Injurious ventilatory strategies increase cytokines and c-fos m-RNA expression in an isolated rat lung model

Ventilation with negative airway pressure induces a cytokine response in isolated mouse lung

We tested the hypothesis that, under relatively low tidal volume (VT) mechanical ventilation, continuing lung decruitment induced by negative end-expiratory pressure (NEEP) would increase the lung cytokine response, potentially contributing to lung injury. Mouse lungs were excised and randomly assigned to one of 3 different ventilatory strategies: 1) the zero end-expiratory pressure group served as a control, 2) the NEEP7 group received a NEEP of -7.5 cm H(2)O, and 3) the NEEP15 group received a NEEP of -15 cm H(2)O. In all 3 groups, a VT of 7 mL/kg was used. After 2 h of ventilation, lung lavage fluid was collected for measurements of tumor necrosis factor-alpha, monocyte chemoattractant protein-1, and lactate dehydrogenase. Increases in plateau pressure before and after mechanical ventilation were significantly greater in the NEEP15 group compared with the zero end-expiratory pressure group or NEEP7 group. Lung compliance was decreased in the NEEP15 compared with the other two groups. Concentrations of tumor necrosis factor-alpha, monocyte chemoattractant protein-1, and lactate dehydrogenase in lung lavage were larger in the NEEP15 group than in the other groups. Atelectatic lung during repeated collapse and reopening of lung units accentuates the lung cytokine response that may contribute to lung injury even during relatively low VT mechanical ventilation.

IMPLICATIONS

Repeated closing and reopening of lung units induced by negative end-expiratory pressure resulted in lung inflammation and cell injury even under mechanical ventilation using a normal tidal volume. This finding may have clinical relevance in certain patients who are prone to atelectasis during mechanical ventilation.

Acute respiratory distress syndrome epidemiology and pathophysiology

Acute respiratory distress syndrome is a devastating syndrome of lung injury following known risk factors, with a persistently high mortality. A consensus conference definition of ARDS has been adopted by clinical researchers, but potential problems remain. ARDS may represent more than one entity, and radiographic and mechanical differences between pulmonary versus extrapulmonary initiated ARDS have been described. There is increasing recognition of inflammatory mediators in the pathophysiology of acute lung injury. Surfactant abnormalities contribute to the associated lung dysfunction. A growing body of evidence supports the presence of VILI and a potential mechanism for developing MOSF, and has led to new management strategies. The importances of apoptosis to the repair process, and mechanisms that may lead to persistent fibrosis, such as the activation of the coagulant pathway with fibrin deposition, are increasingly recognized.

ARDSNet lower tidal volume ventilatory strategy may generate intrinsic positive end-expiratory pressure in patients with acute respiratory distress syndrome

The ARDSNet trial revealed that the use of a smaller tidal volume (VT) reduced mortality by 22%. However, three earlier studies that lowered VT did not find a decrease in mortality. We tested the hypothesis that the increased respiratory rate used in the ARDSNet lower VT strategy might have led to intrinsic positive end-expiratory pressure (PEEP(i)), raising total PEEP (PEEP(total)). Ten patients with acute respiratory distress syndrome (ARDS) were ventilated using the ARDSNet lower VT protocol. Respiratory rate was then reduced (10-15 breaths/minute) to obtain a VT of 12 ml/kg (ARDSNet traditional VT). PEEP on the ventilator (PEEP(nominal): 10.1 +/- 0.7 cm H2O), FIO2 (0.7 +/- 0.1), and minute ventilation (VE: 12.4 +/- 1.7 L/minute) were set using the ARDSNet protocol and maintained constant during the two ventilatory strategies. Values of airway pressure at end-expiration of a regular breath (PEEP(external)) and 3-5 seconds after the onset of an end-expiratory occlusion (PEEP(total)) were measured. PEEP(i) was calculated by subtracting PEEP(external) from PEEP(total). PEEP(total) and PEEP(i) were, respectively, 16.3 +/- 2.9 and 5.8 +/- 3.0 cm H2O during the lower VT strategy and 11.7 +/- 0.9 and 1.4 +/- 1.0 cm H2O during the traditional VT strategy (p < 0.01). The reduced mortality observed with the ARDSNet strategy may have been due to the protective effect of a higher PEEP(total).

Ventilation-induced lung injury and mechanotransduction: stretching it too far?

The Acute Respiratory Distress Syndrome Network clinical trial on ventilation of critically ill patients has drawn attention to the potential side effects of mechanical ventilation. Both clinical and basic research have demonstrated that injurious ventilation strategies can initiate or perpetuate local and systemic inflammatory responses. There are four principal mechanisms that can produce such a response. 1) Ventilation, especially with high ventilation pressures and zero positive end-expiratory pressure, can cause stress failure of the plasma membrane and of epithelial and endothelial barriers. Stress failure of the plasma membrane causes necrosis, which leads to liberation of both preformed inflammatory mediators and agents that stimulate other cells that are still intact to produce such mediators. 2) Stress failure of the barriers causes loss of compartmentalization with spread of mediators and bacteria throughout the body as a consequence. 3) Less injurious ventilation strategies that do not cause tissue destruction can elicit release of mediators by more specific mechanisms, presumably through activation of stretch-activated signaling cascades (mechanotransduction). 4) Ventilation with increasing positive pressures raises the pressure in the pulmonary circulation and thus vascular shear stress, both of which are known stimuli for endothelial cells. These different mechanisms should be taken into account in the design and the interpretation of studies on molecular mechanisms of ventilation-induced lung injury.

Management of the acute respiratory distress syndrome

Significant advances have occurred in the knowledge of the pathogenesis of ARDS. It is now recognized that ARDS is a manifestation of a diffuse process that results from a complicated cascade of events following an initial insult or injury. Mechanical ventilation and PEEP are still important components of supportive therapy. To avoid ventilator-associated lung injury there is emphasis on targeting ventilator management based on measurement of pulmonary mechanics. For those with resistant hypoxia and severe pulmonary hypertension adjunctive modalities, such as prone positioning and low-dose iNO, may provide important benefit. Alternative modes of supporting gas exchange, such as with partial liquid ventilation and extracorporeal gas-exchange, may serve as rescue therapies. Advances in cell and molecular biology have contributed to a better understanding of the role of inflammatory cells and mediators that contribute to the acute lung injury and the pathophysiology of the syndrome that manifests as ARDS. Based on this new understanding, the potential targets for intervention to ameliorate the systemic inflammatory response have proliferated. Examples include the cytokine network and its receptors, antioxidants, and endothelins. Apart from the challenge of testing these agents in experimental models, it seems likely that determination of the optimum combination of agents will become an equally important endeavor. A particular challenge is to develop better methods of predicting which of the many at-risk patients will go on to full-blown ARDS and MODS, thereby targeting subgroups of patients most likely to benefit from anti-inflammatory therapies. Similarly, the adverse effects of immunosuppressive therapy may be diminished by improved, perhaps molecular, techniques to detect microbial pathogens and permit differentiation between Systemic inflammatory response syndrome and sepsis.

