Endothelial cell damage by temporary arterial occlusion with surgical clips. Study of the clip site by scanning and transmission electron microscopy

Enhance Safety in Aneurysm Surgery: Strategies for Prevention of Intraoperative Vascular Complications

Complications during surgery for intracranial aneurysms can be devastating. Notorious pitfalls include premature rupture, parent vessel occlusion, local cerebral injury and brain contusion, and incomplete neck obliteration. These unfavorable intraoperative events can result in major neurological deficits with permanent morbidity and even mortality. Herein, the author highlights the relevant surgical strategies used in his daily practice of aneurysm surgery (e.g., aneurysm clipping with adenosine-induced temporary cardiac arrest), application of which may help prevent vascular complications and enhance surgical safety through reduction of the associated risks, thus allowing improvement of postoperative outcomes. Overall, all described methods and techniques should be considered as small pieces in the complex puzzle of prevention of vascular complications during aneurysm surgery.

Histological changes of vascular clipping in Wistar rats

Background

During aneurysm microsurgery, the aneurysmal sac is excluded from circulation by placing one or more clips at the base of the aneurysm. In some cases of complex aneurysms or subarachnoid hemorrhage history, transient clipping before definitive clipping is necessary. The closing force of the transient clip is less than the permanent clip; however, it is sufficient to stop circulation to the aneurysmal sac. The aim of the following work is to analyze and describe histological changes caused by transient and permanent clipping of the abdominal aorta in Wistar-type rats, to study the correlation between the closing force of the clip and the time, it remains on the vascular tissue structures.

Methods

Six groups were formed, with 10 rats each, whereby temporary clipping of the abdominal aorta was performed with subsequent sampling of the site where the vascular clip was placed. The groups were: control and temporary clipping with: 2, 5, 10, and 15 and permanent clipping with 5 min.

Results

Resection samples of the 3 μm thick aorta were obtained through the routine histological technique and special histochemical techniques (Masson's Trichrome and orcein) from the six groups. Transmural changes were found from Group II-VI.

Conclusion

There is a vascular histological effect after both transient and permanent clipping. The sum of time and strength of the clip induce vascular changes visible at 5 min.

Pilot study of minimum occlusive force of vascular clamps on arterial vessels in rats

Our aims were to determine the accuracy of an improved formula for determining the minimum occlusive force (MOF) of a vascular clamp on rats' abdominal aortas, compare our findings with the calculated theoretical MOF, and provide reference data for clinical research and development of medical instruments that cause minimal damage. We created a vessel closure model and developed a formula for calculating the theoretical MOF of arterial vessels when they are occluded. This formula utilises the blood pressure in the blood vessel, its diameter, and the width of the vascular clamp. We then measured the actual MOF in 24 rat abdominal aortic segments with different diameters and different blood pressures and compared the theoretical and actual MOFs. Analysis of the experimental data showed a probability of 0.315, which means that, under the condition of normal distribution, the difference between the theoretical and actual MOF is not significant at the α = 0.05 level. Thus, the actual measured MOF tended to be consistent with the theoretical MOF calculated by the formula we developed. The improved formula will provide a reference for clinical research and development of medical instruments that cause minimal injury, thus contributing to the development of microsurgery.

Temporary surgical clipping of flow-diverted arteries in an experimental aneurysm model

OBJECTIVE Surgical management of recurrent aneurysms following failed flow diversion may pose difficulties in securing vascular control with temporary clips. The authors tested the efficacy and impact of different types of aneurysm clips on flow-diverted arteries. METHODS Six wide-necked experimental aneurysms were created in canines and treated with Pipeline flow diverters. In 4 aneurysms, occlusion of the artery at the level of the proximal and distal landing zones (n = 2 per aneurysm) was attempted, using temporary, fenestrated, single, and double permanent aneurysm clips. Two aneurysms served as unclipped controls. Serial angiography was performed to investigate the efficacy of clip occlusion, flow diverter deformation, and thrombus formation. After the animals were killed, the flow-diverted aneurysm constructs were opened and photographed to determine neointimal or device damage as a result of clip placement. RESULTS Angiography-confirmed clip occlusion was only possible for 4 of 8 of the tested flow-diverted arterial segments. Clip application attempts led to filling defects consistent with thrombus formation in 2 of 4 flow-diverted constructs, and to minor damage of the flow diverter with neointimal fracture in 1 of 4 cases. CONCLUSIONS Aneurysm clips placed on canine parent arteries bearing a Pipeline flow diverter were unable to reliably stop blood flow. Application of aneurysm clips can cause mild damage to the device and neointima, which might translate into thromboembolic risks. If possible, vascular control should be sought beyond the terminal ends of the implanted device.

Effects of temporary vascular occluder poloxamer 407 gel on the endothelium

Background

Coronary occlusion techniques during OPCAB may lead to an endothelial damage to the target vessel. The adverse effects of these techniques are well-known, and researches have been trying to find out new materials to occlude the coronary artery without an endothelial damage. In the present study, we investigate to the endothelial damage in the rat aorta which is occluded by Poloxamer 407 gel.

