Decreased alpha-adrenergic response in the intestinal microcirculation after "two-hit" hemorrhage/resuscitation and bacteremia

Prevention and Treatment of Gastrointestinal Complications in Patients on Mechanical Ventilation

There exists a complex, dynamic interaction between mechanical ventilation and the splanchnic vasculature that contributes to a myriad of gastrointestinal tract complications that arise during critical illness. Positive pressure-induced splanchnic hypoperfusion appears to play a pivotal role in the pathogenesis of these complications, the most prevalent of which are stress-related mucosal damage, gastrointestinal hypomotility and diarrhea. Furthermore, characteristics of the splanchnic vasculature make the gastrointestinal tract vulnerable to adverse effects related to positive pressure ventilation. While most of these complications seen in mechanically ventilated patients are reflections of altered gastrointestinal physiology, some may be attributed to medical interventions instituted to treat critical illness. Since maintenance of normal hemodynamics cannot always be achieved, pharmacologic prophylactic therapy has become a mainstay in the prevention of gastrointestinal complications in the intensive care unit. Improved understanding of the systemic effects of mechanical ventilation and greater application of lung-protective ventilatory strategies may potentially minimize positive pressure-induced reductions in splanchnic perfusion, systemic cytokine release and, consequently, reduce the incidence of gastrointestinal complications associated with mechanical ventilation. Herein, we discuss the pathophysiology of gastrointestinal complications associated with mechanical ventilation, summarize the most prevalent complications and focus on preventive strategies and available treatment options for these complications. The most common causes of gastrointestinal hemorrhage in mechanically ventilated patients are bleeding from stress-related mucosal damage and erosive esophagitis. In general, histamine H(2) receptor antagonists and proton pump inhibitors prevent stress-related mucosal disease by raising the gastric fluid pH. Proton pump inhibitors tend to provide more consistent pH control than histamine H(2) receptor antagonists. There is no consensus on the drug of choice for stress ulcer prophylaxis with several meta-analyses providing conflicting results on the superiority of any medication. Prevention of erosive esophagitis include careful use of nasogastric tubes and institution of strategies that improve gastric emptying. Many mechanically ventilated patients have gastrointestinal hypomotility and diarrhea. Treatment options for gastrointestinal motility are limited, thus, preventive measures such as correction of electrolyte abnormalities and avoidance of medications that impair gastrointestinal motility are crucial. Treatment of diarrhea depends on the underlying cause. When associated with Clostridium difficile infection antibacterial therapy should be discontinued, if possible, and treatment with oral metronidazole should be initiated.More studies are warranted to better understand the systemic effects of mechanical ventilation on the gastrointestinal tract and to investigate the impact of lung protective ventilatory strategies on gastrointestinal complications.

Microcirculatory function monitoring at the bedside--a view from the intensive care

Microcirculatory dysfunction plays a key role in the pathophysiology of various disease states and may consequently impact patient outcome. Until recently, the evaluation of the microcirculation using different measurement techniques has been mostly limited to animal and human research. With technical advances, microcirculatory monitoring nowadays becomes more and more available for application in clinical praxis. Unfortunately, measurements within the microcirculation are mostly limited to easily accessible surfaces, such as skin, muscle and tongue. Due to major differences in the physiologic regulation of microcirculatory blood flow and in metabolism between organs and even within different tissues in one organ, the clinical importance of regional microcirculatory measurements remains to be determined. In addition, technical methods available demonstrate large differences in the measured parameters and sampling volume, making interpretation of data even more difficult. Nonetheless, the monitoring of the microcirculation may, ahead of time, alert physicians that tissue oxygen supply becomes compromised and it may lead to a better understanding of basic pathophysiological aspects of disease. In the present review, we describe available non-invasive microcirculatory measurement techniques which can be applied clinically at the bedside. After a short discussion of physiologic and pathophysiologic basics related to microcirculatory monitoring, the measuring principles, applications, strengths and limitations of different monitoring systems are discussed.

Downregulation of hepatic cytochrome P-450 isoforms and PPAR-gamma: their role in hepatic injury and proinflammatory responses in a double-hit model of hemorrhage and sepsis

BACKGROUND

The "double-hit" model of hemorrhage and sepsis mimics the critically ill patient admitted to the surgical intensive care unit. Although the protein expression of a cytochrome (CYP) P-450 isoform CYP1A2 is reduced in the late stage of sepsis, the effect of hemorrhage on CYP isoforms and the anti-inflammatory nuclear receptor peroxisome proliferator-activated receptor-gamma (PPAR-gamma) has not been investigated. We hypothesized that hemorrhage down-regulates CYP isoforms and PPAR-gamma in the liver, which plays an important role in producing tissue injury and proinflammatory responses after the subsequent sepsis (i.e., double-hit).

