Assessment of transmural force during application of vascular occlusive devices

Minimally Invasive Partial Nephrectomy: Are All Clamps Created Equal? An Ex Vivo Model Simulation of Vascular Clampage

REASON FOR REVIEW

During the partial nephrectomy, clamping of the vascular pedicle before exision of the tumor is a key step in minimizing blood loss and maintaining adequate visualization. Different vascular clamping devices have been developed for minimal invasive surgery. However, there are no reports comparing them in turn of efficiency RECENT FINDINGS: We present an ex vivo experimental model, designed to demonstrate differences between the clamping devices. All clamps proved to function properly without any leakage at 90 and 120 mmHg, respectively. Our study and the ex vivo model prove that all available clamps are equally efficient at physiologic pressures.

Renal Vascular Clamp Placement: A Potential Cause of Incomplete Hilar Control during Partial Nephrectomy

PURPOSE

Previous benchtop studies have shown that robotic bulldog clamps provide incomplete vascular control of a Penrose drain. We determined the efficacy of robotic and laparoscopic bulldog clamps to ensure hemostasis on the human renal artery. The effect of clamp position on vascular control was also examined.

MATERIALS AND METHODS

Fresh human cadaveric renal arteries were used to determine the leak point pressure of 7 bulldog clamps from a total of 3 manufacturers. Five trials were performed per clamp at 4 locations, including the fulcrum, proximal, middle and distal positions. Comparison was done using the Kruskal-Wallis test with p <0.05 considered significant.

RESULTS

None of the bulldog clamps leaked at a pressure less than 215 mm Hg when applied at the proximal, middle or distal position. In general leak point pressure decreased as the artery was positioned more distal along the clamp. The exception was when the vessel was placed at the fulcrum position. At that position 80% to 100% of trials with the Klein laparoscopic, 100% with the Klein robotic (Klein Robotic, San Antonio, Texas) and 60% to 80% with the Scanlan robotic (Scanlan International, Saint Paul, Minnesota) clamp leaked at pressure below 215 mm Hg.

CONCLUSIONS

Each vascular clamp adequately occluded flow at physiological pressure when placed at the proximal, middle or distal position. Furthermore, these results demonstrate that there is leakage at physiological pressure when the artery is placed at the fulcrum of certain clamp types. These results suggest that applying a bulldog clamp at the fulcrum could potentially lead to inadequate vessel occlusion and intraoperative bleeding.

Arterial clamping leads to stenosis at clamp sites after femoropopliteal bypass surgery

BACKGROUND

To date, the incidence and clinical relevance of arterial stenosis at clamp sites after femoropopliteal bypass surgery is unknown.

METHODS

Ninety-four patients underwent a femoropopliteal bypass in which the arterial inflow and outflow clamp sites were controlled by the Fogarty-Soft-Inlay clamp and marked with an hemoclip. The number of pre-existing atherosclerotic segments, clamp force, and clamp time were recorded and the occurrence of a stenosis at the clamp site was determined.

RESULTS

After a mean follow-up of 83 months, a significant stenosis was confirmed at 23 of the 178 clamp sites (12.9%; 95% confidence interval 8.4 to 18.8). The mean number of pre-existing atherosclerotic segments (P = .28) and the mean clamp force (P = .55) was similar between the groups with and without a stenosis. There was a significant difference regarding clamp time between the group with and without a stenosis (38 minutes and 26 minutes, P = .001).

CONCLUSION

Arterial clamping, even with the Fogarty-Soft-Inlay clamp, can lead to clamp stenosis and seems to be related to the duration of clamping, but not to pre-existent atherosclerotic burden.

Pressure controlled clamp using shape memory alloy for minimal vessel invasion in blood flow occlusion

PURPOSE

Vessel damage after clamping may affect the success of surgical operations. A new pressure controlled clamp (SMA clamp) was designed using super elastic property of shape memory alloy (SMA) to realize atraumatic vessel occlusion. The ability and biological effect of the SMA clamp to control pressure was investigated in vivo.

METHODS

The loading-displacement curves of the SMA clamps (experimental group) and conventional clamp (control group) by occlusion of pig carotid arteries were evaluated using a clamping-pressure analyzing system. To investigate macroscopically and histologically the vessel damage of the SMA and conventional clamps, pig carotid arteries were stained with Evan's blue and its histological sections were stained with Elastica Massion after clamping for fifteen minutes.

RESULTS

Constant value was shown in the loading-displacement curve of SMA clamp. In the control group, damaged area stained with Evan's blue in the vessel wall showed enlargement with the pressure increasing. Less areas in experimental groups are observed than that in the control group. Histological section in the experimental group showed no obvious except a slight compressive damage in the tunica intima. In the control group, vessel wall showed irreversible damages.

CONCLUSIONS

This experiment indicated that the SMA clamp, which has a unique mechanical property, can be used without vessels damage. This pressure controlled clamp can be a selection in clinical apparatus to improve surgical safety.

Application of shape memory alloy pressure-controlled vascular clamp for atraumatic vessel occlusion

BACKGROUND

To realize atraumatic vessel occlusion, a new hemostatic clamp using superelastic shape memory alloy (SMA) as a pressure control limiter has been proposed. It was designed taking advantage of a unique mechanical property of SMA. The ability to control pressure with the newly designed SMA clamp was investigated. The traumatic effect on vessel walls was evaluated in order to confirm the SMA clamp's biological effect of protecting vessels from damage.

METHODS

Twenty-four pig thoracic aortas were divided into four groups: SMA group 1 (0.3mm diameter SMA wire used), SMA group 2 (0.4mm diameter SMA wire used), base model group (hemostatic clamp of Mimura type), and a control group. The biomechanical interaction between the pressure-controlled clamp and animal aortas was evaluated with a micropressure analyzing system. The atraumatic effect of the SMA clamp was examined on pig thoracic aortas in vitro and compared with that of its base model. The morphological injury of each vessel was evaluated after being clamped for 15 min.

