according to antiderecruitment strategy, etiological category of diffuse lung injury, and body position of the patient

Incidence of noninvasive ventilation failure and mortality in patients with acute respiratory distress syndrome: a systematic review and proportion meta-analysis

BACKGROUND

Noninvasive ventilation (NIV) is commonly used in patients with acute respiratory distress syndrome (ARDS). However, the incidence and distribution of treatment failure are unclear.

METHODS

A comprehensive online search was conducted to select potentially eligible studies with reports of the rate of NIV failure in patients with ARDS. A manual search was also performed to identify additional studies. Data were extracted to calculate the pooled incidences of NIV failure and mortality. Based on oxygenation, the severity of the disease was classified as mild, moderate, or severe ARDS. Based on etiologies, ARDS was defined as being of pulmonary origin or extrapulmonary origin.

RESULTS

We enrolled 90 studies in this meta-analysis, involving 98 study arms. The pooled incidence of NIV failure was 48% (n = 5847, 95% confidence interval [CI]: 43-52%). The pooled incidence of ICU mortality was 29% (n = 2363, 95%CI: 22-36%), and that of hospital mortality was 33% (n = 2927, 95%CI: 27-40%). In patients with mild, moderate, and severe ARDS, the pooled incidence of NIV failure was 30% (n = 819, 95%CI: 21-39%), 51% (n = 1332, 95%CI: 43-60%), and 71% (n = 525, 95%CI: 62-79%), respectively. In patients with pulmonary ARDS, it was 45% (n = 2687, 95%CI: 39-51%). However, it was 30% (n = 802, 95%CI: 21-38%) in those with extrapulmonary ARDS. In patients with immunosuppression, the incidence of NIV failure was 62% (n = 806, 95%CI: 50-74%). However, it was 46% (n = 5041, 95%CI: 41-50%) in those without immunosuppression.

CONCLUSIONS

Nearly half of patients with ARDS experience NIV failure. The incidence of NIV failure increases with increasing ARDS severity. Pulmonary ARDS seems to have a higher rate of NIV failure than extrapulmonary ARDS. ARDS patients with immunosuppression have the highest rate of NIV failure.

A Sequent of Gram-Negative Co-Infectome-Induced Acute Respiratory Distress Syndrome Are Potentially Subtle Aggravators Associated to the SARS-CoV-2 Evolution of Virulence

Acute respiratory distress syndrome (ARDS) is one of the major problems in COVID-19 that is not well understood. ARDS is usually complicated by co-infections in hospitals. Although ARDS is inherited by Europeans and Africans, this is not clear for those from the Middle East. There are severe limitations in correlations made between COVID-19, ARDS, co-infectome, and patient demographics. We investigated 298 patients for associations of ARDS, coinfections, and patient demographics on COVID-19 patients' outcomes. Of the 149 patients examined for ARDS during COVID-19, 16 had an incidence with a higher case fatality rate (CFR) of 75.0% compared to those without ARDS (27.0%) (p value = 0.0001). The co-infectome association showed a CFR of 31.3% in co-infected patients; meanwhile, only 4.8% of those without co-infections (p value = 0.01) died. The major bacteria were Acinetobacter baumannii and Escherichia coli, either alone or in a mixed infection with Klebsiella pneumoniae. Kaplan-Meier survival analysis of COVID-19 patients with and without ARDS revealed a significant difference in the survival time of patients with ARDS (58.8 +/- 2.7 days) and without ARDS (41.9 +/- 1.8 days) (p value = 0.0002). These findings prove that increased hospital time was risky for co-infectome-induced SDRS later on. This also explained that while empiric therapy and lethal ventilations delayed the mortality in 75% of patients, they potentially did not help those without co-infection or ARDS who stayed for shorter times. In addition, the age of patients (n = 298) was significantly associated with ARDS (72.9 +/- 8.9) compared to those without it (56.2 +/- 15.1) and was irrespective of gender. However, there were no significant differences neither in the age of admitted patients before COVID-19 (58.5 +/- 15.3) and during COVID-19 (57.2 +/- 15.5) nor in the gender and COVID-19 fatality (p value 0.546). Thus, Gram-negative co-infectome potentially induced fatal ARDS, aggravating the COVID-19 outcome. These findings are important for the specific differential diagnosis of patients with and without ARDS and co-infections. Future vertical investigations on mechanisms of Gram-negative-induced ARDS are imperative since hypervirulent strains are rapidly circulating. This study was limited as it was a single-center study confined to Ha'il hospitals; a large-scale investigation in major national hospitals would gain more insights.

Acute respiratory distress syndrome heterogeneity and the septic ARDS subgroup

Acute respiratory distress syndrome (ARDS) is an acute diffuse inflammatory lung injury characterized by the damage of alveolar epithelial cells and pulmonary capillary endothelial cells. It is mainly manifested by non-cardiogenic pulmonary edema, resulting from intrapulmonary and extrapulmonary risk factors. ARDS is often accompanied by immune system disturbance, both locally in the lungs and systemically. As a common heterogeneous disease in critical care medicine, researchers are often faced with the failure of clinical trials. Latent class analysis had been used to compensate for poor outcomes and found that targeted treatment after subgrouping contribute to ARDS therapy. The subphenotype of ARDS caused by sepsis has garnered attention due to its refractory nature and detrimental consequences. Sepsis stands as the most predominant extrapulmonary cause of ARDS, accounting for approximately 32% of ARDS cases. Studies indicate that sepsis-induced ARDS tends to be more severe than ARDS caused by other factors, leading to poorer prognosis and higher mortality rate. This comprehensive review delves into the immunological mechanisms of sepsis-ARDS, the heterogeneity of ARDS and existing research on targeted treatments, aiming to providing mechanism understanding and exploring ideas for accurate treatment of ARDS or sepsis-ARDS.

Optimizing Fluid Management Guided by Volumetric Parameters in Patients with Sepsis and ARDS

We compared two de-escalation strategies guided by either extravascular lung water or global end-diastolic volume-oriented algorithms in patients with sepsis and ARDS. Sixty patients with sepsis and ARDS were randomized to receive de-escalation fluid therapy, guided either by the extravascular lung water index (EVLWI, n = 30) or the global end-diastolic volume index (GEDVI, n = 30). In cases of GEDVI > 650 mL/m² or EVLWI > 10 mL/kg, diuretics and/or controlled ultrafiltration were administered to achieve the cumulative 48-h fluid balance in the range of 0 to -3000 mL. During 48 h of goal-directed de-escalation therapy, we observed a decrease in the SOFA score (p < 0.05). Extravascular lung water decreased only in the EVLWI-oriented group (p < 0.001). In parallel, PaO₂/FiO₂ increased by 30% in the EVLWI group and by 15% in the GEDVI group (p < 0.05). The patients with direct ARDS demonstrated better responses to dehydration therapy concerning arterial oxygenation and lung fluid balance. In sepsis-induced ARDS, both fluid management strategies, based either on GEDVI or EVLWI, improved arterial oxygenation and attenuated organ dysfunction. The de-escalation therapy was more efficient for direct ARDS.

Clinical Implications of Determining Individualized Positive End-Expiratory Pressure Using Electrical Impedance Tomography in Post-Cardiac Surgery Patients: A Prospective, Non-Randomized Interventional Study

Optimal positive end-expiratory pressure (PEEP) can induce sustained lung function improvement. This prospective, non-randomized interventional study aimed to investigate the effect of individualized PEEP determined using electrical impedance tomography (EIT) in post-cardiac surgery patients (n = 35). Decremental PEEP trials were performed from 20 to 4 cmH2O in steps of 2 cmH2O, guided by EIT. PEEP levels preventing ventilation loss in dependent lung regions (PEEPONLINE) were set. Ventilation distributions and oxygenation before the PEEP trial, and 5 min and 1 h after the PEEPONLINE setting were examined. Furthermore, we analyzed the saved impedance data offline to determine the PEEP levels that provided the best compromise between overdistended and collapsed lung (PEEPODCL). Ventilation distributions of dependent regions increased at 5 min after the PEEPONLINE setting compared with those before the PEEP trial (mean ± standard deviation, 41.3 ± 8.5% vs. 49.1 ± 9.3%; p < 0.001), and were maintained at 1 h thereafter (48.7 ± 9.4%, p < 0.001). Oxygenation also showed sustained improvement. Rescue oxygen therapy (high-flow nasal cannula, noninvasive ventilation) after extubation was less frequent in patients with PEEPONLINE ≥ PEEPODCL than in those with PEEPONLINE < PEEPODCL (1/19 vs. 6/16; p = 0.018). EIT-guided individualized PEEP stabilized the improvement in ventilation distribution and oxygenation. Individual PEEP varies with EIT measures, and may differentially affect oxygenation after cardiac surgery.