MATERIALS AND METHODS

Male Sprague Dawley rats were divided into four groups. Animals in the double-hit group underwent hemorrhage (40 +/- 2 mmHg for 90 min) followed by fluid resuscitation. Polymicrobial sepsis was induced by cecal ligation and puncture (CLP) 20 h after hemorrhage, and the animals were sacrificed 4 h after CLP. Rats in the hemorrhage-alone group were sacrificed 20 h after the insult. Rats in the CLP-alone group were sacrificed 4 h after the onset of sepsis. Animals in the sham-operated group underwent neither hemorrhage nor CLP. The gene expression of P-450 isoforms (i.e., CYP1A2 and 2C11) and PPAR-gamma in the liver was determined using RT-PCR. Serum concentrations of alanine aminotransferase (ALT), aspartate aminotransferase (AST), lactate, and proinflammatory cytokines (i.e., IL-6, TNF-alpha) were also assessed.

RESULTS

In the hemorrhage-alone group, hepatic mRNA expression of CYP1A2, CYP2C11, and PPAR-gamma was significantly down-regulated 20 h after the initial stress compared with sham-operated rats. Double-hit did not appear to further decrease CYP and PPAR-gamma gene expression. In contrast, serum levels of AST, ALT, lactate, IL-6, and TNF-alpha did not change significantly in either hemorrhaged or septic animals. Those organ injury indicators and cytokines, however, were significantly elevated after the double-hit of hemorrhage and sepsis.

CONCLUSIONS

Hepatic CYP1A2, CYP2C11, and PPAR-gamma were down-regulated after the initial stress (hemorrhage). These down-regulated CYPs and PPAR-gamma seem to work as important factors contributing to the progression of organ injury and proinflammatory responses after the second stress (CLP).

Effect of intestinal lymphatic circulation blockage in two-hit rats

AIM: To study the effect of blocking intestinal lymphatic circulation in two-hit rats and explore the significance of intestinal lymphatic circulation in two-hit.

METHODS: Wistar rats were divided equally into three groups: mesenteric lymph duct ligation group, non-ligation group and sham group. Mesenteric lymph was diverted by ligation of mesenteric lymph duct, and the two-hit model was established by hemorrhage and lipopolysaccharide (LPS) methods. All rats were sampled for serum pre-experiment and 24 h post-experiment. The organs including kidney, liver, lung and heart were collected for pathomorphologic observation and biochemical investigation. The nitric oxide (NO), malondialdehyde (MDA) and superoxide dismutase (SOD) were determined in serum and tissue homogenate.

RESULTS: Pathomorphology study showed that the structures of kidney, lung, liver and heart tissues were normal in sham group; congestion, degeneration and necrosis in non-ligation group; but only mild lesions in ligation group. After two-hits, the contents of AST, ALT, BUN, Cr and LDH-1 in the serum of non-ligation group and ligation group were obviously higher than that in pre-experiment group and sham group, but obviously lower than that in non-ligation group. The contents of NO₂^-/NO₃^-, NOS, iNOS and MDA in the serum of non-ligation group were significantly increased, compared with pre-experiment and sham group, but SOD was significantly lower. These parameters were significantly different in ligation group compared with that in sham group, but NO₂^-/NO₃^-, iNOS and MDA in ligation group were significantly lower than that in non-ligation group.

CONCLUSION: Ligation of mesenteric lymph duct could improve the disturbance of organic function and morphologic damage in two-hit rats; the lymphatic mechanism in two-hit should be emphasized.

Granulocyte colony-stimulating factor prophylaxis improves survival and inflammation in a two-hit model of hemorrhage and sepsis

OBJECTIVE

We evaluated the effects of a granulocyte-colony stimulating factor (G-CSF) prophylaxis in two clinically relevant situations, hemorrhage on the day before infection (e.g., trauma) and acute hemorrhage followed subsequently by infection (e.g., operative complication). A two-hit model of hemorrhage and polymicrobial peritoneal contamination and infection (PCI) was used to assess the influence of G-CSF on the outcome, bacterial clearance, and cytokine pattern.

DESIGN

Clinic modeling randomized laboratory trial.

SETTING

University laboratory.

SUBJECTS

One hundred thirty-two male rats.

INTERVENTIONS

In trial 1 we compared a) preoperative PCI only; b) preoperative hemorrhage plus PCI; and c) hemorrhage plus PCI plus G-CSF prophylaxis (n=18 rats/group). In trial 2, intraoperative hemorrhage was assessed with the same trial design. Primary end point was survival at 120 hrs. In trial 2 additionally, six rats per group and six naive control rats were used for secondary end point analysis.

