Platelet reactivity in human aortic grafts: A prospective, randomized midterm study of platelet adherence and release products in Dacron and polytetrafluoroethylene conduits

Prospective randomized trial of ACUSEAL (Gore-Tex) vs Finesse (Hemashield) patching during carotid endarterectomy: long-term outcome

BACKGROUND

Several studies have reported that carotid endarterectomy with patch angioplasty is superior to primary closure. Conventional polytetrafluoroethylene (Gore-Tex, W. L. Gore & Associates, Flagstaff, Ariz) patching has been shown to have results similar to autogenous saphenous vein patching; however, it requires a longer hemostasis time. This study examined the long-term clinical outcome and incidence of restenosis after carotid endarterectomy using the new ACUSEAL (Gore-Tex) patching vs Hemashield Finesse (Boston Scientific Corp, Natick, Mass) patching.

METHODS

The study randomized 200 patients (1:1) undergoing carotid endarterectomy to 100 with ACUSEAL patching and 100 with Hemashield-Finesse patching. All patients underwent immediate and 1-month postoperative duplex ultrasound studies, which were repeated at 6-month intervals. Kaplan-Meier analysis was used to estimate the freedom from stroke, stroke-free survival, and the risk of restenosis for both groups.

RESULTS

The demographic and clinical characteristics, the mean operative diameter of the internal carotid artery, and the length of the arteriotomy were similar in both groups. The mean hemostasis time was 5.1 for the ACUSEAL patching vs 3.7 minutes for Finesse patching (P = .01); however, the mean operative times were similar for both groups (P = .61). The incidence of ipsilateral stroke was 2% for ACUSEAL patching (both early perioperative strokes) vs 3% for Finesse patching (2 early and 1 late stroke) at a mean follow-up of 21 months. The respective cumulative stroke-free rates at 1, 2, and 3 years were 98%, 98%, and 98% for ACUSEAL patching vs 97%, 97%, and 97% for Finesse patching (P = .7). The respective cumulative stroke-free survival rates at 1, 2, and 3 years were 97%, 92%, and 88% for ACUSEAL patching vs 96%, 96%, and 91% for Finesse patching (P = .6). The respective freedom from > or =70% carotid restenosis at 1, 2, and 3 years was 98%, 96%, and 89% for ACUSEAL patching vs 92%, 85%, and 79% for Finesse patching (P = .04).

CONCLUSIONS

Carotid endarterectomy with ACUSEAL patching and Finesse patching had similar stroke-free rates and stroke-free survival rates. The mean hemostasis time for the ACUSEAL patch was 1.4 minutes longer than that for the Finesse patch; however, the Finesse patch had higher restenosis rates than the ACUSEAL patch.

Indium-111-oxine-labeled platelet scintigraphic images in the assessment of thrombogenicity in small-caliber prosthetic vascular grafts

Anti-thrombogenicity is one of the essential factors for successful development of small-caliber prosthetic vascular grafts, and its accurate evaluation is important. The purpose of this study was to investigate the efficacy of indium-111-oxine-labeled (In) platelet scintigraphic images in the assessment of graft thrombogenicity. Fibrin-coated knitted polyester vascular prostheses, 2 mm in diameter and 2 cm in length, were implanted in the bilateral common carotid arteries of 18 Japanese white rabbits. The grafts were explanted on postoperative days 1, 3, 7, 10, 14, and 30 (six grafts on each of the days), and In platelet scintigraphy was performed with visual, semiquantitative, and quantitative analysis. The relationships among the three analyses were evaluated. Platelet depositions on the luminal surface were clearly visualized with In-platelet scintigraphy if the number of In platelets was more than 4.8 x 10 counts per minute, even if a macroscopic thrombus formation was not observed. There was a highly significant correlation between the graft region of interest on the images and the total platelet deposition (p<.0001). The images in the thrombotic grafts have shown a very strong In-platelet accumulation, but there were some limitations in the In-platelet scintigraphic images. In-platelet scintigraphic images are useful for evaluating platelet deposition in small-caliber vascular prostheses if they are performed with a proper understanding of their limitations.

Midterm clinical success and behavior of the aneurysm sac after endovascular AAA repair with the Excluder graft

OBJECTIVE

Recent studies have reported different sac behavior after endovascular repair of abdominal aortic aneurysms, depending on the endografts. This study was designed to evaluate mid-term outcome and sac behavior after treatment with the Gore Excluder stent-graft.

