The American-European Consensus Conference on ARDS, part 2: Ventilatory, pharmacologic, supportive therapy, study design strategies, and issues related to recovery and remodeling. Acute respiratory distress syndrome

The beta-agonist lung injury trial (BALTI): a randomized placebo-controlled clinical trial

RATIONALE

Experimental data suggest that manipulation of alveolar fluid clearance with beta-agonists can accelerate the resolution of alveolar edema and improve survival.

OBJECTIVE

To determine if a sustained infusion of intravenous salbutamol (albuterol) would accelerate the resolution of alveolar edema in adult patients with acute lung injury (ALI) or acute respiratory distress syndrome (ARDS).

METHODS

This was a single-center, double-blind, randomized controlled trial. Patients with ALI/ARDS were randomized to treatment with intravenous salbutamol (15 microg kg(-1) h(-1)) or placebo for 7 d. The primary endpoint was extravascular lung water measured by thermodilution (PiCCO) at Day 7.

MEASUREMENTS AND MAIN RESULTS

Sixty-six patients were screened; of these, 40 met the inclusion criteria and were enrolled during 2001-2003. Patients in the salbutamol group had significantly lower lung water at Day 7 than the placebo group (9.2 +/- 6 vs. 13.2 +/- 3 ml kg(-1); 95% confidence interval difference, 0.2-8.3 ml kg(-1); p = 0.038). Plateau airway pressure was lower at Day 7 in the salbutamol group (23.9 +/- 3.8 cm H2O) versus placebo (29.5 +/- 7.2 cm H2O; p = 0.049). There was a trend toward lower Murray lung injury score at Day 7 in the salbutamol group (1.7 +/- 0.9) versus placebo (2.0 +/- 0.6; p = 0.2). Patients in the salbutamol group had a higher incidence of supraventricular arrhythmias (26 vs. 10%; p = 0.2).

CONCLUSION

Although further research is required to confirm the efficacy and safety of intravenous salbutamol in ALI/ARDS, this trial provides the first proof of principle that, in humans with ALI/ARDS, sustained treatment with intravenous beta-agonists reduces extravascular lung water.

Acute respiratory distress syndrome in children with severe motor and intellectual disabilities

We report 13 severely disabled children with acute respiratory distress syndrome, who were treated at the Department of Pediatrics, Niigata City General Hospital between 1995 and 2002. The children ranged in age from 1 year to 16 years. All were non-ambulant. Chronic aspiration and gastro-esophageal reflux were recognized in 12 patients. Patients had the rapid onset of dyspnea refractory to oxygen therapy. Diffuse bilateral lung infiltrates were present on chest X-ray. Predisposing events included sepsis (3 patients), pneumomia (7 patients), pancreatitis (1 patient) and two children with other infections. All required mechanical ventilation for periods of 3-26 days and received oxygen for 5-64 days. Steroid therapy and surfactant therapy were given to eight and three patients, respectively. Only one patient developed an air leak complication. Despite intensive care, three children died, one underwent tracheostomy and nine recovered completely. Acute respiratory distress syndrome is a commonly recognized cause of acute respiratory failure following a variety of insults. It is characterized by the acute onset of dyspnea refractory to oxygen therapy, and diffuse lung infiltrates. Children with severe motor and intellectual disabilities had various complications. In this study, chronic aspiration and gastro-esophageal reflux are considered to be one of predisposing factors triggering acute respiratory distress syndrome in children with severe motor and intellectual disabilities. Although acute respiratory distress syndrome was considered to be a not infrequent occurrence, its mortality rate might be low despite the severity of the disease in children with severe motor and intellectual disabilities. Acute respiratory distress syndrome can be a complication seen in severely disabled children.

Time course of lung parenchyma remodeling in pulmonary and extrapulmonary acute lung injury

The aim of this study is to test the hypothesis that the early changes in lung mechanics and the amount of type III collagen fiber do not predict the evolution of lung parenchyma remodeling in pulmonary and extrapulmonary acute lung injury (ALI). For this purpose, we analyzed the time course of lung parenchyma remodeling in murine models of pulmonary and extrapulmonary ALI with similar degrees of mechanical compromise at the early phase of ALI. Lung histology (light and electron microscopy), the amount of elastic and collagen fibers in the alveolar septa, the expression of matrix metalloproteinase-9, and mechanical parameters (lung-resistive and viscoelastic pressures, and static elastance) were analyzed 24 h, 1, 3, and 8 wk after the induction of lung injury. In control (C) pulmonary (p) and extrapulmonary (exp) groups, saline was intratracheally (it; 0.05 ml) instilled and intraperitoneally (ip; 0.5 ml) injected, respectively. In ALIp and ALIexp groups, mice received Escherichia coli lipopolysaccharide (10 microg it and 125 microg ip, respectively). At 24 h, all mechanical and morphometrical parameters, as well as type III collagen fiber content, increased similarly in ALIp and ALIexp groups. In ALIexp, all mechanical and histological data returned to control values at 1 wk. However, in ALIp, static elastance returned to control values at 3 wk, whereas resistive and viscoelastic pressures, as well as type III collagen fibers and elastin, remained elevated until week 8. ALIp showed higher expression of matrix metalloproteinase-9 than ALIexp. In conclusion, insult in pulmonary epithelium yielded fibroelastogenesis, whereas mice with ALI induced by endothelial lesion developed only fibrosis that was repaired early in the course of lung injury. Furthermore, early functional and morphological changes did not predict lung parenchyma remodeling.

Mathematical program for outcome prediction and therapeutic support for trauma beginning within 1 hr of admission: a preliminary report

OBJECTIVES

The aims were a) to noninvasively monitor acute emergency trauma patients beginning within 1 hr after admission to the emergency department; b) to prospectively predict outcome; and c) to evaluate the relative effectiveness of various modes of therapy.

DESIGN

Prospective outcome prediction study using a mathematical search and display model based on noninvasive hemodynamic monitoring.

SETTING

A level I trauma service in a large university-run inner-city public hospital.

PATIENTS

We studied 185 consecutively noninvasively monitored emergency patients.

INTERVENTIONS

We noninvasively monitored cardiac index, mean arterial blood pressure, heart rate, pulse oximetry, and transcutaneous oxygen and carbon dioxide tensions beginning within 1-hr after emergency admission.

MEASUREMENTS AND MAIN RESULTS

The cardiac index, pulse oximetry, transcutaneous oxygen tension, transcutaneous carbon dioxide tension, and mean arterial blood pressure were higher in survivors than in nonsurvivors in the initial resuscitation period and at the hemodynamic nadir. Heart rate and transcutaneous carbon dioxide tension were higher in the nonsurvivors. The calculated survival probability in the first hour observation period of survivors averaged 85 +/- 14% vs. 69 +/- 16% for nonsurvivors (p = .0001). Misclassifications of the series as a whole were 11.3%; after excluding brain death from severe head injury, there were 6.4% misclassifications. A decision support system evaluated the effects of various therapies based on responses of patients with similar clinical-hemodynamic states.

CONCLUSION

Noninvasive hemodynamic monitoring and an information system provided a feasible approach to predict outcome early and to evaluate prospectively the efficacy of various therapies.

