The mechanisms and prevention of intravascular fluid loss after occlusion of the supraceliac aorta in dogs

Valproic acid reversed pathologic endothelial cell gene expression profile associated with ischemia-reperfusion injury in a swine hemorrhagic shock model

BACKGROUND

Vascular endothelial cells serve as the first line of defense for end organs after ischemia and reperfusion injuries. The full etiology of this dysfunction is poorly understood, and valproic acid (VPA) has proven to be beneficial after traumatic injury. The purpose of this study was to determine the mechanism of action through which VPA exerts its beneficial effects.

METHODS

Sixteen Yorkshire swine underwent a standardized protocol for an ischemia-reperfusion injury through hemorrhage and a supraceliac cross-clamp with ensuing 6-hour resuscitation. The experimental swine (n = 6), received VPA at cross-clamp application and were compared with a sham (n = 5) and injury-control models (n = 5). Aortic endothelium was harvested, and microarray analysis was performed along with a functional clustering analysis with gene transcript validation using relative quantitative polymerase chain reaction.

RESULTS

Clinical comparison of experimental swine matched for sex, weight, and length demonstrated that VPA significantly decreased resuscitative requirements, with improved hemodynamics and physiologic laboratory measurements. Six transcript profiles from the VPA treatment were compared with the 1536 gene transcripts (529 up and 1007 down) from sham and injury-control swine. Microarray analysis and a Database for Annotation, Visualization and Integrated Discovery functional pathway analysis approach identified biologic processes associated with pathologic vascular endothelial function, specifically through functional cluster pathways involving apoptosis/cell death and angiogenesis/vascular development, with five specific genes (THBS1, TNFRSF12A, ANGPTL4, RHOB, and RTN4) identified as members of both functional clusters. This study also examined gene expression of transforming growth factor (TGF)-β (TGF-β1, TGF-β2, and TGF-β-releasing thrombospondin 1 [THBS1]) and genes expressing vascular endothelial growth factor (VEGF) C, VEGFD, and VEGFR1 and found that these genes were involved in the endothelial functional preservation associated with VPA administration.

CONCLUSIONS

VPA minimized pathologic endothelial cell function through the TGF-β and VEGF functional pathways. This study also implicates that integrated functional modeling and analysis will enable advancements in endothelial dysfunction using a systems biology approach.

d-Lactate is not a reliable marker of gut ischemia–reperfusion in a rat model of supraceliac aortic clamping*

OBJECTIVE

D-lactate is the dextrorotatory form of L-lactate. L-lactate is the isomer routinely tested in clinical practice to assess cell hypoxemia. D-lactate has been recently proposed as a specific marker of gut ischemia-reperfusion (IR), particularly after surgery for ruptured aortic aneurysms. We sought to assess D-lactate as a reliable marker of gut IR in a rat model of supraceliac aortic clamping.

DESIGN

Prospective, randomized trial.

SETTING

Animal research center.

SUBJECTS

Male Wistar rats.

INTERVENTIONS

After general anesthesia, rats were randomized into two groups (n = 8 in each). The IR group underwent a laparotomy, aortic clamping for 40 mins, and 1 hr of reperfusion. The control group underwent the same procedure, except for aortic clamping.

MEASUREMENTS AND MAIN RESULTS

The following variables were tested after 1 hr of reperfusion (IR group) or after the equivalent time (control group): 1) tissue and cell insult via ileum morphometry and electron microscopy, serum glutamic transaminases (serum glutamic-oxaloacetic transaminase and serum glutamic-pyruvic transaminase), pH, and L-lactate; 2) systemic inflammatory response via tumor necrosis factor-alpha; and 3) D-lactate levels. After IR, mucous membrane thickness and villi height decreased significantly, respectively by 30% and 45%, and electron-microscopic examination showed typical IR mucous membrane cell insult. IR also caused lactic acidosis (pH = 7.16 +/- 0.05 vs. 7.31 +/- 0.02, p < .01; L-lactate = 7.1 +/- 1.6 vs. 1.6 +/- 0.4 mmol/L, p = .001) and increased blood levels of transaminases. Concurrently, the inflammatory response was characterized by an increase in tumor necrosis factor-alpha (213 +/- 129 vs. 47 +/- 32 pg/mL, p < .05). However, blood levels of D-lactate never increased after IR.

CONCLUSIONS

D-lactate is not a reliable marker of gut IR in our model of supraceliac aortic clamping in rats.

Systemic and mesenteric hemodynamics, metabolism, and intestinal tonometry in a rat model of supraceliac aortic cross-clamping and declamping

OBJECTIVE

To describe systemic and mesenteric hemodynamics, metabolism, and intestinal tonometry in a rat model of supraceliac aortic cross-clamping and declamping.

DESIGN

Prospective, randomized, experimental study.

SETTING

University cardiovascular research laboratory.

PARTICIPANTS

Twelve male anesthetized and ventilated Sprague-Dawley rats.

INTERVENTION

Supraceliac aortic cross-clamping was performed for 30 minutes, followed by declamping and reperfusion for 180 minutes or sham clamping and sham declamping.

