Effects of sustained inflation and postinflation positive end-expiratory pressure in acute respiratory distress syndrome: focusing on pulmonary and extrapulmonary forms

Translational medicine for acute lung injury

Acute lung injury (ALI) is a complex disease with numerous causes. This review begins with a discussion of disease development from direct or indirect pulmonary insults, as well as varied pathogenesis. The heterogeneous nature of ALI is then elaborated upon, including its epidemiology, clinical manifestations, potential biomarkers, and genetic contributions. Although no medication is currently approved for this devastating illness, supportive care and pharmacological intervention for ALI treatment are summarized, followed by an assessment of the pathophysiological gap between human ALI and animal models. Lastly, current research progress on advanced nanomedicines for ALI therapeutics in preclinical and clinical settings is reviewed, demonstrating new opportunities towards developing an effective treatment for ALI.

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.

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.

Effects of SI and PCV on respiratory mechanics, early central drive and hemodynamics in patients with ARDS

Effects of sustained inflation (SI) and pressure- controlled ventilation (PCV) on respiratory mechanics, early central drive, and hemodynamics in patients with acute respiratory distress syndrome (ARDS) were investigated and compared. A retrospective analysis of 26 patients with ARDS, who were admitted to the Yiwu Central Hospital from March 2015 to March 2016, was performed. According to the ventilation method adopted by the patients with ARDS, 13 patients who received SI treatment were included in the SI group and 13 patients who received PCV treatment were included in the PCV group. The condition of central drive of the patients in the two groups was recorded and calculated continuously before and after recruitment maneuver (RM), the changes of each indicator of the respiratory function and hemodynamics were recorded and calculated before and after RM at 1, 10, 20 and 30 min. The differences were not statistically significant when comparing PIP, Pplate and Crs in patients in the SI group and the PCV group before RM with those after RM at 1, 10, 20 and 30 min (P>0.05), the differences were not statistically significant when comparing heart rate and mean arterial pressure in patients in the SI group and the PCV group before RM with those after RM at 1, 10, 20 and 30 min (P>0.05). Ηowever, central venous pressure in patients in the SI group after RM at 10 and 20 min was significantly higher than that in the PCV group, and the differences were statistically significant (P<0.05). VT/RMS, VE/RMS and ΔPdi/RMS in the SI group and the PCV group after RM were significantly higher than those before RM, and the differences were statistically significant (P<0.05). There was little difference in the effect between SI and PCV on respiratory mechanics, early central drive and hemodynamics in patients with ARDS, and both mechanical ventilation methods enhanced the effect of central-mechanical-ventilation coupling after RM. Therefore, the two mechanical ventilation methods, SI and PCV, were equally available for patients with ARDS.

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.

Plasma microRNAs levels are different between pulmonary and extrapulmonary ARDS patients: a clinical observational study

BACKGROUND

Mesenchymal stem cells (MSC) obviously alleviate the damage of the structure and function of pulmonary vascular endothelial cells (VEC). The therapeutic effects of MSC are significantly different between pulmonary ARDS (ARDSp) and extrapulmonary ARDS (ARDSexp). MicroRNAs (miRNAs), as important media of MSC regulating VEC, are not studied between ARDSp and ARDSexp. We aimed to explore the plasma levels difference of miRNAs that regulate VEC function and are associated with MSC (MSC-VEC-miRNAs) between ARDSp and ARDSexp patients.

METHODS

MSC-VEC-miRNAs were obtained through reviewing relevant literatures screened in PubMed database. We enrolled 57 ARDS patients within 24 h of admission to the ICU and then collected blood samples, extracted plasma supernatant. Patients' clinical data were collected. Then, plasma expression of MSC-VEC-miRNAs was measured by real-time fluorescence quantitative PCR. Simultaneously, plasma endothelial injury markers VCAM-1, vWF and inflammatory factors TNF-α, IL-10 were detected by ELISA method.