High-frequency ventilation versus conventional ventilation for the treatment of acute lung injury and acute respiratory distress syndrome: a systematic review and cochrane analysis

In this review, we examine outcomes from using high-frequency ventilation compared with conventional ventilation as therapy for acute lung injury and acute respiratory distress syndrome in children and adults. We conducted a systematic search of the literature based on the guidelines of the Cochrane Collaboration. Two trials met the inclusion criteria; one recruited children (n = 58), and the other recruited adults (n = 148). Both trials used a high-frequency oscillatory ventilator as the intervention and included variable use of lung-volume recruitment strategies. The intervention groups showed a trend toward less 30-day mortality (children: relative risk [RR], 0.83; 95% confidence interval [CI], 0.43-1.62; adults: RR, 0.72; 95% CI, 0.50-1.03), although neither study showed a statistically significant difference. Similarly, there was no statistically significant difference between the intervention and control groups for "total length of ventilator days." There was a statistically significant reduction in the risk of requiring supplemental oxygen among survivors at 30 days in the pediatric study (RR, 0.36; 95% CI, 0.14-0.93). Overall there is not enough evidence to conclude that high-frequency ventilation reduces mortality or long-term morbidity in patients with acute lung injury or acute respiratory distress syndrome. (This review is published as a Cochrane Review in The Cochrane Library 2004, Issue 3. Cochrane Reviews are regularly updated as new evidence emerges and in response to comments and criticisms, and The Cochrane Library should be consulted for the most recent version of the Review.).

Protective role of urinary trypsin inhibitor in acute lung injury induced by lipopolysaccharide

Urinary trypsin inhibitor (UTI), a serine protease inhibitor, has been widely used as a drug for patients with acute inflammatory disorders such as disseminated intravascular coagulation, shock, and pancreatitis. However, direct contribution of UTI to inflammatory diseases has not been established. The present study analyzed acute inflammatory lung injury induced by lipopolysaccharide (LPS) in UTI-deficient (-/-) mice and corresponding wild-type (WT) mice. UTI (-/-) and WT mice were treated intratracheally with vehicle or LPS (125 mug/kg). The cellular profile of bronchoalveolar lavage fluid, lung water content, histology, and expression of proinflammatory molecules in the lung were evaluated. After LPS challenge, both genotypes of mice revealed neutrophilic lung inflammation and pulmonary edema. UTI (-/-) mice, however, showed more prominent infiltration of inflammatory cells and edema than WT mice. After LPS challenge in both genotypes of mice, the lung levels of mRNA and/or protein expression of interleukin-1beta, macrophage inflammatory protein-1alpha, macrophage chemoattractant protein-1, keratinocyte chemoattractant, and intercellular adhesion molecule-1 (ICAM-1) were elevated in both groups, but to a greater extent in UTI (-/-) mice than in WT mice. These results suggest that UTI protects against acute lung injury induced by bacterial endotoxin, at least partly, through the inhibition of the enhanced local expression of proinflammatory cytokines, chemokines, and ICAM-1.

Mild hypothermia reduces expression of intercellular adhesion molecule-1 (ICAM-1) and the accumulation of neutrophils after acid-induced lung injury in the rat

BACKGROUND

The pathophysiology of the acute phase of acid-induced lung injury (AILI) has been elucidated. However, once acute respiratory distress syndrome (ARDS) develops, the mortality rate remains high and there is, as yet, no effective therapy. There are reports that application of mild hypothermia is an effective treatment for ARDS. In this study, we hypothesize that mild hypothermia inhibits activation of neutrophils and expression of intercellular adhesion molecule-1 (ICAM-1) in an injured lung. We studied the effects of mild hypothermia on the expression of ICAM-1 and the accumulation of neutrophils after AILI in the rat.

METHODS

Male Sprague-Dawley rats were randomly allocated to one of the four groups: control normothermic group, induced mild hypothermia group, acid-instilled normothermic group, and acid-instilled group with mild hypothermia. At 6 h after instillation of acid, lungs were removed to measure neutrophil activity and to detect the expression of ICAM-1 in each group.

RESULTS

Oxygenation in acid-instilled rats was significantly impaired as compared to that in non-instilled groups, but induction of mild hypothermia gradually improved oxygenation. Expression of ICAM-1 was enhanced in the acid-instilled normothermic group. By contrast, no overexpression of ICAM-1 and its mRNA was detected in the acid-instilled hypothermic group. In addition, accumulation of neutrophils was markedly inhibited after exposure to mild hypothermia irrespective of the instillation of acid.

CONCLUSION

Our data suggest mild hypothermia can inhibit the adhesion, activation, and accumulation of neutrophils during the acute phase of AILI in the rat and may have the potential to reduce ongoing inflammation of ALI or ARDS.

Regulation of vascular endothelial growth factor bioactivity in patients with acute lung injury

BACKGROUND

Reduced bioactive vascular endothelial growth factor (VEGF) has been demonstrated in several inflammatory lung conditions including the acute respiratory distress syndrome (ARDS). sVEGFR-1, a soluble form of VEGF-1 receptor, is a potent natural inhibitor of VEGF. We hypothesised that sVEGFR-1 plays an important role in the regulation of the bioactivity of VEGF within the lung in patients with ARDS.

METHODS

Forty one patients with ARDS, 12 at risk of developing ARDS, and 16 normal controls were studied. Bioactive VEGF, total VEGF, and sVEGFR-1 were measured by ELISA in plasma and bronchoalveolar lavage (BAL) fluid. Reverse transcriptase polymerase chain reaction for sVEGFR-1 was performed on BAL cells.

RESULTS

sVEGFR-1 was detectable in the BAL fluid of 48% (20/41) of patients with early ARDS (1.4-54.8 ng/ml epithelial lining fluid (ELF)) compared with 8% (1/12) at risk patients (p = 0.017) and none of the normal controls (p = 0.002). By day 4 sVEGFR-1 was detectable in only 2/18 ARDS patients (p = 0.008). Patients with detectable sVEGFR-1 had lower ELF median (IQR) levels of bioactive VEGF than those without detectable sVEGFR-1 (1415.2 (474.9-3192) pg/ml v 4761 (1349-7596.6) pg/ml, median difference 3346 pg/ml (95% CI 305.1 to 14711.9), p = 0.016), but there was no difference in total VEGF levels. BAL cells expressed mRNA for sVEGFR-1 and produced sVEGFR-1 protein which increased following incubation with tumour necrosis factor alpha.

CONCLUSION

This study shows for the first time the presence of sVEGFR-1 in the BAL fluid of patients with ARDS. This may explain the presence of reduced bioactive VEGF in patients early in the course of ARDS.

Successful Management of Adult Smoke Inhalation with Extracorporeal Membrane Oxygenation

Pulmonary complications remain one of the leading causes of mortality in patients with burns. We report two cases of adult patients with thermal and inhalation injuries who were placed on extracorporeal membrane oxygenation (ECMO) and survived. Patient 1 was a 42-year-old male who suffered 15% TBSA and a severe inhalation injury requiring intubation upon arrival to the emergency department. Patient 2 was a 24-year-old female in a house fire who received 20%TBSA and was noted to be in respiratory distress and intubated on the scene by the paramedic team. Three days after admission, patient 1 developed severe respiratory failure. He decompensated, despite maximum conventional management, and was placed on ECMO. After 300 hours of ECMO, his pulmonary function had improved, and he was decannulated. Patient 2 also developed severe refractory respiratory failure and was placed on ECMO. She was decannulated 288 hours later. Both patients were discharged home shortly afterwards and have managed well. ECMO should be considered when patients are facing a respiratory death from inhalation injury on conventional mechanical ventilation.

Adult respiratory distress syndrome

ARDS or acute respiratory distress syndrome continues to be a considerable critical care challenge. Mortality has not decreased significantly over the last more than 30 years. This article presents an overview of origin, evaluation, and treatment of ARDS. Recent findings relative to onset and precipitators of ARDS have led to changes in evaluation and treatment plans. Clinical and radiologic descriptors in assessment of the patient with ARDS are discussed. Ventilatory modes and nursing interventions to optimize patient outcomes are identified. The challenges of outcomes issues presented offer opportunities for further study.