Prospective, randomized, controlled pilot study of partial liquid ventilation in adult acute respiratory distress syndrome

We evaluated the safety and efficacy of partial liquid ventilation (PLV) with perflubron in adult patients with acute lung injury and the acute respiratory distress syndrome (ARDS) in a multicenter, prospective, controlled, randomized exploratory clinical trial. Ninety adult patients with PaO2/FIO2 ratios > 60 and < 300 with ARDS for no more than 24 hours were randomized to receive PLV (n = 65) with administration of perflubron through an endotracheal tube sideport or conventional mechanical ventilation (CMV, n = 25) for a maximum of five days. Although a significant reduction in progression to ARDS was noted among patients with PLV, no significant differences in the number of days free from the ventilator at 28 days (CMV = 6.7 +/- 1.8, PLV = 6.3 +/- 1.0 days, p = 0.85), the incidence of mortality (CMV = 36%, PLV = 42%, p = 0.63), or any pulmonary-related parameter were observed. During a post hoc subgroup analysis, significantly more rapid discontinuation of mechanical ventilation (p = 0.045) and a trend toward an increase in the number of days free from the ventilator at 28 days (CMV = 3.2 +/- 1.9, PLV = 8.0 +/- 2.2 days, p = 0.06) were observed during PLV among those patients under 55 years of age with acute lung injury or ARDS. Episodes of hypoxia, respiratory acidosis, and bradycardia occurred more frequently in the PLV group, but these were transient and self-limited. Further evaluation of PLV is warranted to further define beneficial effects in well-defined groups of patients and also to gain additional information regarding safety.

Mechanical ventilation of isolated rat lungs changes the structure and biophysical properties of surfactant

Mechanical ventilation is an essential but potentially harmful therapeutic intervention for patients with acute lung injury. The objective of this study was to investigate the effects of mechanical ventilation on large-aggregate surfactant (LA) structure and function. Isolated rat lungs were randomized to either a nonventilated control group, a relatively noninjuriously ventilated group [1 h, 10 ml/kg tidal volume, 3 cmH(2)O positive end-expiratory pressure (PEEP)], or an injuriously ventilated group (1 h, 20 ml/kg tidal volume, 0 cmH(2)O PEEP). Injurious ventilation resulted in significantly decreased lung compliance compared with the other two groups. LA structure, as determined by electron microscopy, revealed that LA from the injurious group had significantly lower amounts of organized lipid-protein structures compared with LA obtained from the other groups. Analysis of the biophysical properties by using a captive bubble surfactometer demonstrated that adsorption and surface tension reduction were significantly impaired with LA from the injuriously ventilated lungs. We conclude that the injurious mechanical ventilation impairs LA function and that this impairment is associated with significant morphological alterations.

Intratracheal endotoxin causes systemic inflammation in ventilated preterm lambs

Intratracheal endotoxin causes acute inflammation in the adult lung, and injurious styles of mechanical ventilation can result in systemic inflammation derived from the lungs. We asked how ventilated premature and near-term lungs responded to intratracheal endotoxin and if systemic inflammation occurred. Lambs delivered at 130 d gestational age (GA) were treated with surfactant or surfactant plus endotoxin (0.1 mg/kg or 10 mg/kg) (Escherichia coli, serotype O55:B5) and were ventilated for 6 h. Both endotoxin doses resulted in impaired gas exchange and systemic inflammation in the preterm lambs. Lambs at 141 d GA (term 146 d) were given either 10 mg/kg intratracheal endotoxin, 10 mg/kg endotoxin plus high tidal volume ventilation for the first 30 min of life, or 5 microg/kg endotoxin given intravenously. Endotoxin alone (10 mg/kg) caused lung inflammation but no systemic effects after 6 h of ventilation. Lambs given 10 mg/kg endotoxin plus high tidal volume ventilation or 5 microg/kg endotoxin intravenously had decreased gas exchange and systemic inflammation. Endotoxin was detected in the plasma of lambs at 130 d GA but not at 141 d GA. Inflammation in the lungs was more severe in preterm animals. Mechanical ventilation of the endotoxin-exposed preterm lung resulted in systemic effects at a low endotoxin dose and without high tidal volume ventilation.

Improved arterial oxygenation with biologically variable or fractal ventilation using low tidal volumes in a porcine model of acute respiratory distress syndrome

We compared biologically variable ventilation (V (bv); n = 9) with control mode ventilation (V (c); n = 8) at low tidal volume (VT)--initial 6 ml/kg--in a porcine model of acute respiratory distress syndrome (ARDS). Hemodynamics, respiratory gases, airway pressures, and VT data were measured. Static P-V curves were generated at 5 h. Interleukin (IL)-8 and IL-10 were measured in serum and tracheal aspirate. By 5 h, higher Pa(O(2)) (173 +/- 30 mm Hg versus 119 +/- 23 mm Hg; mean +/- SD; p < 0.0001 group x time interaction [G x T]), lower shunt fraction (6 +/- 1% versus 9 +/- 3%; p = 0.0026, G x T) at lower peak airway pressure (21 +/- 2 versus 24 +/- 1 cm H(2)O; p = 0.0342; G x T) occurred with V (bv). IL-8 concentrations in tracheal aspirate and wet:dry weight ratios were inversely related; p = 0.011. With V (c), IL-8 concentrations were 3.75-fold greater at wet:dry weight ratio of 10. IL-10 concentrations did not differ between groups. In both groups, ventilation was on the linear portion of the P-V curve. With V (bv), VT variability demonstrated an inverse power law indicating fractal behavior. In this model of ARDS, V (bv) improved Pa(O(2)) at lower peak airway pressure and IL-8 levels compared with V (c).

Reduced tidal volumes and lung protective ventilatory strategies: where do we go from here?

Three major determinants of lung injury associated with mechanical ventilation have been clearly identified: high pressure/high volume, the shear forces caused by intratidal collapse and decollapse leading to barotrauma/volotrauma/biotrauma. The lung protective strategy aims to reduce the impact of all three determinants. A groundbreaking study showed that reduced tidal volume is less dangerous than high tidal volume, but the researchers did not apply "full" lung protective strategy and did not take into account the shear forces. "Full" protective lung strategy was tested in only one study and in a limited number of patients. Several physiologic studies strongly suggest the advantages of the lung protective strategy.

Ventilator-induced lung injury

The clinical relevance of experimental ventilator-induced lung injury has recently received a resounding illustration by the Acute Respiratory Distress Syndrome Network trial that showed a 22% reduction of mortality in patients with acute respiratory disease syndrome when lung mechanical stress was lessened by tidal volume reduction during mechanical ventilation. This clinical confirmation of the concept of ventilator-induced lung injury has also undisputedly substantiated the experimental observation that excessive tidal volume and/or end-inspiratory lung volume is the main determinant of ventilator-induced lung injury. More recently, attention has focused on the roles and implication in the pathogenesis of ventilator-induced lung injury of inflammatory cells and mediators that may be activated and released either in the alveolar space or in the systemic circulation because of the rupture of the alveolar-capillary barrier and on the cellular response to mechanical stress.

