Predictors of diffuse alveolar damage in patients with acute respiratory distress syndrome: a retrospective analysis of clinical autopsies.

BACKGROUND: Although diffuse alveolar damage (DAD) is considered the typical histological pattern of acute respiratory distress syndrome (ARDS), only half of patients exhibit this morphological hallmark. Patients with DAD may have higher mortality than those without DAD. Therefore, we aimed to identify the factors associated with DAD in patients with ARDS. METHODS: We analyzed autopsy samples of 356 patients who had ARDS at the time of death. DAD was assessed by two pathologists, and ARDS criteria were evaluated by two intensivists. Criteria for severe ARDS included the degree of hypoxemia and the ancillary variables of the current Berlin definition assessed within 48 h before death: radiographic severity, high positive end-expiratory pressure (PEEP) level, and physiological variables (i.e., altered respiratory system compliance and large anatomic dead space). RESULTS: After multivariable analysis, high PEEP levels, physiological variables, and opacities involving only three quadrants on chest radiographs were not associated with DAD. The four markers independently associated with DAD were (1) duration of evolution (OR 3.29 [1.95-5.55] for patients with ARDS ≥ 3 days, p < 0.001), (2) degree of hypoxemia (OR 3.92 [1.48-10.3] for moderate ARDS and 6.18 [2.34-16.3] for severe ARDS, p < 0.01 for both), (3) increased dynamic driving pressure (OR 1.06 [1.04-1.09], p = 0.007), and (4) radiographic severity (OR 2.91 [1.47-5.75] for patients with diffuse opacities involving the four quadrants, p = 0.002). DAD was found in two-thirds of patients with a ratio of partial pressure of arterial oxygen to fraction of inspired oxygen ≤ 100 mmHg and opacities involving the four quadrants. CONCLUSIONS: In addition to severe hypoxemia, diffuse opacities involving the four quadrants were a strong marker of DAD.

A Metabolomic Approach to the Pathogenesis of Ventilator-induced Lung Injury.

BACKGROUND: Global metabolic profiling using quantitative nuclear magnetic resonance spectroscopy (MRS) and mass spectrometry (MS) is useful for biomarker discovery. The objective of this study was to discover biomarkers of acute lung injury induced by mechanical ventilation (ventilator-induced lung injury [VILI]), by using MRS and MS. METHODS: Male Sprague-Dawley rats were subjected to two ventilatory strategies for 2.5 h: tidal volume 9 ml/kg, positive end-expiratory pressure 5 cm H2O (control, n = 14); and tidal volume 25 ml/kg and positive end-expiratory pressure 0 cm H2O (VILI, n = 10). Lung tissue, bronchoalveolar lavage fluid, and serum spectra were obtained by high-resolution magic angle spinning and H-MRS. Serum spectra were acquired by high-performance liquid chromatography coupled to quadupole-time of flight MS. Principal component and partial least squares analyses were performed. RESULTS: Metabolic profiling discriminated characteristics between control and VILI animals. As compared with the controls, animals with VILI showed by MRS higher concentrations of lactate and lower concentration of glucose and glycine in lung tissue, accompanied by increased levels of glucose, lactate, acetate, 3-hydroxybutyrate, and creatine in bronchoalveolar lavage fluid. In serum, increased levels of phosphatidylcholine, oleamide, sphinganine, hexadecenal and lysine, and decreased levels of lyso-phosphatidylcholine and sphingosine were identified by MS. CONCLUSIONS: This pilot study suggests that VILI is characterized by a particular metabolic profile that can be identified by MRS and MS. The metabolic profile, though preliminary and pending confirmation in larger data sets, suggests alterations in energy and membrane lipids.SUPPLEMENTAL DIGITAL CONTENT IS AVAILABLE IN THE TEXT.

Comparison of the Berlin definition for acute respiratory distress syndrome with autopsy.