[Altitude, the ratio of PaO2 to fraction of inspired oxygen, and shunt: impact on the assessment of acute lung injury]

The ratio of PaO2 to the fraction of inspired oxygen (PaO2/FIO2) is commonly used to determine the severity of acute lung injury and acute respiratory distress syndrome (ARDS). The research presented here used computational models of the lung to analyze the effect of altitude on the PaO2/FIO2 ratio and pulmonary shunt. At a given shunt, the PaO2/FIO2 ratio is lower at higher altitudes. Therefore, when evaluating for ARDS based on a PaO2/FIO2 ratio of <200 mm Hg, patients residing at high altitudes will have less shunt and, presumably, less severe lung injury than patients at sea level. This should be taken into consideration when comparing patients from different altitudes. Shunt should more often be measured directly or be estimated assuming a constant arteriovenous oxygen content difference.

Keratinocyte growth factor induces Akt kinase activity and inhibits Fas-mediated apoptosis in A549 lung epithelial cells

Acute respiratory distress syndrome (ARDS) is a syndrome characterized by the rapid influx of protein-rich edema fluid into the air spaces. The magnitude of alveolar epithelial cell injury is a key determinant of disease severity and an important predictor of patient outcome. The alveolar epithelium is positioned at the interface of the host response in the initiation, progression, and recovery phase of the disease. Keratinocyte growth factor (KGF) is a potent survival factor unique to the epithelium that promotes lung epithelial cell survival, accelerates wound closure, and reduces fibrosis. We therefore hypothesized that KGF preserves lung function by inhibiting apoptosis through activation of a signal transduction pathway responsible for cell survival. To test this hypothesis we determined that KGF inhibits death following Fas activation, a relevant apoptosis pathway, and then determined that cell survival is mediated through activation of the phosphatidylinositol 3'-kinase (PI3K)/Akt kinase signal transduction pathway. We found that KGF induces a dose- and time-dependent increase in Akt kinase activity and that, as expected, activation of Akt via KGF is PI3K dependent. KGF inhibited Fas-induced apoptosis as measured by a reduction in apoptotic cells and caspase-3 activity. This investigation supports our original hypothesis that KGF protects the lung epithelium by inhibiting apoptosis and that protection occurs through activation of PI3K/Akt-mediated cell survival pathway. Our results are in agreement with other reports that identify the PI3K/Akt axis as a key intracellular pathway in the lung epithelium that may serve as a therapeutic target to preserve epithelial integrity during inflammation.

Carboxypeptidase-mediated enhancement of nitric oxide production in rat lungs and microvascular endothelial cells

Membrane-bound regulatory carboxypeptidases cleave only COOH-terminal basic residues from peptides and proteins. To investigate whether carboxypeptidase-generated arginine can increase nitric oxide (NO) synthesis we perfused rat lungs from animals challenged with LPS or used rat lung microvascular endothelial cells (RLMVEC) stimulated with LPS and IFN-γ, conditions that induced inducible NO synthase (iNOS) expression. Addition of carboxypeptidase substrate furylacryloyl-Ala-Arg (Fa-A-R) or Arg to the lung perfusate increased NO production two- to threefold. The carboxypeptidase inhibitor 2-mercaptomethyl-3-guanidinoethylthiopropanoic acid (MGTA) blocked the effect of Fa-A-R but not free Arg. Lysine, an Arg transport inhibitor, blocked the increase in NO stimulated by Fa-A-R. HPLC analysis showed that Fa-A-R hydrolysis was blocked by MGTA but not lysine. In cytokine-treated RLMVEC, Fa-A-R also stimulated NO production inhibited by MGTA or lysine. Membrane fractions from rat lungs or RLMVEC contained carboxypeptidase M-like activity at neutral pH that increased twofold in RLMVEC treated with LPS + IFN-γ. The kinetics of NO production in RLMVEC was measured with a porphyrinic microsensor. Addition of 1 mM Arg or Fa-A-R to cells preincubated in Arg-free medium resulted in a slowly rising, prolonged (>20 min) NO output. NO production stimulated by Fa-A-R was blocked by MGTA or iNOS inhibitor 1400W. HPLC analysis of Fa-A-R hydrolysis revealed only 3.7 μM Arg was released over 20 min. Thus NO production in RLMVEC is stimulated more efficiently by Arg released from carboxypeptidase substrates than free Arg. These studies reveal a novel mechanism by which the Arg supply for NO production in inflammatory conditions may be maintained.

Hyperoxia-induced emphysematous changes in subacute phase of endotoxin-induced lung injury in rats

We examined the effects of prolonged hyperoxia (75% O2) on lung structure and collagen metabolism in the subacute phase of lung injury induced by continuous infusion of endotoxin (LPS) in a rat model. Experimental groups included control, endotoxin alone, endotoxin plus hyperoxia, and hyperoxia alone. Endotoxin-treated rats received a bolus of LPS (10 mg/kg iv) followed by 500 μg·kg−1·day−1in continuous infusion for 10 days. The bronchoalveolar lavage (BAL) fluid/plasma albumin concentration ratio, an index of capillary permeability, and neutrophil and macrophage counts in BAL fluid were highest in the endotoxin plus hyperoxia group. On pathological examination, prolonged hyperoxia exacerbated destruction of the alveolar wall and caused most prominent emphysematous changes in the endotoxin plus hyperoxia group. Lung tissue hydroxyproline concentration was significantly decreased in the hyperoxia group and increased in the endotoxin group. The latent forms of MMP-2 and MMP-9 increased in BAL fluid of the endotoxin- and/or hyperoxia-treated groups, whereas the activities of collagenase and gelatinase, and the active form of MMP-2 were all increased in the hyperoxia-treated groups. Added to endotoxin, prolonged hyperoxia degraded collagen, the major structural component of basement membranes, and caused emphysematous changes associated with activation of collagenase and MMP-2. Our observations suggest that, in the subacute phase of endotoxin-induced lung injury, prolonged hyperoxia causes pulmonary emphysematous changes with persistent injury to the alveolar capillary barrier. Collagenase and MMP-2 activated by hyperoxia, together with MMP-9, may play prominent roles in disruption of the alveolar basement membranes and degradation of collagen lining the alveolar walls.

Hyperoxia exposure impairs surfactant function and metabolism

OBJECTIVE

To evaluate the effects of hyperoxia exposure on lung function and the endogenous surfactant system in spontaneously breathing adult rats.

DESIGN

Analysis of the pulmonary surfactant system isolated from adult rats following exposure to > 90% oxygen or room air for 48 or 72 hrs.

SETTING

A basic science research laboratory in a university setting.

SUBJECTS

Sixty pathogen-free Sprague-Dawley rats.

INTERVENTIONS

Exposure to > 90% oxygen for 72 hrs.

MEASUREMENTS AND MAIN RESULTS

Exposure to > 90% oxygen for 72 hrs resulted in significant lung dysfunction and an increase in neutrophils and total protein concentrations within the airspace compared with animals exposed to room air or 48 hrs of 90% oxygen exposure. Total alveolar surfactant and large aggregate pool sizes were increased after 72 hrs of hyperoxia compared with the other groups, and there was evidence of lipid peroxidation within these large aggregate subtractions. The biophysical function of large aggregate isolated from 72-hr hyperoxia-exposed animals was also impaired and converted into small aggregate forms faster than large aggregate from normoxia-exposed animals when assessed using in vitro surface area cycling techniques.

CONCLUSIONS

Oxidative stress on the endogenous surfactant system may represent an important mechanism contributing to the surfactant dysfunction and abnormal surfactant metabolism associated with hyperoxia-induced lung injury.

