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 V(T) 9[Symbol: see text]ml/kg and PEEP 5[Symbol: see text]cm[Symbol: see text]H(2)O, or V(T) 35[Symbol: see text]ml/kg and zero PEEP for 1[Symbol: see text]h, and were killed. Other rats received ventilation for 1[Symbol: see text]h with high V(T), to observe survival (n[Symbol: see text]=[Symbol: see text]36), or to be monitored and killed at different points in time (24, 72 and 168[Symbol: see text]h; n[Symbol: see text]=[Symbol: see text]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 V(T) 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 V(T). 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[Symbol: see text]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[Symbol: see text]h after the insult.

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[Symbol: see text]months old) and old (22-24[Symbol: see text]months old) anesthetized Wistar rats were ventilated for 60[Symbol: see text]min with a protective lung strategy (V(T)[Symbol: see text]=[Symbol: see text]9[Symbol: see text]ml/kg and PEEP[Symbol: see text]=[Symbol: see text]5[Symbol: see text]cm H(2)O, control) or with an injurious strategy (V(T)[Symbol: see text]=[Symbol: see text]35[Symbol: see text]ml/kg and PEEP[Symbol: see text]=[Symbol: see text]0[Symbol: see text]cm H(2)O, overventilated; n[Symbol: see text]=[Symbol: see text]6 for each group). MEASUREMENTS AND RESULTS: Mean arterial pressure and airway pressures (P(AW)) 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[Symbol: see text]nM-10[Symbol: see text]muM) in norepinehrine-precontracted rings, and contractions induced by norepinephrine (1[Symbol: see text]nM-10[Symbol: see text]muM) 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-V(T) induced hypotension, increase in mean P(AW), 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.

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 overventiled 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, hiperlactatemia, 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.

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 H2O, control group (C); tidal volume = 35 mL/kg, positive end-expiratory pressure = 0 cm H2O, overventilated group (OV); and tidal volume = 35 mL/kg, positive end-expiratory pressure = 0 cm H2O, plus administration of 6 mg/kg dexamethasone intraperitoneally (OV + dexamethasone). All rats were ventilated for 75 mins with respiratory rate = 70 breaths/min, Fio2 = 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.

BACKGROUND:: Experimental studies have shown that mechanical ventilation using high tidal volumes (VT) damages the lungs, causing pulmonary edema. We tested the hypothesis that high VT ventilation in rats induces major vascular dysfunction. METHODS:: Healthy Sprague-Dawley rats, weighing (mean +/- SD) 340 +/- 15 g, were ventilated with either VT = 9 mL/kg and positive end-expiratory pressure (PEEP)= 8 (n = 8) or VT = 35 mL/kg and PEEP = 0 (n = 8). The high VT used in the injurious ventilation group is in the VT range used in other studies to induce lung damage in a short period of time in rats. Lungs were removed for examination under light microscopy and vascular rings from the thoracic aorta were studied for isometric tension recording. RESULTS:: Relaxations to acetylcholine (p < 0.001) and sodium nitroprusside (p < 0.05) and contractions to norepinephrine were markedly decreased (p < 0.001) in the high VT group, as compared with the low VT group. CONCLUSION:: Injurious mechanical ventilation in normal rats is associated with vascular dysfunction characterized by decreased relaxation to an endothelium-dependent vasodilator and to a nitrous oxide donor and by decreased response to norepinephrine.

BACKGROUND:: High tidal volume (VT) mechanical ventilation was shown to induce organ injury other than lung injury and systemic inflammation in animal models of ventilator-induced lung injury. The authors aimed to explore whether high VT mechanical ventilation per se induces early oxidative stress and inflammation in the diaphragm, limb muscles, and lungs of healthy rats exposed to ventilator-induced lung injury. METHODS:: Protein carbonylation and nitration, antioxidants (immunoblotting), and inflammation (immunohistochemistry) were evaluated in the diaphragm, gastrocnemius, soleus, tibialis anterior, and lungs of mechanically ventilated healthy rats and in nonventilated control animals (n = 8/group) for 1 h, using two different strategies (moderate VT [VT = 9 ml/kg] and high VT [VT = 35 ml/kg]). RESULTS:: The main findings are summarized as follows: compared with controls,(1) the diaphragms and gastrocnemius of high-VT rats exhibited a decrease in reactive carbonyls,(2) the soleus and tibialis of high- and moderate-VT rodents showed a reduction in reactive carbonyls and malondialdehyde-protein adducts,(3) the lungs of high-VT rats exhibited a significant rise in malondialdehyde-protein adducts,(4) the soleus and tibialis of both high- and moderate-VT rats showed a reduction in protein nitration,(5) the lungs of high- and moderate-VT rats showed a reduction in antioxidant enzyme levels, but not in the muscles, and (6) the diaphragms and gastrocnemius of all groups exhibited very low inflammatory cell counts, whereas the lungs of high-VT rats exhibited a significant increase in inflammatory infiltrates. CONCLUSIONS:: Although oxidative stress and inflammation increased in the lungs of rats exposed to high VT, the diaphragm and limb muscles exhibited a decline in oxidative stress markers and very low levels of cellular inflammation.