Partial liquid ventilation reduces release of leukotriene B4 and interleukin-6 in bronchoalveolar lavage in surfactant-depleted newborn pigs

Perfluorocarbons have been shown to reduce the inflammatory process generated by alveolar macrophages in vitro. The aim of this study was to evaluate the impact of different ventilator modalities such as partial liquid ventilation (PLV), conventional ventilation (CV), and high-frequency oscillatory ventilation (HFOV) on the release of inflammatory mediators in vivo. Acute lung injury was induced in 30 male piglets by repeated saline lavage (arterial oxygen tension, <60 mm Hg; fraction of inspired oxygen, 1.0). Thereafter, animals were randomly assigned to one of five groups of six animals each: 1) 24 h of CV; 2) 24 h of CV plus surfactant therapy (S+CV); 3) 24 h of HFOV plus surfactant therapy (S+HFOV); 4) 1 h of PLV followed by 23 h of CV (PLV); and 5) 24 h of CV without previous lung injury (control group). Piglets randomized to S+CV or S+HFOV received natural surfactant (100 mg/kg). PLV with FC-77 was started in an initial dose of 30 mL/kg over 30 min followed by 0.5 mL x kg(-1) x min(-1) for another 30 min. After 1 h of PLV the animals were conventionally ventilated for 23 h. Before acute lung injury and after 24 h the number of inflammatory cells and the levels of IL-6, leukotriene B4, and tumor necrosis factor-alpha were measured in the bronchoalveolar lavage fluid. Additionally, the oxygenation index and the histopathologic damage were evaluated. Before acute lung injury, the number of inflammatory cells and the levels of mediators in bronchoalveolar lavage fluid were not different among the groups. After 24 h, the number of granulocytes in the PLV group was as low as in the control group. leukotriene B4 and IL-6 levels were found to be elevated in all groups except the control group (p < 0.01). The release of leukotriene B4 and IL-6 was lowest in the PLV group when compared with S+HFOV, S+CV, or CV (p < 0.05). No differences among the groups were detected for tumor necrosis factor-alpha. Although the concentrations of leukotriene B4 and IL-6 after PLV were lowest in the PLV group, histopathologic evidence of damage and the oxygenation index in the PLV group did not differ from that found in the S+CV or S+HFOV groups. In conclusion, PLV with perfluorocarbons may protect the lung from acute pulmonary inflammation more effectively than CV or HFOV does.

Genetics and the pathogenesis of adult respiratory distress syndrome

Most human diseases are substantially affected by genetic factors. It now seems clear that the pathogenesis of most diseases lies in complex interactions among the genotype, the environment, and the nature of the process that leads to cell, tissue, organ, or systemic injury. The information derived from the knowledge of the recent completion of the human genome, when combined with the sophisticated tools of molecular biology, will provide the framework for more rapid identification of the genes responsible for susceptibility to disease. Genetic approaches to complex disorders offer great potential to improve our understanding of their pathophysiology, but they also offer significant challenges. There is evidence that cellular and humoral immune responses are subject to polymorphic genetic control, which could explain the well-known diversity of clinical manifestations and outcomes in critically ill patients with the same disease. Therefore, genetic differences between people may affect the likelihood of the development of diseases. Markers of susceptibility will indicate differences in individuals or populations that affect the body's response. The underlying principle of susceptibility markers is the interindividual differences that confer sensitivity or resistance to environmentally induced diseases. This article reviews some of those susceptibility factors for critical illness and acute lung injury.

Ventilation with high tidal volume induces inflammatory lung injury

Mechanical ventilation with high tidal volumes (V(T)) has been shown to induce lung injury. We examined the hypothesis that this procedure induces lung injury with inflammatory features. Anesthetized male Wistar rats were randomized into three groups: group 1 (N = 12): V(T) = 7 ml/kg, respiratory rate (RR) = 50 breaths/min; group 2 (N = 10): V(T) = 21 ml/kg, RR = 16 breaths/min; group 3 (N = 11): V(T) = 42 ml/kg, RR = 8 breaths/min. The animals were ventilated with fraction of inspired oxygen of 1 and positive end-expiratory pressure of 2 cmH2O. After 4 h of ventilation, group 3, compared to groups 1 and 2, had lower PaO2 [280 (range 73-458) vs 517 (range 307-596), and 547 mmHg (range 330-662), respectively, P<0.05], higher wet lung weight [3.62 +/- 0.91 vs 1.69 +/- 0.48 and 1.44 +/- 0.20 g, respectively, P<0.05], and higher wet lung weight/dry lung weight ratio [18.14 (range 11.55-26.31) vs 7.80 (range 4.79-12.18), and 6.34 (range 5.92-7.04), respectively, P<0.05]. Total cell and neutrophil counts were higher in group 3 compared to groups 1 and 2 (P<0.05), as were baseline TNF-alpha concentrations [134 (range <10-386) vs 16 (range <10-24), and 17 pg/ml (range <10-23), respectively, P<0.05]. Serum TNF-alpha concentrations reached a higher level in group 3, but without statistical significance. These results suggest that mechanical ventilation with high V T induces lung injury with inflammatory characteristics. This ventilatory strategy can affect the release of TNF-alpha in the lungs and can reach the systemic circulation, a finding that may have relevance for the development of a systemic inflammatory response.

Low tidal volume reduces epithelial and endothelial injury in acid-injured rat lungs

Using a rat model of acid-induced lung injury, we tested the hypothesis that tidal volume reduction at the same level of PEEP (10 cm H(2)O) would diminish the degree of pulmonary edema by attenuating injury to the alveolar epithelial and endothelial barriers. Tidal volume reduction from 12 to 6 to 3 ml/kg significantly reduced the rate of lung water accumulation from 690 microl/h to 310 microl/h to 210 microl/h. Ventilation with either 6 or 3 ml/kg reduced endothelial injury equally as measured by plasma vWf:Ag and permeability to albumin. Plasma RTI40, a marker of type I epithelial cell injury, decreased 46% when tidal volume was reduced from 12 to 6 ml/kg and decreased an additional 33% with 3 ml/kg (p < 0.05). The rate of alveolar epithelial fluid clearance was significantly faster in the 3-ml/kg group (24 +/- 7%/h) compared with 6 ml/kg (15 +/- 11%/h) and 12 ml/kg (3 +/- 6%/h). We conclude that low tidal volume ventilation protects both the alveolar epithelium and the endothelium in this model of acute lung injury. The additional decrease in pulmonary edema with a tidal volume of 3 ml/kg is partly accounted for by greater protection of the alveolar epithelium.