A Closed-Loop Mechanical Ventilation Controller With Explicit Objective Functions

A closed-loop lung ventilation controller was designed, aiming to: 1) track a desired end-tidal CO2 pressure (Pet CO2), 2) find the positive end-expiratory pressure (PEEP) of minimum estimated respiratory system elastance (Ers,e), and 3) follow objective functions conjectured to reduce lung injury. After numerical simulations, tests were performed in six paralyzed piglets. Respiratory mechanics parameters were estimated by the recursive least squares (RLS) method. The controller incorporated a modified PI controller for Pet CO2 and a gradient descent method for PEEP. In each animal, three automated PEEP control runs were performed, as well as a manual PEEP titration of Ers,e and a multiple PetCO2 step change trial. Overall performance indexes were obtained from PEEP control, such as minimum Ers,e (37.0 +/- 4.5 cmH2O x L(-1)), time to reach the minimum Ers,e (235 +/- 182 s) and associated PEEP (6.5 +/- 1.0 cmH2O), and from Pet CO2 control, such as rise time (53 +/- 22 s), absolute overshoot/undershoot of PetCO2 (3 +/- 1 mmHg), and settling time (145 +/- 72 s). The resulting CO2 controller dynamics approximate physiological responses, and results from PEEP control were similar to those obtained by manual titration. Multiple dependencies linking the involved variables are discussed. The present controller can help to implement and evaluate objective functions that meet clinical goals.

Acute respiratory distress syndrome

Several combination therapies have been described throughout this article: in all likelihood, it is combination therapy that will allow improved survival of ARDS patients. As medicine moves into the future, clinical trials evaluating the efficacy of therapies for ARDS will be performed. In human critical care medicine, a large forward step was taken when ALI and ARDS were clearly defined. Unfortunately. as good as the definition is, ALI and ARDS occur secondary to many different underlying pathologic processes,perhaps obscuring the benefits of certain therapies for ARDS based on the underlying condition, for example, trauma versus sepsis. Selection of patients entering any ARDS trial is crucial: not only must those patients meet the strict definition of ARDS but the underlying disease process should be clearly identified. Identification of patients suffering from different disease processes before the onset of ARDS will allow for stratification of outcomes according to the intervention and the underlying pathology--comparing apples to apples and not to oranges. We are in a unique position in veterinary medicine. Although frequently financially limited by our clients, we have the opportunity to achieve several goals. First, we need to clearly define what constitutes ALI and ARDS in veterinary medicine. Do we want to rely on the human definitions? Probably not; however, as a group, we need to determine what we will accept as definitions. For example, we may not be able perform right heart catheterizations on all our patients to meet the wedge pressure requirement of human beings of less than 18 mm Hg. Do we agree that a PAOP of less than 18 mmHg is appropriate for animals, and is it appropriate for all animals? Will we accept another measure, for example, pulmonary artery diameter increases with echocardiographic evidence of acceptable left heart function? What is acceptable left heart function? As veterinarians, what do we consider to be hypoxemia? Is it the same in all species that we work with? What do we define as acute onset? Most human ARDS cases occur while patients are in hospital being treated for other problems, whereas many of our patients present already in respiratory distress. If we are unable to ventilate patients for economic or practical reasons, what do we use as the equivalent of the Pao2/Flo, ratio'? Reliance on the pathologist is not reasonable, because many disease processes can look similar to ARDS under the microscope. If anything, ALI and ARDS are clinical diagnoses. It is time for veterinarians to reach a consensus on the definition for ALI and ARDS in our patients. Only when we have a consensus of definition can rational prospective clinical trials of therapies be designed.

Effect of acute lung injury and acute respiratory distress syndrome on outcome in critically ill trauma patients

OBJECTIVE

Acute lung injury (ALI) and acute respiratory distress syndrome (ARDS) are known to be associated with increased mortality and costs in trauma patients. We estimated the independent impact of these conditions on mortality and cost, beyond the severity of injury with which they are correlated.

DESIGN

One-year prospective cohort.

PATIENTS AND SETTING

All trauma patients admitted to the intensive care unit in a level I center were evaluated daily for ALI/ARDS using the American-European Consensus Conference definition.

MEASUREMENTS AND MAIN RESULTS

The main outcome measures were hospital mortality and costs. Logistic regression was used to model hospital mortality in relation to the presence of ALI and ARDS, adjusting for trauma severity (Injury Severity Score), Acute Physiology Score, and age. Hospital costs were modeled using multivariable linear regression. Of the 1,296 trauma patients surviving beyond the first day, 4% experienced ALI (defined as Pao2/Fio2 of 201-300 mm Hg) and 12% had ARDS (Pao2/Fio2 < or = 200 mm Hg). The crude relative risk of mortality was 2.24 (95% confidence interval, 0.92-5.45) in patients with ALI and 3.84 (95% confidence interval, 2.41-6.13) in patients with ARDS compared with those without ALI/ARDS. However, there was no association of mortality with ALI (relative risk, 0.99; 95% confidence interval, 0.29-3.36) or with ARDS (relative risk, 1.23; 95% confidence interval, 0.63-2.43) after adjustment for age, Injury Severity Score, and Acute Physiology Score. Among patients of comparable age, severity score, and length of stay, median cost was 20% to 30% higher for those with ALI/ARDS.

CONCLUSIONS

There is no additional mortality associated with ALI/ARDS above and beyond the factors that can be measured at intensive care unit admission. Therefore, mortality in trauma patients is explained by injury severity at admission and is not affected by the subsequent occurrence of ALI/ARDS. Nonetheless, ALI/ARDS was associated with increased intensive care unit stay and hospital cost, independent of trauma severity.

Evaluation of a recruitment maneuver with positive inspiratory pressure and high PEEP in patients with severe ARDS

BACKGROUND

To evaluate the effect of a recruitment maneuver (RM) with constant positive inspiratory pressure and high positive end-expiratory pressure (PEEP) on oxygenation and static compliance (Cs) in patients with severe acute respiratory distress syndrome (ARDS).

METHODS

Eight patients with ARDS ventilated with lung-protective strategy and an arterial partial pressure of oxygen to inspired oxygen fraction ratio (PaO2/FIO2) < or =100 mmHg regardless of PEEP were prospectively studied. The RM was performed in pressure-controlled ventilation at FIO2 of 1.0 until PaO2 reached 250 mmHg or a maximal plateau pressure/PEEP of 60/45 cmH2O was achieved. The RM was performed with stepwise increases of 5 cmH2O of PEEP every 2 min and thereafter with stepwise decreases of 2 cmH2O of PEEP every 2 min until a drop in PaO2 >10% below the recruitment PEEP level. Data was collected before (preRM), during and after 30 min (posRM).

RESULTS

The PaO2/FIO2 increased from 83 +/- 22 mmHg preRM to 118 +/- 32 mmHg posRM (P = 0.001). The Cs increased from 28 +/- 10 ml cmH2O(-1) preRM to 35 +/- 12 ml cmH2O(-1) posRM (P = 0.025). The PEEP was 12 +/- 3 cmH2O preRM and was set at 15 +/- 4 cmH2O posRM (P = 0.025). The PEEP of recruitment was 36 +/- 9 cmH2O and the collapsing PEEP was 13 +/- 4 cmH2O. The PaO2 of recruitment was 225 +/- 105 mmHg, with five patients reaching a PaO2 > or = 250 mmHg. The FIO2 decreased from 0.76 +/- 0.16 preRM to 0.63 +/- 0.15 posRM (P = 0.001). No major complications were detected.

CONCLUSION

Recruitment maneuver was safe and useful to improve oxygenation and Cs in patients with severe ARDS ventilated with lung-protective strategy.

Mechanical ventilation in children with acute respiratory failure

PURPOSE OF REVIEW

Acute respiratory failure requiring mechanical ventilation continues to contribute to mortality and affect long-term functional outcomes in patients admitted to the pediatric intensive care unit (ICU). Studies in adults with acute respiratory distress syndrome (ARDS) far outnumber those conducted in the pediatric age group, and pediatric intensivists are left with the task of carefully selecting and critically appraising relevant adult data and extrapolating results to their domain of practice.