RESULTS

Fourteen miRNAs were picked out after screening. A total of 57 ARDS patients were included in this study, among which 43 cases pertained to ARDSp group and 14 cases pertained to ARDSexp group. Plasma miR-221 and miR-27b levels in ARDSexp group exhibited significantly lower than that in ARDSp group (miR-221, 0.22 [0.12-0.49] vs. 0.57 [0.22-1.57], P = 0.008, miR-27b, 0.34 [0.10-0.46] vs. 0.60 [0.20-1.46], P = 0.025). Plasma vWF concentration in ARDSexp group exhibited significantly lower than that in ARDSp group (0.77 [0.29-1.54] vs. 1.80 [0.95-3.51], P = 0.048). Significant positive correlation was found between miR-221 and vWF in plasma levels (r = 0.688, P = 0.022). Plasma miR-26a and miR-27a levels in non-survival group exhibited significantly lower than that in survival group (miR-26a, 0.17 [0.08-0.20] vs. 0.69 [0.24-2.33] P = 0.018, miR-27a, 0.23 [0.16-0.58] vs. 1.45 [0.38-3.63], P = 0.021) in ARDSp patients.

CONCLUSION

Plasma miR-221, miR-27b and vWF levels in ARDSexp group are significantly lower than that in ARDSp group. Plasma miR-26a and miR-27a levels in non-survival group are significantly lower than that in survival group in ARDSp patients.

Effect of recruitment maneuver on arterial oxygenation in patients undergoing robot-assisted laparoscopic prostatectomy with intraoperative 15 cmH2O positive end expiratory pressure

BACKGROUND

This randomized, controlled study was designed to compare the effects of recruitment maneuvers (RMs) with a 15 cmH₂O positive end-expiratory pressure (PEEP) on the systemic oxygenation and lung compliance of patients with healthy lungs following robot-assisted laparoscopic prostatectomy (RALP).

METHODS

Sixty patients undergoing a RALP with an intraoperative 15 cmH₂O PEEP were randomly allocated to an RM or a Control group. The patients in the RM group received a single RM through the application of a continuous positive airway pressure of 40 cmH₂O for 40 s 15 min after being placed in the Trendelenburg position. The arterial oxygen tension (PaO₂, primary endpoint) and the pulmonary dynamic and static compliances (secondary endpoints) were measured 10 min after the anesthetic induction (T1), 10 min after establishment of the pneumoperitoneum (T2), 10 min after establishment of the Trendelenburg position (T3), 10 min after the RM (T4), 60 min after the RM (T5), and 10 min after deflation of the pneumoperitoneum in the supine position (T6).

RESULTS

The intergroup comparisons of the PaO₂ showed significantly higher values in the RM group than in the Control group at T4 and T5 (193 ± 35 mmHg vs. 219 ± 33 mmHg, P = 0.015, 188 ± 41 mmHg vs. 214 ± 42 mmHg, P = 0.005, respectively). However, the PaO₂ at T6 was similar in the two groups (211 ± 39 mmHg vs. 224 ± 41 mmHg, P = 0.442). Moreover, there were no statistical differences between the groups in the dynamic and static compliances of the lungs at any time point.

CONCLUSIONS

The arterial oxygenation of the patients with a healthy lung function who had undergone a RALP with intraoperative 15 cmH₂O PEEP was improved by a single RM. However, this benefit did not last long, and it did not lead to an amelioration of the lung mechanics.

Paediatric lung recruitment: a review of the clinical evidence

Lung recruitment is used as an adjunct to lung protective ventilation strategies. Lung recruitment is a brief, deliberate elevation of transpulmonary pressures beyond what is achieved during tidal ventilation levels. The aim of lung recruitment is to maximise the number of alveoli participating in gas exchange particularly in distal and dependant regions of the lung. This may improve oxygenation and end expiratory levels. Restoration of end expiratory levels and stabilisation of the alveoli may reduce the incidence of ventilator induced lung injury (VILI). Various methods of lung recruitment have been studied in adult and experimental populations. This review aims to establish the evidence for lung recruitment in the pediatric population.

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.

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.

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.

Molecular mechanism of sustained inflation in acute respiratory distress syndrome

BACKGROUND

The aim of this study was to investigate the effect and the potential molecular mechanism of sustained inflation (SI) recruitment maneuvers in acute respiratory distress syndrome (ARDS) in beagle dog following endotracheal suctioning.

METHODS

ARDS was induced in 24 beagle dogs with oleic acid. They had mechanical ventilation support. They were randomized into four groups after the establishment of the ARDS model: non-SI-open group where no SI was applied in beagle dogs with ARDS following open endotracheal suctioning; non-SI-closed group where no SI was applied in beagle dogs with ARDS following closed endotracheal suctioning; SI-open group where SI was applied in beagle dogs with ARDS following open endotracheal suctioning; and SI-closed group where SI was applied in beagle dogs with ARDS following closed endotracheal suctioning. Oxygenation, indexes of respiratory mechanics, and hemodynamic indexes were serially measured during the procedure. The serum protein level, or the messenger RNA in the heart and lung, of inflammation-related cytokines was investigated.