Association between ARDS Etiology and Risk of Noninvasive Ventilation Failure

RATIONALE

The etiology of acute respiratory distress syndrome (ARDS) may play an important role in the failure of noninvasive ventilation (NIV).

OBJECTIVES

To explore the association between ARDS etiology and risk of noninvasive ventilation failure.

METHODS

A multicenter prospective observational study was performed in 17 ICUs in China from September 2017 to December 2019. Patients with ARDS who used NIV as a first-line therapy were enrolled. The etiology of ARDS was recorded at study entry.

RESULTS

A total of 306 patients were enrolled. Of the patients, 146 were classified as having pulmonary ARDS (ARDSp) and 160 were classified as having extrapulmonary ARDS (ARDSexp). From initiation to 24 h of NIV, the respiratory rate, heart rate, PaO2/FiO2, and PaCO2 improved slower in patients with ARDSp than those with ARDSexp. Patients with ARDSp experienced more NIV failure (55% vs. 28%; p < 0.01) and higher 28-day mortality (47% vs. 14%; p < 0.01). The adjusted odds ratio of NIV failure and 28-day mortality were 5.47 (95%CI: 3.04-9.86) and 10.13 (95%CI: 5.01-20.46), respectively. In addition, we combined the presence of ARDSp, presence of septic shock, age, non-pulmonary SOFA score, respiratory rate at 1-2 h of NIV, and PaO2/FiO2 at 1-2 h of NIV to develop a risk score of NIV failure. With the increase of the risk score, the rate of NIV failure increased. Using 5.5 as cutoff value to predict NIV failure, the sensitivity and specificity was good both in training and validation cohorts.

CONCLUSIONS

Among patients with ARDS who used NIV as a first-line therapy, ARDSp was associated with slower improvement, more NIV failure, and higher 28-day mortality than ARDSexp. The risk score combined presence of ARDSp, presence of septic shock, age, non-pulmonary SOFA score, respiratory rate at 1-2 h of NIV, and PaO2/FiO2 at 1-2 h of NIV has high accuracy to predict NIV failure among ARDS population.

ALVEOLAR RECRUITMENT MANEUVERS FOR CHILDREN WITH CANCER AND ACUTE RESPIRATORY DISTRESS SYNDROME: A FEASIBILITY STUDY

Objective:

Acute respiratory distress syndrome (ARDS) can be a devastating condition in children with cancer and alveolar recruitment maneuvers (ARMs) can theoretically improve oxygenation and survival. The study aimed to assess the feasibility of ARMs in critically ill children with cancer and ARDS.

Methods:

We retrospectively analyzed 31 maneuvers in a series of 12 patients (median age of 8.9 years) with solid tumors (n=4), lymphomas (n=2), acute lymphoblastic leukemia (n=2), and acute myeloid leukemia (n=4). Patients received positive end-expiratory pressure from 25 up to 40 cmH₂0, with a delta pressure of 15 cmH₂O for 60 seconds. We assessed blood gases pre- and post-maneuvers, as well as ventilation parameters, vital signs, hemoglobin, clinical signs of pulmonary bleeding, and radiological signs of barotrauma. Pre- and post-values were compared by the Wilcoxon test.

Results:

Median platelet count was 53,200/mm³. Post-maneuvers, mean arterial pressure decreased more than 20% in two patients, and four needed an increase in vasoactive drugs. Hemoglobin levels remained stable 24 hours after ARMs, and signs of pneumothorax, pneumomediastinum, or subcutaneous emphysema were absent. Fraction of inspired oxygen decreased significantly after ARMs (FiO₂; p=0.003). Oxygen partial pressure (PaO₂)/FiO₂ ratio increased significantly (p=0.0002), and the oxygenation index was reduced (p=0.01), but all these improvements were transient. Recruited patients’ 28-day mortality was 58%.

Conclusions:

ARMs, although feasible in the context of thrombocytopenia, lead only to transient improvements, and can cause significant hemodynamic instability.

Use of Recruitment Maneuvers in Patients With Acute Respiratory Distress Syndrome

Acute respiratory distress syndrome (ARDS) is a deadly complication in critically ill patients that causes significant morbidity and mortality. Patients with ARDS are seen across intensive care unit settings, with treatment being largely supportive involving techniques through mechanical ventilation. Using low-tidal-volume ventilation is a standard of practice for patients with ARDS, as a lung protection strategy; however, alveolar decruitment may occur. Recruitment maneuvers can recruit collapsed alveoli and promote oxygenation. There are several methods of recruitment maneuvers-each with varying levels and durations of positive end-expiratory pressure. It is still uncertain which method is the best. The evidence for the efficacy of recruitment maneuvers has shown a decrease in intensive care unit mortality, but strong evidence is lacking for its routine use, and the decision to use recruitment maneuvers should be based on individual characteristics and responses. This article reviews management of ARDS, recruitment maneuver techniques, and clinical application through a case study.

Effects of positive end-expiratory pressure strategy in supine and prone position on lung and chest wall mechanics in acute respiratory distress syndrome

Background

In acute respiratory distress syndrome (ARDS) patients, it has recently been proposed to set positive end-expiratory pressure (PEEP) by targeting end-expiratory transpulmonary pressure. This approach, which relies on the measurement of absolute esophageal pressure (Pes), has been used in supine position (SP) and has not been investigated in prone position (PP). Our purposes were to assess Pes-guided strategy to set PEEP in SP and in PP as compared with a PEEP/FIO₂ table and to explore the early (1 h) and late (16 h) effects of PP on lung and chest wall mechanics.

Results

We performed a prospective, physiologic study in two ICUs in university hospitals on ARDS patients with PaO₂/FIO₂ < 150 mmHg. End-expiratory Pes (Pes,ee) was measured in static (zero flow) condition. Patients received PEEP set according to a PEEP/F_IO₂ table then according to the Pes-guided strategy targeting a positive (3 ± 2 cmH₂O) static end-expiratory transpulmonary pressure in SP. Then, patients were turned to PP and received same amount of PEEP from PEEP/F_IO₂ table then Pes-guided strategy. Respiratory mechanics, oxygenation and end-expiratory lung volume (EELV) were measured after 1 h of each PEEP in each position. For the rest of the 16-h PP session, patients were randomly allocated to either PEEP strategy with measurements done at the end. Thirty-eight ARDS patients (27 male), mean ± SD age 63 ± 13 years, were included. There were 33 primary ARDS and 26 moderate ARDS. PaO₂/FIO₂ ratio was 120 ± 23 mmHg. At same PEEP/FIO₂ table-related PEEP, Pes,ee averaged 9 ± 4 cmH₂O in both SP and PP (P = 0.88). With PEEP/F_IO₂ table and Pes-guided strategy, PEEP was 10 ± 2 versus 12 ± 4 cmH₂O in SP and 10 ± 2 versus 12 ± 5 cmH₂O in PP (PEEP strategy effect P = 0.05, position effect P = 0.96, interaction P = 0.96). With the Pes-guided strategy, chest wall elastance increased regardless of position. Lung elastance and transpulmonary driving pressure decreased in PP, with no effect of PEEP strategy. Both PP and Pes-guided strategy improved oxygenation without interaction. EELV did not change with PEEP strategy. At the end of PP session, respiratory mechanics did not vary but EELV and PaO₂/F_IO₂ increased while PaCO₂ decreased.