RATIONALE: A revised definition of clinical criteria for acute respiratory distress syndrome (ARDS), the Berlin definition, was recently established to classify patients according to their severity. OBJECTIVE: To evaluate the accuracy of these clinical criteria using diffuse alveolar damage (DAD) at autopsy as the reference standard. METHODS: All patients who died and had a clinical autopsy in our intensive care unit over a 20-year period (1991-2010) were included. Patients with clinical criteria for ARDS were identified from the medical charts and were classified as mild, moderate, or severe according to the Berlin definition using PaO2/FiO2 oxygenation criteria. Microscopic analysis from each pulmonary lobe was performed by two pathologists. MEASUREMENTS AND MAIN RESULTS: Among 712 autopsies analyzed, 356 patients had clinical criteria for ARDS at time of death, classified as mild (n = 49, 14%), moderate (n = 141, 40%), and severe (n = 166, 46%). Sensitivity was 89% and specificity 63% to identify ARDS using the Berlin definition. DAD was found in 159 of 356 (45%) patients with clinical criteria for ARDS (in 12, 40, and 58% of patients with mild, moderate, and severe ARDS, respectively). DAD was more frequent in patients who met clinical criteria for ARDS during more than 72 hours and was found in 69% of those with severe ARDS for 72 hours or longer. CONCLUSIONS: Histopathological findings were correlated to severity and duration of ARDS. Using clinical criteria the revised Berlin definition for ARDS allowed the identification of severe ARDS of more than 72 hours as a homogeneous group of patients characterized by a high proportion of DAD.

Clinical diagnoses and autopsy findings: discrepancies in critically ill patients*.

OBJECTIVES: To determine the proportion of clinical errors by comparing clinical and pathological diagnoses, and to evaluate changes of errors over time. DESIGN: We conducted a prospective study of all consecutive autopsies performed on patients who died in the intensive care unit of the Hospital Universitario de Getafe, Madrid, Spain, between January 1982 and December 2007. The diagnostic errors were classified in two categories: class I errors that were major misdiagnoses with direct impact on therapy, and class II diagnostic errors which comprised major unexpected findings that probably would not have changed therapy. MAIN RESULTS: Of 2,857 deaths during the study period, autopsies were performed in 866 patients (30.3%). Autopsy reports were available in 834 patients, of whom 63 (7.5%) had class I errors and 95 (11.4%) had type II errors. The most frequently missed diagnoses were pulmonary embolism, pneumonia, secondary peritonitis, invasive aspergillosis, endocarditis and myocardial infarction. The autopsy did not determine the cause of death in 22 patients (2.6%). Our rate of diagnostic discrepancy remained relatively constant over time, and the conditions leading to discrepancies have slightly changed, with pneumonia showing a decline in diagnostic accuracy in the last years. CONCLUSIONS: This study found significant discrepancies in 18.5% of patients who underwent autopsy, 7.5% of them were diagnoses with impact on therapy and outcome. This reinforces the importance of the postmortem examination in confirming diagnostic accuracy and improving the quality of care of critically ill patients.

Different patterns of pulmonary vascular disease induced by type 1 diabetes and moderate hypoxia in rats.

Although type 1 and type 2 diabetes are strongly associated with systemic cardiovascular morbidity, the relationship with pulmonary vascular disease had been almost disregarded until recent epidemiological data revealed that diabetes might be a risk factor for pulmonary hypertension. Recent experimental studies suggest that diabetes induces changes in lung function insufficient to elevate pulmonary pressure. The aim of this study was to assess the effects of diabetes on the sensitivity to other risk factors for pulmonary hypertension. We therefore analysed the effects of the combination of diabetes with exposure to moderate hypoxia on classical markers of pulmonary hypertension. Control (saline-treated) and diabetic (70 mg kg(-1) streptozotocin-treated) male Wistar-Kyoto rats were followed for 4 weeks and exposed to normoxia or moderate normobaric hypoxia (14%) for another 2 weeks. Hypoxia, but not diabetes, strongly reduced voltage-gated potassium currents, whereas diabetes, but not hypoxia, induced pulmonary artery endothelial dysfunction. Both factors independently induced pulmonary vascular remodelling and downregulated the lung bone morphogenetic protein receptor type 2. However, diabetes, but not hypoxia, induced pulmonary infiltration of macrophages, which was markedly increased when both factors were combined. Diabetes plus hypoxia induced a modest increase in diastolic and mean pulmonary artery pressure and right ventricular weight, while each of the two factors alone had no significant effect. The pattern of changes in markers of pulmonary hypertension was different for moderate hypoxia and diabetes, with no synergic effect except for macrophage recruitment, and the combination of both factors was required to induce a moderate elevation in pulmonary arterial pressure.