RESULTS

SI in ARDS improved oxygenation, lung compliance, and airway resistance but had no significant effect in the hemodynamic indexes. At molecular level, SI in ARDS neutralized the increases of pro-inflammatory cytokines (tumor necrosis factor α, interleukin 1β [IL-1β], and IL-6), and anti-inflammatory cytokine (IL-10) in the serum. Furthermore, SI in ARDS increased aquaporin 1 and aquaporin 5 messenger RNA in the lung tissue, and decreased IL-6 messenger RNA in the lung and heart tissue.

CONCLUSION

SI in ARDS could improve oxygenation, lung compliance, and airway resistance, which was related to the improved degree of inflammation and better maintained aquaporins.

Mechanical ventilation during acute lung injury: current recommendations and new concepts

Despite a very large body of investigations, no effective pharmacological therapies have been found to cure acute lung injury. Hence, supportive care with mechanical ventilation remains the cornerstone of treatment. However, several experimental and clinical studies showed that mechanical ventilation, especially at high tidal volumes and pressures, can cause or aggravate ALI. Therefore, current clinical recommendations are developed with the aim of avoiding ventilator-induced lung injury (VILI) by limiting tidal volume and distending ventilatory pressure according to the results of the ARDS Network trial, which has been to date the only intervention that has showed success in decreasing mortality in patients with ALI/ARDS. In the past decade, a very large body of investigations has determined significant achievements on the pathophysiological knowledge of VILI. Therefore, new perspectives, which will be reviewed in this article, have been defined in terms of the efficiency and efficacy of recognizing, monitoring and treating VILI, which will eventually lead to further significant improvement of outcome in patients with ARDS.

Optimal duration of a sustained inflation recruitment maneuver in ARDS patients

PURPOSE

To measure the dynamics of recruitment and the hemodynamic status during a sustained inflation recruitment maneuver (RM) in order to determine the optimal duration of RM in acute respiratory distress syndrome (ARDS) patients.

METHODS

This prospective study was conducted in a 12-bed intensive care unit (ICU) in a general hospital. A 40 cmH(2)O sustained inflation RM maintained for 30 s was performed in 50 sedated ventilated patients within the first 24 h of meeting ARDS criteria. Invasive arterial pressures, heart rate, and SpO(2) were measured at 10-s intervals during the RM. The volume increase during the RM was measured by integration of the flow required to maintain the pressure at 40 cmH(2)O, which provides an estimation of the volume recruited during the RM. Raw data were corrected for gas consumption and fitted with an exponential curve in order to determine an individual time constant for the volume increase.

RESULTS

The average volume increase and time constant were 210 ± 198 mL and 2.3 ± 1.3 s, respectively. Heart rate, diastolic arterial pressure, and SpO(2) did not change during or after the RM. Systolic and mean arterial pressures were maintained at 10 s, decreased significantly at 20 and 30 s during the RM, and recovered to the pre-RM value 30 s after the end of the RM (ANOVA, p < 0.01).

CONCLUSIONS

In early-onset ARDS patients, most of the recruitment occurs during the first 10 s of a sustained inflation RM. However, hemodynamic impairment is significant after the tenth second of RM.

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.

N-terminal pro-brain natriuretic peptide as a marker of right ventricular dysfunction after open-lung approach in patients with acute lung injury/acute respiratory distress syndrome

PURPOSE

The purpose of the study was to evaluate the utility of N-terminal pro-brain natriuretic peptide (NT-proBNP) as a marker of right ventricular (RV) dysfunction after open-lung approach (OLA) in patients with acute lung injury (ALI)/acute respiratory distress syndrome (ARDS).

MATERIALS AND METHODS

Twenty-seven patients with ALI/ARDS underwent OLA (2-minute steps of fixed pressure-controlled ventilation with progressive positive end-expiratory pressure levels up to 30 cm H(2)O, followed by stepwise decrement of positive end-expiratory pressure level by 2 cm H(2)O). Patients who showed a PaO(2)/FiO(2) increase of more than 50% from baseline were defined as responders. Plasma NT-proBNP levels were taken immediately before OLA and 2 and 6 hours later. A minimum 30% increase in NT-proBNP level from baseline was considered significant.

