The effect of renin-angiotensin system blockade on visceral blood flow during and after thoracic aortic cross-clamping

Surgical procedures necessitating clamping of the thoracic aorta are associated with a high incidence of postoperative renal dysfunction. Plasma renin activity is elevated during and after thoracic aortic occlusion in animals. The pathophysiology of the renal dysfunction may involve the renin-angiotensin system. Blockade of the renin-angiotensin system was studied in a canine model during occlusion of the thoracic aorta. Saralasin, a competitive blocker of angiotensin II, and the converting enzyme inhibitor MK422 were studied. Sixteen animals were separated into three treatment groups: control (five animals), saralasin (five), and MK422 (six). All dogs underwent clamping of the thoracic aorta for 60 minutes. In control animals, plasma renin activity increased from 0.16 +/- 0.04 to 6.41 +/- 1.57 ng/ml/hr at 30 minutes after thoracic aortic occlusion (p less than 0.05). Thirty minutes after cross-clamp release, plasma renin activity remained 10 times greater than baseline, 1.47 +/- 0.20 ng/ml/hr (p less than 0.05). Renal blood flow was measured with 15 micron microspheres before, during, and after thoracic clamping. In control animals, renal cortical blood flow decreased during cross-clamping and remained below baseline after clamp release: baseline, 7.05 +/- 0.98 ml/gm/min (standard error of the mean); 30 min after clamp release, 3.77 +/- 0.43 ml/gm/min (standard error of the mean) (p less than 0.05). In the MK422 group, renal cortical blood flows returned to baseline after cross-clamp release: baseline, 6.38 +/- 0.49 ml/gm/min; 30 minutes after clamp release, 7.30 +/- 1.6 ml/gm/min. Infusion of MK422 after placement of the thoracic aortic cross-clamp resulted in normal renal blood flow after clamp release. This protective effect was not seen with saralasin. The resumption of normal renal cortical blood flow after the administration of the converting enzyme inhibitor MK422 suggests that elevated plasma renin activity may contribute to renal dysfunction after thoracic aortic occlusion.     

Effect of left atrial to left femoral artery bypass and renin-angiotensin system blockade on renal blood flow and function during and after thoracic aortic occlusion

Temporary thoracic aortic occlusion can result in renal insufficiency with or without adjuncts to avoid distal hypoperfusion. In a canine model of thoracic aortic occlusion, left atrial to left femoral bypass was compared with blockade of the renin-angiotensin system. Renin-angiotensin system blockade with the converting enzyme inhibitor, MK422, resulted in restoration of baseline renal blood flow and glomerular filtration 30 minutes after cross-clamp release. Left atrial to left femoral bypass resulted in significant reduction in both renal blood flow and glomerular filtration 30 minutes after cross-clamp release. Stimulation of the renin-angiotensin system plays a significant role in the altered renal hemodynamics and glomerular filtration rates after thoracic aortic occlusion.     

Influence of mannitol and dopamine on renal function during elective infrarenal aortic clamping in man

The impact of elective infrarenal aortic clamping on parameters of renal function was evaluated in 27 extracellular fluid volume expanded patients. Significant transient decreases (p less than 0.05) in glomerular filtration rate were observed in all three groups either in the early or late post-clamp release period, despite maintenance of hemodynamic stability. This study documents transient decreases in glomerular filtration rate which occurred following release of the infrarenal aortic cross-clamp. No clinically important benefit from the use of mannitol and dopamine over extracellular fluid volume expansion with saline alone was demonstrated in the prevention of the changes in renal function associated with aortic cross-clamping.     

Spinal oxygenation, blood supply localization, cooling, and function with aortic clamping.