Severe acute respiratory failure secondary to acute fibrinous and organizing pneumonia requiring mechanical ventilation: a case report and literature review.

A 27-year-old woman was admitted to our ICU with acute hypoxemic respiratory failure and criteria for ARDS. Despite an F(IO(2)) of 1.0 and a lung protective strategy, the patient died on day 15 without any improvement. The relatives gave consent for post-mortem analysis. The histopathologic study of the lung showed findings typical of an acute fibrinous and organizing pneumonia. Apropos of this case we performed a PubMed search. We found 13 articles, including a total of 29 patients. Acute fibrinous and organizing pneumonia is an unusual cause of acute lung injury. The diagnostic criterion is histopathologic. There is little information regarding the pathophysiology of this illness. Important questions remain regarding this disease, including predisposing factors and management. Patients who require mechanical ventilation have poor outcomes.

Rats surviving injurious mechanical ventilation show reversible pulmonary, vascular and inflammatory changes.

OBJECTIVE: To describe the time course of the changes in pulmonary and vascular function, and systemic inflammation induced by injurious mechanical ventilation. DESIGN: Experimental study in an animal model of ventilator-induced lung injury. SETTING: Animal research laboratory. METHODS: Anesthetized male adult Sprague-Dawley rats were ventilated with VT 9 ml/kg and PEEP 5 cmH2O, or VT 35 ml/kg and zero PEEP for 1 h, and were killed. Other rats received ventilation for 1 h with high VT, to observe survival (n=36), or to be monitored and killed at different points in time (24, 72 and 168 h; n=7 in each group). Blood samples for measuring biochemical parameters were obtained. Post-mortem, a bronchoalveolar lavage (BAL) was performed, the aorta and pulmonary microvessels were isolated to examine ex-vivo vascular responses and pulmonary slices were examined (light microscopy). MEASUREMENTS AND RESULTS: Mortality in rats ventilated with high VT was 19 of 36 (54%). Mechanical ventilation was associated with hypotension, hypoxaemia and membrane hyaline formation. AST, ALT, IL-6, MIP-2 serum and BAL fluid concentrations, as well as VEGF BAL fluid concentration, were increased in rats ventilated with high VT. Lung injury score was elevated. Aortic vascular responses to acetylcholine and norepinephrine, and microvascular responses to acetylcholine, were impaired. These changes resolved by 24-72 h. CONCLUSIONS: Injurious ventilation is associated with respiratory and vascular dysfunction, accompanied by pulmonary and systemic inflammation. The survival rate was about 50%. In survivors, most induced changes completely normalized by 24-72 h after the insult.

Aging increases the susceptibility to injurious mechanical ventilation.

OBJECTIVE: To test the hypothesis that aging increases the susceptibility to organ dysfunction and systemic inflammation induced by injurious mechanical ventilation. DESIGN AND SETTING: Experimental study in an animal model of ventilator-induced lung injury in the animal research laboratory in a university hospital. METHODS: Young (3-4 months old) and old (22-24 months old) anesthetized Wistar rats were ventilated for 60 min with a protective lung strategy (VT=9 ml/kg and PEEP=5 cm H2O, control) or with an injurious strategy (VT=35 ml/kg and PEEP=0 cm H2O, over-ventilated; n=6 for each group). MEASUREMENTS AND RESULTS: Mean arterial pressure and airway pressures (PAW) were monitored. Arterial blood gases and serum AST, ALT, lactate, and IL-6 were measured. Vascular rings from the thoracic aorta were mounted in organ baths for isometric tension recording. We studied relaxations induced by acetylcholine (10 nM-10 microM) in norepinephrine-precontracted rings, and contractions induced by norepinephrine (1 nM-10 microM) in resting vessels. Lungs were examined by light microscopy. Injurious ventilation in young rats was associated with hypoxemia, lactic metabolic acidosis, increased serum AST, hypotension, impairment in norepinephrine and acetylcholine-induced vascular responses ex vivo and hyaline membrane formation. The high-VT induced hypotension, increase in mean PAW, AST, and IL-6, and the impairment in acetylcholine-induced responses were significantly more marked in aged than in young rats. CONCLUSIONS: Elderly rats showed increased susceptibility to injurious mechanical ventilation-induced pulmonary injury, vascular dysfunction, and systemic inflammation.

