Systemic inflammatory response does not correlate with acute lung injury associated with mechanical ventilation strategies in normal lungs.

BACKGROUND: Mechanical ventilation (MV) can lead to ventilator-induced lung injury secondary to trauma and associated increases in pulmonary inflammatory cytokines. There is controversy regarding the associated systemic inflammatory response. In this report, we demonstrate the effects of MV on systemic inflammation. METHODS: This report is part of a previously published study (Hong et al. Anesth Analg 2010;110:1652-60). Female pigs were randomized into 3 groups. Group H-Vt/3 was ventilated with a tidal volume (Vt) of 15 mL/kg predicted body weight (PBW)/positive end-expiratory pressure (PEEP) of 3 cm H(2)O; group L-Vt/3 with a Vt of 6 mL/kg PBW/PEEP of 3 cm H2O; and group L-Vt/10 with a Vt of 6 mL/kg PBW/PEEP of 10 cm H(2)O, for 8 hours. Each group had 6 subjects (n = 6). Prelung and postlung sera were analyzed for inflammatory markers. Hemodynamics, airway mechanics, and arterial blood gases were monitored. RESULTS: There were no significant differences in systemic cytokines among groups. There were similar trends of serum inflammatory markers in all subjects. This is in contrast to findings previously published demonstrating increases in inflammatory mediators in bronchoalveolar lavage. CONCLUSION: Systemic inflammatory markers did not correlate with lung injury associated with MV.

Trauma hemorrhagic shock-induced lung injury involves a gut-lymph-induced TLR4 pathway in mice.

BACKGROUND: Injurious non-microbial factors released from the stressed gut during shocked states contribute to the development of acute lung injury (ALI) and multiple organ dysfunction syndrome (MODS). Since Toll-like receptors (TLR) act as sensors of tissue injury as well as microbial invasion and TLR4 signaling occurs in both sepsis and noninfectious models of ischemia/reperfusion (I/R) injury, we hypothesized that factors in the intestinal mesenteric lymph after trauma hemorrhagic shock (T/HS) mediate gut-induced lung injury via TLR4 activation. METHODS/PRINCIPAL FINDINGS: The concept that factors in T/HS lymph exiting the gut recreates ALI is evidenced by our findings that the infusion of porcine lymph, collected from animals subjected to global T/HS injury, into naïve wildtype (WT) mice induced lung injury. Using C3H/HeJ mice that harbor a TLR4 mutation, we found that TLR4 activation was necessary for the development of T/HS porcine lymph-induced lung injury as determined by Evan's blue dye (EBD) lung permeability and myeloperoxidase (MPO) levels as well as the induction of the injurious pulmonary iNOS response. TRIF and Myd88 deficiency fully and partially attenuated T/HS lymph-induced increases in lung permeability respectively. Additional studies in TLR2 deficient mice showed that TLR2 activation was not involved in the pathology of T/HS lymph-induced lung injury. Lastly, the lymph samples were devoid of bacteria, endotoxin and bacterial DNA and passage of lymph through an endotoxin removal column did not abrogate the ability of T/HS lymph to cause lung injury in naïve mice. CONCLUSIONS/SIGNIFICANCE: Our findings suggest that non-microbial factors in the intestinal mesenteric lymph after T/HS are capable of recreating T/HS-induced lung injury via TLR4 activation.

The anatomic sites of disruption of the mucus layer directly correlate with areas of trauma/hemorrhagic shock-induced gut injury.