Conclusions

There was no impact of PP on Pes measurements. PP had an immediate improvement effect on lung mechanics and a late lung recruitment effect independent of PEEP strategy.

Electronic supplementary material

The online version of this article (10.1186/s13613-018-0434-2) contains supplementary material, which is available to authorized users.

Mechanical Ventilation in Adults with Acute Respiratory Distress Syndrome. Summary of the Experimental Evidence for the Clinical Practice Guideline

RATIONALE

The American Thoracic Society/European Society for Intensive Care Medicine/Society of Critical Care Medicine guidelines on mechanical ventilation in adult patients with acute respiratory distress syndrome (ARDS) provide treatment recommendations derived from a thorough analysis of the clinical evidence on six clinical interventions. However, each of the recommendations contains areas of uncertainty and controversy, which may affect their appropriate clinical application.

OBJECTIVES

To provide a critical review of the experimental evidence surrounding the pathophysiology of ventilator-induced lung injury and to help clinicians apply the clinical recommendations to individual patients.

METHODS

We conducted a literature search and narrative review.

RESULTS

A large number of experimental studies have been performed with the aim of improving understanding of the pathophysiological effects of mechanical ventilation. These studies have formed the basis for the design of many clinical trials. Translational research has fundamentally advanced understanding of the mechanisms of ventilator-induced lung injury, thus informing the design of interventions that improve survival in patients with ARDS.

CONCLUSIONS

Because daily management of patients with ARDS presents the challenge of competing considerations, clinicians should consider the mechanism of ventilator-induced lung injury, as well as the rationale for interventions designed to mitigate it, when applying evidence-based recommendations at the bedside.

Budesonide Attenuates Ventilator-induced Lung Injury in a Rat Model of Inflammatory Acute Respiratory Distress Syndrome

BACKGROUND AND AIMS

Patients with acute respiratory distress syndrome (ARDS) are particularly susceptible to ventilator-induced lung injury (VILI). This study investigated the effect of budesonide on VILI in a rat model of inflammatory ARDS.

METHODS

Forty eight rats were randomized into three groups (n = 16 each): sham group (S), endotoxin/ventilation group (LV), endotoxin/ventilation/budesonide group (LVB). Rats in the S group received anesthesia only. Rats in the LV and LVB groups received endotoxin to simulate ARDS and were mechanically ventilated for 4 h (tidal volume 30 mL/kg). Rats in the LVB group received budesonide 1 mg, and rats in the LV group received saline in airway. PaO2/FiO2, lung wet-to-dry weight ratios, inflammatory factors in serum and bronchoalveolar lavage fluid (BALF), histopathologic analysis of lung tissue, and survival were examined.

RESULTS

PaO2/FiO2 was significantly increased in rats in the LVB group compared to the LV group. Total cell count, macrophages, and neutrophils in BALF, and levels of intercellular adhesion molecule (ICAM)-1, tumor necrosis factor (TNF)-α, interleukin (IL)-1β, and IL-8 in BALF and serum were significantly decreased in rats in the LVB group compared to the LV group, whereas levels of IL-10 in BALF and serum were significantly increased. Histopathological changes of lung injury and apoptosis were reduced, and survival was increased in rats in the LVB group compared to the LV group.

CONCLUSIONS

Budesonide ameliorated VILI in a rat model of inflammatory ARDS.

Recruitment manoeuvres for adults with acute respiratory distress syndrome receiving mechanical ventilation

BACKGROUND

Recruitment manoeuvres involve transient elevations in airway pressure applied during mechanical ventilation to open ('recruit') collapsed lung units and increase the number of alveoli participating in tidal ventilation. Recruitment manoeuvres are often used to treat patients in intensive care who have acute respiratory distress syndrome (ARDS), but the effect of this treatment on clinical outcomes has not been well established. This systematic review is an update of a Cochrane review originally published in 2009.

OBJECTIVES

Our primary objective was to determine the effects of recruitment manoeuvres on mortality in adults with acute respiratory distress syndrome.Our secondary objective was to determine, in the same population, the effects of recruitment manoeuvres on oxygenation and adverse events (e.g. rate of barotrauma).

SEARCH METHODS

For this updated review, we searched the Cochrane Central Register of Controlled Trials (CENTRAL), MEDLINE (OVID), Embase (OVID), the Cumulative Index to Nursing and Allied Health Literature (CINAHL, EBSCO), Latin American and Caribbean Health Sciences (LILACS) and the International Standard Randomized Controlled Trial Number (ISRCTN) registry from inception to August 2016.

SELECTION CRITERIA

We included randomized controlled trials (RCTs) of adults who were mechanically ventilated that compared recruitment manoeuvres versus standard care for patients given a diagnosis of ARDS.

DATA COLLECTION AND ANALYSIS

Two review authors independently assessed trial quality and extracted data. We contacted study authors for additional information.

MAIN RESULTS

Ten trials met the inclusion criteria for this review (n = 1658 participants). We found five trials to be at low risk of bias and five to be at moderate risk of bias. Six of the trials included recruitment manoeuvres as part of an open lung ventilation strategy that was different from control ventilation in aspects other than the recruitment manoeuvre (such as mode of ventilation, higher positive end-expiratory pressure (PEEP) titration and lower tidal volume or plateau pressure). Six studies reported mortality outcomes. Pooled data from five trials (1370 participants) showed a reduction in intensive care unit (ICU) mortality (risk ratio (RR) 0.83, 95% confidence interval (CI) 0.72 to 0.97, P = 0.02, low-quality evidence), pooled data from five trials (1450 participants) showed no difference in 28-day mortality (RR 0.86, 95% CI 0.74 to 1.01, P = 0.06, low-quality evidence) and pooled data from four trials (1313 participants) showed no difference in in-hospital mortality (RR 0.88, 95% CI 0.77 to 1.01, P = 0.07, low-quality evidence). Data revealed no differences in risk of barotrauma (RR 1.09, 95% CI 0.78 to 1.53, P = 0.60, seven studies, 1508 participants, moderate-quality evidence).

AUTHORS' CONCLUSIONS

We identified significant clinical heterogeneity in the 10 included trials. Results are based upon the findings of several (five) trials that included an "open lung ventilation strategy", whereby the intervention group differed from the control group in aspects other than the recruitment manoeuvre (including co-interventions such as higher PEEP, different modes of ventilation and higher plateau pressure), making interpretation of the results difficult. A ventilation strategy that included recruitment manoeuvres in participants with ARDS reduced intensive care unit mortality without increasing the risk of barotrauma but had no effect on 28-day and hospital mortality. We downgraded the quality of the evidence to low, as most of the included trials provided co-interventions as part of an open lung ventilation strategy, and this might have influenced results of the outcome.

High PEEP in acute respiratory distress syndrome: quantitative evaluation between improved arterial oxygenation and decreased oxygen delivery

BACKGROUND

Positive end-expiratory pressure (PEEP) is widely used to improve oxygenation and prevent alveolar collapse in mechanically ventilated patients with the acute respiratory distress syndrome (ARDS). Although PEEP improves arterial oxygenation predictably, high-PEEP strategies have demonstrated equivocal improvements in ARDS-related mortality. The effect of PEEP on tissue oxygen delivery is poorly understood and is difficult to quantify or investigate in the clinical environment.

METHODS

We investigated the effects of PEEP on tissue oxygen delivery in ARDS using a new, high-fidelity, computational model with highly integrated respiratory and cardiovascular systems. The model was configured to replicate published clinical trial data on the responses of 12 individual ARDS patients to changes in PEEP. These virtual patients were subjected to increasing PEEP levels during a lung-protective ventilation strategy (0-20 cm H₂O). Measured variables included arterial oxygenation, cardiac output, peripheral oxygen delivery, and alveolar strain.

RESULTS

As PEEP increased, tissue oxygen delivery decreased in all subjects (mean reduction of 25% at 20 cm H₂O PEEP), despite an increase in arterial oxygen tension (mean increase 6.7 kPa at 20 cm H₂O PEEP). Changes in arterial oxygenation and tissue oxygen delivery differed between subjects but showed a consistent pattern. Static and dynamic alveolar strain decreased in all patients as PEEP increased.