Similar to other methods of organ preservation, "spinoplegia" may protect the spinal cord from the effects of oxygen desaturation during aortic cross-clamping. In porcine experiments, spinal cord O2 saturation was studied during intraoperative localization of the blood supply to the spinal cord using hydrogen; division of arteries not supplying the spinal cord; aortic cross-clamping for 60 minutes; and 60 minutes after unclamping. In 5 animals, 120 mL of cold saline solution with lidocaine (100 mg/dL) was infused into the aorta during aortic cross-clamping. During sequential localization, O2 saturation dropped by 40.02% (standard deviation, 20.16%) for T-14 artery testing versus a decrease of 17.27% (standard deviation, 11.88%; p = 0.0075) for L-5 artery segment testing in the control animals and returned to baseline thereafter. During aortic cross-clamping maximal O2 desaturation was 5% of baseline (15.7%; p less than 0.0001), which improved slightly by 30 minutes after clamping (48% of baseline +/- 37.37%; p = 0.048 versus maximum) and then returned to baseline (97.1% of baseline +/- 41%) with unclamping; 5 minutes later, hyperoxygenation occurred with a progressive decline thereafter (68% of baseline +/- 29.3%; p = 0.025, 45 minutes after unclamping versus baseline). The decrease in spinal motor evoked potentials was significantly less (p less than 0.02) in the treated group. Intraoperative hydrogen testing in 8 patients was demonstrated to be safe. It accurately localized reattached arteries, and O2 saturation of the spinal cord fell by 56% (standard deviation, 29%; p = 0.0025) with aortic cross-clamping. We conclude that spinal cord ischemia occurs with aortic cross-clamping in both animals and humans.(ABSTRACT TRUNCATED AT 250 WORDS)     

Renal and splanchnic circulation during infrarenal aortic cross-clamping

The effect of infrarenal cross-clamping of the aorta on regional splanchnic and renal circulations was studied in seven dogs. Regional blood flow was determined with differentially labeled microspheres (9 and 15 micron in diameter) that were injected simultaneously into the left atrium. Blood flow was measured 30 minutes after surgical preparation was completed (stage I), 20 minutes after infrarenal aortic cross-clamping (stage II), and 20 minutes after supplemented sodium nitroprusside infusion (stage III). Infrarenal aortic cross-clamping was accompanied by a slight increase in the cardiac output (CO) without significant changes in mean arterial pressure (MAP). Blood flow through the gut, hepatic artery, and cortical layer of the kidneys, as determined with 15-micron spheres, was not changed. Nonentrapment of 9-micron spheres in the gut and renal cortex was increased substantially. Blood flow through the juxtamedullary layer of the kidneys was increased. Sodium nitroprusside supplementation decreased MAP by 30%; CO values returned to baseline level. Hepatic artery blood flow, compared with both baseline values and values during aortic cross-clamping, increased significantly. Blood flow, determined with 15-micron spheres, through the gut and renal cortex did not change, and nonentrapment of 9-micron spheres decreased to baseline values. The data suggest a certain shift of blood flow to the juxtamedullary layer of the kidneys during aortic cross-clamping and normalization of intrarenal blood flow distribution during supplemented sodium nitroprusside infusion. Controlled vasoplegia with sodium nitroprusside may help modify peripheral circulatory disturbances in the kidneys and splanchnic system during infrarenal aortic cross-clamping.     

The Effects of Intraoperative Fenoldopam on Renal Blood Flow and Tubular Function following Suprarenal Aortic Cross-clamping

This study evaluated the effect of fenoldopam, a selective dopamine (DA1) agonist, on renal blood flow and renal tubular function following renal ischemia induced by suprarenal aortic cross-clamping. Twenty anesthetized research pigs received either fenoldopam (10 µg/kg/min; n = 10) or saline (n = 10) beginning 20 min before suprarenal aortic cross-clamping and continuing for 20 min after clamp release, for a total infusion time of 160 min (120-min cross-clamp). Recordings of renal blood flow, mean arterial pressure, and heart rate were taken at baseline, during cross-clamping, and immediately postclamp. Ischemic renal injury was evaluated by serum creatinine and by histologic grading of acute tubular necrosis. Treatment with fenoldopam increased renal blood flow in comparison to that in the control group (p = 0.03). The mean creatinine increase from baseline at 6 hr and 18 hr after cross-clamp removal for the fenoldopam-treated group was significantly less than that in the control group (p < 0.001). On histologic evaluation, the mean score for the degree of tubular necrosis was significantly higher in the control group (p = 0.02), indicating less derangement of tubular morphology in the fenoldopam group. This study demonstrated that the intraoperative use of a continuous infusion of fenoldopam during suprarenal aortic cross-clamping results in increased renal blood flow, less postoperative rise in creatinine, and better preservation of tubular histology in the pig model. Presented at the Thirteenth Annual Winter Meeting of the Peripheral Vascular Surgery Society, Snowmass, CO, January 31–February 2, 2003. The opinions or assertions contained herein are the private views of the authors and do not purport to reflect the position of the Department of the Air Force or the Department of Defense.     