METHODS

Between June 1999 and January 2005, 109 selected patients with suitable anatomy were treated electively for abdominal aortic aneurysm with the Excluder stent graft. Data were prospectively collected in a computerised database and included demographics, details of the aortoiliac anatomy, procedural and clinical success, and postoperative complications. Postoperative sac size and the presence of endoleaks were assessed with computed tomography scans obtained at 1, 6, and 12 months, and yearly thereafter. All diameter measures in patients followed for > 1 year (84.4%) were analyzed.

RESULTS

Assisted primary technical success was achieved in 108 cases (99.1%). No type I endoleaks and 12 (11.1%) type II endoleaks were recorded < or = 1 month from the procedure. Mean follow-up was 29.6 +/- 16.1 months. We recorded one new-onset type IA endoleak, complete resolution of five type II endoleaks, and eight new-onset type II endoleaks. The overall prevalence of type II endoleaks was 14%. Shrinkage at 1, 2, 3, and 4 years was observed in 20.7%, 30.5%, 38.9%, and 36.8% of cases. The presence of type II endoleak influenced the trend of aneurysm size throughout the 4 years. Aneurysms without endoleak shrank more than aneurysms with type II endoleak (P < .0001). We observed two cases of sac enlargement due to the presence of endoleaks. No cases of endotension with sac enlargement, late open conversion, or aneurysm-related deaths were observed. Unchanged aneurysmal sacs remained stable during follow-up, with no adverse events.

CONCLUSIONS

Endovascular treatment with the Excluder device in selected patients produces low rates of shrinkage, but this peculiar sac behavior does not affect mid-term clinical success.

Prospective randomized trial of carotid endarterectomy with polytetrafluoroethylene versus collagen-impregnated dacron (Hemashield) patching: late follow-up

OBJECTIVE

To compare the late clinical outcome and incidence of recurrent stenosis after carotid endarterectomy (CEA) with polytetrafluoroethylene (PTFE) versus Hemashield patching.

SUMMARY BACKGROUND DATA

Several randomized trials have confirmed the advantages of patching over primary closure when performing CEA.

METHODS

Two hundred CEAs (180 patients) were randomized into 100 with PTFE patching and 100 with Hemashield. All patients underwent postoperative color duplex ultrasounds at 1, 6, and 12 months, and every year thereafter. The mean follow-up was 26 months. Kaplan-Meier analysis was used to estimate the risk of re-stenosis, stroke, and stroke-free survival. A multivariate analysis of various risk factors was also done.

RESULTS

Demographic and clinical characteristics were similar in both groups. The incidence of all ipsilateral strokes (early and late) was 8% (7% perioperative) for Hemashield versus 0% for PTFE patching. Both groups had similar mortality rates. The cumulative stroke-free rates at 6, 12, 24, and 36 months were 93%, 93%, 93%, and 89% for Hemashield versus 100%, 100%, 100%, and 100% for PTFE patching. The cumulative stroke-free survival rates at 6, 12, 24, and 36 months were 90%, 89%, 87%, and 79% for Hemashield versus 98%, 98%, 92%, and 92% for PTFE patching. Kaplan-Meier analysis also showed that freedom from 50% or greater re-stenosis at 6, 12, 24, and 36 months was 89%, 81%, 73%, and 66% for Hemashield versus 100%, 100%, 100%, and 92% for PTFE. Similarly, the freedom from 70% or greater re-stenosis at 6, 12, 24, and 36 months was 93%, 91%, 86%, and 78% for Hemashield versus 100%, 100%, 100%, and 100% for PTFE. Univariate and multivariate analyses of demographic and preoperative risk factors showed that only Hemashield was significantly associated with a higher incidence of 70% or greater recurrent stenosis.

CONCLUSIONS

PTFE patching was superior to Hemashield in lowering the incidence of postoperative ipsilateral strokes and late recurrent stenosis.

Prospective randomized study of carotid endarterectomy with polytetrafluoroethylene versus collagen-impregnated Dacron (Hemashield) patching: perioperative (30-day) results

PURPOSE

Several studies have reported that carotid endarterectomy (CEA) with patch angioplasty has results that are superior to primary closure. Polytetrafluoroethylene (PTFE) patching has been shown to have results comparable with autogenous vein patching; however, it requires a prolonged hemostasis time. Therefore, many surgeons are using collagen-impregnated Dacron patching (Hemashield [HP]). This study is the first prospective randomized trial comparing CEA with PTFE patching versus HP patching.