CONCLUSIONS

Incremental PEEP in ARDS appears to protect alveoli and improve arterial oxygenation, but also appears to impair tissue oxygen delivery significantly because of reduced cardiac output. We propose that this trade-off may explain the poor improvements in mortality associated with high-PEEP ventilation strategies.

Pediatric Acute Hypoxemic Respiratory Failure: Management of Oxygenation

Acute hypoxemic respiratory failure (AHRF) is one of the hallmarks of acute lung injury (ALI) and acute respiratory distress syndrome (ARDS), which are caused by an inflammatory process initiated by any of a number of potential systemic and/or pulmonary insults that result in heterogeneous disruption of the capillary-pithelial interface. In these critically sick patients, optimizing the management of oxygenation is crucial. Physicians managing pediatric patients with ALI or ARDS are faced with a complex array of options influencing oxygenation. Certain treatment strategies can influence clinical outcomes, such as a lung protective ventilation strategy that specifies a low tidal volume (6 mL/kg) and a plateau pressure limit (30 cm H2O). Other strategies such as different levels of positive end expiratory pressure, altered inspiration to expiration time ratios, recruitment maneuvers, prone positioning, and extraneous gases or drugs may also affect clinical outcomes. This article reviews state-of-the-art strategies on the management of oxygenation in acute hypoxemic respiratory failure in children.

Recruitment maneuvers in acute respiratory distress syndrome: The safe way is the best way

Acute respiratory distress syndrome (ARDS) represents a serious problem in critically ill patients and is associated with in-hospital mortality rates of 33%-52%. Recruitment maneuvers (RMs) are a simple, low-cost, feasible intervention that can be performed at the bedside in patients with ARDS. RMs are characterized by the application of airway pressure to increase transpulmonary pressure transiently. Once non-aerated lung units are reopened, improvements are observed in respiratory system mechanics, alveolar reaeration on computed tomography, and improvements in gas exchange (functional recruitment). However, the reopening process could lead to vascular compression, which can be associated with overinflation, and gas exchange may not improve as expected (anatomical recruitment). The purpose of this review was to discuss the effects of different RM strategies - sustained inflation, intermittent sighs, and stepwise increases of positive end-expiratory pressure (PEEP) and/or airway inspiratory pressure - on the following parameters: hemodynamics, oxygenation, barotrauma episodes, and lung recruitability through physiological variables and imaging techniques. RMs and PEEP titration are interdependent events for the success of ventilatory management. PEEP should be adjusted on the basis of respiratory system mechanics and oxygenation. Recent systematic reviews and meta-analyses suggest that RMs are associated with lower mortality in patients with ARDS. However, the optimal RM method (i.e., that providing the best balance of benefit and harm) and the effects of RMs on clinical outcome are still under discussion, and further evidence is needed.

Apnea testing for brain death in severe acute respiratory distress syndrome: a possible solution

INTRODUCTION

A 42-year-old man with a subarachnoid hemorrhage complicated by anoxic brain injury, respiratory failure requiring mechanical ventilation, and severe acute respiratory distress syndrome (ARDS) presented a clinical conundrum for safe apnea testing in brain death determination due to profound hypoxemia.

METHODS

Case report.

RESULTS

During brain death examination, despite meeting criteria for severe ARDS, apnea testing was successfully completed with the use of a pretest recruitment maneuver and 20 cm H(2)O CPAP valve.

CONCLUSION

A recruitment maneuver and CPAP valve may be used in severe ARDS for safe apnea testing in brain death determination.

Advances in ventilator-associated lung injury: prevention is the target

Mechanical ventilation (MV) is the main supportive treatment in respiratory failure due to different etiologies. However, MV might aggravate ventilator-associated lung injury (VALI). Four main mechanisms leading to VALI are: 1) increased stress and strain, induced by high tidal volume (VT); 2) increased shear stress, i.e. opening and closing, of previously atelectatic alveolar units; 3) distribution of perfusion and 4) biotrauma. In severe acute respiratory distress syndrome patients, low VT, higher levels of positive end expiratory pressure, long duration prone position and neuromuscular blockade within the first 48 hours are associated to a better outcome. VALI can also occur by using high VT in previously non injured lungs. We believe that prevention is the target to minimize injurious effects of MV. This review aims to describe pathophysiology of VALI, the possible prevention and treatment as well as monitoring MV to minimize VALI.

Clinical and biological heterogeneity in acute respiratory distress syndrome: direct versus indirect lung injury

The acute respiratory distress syndrome (ARDS) is a heterogeneous group of illnesses affecting the pulmonary parenchyma with acute onset bilateral inflammatory pulmonary infiltrates with associated hypoxemia. ARDS occurs after 2 major types of pulmonary injury: direct lung injury affecting the lung epithelium or indirect lung injury disrupting the vascular endothelium. Greater understanding of the differences between direct and indirect lung injury may refine the classification of patients with ARDS and lead to development of new therapeutics targeted at specific subpopulations of patients with ARDS.

Effects of alveolar recruitment maneuvers on clinical outcomes in patients with acute respiratory distress syndrome: a systematic review and meta-analysis

PURPOSE

To assess the effects of alveolar recruitment maneuvers (ARMs) on clinical outcomes in patients with acute respiratory distress syndrome (ARDS).

METHODS

We conducted a search of the MEDLINE, EMBASE, LILACS, CINAHL, CENTRAL, Scopus, and Web of Science (from inception to July 2014) databases for all (i.e. no language restriction) randomized controlled trials (RCTs) evaluating the effects of ARMs versus no ARMs in adults with ARDS. Four teams of two reviewers independently assessed the eligibility of the studies identified during the search and appraised the risk of bias and extracted data from those which were assessed as meeting the inclusion criteria. Data were pooled using the random-effects model. Trial sequential analysis (TSA) was used to establish monitoring boundaries to limit global type I error due to repetitive testing for our primary outcome (in-hospital mortality). The GRADE system was used to rate the quality of evidence.

RESULTS

Our database search identified ten RCTs (1,594 patients, 612 events) which satisfied the inclusion criteria. The meta-analysis assessing the effect of ARMs on in-hospital mortality showed a risk ratio (RR) of 0.84 [95 % confidence interval (CI) 0.74-0.95; I(2) = 0 %], although the quality of evidence was considered to be low due to the risk of bias in the included trials and the indirectness of the evidence--that is, ARMs were usually conducted together with other ventilatory interventions which may affect the outcome of interest. There were no differences in the rates of barotrauma (RR 1.11; 95 % CI 0.78-1.57; I(2) = 0 %) or need for rescue therapies (RR 0.76, 95 % CI 0.41-1.40; I(2) = 56 %). Most trials found no difference between groups in terms of duration of mechanical ventilation and length of stay in the intensive care unit and hospital. The TSA showed that the available evidence for the effect of ARMs on in-hospital mortality is precise in the case of a type I error of 5 %, but it is not precise with a type I error of 1 %.

CONCLUSIONS

Although ARMs may decrease the mortality of patients with ARDS without increasing the risk for major adverse events, current evidence is not definitive. Large-scale ongoing trials addressing this question may provide data better applicable to clinical practice.

Alveolar recruitment maneuver and perioperative ventilatory support in obese patients undergoing abdominal surgery

The development of abdominal surgery represents an alternative therapy for the morbidly obese; however, patients undergoing this surgical procedure often experience postoperative pulmonary complications. The use of alveolar recruitment maneuvers and/or perioperative ventilatory strategies is a possible alternative to reduce these complications, focusing on the reduction of postoperative pulmonary complications. In this review, the benefits of perioperative ventilatory strategies and the implementation of alveolar recruitment maneuvers in obese patients undergoing abdominal surgery are described.