RECENT FINDINGS

The recent ARDSNet study reinforces the use of low tidal volumes. Administration of surfactant is safe, but once again its beneficial effect was not sustained in a randomized trial. Surfactant proteins A and D have been shown to be of prognostic value in cases of acute lung injury. The effect of inhaled nitric oxide (NO) in patients with ARDS can be enhanced by aggressive lung recruitment strategies such as can be achieved using high-frequency oscillatory ventilation (HFOV). A recent adult trial shows good response rates but no significant long-term outcome benefit from prone positioning in patients with ARDS. Routine scheduled assessments of readiness for weaning and extubation may be more important than specific weaning modes and weaning criteria for children. A recent meta-analysis suggests that prophylactic dexamethasone use may decrease postextubation stridor and possibly reduce the need for reintubation in selected patients. Outcome data in children requiring mechanical support is encouraging, especially for high-risk groups such as bone marrow transplant (BMT) recipients, and may guide ethically challenging decision-making for these patients.

SUMMARY

Mechanical ventilation strategies aiming for optimal alveolar recruitment with the judicious use of positive end-expiratory pressure (PEEP) and low tidal volumes will remain the mainstay for managing respiratory failure in children. Dexamethasone may prevent postextubation stridor. Prone positioning, surfactant therapy, HFOV, and inhaled NO are used sporadically and need to be evaluated for their effect on mortality and duration of ventilation.

Effect of neuromuscular blocking agents on gas exchange in patients presenting with acute respiratory distress syndrome*

OBJECTIVE

To evaluate the effects of a 48-hr neuromuscular blocking agents (NMBA) infusion on gas exchange over a 120-hr time period in patients with acute respiratory distress syndrome.

DESIGN

Multiple center, prospective, controlled, and randomized trial.

SETTING

Four adult medical or mixed medical-surgical intensive care units.

PATIENTS

A total of 56 patients with acute respiratory distress syndrome with a PaO2/FiO2 ratio of <150 at a positive end-expiratory pressure of > or =5 cm H2O.

INTERVENTIONS

After randomization, patients received either conventional therapy without NMBA (control group) or conventional therapy plus NMBA for the next 48 hrs. The initial ventilator mode was volume-assist/control. The ventilator remained on assist-control mode throughout the initial 48-hr period in both groups. Tidal volume was 6-8 mL/kg ideal body weight.

MEASUREMENTS AND MAIN RESULTS

When analyzed for the entire 120 hrs, there was a significant effect of the NMBA on the course of PaO2/FiO2 ratio (p =.021). Separate comparisons at each time point indicated that patients randomized to the NMBA group had a higher PaO2/FiO2 at 48, 96, and 120 hrs after randomization. Moreover, a decrease of positive end-expiratory pressure (p =.036) was only found in the NMBA group. Two-way repeated-measures analysis of variance exhibited a decrease in positive end-expiratory pressure over time (p =.036). Concerning short-term effects, there was no modification of PaO2/FiO2 ratio 1 hr after randomization in either group. Only one patient (from the control group) developed pneumothorax.

CONCLUSIONS

Use of NMBA during a 48-hr period in patients with acute respiratory distress syndrome is associated with a sustained improvement in oxygenation.

The Role of Open-Lung Biopsy in ARDS

STUDY OBJECTIVES

The role of open-lung biopsy in ARDS has been questioned due to potentially high morbidity and low diagnostic yield. The goals of this study were to better define the frequency of unexpected diagnoses made by open-lung biopsy, the frequency biopsy results lead to a change in clinical management, and the frequency of procedural complications.

DESIGN

Case series.

SETTING

A large tertiary referral center.

PATIENTS

All individuals with available records undergoing open-lung biopsy between 1989 and 2000 for evaluation of ARDS based on the American-European Consensus Conference definition.

INTERVENTIONS

None.

MEASUREMENTS AND RESULTS

The mean age in this cohort of 57 patients was 53 years (SD, 18 years) with PaO(2)/fraction of inspired oxygen ratio of 145 mm Hg (SD, 61 mm Hg) at the time of biopsy. A pathologic diagnosis other than diffuse alveolar damage or fibroproliferation was found in 60% of patients. The most common alternative diagnoses were infection (n = 8), alveolar hemorrhage (n = 5), and bronchiolitis obliterans organizing pneumonia (n = 5). Alternative diagnoses were as frequent in immunocompetent as immunosuppressed hosts (60% vs 59%, respectively). Biopsy results led to a change in management in the majority of patients, with addition of specific therapy in 60% and withdrawal of unneeded therapy in 37%. Although the overall complication rate was 39%, major complications occurred in only 7% of cases. No deaths were attributable to the procedure.

CONCLUSIONS

In selected patients with clinical ARDS, open-lung biopsy can be performed safely, often reveals an unsuspected diagnosis, and frequently leads to alterations in therapy.

Acute respiratory distress syndrome after chemotherapy for lung metastases from non-seminomatous germ-cell tumors

GOALS

To describe an acute respiratory distress syndrome (ARDS) occurring after chemotherapy for non-seminomatous germ-cell tumors (NSGCT) with diffuse lung metastases, we conducted a retrospective study in a 15-bed intensive care unit (ICU) in a comprehensive cancer center.

PATIENTS AND METHODS

During a 10-year period, 16 consecutive patients with diffuse lung metastases from a NSGCT were admitted to the ICU for respiratory distress and high-risk chemotherapy.

MAIN RESULTS

Nine patients developed acute respiratory failure requiring mechanical ventilation (MV) within 3 days of the initiation of chemotherapy, while the respiratory status of the seven other patients improved. The evolution was independent of tumor marker levels and the type of chemotherapy regimen. The SAPS II score did not accurately describe the severity of this population. The only predictor of intubation was the initial PaO2/FiO2 ratio upon admission to the ICU. Six out of seven patients who did not require MV were discharged alive from the hospital, whereas all but one patient requiring MV died. Refractory hypoxemia and ventilator-associated pneumonia were the leading causes of death.

CONCLUSIONS

Acute respiratory distress in patients with lung metastases from NSGCT is a rare cause of ARDS. Chemotherapy could be responsible for triggering the respiratory worsening. Patients with severe respiratory insufficiency (PaO2 <70 mmHg on room air) on admission to hospital should be promptly transferred to the ICU for the first chemotherapy course.

Inhaled iloprost in patients with chronic thromboembolic pulmonary hypertension: effects before and after pulmonary thromboendarterectomy

BACKGROUND

In primary pulmonary hypertension, aerosolized prostanoids selectively reduce pulmonary vascular resistance and improve right ventricular function. In this study, hemodynamic effects of inhaled iloprost, a stable prostacyclin analogue, were evaluated in patients with chronic thromboembolic pulmonary hypertension (CTEPH) before and early after pulmonary thromboendarterctomy (PTE).

METHODS

Ten patients (mean age 49 years old [32 to 70 years old], New York Heart Association functional class III and IV) received a dose of 33 micro g aerosolized iloprost immediately before surgery (T1), after intensive care unit admission (T2), and 12-hours postoperatively (T3). Effects on pulmonary and systemic hemodynamics and gas exchange were recorded and compared with preinhalation baseline values.

RESULTS

Preoperatively, inhaled iloprost did not significantly change mean pulmonary artery pressure (mPAP), cardiac index (CI), or pulmonary vascular resistance (PVR). Postoperatively, inhaled iloprost induced a significant reduction of mPAP and PVR and a significant increase of CI at T2 and T3. Preinhalation versus postinhalation PVR was as follows: at T1, 847 versus 729 dynes. s. cm(-5), p = 0.45; at T2, 502 versus 316 dynes. s. cm(-5), p = 0.008; and at T3, 299 versus 227 dynes. s. cm(-5), p = 0.004.

