Acute lung injury and the acute respiratory distress syndrome: challenges in clinical trial design

Viola yedoensis liposoluble fraction ameliorates lipopolysaccharide-induced acute lung injury in mice

Viola yedoensis is a component of traditional Chinese herb medicine for inflammatory diseases. Chemical constituents of V. yedoensis have been shown to possess antibacterial, anti-HIV, and anticoagulant effects in experimental research; however, their anti-inflammatory properties remain to be demonstrated. In this study, a mouse model of lipopolysaccharide (LPS)-induced acute lung injury was used to investigate the effect of petroleum ether fraction of V. yedoensis (PEVY) on inflammation in vivo. After being shown to have anti-complementary activity in vitro, PEVY was orally administered to the mice at doses of 2, 4, and 8 mg/kg. Treatment with PEVY significantly decreased the wet-to-dry weight ratio of the lung, total cells, red blood cells, protein concentration, and myeloperoxidase activity in bronchoalveolar lavage fluid. PEVY markedly attenuated lung injury with improved lung morphology and reduced complement deposition. In addition, PEVY suppressed the expression of pro-inflammatory cytokines, TNF-α, IL-1β, and IL-6. Taken together, PEVY protects the lung from acute injury, potentially via inhibiting the activation of the complement system and excessive production of proinflammatory mediators.

Role of activated neutrophils in chest trauma-induced septic acute lung injury

More than 50% of severely injured patients have chest trauma. Second insults frequently result in acute lung injury (ALI), with sepsis being the main underlying condition. We aimed to develop a standardized, reproducible, and clinically relevant double-hit mouse model of ALI induced by chest trauma and polymicrobial sepsis and to investigate the pathophysiologic role of activated neutrophils. Lung contusion was applied to C57Bl/6 mice via a focused blast wave. Twenty-four hours later, sepsis was induced by cecal ligation and puncture. For polymorphonuclear leukocyte (PMN) depletion, animals received intravenous injections of PMN-depleting antibody. In response to blunt chest trauma followed by sepsis as well as after sepsis alone, a significant local and systemic inflammatory response with increased cytokine/chemokine levels in lung and plasma was observed. In contrast, lung apoptosis was markedly elevated only after a double hit. Intra-alveolar neutrophils and total bronchoalveolar lavage protein concentrations were markedly increased following isolated chest trauma or the combined insult, but not after sepsis alone. Lung myeloperoxidase activity was enhanced only in response to the double hit accompanied by histological disruption of the alveolar architecture, lung congestion, and marked cellular infiltrates. Neutrophil depletion significantly diminished lung interleukin 1β and interleukin 6 concentrations and reduced the degree of septic ALI. Here we have established a novel and highly reproducible mouse model of chest trauma-induced septic ALI characterizing a clinical relevant double-hit scenario. In particular, the depletion of neutrophils substantially mitigated the extent of lung injury, indicating a pathomechanistic role for neutrophils in chest trauma-induced septic ALI.

Improvement in ARDS experimental model installation: low mortality rate and maintenance of hemodynamic stability

INTRODUCTION

Many experimental models using lung lavage have been developed for the study of acute respiratory distress syndrome (ARDS). The original technique has been modified by many authors, resulting in difficulties with reproducibility. There is insufficient detail on the lung injury models used, including hemodynamic stability during animal preparation and drawbacks encountered such as mortality. The authors studied the effects of the pulmonary recruitment and the use of fixed tidal volume (Vt) or fixed inspiratory pressure in the experimental ARDS model installation.

METHODS

Adult rabbits were submitted to repeated lung lavages with 30 ml/kg warm saline until the ARDS definition (PaO₂/FiO₂ ≤ 100) was reached. The animals were divided into three groups, according to the technique used for mechanical ventilation: 1) fixed Vt of 10 ml/kg; 2) fixed inspiratory pressure (IP) with a tidal volume of 10 ml/kg prior to the first lung lavage; and 3) fixed Vt of 10 ml/kg with pulmonary recruitment before the first lavage.

RESULTS

The use of alveolar recruitment maneuvers, and the use of a fixed Vt or IP between the lung lavages did not change the number of lung lavages necessary to obtain the experimental model of ARDS or the hemodynamic stability of the animals during the procedure. A trend was observed toward an increased mortality rate with the recruitment maneuver and with the use of a fixed IP.