Effects of thoracic aortic occlusion and cerebrospinal fluid drainage on regional spinal cord blood flow in dogs: correlation with neurologic outcome

We studied the effect of thoracic aortic occlusion and cerebrospinal fluid (CSF) drainage on regional spinal cord blood flow and its correlation with neurologic outcome. Using isotope-tagged microspheres, we determined blood flow to the gray and white matter of five regions of the spinal cord in dogs: group I (control), group II (cross-clamp only), group III (cross-clamp plus CSF drainage). At 60 minutes after thoracic aortic occlusion in group II, median gray matter blood flow (GMBF) in the lower thoracic and lumbar cord decreased from 23.1 and 27.0 ml/100 gm/min at baseline to 4.0 and 2.5 ml/100 gm/min, respectively. The addition of CSF drainage improved GMBF during aortic cross-clamping in the lower thoracic and lumbar cord to 11.3 (p less than 0.05) and 15.1 ml/100 gm/min (p less than 0.03), respectively. After removal of the aortic cross-clamp, median blood flow more than tripled from baseline blood flow in group II, whereas CSF drainage prevented significant reperfusion hyperemia. Both low GMBF during cross-clamping and reperfusion hyperemia were associated with a worse neurologic outcome. In group II, no dog was neurologically normal, and more than 60% of the dogs had spastic paraplegia. In contrast, almost 60% of dogs in group III were normal, and none had spastic paraplegia (p less than 0.001). We conclude that CSF drainage in dogs during thoracic aortic occlusion maintained spinal cord perfusion above critical levels, diminished reperfusion hyperemia, and improved neurologic outcome.     

The effect of hyperemia on spinal cord function after temporary thoracic aortic occlusion

Nineteen mongrel dogs had 30 minutes of thoracic aortic occlusion to determine the effects that blockade of the renin-angiotensin system may have on preserving spinal cord blood flow and function during a period of temporary spinal cord ischemia. Cross-clamping of the thoracic aorta causes renal ischemia and activates the renin-angiotensin system with resulting increased production of angiotensin II. Angiotensin II is a potent peripheral constrictor and elevated levels may constrict collateral spinal cord circulation. At the time of aortic cross-clamping, 10 dogs received 100 mg/kg of MK422 (intravenous enalapril maleate), a converting enzyme inhibitor, and nine animals served as controls. The blockade of the renin-angiotensin system had no preserving effects on spinal cord flow as measured by microspheres and on spinal cord function as graded with the Tarlov scale. However, the paraplegic animals all had significantly increased lower thoracic and lumbar spinal cord flows 30 minutes after clamp release when compared with those animals that remained neurologically intact. In conclusion, marked hyperemia occurring after a period of hypoperfusion may lead to spinal cord edema and compartment syndrome with resulting paraplegia.     

Regional blood flow during cross-clamping of the thoracic aorta and infusion of sodium nitroprusside

Labeled microspheres, 15 microns in diameter, were used to determine cardiac output and regional blood flow response to cross-clamping of the midthoracic aorta and subsequent sodium nitroprusside (SNP) infusion in 11 dogs. During aortic cross-clamping, mean arterial pressure above the occlusion (MAPa) increased 30% to 35%, mean arterial pressure below the occlusion (MAPb) decreased 87%, cardiac index decreased 12% to 14%, left atrial pressure (LAP) doubled, and renal and spinal cord (lower part) blood flows decreased substantially (85% to 94%). SNP infusion returned MAPa to baseline values, decreased MAPb by half, and substantially and further decreased renal blood flow (to 3% to 5% of baseline values). Myocardial and cerebral blood flows increased substantially (up to 250% to 400%). An increase in preload (fluid load) was accompanied by an increase in LAP, cardiac index, and myocardial blood flow only but not in renal or spinal cord flow. There was a strong association between cortical renal blood flow and MAPb (r2 = 0.92; p less than 0.0001), which suggests that blood flow through organs and tissues below the occlusion is pressure dependent. The data show that SNP infusion during thoracic aortic cross-clamping improves systemic and regional circulation above the occlusion but decreases MAPb and therefore blood flow below the occlusion. SNP infusion should be used with caution during aortic cross-clamping, since arterial hypotension of any degree may be deleterious to organs below the cross-clamp.     

A porcine model of systemic and renal haemodynamic responses to infrarenal aortic cross-clamping.