MEASUREMENTS AND MAIN RESULTS

Mean arterial blood pressure; abdominal aortic, superior mesenteric, and carotid artery blood flow; intestinal mucosal tonometry; hemoglobin; lactate; and blood gases were measured before and after 30 minutes of aortic cross-clamping and 15, 30, 60, 120, and 180 minutes after declamping during reperfusion. Aortic cross-clamping induced an increase in mean arterial pressure (117+/-20 mm Hg to 147+/-12 mm Hg), an increase in right atrial hemoglobin saturation(66%+/-11% to 81%+/-6%), an increase in lactate levels (1.7+/-0.7 mmol/L to 4.3+/-1.3 mmol/L), and an increase in tonometric PCO2 (49.6+/-5.0 mm Hg to 75.6+/-8.6 mm Hg). Three hours of reperfusion after declamping resulted in significantly decreased mean arterial pressure (38+/-10 mm Hg); decreased aortic (101+/-12 mL/min/kg to 57+/-32 mL/min/kg), mesenteric (19+/-4 to 13+/-6 mL/min/kg), and carotid (12+/-4 mL/min/kg to 5+/-3 mL/min/ kg) blood flows; and elevated lactate levels (4.2+/-2.0 mmol/L). Tonometric PCO2 had normalized to baseline levels (51.9+/-3.8 mm Hg), but PCO2 gap was significantly higher than in sham clamped rats (17.9+/-7.8 mm Hg v. 7.0+/-2.6 mm Hg).

CONCLUSIONS

Hemodynamic and metabolic effects of aortic cross-clamping and declamping known from large animal models are reproducible using a rat model. Intestinal tonometry indicated mesenteric ischemia during aortic cross-clamping, which was reversible to preclamp values within 30 minutes of reperfusion after declamping.

Hemodynamic effects of isovolemic hemodilution during descending thoracic aortic cross clamping and lower torso reperfusion

BACKGROUND

Isovolemic hemodilution has been suggested for blood conservation and to improve hemodynamic tolerance to abdominal aortic cross clamping. However, the hemodynamic effects of hemodilution during descending thoracic aortic cross clamping (DAC) have not been established. We evaluated them in anesthetized swine.

METHODS

Hemodilution (n = 7) was produced by the isovolemic exchange of blood for 6% hetastarch to a target hematocrit of 20%. Hematocrit in control pigs (n = 7) remained at 30%. DAC was performed at the T9 level for 45 minutes. During a 60-minute reperfusion period, control pigs were infused with lactated Ringer's solution; shed blood was returned to hemodilution pigs, followed by lactated Ringer's. If hypotension occurred despite left atrial pressure of 10 mm Hg or greater, boluses of phenylephrine were given to keep mean arterial pressure above 60 mm Hg.

RESULTS

Hemodilution caused a marked reduction in hematocrit and in global oxygen delivery (DO2). DAC produced a significant increase in proximal arterial pressure, cardiac index, and DO2 and oxygen consumption (VO2) was markedly reduced in both groups. A significant increase in systemic vascular resistance during DAC occurred only in control pigs. After reperfusion, vascular resistance was significantly lower than baseline in hemodilution pigs, requiring a sixfold greater dose of phenylephrine to avoid hypotension. A lower global DO2 and supply-limited VO2 were also observed in hemodilution pigs.

CONCLUSIONS

Isovolemic hemodilution maintains hemodynamic stability during DAC. During lower torso reperfusion, however, hemodilution caused hemodynamic instability, decreased global DO2, and limited VO2, which may offset its potential benefits.

Superoxide dismutase (SOD) prevents hypotension after hemorrhagic shock and aortic cross clamping

To determine if superoxide dismutase (SOD) administration attenuates injury caused by supraceliac aortic cross clamping, a randomized controlled study on 12 taconic rats was performed at the university hospital research center at Syracuse, New York. All animals were anesthetized and placed on a ventilator through a tracheotomy. Surgical preparation included catheterization of carotid and femoral arteries, and the jugular vein. A midline laparotomy was performed through which the supraceliac aorta was exposed and isolated. Animals were allowed to stabilize after surgery and baseline measurements [systemic pressure (Psys), central venous pressure, and blood gases] were recorded. Then, animals were subjected to 60 minutes of hemorrhagic shock (mean Psys = 35 mm Hg), followed by 45 minutes of supraceliac aortic cross clamping. After the release of the aortic cross clamp, shed blood was reinfused. After stabilization, all animals were monitored for 60 minutes. Rats were separated into two groups: the experimental group (n = 6) that received intravenous SOD before and during aortic cross clamping, and the control group (n = 6) that received an equivalent volume of saline at the same time periods. No difference was detected in overall arterial pH, partial arterial carbon dioxide pressure, or base excess at any time period between the groups. A significant increase in Psys was measured in the experimental group compared with the control group from the time of aortic cross-clamp release until the experiment was terminated. One hour after aortic cross-clamp release, the Psys for the experimental group was 69.2 +/- 10.6 mm Hg vs. 36.7 +/- 3.8 mm Hg for the control group (P < 0.05). These data demonstrate that superoxide dismutase significantly improves postaortic cross-clamp Psys. This suggests that oxygen-derived free radicals play a role in postaortic cross-clamp hypotension.

Increased intestinal permeability: implications for thoracoabdominal aneurysm repair

Coagulopathy and massive bleeding plays a major role in the mortality of thoraco-abdominal aneurysm repair. Increasing supraceliac aortic cross-clamp time from 0 to 90 minutes increases the degree of disseminated intravascular coagulation, which occurs as a result of occlusion and reperfusion of the superior mesenteric artery. The purpose of this study was to investigate the mechanism of the superior mesenteric artery reperfusion disseminated intravascular coagulation. Twenty dogs were divided into four groups: cross-clamp time of 30 minutes; cross-clamp time of 60 minutes; cross-clamp time of 90 minutes; and control. Permeability was determined by lactulose/mannitol absorption. The venous effluent was sampled for endotoxin, potassium, bacteria, and pH every hour and urine was collected for six hours. Lactulose absorption was significantly higher in all of the experimental groups. There was increased permeability in the 60 and 90 minute groups which correlated significantly with time. Venous endotoxin, potassium, and blood cultures for bacteria did not change significantly. The pH was significantly lower every hour for six hours in the 90 minute group. These data suggest that intestinal permeability is increased with supraceliac aortic clamping and can be kept to a minimum for clamp times of under one hour.