Effects of vascular flow and PEEP in a multiple hit model of lung injury in isolated perfused rabbit lungs.

BACKGROUND: High vascular flow aggravates lung damage in animal models of ventilator-induced lung injury. Positive end-expiratory pressure (PEEP) can attenuate ventilator-induced lung injury, but its continued effectiveness in the setting of antecedent lung injury is unclear. The objective of the present study was to evaluate whether the application of PEEP diminishes lung injury induced by concurrent high vascular flow and high alveolar pressures in normal lungs and in a preinjury lung model. METHODS: Two series of experiments were performed. Fifteen sets of isolated rabbit lungs were randomized into three groups (n = 5): low vascular flow/low PEEP; high vascular flow/low PEEP, and high vascular flow/high PEEP. Subsequently, the same protocol was applied in an additional 15 sets of isolated rabbit lungs in which oleic acid was added to the vascular perfusate to produce mild to moderate lung injury. All lungs were ventilated with peak airway pressure of 30 cm H2O for 30 minutes. Outcome measures included frequency of gross structural failure, pulmonary hemorrhage, edema formation, changes in static compliance, pulmonary vascular resistance, and pulmonary ultrafiltration coefficient. RESULTS: In the context of high vascular flow, application of a moderate level of PEEP reduced pulmonary rupture, edema formation, and lung hemorrhage. The protective effects of PEEP were not observed in lungs concurrently injured with oleic acid. CONCLUSIONS: Under these experimental conditions, PEEP attenuates lung injury in the setting of high vascular flow. The protective effect of PEEP is lost in a two-hit model of lung injury.

Comparison of clinical criteria for the acute respiratory distress syndrome with autopsy findings.

BACKGROUND: The American-European Consensus Conference definition for the acute respiratory distress syndrome (ARDS) has never been validated. OBJECTIVE: To compare clinical criteria for ARDS with autopsy findings. DESIGN: Independent comparison of autopsy findings with clinical characteristics retrospectively abstracted from medical records. SETTING: Tertiary medical-surgical intensive care unit. PARTICIPANTS: 382 patients who underwent clinical autopsy. MEASUREMENTS: Sensitivity, specificity, and likelihood ratios for clinical criteria were calculated in 3 cohorts by using diffuse alveolar damage at autopsy as the reference standard. The 3 cohorts were 1) all patients, 2) patients with any risk factor for ARDS, and 3) patients who were separated according to their pulmonary or extrapulmonary risk factors. RESULTS: 127 patients (33%) met the clinical criteria, and 112 (29%) had diffuse alveolar damage. In all patients, the sensitivity of the clinical definition was 75% (95% CI, 66% to 82%) and the specificity was 84% (CI, 79% to 88%). In 284 patients with risk factors, the sensitivity was 76% (CI, 67% to 83%) and the specificity was 75% (CI, 68% to 81%). Compared with patients with pulmonary risk factors, patients with extrapulmonary risk factors had significantly higher sensitivity (61% vs. 85%; P = 0.009) and the specificity did not statistically significantly differ (69% vs. 78%; P > 0.2). LIMITATIONS: Only patients who died and underwent autopsy could be included in this study, so these results may not apply to less severe cases of ARDS. CONCLUSIONS: In a series of autopsy patients, the accuracy of the American-European Consensus Conference definition of ARDS was only moderate. The definition was more accurate for patients with extrapulmonary risk factors than for patients with pulmonary risk factors.

Inhibition of Nitro-Oxidative Stress Attenuates Pulmonary and Systemic Injury Induced by High-Tidal Volume Mechanical Ventilation.

