Calcium and phospholipase A2 appear to be involved in the pathogenesis of hemorrhagic shock-induced mucosal injury and bacterial translocation

Infarcted intestine: a diagnostic void

The diagnostic approaches to infarction of the small intestine are reviewed in the present paper. The inadequacy of current methods, especially biochemical methods, are highlighted. Additionally, the benefits of a sensitive and specific test of intestinal infarction are discussed.

The role of the intestine in the pathophysiology and management of severe acute pancreatitis

BACKGROUND

The outcome of severe acute pancreatitis has scarcely improved in 10 years. Further impact will require new paradigms in pathophysiology and treatment. There is accumulating evidence to support the concept that the intestine has a key role in the pathophysiology of severe acute pancreatitis which goes beyond the notion of secondary pancreatic infection. Intestinal ischaemia and reperfusion and barrier failure are implicated in the development of multiple organ failure.

DISCUSSION

Conventional management of severe acute pancreatitis has tended to ignore the intestine. More recent attempts to rectify this problem have included 1) resuscitation aimed at restoring intestinal blood flow through the use of appropriate fluids and splanchnic-sparing vasoconstrictors or inotropes; 2) enteral nutrition to help maintain the integrity of the intestinal barrier; 3) selective gut decontamination and prophylactic antibiotics to reduce bacterial translocation and secondary infection. Novel therapies are being developed to limit intestinal injury, and these include antioxidants and anti-cytokine agents. This paper focuses on the role of the intestine in the pathogenesis of severe acute pancreatitis and reviews the implications for management.

Evaluation of intestinal intramucosal pH, arterial and portal venous blood gas values, and intestinal blood flow during small intestinal ischemia and reperfusion in dogs

OBJECTIVES

To determine whether small intestinal ischemia and reperfusion affects intestinal intramucosal pH (pHi), arterial and portal venous blood gas values, and intestinal blood flow (IBF) and to investigate relationships between regional intestinal tissue oxygenation and systemic variables in dogs.

ANIMALS

15 healthy adult Beagles.

PROCEDURE

Occlusion of superior mesenteric artery (SMA) for 0, 30, or 60 minutes, followed by reperfusion for 180 minutes, was performed; IBF, pHi, arterial and portal venous blood gas values, arterial pressure, and heart rate were measured at various time points; and intestinal mucosal injury was histologically graded.

RESULTS

Occlusion of the SMA induced significant decreases in pHi and IBF. After the release of the occlusion, IBF returned rapidly to baseline values, but improvement in pHi was slow. Arterial and portal venous blood gas analyses were less sensitive than tonometric measurements of pHi, and there was no correlation between results of blood gas analyses and tonometric measurements. Histologic score for intestinal mucosal injury increased significantly, depending on duration of ischemia, and there was a correlation between tonometric results and the histologic score.

CONCLUSIONS AND CLINICAL RELEVANCE

Results suggest that it is difficult to accurately evaluate local oxygenation disorders by monitoring at the systemic level, whereas clinically pHi is the only reliable indicator of inadequate regional intestinal tissue oxygenation in dogs.

Role of nitric oxide in hemorrhagic shock-induced bacterial translocation

BACKGROUND

Hemorrhagic shock-induced bacterial translocation is an etiologic factor in the pathogenesis of multiple system organ damage. Excessive production of nitric oxide (NO) during hemorrhagic shock may lead to cellular injury and gut barrier failure that promotes bacterial translocation. We investigated the effect of aminoguanidine (AG) and N(G)-nitro-l-arginine methyl ester (l-NAME), both inhibitors of NO synthase, on hemorrhagic shock- induced bacterial translocation in the rat.

MATERIALS AND METHODS

Anesthetized male Sprague-Dawley rats were subjected to a hemorrhagic shock protocol for 30 min followed by intravenous injection (1 mL/kg body wt) with normal saline, AG (100 mg/kg), or l-NAME (10 mg/kg). Tissues/organs were examined histologically for damage and bacterial translocation. Plasma nitrate/nitrite was measured using a procedure based on the Griess reaction, and nitric oxide synthase (NOS) expression was determined immunohistochemically.