Methods

Forty-five rats were randomized in three groups: (1) segment of the aorta was occluded with Poloxamer 407 gel in P 407 group; (2) segment of the aorta was occluded with microvascular clamp in MV clamp group; and (3) no onclusion was available in the Control group. The rats were sacrificed of observation, and a 15mm segment of the aorta was obtained as a specimen. Integrity of the endothelial lining was observed with a scanning electron microscopy.

Results

Scanning electron microscopy revealed a statistically significant difference among the 3 groups (p<0,001) using the SPSS 13.0 test. No difference was found between the Control group and the P 407 group (p=0,059). The differences between MV clamp–Control group (p<0,001) and MV clamp–P 407 group were statistically significant (p<0,002).

Conclusions

We suggest that Poloxamer 407 gel occlusion may be a safer and more effective method compared to the microvascular clamp occlusion.

Clampage vasculaire temporaire

In many situations, temporary artery occlusion is an integral component of aneurysm surgery. The use of temporary clip may allow safer and easier aneurysmal dissection and clipping. Several points, concerning the duration and overall risks of temporary occlusion and the method of choice for cerebral function monitoring have to be discussed.

MATERIAL AND METHODS

Non exhaustive review of neurosurgical literature.

DISCUSSION

Temporary clip application decreases the risk of intraoperative aneurysmal rupture. The analysis of data published in the literature showed that several questions remain open concerning the optimal method of neuroprotection and cerebral function monitoring, as well as the limit of occlusion duration. Other clinical trials are needed to assess the efficacy and safety of this technique.

Experimental animal studies of clip-induced microvascular trauma

This study was designed to evaluate microvascular clip potential for causing changes in vessel-wall tissue and the extent to which this potential is influenced by features of the clip. Light and scanning electron microscopy were used to examine vessel-wall changes after temporary clip occlusion. Vessel patency is shown to be influenced by anastomosis and clip site, changes in occlusion force due to material fatigue are described, and novel clip features to reduce vessel trauma are proposed. Evaluation of mechanical clip properties showed that material fatigue does not lead to relevant loss of precision in alpha-type clips. While the modified clip designed to reduce trauma cannot abolish trauma altogether, it significantly reduces the associated changes and hence the risk of thrombosis. Arteries were more sensitive than veins to clip-induced trauma, with increased occlusion force producing more severe damage than increased clipping time. Maximal changes were seen in the tunica media. These results indicate the paramount importance of applying modest clip pressure commensurate with the requirements of microvascular Surgery.

Traumatic intracranial aneurysms in childhood and adolescence. Case reports and review of the literature

We report four pediatric traumatic intracranial aneurysms occurring before the age of 10 years. Two of these aneurysms were the result of closed head injury. The remaining two were iatrogenic aneurysms which occurred in unusual circumstances. These four children represent 33% of the pediatric intracranial aneurysms seen at the Children's Hospital of Eastern Ontario from 1974 to 1992. Diagnosis of traumatic intracranial aneurysms requires a high index of suspicion: any head-injured or postoperative child who experiences delayed neurologic deterioration, or who fails to improve as expected following treatment, should promptly undergo diagnostic intracranial imaging. Documented subarachnoid hemorrhage, intracerebral or intraventricular hemorrhage, or subdural haematoma in this clinical setting should be further investigated by cerebral angiography to exclude a traumatic aneurysm or other vascular lesion. Traumatic aneurysms typically arise at the skull base or from distal anterior or middle cerebral arteries or branches consequent to direct mural injury or to acceleration-induced shear. Reported traumatic aneurysms account for 14%-39% of all pediatric aneurysms. Iatrogenic aneurysms also occur with unexpected frequency during childhood and adolescence. Pediatric traumatic cerebral aneurysms may present early or late. Most present early with intracranial hemorrhage. Late presentation occurs infrequently, typically as an aneurysmal mass. Once diagnosed, these aneurysms should be promptly treated by craniotomy employing routine microsurgical techniques, or in some cases, by endovascular detachable balloon techniques. Delay in operative treatment entails significant risks of repeated hemorrhage and death. Outcome in these children is primarily determined by the extent of traumatic cerebral injury and the preoperative clinical status. The latter directly depends upon diagnosis of the aneurysm prior to either initial or repeated hemorrhage.

Basilar artery dissection: an early postoperative complication of aneurysm clipping. Case report

Recurrent subarachnoid hemorrhage (SAH) in the early period following successful clipping of a cerebral aneurysm is unusual. The authors report a unique case of distal basilar artery dissection and fatal SAH on the 6th day postoperatively. It is concluded that this complication was related to vascular trauma inflicted by repositioning the aneurysm clips during a seemingly uneventful procedure for a basilar artery tip aneurysm.

