Variable positive end-expiratory pressure can maintain oxygenation in experimental acute respiratory distress syndrome induced by oleic acid in dogs

The use of positive end-expiratory pressure (PEEP) or lung recruitment maneuvers (RM) to improve oxygenation in acute respiratory distress syndrome (ARDS) is used but it may reduce cardiac output (CO). Intermittent PEEP may avoid these complications. Our objective was to determine if variable PEEP compared with constant PEEP is capable of maintaining arterial oxygenation and minimizing hemodynamic alterations with or without RM. Eighteen dogs with ARDS induced by oleic acid were randomized into three equal groups: group 1, low variable PEEP; group 2, high variable PEEP, and group 3, RM + high variable PEEP. All groups were submitted to constant PEEP, followed by variable PEEP (PEEP was increased from 5 to 10 cmH2O in group 1, and from 5 to 18 cmH2O in the other two groups). PaO2 was higher in group 3 (356.2 ± 65.4 mmHg) than in group 1 (92.7 ± 29.7 mmHg) and group 2 (228.5 ± 72.4 mmHg), P < 0.05. PaO2 was maintained during variable PEEP except in group 2 (318.5 ± 82.9 at constant PEEP to 228.5 ± 72.4 at variable PEEP). There was a reduction in CO in group 3 after RM (3.9 ± 1.1 before to 2.7 ± 0.5 L·min-1·(m2)-1 after; P < 0.05), but there was not any difference between constant and variable PEEP periods (2.7 ± 0.5 and 2.4 ± 0.7 L·min-1·(m2)-1; P > 0.05. Variable PEEP is able to maintain PaO2 when performed in combination with RM in dogs with ARDS. After RM, CO was reduced and there was no relevant difference between the variable and constant PEEP periods.

Effect of saline infusion for the maintenance of blood volume on pulmonary gas exchange during temporary abdominal aortic occlusion

We analyzed the effects of saline infusion for the maintenance of blood volume on pulmonary gas exchange in ischemia-reperfusion syndrome during temporary abdominal aortic occlusion in dogs. We studied 20 adult mongrel dogs weighing 12 to 23 kg divided into two groups: ischemia-reperfusion group (IRG, N = 10) and IRG submitted to saline infusion for the maintenance of mean pulmonary arterial wedge pressure between 10 and 20 mmHg (IRG-SS, N = 10). All animals were anesthetized and maintained on spontaneous ventilation. After obtaining baseline measurements, occlusion of the supraceliac aorta was performed by the inflation of a Fogarty catheter. After 60 min of ischemia, the balloon was deflated and the animals were observed for another 60 min of reperfusion. The measurements were made at 10 and 45 min of ischemia, and 5, 30, and 60 min of reperfusion. Pulmonary gas exchange was impaired in the IRG-SS group as demonstrated by the increase of the alveolar-arterial oxygen difference (21 ± 14 in IRG-SS vs 11 ± 8 in IRG after 60 min of reperfusion, P = 0.004 in IRG-SS in relation to baseline values) and the decrease of oxygen partial pressure in arterial blood (58 ± 15 in IRG-SS vs 76 ± 15 in IRG after 60 min of reperfusion, P = 0.001 in IRG-SS in relation to baseline values), which was correlated with the highest degree of pulmonary edema in morphometric analysis (0.16 ± 0.06 in IRG-SS vs 0.09 ± 0.04 in IRG, P = 0.03 between groups). There was also a smaller ventilatory compensation of metabolic acidosis after the reperfusion. We conclude that infusion of normal saline worsened the gas exchange induced by pulmonary reperfusion injury in this experimental model.

Pentoxifylline decreases tumor necrosis factor and interleukin-1 during high tidal volume

Tumor necrosis factor-alpha (TNF-alpha) is one of the most important proinflammatory cytokines which plays a central role in host defense and in the acute inflammatory response related to tissue injury. The major source of TNF-alpha are immune cells such as neutrophils and macrophages. We tested the hypothesis that pentoxifylline, a methylxanthine derivative, down-regulates proinflammatory cytokine expression during acute lung injury in rats. Male Wistar rats weighing 250 to 450 g were anesthetized ip with 50 mg/kg sodium thiopental and randomly divided into three groups: group 1 (N = 7): tidal volume (V T) = 7 ml/kg, respiratory rate (RR) = 50 breaths/min and normal saline infusion; group 2 (N = 7): V T = 42 ml/kg, RR = 9 breaths/min and normal saline infusion; group 3 (N = 7): V T = 42 ml/kg, RR = 9 breaths/min and pentoxifylline infusion. The animals were ventilated with an inspired oxygen fraction of 1.0, a positive end-expiratory pressure of 3 cmH2O, and normal saline or pentoxifylline injected into the left femoral vein. The mRNA of TNF-alpha rapidly increased in the lung tissue within 180 min of ventilation with a higher V T with normal saline infusion. The concentrations of inflammatory mediators were decreased in plasma and bronchoalveolar lavage (BAL) in the presence of higher V T with pentoxifylline infusion (TNF-alpha: plasma, 102.2 ± 90.9 and BAL, 118.2 ± 82.1; IL-1ß: plasma, 45.2 ± 42.7 and BAL, 50.2 ± 34.9, P < 0.05). We conclude that TNF-alpha produced by neutrophil influx may function as an alert signal in host defense to induce production of other inflammatory mediators

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

Aplicabilidade da escala de Torrington e Henderson / Applicability of the Torrington and Henderson scale