BACKGROUND:: It has been proposed that vasodilatory therapy may increase microcirculatory blood flow and improve tissue oxygenation in septic shock. OBJECTIVES:: To study the effects of levosimendan in systemic and splanchnic hemodynamics in a porcine model of septic shock. DESIGN:: Randomized animal controlled study. SETTING:: Animal research facility in a University Hospital. SUBJECTS:: Anesthetized pigs were monitored with a pulmonary artery catheter and an ultrasonic blood flow probe in the portal vein for measurement of systemic (QTOT) and portal blood flows (QPOR), and with a tonometer placed in the small intestine for measurement of the intramucosal-arterial pCO2 gap (DeltapCO2). Three groups of pigs were studied: nonseptic (n=7), septic (n=7), and septic treated with levosimendan (n=7). INTERVENTIONS:: Levosimendan was administered intravenously at t=-10 min (200mug/kg in iv bolus followed by 200mug/kg*h). Sepsis was induced at t=0 min by the administration of live E coli. Vascular reactivity was tested by the hemodynamic response to noradrenaline. MEASUREMENTS AND MAIN RESULTS:: Levosimendan markedly attenuated the sepsis-induced increase in pulmonary vascular resistance, decrease in QPOR/QTOT, oliguria, impairment in oxygenation, hyperkalemia and the widened DeltapCO2. Systemic blood pressure and vascular resistance did not differ as compared to the septic 2 untreated group. Responses to noradrenaline significantly improved in animals treated with levosimendan. CONCLUSIONS:: Treatment with levosimendan in this animal model of sepsis attenuated pulmonary vasoconstriction, and improved portal blood flow, intestinal mucosal oxygenation, pulmonary function, and vascular reactivity.

BACKGROUND: Hemoglobin (Hb) induces vasoconstriction by heme group binding nitric oxide in an irreversible fashion. Recent in vitro studies indicate that the thiol groups in Hb reversibly bind nitric oxide and participate in trans-nitrosylation reactions with other thiols. Sepsis is a pathophysiologic state characterized by vasodilation mediated, at least in part, by an excessive release of nitric oxide. The role of nitrosothiols (RSNOs) in these changes is unknown. OBJECTIVES: We tested the following in a porcine model of sepsis:(i) whether glutathione (GSH) reverses the hemodynamic effects of Hb;(ii) whether GSH induces an increase in blood flow in sepsis;(iii) whether RSNO plasma concentration increases in sepsis and is related to hypotension. DESIGN: Nonrandomized animal controlled study. SETTING: Animal research facility in a university hospital. SUBJECTS: Anesthetized pigs were monitored with a pulmonary artery catheter and ultrasonic blood flow probes in the mesenteric artery and the portal vein for measurement of systemic, mesenteric, and portal blood flows (Q(TOT), Q(MES), and Q(POR), respectively). Four groups of pigs were studied: nonseptic, septic, nonseptic treated with Hb (stroma-free purified porcine hemoglobin), and septic treated with Hb (n = 6 in each group). INTERVENTIONS: Sepsis was induced at 0 min by the administration of live Escherichia coli. Hb (400 mg/kg/hr) was administered at 240 mins, followed by glutathione (1 g iv). MEASUREMENTS AND MAIN RESULTS: Hb induced a pressor response and a decrease in Q(TOT), Q(MES), and Q(POR). Glutathione reversed the effects of Hb on Q(MES) and Q(POR). In septic pigs not treated with Hb, GSH induced an increase in Q(POR). RSNO plasma concentration increased after the induction of sepsis and correlated significantly with blood pressure. CONCLUSIONS: These results indicate the reversibility of the effects of Hb by GSH, probably by interactions between nitric oxide and the reduced sulfhydryl groups in Hb, and suggest a role of RSNOs in the cardiovascular changes of sepsis.

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.

Acute lung injury (ALI) and acute respiratory distress syndrome (ARDS) have high incidence and mortality rates. Most of the recently introduced treatments have failed to improve the prognosis of patients with ALI or ARDS or to reduce mortality. Several studies have shown improved oxygenation in the prone position during mechanical ventilation in patients with ARDS. However, current evidence strongly suggests that placing ARDS patients in prone position does not improve survival or reduce the duration of mechanical ventilation. Therefore, though in clinical practice this position may improve refractory hypoxemia in patients with ARDS, there is no evidence to support its systematic use.