Mechanisms contributing to pulmonary and systemic injury induced by high tidal volume (VT) mechanical ventilation are not well known. We tested the hypothesis that increased peroxynitrite formation is involved in organ injury and dysfunction induced by mechanical ventilation. Male Sprague-Dawley rats were subject to low- (VT, 9 mL/kg; positive end-expiratory pressure, 5 cmH2O) or high- (VT, 25 mL/kg; positive end-expiratory pressure, 0 cmH2O) VT mechanical ventilation for 120 min, and received 1 of 3 treatments: 3-aminobenzamide (3-AB, 10 mg/kg, intravenous, a poly adenosine diphosphate ribose polymerase [PARP] inhibitor), or the metalloporphyrin manganese(III) tetrakis(1-methyl-4-pyridyl)porphyrin (MnTMPyP, 5 mg/kg intravenous, a peroxynitrite scavenger), or no treatment (control group), 30 min before starting the mechanical ventilation protocol (n = 8 per group, 6 treatment groups). We measured mean arterial pressure, peak inspiratory airway pressure, blood chemistry, and gas exchange. Oxidation (fluorescence for oxidized dihydroethidium), protein nitration (immunofluorescence and Western blot for 3-nitrotyrosine), PARP protein (Western blot) and gene expression of the nitric oxide (NO) synthase (NOS) isoforms (quantitative real-time reverse transcription polymerase chain reaction) were measured in lung and vascular tissue. Lung injury was quantified by light microscopy. High-VT mechanical ventilation was associated with hypotension, increased peak inspiratory airway pressure, worsened oxygenation; oxidation and protein nitration in lung and aortic tissue; increased PARP protein in lung; up-regulation of NOS isoforms in lung tissue; signs of diffuse alveolar damage at histological examination. Treatment with 3AB or MnTMPyP attenuated the high-VT mechanical ventilation-induced changes in pulmonary and cardiovascular function; down-regulated the expression of NOS1, NOS2, and NOS3; decreased oxidation and nitration in lung and aortic tissue; and attenuated histological changes. Increased peroxynitrite formation is involved in mechanical ventilation-induced pulmonary and vascular dysfunction.

Chronology of histological lesions in acute respiratory distress syndrome with diffuse alveolar damage: a prospective cohort study of clinical autopsies.

BACKGROUND: Diffuse alveolar damage is the histological hallmark of acute respiratory distress syndrome (ARDS). However, the chronology of histological lesions is not well established. We aimed to determine the time to onset of exudative or proliferative changes and end-stage fibrosis in ARDS. METHODS: We analysed all patients who died between Jan 1, 1991, and Dec 31, 2010, in the intensive-care unit at the Hospital Universitario de Getafe, Madrid, Spain, and who had a clinical autopsy. Patients had to have clinical criteria for ARDS at time of death and histological features of diffuse alveolar damage at autopsy examination. Capillary congestion and intra-alveolar oedema characterised the exudative phase whereas proliferation of alveolar cell type 2 or fibroblasts, or fibrosis characterised the proliferative phase. FINDINGS: We analysed 159 patients. The prevalence of exudative changes decreased over time, being reported in 74 (90%) of 82 patients with ARDS of less than 1 week duration, 40 (74%) of 54 patients with disease of 1-3 week duration, and only four (17%) of 23 patients with disease of longer than 3 weeks' duration (p<0·0001). The incidence of proliferative changes increased over time, and was reported in 44 (54%) of 82 patients with ARDS of less than 1-week duration, 42 (78%) of 54 patients with disease duration of 1-3 weeks, and 23 (100%) of 23 patients with disease duration longer than 3 weeks (p<0·0001). Fibrosis was noted in three (4%) of 82 patients with disease of less than 1 week duration, 13 (24%) of 54 patients with disease of 1-3-weeks' duration, and 14 (61%) of 23 patients with disease longer than 3-week duration (p<0·0001). Fibrosis was more frequent in ARDS of pulmonary origin than in that of extrapulmonary origin. INTERPRETATION: Histological features of the lungs were related to duration of ARDS. Within the first week of evolution, exudative changes were predominant and fibrosis was rarely noted. Beyond the third week of evolution, proliferative changes were noted in all patients and fibrosis in two-thirds of them. Treatments with a potential effect on inflammation or fibrosis, or both, should probably focus on the first week after the onset of ARDS. FUNDING: None.