OBJETIVO: Validar a escala de Torrington e Henderson na estratificação do risco cirúrgico da nossa população, fornecendo a quantificação do mesmo. Tipo de estudo: coorte prospectivo longitudinal. Duração do estudo: 30 meses. MÉTODOS: Foram avaliados 1162 pacientes no pré-operatório de cirurgia geral eletiva no Ambulatório de Risco Cirúrgico da Disciplina de Pneumologia da EPM/Unifesp. De acordo com a escala de Torrington e Henderson os pacientes foram classificados no período pré-operatório em portadores de baixo (n=785), moderado (n=317) e alto risco (n=60) para a ocorrência de complicações pulmonares e óbito, no período pós-operatório. No pós-operatório realizou-se avaliação clínica diária dos mesmos até alta hospitalar ou óbito verificando-se a ocorrência das seguintes complicações pulmonares neste período: infecção respiratória aguda (pneumonia ou traqueobronquite),atelectasia, insuficiência respiratória aguda, entubação orotraqueal ou ventilação mecânica por mais de 48 horas e broncoespasmo. RESULTADOS: Complicações pulmonares no pós-operatório ocorreram em 6,1 por cento dos pacientes de baixo risco, 23,3 por cento nos de moderado e 35 por cento nos de alto risco (p < 0,05). O risco relativo de ocorrer complicações pulmonares foi de 3,8 vezes para os pacientes de moderado risco e de 5,7 vezes para os de alto risco em relação aos de baixo risco. A incidência de óbito de causa pulmonar no pós-operatório foi, respectivamente, de 1,7 por cento , 6,3 e 11,7 por cento entre os pacientes de baixo, moderado e de alto risco (p < 0,001). O risco relativo de óbito pulmonar foi de 3,7 vezes para os pacientes de moderado risco e de 6,9 vezes para aqueles de alto risco em relação aos de baixo risco. CONCLUSÃO: A escala de Torrington e Henderson é útil na estratificação do risco cirúrgico nesta população estudada.

Pulmonary emphysema induced by passive smoking: an experimental study in rats

We describe a short time model for inducing experimental emphysema in rats chronic tobacco smoke inhalation. Three groups of male Wistar rats (6 months old) were studied: controls (N = 8), rats intoxicated for 45 days (s-45, N = 7) or for 90 days (s-90, N = 8). The exposed animals were intoxicated 3 times a day (10 cigarettes per exposure period), 5 days a week. Pulmonary damage was assessed by means of functional tests and quantitative pathological examination of the airways and lung parenchyma. The s-45 and s-90 animals were similar in terms of functional residual capacity (FRC) corrected for body weight (FRC/kg) but both groups of smoking rats exhibited significantly higher FRC/kg values than the controls (s-45=6.33; s-90=6.46; controls=3.78;P<0.05). When the two groups of smoking rats were pooled together and compared to controls, they showed decreased lung elastance (1.6 vs 2.19; P = 0.046) and increased mean linear intercept (Lm) (85.14 vs 66.44; P = 0.025). The s-90 animals presented higher inflammation and muscular hypertrophy at the level of the axial bronchus than the controls (P<0.05). When smoking groups were pooled and compared to controls, they presented significantly higher inflammation at the lateral level (P = 0.028), as well as airway secretory hyperplasia (P = 0.024) and smooth muscle hypertrophy ( P = 0.005) at the axial level. Due to its simplicity, low cost and short duration, this technique may be a useful model to obtain new information about airspace remodeling due to chronic tobacco consumption.

Effect of malnutrition on lung phospholopid, pressure-volume curve and arterial blood gases: experimental study in rats

In order to study the effects of chronic malnutrition on lung surfactant, adult male Wistar rats reciving a standard diet (SD) were comparaed to animals submitted to food restriction (FR). SD rats given food and water and libitum and FR rats were allowed half (10g) of their usual food comsumption and water ad libitum, for 28 days. the evaluation of the pulmonary surfactant included pressure-volume curve with air inflation, pH and artherial blood gas measurements with rats breathing room air and 100 percent oxygen and determination of phospholipids in the lung washouts. In the pressure-volume curve, the volumes retained at 5 and 10 cmH2O of transpulmonary pressure (Tpt) and the Tpt of 40 percent of total lung capacity (TLC) were not significantly different between the two groups, showing that food restriction did not increase the surface forces. the increase in TLC/lung wet weight ratio in the FR group, probably was secondary to decrease in the elastic recoil forces in the lungs. The PaO2 did not show any significant difference between the groups. The arterial blood pH and PCO2 were also similar in both, SD and FR groups. Total phospholipid content in the lung washouts related to be weight was not signifiantly different in SD as compared with FR rats. Therefore, in this malnutrition model of rats, no alterations in pulmonary surfactant could be shown

Inverse ratio ventilation in adult respiratory distress syndrome: an experimental study in dogs regarding gasometric and hemodynamic aspects

Cardiorespiratory values were measured in 14 mongrel dogs with adult respiratory distress syndrome (ARDS), before and following the pressure controlled inverse ratio ventilation (IRV) at an inspiratory to expiratory ratio of 2:1. After the administration of oleic acid, the dogs developed metabolic acidosis, arterial hypoxemia, decreased compliance and cardiac index. There were no significant changes in any hemodynamic or arterial blood gases with the institution of inverse ratio ventilation. We concluded that the IRV with I:E of 2:1 and respiratory ratio of 12 bpm did not improve the arterial blood gases in ARDS. We speculate that to get better oxygenation in this model of mechanical ventilation we'll need increase the respiratory ratio to decrease the expiratory time and provoke the intrinsic positive end expiration pressure (PEEP).