Cerebral arterial blood flow and aneurysm surgery

Abstract

A study of 21 patients was conducted to clarify the autoregulatory capacity in patients subjected to induced hypotension during intracranial surgery for saccular aneurysms. Trimethaphan camsylate (Arfonad) was used for induced hypotension and arterial blood flow was measured with an electromagnetic flow probe on the internal carotid artery or one of its main intracranial branches. In Grade I and II patients the control arterial blood pressure (ABP) ranged from a mean of 90-135 mm Hg (average 110 mm Hg), with a lower level of autoregulation (LLAR) from 35-85 mm Hg (average 62 mm Hg). Grade III patients had a control ABP of between 105 and 145 mm Hg (average 124 mm Hg) and the LLAR was 60-95 mm Hg (average 76 mm Hg). There was a significant difference between the 2 groups with regard to the control ABP and the LLAR. A surprising result obtained was that the average lower autoregulatory range (the difference between control ABP and LLAR) is practically the same in the 2 groups. A systematic investigation of the upper limit of autoregulation was not possible for ethical reasons. In those few patients in whom spontaneous increase in the ABP made such observations possible, upper limits up to 150 mm Hg with a total autoregulatory capacity of about 75 mm Hg were observed. In some patients lower limits and corresponding breakthroughs of cerebral blood flow were seen, demonstrating that the upper limit of autoregulation is markedly influenced by several factors.