Rupture of an abdominal aortic aneurysm causes priming of phagocytic oxidative burst

The Effect of Perioperative Ischemia and Reperfusion on Multiorgan Dysfunction following Abdominal Aortic Aneurysm Repair

Abdominal aortic aneurysms (AAAs) are relatively common and are potentially life-threatening medical problems. The aim of this review is to provide an overview of the effect of I/R injury on multiorgan failure following AAA repair. The PubMed, CINAHL, EMBASE, Medline, Cochrane Review, and Scopus databases were comprehensively searched for articles concerning the pathophysiology of I/R and its systemic effects. Cross-referencing was performed using the bibliographies from the articles obtained. Articles retrieved were restricted to those published in English. One of the most prominent characteristics of AAA open repair is the double physiological phenomenon of ischemia-reperfusion (I/R) that happens either at the time of clamping or following the aortic clamp removal. Ischemia-reperfusion injury causes significant pathophysiological disturbances to distant organs, increasing the possibility for postoperative multiorgan failure. Although tissue injury is mediated by diverse mechanisms, microvascular dysfunction seems to be the final outcome of I/R.

C5 complement inhibition attenuates shock and acute lung injury in an experimental model of ruptured abdominal aortic aneurysm

BACKGROUND

Ruptured abdominal aortic aneurysm (RAAA) is associated with a systemic inflammatory response syndrome and multiple organ dysfunction. The potential role of a novel C5 complement inhibitor in attenuation of pathological complement activation and tissue injury was explored in a model of RAAA.

METHODS

Anaesthetized rats were randomized to sham (control) or shock and clamp (SC) groups. Animals in the SC group underwent 1 h of haemorrhagic shock (mean arterial pressure 50 mmHg or less), 45 min of supramesenteric aortic clamping and 2 h of reperfusion. They were randomized to receive an intravenous bolus of a functionally blocking anti-C5 monoclonal antibody (C5 inhibitor), at a dose of 20 mg/kg, or saline. Lung injury was assessed by permeability to 125I-labelled albumin, tissue myeloperoxidase (MPO) activity, and semiquantitative reverse transcriptase-polymerase chain reaction (RT-PCR) for mRNAs encoding tumour necrosis factor (TNF) alpha and interleukin (IL) 6.

RESULTS

The lung permeability index was significantly increased in the SC compared with the sham group (P = 0.032); this was prevented by the C5 inhibitor (P = 0.015). Lung MPO activity was significantly increased in the SC compared with the sham group (P < 0.001), and this increase was attenuated by treatment with the C5 inhibitor (P < 0.001). Semiquantitative RT-PCR in SC group demonstrated downregulation of TNF-alpha mRNA (P = 0.050) and upregulation of IL-6 mRNA (P < 0.001), which were both prevented by the C5 inhibitor (P = 0.014 and P < 0.001 respectively).

CONCLUSION

These results indicated that C5 complement inhibition can reduce shock and acute lung injury in an experimental model of RAAA.

Ischaemia-Reperfusion Injury and Regional Inflammatory Responses in Abdominal Aortic Aneurysm Repair

OBJECTIVES

The inflammatory response to abdominal aortic aneurysm repair is likely to result in response to an ischaemia-reperfusion injury (IRI) to the lower-limbs and gastrointestinal tract. This paper reviews the pathogenesis of the inflammatory response to abdominal aortic aneurysm repair, with specific reference to the levels of evidence in the current literature regarding the potential origin of the inflammatory response.

DESIGN

Review article.

METHODS

The current literature (1966 to August 2003) was reviewed specifically for all articles employing techniques of regional blood sampling from the venous drainage of the lower limbs or gastrointestinal tract during abdominal aortic aneurysm repair.

RESULTS

Ten relevant studies were identified. These demonstrated that regional blood sampling techniques could be easily performed, and provided useful information regarding the potential sites of origin of the inflammatory response.

CONCLUSIONS

Regional blood sampling techniques provide useful information regarding the potential sites of origin of the inflammatory response. Current evidence suggests that both the lower limbs and gastrointestinal tract are clearly important in their roles, however more work is now required to compare directly the roles and contributions of the lower limbs and gastrointestinal tract to the inflammatory response during abdominal aortic aneurysm repair.