DISCUSSION

There were no differences between the three study groups, with no disadvantage in method of lung recruitment, either fixed tidal volume or fixed inspiratory pressure, regarding the number of lung lavages necessary to obtain the ARDS animal model. Furthermore, the three different procedures resulted in good hemodynamic stability of the animals, and low mortality rate.

Persistent organ dysfunction plus death: a novel, composite outcome measure for critical care trials

INTRODUCTION

Due to resource limitations, few critical care interventions have been rigorously evaluated with adequately powered randomized clinical trials (RCTs). There is a need to improve the efficiency of RCTs in critical care so that more definitive high quality RCTs can be completed with the available resources. The objective of this study was to validate and demonstrate the utility of a novel composite outcome measure, persistent organ dysfunction (POD) plus death, for clinical trials of critically ill patients.

METHODS

We performed a secondary analysis of a dataset from a prospective randomized trial involving 38 intensive care units (ICUs) in Canada, Europe, and the United States. We define POD as the persistence of organ dysfunction requiring supportive technologies during the convalescent phase of critical illness and it is present when a patient has an ongoing requirement for vasopressors, dialysis, or mechanical ventilation at the outcome assessments time points. In 600 patients enrolled in a randomized trial of nutrition therapy and followed prospectively for six months, we evaluated the prevalence of POD and its association with outcome.

RESULTS

At 28 days, 2.3% of patients had circulatory failure, 13.7% had renal failure, 8.7% had respiratory failure, and 27.2% had died, for an overall prevalence of POD + death = 46.0%. Of survivors at Day 28, those with POD, compared to those without POD, had a higher mortality rate in the six-month follow-up period, had longer ICU and hospital stays, and a reduced quality of life at three months. Given these rates of POD + death and using a two-sided Chi-squared test at alpha = 0.05, we would require 616 patients per arm to detect a 25% relative risk reduction (RRR) in mortality, but only 286 per arm to detect the same RRR in POD + mortality.

CONCLUSIONS

POD + death may be a valid composite outcome measure and compared to mortality endpoints, may reduce the sample size requirements of clinical trials of critically ill patients. Further validation in larger clinical trials is required.

Urinary trypsin inhibitor attenuates lipopolysaccharide-induced acute lung injury by blocking the activation of p38 mitogen-activated protein kinase

OBJECTIVE

To investigate the protective effect of urinary trypsin inhibitor (UTI) in a rat model of lipopolysaccharide (LPS)-induced acute lung injury (ALI) and the underlying molecular mechanism.

METHODS

Rats were randomly assigned into three groups: control group, LPS treatment group and LPS/UTI treatment group. The serum concentrations of tumor necrosis factor (TNF)-α and interleukin (IL)-10 were measured by ELISA. The expression of p38 mitogen-activated protein kinase (MAPK) in lung tissues was determined by Western blot analysis.

RESULTS

Administration of UTI reduced the lung wet/dry weight ratio and ameliorated the tissue damage. In the LPS/UTI treatment group, levels of TNF-α were significantly lower than those in the LPS treatment group, while the levels of IL-10 were significantly higher than those in the LPS treatment group. Western blot analysis revealed that UTI inhibited the phosphorylation of p38 MAPK in lung tissues.

CONCLUSIONS

UTI attenuates LPS-induced ALI, probably by adjusting the balance between proinflammatory and anti-inflammatory cytokines. The mechanism responsible for the decreased TNF-α expression may be related to the inhibitory effect of UTI on p38 MAPK activation.

An alternative method of acute lung injury classification for use in observational studies

BACKGROUND

In observational studies using acute lung injury (ALI) as an outcome, a spectrum of lung injury and difficult-to-interpret chest radiographs (CXRs) may hamper efforts to uncover risk factor associations. We assessed the impact of excluding patients with difficult-to-classify or equivocal ALI diagnosis on clinical and genetic risk factor associations for ALI after trauma.

METHODS

This study was of a prospective cohort of 280 critically ill trauma patients. The primary outcome was the development of ALI. Patients were classified into one of three groups: (1) definite ALI (patients who fulfilled the American-European Consensus Conference [AECC] criteria for ALI), (2)equivocal ALI (patients who had difficult-to-interpret CXRs), and (3) definite non-ALI. We compared clinical and genetic ALI risk factor associations between two classification schemes: AECC classification (definite ALI vs rest) and alternative classification (definite ALI vs definite non-ALI, excluding equivocal ALI).

RESULTS

Ninety-three (35%) patients were classified as definite ALI, 67 (25%) as equivocal, and 104 (39%) as definite non-ALI. Estimates of clinical and genetic ALI risk factor associations were farther from the null using the alternative classification. In a multivariable risk factor model, the C statistic of the alternative classification was significantly higher than that derived from the AECC classification (0.82 vs 0.74; P < .01).