RESULTS

The shocked animals treated with saline died within 90 min, and deaths were associated with 100% bacterial translocation, increased tissue/organ damage, and elevated nitrate/nitrite production. In contrast, both AG and l-NAME increased the survival time of shocked rats to >72 h, abrogated bacterial translocation, reduced tissue/organ damage, and prevented excessive nitrate/nitrite production and upregulation of expression of endothelial NOS and inducible NOS.

CONCLUSIONS

Prevention of bacterial translocation by pharmacologic agents such as aminoguanidine and l-NAME could be an important therapeutic approach to lessen mortality rates following hemorrhagic shock.

Heparin induces release of phospholipase A(2) into the splanchnic circulation

Cardiopulmonary bypass results in increased plasma activity of phospholipase A(2) (PLA(2)) that appears to be caused by the administration of heparin. High PLA(2) activity may be responsible for increased production of eicosanoids and, thus, may be implicated in various pathophysiologic events associated with cardiac surgery. To investigate the site of PLA(2) secretion, blood samples were simultaneously collected from the radial artery, the pulmonary artery, and the hepatic vein at 2, 4, 6, and 20 min after systemic heparinization (350 U/kg). Within 2 min of the heparin injection, plasma activity of PLA(2) increased 4- to 9-fold and remained so for at least 20 min. Two minutes after the heparin injection, PLA(2) was significantly higher in the hepatic vein than in the radial artery (P: < 0.01). No such difference was detected between pulmonary and radial arteries. When heparin was added to blood samples in vitro (5-100 U/mL), plasma activity of PLA(2) did not increase, which suggests that the enzyme was not secreted by blood cells.

IMPLICATIONS

Heparin, given in the dosage required for cardiopulmonary bypass, caused release of phospholipase A(2) into the splanchnic circulation.

Pancreatic phospholipase A2 induces bacterial translocation in rats

The importance of pancreatic enzymes, particularly phospholipase A2 (PLA2), for bacterial translocation, which is considered to be one of the aggravating causes of acute pancreatitis, was investigated. Male rats were administered an intraperitoneal or intravenous injection of normal saline, PLA2, or amylase. Four days later, the mesenteric lymph nodes (MLNs) and portal blood of the animals were cultured. None of the animals had a positive portal blood culture. The MLNs contained enteric bacteria in 78% of the animals given 50 mg/kg of PLA2 intraperitoneally. 5 mg/kg of PLA2 intraperitoneally, 50 mg/kg of amylase intraperitoneally, or 50 mg/kg of PLA2 intravenously showed positive cultures in 25%, 20%, and 11%, respectively. None of the animals given intraperitoneal or intravenous normal saline had positive cultures of their MLNs. Intraperitoneal injection of 25 mg/kg of nafamostat mesilate just before intraperitoneal PLA2 (50 mg/kg) resulted in a reduction of positive MLNs from 70% to 30%. The cecal myeroperoxidase (MPO) activity of animals administered 50 mg/kg of PLA2 intraperitoneally was significantly higher compared with animals administered saline intraperitoneally. These results indicate that intraperitoneal leakage of PLA2 plays an important role in bacterial translocation during acute pancreatitis and that administration of a protease inhibitor may be effective against the bacterial translocation.

Serum creatinine and chest radiographs in the early assessment of acute pancreatitis

BACKGROUND

We previously identified serum creatinine values >2 mg/dL (176.8 micromol/L) and pathological chest radiographs due to the presence of pleural effusions or pulmonary densifications as two early prognostic factors of life-threatening acute pancreatitis (AP). The aim of the present study was to validate their prognostic efficacy in combination.

METHODS

We analyzed as prognostic factors only the data obtained within 24 hours of admission in 539 cases of AP, including 163 patients (30.2%) with acute necrotizing pancreatitis (NP). Eleven patients (2%) presented with infected pancreatic necrosis, and 20 patients (3.7%) died.

