Cerebral autoregulation under moderate hypothermia in patients with acute stroke.
OBJECTIVE
We undertook this study to examine the integrity of cerebral autoregulation in patients with acute ischemic stroke treated with moderate hypothermia (33 degrees C).


METHODS
Fourteen patients, aged 58+/-11 years, with an acute anterior circulation infarction and National Institutes of Health Stroke Scale score >15 were evaluated. Patients received catecholamines (norepinephrine) via continuous intravenous infusion and were mechanically ventilated. Alpha-stat was used for pH maintenance. Arterial pressure (AP) and intracranial pressure (ICP) were invasively monitored. Flow velocity in the middle cerebral artery (MCA) supplying the unaffected hemisphere was continuously monitored. Instantaneous maximum flow velocity (V(max) MCA), ICP, and AP were simultaneously recorded in real time. Mean values of V(max) MCA (V(mean) MCA) and AP (MAP) were calculated over 1 minute. Static cerebral autoregulation (sCA) was calculated as sCA=(%DeltaCVR/%DeltaMAP)x100% (where %DeltaCVR is an estimate of percent change in cerebrovascular resistance). An sCA value of 0% indicates absent autoregulation, and a value of 100% indicates perfect autoregulation. Autoregulation is considered impaired when sCA values are <40%. MAP changes were produced by increasing the rate of the norepinephrine infusion. Six patients were examined under both normothermic and hypothermic conditions, while 8 were examined only under hypothermia.


RESULTS
The induced MAP increase was 22+/-7 mm Hg (minimum 13, maximum 40 mm Hg). Mean sCA was 64+/-16% (minimum 40%, maximum 100%). No effect of moderate hypothermia on sCA or V(mean) MCA was evident in any of the 6 serially examined patients. Normocapnia was observed in all cases.


CONCLUSIONS
sCA appears intact under moderate hypothermia with the use of alpha-stat for pH maintenance.
Georgiadis
D
D
Department of Neurology, University of Heidelberg, Heidelberg, Germany. Dimitrios.Georgiadis@nos.usz.ch
Schwarz
S
S
Evans
D H
DH
Schwab
S
S
Baumgartner
R W
RW
D000208:Acute Disease; D000328:Adult; D000368:Aged; D001783:Blood Flow Velocity / Q000187:drug effects; D001794:Blood Pressure / Q000187:drug effects; D002560:Cerebrovascular Circulation / Q000187:drug effects / Q000502:physiology; D005260:Female; D006801:Humans; D006863:Hydrogen-Ion Concentration / Q000187:drug effects; D007036:Hypothermia, Induced; D007262:Infusions, Intravenous; D007427:Intracranial Pressure / Q000187:drug effects; D008297:Male; D008875:Middle Aged; D020768:Middle Cerebral Artery / Q000187:drug effects / Q000503:physiopathology; D009638:Norepinephrine / Q000008:administration & dosage; D011446:Prospective Studies; D012121:Respiration, Artificial; D020521:Stroke / Q000503:physiopathology* / Q000628:therapy*; D016896:Treatment Outcome; D014655:Vascular Resistance / Q000187:drug effects; D014662:Vasoconstrictor Agents / Q000008:administration & dosage
D014662:Vasoconstrictor Agents; D009638:Norepinephrine