METHODS

Two hundred CEAs were randomized into two groups, 100 PTFE and 100 HP patching. All patients underwent immediate postoperative and 1-month postoperative color duplex ultrasound scanning studies. Demographic and clinical characteristics were similar in both groups, including the mean operative diameter of the internal carotid artery.

RESULTS

The perioperative stroke rates were 0% for PTFE, versus 7% for HP (4 major and 3 minor strokes, P =.02). The combined perioperative stroke and transient ischemic attack rates were 3% for PTFE, versus 12% for HP (P =.047). The operative mortality rate for PTFE was 0%, versus 2% for HP (P =.477). Five perioperative carotid thromboses were noted in patients undergoing HP patching, versus none in patients undergoing PTFE patching (P =.07). After 1 month of follow-up, 2% of patients in the PTFE group had a 50% or more restenosis, versus 12% of patients in the HP group (P =.013). The mean operative time for PTFE patching was 119 minutes, versus 113 minutes for HP patching (P =.081). The mean hemostasis time was significantly higher for PTFE patching than for HP patching, 14.4 versus 3.4 minutes (P <.001).

CONCLUSION

CEA with HP patching had a higher incidence of perioperative strokes, carotid thrombosis, and 50% or more early restenosis than CEA with PTFE patching. However, the mean hemostasis time was higher for PTFE patching than for HP patching.

Prospective controlled study of carotid endarterectomy with hemashield patch: is it thrombogenic?

The use of patch angioplasty after carotid endarterectomy (CEA) has been shown to have superior results to CEA with primary closure. Polytetrafluoroethylene (PTFE) patches have been shown to have comparable results to autogenous vein patching; however, PTFE has the disadvantage of prolonged hemostasis time. Therefore, many surgeons are using collagen-impregnated Dacron patches (Hemashield[HP]). We believe this is the first prospective controlled study of the use of HP in carotid endarterectomy. This study included 144 consecutive patients who had 151 CEAs with HP. Postoperative duplex ultrasounds were done at 1 month and every 6 months thereafter. The mean follow-up was 12 months (range: 1-30 months). Indications for CEA included symptomatic (64%) and asymptomatic (36%) stenoses. The overall incidence of ipsilateral stroke was 5% (4% perioperative), with a combined TIA and stroke rate of 12%. Incidence of > or =50% recurrent stenosis was 21% (7% symptomatic TIA/stroke) and > or =80% recurrent stenosis was 9%. Kaplan-Meier analysis showed that at 1 year and 2.5 years freedom from > or =50% recurrent stenosis was 78% and 57%, respectively, freedom from > or =80% recurrent stenosis was 92% and 77%, respectively, and a stroke-free survival rate of 94% and 72%, respectively. Women had a 22% and men a 14% recurrent stenosis rate (p=0.04). There was no correlation between other specific risk factors and recurrent stenosis except for hypertension (33% vs 12%, p=0.003). The authors concluded that CEA with HP had a higher incidence of recurrent stenosis (21%), and a higher perioperative stroke rate (4%) after a mean follow-up of 12 months than previously reported using PTFE or saphenous vein patching (2% and 9% recurrent stenosis rates, respectively, and 1% and 0% perioperative stroke rates, respectively after a mean follow-up of 30 months). This raises the question as to whether this patch is thrombogenic in this location. Therefore, a randomized controlled trial comparing this patch with other patches (PTFE or vein) is warranted.

Coagulopathy associated with residual dissection after surgical treatment of type A aortic dissection

PURPOSE

This study was performed to evaluate the effects of a residual dissection on coagulation, fibrinolysis, and platelet function after surgical treatment of acute type A aortic dissection.

METHODS

Between 1987 and 1995, 48 consecutive patients underwent emergency surgery for acute type A aortic dissection. Thirty-five of 41 survivors were followed-up for periods ranging from 6 to 112 months (median, 30.3 months). These survivors were classified into three groups by computed tomographic scanning and angiography. Fifteen patients had no residual dissection (group I). Of the 20 patients who had residual dissection, nine had an enlarged aorta greater than 45 mm in maximal diameter (group II), and 11 had an aorta less than 45 mm in maximal diameter (group III). For all patients, blood samples were collected for coagulation, fibrinolysis, and platelet function studies on the same day that the computed tomographic scanning had been performed.