Optimal peep in ARDS. Changing concepts and current controversies

From many recently performed studies, it is clear that a criterion standard for determining the optimal positive end-expiratory pressure (PEEP) level in patients with acquired respiratory distress syndrome (ARDS) does not exist. What is evident and consistent, however, are several points such the optimal PEEP level ultimately represents a balance between regional areas of overstretching and regional derecruitment; higher levels of PEEP may be required early in ARDS, independent of oxygenation requirements; and the exact method for titrating PEEP in patients with ARDS remains to be determined. These points and others are delineated and discussed in this article.

New therapies for adults with acute lung injury. High-frequency oscillatory ventilation

High-frequency oscillatory ventilation seems theoretically ideal for the treatment of patients with ARDS, allowing adequate oxygenation and ventilation to be maintained without causing further damage to the already injured lung. High-frequency oscillating ventilation also seems a sound strategy for improving oxygenation in patients who are no longer responding to conventional mechanical ventilation. Currently, HFOV should be used in the adult ICU as one of many ancillary therapies available for the treatment of extremely ill, hypoxemic patients with ARDS. Future research may define the role of HFOV as a more routine strategy for preventing VALI in this patient population.

Elevated expression of inducible nitric oxide synthase and inflammatory cytokines in the alveolar macrophages after esophagectomy

OBJECTIVE

To evaluate the role of inducible nitric oxide (NO) synthase (iNOS) and inflammatory cytokines in alveolar macrophages (AMs) after esophagectomy in the pathogenesis of acute lung injury.

DESIGN

Prospective, exploratory, open-labeled clinical study.

SETTING

Intensive care unit and operating room in a university hospital.

PATIENTS

Thirteen patients receiving esophagectomy with carcinoma of the esophagus (postesophagectomy group), ten patients just before the surgery (preoperation group), and seven patents receiving surgery less invasive than esophagectomy (other surgery group) were selected.

INTERVENTIONS

Bronchoalveolar lavage fluid (BALF) and blood samples were obtained from study groups.

MEASUREMENTS AND MAIN RESULTS

The AMs in the BALF collected from each group were stained immunohistochemically with antibodies against iNOS, interleukin (IL)-6, and IL-8. The intensities of these expressions were determined by semiquantitative cytofluorometric system. NOx (NO2- + NO3-), IL-6, and IL-8 levels in the BALF and plasma were measured concurrently. The expressional intensities of iNOS, IL-6, and IL-8 in AMs obtained from the postesophagectomy group were maximal 24 hrs after the skin incision and significantly more evident than those from other groups. The IL-6, IL-8, and NOx levels in BALF and IL-6 and IL-8 levels in plasma in the postesophagectomy patients were also elevated. The intensities of iNOS and inflammatory cytokines expressions in AMs were closely related to postoperative respiratory failure.

CONCLUSIONS

The activation of topical alveolar macrophages may be involved in the pathogenesis of pulmonary complications in the postoperative period after esophagectomy.

Reducing mortality in sepsis: new directions

Considerable progress has been made in the past few years in the development of therapeutic interventions that can reduce mortality in sepsis. However, encouraging physicians to put the results of new studies into practice is not always simple. A roundtable was thus convened to provide guidance for clinicians on the integration and implementation of new interventions into the intensive care unit (ICU). Five topics were selected that have been shown in randomized, controlled trials to reduce mortality: limiting the tidal volume in acute lung injury or acute respiratory distress syndrome, early goal-directed therapy, use of drotrecogin alfa (activated), use of moderate doses of steroids, and tight control of blood sugar. One of the principal investigators for each study was invited to participate in the roundtable. The discussions and questions that followed the presentation of data by each panel member enabled a consensus recommendation to be derived regarding when each intervention should be used. Each new intervention has a place in the management of patients with sepsis. Furthermore, and importantly, the therapies are not mutually exclusive; many patients will need a combination of several approaches--an "ICU package". The present article provides guidelines from experts in the field on optimal patient selection and timing for each intervention, and provides advice on how to integrate new therapies into ICU practice, including protocol development, so that mortality rates from this disease process can be reduced.

Ventilator-induced lung injury upregulates and activates gelatinases and EMMPRIN: attenuation by the synthetic matrix metalloproteinase inhibitor, Prinomastat (AG3340)

Mechanical ventilation has become an indispensable therapeutic modality for patients with respiratory failure. However, a serious potential complication of MV is the newly recognized ventilator-induced acute lung injury. There is strong evidence suggesting that matrix metalloproteinases (MMPs) play an important role in the development of acute lung injury. Another factor to be considered is extracellular matrix metalloproteinase inducer (EMMPRIN). EMMPRIN is responsible for inducing fibroblasts to produce/secrete MMPs. In this report we sought to determine: (1) the role played by MMPs and EMMPRIN in the development of ventilator-induced lung injury (VILI) in an in vivo rat model of high volume ventilation; and (2) whether the synthetic MMP inhibitor Prinomastat (AG3340) could prevent this type of lung injury. We have demonstrated that high volume ventilation caused acute lung injury. This was accompanied by an upregulation of gelatinase A, gelatinase B, MT1-MMP, and EMMPRIN mRNA demonstrated by in situ hybridization. Pretreatment with the MMP inhibitor Prinomastat attenuated the lung injury caused by high volume ventilation. Our results suggest that MMPs play an important role in the development of VILI in rat lungs and that the MMP-inhibitor Prinomastat is effective in attenuating this type of lung injury.

Keratinocyte growth factor reduces alveolar epithelial susceptibility to in vitro mechanical deformation

Keratinocyte growth factor (KGF) is a potent mitogen that prevents lung epithelial injury in vivo. We hypothesized that KGF treatment reduces ventilator-induced lung injury by increasing the alveolar epithelial tolerance to mechanical strain. We evaluated the effects of in vivo KGF treatment to rats on the response of alveolar type II (ATII) cells to in vitro controlled, uniform deformation. KGF (5 mg/kg) or saline (no-treatment control) was instilled intratracheally in rats, and ATII cells were isolated 48 h later. After 24 h in culture, both cell groups were exposed to 1 h of continuous cyclic strain (25% change in surface area); undeformed wells were included as controls. Cytotoxicity was evaluated quantitatively with fluorescent immunocytochemistry. There was >1% cell death in undeformed KGF-treated and control groups. KGF pretreatment significantly reduced deformation-related cell mortality to only 2.2 +/- 1.3% (SD) from 49 +/- 5.5% in control wells (P < 0.001). Effects of extracellular matrix, actin cytoskeleton, and phenotype of KGF-treated and control cells were examined. The large reduction in deformation-induced cell death demonstrates that KGF protects ATII cells by increasing their strain tolerance and supports KGF treatment as a potential preventative measure for ventilator-induced lung injury.