RESULTS

Right-over-left ventricular stroke work ratio and its percentage change did not differ between responders and nonresponders, whereas these values were higher in patients showing NT-proBNP increase (P < .05). The NT-proBNP percentage change correlated with right-over-left ventricular stroke work ratio percentage change (r = 0.83), pulmonary vascular resistance (r = 0.81), and RV ejection fraction (r = -0.79) and correlated with plateau pressure in nonresponders only (r = 0.82).

CONCLUSIONS

In patients with ALI/ARDS, intraindividual NT-proBNP changes correlated with RV afterload following OLA, thereby serving as a potential marker for RV dysfunction after OLA.

Severe hypoxemic respiratory failure: part 1--ventilatory strategies

Approximately 16% of deaths in patients with ARDS results from refractory hypoxemia, which is the inability to achieve adequate arterial oxygenation despite high levels of inspired oxygen or the development of barotrauma. A number of ventilator-focused rescue therapies that can be used when conventional mechanical ventilation does not achieve a specific target level of oxygenation are discussed. A literature search was conducted and narrative review written to summarize the use of high levels of positive end-expiratory pressure, recruitment maneuvers, airway pressure-release ventilation, and high-frequency ventilation. Each therapy reviewed has been reported to improve oxygenation in patients with ARDS. However, none of them have been shown to improve survival when studied in heterogeneous populations of patients with ARDS. Moreover, none of the therapies has been reported to be superior to another for the goal of improving oxygenation. The goal of improving oxygenation must always be balanced against the risk of further lung injury. The optimal time to initiate rescue therapies, if needed, is within 96 h of the onset of ARDS, a time when alveolar recruitment potential is the greatest. A variety of ventilatory approaches are available to improve oxygenation in the setting of refractory hypoxemia and ARDS. Which, if any, of these approaches should be used is often determined by the availability of equipment and clinician bias.

PEEP titration guided by ventilation homogeneity: a feasibility study using electrical impedance tomography

Introduction

Lung protective ventilation requires low tidal volume and suitable positive end-expiratory pressure (PEEP). To date, few methods have been accepted for clinical use to set the appropriate PEEP. The aim of this study was to test the feasibility of PEEP titration guided by ventilation homogeneity using the global inhomogeneity (GI) index based on electrical impedance tomography (EIT) images.

Methods

In a retrospective study, 10 anesthetized patients with healthy lungs mechanically ventilated under volume-controlled mode were investigated. Ventilation distribution was monitored by EIT. A standardized incremental PEEP trial (PEEP from 0 to 28 mbar, 2 mbar per step) was conducted. During the PEEP trial, "optimal" PEEP level for each patient was determined when the air was most homogeneously distributed in the lung, indicated by the lowest GI index value. Two published methods for setting PEEP were included for comparison based on the maximum global dynamic compliance and the intra-tidal compliance-volume curve.

Results

No significant differences in the results were observed between the GI index method (12.2 ± 4.6 mbar) and the dynamic compliance method (11.4 ± 2.3 mbar, P > 0.6), or between the GI index and the compliance-volume curve method (12.2 ± 4.9 mbar, P > 0.6).

Conclusions

According to the results, it is feasible and reasonable to use the GI index to select the PEEP level with respect to ventilation homogeneity. The GI index may provide new insights into the relationship between lung mechanics and tidal volume distribution and may be used to guide ventilator settings.

Acute hemodynamic effects of recruitment maneuvers in patients with acute respiratory distress syndrome

BACKGROUND

The recruitment maneuver (RM) in acute respiratory distress syndrome (ARDS) can cause hemodynamic derangement. We evaluated circulatory and cardiac changes during RMs.

METHODS

We performed sustained inflation (SI) with a pressure of 40 cm H(2)O for 30 seconds as an RM on 22 patients with ARDS. Blood pressure (BP) and heart rate were recorded immediately before, every 10 seconds during, and 30 seconds after the RM. Ventricular dimensions were obtained simultaneously using M-mode echocardiography, and tissue Doppler imaging was performed on the left ventricular wall.

RESULTS

Mean, systolic, and diastolic BP decreased at 20 and 30 seconds during 30-second RMs (mean BP: 92 +/- 12 at baseline to 83 +/- 18 mm Hg at the end of the RM, P < .05) and subsequently recovered. Heart rate decreased at 10 and 20 seconds during the RM, and tended to increase afterward. Both ventricular dimensions decreased significantly during the RM. The left ventricular ejection fraction and peak velocity of the left ventricle during systole remained stable. The fractional changes in mean BP and left ventricular end-diastolic dimension during the RMs were correlated significantly with each other (r(s) = 0.59). Static compliance of the respiratory system (Crs) was lower in patients with mean BP change > or =15% than in patients in whom the change was <15% (P < .05).