Transcriptional profiling and genotyping of degraded nucleic acids from autopsy tissue samples after prolonged formalin fixation times.

BACKGROUND: Samples used for genotyping and transcription studies are obtained and conserved in very specific conditions. The possibility to use autopsy tissue samples, which contain nucleic acids of very poor quality, would open new possibilities for genetic studies. METHODS: We have used liver tissue samples from autopsy cases to (i) determine its quality; (ii) study gene expression of 13 genes involved in different cell processes, before and after cDNA pre-amplification (quantitative reverse transcriptase polymerase chain reaction); and (iii) analyze the presence of 2 common polymorphisms of relevance for illness (ACE I/D genotype by PCR amplification, and TNF-α promoter gene polymorphism, by DNA sequencing). RESULTS: Samples were grouped according to different buffered formalin fixation times (group 1, <15 days; group 2, 60-90 days; group 3, 150-180 days; group 4, 240-270 days). Nucleic acids showed a time-dependent degradation. The expression of 13 genes could be studied in all cases from groups 1 and 2, only 7 from group 3 and none from group 4. cDNA preamplification allowed the study of all genes in all samples. DNA genotyping for ACE and TNF-α promoter region was possible in all cases. CONCLUSIONS: We conclude that nucleic acids extracted from autopsy specimens after prolonged periods of time in formalin were of sufficient quality to study gene expression and genotyping using currently available methodology and cDNA pre-amplification.

A metabolomic approach for diagnosis of experimental sepsis.

BACKGROUND: The search for reliable diagnostic biomarkers of sepsis remains necessary. Assessment of global metabolic profiling using quantitative nuclear magnetic resonance (NMR)-based metabolomics offers an attractive modern methodology for fast and comprehensive determination of multiple circulating metabolites and for defining the metabolic phenotype of sepsis. OBJECTIVE: To develop a novel NMR-based metabolomic approach for diagnostic evaluation of sepsis. METHODS: Male Sprague-Dawley rats (weight 325-375 g) underwent cecal ligation and puncture (n = 14, septic group) or sham procedure (n = 14, control group) and 24 h later were euthanized. Lung tissue, bronchoalveolar lavage (BAL) fluid, and serum samples were obtained for (1)H NMR and high-resolution magic-angle spinning analysis. Unsupervised principal components analysis was performed on the processed spectra, and a predictive model for diagnosis of sepsis was constructed using partial least-squares discriminant analysis. RESULTS: NMR-based metabolic profiling discriminated characteristics between control and septic rats. Characteristic metabolites changed markedly in septic rats as compared with control rats: alanine, creatine, phosphoethanolamine, and myoinositol concentrations increased in lung tissue; creatine increased and myoinositol decreased in BAL fluid; and alanine, creatine, phosphoethanolamine, and acetoacetate increased whereas formate decreased in serum. A predictive model for diagnosis of sepsis using these metabolites classified cases with sensitivity and specificity of 100%. CONCLUSIONS: NMR metabolomic analysis is a potentially useful technique for diagnosis of sepsis. The concentrations of metabolites involved in energy metabolism and in the inflammatory response change in this model of sepsis.

Accuracy of clinical definitions of ventilator-associated pneumonia: comparison with autopsy findings.

METHODS: We studied patients requiring mechanical ventilation for more than 48 hours who died in the intensive care unit and whose bodies were autopsied. We evaluated 3 clinical definitions of ventilator-associated pneumonia: loose definition, defined as chest radiograph infiltrates and 2 of 3 clinical criteria (leukocytosis, fever, purulent respiratory secretions); rigorous definition, defined as chest radiograph infiltrates and all of the clinical criteria; and a clinical pulmonary infection score higher than 6 points. Sensitivity, specificity, and likelihood ratios were calculated by using pathology pattern as criterion standard. RESULTS: One hundred forty-two (56%) of the 253 patients included had histological criteria of pneumonia. Patients who met the clinical criteria of ventilator-associated pneumonia were 163 (64%) for the loose definition, 32 (13%) for the rigorous definition, and 109 (43%) for the clinical pulmonary infection score. The operative indexes (sensitivity and specificity) of each definition were as follows: loose definition, 64.8% and 36%; rigorous definition, 91% and 15.5%; and clinical pulmonary infection score higher than 6, 45.8% and 60.4%. The addition of microbiological data to the clinical definitions increased the specificity and decreased the sensitivity but not significantly. CONCLUSIONS: Accuracy of 3 commonly used clinical definitions of ventilator-associated pneumonia was poor taking the autopsy findings as reference standard.