A monoclonal antibody against cytokine-induced neutrophil chemoattractant attenuates injury in the small intestine in a model of ruptured abdominal aortic aneurysm

PURPOSE

Ruptured abdominal aortic aneurysm (RAAA) continues to be a major source of aneurysm-related morbidity and mortality. Neutrophils have been implicated in RAAA repair-induced organ injury; however, the agents responsible for neutrophil activation and organ sequestration have not been identified. This study investigated the role of cytokine-induced neutrophil chemoattractant (CINC) in organ injury in an RAAA model.

METHODS

Rats were subjected to 1 hour of hemorrhagic shock with resuscitation, followed by 45 minutes of lower torso ischemia and 2 hours of reperfusion, and randomly were selected to receive saline solution or anti-rat CINC monoclonal antibody at the start of hemorrhagic shock. Another group of animals underwent sham operation, and served as a control group. Intestinal and lung permeability, intestinal and lung myeloperoxidase (MPO) activity, intestinal and lung CINC, and tumor necrosis factor-alpha (TNF-alpha) levels, resuscitation fluid requirements, and histologic mucosal injury were evaluated in all groups.

RESULTS

The RAAA model resulted in increased lung and intestinal permeability to radiolabeled albumin and lung MPO activity (P <.01), with increases in intestinal TNF-alpha (P <.001) and CINC (P <.01) levels, when compared with sham-operated animals. Treatment with anti-rat CINC monoclonal antibody attenuated the increases in intestinal permeability and histologic mucosal injury (P <.01), gut TNF-alpha level (P <.001), and resuscitation fluid volume required (P <.05), without significantly affecting lung and intestinal MPO activity, lung permeability, and intestinal CINC level (P = NS), compared with animals given saline solution.

CONCLUSION

Neutralization of CINC by the anti-rat CINC monoclonal antibody attenuated intestinal injury and induction of intestinal TNF-alpha, but failed to significantly attenuate remote pulmonary injury in this model of RAAA.

Expression of Toll-like receptors 2 and 4 is downregulated after operation

BACKGROUND

Toll-like receptors (TLR) that recognize microbial pathogens play a critical role in innate immunity; however, their expression and function after surgery remain unknown. The aim of this study was to examine TLR2 and TLR4 expression on monocytes and their responses to each agonist after surgical insults.

METHODS

Blood samples were obtained from 83 patients who underwent gastrointestinal surgery. TLR2, TLR4, and inducible nitric oxide synthase expressions on peripheral blood mononuclear cells (PBMCs) were analyzed by flow cytometry. Macrophage-activating lipopeptide-2 or lipopolysaccharide-induced tumor necrosis factor-alpha and interleukin-6 production was measured by enzyme-linked immunosorbent assay.

RESULTS

TLR2 and TLR4 decreased and showed the lowest values on the postoperative days 3 and 1, respectively. Macrophage-activating lipopeptide-2-stimulated tumor necrosis factor-alpha and interleukin-6 production was decreased immediately after the operation (P<.05), increased to a maximum value on postoperative day 1, and then decreased gradually. Lipopolysaccharide-stimulated tumor necrosis factor-alpha production was also suppressed immediately (P<.05) after operation then showed a gradual increase to maximum values on postoperative day 3. Inducible nitric oxide synthase in cultured PBMC that was obtained immediately after operation was upregulated (P<.05).

CONCLUSION

Expressions of TLR2 and TLR4 were downregulated by operation, and agonist-induced cytokine production was suppressed transiently and soon increased through the activation of PBMC. The present study may offer new insights for postoperative modulation of innate immunity under surgical stress.

Complement C5a receptor antagonist attenuates multiple organ injury in a model of ruptured abdominal aortic aneurysm

OBJECTIVE

Abdominal aortic aneurysm (AAA) rupture is associated with a systemic inflammatory response syndrome, characterized by increased microvascular permeability and neutrophil sequestration, leading to multiorgan dysfunction. We examined the role of a novel complement factor 5a (C5aR) receptor antagonist, the cyclic peptide AcF-(OpdChaWR), in attenuation of pathologic complement activation and tissue injury in a model of AAA rupture.