CONCLUSIONS

A transient decrease in mean BP was observed during the RM, and its degree was correlated with the preload decrease, while cardiac contractility was maintained.

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.

A comparison of methods to identify open-lung PEEP

PURPOSE

Many methods exist in the literature for identifying PEEP to set in ARDS patients following a lung recruitment maneuver (RM). We compared ten published parameters for setting PEEP following a RM.

METHODS

Lung injury was induced by bilateral lung lavage in 14 female Dorset sheep, yielding a PaO(2) 100-150 mmHg at F(I)O(2) 1.0 and PEEP 5 cmH(2)O. A quasi-static P-V curve was then performed using the supersyringe method; PEEP was set to 20 cmH(2)O and a RM performed with pressure control ventilation (inspiratory pressure set to 40-50 cmH(2)O), until PaO(2) + PaCO(2) > 400 mmHg. Following the RM, a decremental PEEP trial was performed. The PEEP was decreased in 1 cmH(2)O steps every 5 min until 15 cmH(2)O was reached. Parameters measured during the decremental PEEP trial were compared with parameters obtained from the P-V curve.

RESULTS

For setting PEEP, maximum dynamic tidal respiratory compliance, maximum PaO(2), maximum PaO(2) + PaCO(2), and minimum shunt calculated during the decremental PEEP trial, and the lower Pflex and point of maximal compliance increase on the inflation limb of the P-V curve (Pmci,i) were statistically indistinguishable. The PEEP value obtained using the deflation upper Pflex and the point of maximal compliance decrease on the deflation limb were significantly higher, and the true inflection point on the inflation limb and minimum PaCO(2) were significantly lower than the other variables.

CONCLUSION

In this animal model of ARDS, dynamic tidal respiratory compliance, maximum PaO(2), maximum PaO(2) + PaCO(2), minimum shunt, inflation lower Pflex and Pmci,i yield similar values for PEEP following a recruitment maneuver.

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.

Recruitment maneuvers for acute lung injury: a systematic review

RATIONALE

There are conflicting data regarding the safety and efficacy of recruitment maneuvers (RMs) in patients with acute lung injury (ALI).

OBJECTIVES

To summarize the physiologic effects and adverse events in adult patients with ALI receiving RMs.

METHODS

Systematic review of case series, observational studies, and randomized clinical trials with pooling of study-level data.

MEASUREMENTS AND MAIN RESULTS

Forty studies (1,185 patients) met inclusion criteria. Oxygenation (31 studies; 636 patients) was significantly increased after an RM (PaO2): 106 versus 193 mm Hg, P = 0.001; and PaO2/FiO2 ratio: 139 versus 251 mm Hg, P < 0.001). There were no persistent, clinically significant changes in hemodynamic parameters after an RM. Ventilatory parameters (32 studies; 548 patients) were not significantly altered by an RM, except for higher PEEP post-RM (11 versus 16 cm H2O; P = 0.02). Hypotension (12%) and desaturation (9%) were the most common adverse events (31 studies; 985 patients). Serious adverse events (e.g., barotrauma [1%] and arrhythmias [1%]) were infrequent. Only 10 (1%) patients had their RMs terminated prematurely due to adverse events.

CONCLUSIONS

Adult patients with ALI receiving RMs experienced a significant increase in oxygenation, with few serious adverse events. Transient hypotension and desaturation during RMs is common but is self-limited without serious short-term sequelae. Given the uncertain benefit of transient oxygenation improvements in patients with ALI and the lack of information on their influence on clinical outcomes, the routine use of RMs cannot be recommended or discouraged at this time. RMs should be considered for use on an individualized basis in patients with ALI who have life-threatening hypoxemia.

Recruitment maneuver in pulmonary and extrapulmonary experimental acute lung injury

OBJECTIVE

The aim of this study is to test the hypothesis that recruitment maneuvers (RMs) might act differently in models of pulmonary (p) and extrapulmonary (exp) acute lung injury (ALI) with similar transpulmonary pressure changes.

DESIGN

Prospective, randomized, controlled experimental study.

SETTING

University research laboratory.