MEASUREMENTS AND MAIN RESULTS

Primary end point was mortality at 120 hrs. Secondary end points were granulocyte counts, bacterial clearance, and local cytokine levels. In trial 1 survival rate was 56% after PCI only, 17% after hemorrhage plus PCI, and 61% after hemorrhage plus PCI plus G-CSF (p<.01). In trial 2 survival rate was 33% after PCI only, 17% after hemorrhage plus PCI, and 50% after hemorrhage plus PCI plus G-CSF (p<.05). In trial 2, neutrophil counts were doubled to 66% 1 hr after hemorrhage (p<.05), colony-forming units of microbes in the lung and liver were halved to 166+/-56 and 134+/-28 colony-forming units (p<.05 for liver), and the macrophage inflammatory protein-2 expression in the lung was halved to 0.88+/-0.06 pg of complementary DNA (p<.05) by G-CSF prophylaxis compared with hemorrhage and PCI.

CONCLUSIONS

Hemorrhage (first hit) sensitized the host for a second hit of polymicrobial PCI independent of the timing. G-CSF prophylaxis improved survival and clearance of microbes and reduced the proinflammatory chemokine macrophage inflammatory protein-2 in the lung.

Hypoxia aggravates lipopolysaccharide-induced lung injury

The animal model of inflammatory response induced by intratracheal application of lipopolysaccharide includes many typical features of acute lung injury or the acute respiratory distress syndrome. A number of experimental investigations have been performed to characterize the nature of this injury more effectively. In inflammatory conditions, hypoxia occurs frequently before and in parallel with pulmonary and non-pulmonary pathological events. This current study was designed to examine the in vivo effect of hypoxia as a potentially aggravating condition in endotoxin-induced lung injury. Lipopolysaccharide, 150 microg, was instilled intratracheally into rat lungs, and thereafter animals were exposed to either normoxia or hypoxia (10% oxygen). Lungs were collected 2, 4, 6 and 8 h later. Inflammatory response and tissue damage were evaluated by quantitative analysis of inflammatory cells and mediators, surfactant protein and vascular permeability. A significantly enhanced neutrophil recruitment was seen in lipopolysaccharide-animals exposed to hypoxia compared to lipopolysaccharide-animals under normoxia. This increased neutrophil accumulation was triggered by inflammatory mediators such as tumour necrosis factor-alpha and macrophage inflammatory protein-1beta, secreted by alveolar macrophages. Determination of vascular permeability and surfactant protein-B showed enhanced concentrations in lipopolysaccharide-lungs exposed to hypoxia, which was absent in animals previously alveolar macrophage-depleted. This study demonstrates that hypoxia aggravates lipopolysaccharide injury and therefore represents a second hit injury. The additional hypoxia-induced inflammatory reaction seems to be predominantly localized in the respiratory compartment, underlining the compartmentalized nature of the inflammatory response.

Hypertonic saline resuscitation attenuates neutrophil lung sequestration and transmigration by diminishing leukocyte-endothelial interactions in a two-hit model of hemorrhagic shock and infection

BACKGROUND

Hypertonic saline (HTS) attenuates polymorphonuclear neutrophil (PMN)-mediated tissue injury after hemorrhagic shock. We hypothesized that HTS resuscitation reduces early in vivo endothelial cell (EC)-PMN interactions and late lung PMN sequestration in a two-hit model of hemorrhagic shock followed by mimicked infection.

METHODS

Thirty-two mice were hemorrhaged (40 mm Hg) for 60 minutes and then given intratracheal lipopolysaccharide (10 microg) 1 hour after resuscitation with shed blood and either HTS (4 mL/kg 7.5% NaCl) or Ringer's lactate (RL) (twice shed blood volume). Eleven controls were not manipulated. Cremaster intravital microscopy quantified 5-hour EC-PMN adherence, myeloperoxidase assay assessed lung PMN content (2 1/2 and 24 hours), and lung histology determined 24-hour PMN transmigration.

RESULTS

Compared with RL, HTS animals displayed 55% less 5-hour EC-PMN adherence (p = 0.01), 61% lower 24-hour lung myeloperoxidase ( p= 0.007), and 57% lower mean 24-hour lung histologic score ( p= 0.027).

CONCLUSION

Compared with RL, HTS resuscitation attenuates early EC-PMN adhesion and late lung PMN accumulation in hemorrhagic shock followed by inflammation. HTS resuscitation may attenuate PMN-mediated organ damage.

GI complications in patients receiving mechanical ventilation

Mechanical ventilation (MV) can be lifesaving by maintaining gas exchange until the underlying disorders are corrected, but it is associated with numerous organ-system complications, which can significantly affect the outcome of critically ill patients. Like other organ systems, GI complications may be directly attributable to MV, but most are a reflection of the severity of the underlying disease that required intensive care. The interactions of the underlying critical illness and MV with the GI tract are complex and can manifest in a variety of clinical pictures. Incorporated in this review are discussions of the most prevalent GI complications associated with MV, and current diagnosis and management of these problems.