Autoregulation of cerebral blood flow in patients resuscitated from cardiac arrest

Background and Purpose-Under normal circumstances, autoregulation maintains cerebral blood flow (CBF) constant within a wide range of mean arterial pr essure (MAP). It remains unknown whether patients resuscitated from cardiac arrest have preserved CBF autoregulation. In this study, CBF autoregulatio n was investigated within the first 24 hours after resuscitation from cardi ac arrest. Methods-Eighteen patients and 6 healthy volunteers had relative changes in CBF determined by transcranial Doppler mean flow velocity (V-mean) in the m iddle cerebral artery during a stepwise rise in MAP by use of norepinephrin e infusion. V-mean was plotted against MAP, and a lower limit of autoregula tion was identified by double regression analysis based on the least-square s method. Results-In patients, V-mean 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 MA P from 78 (46 to 118) to 106 (60 to 149) mm Hg. Eight of 18 patients had im paired CBF autoregulation, and in 5 of the 10 patients with preserved CBF a utoregulation, the lower limit of autoregulation could be identified. The l ower limit of CBF autoregulation was 76 mm Hg (41 to 105 mm Hg) in the volu nteers and 114 mm Hg (80 to 120 mm Hg) in the 5 patients with preserved aut oregulation (P<0.01). Conclusions-We conclude that in a majority of patients in the acute phase a fter cardiac arrest, cerebral autoregulation is either absent or right-shif ted. 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 symp athomimetic drugs improve neurological outcome.