CONCLUSIONS

In patients with CTEPH, inhalation of iloprost elicits no significant pulmonary vasodilation before surgery, and may have detrimental effects on systemic hemodynamics. Postoperatively, it significantly reduces mPAP and PVR, and enhances CI. Following PTE, inhalation of iloprost is useful to improve early postoperative hemodynamics.

[Pharmacological profile of a specific neutrophil elastase inhibitor, Sivelestat sodium hydrate]

Imbalance between neutrophil elastase (NE) and its endogenous protease inhibitors has been considered to be one of possible mechanisms by which NE causes lung tissue destruction. It has been shown that the amount and/or activity of NE is increased in blood and bronchoalveolar lavage fluid in patients with acute lung injury. Accordingly, animals undergoing acute lung injury have increased NE activity such as in blood and bronchoalveolar lavage fluid. Sivelestat sodium hydrate (Sivelestat) is a synthetic inhibitor of NE with highly specificity to NE. Many studies have indicated that Sivelestat treatment improves inflammatory and edematous changes of lungs and survival as well as increased NE activity in several animal models of acute lung injury. Clinical studies have demonstrated that Sivelestat improves this injury that is associated with systemic inflammatory response syndrome. As compared with endogenous protease inhibitors that have high molecular mass, Sivelestat, a synthetic and low molecular weight elastase inhibitor, may be delivered to the inflammatory sites more easily and effectively and is considred to improve typical symptoms of acute lung injury. Clinical use of Sivelestat would further clarify the usefulness of this compound in clinical acute lung injury.

New aspects of ventilation in acute lung injury

Recent recognition that artificial ventilation may cause damage to the acutely injured lung has caused renewed interest in ventilation techniques that minimise this potential harm. Many ventilation techniques have proved beneficial in small trials of very specific patient groups, but most have subsequently failed to translate into improved patient outcome in larger trials. An exception to this is 'protective ventilation' using reduced tidal volumes (to lower airway pressure) and increased PEEP (to reduce pulmonary collapse). Results of trials of protective ventilation have been encouraging, and the technique should now be adopted more widely. High frequency ventilation, inverse ratio ventilation, prone positioning and inhaled nitric oxide are all techniques that may be considered when, in spite of optimal artificial ventilation, the patient's gas exchange remains dangerously poor. Under these circumstances, the choice of technique is dependent on their availability, local expertise and individual patient needs.

The role of exogenous surfactant in the treatment of acute lung injury

A number of conditions, such as pneumonia, trauma, or systemic sepsis arising from the gut, may result in the acute respiratory distress syndrome (ARDS). Because of its significant morbidity and mortality, ARDS has been the focus of extensive research. One specific area of interest has been the investigation of the role of the surfactant system in the pathophysiology of this disease. Several studies have demonstrated that alterations of surfactant contribute to the lung dysfunction associated with ARDS, which has led to investigations into the use of exogenous surfactant as a therapy for this syndrome. Clinical experience with surfactant therapy has been variable owing to a number of factors including the nature of the injury at the time of treatment, the specific surfactant preparation utilized, the dose and delivery method chosen, the timing of surfactant administration over the course of the disease, and the mode of ventilation used during and after surfactant administration.

Significant involvement of CCL2 (MCP-1) in inflammatory disorders of the lung

Mounting evidence suggests that CCL2 (MCP-1) and its hematopoietic cell receptor CC chemokine receptor 2 (CCR2) are involved in inflammatory disorders of the lung. In animal models of allergic asthma, idiopathic pulmonary fibrosis (IPF), and bronchiolitis obliterans syndrome (BOS), CCL2 expression and protein production are increased and the disease process is attenuated by CCL2 immunoneutralization. Mechanisms by which CCL2 may be acting include recruitment of regulatory and effector leukocytes; stimulation of histamine or leukotriene release from mast cells or basophils; induction of fibroblast production of transforming growth factor-beta (TGF-beta) and procollagen; and enhancement of Th2 polarization. Recently, polymorphism for CCL2 has been described with increased cytokine-induced release of CCL2 by monocytes and increased risk of allergic asthma. These studies identify potentially important roles for CCL2 in these lung inflammatory disorders. While CCL2 inhibition in patients with acute respiratory distress syndrome (ARDS) may be hazardous by interfering with defense against bacteremia, future studies are needed to determine if CCL2/CCR2 antagonism will offer breakthrough therapy for patients with allergic asthma, IPF, or BOS, and to confirm the hypothesis that CCL2 polymorphism places patients at greater risk for these disorders.

Early surfactant administration protects against lung dysfunction in a mouse model of ARDS

Sepsis can predispose the lung to insults such as mechanical ventilation (MV). It was hypothesized that treating the lung with exogenous surfactant early in the development of sepsis will reduce the lung dysfunction associated with MV 18 h later. Mice underwent sham or cecal ligation and perforation (CLP) surgery. Immediately after surgery, mice were either untreated or given 100 mg/kg of bovine lipid extract surfactant intratracheally. Eighteen hours later, the lungs were removed and analyzed either immediately or following ventilation ex vivo for 2 h by an "injurious" mode of ventilation (20 ml/kg, 0 cm positive end-expiratory pressure). In nonventilated lungs, exogenous surfactant had no impact on compliance or IL-6 concentrations in the lungs. In the ventilated groups, the administered surfactant had a significant protective effect on the lung dysfunction induced by MV, but only in the CLP lungs. We conclude that administration of exogenous surfactant at the time of a systemic insult can protect the lung from the damaging effects of MV 18 h later.

High-frequency oscillatory ventilation for acute respiratory distress syndrome in adult patients

INTRODUCTION

High-frequency oscillatory ventilation (HFOV) using an open-lung strategy has been demonstrated to improve oxygenation in neonatal and pediatric respiratory failure, without increasing barotrauma. Animal studies using small (<4 mm) endotracheal tubes have shown reduced histopathologic evidence of lung injury and inflammatory mediator release, suggesting reduced ventilator-induced lung injury.

CLINICAL STUDIES

During the last decade, case reports and observational studies of HFOV in patients failing conventional ventilation strategies have suggested improved oxygenation in adult patients with severe acute respiratory distress syndrome. These reports have also suggested that early (2 days) initiation of HFOV is more likely to result in survival than delayed initiation (>7 days). A recently published randomized, controlled trial in acute respiratory distress syndrome patients (n = 148) comparing HFOV with a pressure-control ventilation strategy (Pao(2)/Fio(2) ratio of <or=200 mm Hg on positive end-expiratory pressure of >10 cm H(2)O) demonstrated early (<16 hrs) improvement in Pao(2)/Fio(2) (p =.008) in the HFOV group but no significant difference in oxygenation index between the two groups during the initial 72 hrs of treatment. Thirty-day mortality was 37% in the HFOV group and 52% in the conventional ventilation group (p =.102). There was no significant difference between treatment groups in the prevalence of barotrauma, hemodynamic instability, or mucus plugging. This study suggests that HFOV is as effective and safe as the conventional strategy to which it was compared.

CLINICAL APPLICATION

For clinical use in adults, a trial of HFOV may be considered when Fio(2) requirements exceed 60% and mean airway pressure is approaching 20 cm H(2)O or higher (or, alternatively, positive end-expiratory pressure of >15 cm H(2)O). It is currently unknown whether initiating HFOV at a lower severity threshold would result in reduced ventilator-associated lung injury or mortality.

FUTURE DIRECTIONS

Future studies should compare different algorithms of applying HFOV to determine the optimal techniques for achieving oxygenation and ventilation, while minimizing ventilator-associated lung injury. The potential role of adjunctive therapies used with HFOV (e.g., prone ventilation, inhaled nitric oxide, aerosolized vasodilators, liquid ventilation) will require further research.

Long-term assessment of lung function in survivors of severe ARDS

STUDY OBJECTIVES

To investigate the long-term outcome of lung function in survivors of severe ARDS after modern treatment strategies including lung protective mechanical ventilation and prone positioning maneuvers.