Acute phase vascular endothelial injury: a comparison of temporary arterial occlusion using an endovascular occlusive balloon catheter versus a temporary aneurysm clip in a pig model

We compared the degree of acute endothelial injury after temporary vessel occlusion using two different occlusion modalities--external clipping and endovascular balloon occlusion. The common carotid and subclavian arteries in eight weanling pigs were temporarily occluded with either a 5 Fr occlusion balloon catheter or a temporary microvascular clip for 0 (control), 5, 10, and 30 minutes. Two animals (eight vessels; four clip and four balloon occluded) were used at each time interval. Segments of each experimental vessel were harvested and analyzed by scanning electron microscopy. Each vessel specimen was graded on the following scale: Grade 1 showed no evidence of injury; Grade 2 showed minimal evidence of endothelial cell injury; Grade 3 showed moderate evidence of endothelial cell injury; Grade 4 showed marked evidence of endothelial cell injury; Grade 5 showed severe endothelial and subendothelial injury. Control vessels showed no evidence of injury. Grade 2 injuries were seen in both clip- and balloon-occluded vessels at 5 minutes. At 10 minutes, focal Grade 2 and 3 injuries were appreciated in the clip group, with diffuse Grade 2 and 3 injuries in the balloon group. After the 30-minute occlusion, the balloon group showed Grade 2, 3, and 4 injuries, whereas the clip group showed entirely Grade 2 injuries. The degree of injury with either occlusion modality was equivalent and worsened with time. However, clip-occluded vessels displayed injury that was confined to an area closely adjacent to the clip site, whereas balloon-occluded vessels demonstrated a more widespread injury centered around the balloon site.

Quantitation of platelet deposition on human arteries: assessment of the disparity between results obtained with 111indium (111In)-labelling versus scanning electron microscopy

Quantitation techniques for measuring platelet deposition (PD) to vessel surfaces are important to an understanding of thrombogenesis. In previous studies, scanning electron microscopy (SEM) has been shown to indicate a lower extent of PD than platelet 111In-scintigraphy. Part of this disparity may be explained by nonspecific binding of 111In to the vessel surface during perfusion, or loss of adherent 111In-labelled platelets by lysis or dissociation from the surface during specimen preparation for SEM. To assess whether these independent processes occur, we used a previously described human placental artery (HPA) perfusion model to quantify vessel 111In retention. Of the total 111In that bound to the vessel surface during perfusion, 77 +/- 42% (N = 9) was platelet associated 111In (111In-labelled platelets) and 23 +/- 19% (N = 9) was non-platelet associated 111In (nonspecific binding). After specimen fixation, 67 +/- 32% (N = 9) of the initial total surface 111In remained. This decrease is due to dissociation of both adherent 111In-labelled platelets, and nonplatelet associated 111In. After fixation, 57 +/- 34% (N = 9) of the initial total surface 111In remained as 111In-labelled platelets and 10 +/- 13% (N = 9) remained as nonplatelet associated 111In. Fixation caused no measurable lysis of platelets. These data suggest that PD may be overestimated by 111In-scintigraphy because of nonspecific binding of 111In and underestimated by SEM because of dissociation of adherent platelets during specimen preparation for SEM.

Variations in regional cerebral blood flow investigated by single photon emission computed tomography with technetium-99m-d, l-hexamethylpropyleneamineoxime = l-h during temporary clipping in intracranial aneurysm surgery: preliminary results

Single photon emission computed tomography with technetium-99m-d, l-hexamethylpropyleneamineoxime was used to assess variations in regional cerebral blood flow during temporary clipping in the course of intracranial aneurysm surgery and during the postoperative period in 20 patients, 14 of whom underwent temporary clipping. Of these 14 patients (Group A), 9 had aneurysms of the anterior communicating artery, 2 had aneurysms of the middle cerebral artery, and 3 had aneurysms of the carotid siphon. Temporary clips were applied, according to the site of the lesion, on A1, on the trunk of the middle cerebral artery, or on the trunk of the internal carotid artery. The occlusion time ranged from 2 to 31 minutes. The six patients who did not undergo temporary clipping served as controls (Group B), as follows: three had aneurysms of the posterior communicating artery, one of the anterior communicating artery, one of the middle cerebral artery, and one of the internal carotid artery. All patients were investigated with cerebral single photon emission computed tomography preoperatively, perioperatively, and postoperatively. In all the patients of Group A, the preliminary results of the study show a sharp fall in the perfusion of the territories of the temporarily clipped parent vessel and practically a complete recovery within 2 to 7 days of surgery, with no significant neurological symptoms. No similar disturbance of perfusion was found in the patients of Group B.