OBJECTIVES: cross-clamping of the infrarenal aorta is associated with complex haemodynamic disturbances. Several experimental models of aortic cross-clamping (AXC) have been described with heterogeneous results. The main purpose of this study was to establish an animal model in which infrarenal AXC could reproduce similar systemic and renal haemodynamic changes to those observed in humans. METHODS: eleven anaesthetised pigs underwent AXC just below the renal arteries. Renal blood flow was measured using clearance of (131)I hippuran. Systemic and renal parameters were collected at 3 consecutive 30-min periods. RESULTS: AXC did not alter the extraction fraction of (131)I hippuran but was accompanied by significant (13%) decrease in cardiac index (p = 0.005) and a 23% increase in mean arterial pressure (p = 0.005). AXC induced significant 135% increase in renal vascular resistance (p = 0.012) and a 35% decrease in renal blood flow (p = 0.016). This worsened after removal of the aortic clamp, whereas systemic variables returned to baseline levels. CONCLUSIONS: this AXC animal model reproduces the changes observed in humans. It provides a reliable animal model which allows to investigate the underlying mechanisms of renal vasoconstriction and the effect of new drugs.     

Cardiac and renal responses to cross-clamping of the descending thoracic aorta

The present study was performed to document the relative efficacy of commonly applied techniques used adjunctively during 1 hour of descending thoracic aortic cross-clamping. Renal and cardiac responses were determined by standard laboratory methods. There were four experimental groups: (1) heparin-bonded shunt; (2) partial femoral-femoral bypass; (3) sodium nitroprusside; (4) control. Each of the experimental groups showed abnormal hemodynamic responses during cross-clamping. Elevations in left ventricular end-diastolic pressure (LVEDP) and systolic blood pressure were common events during clamping, and cardiac output often decreased. Nevertheless, left ventricular performance curves after cross-clamping showed similar increases in left ventricular stroke work (LVSW) with increasing preload. In addition, left ventricular biopsy specimens showed preservation of myocardial high-energy phosphate stores and essentially normal ultrastructural integrity. Radioactive microspheres generally showed increased myocardial blood flow during and after cross-clamping, but no evidence of preferential subendocardial ischemia. Examination of renal function showed a marked decrease in urine output, glomerular filtration rate, and renal plasma flow during cross-clamping. Following the release of the cross-clamp, renal function returned to 50% to 85% of baseline status. Since we could find no major advantage of any of the techniques employed under the present experimental conditions, we suggest that all of the techniques should be part of the surgical armamentarium and the particular preoperative and/or intraoperative findings in a specific case should determine which technique is most appropriate for a given patient.     

Renal vasoconstriction and transient declamp hypotension after infrarenal aortic occlusion: role of plasma purine degradation products

To better understand renal and systemic hemodynamics associated with hindquarter ischemia produced by aortic compression, chloralose-anesthetized dogs were given phentolamine while an external clamp maintained infrarenal aortic pressure below 25 mm Hg for 45 minutes. In four sham-operated dogs, infrarenal pressure was maintained; reinforced cannulas, capable of resisting clamp compression, were placed within the aorta and the inferior vena cava. Suprarenal and infrarenal arterial pressure and renal blood flow were continuously monitored. Blood samples taken before clamp application and at 1, 3, 5, and 10 minutes after clamp removal were assayed for adenosine, inosine, xanthine, and hypoxanthine. On clamp removal suprarenal pressure immediately dropped from a preclamp pressure of 114 to 82 mm Hg but returned to preclamp values within 1 minute. Renal blood flow was significantly reduced after clamp release, reaching a nadir of 39% of preclamp flow. This reduction persisted despite a normalization of arterial pressure. Summed plasma purines were significantly elevated 1 minute after clamp removal. Sham-operated dogs showed no significant alterations in arterial pressure, renal blood flow, or plasma purine levels. This study demonstrates a significant non-alpha-adrenergic receptor-mediated reduction in renal blood flow and a coincident increase in purine degradation products after removal of an infrarenal aortic cross-clamp.     