RESULTS

One hundred and nine cases (20.2%) presented pathological chest radiographs: 32 (5.9%) pulmonary densifications and 77 (14.3%) pleural effusions (18 right, 25 left, 34 bilateral). Fifty-one patients (9.5%) had serum creatinine values >2 mg/dL. Pathological chest radiographs and serum creatinine values >2 mg/dL were significantly associated both with mortality risk (P <0.00001), with a diagnosis of NP (P <0.00001), and with risk of developing infected necrosis (P <0.0001). Considering positivity of either or both tests, the mortality risk sensitivity was 90% (95% confidence interval [CI] 70.7 to 98.3) with a specificity of 76% (CI 72.5 to 79.8), for the NP diagnosis the sensitivity was 60% (CI 52.5 to 67.4) and the specificity 88% (CI 85.0-91.5), whereas for the risk of infected necrosis the sensitivity was 73% (CI 42.2 to 92.6) and specificity 75% (CI 70.1 to 78.4). These data are comparable to those obtained with the Ranson or Glasgow scores at 24 hour in this patient group, with a cut-off > or =3.

CONCLUSIONS

Serum creatinine and chest radiographs are two indices capable of identifying, within 24 hour of admission, a subgroup of acute pancreatitis patients with a more severe or adverse clinical course.

Ischaemia-reperfusion injury to the intestine

Ischaemia-reperfusion injury (IRI) is of obvious relevance in situations where there is an interruption of blood supply to the gut, as in vascular surgery, or in the construction of free intestinal grafts. It is now appreciated that IRI also underlies the guy dysfunction that occurs in early shock, sepsis, and trauma. The events that occur during IRI are complex. However, recent advances in cellular biology have started to unravel these underlying processes. The aim of this review is to provide an outline of current knowledge on the mechanisms and consequences of IRI. Initially, IRI appears to be mediated by reactive oxygen metabolites and, at a later stage, by the priming and activation of polymorphonuclear neutrophils (PMN). Ischaemia-reperfusion injury can diminish the barrier function of the gut, and can promote an increase in the leakage of molecules (intestinal permeability) or the passage of microbes across the wall of the bowel (bacterial translocation). Ischaemia-reperfusion injury to the gut can result in the generation of molecules that may also harm distant tissues.

Failure of splanchnic resuscitation in the acutely injured trauma patient correlates with multiple organ system failure and length of stay in the ICU

INTRODUCTION

The purpose of our study was to evaluate the relationship between the state of splanchnic perfusion and morbidity and mortality in the hemodynamically unstable trauma patient acutely resuscitated in the ICU.

METHODS

Gastric intramucosal pH (pHi) was monitored in a blinded fashion in 19 consecutive critically ill trauma patients with evidence of systemic hypoperfusion (arterial pH [pHa] <7.35, base excess >2.3 mmol/L, lactic acid >2.3 mEq/L) who received right heart catheters to guide resuscitation and subsequent hemodynamic monitoring.

DESIGN

Prospective randomized consecutive series with retrospective analysis of data.

SETTING

University hospital, surgical ICU.

RESULTS

The mean values of APACHE II (acute physiology and chronic health evaluation) Injury Severity Score, pHa, arterial base excess, cardiac index, oxygen delivery index, and oxygen consumption index by 24 h were similar (Student's t test, p>0.1) between survivors and nonsurvivors and between those who developed at most a single (SOF) vs multiple organ system failure (MOSF). Supranormal oxygen delivery and utilization parameters were evenly distributed among survivors and nonsurvivors and patients with SOF and MOSF (chi2, p>0.5). Ten patients had a pHi <7.32 and nine patients had a pHi > or = 7.32 by 24 h. Fifty percent of patients with a pHi <7.32 died, compared with 11% of patients with a pH > or = 7.32 (chi2, p=0.07). Sixty percent of patients with a pHi <7.32 developed MOSF compared with 11% of patients with a pHi > or = 7.32 (chi2, p=0.03). The one patient who developed MOSF and died in the pHi > or = 7.32 cohort suffered from massive head trauma and had all futile medical interventions halted. No other patients who achieved a pH > or = 7.32 by hour 24 developed MOSF. Survivors with a pHi <7.32 at hour 24 had an increased ICU stay (pHi <7.32=46+/-15 days, pHi > or = 7.32=13+/-9 days; p<0.01). A pHi <7.32 carried a relative risk of 4.5 for death and 5.4 for the occurrence of MOSF.