The endothelium: a key to the future

The vascular endothelium is a complex modulator of a variety of biological systems and may well be the key to definitive success in the treatment of cardiovascular disorders. Surgically-induced endothelial injury may occur preoperatively during cardiac catheterization and intraoperatively from mechanical manipulation, ischemia, hypothermia, and exposure to cardioplegic solutions. The normal endothelium is antithrombogenic and yet promotes platelet aggregation and coagulation if injured. Vasospasm, occlusive intimal hyperplasia, and accelerated arteriosclerosis can also all occur as a result of endothelial injury. Furthermore, endothelial injury is harmful even in the absence of disruption of its monolayer integrity. Thus, preservation of the endothelium should be an additional objective for all cardiovascular surgeons. Synthetic vascular grafts, cardiac valves, and artificial ventricles do not spontaneously endothelialize and thus usually require some form of anticoagulation to maintain patency. Hence, endothelialization of prosthetic implants became an attractive concept. A number of different methods of obtaining an endothelial lining of prosthetic material has since been developed; these include facilitated endothelial cell migration, and endothelial cell seeding by using either venous or microvascular endothelial cells. Manipulating the endothelium might well provide the next major advancement for therapeutic and preventive measures for cardiovascular disease.

Management of giant intracranial aneurysms

Based on an own material of 64 cases a survey is given on the management of giant intracranial aneurysms. Essential investigations are as well CT and Magnetic Resonance Scanning as detailed angiographic studies. With regard to the operative handling the following questions are discussed: approach; use of temporary vascular occlusion and related monitoring; preparation of the aneurysm neck for occlusion. In cases without recent subarachnoid haemorrhage morbidity and mortality were less than 10%. It was 15% in cases where recent haemorrhage had occurred.

Temporary clipping in aneurysm surgery: technique and results

The use of temporary clipping has become an established tool in the armamentarium of the aneurysm surgeon. Our experience with 62 consecutive patients is presented, detailing operative protocols and results. Twenty-two had unruptured aneurysms (35%), 15 were grade I (24%), 16 grade II (25%), five grade III (8%), and four grade IV (7%). The aneurysms were mainly located in the middle cerebral artery (29 patients) and the anterior communicating artery (13 patients). Eleven of our 62 patients (17%) developed a new, persistent postoperative deficit. However, in only one case (2%) was temporary clipping felt to be implicated in the development of the deficit. In three other patients (5%), the effect of temporary clipping, although unlikely, could not be excluded. Overall, 92% of our patients with temporary clipping had good to excellent outcome, with 3% mortality and 5% morbidity. We believe that temporary clipping is a safe procedure that contributes significantly to a better outcome.

Morphologic and morphometric analyses of rat femoral arteries after crush injury

Replantation after crush amputation has a relatively low success rate. An arterial crush injury was produced in rats under a range of pressure (8.5 to 2,551 g/mm2) and durations (10 to 60 minutes). The degrees of vessel injury and thrombus formation were evaluated as functions of both crush force and duration, and the healing process was followed for 8 weeks. Crushing resulted in morphologic damage to the arterial wall but did not impair patency. Damage was directly proportional to crush pressure and duration. Intimal denudation caused flat platelet adhesion but no thrombus formation or thrombosis. Re-endothelialization was completed by 2 weeks. Intimal hyperplasia appeared at 1 week and consisted of endothelia in the most luminal layers and smooth muscle in the deeper layers. the internal elastic lamina was intact in all specimens and was thought to minimize platelet aggregation on the arterial wall after denudation of the intima.

Preservation and structural adaptation of endothelium over experimental foam cell lesions. Quantitative ultrastructural study

To assess the extent to which endothelial cell (EC) structure is modified by hyperlipidemia and by the formation of intimal plaques, we undertook a quantitative ultrastructural study of aortic EC of cynomolgus monkeys after 3 or 6 months on an atherogenic diet. We compared EC in lesion-free areas (LFA) with EC overlying focal discrete foam cell accumulations (FDA) or covering multilayered confluent plaques (MCP). There was a 15% increase in cross-sectional lumen surface profile length over FDA or MCP compared to LFA (p less than 0.005) corresponding to the bulging contours of immediately underlying foam cells. There was, however, no increase in the number of EC per unit of surface area (26.2 +/- 4.47 per 10(4) mm2 for LFA and 26.0 +/- 4.22 for FDA) or, on cross-section, per 100 microns length of underlying internal elastic lamina (8.79 +/- 2.42 for LFA, 8.26 +/- 2.01 for MCP). Nor did the number of surrounding cells contacted by each cell over LFA or MCP differ from normolipemic controls (6.56 +/- 0.85 for LFA and 5.58 +/- 0.86 for MCP). Most ECs were markedly attenuated over lesions, and while the extent and complexity of lateral contact regions between adjacent EC was diminished, the number and complexity of basilar projections was greatly increased. These structures extended among the intimal foam cells to insert on the internal elastic lamina or on intimal matrix fibers, resulting in a 2.7-fold increase in the length of the abluminal portion of the EC profile. The perimeter of the transverse EC profiles was thereby increased from 41.4 +/- 2.12 microns in LFA to 82.2 +/- 5.21 microns over MCP (p less than 0.0001). Polarization of EC in the direction of flow diminished as lesions developed. The ratio of length to width, as well as the standard deviation of the ratio, decreased from 3.51 +/- 3.92 in LFA to 2.35 +/- 0.25 over MCP, due mainly to increases in the proportion of the cell perimeter exposed to the lumen. Lesion localization bore no relationship to the orientation of EC in corresponding locations in the normolipemic controls or in LFA immediately adjacent to plaques. Organelles of EC in hyperlipidemic animals showed features suggestive of increased metabolic activity in all regions, and stress filaments were increased in the EC attenuated over lesions. There was no evidence of EC degeneration, necrosis, or sloughing regardless of lesion location, size, or complexity.