DESIGN

Follow-up cohort study.

SETTING

University hospital pulmonary division and level 1 trauma center.

PATIENTS

Sixteen survivors of severe ARDS (from 1992 to 1994) with a lung injury score > or = 2.5.

MEASUREMENTS

The follow-up study (from 1995 to 1996) included interview, physical examination, chest radiographs, static and dynamic lung volumes, diffusion capacity of the lung for carbon monoxide (DLCO), blood gas analysis, and cardiopulmonary exercise testing (CPET).

RESULTS

The mean +/- SD interval between hospital discharge and functional assessment was 29.5 +/- 8.7 months (range, 15.0 to 40.7 months). In approximately one half of the patients, mild abnormalities in static and dynamic lung volumes were found. In 25% (4 of 16 patients), lung function was obstructive; in 25% (4 of 16 patients), lung function was restrictive; and in 6.3% (1 of 16 patients), a combined obstructive-restrictive pattern was revealed. DLCO was impaired in 12.5% (2 of 16 patients); gas exchange during exercise was impaired in 45.5% (5 of 11 patients).

CONCLUSIONS

Residual obstructive and restrictive defects as well as impaired pulmonary gas exchange remain common after severe ARDS. CPET is a very sensitive measure to evaluate residual impairment of lung function after ARDS. Using CPET, reduced pulmonary gas exchange can be detected in many patients with normal DLCO.

Early multiple organ failure after recurrent endotoxemia in the presence of vasoconstrictor-masked hypovolemia

OBJECTIVE

Critically ill patients who develop multiple organ failure during systemic inflammatory states are often predisposed to hypovolemia and vasoconstrictor therapy. Although numerous investigations have evaluated the sequelae of systemic inflammation, no data are available on the contribution of chronic vasoconstrictor-masked hypovolemia to organ dysfunction and morphology.

DESIGN

Prospective, randomized laboratory investigation.

SETTING

University research laboratory.

SUBJECTS

Eighteen adult chronically instrumented sheep.

INTERVENTIONS

The animals were randomly assigned to one of three groups. In the norfenefrine-masked hypovolemia plus endotoxemia (NMH+ENDO) group, mean arterial pressures of 80 mm Hg were maintained by using the alpha1-adrenergic catecholamine norfenefrine for 52 hrs during hypovolemia. Hypovolemia was induced by hemorrhage (about 23 mL x kg(-1)) until mean arterial pressures reached 40 mm Hg. Endotoxin (0.5 microg x k(-1)) was then injected after 4, 16, 28, and 40 hrs. The NMH group received norfenefrine-masked hypovolemia but no endotoxin. In the ENDO group, recurrent endotoxemia was induced during normovolemia.

MEASUREMENTS AND MAIN RESULTS

Despite profound differences in fluid management, cardiovascular filling pressures were not statistically different between groups. Endotoxemia induced norfenefrine-refractory shock (p < .05 vs. the other groups) and contributed to renal dysfunction only during vasoconstrictor-masked hypovolemia. Norfenefrine-masked hypovolemia caused disseminated cardiac cell necrosis independent of endotoxemia (p < .05 vs. ENDO).

CONCLUSIONS

Hypovolemia can be masked when volume status is monitored by filling pressures. In this new model of endotoxemia-associated multiple organ failure, chronic vasoconstrictor-masked hypovolemia turned systemic inflammation into a life-threatening condition with renal and cardiovascular failure. Cardiomyocyte necroses were caused by vasoconstrictor-masked hypovolemia but were unrelated to cardiovascular failure.

High oxygen concentrations predispose mouse lungs to the deleterious effects of high stretch ventilation

Mechanical ventilation is a necessary intervention for patients with acute lung injury. However, mechanical ventilation can propagate acute lung injury and increase systemic inflammation. The exposure to >21% oxygen is often associated with mechanical ventilation yet has not been examined within the context of lung stretch. We hypothesized that mice exposed to >90% oxygen will be more susceptible to the deleterious effects of high stretch mechanical ventilation. C57B1/6 mice were randomized into 48-h exposure of 21 or >90% oxygen; mice were then killed, and isolated lungs were randomized into a nonstretch or an ex vivo, high-stretch mechanical ventilation group. Lungs were assessed for compliance and lavaged for surfactant analysis, and cytokine measurements or lungs were homogenized for surfactant-associated protein analysis. Mice exposed to >90% oxygen + stretch had significantly lower compliance, altered pulmonary surfactant, and increased inflammatory cytokines compared with all other groups. Our conclusion is that 48 h of >90% oxygen and high-stretch mechanical ventilation deleteriously affect lung function to a greater degree than stretch alone.

Imbalance in the expression of CXC chemokines correlates with bronchoalveolar lavage fluid angiogenic activity and procollagen levels in acute respiratory distress syndrome

Diffuse alveolar damage is the histopathological hallmark of acute respiratory distress syndrome (ARDS) and is a stereotypic response to a variety of etiologies. Moreover, a significant proportion of ARDS survivors have residual pulmonary fibrosis and compromised pulmonary function. This suggests that the pathogenesis of diffuse alveolar damage that ultimately leads to the chronic fibrosis of ARDS has features of dysregulated repair exemplified by exaggerated intra-alveolar angiogenesis and fibrogenesis (i.e., fibroproliferation and deposition of extracellular matrix), leading to progressive alveolar fibrosis and impaired lung function. We obtained bronchoalveolar lavage fluid (BALF) from patients with ARDS or ventilated control patients and assessed CXC chemokine levels by ELISA. We found an imbalance in the expression of ELR(+) as compared with ELR(-) CXC chemokines from BALF of patients with ARDS as compared with controls. This imbalance correlated with angiogenic activity as assessed by the corneal micropocket assay. Furthermore, these levels correlated with both procollagen I and procollagen III levels in BALF. In contrast, while BALF levels of vascular endothelial growth factor were elevated, vascular endothelial growth factor did not appear to be significantly contributing to the angiogenic activity. These findings suggest that CXC chemokines have an important role in the fibroproliferative phase of ARDS via the regulation of angiogenesis.

Permissive hypercapnia

Although lifesaving, mechanical ventilation can result in lung injury and contribute to the development of bronchopulmonary dysplasia. The most critical determinants of lung injury are tidal volume and end-inspiratory lung volume. Permissive hypercapnia offers to maintain gas exchange with lower tidal volumes and thus decrease lung injury. Further physiologic benefits include improved oxygen delivery and neuroprotection, the latter through both avoidance of accidental hypocapnia, which is associated with a poor neurologic outcome, and direct cellular effects. Clinical trials in adults with acute respiratory failure indicated improved survival and reduced incidence of organ failure in subjects managed with low tidal volumes and permissive hypercapnia. Retrospective studies in low birth weight infants found an association of bronchopulmonary dysplasia with low PaCO(2). Randomized clinical trials of low birth weight infants did not achieve sufficient statistical power to demonstrate a reduction of BPD by permissive hypercapnia, but strong trends indicated the possibility of important benefits without increased adverse events. Herein, we review the mechanisms leading to lung injury, the physiologic effects of hypercapnia, the dangers of hypocapnia, and the available clinical data.

Effects of short-term pressure-controlled ventilation on gas exchange, airway pressures, and gas distribution in patients with acute lung injury/ARDS: comparison with volume-controlled ventilation

STUDY OBJECTIVES

The potential clinical benefits of pressure-controlled ventilation (PCV) over volume-controlled ventilation (VCV) in patients with acute lung injury (ALI) or ARDS still remain debated. We compared PCV with VCV in patients with ALI/ARDS with respect to the following physiologic end points: (1) gas exchange and airway pressures, and (2) CT scan intrapulmonary gas distribution at end-expiration.

DESIGN

Prospective, observational study.