METHODS

Anesthetized rats were randomized to sham (control) or shock and clamp (s+c) groups. Animals in the s+c group underwent 1 hour of hemorrhagic shock (mean arterial blood pressure < or =50 mm Hg), followed by 45 minutes of supramesenteric aortic clamping, then 2 hours of resuscitated reperfusion. Animals in the s+c group were randomized to receive an intravenous bolus of C5aR antagonist at 1 mg/kg or saline solution control at the end of hemorrhagic shock. Intestinal and pulmonary permeability to iodine 125-labeled albumin was measured as an indicator of microvascular permeability. Tissue myeloperoxidase activity, proinflammatory cytokine tissue necrosis factor-alpha (TNF-alpha) protein and mRNA, and C5aR mRNA levels were measured as indicators of neutrophil sequestration and inflammatory signaling, respectively.

RESULTS

Lung permeability index was significantly increased in the s+c group compared with the sham group (4.43 +/- 0.96 vs 1.30 +/- 0.17; P <.01), and prevented with treatment with C5aR antagonist (1.74 +/- 0.50; P <.03). Lung myeloperoxidase activity was significantly increased in the the s+c group compared with the sham group (2.41 +/- 0.34 U/mg vs 1.03 +/- 0.29 U/mg; P <.009), and significantly attenuated with treatment with C5aR antagonist (1.11 +/- 0.09 U/mg; P <.006). Lung TNF-alpha protein levels were significantly elevated in both s+c groups, whereas lung TNF-alpha mRNA expression was significantly downregulated in both s+c groups compared with the sham group. Intestinal permeability index was significantly increased in animals in the s+c groups during reperfusion, compared with sham (P <.001), which was attenuated in early reperfusion with treatment with C5a receptor antagonist. Data represent mean +/- SEM, group comparisons with analysis of variance and post hoc Scheffé test.

CONCLUSIONS

These results indicate that a potent antagonist of C5a receptor protects the rat intestine and lung from neutrophil-associated injury in a model of AAA rupture. These data suggest that complement-mediated inflammation can be modulated at the C5a receptor level, independent of proinflammatory TNF-alpha production, and prevent acute local and remote organ injury.

Ruptured abdominal aortic aneurysm, a "two-hit" ischemia/reperfusion injury: evidence from an analysis of oxidative products

PURPOSE

Ruptured abdominal aortic aneurysm (RAAA) remains a lethal condition despite improvements in perioperative care. The consequences of RAAA are hypothesized to result from a combination of two ischemia/reperfusion events: hemorrhagic shock and lower torso ischemia. Ischemia/reperfusion results in tissue injury by diverse mechanisms, which include oxygen free radical-mediated injury produced from activated neutrophils, xanthine oxidase, and mitochondria. Oxygen-free radicals attack membrane lipids, resulting in membrane and subsequently cellular dysfunction that contributes to postoperative organ injury/failure. The purpose of this investigation was to quantify the oxidative injury that occurs as a result of the ischemia/reperfusion events in RAAAs and elective AAAs.

METHODS

Blood samples were taken from 22 patients for elective AAA repair and from 14 patients for RAAA repair during the perioperative period. Plasma F(2)-isoprostanes were extracted, purified, and measured with an enzyme immunoassay. Aldehydes and acyloins were purified and quantified. Neutrophil oxidative burst was measured in response to a receptor independent stimulus (phorbol 12-myristate 13-acetate) with luminol-based chemiluminescence.

RESULTS

Plasma from patients with RAAAs showed significantly elevated F(2)-isoprostane levels on arrival at hospital and were significantly elevated as compared with the levels of patients for elective repair throughout the perioperative period (two-way analysis of variance, P <.0001). Multiple regression showed a significant relationship between the phagocyte oxidative activity and F(2)-isoprostane levels (P <.013). Total acyloin levels were significantly higher in patients with RAAAs as compared with the levels in elective cases.