Symptomatic arterial luminal narrowing presenting months after subarachnoid hemorrhage and aneurysm clipping

The authors describe three cases of clinical cerebral ischemia associated with angiographic evidence of cerebral arterial luminal narrowing presenting 7, 14, and 52 weeks after subarachnoid hemorrhage (SAH) and aneurysm clipping. Delayed vasospasm, in its usual time setting 1 or 2 weeks after hemorrhage, did not occur symptomatically in these patients. No evidence for aneurysm clip migration or rebleed was present. All patients responded favorably to volume expansion and elevation of blood pressure. This unusual occurrence of a very delayed vasospasm may further the understanding of the vasospastic process. The symptomatic onset of arterial luminal narrowing months after SAH may suggest that a proliferative vasculopathy more accurately explains the observed vessel narrowing, rather than conventional active constriction of vascular smooth muscle.

The complement system in atherosclerosis

Complement is a term referring to a collection of plasma proteins, specific cellular receptors and cell surface regulatory molecules. Activation of the complement system to completion results in the formation of C5b-9 terminal complexes. These complexes have been observed in human atherosclerotic lesions by immunohistochemistry. Although the structure(s) which activate complement in lesions have not been defined, cholesterol and oxysterols exhibit this property in vitro. Endothelial cell damage leads to complement activation and endothelial cells overlying atherosclerotic lesions have been observed to contain C3 and C5b-9 antigens. Cardiac myocytes stain for complement proteins (C3, C4 and C5b-9) following myocardial infarction. Infarct size and extent of inflammatory cell infiltrates are diminished by decomplementation prior to experimentally-induced myocardial ischemia. Following myocardial infarction and ulceration of atherosclerotic lesions in human patients there is an increase in circulating complement activation products and a decrease in the level of native C1 through C4 proteins. Thus, it appears that complement plays a role in atherogenesis and its sequelae. Little is known however, about the pathophysiological effects complement activation products exert on lesion development, for example through modulation of macrophage functions, or how complement activation is regulated in lesions. Implications for complement in atherogenesis are discussed.

Complement C5a (desArg) generation in serum exposed to damaged aortic endothelium

Complement activation by injured endothelial cells was investigated using ex vivo rabbit thoracic aortas as a source of endothelium and a neutrophil aggregation (NA) bioassay to detect the complement cleavage product C5a (desArg). Endothelium, oxygen-starved by incubating aortas 30 min with Tyrode's buffer, activated complement as demonstrated by a 57% increase in the NA response induced by serum from buffer-treated aortas as compared to serum from untreated control aortas. Incubation of MgEGTA serum in injured aortas resulted in a 27% (P less than 0.025) weaker NA response than normal serum, indicating participation by both classical and alternative pathways of complement activation. Serum from aortas incubated 30 min with 100 micrograms/ml cholestane-3 beta, 5 alpha, 6 beta-triol, a cytotoxic cholesterol oxidation derivative, induced a NA response comparable to that from serum from aortas treated 30 min with Tyrode's buffer. Heat inactivation of serum prior to aortic incubation abolished NA activity and serum incubated in deendothelialized aortas lacked NA activity. Fractionation of serum samples from these experiments on Sephadex G-100 revealed a single peak of NA activity corresponding to the molecular weight of C5a (desArg). Endothelial cell injury was demonstrated by the inability to exclude Trypan blue dye and by scanning electron microscopy. These data demonstrate that damaged arterial endothelium can effectively activate the complement system, resulting in the production of an anaphylatoxic inflammatory mediator.

Current management of cerebral aneurysms: is it based on facts or myths?

The overall morbidity and mortality from aneurysmal subarachnoid hemorrhage have not changed significantly over the past 30 years in spite of great progress in surgical technology and diagnostic capabilities. Most series report major morbidity and mortality figures of approximately 60%. The reason for the currently poor prognosis is due, in part, to the sometimes devastating effect of the initial hemorrhage over which we have no control. Another reason for our inability to improve these dismal statistics may be that the currently accepted treatment regimens have proven to be ineffective. Eighteen misconceptions or "myths" surrounding the treatment of aneurysmal subarachnoid hemorrhage have been identified as factors that have largely determined the currently accepted, ineffective treatment protocols, and these are discussed.