Paraplegia after thoracic aortic occlusion: influence of cerebrospinal fluid drainage. Experimental and early clinical results

Paraplegia occurs in 6.5% to 40% of patients after repair of extensive thoracoabdominal aortic aneurysms requiring aortic clamping. This study aimed to determine whether drainage of cerebrospinal fluid (CSF) done before aortic cross-clamping could decrease the incidence of paraplegia in dogs. The descending thoracic aorta was clamped distal to the left subclavian artery for either 40 minutes (group I) or 60 minutes (group II). All control animals in group I (10) and group II (10) showed evidence of spinal cord injury with paraparesis or paraplegia. In contrast, 9 of 10 animals (90%) in group I and 7 of 10 animals (70%) in group II that had CSF drainage before aortic cross-clamping were neurologically normal (p less than 0.001 and p less than 0.01, respectively). Aortic pressure distal to the aortic cross clamp was the same in all groups; however, spinal cord perfusion pressure (distal aortic pressure minus CSF pressure) was significantly higher in neurologically normal animals (34 +/- 5 mm Hg, n = 15) compared with those with paraparesis (26 +/- 4 mm Hg, n = 8) or paraplegia (19 +/- 5 mm Hg, n = 8) (r = 0.871, p less than 0.001). This study demonstrates that drainage of CSF before thoracic aortic occlusion significantly increases spinal cord perfusion pressure and decreases the incidence of paraplegia. Limited early clinical experience suggests that CSF drainage may be a useful adjunct to prevent paraplegia in patients who are having repair of thoracoabdominal aortic aneurysms.     

Relationship of spinal cord blood flow to vascular anatomy during thoracic aortic cross-clamping and shunting

No satisfactory explanation exists as to why paraplegia occurs despite distal aortic perfusion during thoracic aortic operations. We studied the hemodynamics, paraplegia rate, and spinal cord blood flow with radioactive microspheres in 17 male adult baboons, with particular reference to the arteria radicularis magna. The groups consisted of control animals, subjected to cross-clamping for 60 minutes, and animals with aorto-aortic shunts operational for 60 minutes. There were no significant left ventricular hemodynamic advantages with shunting. Shunting significantly increased lumbar spinal cord blood flow (p = 0.0009), which correlated with the distal aortic mean pressure (r = 0.59, p = 0.008). However, lower thoracic spinal cord blood flow did not increase during shunting (p = 0.2) and did not correlate with the distal aortic pressure (r = 0.11, p = 0.64). This is due to the vascular anatomy of the anterior spinal artery, which was, as in man, smaller above (0.278 mm) than below (0.744 mm) the entry of the arteria radicularis magna. Resistance to flow, as calculated by Poiseuille's equation, was 51.7 times greater up the anterior spinal artery as compared with down this artery. The vascular anatomy explains the absence of paraplegia in one baboon in the cross-clamp group and paraplegia in one baboon in the shunt group. Thus, distal aortic perfusion protects the spinal cord below the arteria radicularis magna but not above it.     

The effects of fenoldopam on renal function in patients undergoing elective aortic surgery

BACKGROUND AND OBJECTIVE: Postoperative renal impairment is a recognized complication of infrarenal aortic cross-clamping. Our hypothesis was that the renal vasodilating and natriuretic effects of fenoldopam mesylate, a selective dopamine (DA1) agonist, would preserve renal function in patients undergoing elective infrarenal aortic cross-clamping. METHODS: A prospective, randomized, double blind controlled clinical trial was performed. Twenty-eight ASA II-III patients undergoing elective aortic surgery requiring infrarenal aortic cross-clamping were studied. According to random allocation, patients received either fenoldopam (0.1 microg kg(-1) min(-1)) or placebo intravenously prior to surgical skin incision until release of the aortic clamp. Plasma creatinine, creatinine clearance, urinary output, fractional excretion of sodium, and free water clearance were measured: (a) prior to admission to hospital; (b) during the period from insertion of the urinary catheter until application of the aortic cross-clamp; (c) during the period of aortic cross-clamping; (d) 0-4 h, and (e) 4-8 h after release of the clamp and on days 1, 2, 3, and 5 postoperatively. RESULTS: Fenoldopam (0.1 microg kg(-1)min(-1)) administration was not associated with haemodynamic instability. On application of the aortic cross-clamp creatinine clearance decreased significantly in the placebo (83 +/- 20 to 42 +/- 29 mL min(-1) (mean +/- SD)) (P < 0.01) but not in the fenoldopam group, and this decrease persisted for at least 8 h after release of the cross-clamp (83 +/- 20 to 54 +/- 33 mL min(-1) (mean +/- SD)) (P < 0.05). Plasma creatinine concentration increased significantly from baseline on the first postoperative day in the placebo group (87 +/- 12 to 103 +/- 28 micromolL(-1) (mean +/- SD)) (P < 0.01) but not in the fenoldopam group. CONCLUSIONS: These findings are consistent with the hypothesis that fenoldopam possesses a renoprotective effect during and after infrarenal aortic cross-clamping.     