CONCLUSION

Attainment of a pHi > or = 7.32 at hour 24 carried a significantly reduced likelihood of MOSF. Being an inference of the state of regional perfusion, in a high-risk microvascular bed, gastric intraluminal tonometry should identify perfusion states of compensated or uncompensated shock during hemodynamic resuscitation of the critically ill injury patient. A low pHi appears to be a marker of postresuscitative morbidity and subsequent increased length of stay.

Protective effects of lazaroid U74389G on intestinal graft after heterotopic small bowel transplantation in rats

BACKGROUND

Experimental studies have shown that 21-aminosteroids (21-A) are powerful inhibitors of superoxide-mediated iron-dependent lipid peroxidation. This study was aimed at determining how far the blocking effect of one of these substances (lazaroid U74389G) on lipid peroxidation protects intestinal grafts morphologically and biologically in a heterotopic transplant model (SBT) in rats.

ANIMALS AND METHODS

Heterotopic LEW were performed using Ringer lactate (4 degrees C) as preservation solution. In Group 1 (n = 7) the donor and recipient animals received 3 and 6 mg/kg of the 21-A U74389G, respectively. Group 2 (n = 7) received the same doses of the vehicle of the drug. Sham group underwent only a laparotomy. Bacterial translocation (BT) was determined in mesenteric lymph nodes (MLN), liver (L), and spleen (S) 60 min after reperfusion. Tissue myeloperoxidase (MPO), malondialdehyde (MDA), and percentage conversion xanthine dehydrogenase/xanthine oxidase (XD/XO) were also determined in the ileal graft. Histological damage was graded according to Park's classification.

RESULTS

Tissue MDA (nmol/mg prot) was significantly lower in Group 1 (0.53 +/- 0.09) than in Group 2 (3.66 +/- 1, P < 0.05) and showed levels similar to those of the sham-operated group (0.40 +/- 0.05). Injury grades were also significantly different in both study groups (Group 1, 0-1; Group 2, 2-3, P < 0.05). BT (log CFU/g tissue) in Group 1 were MLN, 0; L, 0.36; and S, 0. In Group 2, MLN, 1.07; L, 0.81; and S, 1.49 (P < 0.05 in MLN). Increase in MPO activity (U/g prot) in comparison with sham-operated animals was similar in the two study groups (Group 1, 1.49 +/- 0.58; Group 2, 1.22 +/- 0.46; Sham, 0.34 +/- 0.37 (P < 0.05 1,2 vs sham). Conversion of XD to XO was unaffected by the supplementation of the drug.

CONCLUSION

21A U74389G inhibits lipid peroxidation, protects intestinal graft, and reduces BT after heterotopic SBT in rats.

The impact of antioxidant and splanchnic-directed therapy on persistent uncorrected gastric mucosal pH in the critically injured trauma patient

BACKGROUND

Critically ill trauma patients with gastric intramucosal acidosis, as measured by gastric tonometry, have an increased incidence of multiple organ dysfunction syndrome despite supranormal O2 delivery. We altered our resuscitation protocol to maximize splanchnic blood flow and decrease oxygen-derived free radical damage.

DESIGN

Prospective clinical trial with historical controls.

METHODS

The protocol differed from control by including administration of folate, mannitol, and low-dose isoproterenol. All patients had gastric tonometers and pulmonary artery catheters. If the intramucosal pH (pHi) was less than 7.25, splanchnic-sparing inotropic and vasodilatory agents were used to optimize systemic cardiac output. Two groups of trauma patients with persistent intramucosal acidosis at 24 hours (pHi < 7.25) were compared: a control group (n = 7), and patients who received the splanchnic/antioxidant protocol (n = 13).

RESULTS

The two groups were similar based on Acute Physiology and Chronic Health Evaluation II score, Injury Severity Score, age, cardiac index, oxygen delivery, and oxygen consumption. The "splanchnic therapy" group had fewer organ system failures as well as shortened length of intensive care unit and hospital stay. Three of 7 patients in the control group and 2 of 13 patients in the splanchnic therapy group had a final pHi < 7.25.

CONCLUSION

Gastric tonometry-guided resuscitation and antioxidant/splanchnic therapy in critically ill trauma patients with persistent gastric mucosal acidosis may decrease multiple organ dysfunction syndrome.