CONCLUSIONS

The ability to detect ALI risk factors may be improved by excluding patients with equivocal or difficult-to-classify ALI. Such analyses may provide improved ability to detect clinical and genetic risk factor associations in future epidemiologic studies of ALI.

Plasma C-reactive protein levels are associated with improved outcome in ARDS

BACKGROUND

C-reactive protein (CRP) has been studied as a marker of systemic inflammation and outcome in a number of diseases, but little is known about its characteristics in ARDS. We sought to examine plasma levels of CRP in patients with ARDS and their relationship to outcome and measures of illness severity.

METHODS

We measured CRP levels in 177 patients within 48 h of disease onset and tested the association of protein level with 60-day mortality, 28-day daily organ dysfunction scores, and number of ventilator-free days.

RESULTS

We found that CRP levels were significantly lower in nonsurvivors when compared with survivors (p = 0.02). Mortality rate decreased with increasing CRP decile (p = 0.02). An increasing CRP level was associated with a significantly higher probability of survival at 60 days (p = 0.005). This difference persisted after adjustment for age and severity of illness in a multivariable model (p = 0.009). Multivariable models were also used to show that patients in the group with higher CRP levels had significantly lower organ dysfunction scores (p = 0.001) and more ventilator-free days (p = 0.02).

CONCLUSIONS

Increasing plasma levels of CRP within 48 h of ARDS onset are associated with improved survival, lower organ failure scores, and fewer days of mechanical ventilation. These data appear to be contrary to the established view that CRP is solely a marker of systemic inflammation.

Important issues in the design and reporting of clinical trials in severe sepsis and acute lung injury

Severe sepsis and acute lung injury are challenging diagnoses as they relate to designing and reporting of clinical trials. The limited success in bringing forward new therapies in these areas is likely proof of that premise. The ability to use preclinical and phase I and II trial data to predict which patients and which dosing regimens are more likely to benefit is perhaps the greatest challenge. Animal models continue to be refined in attempts to more accurately reproduce human sepsis and acute lung injury. Oncology research should serve as a model for optimizing the integration of pharmacodynamics and pharmacogenetics into trial design. The European Organization for Research and Treatment of Cancer provides a valuable template for nonfunded multicenter clinical trial success. The marked heterogeneity of the patient population and small signal (tested therapy)-to-noise (comorbidities) ratio makes identification of treatment effect difficult. Dedicated investigators still enroll ineligible patients who are included in intent to treat analysis. High enrolling centers create less problems in an adequate test of a new therapy. Much has been learned from negative trials as to value of post hoc subgroup and interim analyses. Debate continues on fair and appropriate end point of trials. Extrapolation of adult positive trial results to children is problematic. Conflict of interest issues which rested dormantly for years are now at the forefront of discussion, and journal editorial board responsibility in this area is being recognized. Protocols may also help reduce heterogeneity of treatment across centers in clinical trials. This article reviews many of the problems encountered in clinical trial design and reporting and offers a perspective on dealing with them to the betterment of a clinical trial.

Mortality rates for patients with acute lung injury/ARDS have decreased over time

BACKGROUND

Over the last decade, several studies have suggested that survival rates for patients with acute lung injury (ALI) or ARDS may have improved. We performed a systematic analysis of the ALI/ARDS literature to document possible trends in mortality between 1994 and 2006.

METHODS

We used the Medline database to select studies with the key words "acute lung injury," "ARDS," "acute respiratory failure," and "mechanical ventilation." All studies that reported mortality rates for patients with ALI/ARDS defined according to the criteria of the American European Consensus Conference were selected. We excluded studies with < 30 patients and studies limited to specific subgroups of ARDS patients such as sepsis, trauma, burns, or transfusion-related ARDS.

RESULTS

Seventy-two studies were included in the analysis. There was a wide variation in mortality rates among the studies (15 to 72%). The overall pooled mortality rate for all studies was 43% (95% confidence interval, 40 to 46%). Metaregression analysis suggested a significant decrease in overall mortality rates of approximately 1.1%/yr over the period analyzed (1994 to 2006). The mortality reduction was also observed for hospital but not for ICU or 28-day mortality rates.

CONCLUSIONS

In this literature review, the data are consistent with a reduction in mortality rates in general populations of patients with ALI/ARDS over the last 10 years.