RESULTS

Pressure saturation was shown in the displacement-pressure curve of the SMA clamp. In both SMA group 1 and SMA group 2, except for a slight imprint of compression in the intima, no obvious injury was observed, while in the base model group the endothelial laceration was observed when the clamp was closed to notch I. More serious injuries in the endothelial intima and media were observed when the clamp was closed to notches II and III.

CONCLUSION

The effect of pressure-controlling SMA clamps on the in vitro vessel model was evaluated. Histological observation and the traumatic score proved that the safety of the clamps was improved with the new design of pressure control. This technique supplies an effective and applicable way of realizing atraumatic clamping.

A three-dimensional finite element model for arterial clamping

Clamp induced injuries of the arterial wall may determine the outcome of surgical procedures. Thus, it is important to investigate the underlying mechanical effects. We present a three-dimensional finite element model, which allows the study of the mechanical response of an artery-treated as a two-layer tube-during arterial clamping. The important residual stresses, which are associated with the load-free configuration of the artery, are also considered. In particular, the finite element analysis of the deformation process of a clamped artery and the associated stress distribution is presented. Within the clamping area a zone of axial tensile peak-stresses was identified, which (may) cause intimal and medial injury. This is an additional injury mechanism, which clearly differs from the commonly assumed wall damage occurring due to compression between the jaws of the clamp. The proposed numerical model provides essential insights into the mechanics of the clamping procedure and the associated injury mechanisms. It allows detailed parameter studies on a virtual clamped artery, which can not be performed with other methodologies. This approach has the potential to identify the most appropriate clamps for certain types of arteries and to guide optimal clamp design.

Tourniquets in arterial bypass surgery

BACKGROUND

successful infra-popliteal bypass depends on precise, atraumatic technique in performing the distal anastomosis. The use of a tourniquet facilitates the distal anastomosis, reducing dissection, avoiding traumatising clamping of the vessels and providing an "uncluttered" operating field. Despite these advantages the technique is under-used.

OBJECTIVES

to review the use of tourniquets in arterial reconstruction, with particular reference to safety issues and complications. DESIGN, METHODS AND MATERIALS: a Medline search was performed (last search Feb. 2000), and keywords from relevant papers were used to perform subsequent searches. References were reviewed from each relevant paper.

RESULTS

no randomised controlled trials were found. The review details reported use of tourniquets in arterial reconstruction, including techniques, outcomes and potential complications.

CONCLUSION

the use of a tourniquet is a safe and effective technique to facilitate arterial reconstruction.

A new technique for hemodialysis access surgery: use of the pneumatic tourniquet

The purpose of this study was to determine whether tourniquet occlusion could be safely used on the upper extremity for vascular control during hemodialysis access surgery. The hospital and outpatient records of 44 patients undergoing 105 hemodialysis access procedures were retrospectively reviewed. In 48 procedures tourniquet occlusion was used for vascular control, whereas in 57 procedures vascular clamps were used. In those procedures in which the tourniquet was used, the mean tourniquet time was 30 minutes and the mean tourniquet pressure was 242 mm Hg. The operative time was significantly less in the tourniquet group as compared to the clamp group (72.5 minutes vs. 84 minutes, respectively; p = 0.029). There was no statistically significant difference in the incidence of nerve injury, bleeding, hematoma, vascular steal, infection, or swelling between the two groups. There were no complications related specifically to the use of the tourniquet. There was no difference in primary patency in comparing the tourniquet control group with the clamp control group (p > 0.5). The use of a pneumatic tourniquet for vascular control during hemodialysis access surgery allows for a faster, technically easier operation with no increase in the complication rate and no effect on primary patency.

Procion yellow fluorescent microscopy: a new method of studying arterial and venous pathology

A new means of studying vessel wall pathology is presented. This technique utilizes Procion yellow, a vital fluorescent dye, to stain and delineate the connective elements, matrix, and elastic tissue within the arterial wall. In addition, penetration of the dye into cells provides evidence of membrane pathology. A canine model was used, and clamped segments of femoral artery were stained and examined. The appreciation of this approach for the examination of the vessel wall shows alterations in tissue elements that have not been reported previously. This technique makes possible a unique means of studying connective tissue elements as well as membrane integrity.

Chronic histologic changes after vascular clamping are not associated with altered vascular mechanics

The mechanical properties of arteries, along with the histologic and scanning electron microscopy characteristics of the nonatherosclerotic canine arteries, were investigated six months after vascular clamping. Different vessel clamps were applied to 73 sites on the carotid and femoral arteries in five anesthetized dogs. Each clamp was applied for 30 minutes with (a) sufficient force to just occlude blood flow or (b) as tightly as the clamp could be placed. After six months the vessels were excised, filled with barium sulfate suspension, and pressurized in 25 mmHg steps up to 150 mmHg. High resolution contact radiographs were taken at each pressure. These were magnified 35x and measured. Scanning electron microscopy and conventional histology disclosed that the clamped sites exhibited serrated clamp "tracks" in the intima, intimal hyperplasia, and, in a few cases, fractured elastic lamellae. These histologic changes were seen more frequently in the femoral artery than in the carotid artery (p less than .01). The mechanical properties, as determined from radiographic measurements, demonstrated that, for all types of clamps, the luminal diameter, pressure-diameter relationship, and compliance of the clamped vessels were not significantly different from nonclamped control regions (ANOVA). These studies demonstrate that careful application of clamps to nonatherosclerotic arteries produces persistent morphologic changes, but these are not associated with altered mechanical properties of the vessel wall.