Gas exchange in the respiratory distress syndromes

This article describes the gas exchange abnormalities occurring in the acute respiratory distress syndrome seen in adults and children and in the respiratory distress syndrome that occurs in neonates. Evidence is presented indicating that the major gas exchange abnormality accounting for the hypoxemia in both conditions is shunt, and that approximately 50% of patients also have lungs regions in which low ventilation-to-perfusion ratios contribute to the venous admixture. The various mechanisms by which hypercarbia may develop and by which positive end-expiratory pressure improves gas exchange are reviewed, as are the effects of vascular tone and airway narrowing. The mechanisms by which surfactant abnormalities occur in the two conditions are described, as are the histological findings that have been associated with shunt and low ventilation-to-perfusion.

Respiratory and hemodynamic effects of a stepwise lung recruitment maneuver in pediatric ARDS: a feasibility study

BACKGROUND

Little is known about the efficacy and safety of recruitment maneuvers (RMs) in pediatric patients with acute respiratory distress syndrome (ARDS). We therefore assessed the effects on gas exchange and lung mechanics and the possible detrimental effects of a sequential lung RMs and decremental positive end-expiratory pressure (PEEP) titration in pediatric ARDS patients.

METHODS

We enrolled patients <15 years of age with ARDS, progressive hypoxemia, <72 hr of mechanical ventilation, and hemodynamic stability. A step-wise RM and decremental PEEP trial were performed. Safety was evaluated as the occurrence of hypotension and low pulse oxymeter oxygen saturation during the maneuver and development of airleaks after. Efficacy was evaluated as changes in lung compliance (Cdyn ) and gas exchange 1, 12, and 24 hr after the RM.

RESULTS

We included 25 patients, of median age 5 (1-16) months, median weight 7.0 (4.1-9.2) kg, median PaO2 /FIO2 117 (96-139), and median Cdyn 0.48 (0.41-0.68) ml/cmH2 O/kg at baseline. Thirty RM were performed, with all completed successfully. No airleaks developed. Mild hypotension was detected during four procedures. Following RM, Cdyn , and PaO2 /FIO2 increased significantly (P < 0.01 each), without changes in PaCO2 (P = 0.4). A >25% improvement in lung function (Cdyn or PaO2 /FIO2 ) was observed after 90% of the RM procedures. Gas exchange worsening over the next 24 hr resulted in HFOV use in 36% of patients, while the remaining subjects sustained improvements in oxygenation at 12 and 24 hr. The 28-day mortality rate was 16%.

CONCLUSIONS

Sequential RMs were safe and well tolerated in hemodynamically stable children with ARDS. RMs and a decremental PEEP trial may improve lung function in pediatric patients with ARDS and severe hypoxemia.

Risk factors for the development of acute lung injury in patients with infectious pneumonia

INTRODUCTION

Although pneumonia has been identified as the single most common risk factor for acute lung injury (ALI), we have a limited knowledge as to why ALI develops in some patients with pneumonia and not in others. The objective of this study was to determine frequency, risk factors, and outcome of ALI in patients with infectious pneumonia.

METHODS

A retrospective cohort study of adult patients with microbiologically positive pneumonia, hospitalized at two Mayo Clinic Rochester hospitals between January 1, 2005, and December 31, 2007. In a subsequent nested case-control analysis, we evaluated the differences in prehospital and intrahospital exposures between patients with and without ALI/acute respiratory distress syndrome (ARDS) matched by specific pathogen, isolation site, gender, and closest age in a 1:1 manner.

RESULTS

The study included 596 patients; 365 (61.2%) were men. The median age was 65 (IQR, 53 to 75) years. In total, 171 patients (28.7%) were diagnosed with ALI. The occurrence of ALI was less frequent in bacterial (n = 99 of 412, 24%) compared with viral (n = 19 of 55, 35%), fungal (n = 39 of 95, 41%), and mixed isolates pneumonias (n = 14 of 34, 41%; P = 0.002). After adjusting for baseline severity of illness and comorbidities, patients in whom ALI developed had a markedly increased risk of hospital death (ORadj 9.7; 95% CI, 6.0 to 15.9). In a nested case-control study, presence of shock (OR, 8.9; 95% CI, 2.8 to 45.9), inappropriate initial antimicrobial treatment (OR, 3.2; 95% CI, 1.3 to 8.5), and transfusions (OR, 4.8; 95% CI, 1.5 to 19.6) independently predicted ALI development.

CONCLUSIONS

The development of ALI among patients hospitalized with infectious pneumonia varied among pulmonary pathogens and was associated with increased mortality. Inappropriate initial antimicrobial treatment and transfusion predict the development of ALI independent of pathogen.

Recruitment and PEEP level influences long-time aeration in saline-lavaged piglets: an experimental model

OBJECTIVES

To evaluate aeration/ventilation in saline-lavaged piglets during a 3-h follow-up after a recruitment maneuver (RM)/PEEP titration compared with PEEP 10 cmH2O without a RM.

BACKGROUND

Lung recruitment and PEEP titration are used to find a PEEP preventing repetitive opening/collapsing of lung.

METHODS

Twenty-one lung-lavaged piglets, mean age 7 weeks and mean weight 10 kg; a RM-group and a PEEP10-group, were ventilated at PEEP 5 cmH2O (baseline) followed by zero PEEP ventilation. In the RM-group, tidal elimination of CO2 and dynamic compliance (Cdyn) guided recruitment and PEEP titration, respectively. A final 3-h ventilation followed using PEEP 2 cmH2O above the first decline of Cdyn and end-inspiratory pressure (EIP) for a target tidal volume (VT) of 10 ml · kg(-1). In the PEEP10-group, PEEP 10 cmH2O without a RM was used during the final 3-h ventilation. CT scans and blood gases were repeated every 30 min. Airway pressures, Cdyn and hemodynamics were continuously recorded.

RESULTS

Aeration improved without differences between groups. The RM-group PEEP level of 10 ± 0.6 cmH2O did not differ from the PEEP10-group. Compared to baseline EIP was lower in the RM-group after 3-h ventilation. In both groups, driving pressure (DP) was lower and Cdyn higher than baseline. In the RM-group, final EIP and DP were lower and Cdyn higher than in the PEEP10-group.

CONCLUSIONS

Both RM/PEEP titration and PEEP elevation resulted in improved aeration without differences between groups at the end point. Lung aeration was achieved at lower EIP and DP and higher Cdyn in the RM-group than in the PEEP10-group.

Distinct and replicable genetic risk factors for acute respiratory distress syndrome of pulmonary or extrapulmonary origin

BACKGROUND

The role of genetics in the development of acute lung injury (ALI)/acute respiratory distress syndrome (ARDS) from direct or indirect lung injury has not been specifically investigated. The aim of this study was to identify genetic variants contributing to ALI/ARDS from pulmonary or extrapulmonary causes.

METHODS

We conducted a multistage genetic association study. We first performed a large-scale genotyping (50K ITMAT-Broad_CARe Chip) in 1717 critically ill Caucasian patients with either pulmonary or extrapulmonary injury, to identify single nucleotide polymorphisms (SNPs) associated with the development of ARDS from direct or indirect insults to the lung. Identified SNPs (p≤0.0005) were validated in two separated populations (Stage II), with trauma (Population I; n=765) and pneumonia/pulmonary sepsis (Population II; n=838), as causes for ALI/ARDS. Genetic variants replicating their association with trauma related-ALI in Stage II were validated in a second trauma-associated ALI population (n=224, Stage III).

RESULTS

In Stage I, non-overlapping SNPs were significantly associated with ARDS from direct/indirect lung injury, respectively. The association between rs1190286 (POPDC3) and reduced risk of ARDS from pulmonary injury was validated in Stage II (p<0.003). SNP rs324420 (FAAH) was consistently associated with increased risk of ARDS from extrapulmonary causes in two independent ALI-trauma populations (p<0.006, Stage II; p<0.05, Stage III). Meta-analysis confirmed these associations.

CONCLUSIONS

Different genetic variants may influence ARDS susceptibility depending on direct versus indirect insults. Functional SNPs in POPDC3 and FAAH genes may be driving the association with direct and indirect ALI/ARDS, respectively.

