Extracorporeal circulation increases proliferation in the intestinal mucosa in a large animal model.

OBJECTIVE: Extracorporeal circulation induces ischemia/reperfusion injury in the small intestinal wall. One reason for this damage is a perfusion shift from the muscular toward the mucosal layer. This study investigated the effect of this perfusion shift on the small-intestinal apoptosis and proliferation. METHODS: Twenty-eight pigs were randomly assigned to the following cohorts and underwent a thoracolaparotomy and a 1 hour main procedure: cohort I: control; cohort II: thoracic aortic cross-clamping (TAC) without perfusion; cohort III: TAC and distal aortic perfusion (DAP); cohort IV: TAC, DAP, and selective visceral perfusion. The main procedure was followed by 2 hours of reperfusion in all cohorts. Tissue samples were taken during the experiment, stained, and analyzed for apoptosis and proliferation (caspase-3, annexin-V, terminal deoxynucleotide transferase-mediated deoxy uridine triphosphate nick-end labeling, and proliferating cell nuclear antigen). Six animals died unexpectedly during the experiment and were excluded from the analysis. RESULTS: Extensive tissue damage and necrosis was only found in cohort II after the main procedure. In the mucosa, the proliferation was increased in cohort III at the end of the experiment (P = .0157 cohort I vs II). In contrast, the annexin-V/proliferating cell nuclear antigen ratio was significantly higher in cohorts II and IV than in cohorts I and II at the end of the experiment (P = .0034). Furthermore, the caspase-3/annexin-V ratio was increased in all cohorts at the end of the experiment (P = .0015). CONCLUSIONS: Mucosal proliferation is the early repair mechanism of the limited small intestinal ischemia/reperfusion injury after DAP. Furthermore, the extensive surgical trauma shifted the mucosal apoptosis into an advanced state.

The impact of selective visceral perfusion on intestinal macrohemodynamics and microhemodynamics in a porcine model of thoracic aortic cross-clamping.

INTRODUCTION: Despite its presumed effectiveness and clinical use, the physiology of selective visceral perfusion combined with distal aortic perfusion during open thoracoabdominal aortic surgery has not been characterized. Thus, the aim of this study was to establish a translatable model of thoracic aortic-clamping to assess the effect of selective visceral perfusion with added distal aortic perfusion on local intestinal macrohemodynamics and microhemodynamics, intestinal histopathology, and markers of inflammation and intestinal damage. METHODS: A thoracolaparotomy was performed in 15 pigs, and the aorta was exposed, including the origins of celiac trunk and superior mesenteric artery. The animals were divided into three cohorts: control (I), thoracic aortic cross-clamping (II), and thoracic aortic cross-clamping with selective visceral perfusion plus distal aortic perfusion using extracorporeal circulation (III). Macrocirculatory and microcirculatory blood flow was assessed by transit time ultrasound volume flow measurements and fluorescent microspheres. Intestinal ischemia-reperfusion injury was determined by the analysis of perioperative intestinal fatty acid-binding protein (IFABP) and interleukin-8 (IL-8) levels and correlated with histopathologic changes. RESULTS: Severe intestinal tissue injury and an inflammatory response were observed in cohort II compared with cohort III for IL-8 (38.2 vs 3.56 pg/mL; P = .04). The procedure in cohort III resulted in a flow and pressure-associated intestinal hypoperfusion compared with cohort I in the superior mesenteric artery (mean blood pressure, 24.1 ± 10.4 vs 67.2 ± 7.4 mm Hg; P < .0001; mean flow rates: 353.3 ± 133.8 vs 961.7 ± 310.8 mL/min; P < .0001). This was paralleled in cohort III vs cohort I by a significant mucosal injury (IFABP, 713 ± 307.1 vs 170 ± 115.4 pg/mL; P = .014) despite a profound recruitment of intestinal microcirculation (338% ± 206.7% vs 135% ± 123.7%; P = .05). CONCLUSIONS: This study reports a novel large-animal model of thoracic aortic cross-clamping that allows the study of visceral perfusion strategies. However, we demonstrated with IL-8 and IFABP measurements that thoracoabdominal aortic aneurysm surgery with selective visceral perfusion and distal aortic perfusion is superior to the clamp-and-sew technique, even though small intestinal tissue damage cannot be completely avoided by selective visceral perfusion and distal aortic perfusion. In any case, this model seems to be a platform to evaluate and optimize measures for gut wall protection.