RESULTS

beta-thromboglobulin, thrombin-antithrombin III complex, D-dimer, and alpha 2 plasmin inhibitor-plasmin complex concentrations were significantly higher in group II than in the other two groups. Strong correlations between the maximal diameter of the dissected aorta and beta-thromboglobulin, thrombin-antithrombin III complex, D-dimer, and plasmin inhibitor-plasmin complex concentrations were evident. In contrast, correlations between the length of the dissected aorta and coagulation/fibrinolysis measurements were weak.

CONCLUSIONS

Our findings suggest that the coagulopathy worsened in proportion to the degree of dilatation of the dissected aorta.

Surface adhesion molecule expression on human blood cells induced by vascular graft materials in vitro

The expression of surface adhesion molecules on granulocytes, monocytes (CD11a, CD11b, CD11c, CD18, L-selectin), and platelets (P-selectin, gpIIb-IIIa) was determined after incubation with different graft surfaces [expanded polytetrafluoroethylene (ePTFE) or woven Dacron]. Woven Dacron grafts upregulated the CD11b and CD11c surface antigens on both granulocytes and monocytes. Both graft materials demonstrated increased expression of CD11a and CD18 adhesion molecules on white blood cells at 30 min, followed by a downregulation. Maximum L-selectin expression was seen at 120 min on granulocytes and at 90 min on monocytes without differences between the graft materials. A rapid downregulation of gpIIb-IIIa complexes on platelets was noticed, while no expression of platelet P-selectin molecules was observed. In conclusion, both graft materials induced alteration of the white blood cell adhesion molecule expression, but the intensity and time course were dependent on the cell type and the graft material, suggesting that different mechanisms might be implicated. The expression of platelet surface antigens was less clearly influenced. The clinical significance of an enhanced cell surface antigen receptor expression caused by woven Dacron (CD11b, CD11c) has to be further studied. However, determination of adhesion molecule expression might offer possibilities to predict biocompatibility.

Fibrinolysis profiles and platelet activation after endothelial cell seeding of prosthetic vascular grafts

There is no convincing evidence that endothelial cell seeding of prosthetic grafts in humans confers any of the advantages seen in animals. However, partial endothelial coverage might exert a subtle effect not detectable with indirect end points such as patency or scintigraphy. This study examined seeded cell function by measuring fibrinolytic and platelet activation markers in patients receiving seeded and control prosthetic grafts. Thirty-two patients were randomly assigned to seeded (n = 15) and control (n = 17) groups. Preoperatively and 3, 6, and 12 months postoperatively, plasma levels of fibrinopeptide A (FPA), B beta 1-42 fragment, cross-linked fibrin degradation products (XL-FDP), thromboxane A2 (TXA2), platelet factor 4 (PF4), and beta-thromboglobulin (beta TG) were measured. Patients with seeded grafts had significantly lower levels of FPA at 6 and 12 months (p < 0.05) and a significant overall group effect (p < 0.05). These patients also tended to have higher levels of XL-FDP (p < 0.1). No other significant differences were seen. The lower rate of conversion of fibrinogen to fibrin and the trend toward increased fibrinolysis seen in seeded grafts may be due to the metabolic effects of viable retained seeded cells. Although comparable platelet activation indicates that endothelial coverage remains limited, seeding may exert an antithrombotic influence at the graft surface.

Indium-111 platelet scintigraphy in vascular disease

Indium-111 labelled platelet scintigraphy permits simple, accurate evaluation of platelet kinetics and sites of deposition. The most meaningful results are obtained from serial scans, although these are clinically useful in only a few of the many applications that have been suggested, principally in studies of acute thrombosis, prosthetic graft thrombogenicity and antiplatelet medication. Key pitfalls are associated with selection of regions and patient variation.

Effect of dextran and enoxaparin on early ePTFE graft thrombogenicity in sheep

OBJECTIVES

To evaluate the effect of low molecular weight heparin (LMWH), dextran 70 and their combination on platelet adhesion and fibrinogen uptake in ePTFE grafts in an experimental sheep model.

DESIGN

Prospective open study.

SETTING

Animal Laboratory of a University Hospital.

MATERIALS

Early thrombogenicity of ePTFE grafts was studied after interposition in the two common carotid arteries of 40 adult sheep. The animals received one of four different treatment regimens in a double blind randomised way: enoxaparin and polygeline, saline and dextran 70, enoxaparin and dextran 70 or saline and polygeline (control). The substances were administered i.v. with a total dose of 73 antifactor-Xa U/kg for enoxaparin and 1.0 g/kg for dextran 70. Polygeline and saline were used as placebo substances in equivalent volumes. On one side (random allocation) the carotid blood flow was restricted to 25 ml/min, on the other side it was left unrestricted.