Pathophysiology of ventilator-associated lung injury

PURPOSE OF REVIEW

Mechanical ventilation is essential for the support of critically ill patients, but may aggravate lung damage, leading to ventilator-associated lung injury (VALI). VALI results from a succession of events beginning with mechanical alteration of lung parenchyma, because of disproportionate stress and strain. The resulting structural tension initiates a biological inflammatory cascade; however, tension can reach the limits of stress, triggering the destruction of structures. This article reviews and discusses the ongoing research into the mechanisms of VALI and their implications for the management of ventilated patients.

RECENT FINDINGS

Several experimental and clinical studies have been performed to evaluate the contribution of pathogenic mechanical forces to organ and cellular deformation and the implications for guiding ventilator management in patients at risk for VALI. VALI may be attenuated by reducing tidal volume, but the key variable in determining pulmonary overdistension is transpulmonary pressure. Other parameters associated with the induction of VALI include positive end-expiratory pressure, inspiratory airflow and time, and respiratory frequency.

SUMMARY

How ventilation strategy, specific mechanisms of mechanotransduction, and their individual threshold values impact on VALI remains to be elucidated. In addition, clinical studies are required to evaluate the usefulness of individualized ventilator strategies based on lung mechanics.

A positive response to a recruitment maneuver with PEEP titration in patients with ARDS, regardless of transient oxygen desaturation during the maneuver

Recruitment maneuvers (RMs) can expand collapsed alveoli in ventilated patients. The optimal method for delivering RMs is unknown.

PURPOSE

To evaluate the safety and the respiratory and hemodynamic effects of a staircase recruitment maneuver (SRM) with decremental positive end expiratory pressure (PEEP) titration and the consequences of desaturation during the SRM in patients with early acute lung injury (ALI).

METHODS

In total, 20 consecutive patients with early ALI were enrolled and received an SRM. Patients were given 15 ± 3 cm H(2)O pressure-controlled ventilation. Positive end expiratory pressure was increased from baseline (range 10-18) to 20, 30, and 40 cm H(2)O every 2 minutes to achieve maximum alveolar pressure of 55 ± 3 cm H(2)O, then decreased at 3-minute intervals to 25, 22.5, 20, 17.5, and 15 cm H(2)O until a decrease of 1% to 2% oxygen saturation from maximum was detected. Positive end expiratory pressure was left at the level where the fall in oxygen saturation occurred. Standard respiratory and circulatory variables, arterial and central venous gases were measured before, during, and after the SRM.

RESULTS

There were significant improvements in shunt fraction (36.3% ± 10% to 26.4% ± 14%, P < .001), oxygen saturation (93.4% ± 2% to 96.8% ± 3%, P = .007), partial pressure of oxygen, arterial (PaO(2))/fraction of inspired oxygen ([FIO(2)]; 150 ± 42 to 227 ± 100, P = .004), lung compliance (33.9 ± 9.1 to 40.1 ± 11.4 mL/cm H(2)O, P < .01), and chest x-ray (CXR) after the SRM. Briefly, 80% of the patients responded and the response was maintained at 1 hour. In total, 8 patients desaturated 6.1% ± 2.8% in SaO(2) during the SRM but 5 of those improved SaO(2) relative to baseline by the end of the SRM.

CONCLUSIONS

In all, 80% of the patients with early ALI responded to the SRM with decremental PEEP titration. Desaturation during the SRM did not indicate a failed response 1 hour later.

Year in review 2011: Critical Care - respirology

Management of acute respiratory failure is an important component of intensive care. In this review, we analyze 21 original research articles published last year in Critical Care in the field of respiratory and critical care medicine. The articles are summarized according to the following topic categories: acute respiratory distress syndrome, mechanical ventilation, adjunctive therapies, and pneumonia.

Pediatric acute respiratory failure: areas of debate in the pediatric critical care setting

Pediatric intensive care units across the world care for large numbers of mechanically ventilated infants and children on a daily basis, yet management of these patients is far from standardized. This lack of standardization may be a necessity in certain situations given variation between underlying disease processes, pathophysiology, response to therapy and available resources. However, there are many situations in which similar patients are managed differently across pediatric intensive care units simply because there are a shortage of available data to guide the management of these critically ill infants and children. Thus, a large fraction of pediatric critical care involves a combination of institutional preference, individual experience, opinion and extrapolation of adult data.

Efficacy and safety of lung recruitment in pediatric patients with acute lung injury

OBJECTIVE

To assess the safety and efficacy of a recruitment maneuver, the Open Lung Tool, in pediatric patients with acute lung injury and acute respiratory distress syndrome.

DESIGN

Prospective cohort study using a repeated-measures design.

SETTING

Pediatric intensive care unit at an urban tertiary children's hospital.

PATIENTS

Twenty-one ventilated pediatric patients with acute lung injury.

INTERVENTION

Recruitment maneuver using incremental positive end-expiratory pressure.

MEASUREMENTS AND MAIN RESULTS

The ratio of partial pressure of arterial oxygen over fraction of inspired oxygen (Pao2/Fio2 ratio) increased 53% immediately after the recruitment maneuver. The median Pao2/Fio2 ratio increased from 111 (interquartile range, 73-266) prerecruitment maneuver to 170 (interquartile range, 102-341) immediately postrecruitment maneuver (p < .01). Improvement in Pao2/Fio2 ratio persisted with an increase of 80% over the baseline at 4 hrs and 40% at 12 hrs after the recruitment maneuver. The median Pao2/Fio2 ratio was 200 (interquartile range, 116-257) 4 hrs postrecruitment maneuver (p < .05) and 156 (interquartile range, 127-236) 12 hrs postrecruitment maneuver (p < .01). Compared with prerecruitment maneuver, the partial pressure of arterial carbon dioxide (Paco2) was significantly decreased at 4 hrs postrecruitment maneuver but not immediately after the recruitment maneuver. The median Paco2 was 49 torr (interquartile range, 44-60) prerecruitment maneuver compared with 48 torr (interquartile range, 43-50) immediately postrecruitment maneuver (p = .69), 45 torr (interquartile range, 41-50) at 4 hrs postrecruitment maneuver (p < .01), and 43 torr (interquartile range, 38-51) at 12 hrs postrecruitment maneuver. Recruitment maneuvers were well tolerated except for significant increase in Paco2 in three patients. There were no serious adverse events related to the recruitment maneuver.

CONCLUSIONS

Using the modified open lung tool recruitment maneuver, pediatric patients with acute lung injury may safely achieve improved oxygenation and ventilation with these benefits potentially lasting up to 12 hrs postrecruitment maneuver.

Prone position and recruitment manoeuvre: the combined effect improves oxygenation

Introduction

Among the various methods for improving oxygenation while decreasing the risk of ventilation-induced lung injury in patients with acute respiratory distress syndrome (ARDS), a ventilation strategy combining prone position (PP) and recruitment manoeuvres (RMs) can be practiced. We studied the effects on oxygenation of both RM and PP applied in early ARDS patients.

Methods

We conducted a prospective study. Sixteen consecutive patients with early ARDS fulfilling our criteria (ratio of arterial oxygen partial pressure to fraction of inspired oxygen (PaO₂/FiO₂) 98.3 ± 28 mmHg; positive end expiratory pressure, 10.7 ± 2.8 cmH₂O) were analysed. Each patient was ventilated in both the supine position (SP) and the PP (six hours in each position). A 45 cmH₂O extended sigh in pressure control mode was performed at the beginning of SP (RM1), one hour after turning to the PP (RM2) and at the end of the six-hour PP period (RM3).

Results

The mean arterial oxygen partial pressure (PaO₂) changes after RM1, RM2 and RM3 were 9.6%, 15% and 19%, respectively. The PaO₂ improvement after a single RM was significant after RM3 only (P < 0.05). Improvements in PaO₂ level and PaO₂/FiO₂ ratio were transient in SP but durable during PP. PaO₂/FiO₂ ratio peaked at 218 mmHg after RM3. PaO₂/FiO₂ changes were significant only after RM3 and in the pulmonary ARDS group (P = 0.008). This global strategy had a benefit with regard to oxygenation: PaO₂/FiO₂ ratio increased from 98.3 mmHg to 165.6 mmHg 13 hours later at the end of the study (P < 0.05). Plateau airway pressures decreased after each RM and over the entire PP period and significantly after RM3 (P = 0.02). Some reversible side effects such as significant blood arterial pressure variations were found when extended sighs were performed.