Is gut the "motor" for producing hepatocellular dysfunction after trauma and hemorrhagic shock?

BACKGROUND

Although studies suggest that the gut may be the "motor" responsible for producing sepsis and multiple organ failure after injury, it is not known whether enterectomy prior to the onset of hemorrhage alters proinflammatory cytokines TNF and IL-6 and, if so, whether hepatocellular dysfunction and damage are prevented or attenuated under such conditions.

MATERIALS AND METHODS

Under methoxyflurane anesthesia, an enterectomy in the rat was performed by excision of the duodenum, jejunum, and ileum. The rats were then bled to and maintained at a mean arterial pressure of 40 mm Hg until 40% of the maximal shed volume was returned in the form of Ringer's lactate. The animals were then resuscitated with four times the volume of shed blood with Ringer's lactate over 1 h. At 1.5 h after the completion of resuscitation, hepatocellular function [i.e., the maximal velocity (Vmax) and transport efficiency (Km) of indocyanine green (ICG) clearance] was assessed by an in vivo ICG clearance technique. Blood samples were taken for the measurement of TNF, IL-6, and liver enzymes (i.e., SGPT and SGOT). Cardiac output and microvascular blood flow were determined by ICG dilution and laser Doppler flowmetry, respectively.

RESULTS

The increase in circulating levels of TNF but not IL-6 was prevented by enterectomy prior to hemorrhage. The reduced Vmax and K(m) and elevated SGPT and SGOT following hemorrhage and resuscitation, however, were not significantly affected by prior enterectomy. Moreover, enterectomy before hemorrhage further reduced hepatic perfusion.

CONCLUSION

Since enterectomy prior to the onset of hemorrhage does not prevent or attenuate the reduced ICG clearance and elevated liver enzymes despite downregulation of TNF production, it appears that the small intestine does not play a significant role in producing hepatocellular dysfunction and injury following trauma and hemorrhagic shock.

Effect of hypoxia on enterocyte endocytosis of enteric bacteria

OBJECTIVE

To clarify the effect of hypoxia on bacteria-enterocyte interactions.

DESIGN

Randomized.

SETTING

Research laboratory.

SUBJECTS

Enteric bacterial and cultured human intestinal epithelial cells, HT-29 cells.

INTERVENTIONS

The effect of hypoxia on bacterial internalization and intracellular survival was studied, using enterocytes cultured for 21 days in either 20%, 10%, or 5% oxygen. The effect of bacterial growth conditions on bacterial internalization by enterocytes was studied, using bacterial cells in either the log phase or stationary phase of aerobic growth, and using bacterial cells in stationary phase, grown either under low oxygen conditions or under anaerobic conditions.

MEASUREMENTS AND MAIN RESULTS

Individual strains of enteric bacteria were incubated with HT-29 cells for 1 hr. Numbers of internalized bacteria were subsequently quantified after enterocyte lysis. Bacterial growth conditions (anaerobic vs. aerobic and log-phase vs. stationary-phase bacterial cells) had no noticeable effect on the numbers of Salmonella typhimurium, Proteus mirabilis, and Escherichia coli internalized by enterocytes. Enterocytes cultivated in 20%, 10%, or 5% oxygen were >95% viable. Enterocytes cultivated in 20% oxygen were confluent, but those enterocytes cultivated in hypoxia were not confluent and were fewer in number compared with enterocytes cultivated in normoxia. Compared with enterocytes grown in normoxia, enterocytes cultivated in 5% and 10% oxygen internalized greater numbers of each of seven strains of enteric bacteria, including Listeria monocytogenes (two strains), Enterococcus faecalis (two strains), and P. mirabilis, E. coli (two strains), with statistically significant increases noted for five of these seven bacterial strains. Intracellular survival of L. monocytogenes and P. mirabilis was assayed. Both species survived intracellularly for 22 hrs, with no noticeable differences in the numbers of intracellular bacteria recovered from enterocytes cultivated in 20%, 10%, and 5% oxygen.

CONCLUSION

These in vitro results suggest that augmented bacterial endocytosis by enterocytes might at least partially explain the increased frequency of bacterial translocation associated with tissue ischemia.