BACKGROUND: The intestinal mucus layer is an important but understudied component of the intestinal barrier. Consequently, we tested the hypothesis that the anatomic sites of loss of the mucus layer would directly correlate with sites of intestinal villous injury after trauma-hemorrhagic shock (T/HS) and may, therefore, serve as loci of gut barrier failure. Consequently, to investigate this hypothesis, we used Carnoy's fixative solution to prepare fixed tissue blocks where both the gut morphology and the mucus layer could be assessed on the same tissues slides. METHODS: Male Sprague-Dawley rats were subjected to a laparotomy (trauma) and 90 minutes of sham shock (T/SS) or 35 mm Hg × 90 minutes of actual shock (T/HS). Three hours after resuscitation, the rats were killed, and samples of the terminal ileum were processed by fixation in Carnoy's solution. Gut injury was evaluated by determining the percentage of villi injured. The status of the intestinal mucus layer was quantified by determining the percentage of the villi covered by the mucus and the mucus thickness. RESULTS: Histologic analysis of gut injury showed that the incidence of gut injury was ∼10-fold higher in the T/HS than the T/SS rats (T/SS=2.5% ± 0.5% vs. T/HS=22.4% ± 0.5% of injured villi; p<0.01). The T/SS rats had 98% of their ileal mucosa covered with a mucus layer, and this was decreased after T/HS to 63% ± 3% (T/HS vs. T/SS; p<0.001). Furthermore, loss of the mucus layer was found to directly correlate with villous injury with a regression coefficient of r=0.94 (p<0.001). CONCLUSION: This study shows that T/HS significantly reduces the intestinal mucus layer and causes villous injury and that a correlation exists between specific anatomic sites of T/HS-induced loss of the mucus layer and gut injury.

Low tidal volume and high positive end-expiratory pressure mechanical ventilation results in increased inflammation and ventilator-associated lung injury in normal lungs.

BACKGROUND: Protective mechanical ventilation with low tidal volume (Vt) and low plateau pressure reduces mortality and decreases the length of mechanical ventilation in patients with acute respiratory distress syndrome. Mechanical ventilation that will protect normal lungs during major surgical procedures of long duration may improve postoperative outcomes. We performed an animal study comparing 3 ventilation strategies used in the operating room in normal lungs. We compared the effects on pulmonary mechanics, inflammatory mediators, and lung tissue injury. METHODS: Female pigs were randomized into 3 groups. Group H-Vt/3 (n = 6) was ventilated with a Vt of 15 mL/kg predicted body weight (PBW)/positive end-expiratory pressure (PEEP) of 3 cm H(2)O, group L-Vt/3 (n = 6) with a Vt of 6 mL/kg PBW/PEEP of 3 cm H(2)O, and group L-Vt/10 (n = 6) with a Vt of 6 mL/kg PBW/PEEP of 10 cm H(2)O, for 8 hours. Hemodynamics, airway mechanics, arterial blood gases, and inflammatory markers were monitored. Bronchoalveolar lavage (BAL) was analyzed for inflammatory markers and protein concentration. The right lower lobe was assayed for mRNA of specific cytokines. The right lower lobe and right upper lobe were evaluated histologically. RESULTS: In contrast to groups H-Vt/3 and L-Vt/3, group L-Vt/10 exhibited a 6-fold increase in inflammatory mediators in BAL (P < 0.001). Cytokines in BAL were similar in groups H-Vt/3 and L-Vt/3. Group H-Vt/3 had a significantly lower lung injury score than groups L-Vt/3 and L-Vt/10. CONCLUSION: Comparing intraoperative strategies, ventilation with high PEEP resulted in increased production of inflammatory markers. Low PEEP resulted in lower levels of inflammatory markers. High Vt/low PEEP resulted in less histologic lung injury.

Ethyl pyruvate prevents inflammatory responses and organ damage during resuscitation in porcine hemorrhage.