Conclusions

In our study, interventions such as a 45 cmH₂O extended sigh during PP resulted in marked oxygenation improvement. Combined RM and PP led to the highest increase in PaO₂/FiO₂ ratio without major clinical side effects.

Efficacy and safety of recruitment maneuvers in acute respiratory distress syndrome

Recruitment maneuvers (RM) consist of a ventilatory strategy that increases the transpulmonary pressure transiently to reopen the recruitable lung units in acute respiratory distress syndrome (ARDS). The rationales to use RM in ARDS are that there is a massive loss of aerated lung and that once the end-inspiratory pressure surpasses the regional critical opening pressure of the lung units, those units are likely to reopen. There are different methods to perform RM when using the conventional ICU ventilator. The three RM methods that are mostly used and investigated are sighs, sustained inflation, and extended sigh. There is no standardization of any of the above RM. Meta-analysis recommended not to use RM in routine in stable ARDS patients but to run them in case of life-threatening hypoxemia. There are some concerns regarding the safety of RM in terms of hemodynamics preservation and lung injury as well. The rapid rising in pressure can be a factor that explains the potential harmful effects of the RM. In this review, we describe the balance between the beneficial effects and the harmful consequences of RM. Recent animal studies are discussed.

The acute effectiveness and safety of the constant-flow, pressure-volume curve to improve hypoxemia in acute lung injury

OBJECTIVE

To investigate the effectiveness of the constant-flow, pressure-volume curve (PVC) to prescribe positive end-expiratory pressure (PEEP) in acute lung injury (ALI) and risk of cardiopulmonary deterioration during the PVC process.

DESIGN

A retrospective, cohort study.

SETTING

A surgical intensive care unit (ICU) of a tertiary, university hospital.

PATIENTS

Fifty consecutive ventilated patients diagnosed with ALI undergoing the PVC maneuver from 1999 to 2003.

INTERVENTIONS

Titration of PEEP based on the lower inflection point of the constant-flow, pressure-volume curve.

MEASUREMENTS AND MAIN RESULTS

Patients were divided into 2 groups based on PVC-guided PEEP changes of <3 cm H2O (PVC-NC or "no change") or ≥3 cm H2O (PVC-CHG or "change") from the initial empiric prescription. There was a greater increase in partial pressure of arterial oxygen (PaO2)/fractional concentration of inspired oxygen (FiO2) in the PVC-CHG group, with a mean change of 80 ± 50 (95% confidence interval [CI] 61, 98) versus 42 ± 54 (95% CI 17, 67) in the PVC-NC group. Eighty-two percent of patients (41/50) showed an increase in ratio of partial pressure of arterial oxygen to fraction of inspired oxygen (PaO2/FiO2) by 20% within 6 to 24 hours after the PVC test-greater in the PVC-CHG group (OR 1.44, 95% CI 1.02, 2.01). Thirteen percent (4/30) within the PVC-CHG group and none within the PVC-NC group (0/20) required a 25% increase in vasoactive infusion rates (P = .089) in relation to the procedure. Univariate logistic regression showed that PVC-CHG was significantly associated with a 20% change in PaO2/FiO2 (OR 7.54, 95% CI 1.37, 41.41). Multivariate logistic modeling showed that PVC-guided PEEP changes of ≥3 cm H2O, age ≤65 years, and pre-PVC FiO2 ≥ .85 were significantly associated with a 20% increase in PaO2/FiO2 (receiver operator area under the curve = .86).

CONCLUSIONS

In the setting of acute lung injury, use of the constant-flow, pressure-volume curve to prescribe PEEP appears associated with improvement in oxygenation with limited risk of acute, process-related, cardiopulmonary deterioration.

Pros and cons of recruitment maneuvers in acute lung injury and acute respiratory distress syndrome

In patients with acute lung injury and acute respiratory distress syndrome, a protective mechanical ventilation strategy characterized by low tidal volumes has been associated with reduced mortality. However, such a strategy may result in alveolar collapse, leading to cyclic opening and closing of atelectatic alveoli and distal airways. Thus, recruitment maneuvers (RMs) have been used to open up collapsed lungs, while adequate positive end-expiratory pressure (PEEP) levels may counteract alveolar derecruitment during low tidal volume ventilation, improving respiratory function and minimizing ventilator-associated lung injury. Nevertheless, considerable uncertainty remains regarding the appropriateness of RMs. The most commonly used RM is conventional sustained inflation, associated with respiratory and cardiovascular side effects, which may be minimized by newly proposed strategies: prolonged or incremental PEEP elevation; pressure-controlled ventilation with fixed PEEP and increased driving pressure; pressure-controlled ventilation applied with escalating PEEP and constant driving pressure; and long and slow increase in pressure. The efficiency of RMs may be affected by different factors, including the nature and extent of lung injury, capability of increasing inspiratory transpulmonary pressures, patient positioning and cardiac preload. Current evidence suggests that RMs can be used before setting PEEP, after ventilator circuit disconnection or as a rescue maneuver to overcome severe hypoxemia; however, their routine use does not seem to be justified at present. The development of new lung recruitment strategies that have fewer hemodynamic and biological effects on the lungs, as well as randomized clinical trials analyzing the impact of RMs on morbidity and mortality of acute lung injury/acute respiratory distress syndrome patients, are warranted.

Novel technologies to detect atelectotrauma in the injured lung

Cyclical recruitment and derecruitment of lung parenchyma (R/D) remains a serious problem in ALI/ARDS patients, defined as atelectotrauma. Detection of cyclical R/D to titrate the optimal respiratory settings is of high clinical importance. Image-based technologies that are capable of detecting changes of lung ventilation within a respiratory cycle include dynamic computed tomography (dCT), synchrotron radiation computed tomography (SRCT), and electrical impedance tomography (EIT). Time-dependent intra-arterial oxygen tension monitoring represents an alternative approach to detect cyclical R/D, as cyclical R/D can result in oscillations of PaO₂ within a respiratory cycle. Continuous, ultrafast, on-line in vivo measurement of PaO₂ can be provided by an indwelling PaO₂ probe. In addition, monitoring of fast changes in SaO₂ by pulse oximetry technology at the bedside could also be used to detect those fast changes in oxygenation.

Clinical meaning of early oxygenation improvement in severe acute respiratory distress syndrome under prolonged prone positioning

BACKGROUND/AIMS

Ventilating patients with acute respiratory distress syndrome (ARDS) in the prone position has been shown to improve arterial oxygenation, but prolonged prone positioning frequently requires continuous deep sedation, which may be harmful to patients. We evaluated the meaning of early gas exchange in patients with severe ARDS under prolonged (> or = 12 hours) prone positioning.

METHODS

We retrospectively studied 96 patients (mean age, 60.1 +/- 15.6 years; 75% men) with severe ARDS (PaO(2)/FiO2 < or = 150 mmHg) admitted to a medical intensive care unit (MICU). The terms "PaO2 response" and "PaCO2 response" represented responses that resulted in increases in the PaO2/FiO2 ratio of > or = 20 mmHg and decreases in PaCO2 of > or = 1 mmHg, respectively, 8 to 12 hours after first placement in the prone position.

RESULTS

The mean duration of prone positioning was 78.5 +/- 61.2 hours, and the 28-day mortality rate after MICU admission was 56.3%. No significant difference in clinical characteristics was observed between PaO2 and PaCO2 responders and non-responders. The PaO2 responders after prone positioning showed an improved 28-day outcome, compared with non-responders by Kaplan-Meier survival estimates (p < 0.05 by the log-rank test), but the PaCO12 responders did not.