Changes in proteoglycans and lung tissue mechanics during excessive mechanical ventilation in rats

Excessive mechanical ventilation results in changes in lung tissue mechanics. We hypothesized that changes in tissue properties might be related to changes in the extracellular matrix component proteoglycans (PGs). The effect of different ventilation regimens on lung tissue mechanics and PGs was examined in an in vivo rat model. Animals were anesthetized, tracheostomized, and ventilated at a tidal volume of 8 (VT(8)), 20, or 30 (VT(30)) ml/kg, positive end-expiratory pressure of 0 (PEEP(0)) or 1.5 (PEEP(1.5)) cmH(2)O, and frequency of 1.5 Hz for 2 h. The constant-phase model was used to derive airway resistance, tissue elastance, and tissue damping. After physiological measurements, one lung was frozen for immunohistochemistry and the other was reserved for PG extraction and Western blotting. After 2 h of mechanical ventilation, tissue elastance and damping were significantly increased in rats ventilated at VT(30)PEEP(0) compared with control rats (ventilated at VT(8)PEEP(1.5)). Versican, basement membrane heparan sulfate PG, and biglycan were all increased in rat lungs ventilated at VT(30)PEEP(0) compared with control rats. At VT(30)PEEP(0), heparan sulfate PG and versican staining became prominent in the alveolar wall and airspace; biglycan was mostly localized in the airway wall. These data demonstrate that alterations in lung tissue mechanics with excessive mechanical ventilation are accompanied by changes in all classes of extracellular matrix PG.

Comparison of lung protective ventilation strategies in a rabbit model of acute lung injury

OBJECTIVE

To determine the impact of different protective and nonprotective mechanical ventilation strategies on the degree of pulmonary inflammation, oxidative damage, and hemodynamic stability in a saline lavage model of acute lung injury.

DESIGN

A prospective, randomized, controlled, in vivo animal laboratory study.

SETTING

Animal research facility of a health sciences university.

SUBJECTS

Forty-six New Zealand White rabbits.

INTERVENTIONS

Mature rabbits were instrumented with a tracheostomy and vascular catheters. Lavage-injured rabbits were randomized to receive conventional ventilation with either a) low peak end-expiratory pressure (PEEP; tidal volume of 10 mL/kg, PEEP of 2 cm H2O); b) high PEEP (tidal volume of 10 mL/kg, PEEP of 10 cm H2O); c) low tidal volume with PEEP above Pflex (open lung strategy, tidal volume of 6 mL/kg, PEEP set 2 cm H2O > Pflex); or d) high-frequency oscillatory ventilation. Animals were ventilated for 4 hrs. Lung lavage fluid and tissue samples were obtained immediately after animals were killed. Lung lavage fluid was assayed for measurements of total protein, elastase activity, tumor necrosis factor-alpha, and malondialdehyde. Lung tissue homogenates were assayed for measurements of myeloperoxidase activity and malondialdehyde. The need for inotropic support was recorded.

MEASUREMENTS AND MAIN RESULTS

Animals that received a lung protective strategy (open lung or high-frequency oscillatory ventilation) exhibited more favorable oxygenation and lung mechanics compared with the low PEEP and high PEEP groups. Animals ventilated by a lung protective strategy also showed attenuation of inflammation (reduced tracheal fluid protein, tracheal fluid elastase, tracheal fluid tumor necrosis factor-alpha, and pulmonary leukostasis). Animals treated with high-frequency oscillatory ventilation had attenuated oxidative injury to the lung and greater hemodynamic stability compared with the other experimental groups.

CONCLUSIONS

Both lung protective strategies were associated with improved oxygenation, attenuated inflammation, and decreased lung damage. However, in this small-animal model of acute lung injury, an open lung strategy with deliberate hypercapnia was associated with significant hemodynamic instability.

Mechanisms of pulmonary gas exchange improvement during a protective ventilatory strategy in acute respiratory distress syndrome

To investigate the mechanisms underlying improvement of arterial oxygenation during a protective ventilatory strategy (PVS) in early acute respiratory distress syndrome (ARDS), we studied eight patients during volume-controlled mechanical ventilation, keeping respiratory rate and fraction of inspired oxygen (FI(O(2))) (0.82 +/- 0.20) unchanged: (1) at baseline (tidal volume [VT] 10 to 12 ml x kg(-1); positive end-expiratory pressure [PEEP] 8 to 10 cm H(2)O); (2) during PVS (PEEP 2 cm H(2)O above the low inflexion point (P(FLEX)) and VT of 5 to 7 ml x kg(-1)); and (3) post-PVS, back to baseline conditions. Inert gas measurements were done after 30 min in each ventilatory modality. During PVS, Pa(O(2)) increased significantly from 93 +/- 27 to 166 +/- 77 mm Hg (p < 0.008) and Pa(CO(2)) rose from 39 +/- 7 to 57 +/- 11 mm Hg (p < 0.0002) because of the decrease in minute ventilation (V E) (-3.6 L x min(-1)) (p < 0.005). Both heart rate (HR, +13 min(-1)) (p < 0.002) and cardiac output (Q, +1.2 L x min(-1)) (p < 0.05) increased. Static respiratory system linear compliance increased from 36 +/- 14 to 44 +/- 16 ml. cm H(2)O(-1) (p < 0.0002). PVS provoked recruitment of previously collapsed alveoli and redistribution of pulmonary blood flow from nonventilated alveoli to normal lung. Despite the increase in Q, intrapulmonary shunt fell from 39 +/- 15% to 31 +/- 11% (p < 0.04). We conclude that the decrease in intrapulmonary shunt owing to alveolar recruitment remains the pivotal mechanism to explain improvement of arterial oxygenation during this PVS.

Comparison of lung protection strategies using conventional and high-frequency oscillatory ventilation

This study compared pathophysiological and biochemical indexes of acute lung injury in a saline-lavaged rabbit model with different ventilatory strategies: a control group consisting of moderate tidal volume (V(T)) (10-12 ml/kg) and low positive end-expiratory pressure (PEEP) (4-5 cmH(2)O); and three protective groups: 1) low V(T) (5-6 ml/kg) high PEEP, 2-3 cmH(2)O greater than the lower inflection point; 2) low V(T) (5-6 ml/kg), high PEEP (8-10 cmH(2)O); and 3) high-frequency oscillatory ventilation (HFOV). The strategy using PEEP > inflection point resulted in hypotension and barotrauma. HFOV attenuated the decrease in pulmonary compliance, the lung inflammation assessed by polymorphonuclear leukocyte infiltration and tumor necrosis factor-alpha concentration in the alveolar space, and pathological changes of the small airways and alveoli. Conventional mechanical ventilation using lung protection strategies (low V(T) high PEEP) only attenuated the decrease in oxygenation and pulmonary compliance. Therefore, HFOV may be a preferable option as a lung protection strategy.

Treatment of ARDS

Improved understanding of the pathogenesis of acute lung injury (ALI)/ARDS has led to important advances in the treatment of ALI/ARDS, particularly in the area of ventilator-associated lung injury. Standard supportive care for ALI/ARDS should now include a protective ventilatory strategy with low tidal volume ventilation by the protocol developed by the National Institutes of Health ARDS Network. Further refinements of the protocol for mechanical ventilation will occur as current and future clinical trials are completed. In addition, novel modes of mechanical ventilation are being studied and may augment standard therapy in the future. Although results of anti-inflammatory strategies have been disappointing in clinical trials, further trials are underway to test the efficacy of late corticosteroids and other approaches to modulation of inflammation in ALI/ARDS.

