Effectiveness of assistance circulations for distal circulatory support during cross-clamping of the descending thoracic aorta.

In order to find the ideal distal circulatory support during cross-clamping of the descending thoracic aorta, the author compared the effects of simple shunting (SS) and centrifugal pump (CP) on hemodynamics and metabolisms in mongrel dogs. In group I (control), the aorta was cross-clamped for two hours without SS or CP; in group II (SS), a temporary shunt was placed between the left common carotid and left femoral arteries during cross-clamping; in group III (CP), with left heart bypass, the flow was maintained about the same as that in group II; in group IV (CP), proximal pressure was maintained unchanged. Hemodynamic and metabolic parameters were recorded prior to cross-clamping and every 30 min for four hours during and after cross-clamping. All animals in group I suffered from hemodynamic instability, metabolic abnormalities and neurologic injury and died within 12 hours. Hemodynamic changes were more unstable in group III than in groups II and IV. Three dogs in group III and also in group IV but none in group II, suffered from neurologic injury. Metabolic changes in groups II, III and IV were not significant. The author conclude that hemodynamic and metabolic abnormalities can be minimized through the efficient use of a shunt in cross-clamping of the descending thoracic aorta and postoperative complications such as paraplegia, renal failure and hepatic dysfunction can be prevented. The centrifugal pump as a distal circulatory support device is able to maintain stable hemodynamics and normal distal organic metabolisms if aortic pressure proximal to the clamp is maintained essentially unchanged through regulation of pump flow. However, it is unable to prevent paraplegia during cross-clamping of the descending thoracic aorta for two hours. Shortening the time of cross-clamping of the descending thoracic aorta is necessary to prevent paraplegia.