SUBJECTS

Wistar rats were randomly divided into four groups. In control groups, sterile saline solution was intratracheally (0.1 mL, Cp) or intraperitoneally (1 mL, Cexp) injected, whereas ALI animals received Escherichia coli lipopolysaccharide intratracheally (100 microg, ALIp) or intraperitoneally (1 mg, ALIexp). After 24 hrs, animals were mechanically ventilated (tidal volume, 6 mL/kg; positive end-expiratory pressure, 5 cm H2O) and three RMs (pressure inflations to 40 cm H2O for 40 secs, 1 min apart) applied.

MEASUREMENTS AND MAIN RESULTS

PaO2, lung resistive and viscoelastic pressures, static elastance, lung histology (light and electron microscopy), and type III procollagen messenger RNA expression in pulmonary tissue were measured before RMs and at the end of 1 hr of mechanical ventilation. Mechanical variables, gas exchange, and the fraction of area of alveolar collapse were similar in both ALI groups. After RMs, lung resistive and viscoelastic pressures and static elastance decreased more in ALIexp (255%, 180%, and 118%, respectively) than in ALIp (103%, 59%, and 89%, respectively). The amount of atelectasis decreased more in ALIexp than in ALIp (from 58% to 19% and from 59% to 33%, respectively). RMs augmented type III procollagen messenger RNA expression only in the ALIp group (19%), associated with worsening in alveolar epithelium injury but no capillary endothelium lesion, whereas the ALIexp group showed a minor detachment of the alveolar capillary membrane.

CONCLUSIONS

Given the same transpulmonary pressures, RMs are more effective at opening collapsed alveoli in ALIexp than in ALIp, thus improving lung mechanics and oxygenation with limited damage to alveolar epithelium.

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

OBJECTIVES

The plotting of pressure-volume curves and the performance of alveolar recruitment maneuvers are common practices in the care of patients with adult respiratory distress syndrome (ARDS), even though potentially harmful hemodynamic effects are associated with sustaining a high intrathoracic pressure. Our aim was to analyze hemodynamic and ventilatory changes related to these 2 maneuvers and to assess the short-term effectiveness of recruitment.

PATIENTS AND METHODS

The patients had ARDS and were being monitored with a catheter connected to a PiCCO system. All measurements were taken in sinus rhythm and with adequate vascular filling. Values recorded during plotting of the quasistatic pressure-volume curve and the recruitment maneuver (sustained airway pressure of 40 cm H2O) were the cardiac index, mean arterial pressure, heart rate, systolic volume index, and oxygen saturation (SpO2). Blood gas measurements were recorded before the maneuvers and 15 minutes afterwards.

RESULTS

All parameters decreased significantly in the 14 patients studied. The mean (SD) maximum decreases, from which all patients recovered within 2 minutes, were as follows: cardiac index, 26% (16%); mean arterial pressure, 6% (6%); heart rate, 4% (5%), systolic volume index, 21% (15%); and SpO2, 3% (3%). Significant increases in PaO2 (7% [6%]) and the ratio of PaO2 to the fraction of inspired oxygen were recorded after the recruitment maneuver (P=.016 and P=.014, respectively), but the changes were not clinically significant.

CONCLUSIONS

The hemodynamic disturbances associated with the alveolar recruitment maneuver based on sustaining a high end-expiratory pressure and the minor improvement in oxygenation achieved as a result suggest that the routine use of that maneuver in ARDS patients is of questionable value.

Chest physiotherapy prolongs duration of ventilation in the critically ill ventilated for more than 48 hours

OBJECTIVE

This study aimed to determine the impact of providing chest physiotherapy after routine clinical assessment on the duration of mechanical ventilation, outcome and intensive care length of stay.

DESIGN AND SETTING

Single-centre, single-blind, prospective, randomised, controlled trial in a university hospital general intensive care unit.

PATIENTS AND PARTICIPANTS

180 patients requiring mechanical ventilation for more than 48 h.

INTERVENTIONS

Patients randomly allocated, one group receiving physiotherapy as deemed appropriate by physiotherapists after routine daily assessments and another group acting as controls were limited to receiving decubitus care and tracheal suctioning.

MEASUREMENTS AND RESULTS

Primary endpoints were initial time to become ventilator-free, secondary endpoints included intensive care unit (ICU) and hospital mortality and ICU length of stay. Kaplan-Meier analysis censored for death revealed a significant prolongation of median time to become ventilator-free among patients receiving physiotherapy (p=0.047). The time taken for 50% of patients (median time) to become ventilator-free was 15 and 11 days, respectively, for physiotherapy and control groups. There were no differences between groups in ICU or hospital mortality rates, or length of ICU stay. The number of patients needing re-ventilation for respiratory reasons was similar in both groups.