Childhood outcome after early high-frequency oscillatory ventilation for neonatal respiratory distress syndrome

OBJECTIVE

In a previous multicenter controlled clinical trial, we randomly assigned surfactant-treated premature newborns with moderate to severe respiratory distress syndrome to early treatment with high-frequency oscillatory ventilation (HFOV) or to conventional ventilation (CV). Compared with control infants who were treated with CV, neonates who were treated with HFOV using a strategy designed to recruit and maintain lung volume and minimize oxygen exposure had clinical evidence of improved pulmonary outcome and less lung injury. We report a follow-up study designed to determine whether clinical differences persisted between these study groups.

METHODS

Patients were recruited from 81 survivors at 1 center (Provo, Utah) and evaluated for sociodemographic and health history, growth, mental development, motor proficiency, and pulmonary function.

RESULTS

Eighty-seven percent of the cohort who originally were assigned to treatment with HFOV (n = 36) or CV (n = 33) were seen in follow-up at a mean age of 77 months (6.4 years). There were no differences in the frequency of hospitalization, pulmonary illness, asthma, or disabilities. Growth, verbal IQ, and motor development were appropriate for age and not different between groups. Patients who initially were randomized to treatment with CV showed pulmonary function evidence of decreased peak expiratory flow, increased residual lung volume, and maldistribution of ventilation.

CONCLUSION

Neurodevelopmental childhood outcome after early intervention HFOV was normal and not different compared with patients who were treated with CV. Surfactant replacement combined with early HFOV using a lung recruitment strategy ameliorates the acute lung injury in respiratory distress syndrome that predisposes some preterm infants to develop chronic lung disease.

Lung recruitment at birth does not improve lung function in immature lambs receiving surfactant

BACKGROUND

In mature animals with surfactant deficiency induced by lung lavage, the therapeutic effect of exogenous surfactant is enhanced by a lung recruitment maneuver. We then tested whether a lung recruitment maneuver at birth immediately before surfactant treatment would improve lung function also in preterm lambs with surfactant deficiency due to immaturity.

METHODS

Ten newborn lambs with a gestational age of 127 days were randomized to receive surfactant either before the first breath or immediately after a lung recruitment maneuver consisting of five sustained inflations of 8, 16 or 32 ml/kg. Functional residual capacity was measured by sulfur hexafluoride washout, and inspiratory capacity as well as maximal compliance were obtained from a static expiratory pressure-volume curve after the lungs had been inflated to 35 cm H2O. In addition, blood gases were obtained. Measurements were made at 15, 45, 175, 135, 170 and 230 min after birth. Post mortem histological examinations of the lungs were performed in a blinded fashion.

RESULTS

The lung recruitment maneuvers did not improve oxygenation. Inspiratory capacity, static compliance and functional residual capacity at 4 h, as well as post mortem intrapulmonary air volume, had an inverse relation to the size of inflations given at birth. There was also a negative correlation between size of inflations at birth and response to surfactant therapy, as assessed by lung microscopy.

CONCLUSION

Lung recruitment at birth does not improve the response to surfactant in immature lambs, but may instead have an adverse effect on lung function and morphology.

Airway inflammation in nonasthmatic amateur runners

Elite athletes show a high prevalence of symptoms and signs of asthma, but no study has assessed the acute effects of endurance exercise on airway cells in nonasthmatic athletes. We measured exhaled nitric oxide (NO) and collected samples of induced sputum after 3% NaCl aerosol administration for 20 min in nonasthmatic middle-aged amateur runners after the Fourth Palermo International Marathon and 6--9 wk later (habitual training period) at baseline. After the marathon, exhaled NO (n = 9 subjects) was higher [27 +/- 9 parts/billion (ppb)] than at baseline (12 +/- 4 ppb; P < 0.0005). Polymorphonuclear neutrophil (PMN) counts in induced sputum were much higher in runners (91.2 +/- 3.6% of total cells postmarathon and 78.7 +/- 9.1% at baseline) than in sedentary control subjects (9.9 +/- 5.9%; P < 0.001). Expression of L-selectin and CD11b/CD18 in sputum PMNs was lower after the race than at baseline and inversely related to the amount of exhaled NO (r = -0.66 and -0.69, respectively; P < 0.05). Our data indicate that sputum PMNs are increased in nonasthmatic runners both after a marathon and at baseline and suggest that NO may modulate exercise-associated inflammatory airway changes.

Mechanical ventilation of isolated septic rat lungs: effects on surfactant and inflammatory cytokines

The effects of mechanical ventilation (MV) on the surfactant system and cytokine secretion were studied in isolated septic rat lungs. At 23 h after sham surgery or induction of sepsis by cecal ligation and perforation (CLP), lungs were excised and randomized to one of three groups: 1) a nonventilated group, 2) a group subjected to 1 h of noninjurious MV (tidal volume = 10 ml/kg, positive end-expiratory pressure = 3 cmH(2)O), or 3) a group subjected to 1 h of injurious MV (tidal volume = 20 ml/kg, positive end-expiratory pressure = 0 cmH(2)O). Nonventilated sham and CLP lungs had similar compliance, normal lung morphology, surfactant, and cytokine concentrations. Injurious ventilation decreased compliance, altered surfactant, increased cytokines, and induced morphological changes compared with nonventilation in sham and CLP lungs. In these lungs, the surfactant system was similar in sham and CLP lungs; however, tumor necrosis factor-alpha and interleukin-6 levels were significantly higher in CLP lungs. We conclude that injurious ventilation altered surfactant independent of sepsis and that the CLP lungs were predisposed to the secretion of larger amounts of cytokines because of ventilation.

Visual validation of the mechanical stabilizing effects of positive end-expiratory pressure at the alveolar level

BACKGROUND

Positive end-expiratory pressure (PEEP) reduces ventilator-induced lung injury (VILI), presumably by mechanically stabilizing alveoli and decreasing intrapulmonary shear. Although there is indirect support for this concept in the literature, direct evidence is lacking. In a surfactant depletion model of acute lung injury we observed unstable alveolar mechanics referred to as repeated alveolar collapse and expansion (RACE) as measured by changes in alveolar area from inspiration to expiration (I - E(Delta)). We tested the hypothesis that over a range of tidal volumes PEEP would prevent RACE by mechanically stabilizing alveoli.

MATERIALS AND METHODS

Yorkshire pigs were randomized to three groups: control (n = 4), Tween (surfactant-deactivating detergent) (n = 4), and Tween + PEEP (7 cm H(2)O) (n = 4). Using in vivo video microscopy individual alveolar areas were measured with computer image analysis at end inspiration and expiration over consecutive increases in tidal volume (7, 10, 15, 20, and 30 cc/kg.) I - E(Delta) was calculated for each alveolus.

RESULTS

Surfactant deactivation significantly increased I - E(Delta) at every tidal volume compared to controls (P < 0.05). PEEP prevented this change, returning I - E(Delta) to control levels over a spectrum of tidal volumes.

