Autoregulation of cortical blood flow during surgery for ruptured intracranial aneurysms.

BACKGROUND: Little information is available about the extent and the time course of possible impairment of cerebral circulation occurring after aneurysmal subarachnoid haemorrhage (SAH). The aim of this study was to correlate cerebral autoregulation, neurological impairment at surgery and timing of surgery in patients with ruptured intracerebral aneurysms. METHODS: Cortical blood flow (CoBF) was measured intraoperatively by a thermal diffusion probe in 77 patients during surgery for ruptured supratentorial aneurysms, who were operated on at different time intervals after bleeding. An autoregulation index (AI), expressed as the ratio between the change in CoBF and the change of mean arterial blood pressure at the time of rising the systemic blood pressure after occlusion of the aneurysm(s), was determined in each case. RESULTS: Among good-grade patients (WFNS grade I-II), those operated on days 0-2 after SAH had a significantly better autoregulatory response, compared either with patients who underwent surgery on days 3-7 after bleeding (p<0.01), or with those whose aneurysm was occluded more than 7 days after rupture (p<0.03). The mean AI of poor-grade patients (WFNS grade IV-V), who received surgery on days 0-2 after SAH, was significantly higher (p<0.01) compared with the corresponding value of good-grade patients. No significant difference was found between the mean AIs of patients who subsequently did, or did not, develop symptomatic vasospasm. CONCLUSIONS: It is concluded that good-grade patients operated on within 48 hours after bleeding take advantage of a preserved autoregulatory function during controlled hypotension.