CHIEF OUTCOME MEASURES

The following variables were studied: 1) fibrinogen uptake; 2) platelet uptake; 3) early graft patency; 4) blood flow in patient grafts; 5) visible presence of graft thrombus; 6) thrombus weight.

MAIN RESULTS

The results verified the importance of adequate blood flow as only 30% of grafts with restricted blood flow in the control group were patent compared with 80% of those with unrestricted blood flow (p = 0.038). Dextran 70, enoxaparin and the combination of the two increased early graft patency (p < 0.05) and reduced thrombus weights (p < 0.05) in grafts with restricted blood flow. The relative number of grafts with thrombus free surface was increased in the unrestricted blood flow situation.

CONCLUSIONS

Dextran 70 and enoxaparin appeared to be equally effective in decreasing fibrinogen and platelet uptake in the grafts. Their combination was not significantly more effective although there was a favourable trend.

Acute thrombogenicity and 4 weeks healing properties of a new stretch-ePTFE graft

Recently a new expanded polytetrafluoroethylene (ePTFE) graft with length compliant characteristics has been developed. The present study compared the acute thrombogenicity and 4 weeks healing characteristics of the stretch ePTFE graft to standard ePTFE grafts in vivo. Grafts of 6 cm length and 8 mm internal diameter were inserted end-to-side into the iliac arteries in pigs. Platelet adhesion was assessed by infusing indium-111-oxine (20 MBq) labelled autologous platelets and dynamically imaging the grafts. Explanted grafts (n = 14) were opened longitudinally and the thrombus-free surface (TFS) and segmental accumulation of platelets were determined. Stretch ePTFE grafts had significantly less platelet deposition when compared to standard ePTFE graft (p < 0.01). The dynamic increase of activity from 10 min after start of measurement was also significantly reduced (p < 0.05) for 170 min as compared to standard ePTFE grafts. TFS was 68 +/- 5% for stretch ePTFE and 37 +/- 5% for standard ePTFE grafts (p < 0.01). After explanation and fixation the grafts were investigated by light microscopy, scanning and transmission electron microscopy. At 1 week after surgery, both kind of grafts were covered by a fibrinous layer containing platelets and leukocytes. After 2 weeks a pseudoendothelial layer was found in the perianastomotic regions. After 4 weeks, two out of four standard ePTFE grafts were occluded due to intimal hyperplasia and subsequent thrombosis in the midportion of the grafts. All stretch ePTFE grafts were patent and covered by a smooth pseudointima. This study thus demonstrates a lower acute thrombogenicity in stretch ePTFE grafts compared to the standard graphs.

Cytokine and growth factor production by monocytes/macrophages on protein preadsorbed polymers

These studies evaluate the effect of biomedical polymers: Biomer, polydimethyl-siloxane (PDMS), polyethylene, expanded polytetrafluoroethylene (ePTFE), Dacron, and the control polystyrene with or without adsorbed proteins IgG, fibrinogen, and fibronectin on the ability of activated human monocytes/macrophages to produce Interleukin 1 Beta (IL-1-B), Interleukin 6 (IL-6), and Tumor Necrosis Factor Alpha (TNF-A). Monocytes/macrophages incubated on biomedical polymers with or without protein preadsorption produce variable levels of IL-1-B, IL-6, and TNF-A dependent on the polymer and adsorbed protein. IL-6 was produced in the greatest quantity and was the most influenced by protein adsorption. ePTFE and PDMS polymers were least stimulating while polystyrene was the most stimulating of monocyte activity. Adsorbed IgG consistently altered the ability of the polymers to activate monocytes/macrophages to produce cytokines. These studies provide important insight into conditions which modulate monocyte/macrophage activity in response to protein preadsorbed biomedical polymers.

Direct platelet effect of low molecular weight dextran in small calibre PTFE grafts

The thrombogenicity of synthetic vascular grafts is a major factor in occlusion of grafts when they are used to bypass small calibre arteries. In this paper, the effect of low molecular weight dextran (LMWD, Dextran-40) on graft surface-platelet interaction was studied using Indium-III-oxine labelled platelets. It was found that LMWD significantly reduced platelet deposition onto graft surfaces (P less than 0.001). Dextran had a direct antiplatelet effect independent of plasma volume expansion as dextran-soaked grafts significantly reduced platelet deposition when compared to systemic dextran administration (P less than 0.001). We therefore conclude that LMWD has a direct antiplatelet effect which is beneficial in reducing platelet deposition on synthetic PTFE grafts which may improve the early patency of such grafts.

