Distal circulatory support for thoracic aortic operations: effects on intracranial pressure

Spinal cord ischemia can result from aortic clamping during thoracic aortic operations. The perfusion gradient for spinal cord perfusion is positively influenced by distal aortic pressure and negatively influenced by intracranial pressure (ICP). Hemodynamic and ICP changes were examined in a swine model of descending thoracic aortic surgery where distal aortic perfusion was achieved under one of three conditions: (1) clamping without support, (2) a passive aortofemoral shunt, or (3) a left atrium-femoral artery bypass system. With aortic clamping alone, ICP increased from 9.8 +/- 2.2 mm Hg to 15.2 +/- 2.8 mm Hg (p < 0.05). With passive shunting, ICP was decreased to 13.8 +/- 3.0 mm Hg, which was still significantly elevated above baseline. However, with active bypass, ICP remained at control level (9.8 +/- 2.2 mm Hg). Mean distal aortic pressure, which was 82 +/- 10 mm Hg in the control state, decreased to 20 +/- 0.5 mm Hg with clamping alone and to 39 +/- 9 mm Hg with passive shunting, whereas with active support, a distal pressure of 64 +/- 8 mm Hg was achieved. In contrast to passive shunting, active distal bypass results in maintenance of ICP at baseline levels and results in distal aortic pressure significantly greater than that achieved with either aortic clamping alone or passive shunting. Thus, active distal circulatory support produces the greatest salutary effect on the two determinants of the spinal cord perfusion pressure gradient: ICP and distal aortic pressure. This support modality may be the best adjunctive technique to maintain the spinal cord perfusion gradient and hence minimize the risk of ischemic injury.