CONCLUSIONS

RACE occurs in our surfactant deactivation model of acute lung injury. PEEP mechanically stabilizes alveoli and prevents RACE over a range of tidal volumes. This is the first study to visually document the existence of RACE and the mechanical stabilizing effects of PEEP at the alveolar level. The ability of PEEP to stabilize alveoli and reduce shear during mechanical ventilation has important implications for therapeutic strategies directed at VILI and acute respiratory distress syndrome.

Effects of ventilation with different positive end-expiratory pressures on cytokine expression in the preterm lamb lung

Ventilator-induced lung injury increases proinflammatory cytokines in the adult lung. We asked if positive end-expiratory pressure (PEEP) affects proinflammatory cytokine mRNA expression in the preterm lung. Preterm lambs at 129 +/- 3 d gestation were treated with 100 mg/kg recombinant human surfactant protein-C surfactant and ventilated for 2 or 7 h with 0, 4, or 7 cm H(2)O of PEEP. Unventilated fetal lambs were used as controls. Within 2 h of ventilation, alveolar total protein and activated neutrophils were increased and expression of mRNAs for the proinflammatory cytokines interleukin (IL)-1beta, IL-6, IL-8, and tumor necrosis factor-alpha (TNF-alpha) was increased in lung tissue of all ventilated animals relative to unventilated controls. Alveolar protein and neutrophils were higher for 0 and 7 PEEP animals than 4 PEEP animals. IL-1beta, IL-6, and IL-8 mRNAs were significantly elevated in animals ventilated with 0 PEEP compared with 4 PEEP. The percentage fractional area of collapsed alveoli was significantly higher for 0 PEEP compared with 4 and 7 PEEP groups. Mechanical ventilation increased the expression of proinflammatory mediators in surfactant-treated preterm lungs and the use of 4 PEEP minimized this response.

Repetitive high-pressure recruitment maneuvers required to maximally recruit lung in a sheep model of acute respiratory distress syndrome

OBJECTIVE

To compare the effects of two different recruitment maneuvers repeated multiple times on gas exchange lung injury, hemodynamic, and lung mechanics.

DESIGN

Randomized prospective comparison.

SETTINGS

Animal research laboratory.

SUBJECT

Nineteen fasted Hampshire sheep.

INTERVENTIONS

In 15 27-kg sheep with saline lavage lung injury, we compared the effects of two recruitment maneuvers: 40 cm H2O continuous positive airway pressure for 60 secs and 40 cm H2O positive end-expiratory pressure with 20 cm H2O pressure control, rate 10 breaths/min, inspiratory to expiratory ratio 1:1 for 2 mins. Each recruitment maneuver was repeated four times, every 30 mins after a 30-sec ventilator disconnection. An additional group received no recruitment maneuvers. Animals were assigned randomly to the three groups and ventilated with 20 cm H2O positive end-expiratory pressure, pressure control 15 cm H2O, rate 20 breaths/min, inspiratory to expiratory ratio 1:1, and Fio2 1.0 between recruitment maneuver periods.

MEASUREMENTS AND MAIN RESULTS

Significant and marked increases in Pao2 were observed in the pressure control recruitment maneuver group but only after the second recruitment maneuver. In both the control group and continuous positive airway pressure groups, Pao2 did not significantly increase after any recruitment maneuver compared with baseline injury. There was a significant decrease in cardiac output immediately after some continuous positive airway pressure recruitment maneuvers and a significant increase in mean pulmonary artery pressure in both continuous positive airway pressure and pressure control groups immediately after recruitment maneuvers, but these changes resolved within 10 mins. There were no marked histologic differences between groups and no volutrauma.

CONCLUSION

In this model, maximal lung recruitment was obtained with 40 cm H2O positive end-expiratory pressure and 20 cm H2O pressure control applied repetitively every 30 mins for 2 mins without physiologic or histologic harm. Multiple recruitment maneuvers in some animals were required for maximum effect.

Prospective trial of high-frequency oscillation in adults with acute respiratory distress syndrome

OBJECTIVE

To evaluate the safety and efficacy of high-frequency oscillatory ventilation (HFOV) in adult patients with the acute respiratory distress syndrome (ARDS) and oxygenation failure.

DESIGN

Prospective, clinical study.

SETTING

Intensive care and burn units of two university teaching hospitals.

PATIENTS

Twenty-four adults (10 females, 14 males, aged 48.5 +/- 15.2 yrs, Acute Physiology and Chronic Health Evaluation II score 21.5 +/- 6.9) with ARDS (lung injury score 3.4 +/- 0.6, Pao2/Fio2 98.8 +/- 39.0 mm Hg, and oxygenation index 32.5 +/- 19.6) who met one of the following criteria: Pao2 < or =65 mm Hg with Fio2 > or =0.6, or plateau pressure > or =35 cm H2O.

INTERVENTIONS

HFOV was initiated in patients with ARDS after varying periods of conventional ventilation (CV). Mean airway pressure (Paw) was initially set 5 cm H2O greater than Paw during CV, and was subsequently titrated to maintain oxygen saturation between 88% and 93% and Fio2 < or =0.60.

MEASUREMENTS AND MAIN RESULTS

Fio2, Paw, pressure amplitude of oscillation, frequency, blood pressure, heart rate, and arterial blood gases were monitored during the transition from CV to HFOV, and every 8 hrs thereafter for 72 hrs. In 16 patients who had pulmonary artery catheters in place, cardiac hemodynamics were recorded at the same time intervals. Throughout the HFOV trial, Paw was significantly higher than that applied during CV. Within 8 hrs of HFOV application, and for the duration of the trial, Fio2 and Paco2 were lower, and Pao2/Fio2 was higher than baseline values during CV. Significant changes in hemodynamic variables following HFOV initiation included an increase in pulmonary artery occlusion pressure (at 8 and 40 hrs) and central venous pressure (at 16 and 40 hrs), and a reduction in cardiac output throughout the course of the study. There were no significant changes in systemic or pulmonary pressure associated with initiation and maintenance of HFOV. Complications occurring during HFOV included pneumothorax in two patients and desiccation of secretions in one patient. Survival at 30 days was 33%, with survivors having been mechanically ventilated for fewer days before institution of HFOV compared with nonsurvivors (1.6 +/- 1.2 vs. 7.8 +/- 5.8 days; p =.001).

CONCLUSIONS

These findings suggest that HFOV has beneficial effects on oxygenation and ventilation, and may be a safe and effective rescue therapy for patients with severe oxygenation failure. In addition, early institution of HFOV may be advantageous.

Pentoxifylline rescue preserves lung function in isolated canine lungs injured with phorbol myristate acetate

OBJECTIVE

We hypothesized that pentoxifylline, administered after phorbol myristate acetate (PMA), would diminish the severity of lung injury.

SETTING

Animal research laboratory.

DESIGN

Comparative study.

SUBJECTS

Mongrel dogs (n = 33).

