Achieving optimal pulmonary blood flow in the first-stage of palliation in early infancy for complex cardiac defects with hypoplastic left ventricles

Abstract

The aim of the study was to determine the optimal size and technique for construction of the systemicto-pulmonary arterial shunt which will provide suitable pulmonary blood flow in first-stage Norwood palliation for hypoplastic left heart syndrome in neonates. Our clinical experience suggested that an arterial oxygen tension of about 30 mm Hg immediately after cardiopulmonary bypass, with the patients being ventilated at the lowest possible mean airway pressure with an FiO 2 of 1.0, provided a suitable pulmonary-to-systemic flow ratio. We also aimed to clarify the characteristics of pulmonary blood flow in accordance with the size of the shunt and the change in the pulmonary vascular resistance in a simplified rigid model of the Norwood procedure. A hole of 2.0 mm diameter proved adequate to provide a suitable pulmonary blood flow of 200-300 ml/min in the presence of a pressure gradient of 20-40 mm Hg between the systemic and pulmonary circulations in neonates weighing 3 kg. A short central shunt with a prosthesis of 4 mm in diameter produced an excessive flow of pulmonary blood. Our data suggest that using a smaller shunt than that commonly used is necessary to decrease the early and intermediate postoperative mortality. A prosthesis of 3.0 or 3.5 mm in diameter arising from the brachiocephalic artery would be acceptable and can be recommended for first-stage Norwood palliation in small infants, especially in view of the operative difficulties encountered in taking down the shunt at the time of subsequent operations.Key words: Hypoplastic left heart syndrome; first-stage Norwood palliation; pulmonary blood flow; hydrodynamic experiment T HEOUTCOME AND CLINICAL COURSE AFTER FIRST-STAGE Norwood palliative surgery for complex cardiac defects with hypoplastic left ventricles in early infancy have recently been reviewed, and several problems were identified for the second-stage Fontan procedure. 1 ' 2 Although many complex issues are related to the high early mortality resulting from acute cardiovascular collapse during the first postoperative day, and the high intermediate mortality due to chronic exposure of the right ventricle to volume load at systemic pressures, one of the important problems is the regulation of the pulmonary blood flow established by construction of the systemic-to-pulmonary arterial shunt. Our present aim, therefore, is to find a mote optimal size and technique for the systemic-to-pulmonary arterial shunt which would provide the most suitable pulmonary blood flow in the first-stage Norwood palliation carried out in early infancy.

Computational modeling of vascular anastomoses

“…Literature studies are limited to either three-dynamics computational models or in vitro models of local fluid dynamics in a sole systemic-to-pulmonary shunt (Kitagawa et al 1995;Tacy et al 1998;Migliavacca et al 2000a, b;DeGroff et al 2000;Pennati et al 2001). In such studies, boundary conditions for the model (flow and/or pressure) were enforced without feedback from the remainder of the circulatory network.…”

Multiscale modeling of the cardiovascular system: application to the study of pulmonary and coronary perfusions in the univentricular circulation

“…Literature studies are limited to either 3-D computational models or in vitro models of local fluid dynamics in a sole systemic-to-pulmonary shunt (Kitagawa et al, 1995;Tacy et al, 1998;Migliavacca et al, 2000a, b;DeGroff et al, 2000;Pennati et al, 2001). In such studies, boundary conditions for the model (flow and/or pressure) were enforced without feed back from the remainder of the circulatory network.…”

Computational fluid dynamics models and congenital heart diseases

“…Furthermore, in infants and small babies, mathematically accurate measurements and data needed for modeling purposes are difficult to obtain. Most studies have been limited to either 3D computational models ( 9 – 14 ) or in vitro models ( 15 – 19 ) of the local fluid dynamics. Such models, although providing a very detailed description of the local hemodynamics, could not describe the mutual interactions with the remainder of the circulatory system, because boundary conditions (flows or pressures) were enforced to the model.…”