A computer simulation of the plasma leakage through a vascular prosthesis made of expanded polytetrafluoroethylene

Pleural flap for treating perigraft leak after a modified Blalock-Taussig shunt

Plasa oozing through the graft after a modified Blalock-Taussig shunt is a troublesome complication. We encountered a massive leak following a modified Blalock-Taussig shunt in a 2 1/2 year-old-girl which required reexploration. The leak was treated by wrapping the polytetrafluoroethylene shunt with the parietal pleura flap harvested from the adjacent chest wall. The patient had an uneventful recovery. Covering of the polytetrafluoroethylene shunt with parietal pleura appears to stop plasma leak through the graft following a modified Blalock-Taussig shunt.

Mechanisms of heparin transport through expanded poly(tetrafluoroethylene) vascular grafts

Thrombosis and neointimal hyperplasia limit the utility of small-caliber artificial vascular grafts. Surface modifications and adjunctive pharmacological therapy might mediate these complications. We examined the mechanisms by which a model vasoactive compound, heparin, transverses porous graft materials and how material modifications alters this drug's transport. The effective permeance of [(3)H]heparin was measured after application of a uniform concentration of drug to either the internal or external surface of the graft and in the presence or absence of pressure-driven physiologic hydraulic flows. Transgraft permeance was equivalent to those observed in normal arteries and, while enhanced by convection, was mediated in major part by diffusion. Peclet numbers under the various conditions examined ranged from 0.05 to 1.2, indicating that diffusive forces were equal to or exceeded convective forces in governing transmural heparin motion. Heparin traversed the graft even when applied from the outer perivascular surface, against adverse hydraulic flows. Modifications of the grafts that included a yarn barrier of spun poly(tetrafluoroethylene) or chemical modification of surface tension energy altered permeances as well. A unifying model for interpretation of these data incorporates the concept of entrapped air and surface tension energy in the graft. These characterizations allow for the design of vascular grafts that are optimized for pharmacotherapy to help prolong graft patency, especially in small-caliber vascular beds.

Heparin as a risk factor for perigraft seroma complicating the modified Blalock-Taussig shunt

OBJECTIVE

The purpose of this study was to determine the risk factors associated with the occurrence of perigraft seromas complicating systemic-to-pulmonary polytetrafluoroethylene grafts.

METHODS

Clinical and perioperative variables were reexamined, blinded for the outcome variable perigraft seroma, in 60 patients undergoing 67 consecutive graft procedures in a 3.5-year period.

RESULTS

Eight cases of perigraft seroma were diagnosed in six patients. Univariate analysis revealed age (p = 0.02), a diagnosis of pulmonary atresia with ventricular septal defect and systemic-pulmonary collaterals (p = 0.001), reimplantation of collaterals during the procedure (p < 0.001), and intravenous heparin administered after operation (p < 0.0001) as risk factors for symptomatic perigraft seroma. Multivariable analysis defined heparin as the only significant factor associated with symptomatic perigraft seroma. Consolidation of the upper lobe on chest radiograph, ipsilateral to the shunt, directly after operation (p = 0.01), but especially 8 to 10 days after operation (p < 0.0001), or the need for prolonged drainage of pleural fluid (p < 0.0001) were correlated with the occurrence of perigraft seroma. Perigraft seroma led to four early rethoracotomies in three patients and to accelerated corrective surgery in three cases. Consolidation and absent perfusion of lung segments persisted in two patients.

CONCLUSIONS

Our data suggest that the use of heparin leads to an increased risk of perigraft seroma, complicating systemic-pulmonary polytetrafluoroethylene grafts. Prolonged pleural drainage and/or postoperative consolidation of the upper lobe indicate the development of symptomatic perigraft seroma. Treatment is controversial and results are unpredictable. Expectative management seems to be justified so long as permitted by the clinical condition.