Time required for equilibration of arterial oxygen pressure after setting optimal positive end-expiratory pressure in acute respiratory distress syndrome

OBJECTIVE

To evaluate the time course of Pao2 change following the setting of optimal positive end-expiratory pressure (PEEP) in patients with acute respiratory distress syndrome (ARDS).

DESIGN

Prospective clinical study.

SETTING

Multidisciplinary intensive care unit of a university hospital.

PATIENTS

Twenty-five consecutive patients with ARDS.

INTERVENTIONS

ARDS was diagnosed during pressure-regulated volume control ventilation with tidal volume of 7 mL/kg actual body weight, respiratory rate of 12 breaths/min, inspiratory/expiratory ratio of 1:2, Fio2 of 1, and PEEP of 5 cm H2O. A critical care attending physician obtained pressure volume curves and determined the lower inflection point. Following a rest period of 30 mins with initial ventilation variables, PEEP was set at 2 cm H2O above the lower inflection point, and serial blood samples were collected during 1-hr ventilation with optimal PEEP. Arterial blood gas analyses were performed at 1, 3, 5, 7, 9, 11, 15, 20, 30, 45, and 60 mins.

MEASUREMENTS AND MAIN RESULTS

Twenty-five patients were found eligible for the study. Three patients were excluded due to deterioration of oxygen saturation and hemodynamic instability following the initiation of optimal PEEP. Eight cases (36%) were considered to be of pulmonary origin and 14 cases (64%) of extrapulmonary origin. Optimal PEEP levels were 14 +/- 3 cm H2O and 14 +/- 4 cm H2O in pulmonary and extrapulmonary ARDS, respectively. Pao2 demonstrated a 130 +/- 101% increase at the end of 1-hr period in total study population. This improvement did not differ significantly between pulmonary and extrapulmonary forms of ARDS (135 +/- 118% vs. 127 +/- 95%, p = .8). Mean 90% oxygenation time was found to be 20 +/- 19 mins. In the subset of patients with ARDS of pulmonary origin, 90% oxygenation time was 25 +/- 26 mins, whereas it was 17 +/- 15 mins in patients with ARDS of extrapulmonary origin (p = .8).

CONCLUSIONS

Our data showed that 20 mins would be adequate for obtaining a blood gas sample in ARDS patients with pulmonary and extrapulmonary origin after application of optimal PEEP 2 cm H2O above the lower inflection point.

Combining high-frequency oscillatory ventilation and recruitment maneuvers in adults with early acute respiratory distress syndrome: The Treatment with Oscillation and an Open Lung Strategy (TOOLS) Trial pilot study*

OBJECTIVE

To determine the safety, feasibility, and lung-recruitment efficacy of an explicit ventilation protocol combining high-frequency oscillatory ventilation and recruitment maneuvers.

DESIGN

Prospective, multiple-center, single-intervention pilot study.

SETTING

Four university-affiliated intensive care units.

PATIENTS

Twenty-five patients with early acute respiratory distress syndrome and severe oxygenation failure.

INTERVENTIONS

Patients were transitioned from standardized conventional ventilation to high-frequency oscillatory ventilation beginning with an initial cycle of up to three sustained inflation recruitment maneuvers (40 cm H2O x 40 secs), followed by a decremental titration of Fio2 and then mean airway pressure. Recruitment maneuvers were repeated for hypoxemia and routinely at least twice daily if the Fio2 was >0.4. A specific protocol was used for weaning high-frequency oscillatory ventilation, for transitioning to conventional ventilation, and for judging intolerance of conventional ventilation whereby patients should be put back on high-frequency oscillatory ventilation.

MEASUREMENTS AND MAIN RESULTS

Patients (median [interquartile range] Acute Physiology and Chronic Health Evaluation II, 24 [19-32]; age, 50 [41-64]) were enrolled after 13 (range, 6-51) hrs of conventional ventilation. Following the initial cycle of recruitment, the mean (+/-sd) Pao2/Fio2 increased significantly compared with standardized conventional ventilation (200 +/- 117 vs. 92 +/- 36 mm Hg, p < .001). After a mean of 12 hrs of high-frequency oscillatory ventilation, the mean Fio2 was significantly reduced compared with prestudy levels (0.5 +/- 0.2 vs. 0.9 +/- 0.1, p < .001). A median of seven (four to 11) recruitment maneuvers was performed per patient over the study period, with only eight of 244 (3.3%) being aborted. Six of 19 patients transitioned to conventional ventilation (32%) were deemed intolerant and were switched back to high-frequency oscillatory ventilation. Protocol adherence was excellent with documented rates >90%.