CONCLUSIONS

Our results suggest that the early oxygenation improvement after prone positioning might be associated with an improved 28-day outcome and may be an indicator to maintain prolonged prone positioning in patients with severe ARDS.

Acute lung injury and acute respiratory distress syndrome

Every year, more information accumulates about the possibility of treating patients with acute lung injury or acute respiratory distress syndrome with specially designed mechanical ventilation strategies. Ventilator modes, positive end-expiratory pressure settings, and recruitment maneuvers play a major role in these strategies. However, what can we take from these experimental and clinical data to the clinical practice? In this article, we discuss substantial options of mechanical ventilation together with some adjunctive therapeutic measures, such as prone positioning and inhalation of nitric oxide.

Prolonged recruitment manoeuvre improves lung function with less ultrastructural damage in experimental mild acute lung injury

The effects of prolonged recruitment manoeuvre (PRM) were compared with sustained inflation (SI) in paraquat-induced mild acute lung injury (ALI) in rats. Twenty-four hours after ALI induction, rats were anesthetized and mechanically ventilated with VT=6 ml/kg and positive end-expiratory pressure (PEEP)=5 cmH(2)O for 1h. SI was performed with an instantaneous pressure increase of 40 cmH(2)O that was sustained for 40s, while PRM was done by a step-wise increase in positive inspiratory pressure (PIP) of 15-20-25 cmH(2)O above a PEEP of 15 cm H(2)O (maximal PIP=40 cmH(2)O), with interposed periods of PIP=10 cmH(2)O above a PEEP=15 cmH(2)O. Lung static elastance and the amount of alveolar collapse were more reduced with PRM than SI, yielding improved oxygenation. Additionally, tumour necrosis factor-alpha, interleukin-6, interferon-gamma, and type III procollagen mRNA expressions in lung tissue and lung epithelial cell apoptosis decreased more in PRM. In conclusion, PRM improved lung function, with less damage to alveolar epithelium, resulting in reduced pulmonary injury.

Lung recruitment--a guide for clinicians

Recruitment manoeuvres play an important role in minimising ventilator associated lung injury (VALI) particularly when lung protective ventilation strategies are employed and as such clinicians should consider their application. This paper provides evidence-based recommendations for clinical practice with regard to alveolar recruitment. It includes recommendations for timing of recruitment, strategies of recruitment and methods of measuring the efficacy of recruitment manoeuvres and contributes to knowledge about the risks associated with recruitment manoeuvres. There are a range of methods for recruiting alveoli, most notably by manipulating positive end expiratory pressure (PEEP) and peak inspiratory pressure (PIP) with consensus as to the most effective not yet determined. A number of studies have demonstrated that improvement in oxygenation is rarely sustained following a recruitment manoeuvre and it is questionable whether improved oxygenation should be the clinician's goal. Transient haemodynamic compromise has been noted in a number of studies with a few studies reporting persistent, harmful sequelae to recruitment manoeuvres. No studies have been located that assess the impact of recruitment manoeuvres on length of ventilation, length of stay, morbidity or mortality. Recruitment manoeuvres restore end expiratory lung volume by overcoming threshold opening pressures and are most effective when applied after circuit disconnection and airway suction. Whether this ultimately improves outcomes in adult or paediatric populations is unknown.

Efficacy of positive end-expiratory pressure titration after the alveolar recruitment manoeuvre in patients with acute respiratory distress syndrome

Introduction

In acute respiratory distress syndrome (ARDS), adequate positive end-expiratory pressure (PEEP) may decrease ventilator-induced lung injury by minimising overinflation and cyclic recruitment-derecruitment of the lung. We evaluated whether setting the PEEP using decremental PEEP titration after an alveolar recruitment manoeuvre (ARM) affects the clinical outcome in patients with ARDS.

Methods

Fifty-seven patients with early ARDS were randomly assigned to a group given decremental PEEP titration following ARM or a table-based PEEP (control) group. PEEP and inspired fraction of oxygen (FiO₂) in the control group were set according to the table-based combinations of FiO₂ and PEEP of the ARDS network, by which we aimed to achieve a PEEP level compatible with an oxygenation target. In the decremental PEEP titration group, the oxygen saturation and static compliance were monitored as the patients performed the ARM along with the extended sigh method, which is designed to gradually apply and withdraw a high distending pressure over a prolonged period, and the decremental titration of PEEP.

Results

The baseline characteristics did not differ significantly between the control and decremental PEEP titration groups. Initial oxygenation improved more in the decremental PEEP titration group than in the control group. However, dynamic compliance, tidal volume and PEEP were similar in the two groups during the first week. The duration of use of paralysing or sedative agents, mechanical ventilation, stay in the intensive care unit and mortality at 28 days did not differ significantly between the decremental PEEP titration and control groups.

Conclusions

The daily decremental PEEP titration after ARM showed only initial oxygenation improvement compared with the table-based PEEP method. Respiratory mechanics and patient outcomes did not differ between the decremental PEEP titration and control groups.

Trial registration

ClinicalTrials.gov identifier: ISRCTN79027921.

Effect of recruitment and body positioning on lung volume and oxygenation in acute lung injury model

The mechanism of oxygenation improvement after recruitment manoeuvres or prone positioning in acute lung injury or acute respiratory distress syndrome is still unclear. We tried to determine the mechanism responsible for the effects of recruitment manoeuvres or prone positioning on lung aeration using a whole lung computed tomography scan in an oleic acid induced acute lung injury canine model. Twelve adult mongrel dogs were allocated into either the supine group (n=6) or the prone group (n=6). After the establishment of acute lung injury, three recruitment manoeuvres were performed at one-hour intervals. Haemodynamic and ventilatory variables, arterial blood gas analyses and CT scans of the whole lung were obtained 90 minutes after oleic acid injection and five minutes before and after each recruitment manoeuvre. Recruitment manoeuvres in the supine position improved oxygenation (P=0.025) that correlated with increase of the poorly- and well-aerated dorsal (dependent) lung volume (r=0.436, P=0.016). Prone positioning increased oxygenation (P=0.004) that also correlated with increase of the poorly- and well-aerated dorsal (nondependent) lung volume (r=0.787, P<0.001). However, the recruitment manoeuvre in the prone position had no effect on oxygenation despite an increase in ventral (dependent) lung volume. The increase in PaO2 after recruitment manoeuvres in the supine position or after prone positioning is related to the increase of the poorly- and well-aerated dorsal lung.

Acute respiratory distress syndrome 40 years later: time to revisit its definition

OBJECTIVE

Acute respiratory distress syndrome is a common disorder associated with significant mortality and morbidity. The aim of this article is to critically evaluate the definition of acute respiratory distress syndrome and examine the impact the definition has on clinical practice and research.

DATA SOURCES

Articles from a MEDLINE search (1950 to August 2007) using the Medical Subject Heading respiratory distress syndrome, adult, diagnosis, limited to the English language and human subjects, their relevant bibliographies, and personal collections, were reviewed.

DATA SYNTHESIS

The definition of acute respiratory distress syndrome is important to researchers, clinicians, and administrators alike. It has evolved significantly over the last 40 years, culminating in the American-European Consensus Conference definition, which was published in 1994. Although the American-European Consensus Conference definition is widely used, it has some important limitations that may impact on the conduct of clinical research, on resource allocation, and ultimately on the bedside management of such patients. These limitations stem partially from the fact that as defined, acute respiratory distress syndrome is a heterogeneous entity and also involve the reliability and validity of the criteria used in the definition. This article critically evaluates the American-European Consensus Conference definition and its limitations. Importantly, it highlights how these limitations may contribute to clinical trials that have failed to detect a potential true treatment effect. Finally, recommendations are made that could be considered in future definition modifications with an emphasis on the significance of accurately identifying the target population in future trials and subsequently in clinical care.

CONCLUSION

How acute respiratory distress syndrome is defined has a significant impact on the results of randomized, controlled trials and epidemiologic studies. Changes to the current American-European Consensus Conference definition are likely to have an important role in advancing the understanding and management of acute respiratory distress syndrome.