Hemolysis compromises nitric oxide-dependent vasodilatory responses in patients undergoing major cardiovascular surgery.

BACKGROUND: The hemolytic products cell-free oxyhemoglobin (FHb) and arginase-1 reduce nitric oxide (NO) bioavailability by scavenging NO and by degrading the NO precursor arginine to ornithine, respectively. In this study we evaluated the relevance of hemolysis to NO-dependent blood flow in patients undergoing cardiovascular surgery. METHODS: Plasma FHb, arginase-1, and amino acid concentrations were measured perioperatively. Forearm blood flow (FBF) responses to the intra-arterial administered NO-donor sodium nitroprusside (SNP) and the endothelium-dependent vasodilator acetylcholine (ACh) were measured by venous occlusion plethysmography. RESULTS: When peak values plasma FHb and arginase-1 were found, vascular dilatation to SNP, but not ACh, was significantly reduced compared with 1 day postoperatively, when FHb had returned to baseline levels (p < 0.05). Interestingly, plasma FHb concentration was inversely correlated to FBF responses to SNP (r -0.93, p < 0.001). In contrast, the increase in arginase-1 was not biologically relevant as the ratio of plasma arginine to ornithine remained constant. CONCLUSION: We conclude that hemolysis with concomitant release of FHb during cardiovascular surgery is associated with impaired NO-dependent forearm blood flow.

Hemolysis is associated with acute kidney injury during major aortic surgery.

Hemolysis is an inevitable side effect of cardiopulmonary bypass resulting in increased plasma free hemoglobin that may impair tissue perfusion by scavenging nitric oxide. Acute kidney injury after on-pump cardiovascular surgery arises from a number of causes and severely affects patient morbidity and mortality. Here, we studied the effect of acute hemolysis on renal injury in 35 patients undergoing on-pump surgical repair of thoracic and thoracoabdominal aortic aneurysms of whom 19 experienced acute kidney injury. During surgery, plasma free hemoglobin increased, as did urinary excretion of the tubular injury marker N-acetyl-beta-D-glucosaminidase, in patients with and without acute kidney injury, reaching peak levels at 2 h and 15 min, respectively, after reperfusion. Furthermore, plasma free hemoglobin was independently and significantly correlated with the urine biomarker, which, in turn, was independently and significantly associated with the later postoperative increase in serum creatinine. Importantly, peak plasma free hemoglobin and urine N-acetyl-beta-D-glucosaminidase concentrations had significant predictive value for postoperative acute kidney injury. Thus, we found an association between increased plasma free hemoglobin and renal injury casting new light on the pathophysiology of acute kidney injury. Therefore, free hemoglobin is a new therapeutic target to improve clinical outcome after on-pump cardiovascular surgery.

Visceral injury and systemic inflammation in patients undergoing extracorporeal circulation during aortic surgery.