Assessment of gut mucosal perfusion and colonic tissue blood flow during abdominal aortic surgery with gastric tonometry and laser Doppler flowmetry

The objective of this study was to investigate the effect of infrarenal aortic cross-clamping and unclamping on gut mucosal perfusion by gastric tonometry and on sigmoid colonic tissue blood flow by laser Doppler flowmetry during abdominal aortic surgery. This was a prospective before-and-after intervention comparison study in a university hospital of 8 male patients, aged 57-87, undergoing elective infrarenal abdominal aortic surgery. Each patient was pretreated with ranitidine. Following general anesthesia, a nasogastric tonometer was inserted into the stomach. The balloon of the tonometer was filled with 2.5 mL of normal saline for gas tension and pH analysis. This process was repeated before and after aortic cross-clamping and unclamping. Gastric mucosal pHi was calculated with the Henderson-Hasselbalch equation from the arterial Hco3- and the tonometrically measured mucosal Pco2. A laser Doppler flow probe was placed in contact with the serosa of the sigmoid colon against the mesentery after the abdomen was opened. Sigmoid colonic tissue blood flow (SCBF) was assessed by the laser Doppler flowmeter. Gastric mucosal pHi by gastric tonometry and colonic tissue blood flow by laser Doppler flowmetry were measured before and after aortic cross-clamping and unclamping. Gastric mucosal pHi decreased significantly 30 minutes after aortic cross-clamping (7.37 +/-0.07) (p < 0.01), 60 minutes after aortic cross-clamping (7.39 +/-0.08) (p < 0.05), and 30 minutes after aortic unclamping (7.37 +/-0.08) (p < 0.01), compared with pHi before aortic cross-clamping (7.50 +/-0.06). Gastric mucosal pHi increased to the original level 60 minutes after aortic unclamping (7.46 +/-0.08). Since a gastric mucosal pH above 7.35 is considered normal, these mean values of pHi were clinically insignificant. However, gastric mucosal pHi decreased below 7.32 in 5 patients during abdominal aortic surgery. Gastric mucosal pHi decreased further to 7.30 in 1 patient following aortic cross-clamping and below 7.30 in 3 patients 30 minutes after aortic unclamping. SCBF decreased significantly after aortic cross-clamping (28.1 +/-4.8 mL/min/100 g) compared with the value before aortic cross-clamping (51.9 +/-11.3 mL/min/100 g) (p < 0.01). Following aortic unclamping, SCBF returned to 41.7 +/-7.4 mL/min/100 g. It is concluded that transient episodes of significant intestinal mucosal ischemia may have been encountered occasionally in patients undergoing abdominal aortic surgery, but a sigmoid colonic tissue blood flow of 41.7 +/-7.4 mL/min/100 g was sufficient to prevent postoperative ischemic colitis regardless of whether there was ligation or no ligation of inferior mesenteric artery among the studied population since none of the patients developed clinically significant ischemic colitis.     

The effects of thoracic aortic cross-clamping and declamping on visceral organ blood flow.

Blood flow was measured using radioactive microspheres in 11 macaque monkeys 1) before hemorrhage shock, 2) after onset of shock, 3) after aortic cross-clamping and resuscitation, and 4) after release of the cross-clamp and stabilization. Hemodynamic parameters (cardiac output, arterial, right atrial and left atrial pressure) and blood gases were also monitored. Total abdominal organ flow fell with hemorrhage and fell further with aortic clamping. Reinfusion of shed volume did not restore abdominal organ flow (4.7% baselines) but increased LAP and cardiac output to the upper body. Release of the cross-clamp produced profound acidosis that was treated effectively with NcHCO3. After stabilization of blood, flow to kidney remained low (49% baseline) although intestinal flow was increased threefold (320% of baseline). It is clear that thoracic aortic cross-clamping in shock further compromises already reduced visceral blood flow and may contribute to the problem of ischemic multiple organ failure after resuscitation from hemorrhagic shock.     