SETTING

A multidisciplinary ICU in a nonuniversity, acute-care hospital.

PATIENTS

Ten patients with ALI or ARDS (9 men and 1 woman; age range, 17 to 80 years).

INTERVENTIONS

Sequential ventilation in PCV and VCV with a constant inspiratory/expiratory ratio, tidal volume, respiratory rate, and total positive end-expiratory pressure; measurement of gas exchange and airway pressures; and achievement of CT sections at lung base, hilum, and apex for the quantitative analysis of lung densities and of aerated vs nonaerated zones.

RESULTS

PaO(2), PaCO(2), and PaO(2)/fraction of inspired oxygen ratio levels did not differ between PCV and VCV. Peak airway pressure (Ppeak) was significantly lower in PCV compared with VCV (26 +/- 2 cm H(2)O vs 31 +/- 2 cm H(2)O; p < 0.001; mean +/- SEM). The surface areas of the nonaerated zones as well as the total areas at each section level were unchanged in PCV compared with VCV, except at the apex level, where there was a significantly greater nonaerated area in VCV (11 +/- 2 cm(2) vs 9 +/- 2 cm(2); p < 0.05). The total mean CT number of each lung (20 lungs from 10 patients) was similar in the two modes, as were the density values at the basal and apical levels; the hilum mean CT number was - 442 +/- 28 Hounsfield units (HU) in VCV and - 430 +/- 26 HU in PCV (p < 0.005).

CONCLUSIONS

These data show that PCV allows the generation of lower Ppeaks through the precise titration of the lung distending pressure, and might be applied to avoid regional overdistension by means of a more homogeneous gas distribution.

High-frequency oscillatory ventilation for acute respiratory distress syndrome in adults: a randomized, controlled trial

Observational studies of high-frequency oscillatory ventilation in adults with the acute respiratory distress syndrome have demonstrated improvements in oxygenation. We designed a multicenter, randomized, controlled trial comparing the safety and effectiveness of high-frequency oscillatory ventilation with conventional ventilation in adults with acute respiratory distress syndrome; 148 adults with acute respiratory distress syndrome (Pa(O2)/fraction of inspired oxygen <or= 200 mm Hg on 10 or more cm H2O positive end-expiratory pressure) were randomized to high-frequency oscillatory ventilation (n = 75) or conventional ventilation (n = 73). Applied mean airway pressure was significantly higher in the high-frequency oscillation group compared with the conventional ventilation group throughout the first 72 hours (p = 0.0001). The high-frequency oscillation group showed early (less than 16 hours) improvement in Pa(O2)/fraction of inspired oxygen compared with the conventional ventilation group (p = 0.008); however, this difference did not persist beyond 24 hours. Oxygenation index decreased similarly over the first 72 hours in both groups. Thirty-day mortality was 37% in the high-frequency oscillation group and was 52% in the conventional ventilation group (p = 0.102). The percentage of patients alive without mechanical ventilation at Day 30 was 36% and 31% in the high-frequency oscillation and conventional ventilation groups, respectively (p = 0.686). There were no significant differences in hemodynamic variables, oxygenation failure, ventilation failure, barotraumas, or mucus plugging between treatment groups. We conclude that high-frequency oscillation is a safe and effective mode of ventilation for the treatment of acute respiratory distress syndrome in adults.

Principles of mechanical ventilation

Mechanical ventilation is an enormous undertaking for a veterinary hospital in general and for any patient in particular. It is a team effort requiring large amounts of space, supplies, labor, and time. It requires committed owners and clinicians who communicate clearly with each other. It also requires a significant financial commitment initially from the hospital to obtain the equipment and expertise and then from the owner to maintain the patient. All members of the patient care team should have a basic understanding of respiratory physiology and ventilator mechanics. Clear goals for therapy and end points should be established. If they cannot be met, the goals should be reassessed in light of changes in patient condition. Weaning may be difficult and long, but once successful, it is most rewarding for the patient, family, clinician, and team.

Meta-analysis of hemodynamic optimization in high-risk patients

OBJECTIVE

The aim of this evidence-based report was to review pertinent randomized controlled studies that describe hemodynamic goals in acute, critically ill patients and to evaluate outcome of resuscitation therapy in association with physiologic, clinical, and therapeutic influences.

METHODS

MEDLINE was the source of randomized controlled studies written in English. The inclusion criteria were acutely ill, high-risk elective surgery, trauma, and septic patients. The goals of therapy were to resuscitate to either normal or supranormal values; the latter were described as a cardiac index of >4.5 L x min(-1) x m(-2), pulmonary artery occlusion pressure of <18 mm Hg, oxygen delivery of >600 mL x min(-1) x m(-2), and oxygen consumption of >170 mL x min(-1) x m(-2). The outcome criterion was survival or death. We found 21 randomized clinical trials described in 20 articles. The studies were divided into groups based on the time that goals were implemented (i.e., "early," 8 to 12 hrs postoperatively or before organ failure, vs. "late," or after onset of organ failure) and the severity of illness, determined by the control group mortality as >20% (12 studies) or <15% (nine studies).

RESULTS

In severely ill patients (control mortalities group >20%), six studies had a 23% mortality difference (p <.05) between the control and protocol groups with early optimization, but seven studies optimized after the development of organ failure did not have significantly improved mortality. Moreover, outcome was not significantly improved in less severely ill patients (control mortalities group <15%) and normal values as goals or when therapy did not improve oxygen delivery.

CONCLUSION

Review of 21 randomized controlled trials with various approaches to treatment revealed statistically significant mortality reductions, with hemodynamic optimization, when patients with acute critical illness were treated early to achieve optimal goals before the development of organ failure, when there were control group mortalities of >20% and when therapy produced differences in oxygen delivery between the control and protocol groups.

Inosine exerts a broad range of antiinflammatory effects in a murine model of acute lung injury

OBJECTIVE

To investigate the effects of inosine on the acute lung inflammation induced by lipopolysaccharide (LPS) in vivo and on the activation and cytotoxicity elicited by proinflammatory cytokines on human lung epithelial (A549) cells in vitro.

SUMMARY BACKGROUND DATA

Inosine is an endogenous purine recently shown to exert immunomodulatory and antiinflammatory effects.

METHODS

Mice challenged with intratracheal LPS (50 microg) were treated after 1, 6, and 12 hours with inosine (200 mg/kg intraperitoneal) or vehicle. After 24 hours, bronchoalveolar lavage fluid was obtained to measure proinflammatory (tumor necrosis factor-alpha [TNF-alpha], interleukin [IL]-1beta, IL-6), and antiinflammatory (IL-10, IL-4) cytokines, chemokines (MIP-1alpha and MIP-2), myeloperoxidase activity and total cell counts, nitric oxide production, and proteins. Lung histology and immunohistochemical detection of 3-nitrotyrosine, a marker of nitrosative stress, were performed in inflated-fixed lungs. In vitro, cell viability and production of the chemokine IL-8 were evaluated in A549 cells stimulated with a mixture of cytokines in the presence or absence of inosine.

RESULTS

Inosine downregulated the LPS-induced expression of TNF-alpha, IL-1beta, IL-6 and MIP-2 and tended to reduce MIP-1alpha, whereas it enhanced the production of IL-4. Total leukocyte counts, myeloperoxidase, nitric oxide production, and proteins were all significantly decreased by inosine. The purine also improved lung morphology and suppressed 3-nitrotyrosine staining in the lungs after LPS. Inosine attenuated the cytotoxicity and the expression of IL-8 induced by proinflammatory cytokines in A549 cells.

CONCLUSIONS

Inosine largely suppressed LPS-induced lung inflammation in vivo and reduced the toxicity of cytokines in lung cells in vitro. These data support the proposal that inosine might represent a useful adjunct in the therapy of acute respiratory distress syndrome.