Autoregulation of cerebral blood flow in patients resuscitated from cardiac arrest

Abstract

Background and Purpose - Under normal circumstances, autoregulation maintains cerebral blood flow (CBF) constant within a wide range of mean arterial pressure (MAP). It remains unknown whether patients resuscitated from cardiac arrest have preserved CBF autoregulation. In this study, CBF autoregulation was investigated within the first 24 hours after resuscitation from cardiac arrest. Methods - Eighteen patients and 6 healthy volunteers had relative changes in CBF determined by transcranial Doppler mean flow velocity (Vmean) in the middle cerebral artery during a stepwise rise in MAP by use of norepinephrine infusion. Vmean was plotted against MAP, and a lower limit of autoregulation was identified by double regression analysis based on the least-squares method. Results - In patients, Vmean increased from a median of 33 (range 19 to 73) to 37 (22 to 100) cm/s (P<0.001) during a norepinephrine-induced rise in MAP from 78 (46 to 118) to 106 (60 to 149) mm Hg. Eight of 18 patients had impaired CBF autoregulation, and in 5 of the 10 patients with preserved CBF autoregulation, the lower limit of autoregulation could be identified. The lower limit of CBF autoregulation was 76 mm Hg (41 to 105 mm Hg) in the volunteers and 114 mm Hg (80 to 120 mm Hg) in the 5 patients with preserved autoregulation (P<0.01). Conclusions - We conclude that in a majority of patients in the acute phase after cardiac arrest, cerebral autoregulation is either absent or right-shifted. These results indicate that MAP should be kept at a higher level than commonly accepted to secure cerebral perfusion. We recommend, however, that further randomized clinical trials are performed to determine whether sympathomimetic drugs improve neurological outcome.