CONCLUSIONS

The combination of high-frequency oscillatory ventilation and recruitment maneuvers resulted in rapid and sustained improvement in oxygenation, likely through lung recruitment. This explicit high-frequency oscillatory ventilation protocol appears well tolerated, feasible, and physiologically sound.

Pulmonary and extrapulmonary acute respiratory distress syndrome: are they different?

PURPOSE OF REVIEW

Acute respiratory distress syndrome has been considered a morphologic and functional expression of lung injury caused by a variety of insults. Two distinct forms of acute respiratory distress syndrome/acute lung injury are described, because there are differences between pulmonary acute respiratory distress syndrome (direct effects on lung cells) and extrapulmonary acute respiratory distress syndrome (reflecting lung involvement in a more distant systemic inflammatory response). This article will focus on the differences in lung histology and morphology, respiratory mechanics, and response to ventilatory strategies and pharmacologic therapies in pulmonary and extrapulmonary acute respiratory distress syndrome.

RECENT FINDINGS

Many researchers recognize that experimental pulmonary and extrapulmonary acute respiratory distress syndrome are not identical. In addition, clinical studies have described the detection of differences radiographically, functionally, and by analysis of the responses to therapeutic interventions (ventilatory strategies, positive end-expiratory pressure, prone position, drugs). However, there are contradictions among the different studies addressing these issues, which could be attributed to the fact that the distinction between pulmonary and extrapulmonary acute respiratory distress syndrome is not always clear and simple. Furthermore, there may be frequent overlapping in pathogenetic mechanisms and morphologic alterations.

SUMMARY

The understanding of acute respiratory distress syndrome needs to take into account its origin. If each pathogenetic mechanism were to be considered, clinical management would be more precise, and probably the outcome could include real amelioration.

Recruitment maneuvers during prone positioning in patients with acute respiratory distress syndrome

OBJECTIVE

To evaluate the interaction of recruitment maneuvers and prone positioning on gas exchange and venous admixture in patients with early extrapulmonary acute respiratory distress syndrome ventilated with high levels of positive end-expiratory pressure. We hypothesized that a sustained inflation performed after 6 hrs of prone positioning would induce sustained improvement in oxygenation (Pao2/Fio2) and venous admixture.

DESIGN

Prospective, interventional study.

SETTING

Tertiary care, postoperative intensive care unit.

PATIENTS

Fifteen patients with early extrapulmonary acute respiratory distress syndrome.

INTERVENTIONS

After 6 hrs of prone positioning, a sustained inflation was performed with 50 cm H2O maintained for 30 secs. Data were recorded in supine position, after 6 hrs of prone positioning, at 3, 30, and 180 mins following the sustained inflation.

MEASUREMENTS AND MAIN RESULTS

A response to prone positioning was observed in nine of 15 patients leading to an improvement of Pao2/Fio2 (147 +/- 37 torr vs. 225 +/- 77 torr, p = .005) and venous admixture (35.4 +/- 8.3% vs. 28.9 +/- 9.8%, p = .001). Six patients did not respond to prone positioning. Following the sustained inflation, the responders to prone positioning showed a further increase of Pao2/Fio2 and decrease of venous admixture at 3 mins (Pao2/Fio2, 225 +/- 77 torr vs. 368 +/- 90 torr, p = .018; venous admixture, 28.9 +/- 9.8% vs. 18.9 +/- 6.7%, p = .05). In all six nonresponders to prone positioning, an improvement of Pao2/Fio2 and venous admixture occurred at 3 mins following the sustained inflation (128 +/- 18 torr vs. 277 +/- 59 torr, p = .03; venous admixture, 34.2 +/- 6.0% vs. 23.8 +/- 6.3%, p = .05). The beneficial effects of the sustained inflation remained significantly elevated over 3 hrs in responders and nonresponders to prone positioning.

CONCLUSION

In patients with early extrapulmonary acute respiratory distress syndrome, a sustained inflation performed after 6 hrs of prone positioning induced further and sustained improvement of oxygenation and venous admixture in both responders and nonresponders to prone positioning.