Hemorrhage remains a common cause of death despite the recent advances in critical care, in part because conventional resuscitation fluids fail to prevent lethal inflammatory responses. Here, we analyzed whether ethyl pyruvate can provide a therapeutic anti-inflammatory potential to resuscitation fluids and prevent organ damage in porcine hemorrhage. Adult male Yorkshire swine underwent lethal hemorrhage with trauma and received no resuscitation treatment or resuscitation with Hextend alone, or supplemented with ethyl pyruvate. Resuscitation with ethyl pyruvate did not improve early hemodynamics but prevented hyperglycemia, the intrinsic coagulation pathway, serum aspartate aminotransferase, and myeloperoxidase in the major organs. Resuscitation with ethyl pyruvate provided an anti-inflammatory potential to restrain serum TNF and high-mobility group B protein 1 levels. Ethyl pyruvate inhibited nuclear factor [kappa]B in the spleen but not in the other major organs. In contrast, ethyl pyruvate inhibited NO in all the major organs, and it also inhibited TNF production in the major organs but in the lung and heart. The most significant effects were found in the terminal ileum where ethyl pyruvate inhibited cytokine production, restrained myeloperoxidase activity, preserved the intestinal epithelium, and prevented the systemic distribution of bacterial endotoxin. Ethyl pyruvate can provide therapeutic anti-inflammatory benefits to modulate splenic nuclear factor [kappa]B, restrain inflammatory responses, and prevent hyperglycemia, the intrinsic coagulation pathway, and organ injury in porcine hemorrhage without trauma.

Mesenteric lymph duct ligation improves survival in a lethal shock model.

The goal of this study was to test the hypothesis that factors released from the gut and carried in the mesenteric lymph contribute to mortality in a lethal gut I/R model. To test this hypothesis, a lethal splanchnic artery occlusion (SAO) shock model was used in male Sprague-Dawley rats. In the first set of experiments, ligation of the mesenteric lymph duct (LDL), which prevents gut-derived factors carried in the intestinal lymphatics from reaching the systemic circulation, significantly improved 24-h survival after a 20-min SAO insult (0% vs. 60% survival; P < 0.05). This increase in survival in the LDL-treated rats was associated with a blunted hypotensive response. Because increased iNOS-induced NO levels have been implicated in SAO-induced shock, we measured plasma nitrite/nitrate levels and liver iNOS protein levels in a second group of animals. Ligation of the mesenteric lymph duct significantly abrogated the SAO-induced increase in plasma nitrite/nitrate levels and the induction of hepatic iNOS (P < 0.05). In an additional series of studies, we documented that LDL increased not only 24-h but also long-term 7-day survival. During the course of these studies, we made the unexpected finding that Sprague-Dawley rats from different animal vendors had differential resistance to SAO, and that the time of the year that the experiments were carried out also influenced the results. Nonetheless, in conclusion, these studies support the hypothesis that factors carried in the mesenteric lymph significantly contribute to the development of irreversible shock after SAO.

Trauma-shock-induced gut injury and the production of biologically active intestinal lymph is abrogated by castration in a large animal porcine model.

Although small animal rodent studies indicate that there is a sexual dimorphism in the resistance to organ injury after trauma-hemorrhagic shock (T/HS), confirmatory studies are largely lacking in more clinically relevant large animal species. Thus, we tested the hypothesis that castration would reduce the susceptibility of adult minipigs to gut injury and abrogate the production of biologically active intestinal (mesenteric) lymph after T/HS. The hemodynamic response to T/HS was similar between castrated and noncastrated minipigs. Mesenteric lymph collected during the preshock period and in the trauma-sham shock (T/SS) animals did not have increased biological activity. However, T/HS-lymph from the noncastrated males increased the respiratory burst of normal neutrophils, increased endothelial cell monolayer permeability, and was cytotoxic for endothelial cells. Castration abrogated the T/HS-induced neutrophil-activating and endothelial-injurious activities of mesenteric lymph, and the biological activity of the T/HS-lymph from the castrated minipigs was not different from the T/SS animals. As compared with the T/SS minipigs, T/HS increased ileal mucosal injury and intestinal permeability. This increase in gut permeability after T/HS was manifest by in vivo bacterial translocation and by the increased passage of bacteria as well as permeability probes across intestinal segments when tested in the Ussing chamber system. In contrast, neither mucosal injury nor increased intestinal permeability was observed in the castrated minipigs subjected to T/HS. In summary, this large animal porcine study validates the notion that castration limits gut injury and the production of biologically active intestinal lymph after T/HS.