Cholesterol oxidation derivatives and arterial endothelial damage

Three groups of New Zealand male while rabbits were given either 2.5 mg/kg of 25-hydroxycholesterol, cholestane-3 beta, 5 alpha, 6 beta-triol or vehicle only, intravenously. 24 h after treatment, the luminal surfaces of aortae of rabbits receiving 25-hydroxycholesterol were examined by scanning electron microscopy (SEM) and showed numerous balloon-like protrusions and crater-like defects as well as circulating, formed elements adhering on the luminal surface. The luminal surface of aortae of rabbits given cholestane-3 beta, 5 alpha, 6 beta-triol had similar but more frequent lesions when compared with those of the 25-hydroxycholesterol group. Microthrombi were occasionally found. The aortae of the control group had significantly fewer lesions. Transmission electron-microscopic studies showed intracytoplasmic vacuoles and diffuse subendothelial edema in the aortae of the two groups receiving the oxidation derivatives of cholesterol. The balloon-like protrusions and crater-like defects observed by SEM appeared to represent the initial sterol-induced endothelial cell injury. Repeated episodes of arterial injury followed by thrombus formation could eventually lead to atherosclerosis.

New disposable microvascular clamp

A new design for a plastic microvascular clamp is described. The clamp consists of two flat blades, with eyes permitting application and removal of the clamp with cross-forceps. Closure is effected by the elasticity of a rubber ring placed around the blades, obviating the need for an articular joint or a spring mechanism. The new design simplifies production of the clamp, which is intended to be disposable, i.e., for once-only use.

Morphologic quantitation of pseudointima and effects of antiplatelet drugs on vascular prostheses in goats

The natural process of endothelialization, pseudointimal formation, and connective tissue incorporation of the expanded PTFE grafts in the goat was documented through histologic examination of specimens harvested at 2, 4, 6, and 8 weeks. The goats demonstrated a progressive increase in pseudointimal pannus ingrowth from the anastomoses at a rate of 11.3 mm over a 12 week period. Histologic changes according to time of vascular graft incorporation in the goat model were found to be comparable to those of the dog, pig, and calf models reported in the literature. Platelet-inhibiting drugs, aspirin, dipyridamole, nifedipine, and ibuprofen were administered to goats after replacement of their infrarenal aorta with 5 cm of 8 mm diameter expanded PTFE grafts. The effects of the drugs on graft endothelialization and anastomotic pseudointimal formation was compared with those in the untreated control group after 12 weeks. Aspirin and dipyridamole had no detrimental effect on the healing process compared with the untreated control group. Studies with nifedipine and ibuprofen did not demonstrate a decrease in pseudointimal hyperplasia. Antiplatelet treatment resulted in no significant change in the rate of endothelialization of expanded PTFE grafts.

The thermic vascular anastomosis (TVA). IV. Analysis by scanning electron microscopy

In the present study 48 thermic vascular anastomoses performed in Sprague Dawley Wistar rats were subjected to analysis by scanning electron microscopy. Depending on the period of postoperative survival (up to 18 months) normal smooth endothelium, dissected cuffs and aneurysms were seen. Endothelial damage through heat application following bipolar coagulation was only slight. In one 18 months old anastomosis an aneurysm with a delicate network of endothelialized filaments was seen leaving a free passage for the blood flow centrally. A comparison of the literature describing the healing processes of intima following various traumas is made.

Mechanical and metallurgical properties of vascular clips designed for temporary use

Six commonly used surgical clips (Kleinert-Kutz, Pivot, Vari-Angle, Yasargil, Biemer, and Acland) that have been designated by their manufacturer as being suitable for temporary occlusion were studied in terms of their mechanical and metallurgical properties. Opening and closing forces were determined for all of the clips. Significant variations in clip force with respect to blade gap were found in all of the pivot-type clips. Metallurgical testing showed that all six clips exhibited properties that contraindicate long-term implantation.

[Lesions of the carotid artery wall in guinea pigs after temporary clipping with emphasis on the vasa vasorum network]

Foram estudadas as lesões provocadas nas artérias carótidas de cobaias (Cavia porcellus), com diâmetros variando de 1 a 2 mm, submetidas à clampagem temporária (10 e 30 minutos), com microclampes empregados em microneurocirurgia, utilizando-se injeção intravital da mistura de gelatina líquida e tinta da China para contrastação dos vasa vasorum. As artérias foram diafanizadas e observadas ao microscópio óptico e posteriormente observadas através de cortes histológicos. Foram verificadas lesões agudas na íntima, na camada média e na rede de vasa vasorum adventicial, que ocorreram independentemente da duração da clampagem. Os resultados sugerem que existe uma pressão crítica exercida pelos microclampes, acima da qual deixa de haver uma relação direta entre a pressão exercida e o grau de lesão da parede arterial. A observação das artérias 30 dias após a clampagem temporária evidenciou recuperação parcial em relação às lesões agudas embora tenham persistido alterações na íntima e na camada média, que poderão constituir pontos fracos na parede arterial. As alterações graves dos vasa vasorum observadas agudamente e o quadro morfológico reacional verificado tardiamente não apresentaram diferenças quanto à pressão exercida pelo microclampe. Não foi possível correlacionar o grau de lesão da parede arterial e as alterações dos vasa vasorum. O trauma mecânico provocado pelas lâminas do microclampe pareceu mais importante na gênese destas lesões. Apesar das lesões graves observadas na parede das artérias clampadas temporariamente, em nenhum caso verificou-se trombose e oclusão vascular no local da clampagem.