CONCLUSION

The F(2)-isoprostane levels, specific markers of lipid peroxidation, showed that patients with RAAAs had two phases of oxidative injury: before arrival at hospital and after surgery. The significant relationship between the postoperative increases in F(2)-isoprostane levels and the neutrophil oxidant production implicates neutrophils in the oxidative injury that occurs after RAAA. New therapeutic interventions that attenuate neutrophil-mediated oxidant injury during reperfusion may decrease organ failure and ultimately mortality in patients with RAAAs.

Lower limb ischemia: phase 1 results of salvage perfusion

Revascularization of an ischemic lower extremity is associated with high morbidity (20-30%) and perioperative mortality (10-20%) regardless of the mode of intervention, surgical or thrombolytic, considered to be due to polymorphonuclear (PMN) activation and mediator release. In this study, the safety and feasibility of cell-free extracorporeal perfusion of the limb with a solution designed to minimize both local and systemic injury was tested. Methods. Patients with severe limb ischemia (sensory/motor loss, rest pain/gangrene) were studied prospectively by random assignment into the treatment arm (n = 14) or control arm (n = 21). Surgical management consisted of restorative procedure, thrombectomy or embolectomy (n = 21), or reconstruction (n = 14). Reperfusion of the ischemic limb was achieved with hypertonic, hyperoncotic perfusate containing anti-oxidants delivered via the arterial tree (mean volume 1835 +/- 824 ml) with initial venous drainage (mean volume 775 +/- 263 ml) in the restorative group. Means were compared by paired t test. Results. No adverse systemic effects were detected after limb perfusion (electrolytes, coagulation, platelet function, CBC). Rapid lactate wash-out was observed within 30 min of perfusion (preperfusion 3.2 +/- 4.1 mM, 30 min postperfusion 0.7 +/- 0.71 mM, P < 0.01). Blunting of PMN activation was shown by chemiluminescence (CL) analysis (preischemic CL: 0.68 +/- 0.2; 30 min CL: 0.47 +/- 0. 2; P < 0.013). F2-isoprostanes, a marker of free radical-mediated systemic lipid peroxidation, were significantly reduced in patients treated with study perfusion method (70.55 +/- 39.54 versus control 194.38 +/- 25.24, P < 0.005). Mortality with treatment was 0/14 versus 5/21 in the control. Complication frequency: MI 0/14 vs 3/21; renal 0/14 vs 1/21; leg edema 1/14 vs 5/21; amputations 2/14 vs 1/21. Conclusion. Modification of limb perfusion in patients with severe limb ischemia, using our simple and rapid (15-20 min) method provides beneficial systemic effects.

The impact of multiple organ dysfunction on mortality following ruptured abdominal aortic aneurysm repair

The in-hospital mortality for a patient with a ruptured abdominal aortic aneurysm (RAAA) ranges from 30% to 70% and remains unchanged despite aggressive surgical, anesthetic, and intensive-care management. The purpose of this investigation is to determine the relationship between the development of organ dysfunction and mortality in ruptured AAA patients. Eighty-eight consecutive patients admitted to the Toronto Hospital for repair of RAAAs were studied. APACHE II and multiple organ dysfunction (MOD) scores were calculated for all patients. The MOD scoring system measures daily alterations in the function of six key organs, with increased dysfunction indicated by an increasing score. The overall 30-day mortality rate was 40%; 10% of patient deaths occurred intraoperatively. ICU mortality was bimodal; 11.5% deaths occurred within the first 48 hours compared to 18.2% after 48 hours (late deaths). The APACHE II score was significantly higher in those who died within 48 hours of ICU admission (28.5 +/- 6.36) compared to both those who died late (17.2 +/- 5.7, p < 0.0001) and survivors (11.2 +/- 4.2, p < 0.0001). The survivors' daily mean MOD scores did not increase significantly, while the MOD scores for late deaths increased progressively (p < 0.01). The renal and hepatic dysfunction components of the MOD score were significantly lower in the survivors compared to late deaths (p < 0.001), however the respiratory MOD score did not differ between the groups (p > 0.05). The change in MOD (delta MOD) score over the intensive care stay was significantly greater in late deaths compared to survivors (p < 0.01). The rates of infection were similar in both groups and were not responsible for mortality. We conclude that mortality is better predicted following RAAA by the development of renal and hepatic dysfunction rather than by initial physiologic derangement measured by the APACHE II score.