title: Preoperative carbon dioxide reactivity studies do not predict the hemodynamic changes seen during carotid endarterectomy after internal carotid artery clamping.
abstract: OBJECTIVE
  A preoperative warning of progressive cerebral ischemia during surgery may be of use in planning carotid endarterectomy (CE). We have set out to determine whether preoperative cerebrovascular reactivity studies predict the late hemodynamic changes detected during the procedure.
  
  
  METHODS
  Sixty-seven patients awaiting CE for high-grade carotid stenosis underwent preoperative cerebral CO(2) reactivity assessment using standard transcranial Doppler (TCD) methods. During subsequent surgery, hemodynamic changes were monitored with TCD, near-infrared spectroscopy, and a cerebral function monitor. Signals of mean MCA flow velocity (FV) and of cerebral oxyhemoglobin and deoxyhemoglobin concentration were recorded continuously, and the mean values were measured at 5, 10, and 15 minutes after internal carotid clamping. For each variable, the maximum signal change was measured 5 minutes after clamp application (Max(5)), and in addition the spontaneous hemodynamic recovery over the next 10 minutes (I(rec)) was calculated. Scatterplots of Max(5) and I(rec) against preoperative CO(2) reactivity indices (ipsilateral, bihemispheric mean, and interhemispheric assymmetry) were generated for correlative analysis.
  
  
  RESULTS
  The Max(5) for oxyhemoglobin and deoxyhemoglobin were inversely related (r=-.302, P=.015). There was no relationship between ipsilateral preoperative CO(2) reactivity index and Max(5) for any intraoperative variable measured. In addition, the reactivity did not predict the hemodynamic recovery (I(rec)) observed during clamp application. However, the interhemispheric asymmetry did show a modest inverse correlation to Max(5) FV (r=-.256, P=.046).
  
  
  CONCLUSIONS
  Preoperative TCD cerebral CO(2) reactivity cannot be used clinically to predict the intraoperative hemodynamic changes seen during CE.
authors: Addenbrookes Hospital, Cambridge, England.
authors: P S
authors: PS
authors: Minhas
authors: P
authors: P
authors: Smielewski
authors: M
authors: M
authors: Czosnyka
authors: P J
authors: PJ
authors: Kirkpatrick