High-tidal volume ventilation aggravates sepsis-induced multiorgan dysfunction in a dexamethasone-inhibitable manner.

High-tidal volume (Vt) ventilation induces lung injury and systemic inflammation, and small doses of endotoxin have been shown to increase the susceptibility to ventilation-induced lung injury. We studied whether high-Vt ventilation increases organ injury in a model of bacterial sepsis and whether an anti-inflammatory treatment averts those changes. Anesthetized rats, monitored with an arterial catheter and a blood flow probe in the aorta, were assigned to one of four different groups: nonseptic low-Vt group (Vt = 9 mL/kg, positive end-expiratory pressure = 8 cm H2O, control group), septic low-Vt group, septic overventilated group (Vt = 35 mL/kg, positive end-expiratory pressure = 0), and septic overventilated group pretreated with dexamethasone (6 mg/kg i.p., 30 min before mechanical ventilation). Rats were ventilated for 75 min. Septic rats had undergone cecal ligation and puncture 48 h before mechanical ventilation. We measured hemodynamics, lung mechanics, blood chemistry and gas exchange, liver and heart expression of cyclooxygenase 2 (COX-2) and iNOS (reverse transcriptase-polymerase chain reaction), and lung histopathology. Septic rats showed metabolic acidosis, hyperlactatemia, lung and liver injury, increased liver and heart COX-2, and liver iNOS expression. High-Vt ventilation of septic rats was associated with more marked liver injury and heart COX-2 upregulation, as well as lung inflammation and dysfunction (impaired oxygenation, increased bronchoalveolar lavage fluid protein and IL-6 concentration, decreased thoracic system compliance) and systemic hypotension. All inflammatory changes, as well as pulmonary and vascular dysfunctions, were abrogated by dexamethasone. High-Vt ventilation in bacterial sepsis upregulates the inflammatory response and aggravates the sepsis-induced cardiovascular, pulmonary, and liver dysfunction. Dexamethasone averts mechanical ventilation-induced changes under conditions of bacterial sepsis.

Role of free radicals in vascular dysfunction induced by high tidal volume ventilation.

OBJECTIVE: To demonstrate that increased formation of reactive oxygen (ROS) and nitrogen species (RNS) is involved in VILI-induced vascular dysfunction. METHODS: Male Sprague-Dawley anesthetized rats were ventilated for 60 min using low V(T) ventilation [V(T) 9 ml/kg, positive end-expiratory pressure (PEEP) 5 cmH(2)O, n = 18], and high V(T) ventilation (V(T) 35 ml/kg, zero PEEP, n = 18). Arterial pressure and respiratory system mechanics were monitored. Blood samples for the determination of arterial blood gases and lactate concentration were drawn. Vascular rings from the thoracic aortae were mounted in organ baths for isometric tension recording. We studied endothelium-dependent relaxation in norepinephrine-precontracted rings (acetylcholine, 10 nM-10 microM) and contraction induced by norepinephrine (1 nM-10 microM) in resting vessels. Vascular rings were preincubated for 30 min with Zn-Mn-SOD (100 u/ml) or tempol (10(-4) M) (extracellular and intracellular superoxide scavengers, respectively) or MnTMPyP (10(-5) M) (a superoxide and peroxynitrite scavenger). The presence of superoxide and nitrotyrosine in aortic rings was evaluated by immunofluorescence. RESULTS: High V(T) ventilation induced hypotension, systemic acidosis, hypoxemia and hyperlactatemia, as well as impairment in acetylcholine and norepinephrine-induced responses in vitro. Responses to acetylcholine were improved by tempol (P = 0.004) and completely corrected (P < 0.001) by MnTMPyP. Responses to norepinephrine were also improved by treatment with tempol (P < 0.001) and MnTMPyP (P < 0.001). However, Zn-Mn-SOD did not improve acetylcholine- or norepinephrine-induced responses. Immunostaining for both superoxide and nitrotyrosine was increased in aortic rings from the high V(T) group. CONCLUSIONS: Our data support a role for intracellular ROS and peroxynitrite in the high V(T) ventilation-induced vascular dysfunction.