Histological change in permanently clipped or ligated cerebral arterial wall. Part I. An experimental study in dogs

In this paper, we discuss the results of a study by light microscope of the effect of permanent clipping or ligation on the intracranial arteries of 38 operation dogs and 7 control dogs. The findings obtained are: 1. In the cerebral arterial circle, necrosis could easily result from ordinary clipping or ligation because of scarce vasa vasorum. 2. As for the incidence of necrosis, the greatest was found in the case of the Yaşargil clip after electric coagulation, next came the Yaşargil clip alone, next ligation, and last the silver clip. The degree of necrosis correlated with the duration of clipping in the cases treated with a spring type clip, and was influenced more by the closing strength at the time of application in the cases with non-spring type clips or ligation. 3. In some of the cases ligated for long duration, recanalization was caused by the passage of the ligature through the vessel wall, suggesting that ligation is not a certain procedure if it is applied alone. 4. The granulation tissue round the clip and ligature began to grow after one month. As for its degree, the most marked granulation was that caused by the silver clip, next the ligature, than the Yaşargil clip after electric coagulation, and finally the Yaşargil clip used normally; in all of them the correlation with the passage of time was noted. 5. In the group of duration three months or more, concentric intimal proliferation was noted peripheral to the clip, and intimal proliferation was also noted exclusively localized to the side of a branch on the central or truncal side of a clip. This correlated in degree with the passage of time. 6. Clipping and ligation are liable to cause necrosis and fragmentation, but on the other hand it was considered that rupture of the vessel wall did not result because of the reinforcing and reparative effect of the reactive granulation tissue and the intimal proliferation which developed in such a manner as to strengthen the area involved.

End-to-side vascular anastomosis: a study of technical considerations in the rat

A study of technical problems in the performance of microvascular anastomosis has been carried out in the rat. A comparison of two types of suture material suggested that handling characteristics had a significant effect on the time taken to complete the anastomosis, and on the accuracy of apposition of the vessel walls. Technical difficulties encountered intraoperatively proved predictive of subsequent compromise of the lumen, shown angiographically and histologically. The optimum conditions are discussed, and it is argued that postoperative antithrombotic medication is indicated when technical problems are encountered.

Histological change in permanently clipped or ligated cerebral arterial wall. Part II: Autopsy cases of aneurysmal neck clipping

An investigation was carried out on clinical autopsy cases into histological changes in the vessel wall and into the surrounding tissue reaction after permanent clipping. 1. There were 17 autopsy cases of cerebral aneurysm, which included seven cases treated with the Yaşargil clip, five with the Heifetz clip, and five control cases. 2. Clipping period ranged from 6 days to 11 months. Both the Yaşargil and the Heifetz clips, even with long duration of clipping, caused no changes, and inflammatory reaction was slight. 3. As for the necrosis of the vessel wall beneath the blade, the Yaşargil clip produced marked necrosis at the blade edge in 4 of 7 cases (57%), while the Heifetz clip caused necrosis under the midconvexity of the blades in all 5 cases (100%). 4. The granulation tissue reaction round the clip began to occur after one month, and was enough to embed the blade of the clip after three months. We considered it very unlikely for a slip-out accident to occur after this stage. 5. Formation of mural red thrombus and deposition of fibrin with irregular intimal thickening were noted in the aneurysmal lumen in cases clipped for less than 13 days. After one month the intimal thickening was diffuse, and organized thrombus was noted. After three months or more, the aneurysmal lumen was found to have been filled almost completely by intimal thickening. Based on the above finding, the optimum condition for temporary and permanent clips was also considered.

Reduced vascular trauma after temporary occlusion with modified Biemer and Yasargil clips

The Biemer and Yasargil microvascular clips that are currently available commercially can traumatize the vascular endothelium. In an effort to resolve this problem, both clip designs were structurally modified by changing the length, width, and surface of the clip blades in various ways. Also, the occlusion force of the clips was set at either 15 or 30 g. Studies on the carotid arteries of 140 rats showed a correlation between the structural and mechanical alterations of the clips and the degree of endothelial trauma produced by temporary occlusion for 1 hour. The most favorable results were obtained with a Biemer clip that had long, wide, smooth blades and an occluding force of 15 g.