Thrombogenicity of metallic vascular stents in arteries and veins--an experimental study in pigs

Endovascular expanding metallic stents were percutaneously implanted in the iliac arteries and veins of pigs. The vessels had been stenosed by a ligature of catgut 4 weeks prior to this. Platelets were labeled with Indium 111 and the deposition onto the dilated and stented areas was dynamically registered for 240 min with a scintillation camera. All six arterial and six venous stents remained patent throughout the examination period. At the site of arterial stenting there was an increase, of deposited activity, and in the veins a decrease. These experimental findings support the use of endovascular stents after dilation, especially in venous stenoses.

Heparin-resistant thrombus formation by endovascular stents in baboons. Interruption by a synthetic antithrombin

Intravascular mechanical support has been proposed as a solution to the frequent occurrence of vascular narrowing and occlusion after transluminal balloon angioplasty or surgical endarterectomy. Although several endovascular stents are currently in clinical use for angioplasty of larger vessels, acute thrombosis is a troublesome complication of their use with coronary angioplasty. To study thrombus formation associated with metallic mesh endoprostheses, we have evaluated stents placed inside 3-mm expanded polytetrafluoroethylene (ePTFE) grafts incorporated into chronic exteriorized arteriovenous silicone rubber shunts in baboons. We have also compared the antithrombotic capacities of heparin and the synthetic antithrombin D-phenylalanyl-L-prolyl-L-arginyl-chloromethylkene (D-FPRCH2Cl) to interrupt this platelet-dependent process for two different endovascular stents. Acute platelet deposition was continuously measured during 1 hour using gamma camera imaging of platelets labeled with indium-111 oxine. On untreated control ePTFE grafts (n = 11), 0.87 +/- 0.15 x 10(9) platelets/cm were deposited during 60 minutes. In contrast, balloon-expandable endovascular stents within ePTFE (n = 6) accumulated 4.37 +/- 0.68 x 10(9) platelets/cm (p = 0.003 compared with controls), and self-expandable stents (n = 6) accumulated 3.91 +/- 0.42 x 10(9) platelets/cm (p = 0.006 compared with controls); no difference between stents was detected in this test system (p greater than 0.5). Systemic heparin treatment did not reduce platelet deposition (4.20 +/- 0.41 x 10(9) platelets/cm at 60 minutes; p greater than 0.5).(ABSTRACT TRUNCATED AT 250 WORDS)

[Mechanisms and prediction of hemorrhagic complications during surgery of thoraco-abdominal aortic aneurysms]

This study, including 33 consecutive patients was designed to assess the haemostatic alterations occurring during repair of thoracoabdominal aneurysms. The surgical procedure consisted in Dacron graft replacement of the diseased aorta, using neither cardiopulmonary bypass, nor any shunting technique, nor any heparin. Blood samples were drawn before anaesthesia, before and 30 min after unclamping, and on the first postoperative day. The measured parameters were: haematocrit, platelet count, bleeding, activated cephalin, thrombin and prothrombin times, and concentrations of fibrinogen, factors V, VII, X and II, anti-thrombin III, proteins C and S, fibrin degradation products, D-dimers, alpha 2-antiplasmin, plasminogen, tissue plasminogen activator, plasminogen activator inhibitor, and serum protein. Eight patients developed severe multiple haemorrhages; 3 of them died during the procedure because of uncontrollable bleeding. Although the measured parameters were similar in the "bleeding" and control (n = 25) groups before surgery, there was, before unclamping in the first group, an important increase in activated cephalin and thrombin times, with a fall in concentrations of factor II and V, protein C, fibrinogen, and alpha 2-antiplasmin, and in platelet numbers. After unclamping, these changes worsened further, with an increase in prothrombin time and in fibrinogen levels (0,8 g.l-1), without any increase in fibrin degradation products. Abnormal bleeding started about 30 min after this in all the patients of the "bleeding" group. These changes, involving the fibrinolytic system as well as a fall in concentration of all the coagulation factors, can probably be partly explained by the clamping and unclamping of mesenteric vessels.(ABSTRACT TRUNCATED AT 250 WORDS)