Ventilation-induced lung injury in rats is associated with organ injury and systemic inflammation that is attenuated by dexamethasone.

OBJECTIVE: To determine whether mechanical ventilation using high tidal volume is associated with nonpulmonary organ dysfunction that can be attenuated by dexamethasone. DESIGN: Prospective randomized animal intervention study. SETTING: Animal care facility in a university hospital. SUBJECTS: Sedated and tracheostomized male Sprague-Dawley rats. INTERVENTIONS: Three groups of rats were ventilated with different strategies: tidal volume = 9 mL/kg, positive end-expiratory pressure = 8 cm H(2)O, control group (C); tidal volume = 35 mL/kg, positive end-expiratory pressure = 0 cm H(2)O, overventilated group (OV); and tidal volume = 35 mL/kg, positive end-expiratory pressure = 0 cm H(2)O, plus administration of 6 mg/kg dexamethasone intraperitoneally (OV + dexamethasone). All rats were ventilated for 75 mins with respiratory rate = 70 breaths/min, FIO(2) = 0.35, and plateau time = 0. MEASUREMENTS AND MAIN RESULTS: Mean arterial pressure and peak airway pressure were monitored. We measured arterial blood gases, aspartate aminotransferase, alanine aminotransferase, lactate, nitrates and nitrites, tumor necrosis factor-alpha, and interleukin-6 serum concentration. Lung slices were prepared for blind histologic examination. Heart tissue was analyzed for cyclooxygenase-1 and -2 expression (reverse transcription-polymerase chain reaction). Compared with the C group, the OV group showed hypotension; worsened gas exchange; increased aspartate aminotransferase, lactate, nitrates and nitrites, and interleukin-6 serum concentrations; and hyaline membrane formation in the lungs, as well as increased cyclooxygenase-1 and cyclooxygenase-2 expression in the heart. Dexamethasone prevented the pulmonary and cardiovascular injury and attenuated the increase in aspartate aminotransferase, nitrates and nitrites, interleukin-6, and cyclooxygenase-1 and cyclooxygenase-2 expression. CONCLUSIONS: High tidal volume ventilation induces cardiovascular, pulmonary, and liver injury as well as a systemic proinflammatory response. These changes are attenuated by dexamethasone, suggesting that inflammatory rather than purely hemodynamic mechanisms are involved in the changes induced by high tidal volume ventilation.

Contributions of vascular flow and pulmonary capillary pressure to ventilator-induced lung injury.

OBJECTIVE: To evaluate the influence of vascular flow on ventilator-induced lung injury independent of vascular pressures. DESIGN: Laboratory study. SETTING: Hospital laboratory. SUBJECTS: Thirty-two New Zealand White rabbits. INTERVENTIONS: Thirty-two isolated perfused rabbit lungs were allocated into four groups: low flow/low pulmonary capillary pressure; high flow/high pulmonary capillary pressure; low flow/high pulmonary capillary pressure, and high flow/low pulmonary capillary pressure. All lungs were ventilated with peak airway pressure 30 cm H2O and positive end-expiratory pressure 5 cm H2O for 30 mins. MEASUREMENTS AND MAIN RESULTS: Outcome measures included frequency of gross structural failure (pulmonary rupture), pulmonary hemorrhage, edema formation, changes in lung compliance, pulmonary vascular resistance, and pulmonary ultrafiltration coefficient. Lungs exposed to high pulmonary vascular flow ruptured more frequently, displayed more hemorrhage, developed more edema, suffered larger decreases in compliance, and had larger increases in vascular resistance than lungs exposed to low vascular flows (p < .05 for each pairwise comparison between groups). CONCLUSIONS: These findings suggest that high pulmonary vascular flows might exacerbate ventilator-induced lung injury independent of their effects on pulmonary vascular pressures.