OBJECTIVES: Visceral injury and inflammation are evaluated in patients undergoing extracorporeal circulation (ECC) either with distal aortic perfusion (DAP) during thoracic aortic aneurysm (TAA) repair or DAP and selective organ perfusion (DAP and SP) during thoracoabdominal aortic aneurysm (TAAA) repair. SUMMARY BACKGROUND DATA: Visceral hypoperfusion and subsequent visceral injury, mainly to the gut, have been implicated as central events in the development of systemic inflammatory response syndrome (SIRS) and organ dysfunction after major surgery. Patients undergoing DAP or DAP and SP are exposed to artificial visceral perfusion, potentially leading to the development of intestinal injury and systemic inflammation. METHODS: To assess visceral injury arteriovenous differences of fatty acid binding proteins were measured for the gut (I-FABP and L-FABP) and left kidney (L-FABP) along with systemic plasma concentrations. Systemic ALT was used as liver injury marker. Plasma IL-6 and IL-8 denoted systemic inflammation. RESULTS: During ECC systemic I-FABP and L-FABP levels increased in both groups, representing intestinal injury. Significantly elevated levels of I-FABP (P < 0.001) and L-FABP (P < 0.001) were found in the DAP and SP group, after ECC was stopped and normal circulation restored. Liver and renal tubular cell injury was not detected. Significant increases in systemic IL-6 and IL-8 values were measured only in patients undergoing DAP and SP. Additionally, the extent of intestinal injury correlated positively with systemic inflammation. CONCLUSIONS: This study shows the development of intestinal mucosal injury during ECC with DAP or DAP and SP, indicative of insufficient intestinal perfusion. Intestinal injury was associated with a systemic pro-inflammatory response.

Elevated plasma arginase-1 does not affect plasma arginine in patients undergoing liver resection.

Arginine is an important substrate in health and disease. It is a commonly held view that arginase-1 release from injured erythrocytes and hepatocytes leads to arginine breakdown; however, the true relationship between plasma arginase-1 concentration and activity has remained unaddressed. In the present study, blood was sampled from patients undergoing liver resection, a known cause of hepatocyte injury and arginase-1 release, to determine arginase-1, arginine and ornithine plasma levels. Arginase activity was assessed in vitro by measuring changes in arginine and ornithine plasma levels during incubation of plasma and whole-blood samples at 37 degrees C. Arginase-1 plasma levels increased 8-10-fold during liver resection, whereas arginine and ornithine levels remained unchanged. In accordance with these in vivo findings, arginine and ornithine levels remained unchanged in plasma incubated at 37 degrees C irrespective of the arginase-1 concentration. In contrast, arginine plasma levels in whole blood decreased significantly during incubation, with ornithine increasing stoichiometrically. These changes were irrespective of arginase-1 plasma levels and were explained by arginase activity present in intact erythrocytes. Next, plasma samples with 1000-fold normal arginase-1 concentrations were obtained from patients undergoing cadaveric liver transplantation. A significant decrease in arginine plasma levels occurred in vivo and in vitro. In contrast with commonly held views, moderately increased arginase-1 plasma levels do not affect plasma arginine. Very high plasma arginase-1 levels are required to induce potential clinically relevant effects.

Hemolysis results in impaired intestinal microcirculation and intestinal epithelial cell injury.

AIM: To study the effect of circulating cell-free oxyhemoglobin (FHb) on intestinal microcirculation and intestinal epithelial injury in a rat model. METHODS: To induce elevated intravascular circulating FHb, male Sprague-Dawley rats received water or FHb infusion. Microcirculatory changes in jejunum, ileum and colon were evaluated using fluorescent microspheres. Intestinal injury was quantified as plasmatic release of ileal lipid binding protein (iLBP) and verified by histological analysis of the ileum. RESULTS: Water and FHb infusions resulted, when compared with saline infusion, in reduced intestinal microcirculation (after 30 min P < 0.05, or better; after 60 min FHb infusion P < 0.05 for jejunum and colon). Circulating FHb levels correlated significantly with release of iLBP (Spearman r = 0.72, P = 0.0011). Epithelial cell injury of the villi was histologically observed after water and FHb infusions. CONCLUSION: This study shows that circulating FHb leads to a reduction in intestinal microcirculatory blood flow with marked injury to intestinal epithelial cells. These data support the hypothesis that circulating FHb contributes to the development of intestinal injury.