Prevention of Ischemic Spinal Cord Injury Following Aortic Cross-Clamping: Use of Corticosteroids

Prior to proximal aortic cross-clamping, baseline measurements of spinal cord blood flow and function were done. Blood flow was evaluated with radioactive microspheres and function determined by assessment of somatosensory evoked potential (SEP). Group 1 (N = 6) animals had aortic cross-clamping for 5 minutes after ischemic spinal cord dysfunction (SEP loss) was documented. Group 2 (N = 9) underwent aortic cross-clamping for 10 minutes after loss of SEP. Group 3 (N = 6) also underwent 10 minutes of cross-clamping after initial SEP loss, but were treated intravenously with methylprednisolone (30 mg per kilogram of body weight) 10 minutes prior to cross-clamping and again 4 hours postoperatively. After release of the cross-clamp, the animals were allowed to recover and serial evaluations of spinal cord blood flow and neurological status were carried out for seven days. Group 1 animals recovered uneventfully without evidence of neurological injury. Group 2 animals sustained a 67% incidence of permanent spastic paraplegia (p = 0.02 versus Group 1). In contrast, methylprednisolone-treated animals sustained no clinically detectable neurological injury (p = 0.02 versus Group 2). Measurements of spinal cord blood flow at the time of SEP loss revealed similar degrees of spinal cord ischemia in all groups. No significant differences were observed in the duration of aortic cross-clamping prior to SEP loss among the three groups. The data indicate that short periods of cross-clamping (5 minutes) following SEP loss are well tolerated, whereas longer periods (10 minutes) are associated with a high incidence of paraplegia. This injury can be prevented if an adequate dose of methylprednisolone is given before and after cross-clamping. Beneficial effects of steroid administration do not appear to be related to changes in spinal cord blood flow, but may be related to protective effects on cellular and subcellular components. Clinical investigations employing this regimen of corticosteroid protection during surgical procedures on the thoracoabdominal aorta appear to be indicated.     

股静脉-股动脉转流在降主动脉重建术中的作用

目的：评价股静脉－股动脉转流在降主动脉人工血管重建术中的作用。方法：1999年12月至2001年6月间，在股静脉－股动脉转流下行降主动脉人工血管重建术12例为转流组；1994年6月至1999年8月15例降主动脉人工血管重建术为非转流组，比较两组在术后发生截瘫、内脏缺血、输血量和凝血功能异常等方面的差别。资料统计采用t检验或χ^2检验。结果：阻断时间超过60min者中，转流组的截瘫发生低于非转流组（P＜0．05）。转流组术后发生黄疸低于非转流组（P＜0．05），两组在术后肾功能异常上无明显差异（P＞0．05）。转流组输血量较非转流组明显减少（P＜0．01）。转流组术后凝血功能异常发生率低于非转流组（P＜0．05）。结论：股静脉－股动脉转流在预防降主动脉人工血管重建术后的截瘫发生、保护内脏功能、减少输血量和避免凝血功能异常等方面优于单纯阻断降主动脉，是一简便、安全的转流方式。     

Cerebrospinal fluid drainage and steroids provide better spinal cord protection during aortic cross-clamping than does either treatment alone

We investigated whether intravenous methylprednisolone (30 mg/kg) before 30 minutes of aortic cross-clamping and after 4 hours could enhance the effects of cerebrospinal fluid drainage on spinal cord perfusion pressure and postoperative paraplegia when proximal blood pressure was controlled with sodium nitroprusside and partial exsanguination. Dogs were randomized into three groups: group 1 (n = 6), control; group 2 (n = 7), steroids; and group 3 (n = 6), steroids with cerebrospinal fluid drainage. During aortic cross-clamping, blood pressure proximal to the clamp decreased significantly in each group compared with baseline (p less than 0.05), but did not differ among groups (group 1 = 82.2, group 2 = 82.1, group 3 = 86.6 mm Hg, p greater than 0.05). Mean distal pressure decreased from systemic values to 8.4, 8.5, and 3.7 mm Hg, respectively, after aortic cross-clamping (p less than 0.05); these values did not differ from one another (p greater than 0.05). During aortic cross-clamping, cerebrospinal fluid pressure in groups 1 and 2 did not differ significantly compared with baseline (12.2 versus 8.2, 14.2 versus 10.7 mm Hg, p greater than 0.05), whereas in group 3 the baseline cerebral spinal fluid pressure of 10.7 mm Hg decreased to 0.4 mm Hg (p less than 0.05). Spinal cord perfusion pressure in group 3 was significantly higher than in groups 1 and 2 (3.3 versus -3.9 and -5.7 mm Hg, p less than 0.05), but did not differ between groups 1 and 2 (p greater than 0.05).(ABSTRACT TRUNCATED AT 250 WORDS)