INTERVENTIONS

Baseline measurements were obtained from the isolated blood-perfused dog lung lobes after 1 h of stable perfusion and ventilation. Four different measures of lung compliance were obtained along with WBC and neutrophil counts. Pulmonary vascular resistance (PVR) and capillary filtration coefficient (Kf) were calculated, and the ratio of a normalized maximal enzymatic conversion rate to the Michaelis-Menten constant (Amax/Km) was used to assess perfused capillary surface area. The control lobes (n = 8) were ventilated and perfused for an additional 40 min while the injured lobes (n = 17) received PMA (0.1 microg/mL of perfusate). The pentoxifylline-protected lobes (n = 8) were treated with pentoxifylline (1 mg/mL of perfusate) 10 min after injury with PMA. All measurements were then repeated.

MEASUREMENT AND MAIN RESULTS

The three groups did not differ significantly at baseline. The control lobes remained relatively stable over time. The injured lobes demonstrated marked deterioration in compliance: 8.79 +/- 0.7 to 5.97 +/- 0.59 mL/cm H(2)O (p < 0.05) vs 10.1 +/- 1.0 to 8.07 +/- 0.72 mL/cm H(2)O and 9.6 +/- 1.1 to 9.9 +/- 0.85 mL/cm H(2)O in the control and protected lobes, respectively. Both groups receiving PMA had similar drops in WBC and neutrophil counts, but the pentoxifylline-protected lobes had preservation of all four compliance measures. PVR increased from 37.8 +/- 1.8 to 118.6 +/- 12.7 cm H(2)O/L/min (p < 0.05) in the injured lobes vs 35.4 +/- 0.5 to 36.3 +/- 2.8 cm H(2)O/L/min and 40.4 +/- 0.04 to 46.7 +/- 2.8 cm H(2)O/L/min (p < 0.05) in the control and protected lobes, respectively. Kf increased < 25% in the protected group but more than tripled in the injured group. Amax/Km dropped from 559 +/- 36 to 441 +/- 33 mL/min (p < 0.05) in the injured lobes vs 507 +/- 14 to 490 +/- 17 mL/min and 609 +/- 34 to 616 +/- 37 mL/min in the control and pentoxifylline-protected lobes, respectively.

CONCLUSIONS

The use of pentoxifylline as a rescue agent prevented the PMA-induced deterioration of lung compliance, vascular integrity, and endothelial metabolic function in this acute lung injury model, despite significant pulmonary neutrophil sequestration.

Lung salvage and protection ventilatory techniques

Physicians are in the beginning of an era in intensive care medicine in which they finally are starting to see improved outcomes in patients with AHRF. At the same time, intensivists are presented with a bewildering choice of ventilator options and adjunctive therapies. Trying to sort out which are "cosmetic," that is, improve the blood gases as opposed to influencing the outcome, remains a challenge and will be resolved only with additional RCTs. Principles of ventilator management that are driven by mimicking normal physiology are inappropriate and must be rethought.

Influence of tidal volume on alveolar recruitment. Respective role of PEEP and a recruitment maneuver

Both reduction in tidal volume (VT) and alveolar recruitment may be important to limit ventilator-associated lung injury during mechanical ventilation of patients with the acute respiratory distress syndrome (ARDS). The aim of this study was to assess the risk of alveolar derecruitment associated with VT reduction from 10 to 6 ml/kg. Whether this VT-related derecruitment could be reversed, either by a recruitment maneuver or by an increase in positive end-expiratory pressure (PEEP) level, was also investigated. Fifteen patients with ARDS were successively ventilated using conventional VT (CVT = 10 +/- 1 ml/kg) and low VT (LVT = 6 +/- 1 ml/ kg); total PEEP (PEEPtot) was individually set at the lower inflection point (Plip) of the pressure-volume curve (PEEPtot = 11 +/- 4 cm H(2)O). Pressure-volume curves were recorded from zero PEEP (ZEEP) and from PEEP, and recruited volume (Vrec) was calculated as the volume difference between the two curves for a given pressure. Despite a similar PEEPtot, Vrec was significantly lower with LVT than with CVT, indicating low VT-induced alveolar derecruitment. Reduction in VT was associated with a reduced Sa(O(2)). In 10 patients, Vrec was also measured before and after a recruitment maneuver (two sustained inflations at 45 cm H(2)O), and after an increase in PEEP (by 4 cm H(2)O). Low VT-induced derecruitment was reversed by a recruitment maneuver and by increasing PEEP. We conclude that a reduction in VT could be responsible for alveolar derecruitment, which may be transiently reversed by a reexpansion maneuver or prevented by a PEEP increase above Plip.

Validation of a new live cell strain system: characterization of plasma membrane stress failure

Motivated by our interest in lung deformation injury, we report on the validation of a new live cell strain system. We showed that the system maintains a cell culture environment equivalent to that provided by conventional incubators and that its strain ouput was uniform and reproducible. With this system, we defined cell deformation dose (i.e., membrane strain amplitude)-cell injury response relationships in alveolar epithelial cultures and studied the effects of temperature on them. Deformation injury occurred in the form of reversible, nonlethal plasma membrane stress failure events and was quantified as the fraction of cells with uptake and retention of fluorescein-labeled dextran (FITC-Dx). The undeformed control population showed virtually no FITC-Dx uptake at any temperature, which was also true for cells strained by 3%. However, when the membrane strain was increased to 18%, ∼5% of cells experienced deformation injury at a temperature of 37°C. Moreover, at that strain, a reduction in temperature to 4°C resulted in a threefold increase in the number of cells with plasma membrane breaks (from 4.8 to 15.9%; P < 0.05). Cooling of cells to 4°C also lowered the strain threshold at which deformation injury was first seen. That is, at a 9% substratum strain, cooling to 4°C resulted in a 10-fold increase in the number of cells with FITC-Dx staining (0.7 vs. 7.5%, P < 0.05). At that temperature, A549 cells offered a 50% higher resistance to shape change (magnetic twisting cytometry measurements) than at 37°C. We conclude that the strain-injury threshold of A549 cells is reduced at low temperatures, and we consider temperature effects on plasma-membrane fluidity, cytoskeletal stiffness, and lipid trafficking as responsible mechanisms.

Critical care medicine in the 21st century: from CPR to PCR

As in other areas of medicine, the specialty of critical care medicine, which has made important contributions in the pathophysiology of critical illness, is facing challenges that must be recognized and addressed in the current century. In this review, we argue that the skill set required to adequately treat critically ill patients will also require knowledge of molecular biology for better diagnosis and treatment. The foundations of molecular biology and genetics are essential for the understanding of the mechanisms of disease. Incorporating molecular biology techniques in the research arsenal of the intensivist will provide the opportunity to dissect out and define the reversible and irreversible intracellular processes giving rise to the major causes of mortality in intensive care units. Two historical paradigms, the cardiopulmonary resuscitation and polymerase chain reaction, summarize how critical care medicine began, and how it could mature in the years to come.