A variable-force microvascular clip

An easily adjustable, variable-force microvascular clip is described. This clip is superior to other clips currently available because it is essentially three clips in one. Its advantages are that it can reduce the amount of table area needed to store clips during surgery and it offers the surgeon greater flexibility in the selection of clips with different closing forces. This clip was developed by modifying the segments of a basic alpha-type clip, designing a computer program to analyze the force contributions made by each segment of the clip, constructing several clips with different blade lengths, and testing them in a microvascular surgery research program. The clip we have developed is easy to use, reduces clutter on the instrument table, aand offers the surgeon a wide choice of closing forces with a minimal number of clips.

Re-endothelialization of microvascular carotid end-to-side anastomosis in the rat

A carotid end-to-side anastomosis was performed on 25 male and female Wistar rats (mean weight 197.8 gm). The animals were sacrificed at time intervals varying from 0 to 21 days after the operation. The anastomosis was exposed, the aorta cannulated, and the animals perfused with a 2.5% buffered glutaraldehyde solution at a constant pressure of 80 mm Hg. The anastomoses were removed for scanning electron microscopic (SEM) and light microscopic studies. The SEM results indicate that after the acute platelet-fibrin reaction in the first 48 hours, the suture line itself becomes re-endothelialized after 4 days. On the stitches, however, a cellular population consisting of leukocytes transforming into flattened cells was seen after 2 days. The morphology of these cells and their role in the regeneration of endothelium is discussed. This study presents evidence supporting a blood-borne genesis of endothelial cells in vivo.

Minimum vascular occlusive force

A mathematical analysis of the minimum occlusion force necessary to occlude small vessels based on the parametric influence of blood pressure, vessel diameter, clamp width, and vessel shape after clamping was performed. The results were confirmed by in vivo experimentation with 60 rat aortas (of 1.8 to 2.4 mm caliber) using a variable-force clamp gauge developed in our laboratory. Experimental and theoretical results differed by only 3 gm. Scanning electron microscopy revealed that the initial changes in the endothelium occurred in smaller radii of curvature. Increased pressure resulted in gross morphological changes across the vessel. The minimum occlusion force (as determined by the variable-force clamp gauge) produced only minimal endothelial damage.

Endothelial cell damage and thrombus formation following temporary arterial occlusion. Effects of pretreatment with aspirin or heparin

✓ The effects of restoration of blood flow on endothelial damage that occurs distal to the site of temporary arterial occlusion with surgical clips, and the effects of heparin and aspirin on thrombus formation at the site of the clip, were studied by scanning electron microscopy (SEM). The right carotid artery of 45 rabbits was occluded with a Heifetz clip for 30 minutes. The clips were then removed and blood flow resumed for periods of 30 minutes, 1 hour, 2 hours, and 24 hours. A second group was preteated intravenously with heparin (1400 units/kg), and a third group was pretreated orally with aspirin (50 mg/kg). The SEM analysis of arterial segments distal and proximal to the clip indicated that the frequency of occurrence of endothelial crater- and balloon-like vesicular defects decreased to zero within 24 hours of restoration of blood flow. Examination of arterial segments compressed by the clip revealed endothelial desquamation and thrombus formation within 30 minutes of resumption of flow. The maximum degree of thrombus formation occurred within 1 to 2 hours of resumption of flow, with a subsequent decrease in the extent of deposition of platelets, fibrin, erythrocytes, and leukocytes within 24 hours. No change was found in composition or quantity of thrombus formation after pretreatment with heparin although, in the latter specimens, fibrin deposition appeared considerably less. However, pretreatment with aspirin resulted in marked reduction in the overall quantity of thrombus formation at the site of the clip following temporary occlusion.

Early vascular changes in the spinal grey matter following impact injury

The ultrastructural changes of the microvasculature in the spinal grey matter were studied after impact injuries of varying severity in cats. Survival times ranged from 3 min to 6 h after injuries. The main vessels affected were capillaries and postcapillary venules. Perivascular haemorrhage and protein extravasation were present immediately after impact. Astrocytic foot processes could be swollen or shrunken and of increased electron density. The extra cellular space (ECS) was often distended with proteinaceous material. Some vessels showed an apparent increase in vesicles and small dense inclusions were seen in pericytes. By 20--30 min after impact, a number of vessels at greater impact energies showed degenerative changes in organelles and endothelial gaps. The lumina of these vessels often contained plasma, platelets, red cells and occasional neutrophils. Similar changes were seen between 3 and 6 h and at this stage neutrophils and some monocytes were present in the perivascular spaces and neuropil. Endothelial balloons and pericytic dense inclusions were also seen. It is suggested that initial events are mechanical, perhaps due to a rapid displacement of blood in venules followed by arterial hypertension (which commonly accompanies spinal cord impacts). Although initially many lumena are patent by 30 min there is a difference between the lesser and greater severities of impact.