Correlation of Cerebral Oximetry with Internal Carotid Artery Stump Pressures in Carotid Endarterectomy

Mark L. Manwaring, MD, Frank M. Parker, DO, Clark M. Kardys, MD, C. Steven Powell, MD, William M. Bogey, MD, Michael C. Stoner, MD.
East Carolina University, Greenville, NC, USA.

Objectives: Cerebral Oximetry(CO) is a non-invasive method of monitoring patients during carotid endarterectomy. Studies in awake patients and using EEG have suggested that >15-20% saturation drop in CO correlates with development of cerebral ischemia. It has also been suggested that internal carotid artery stump pressure(SP)<40mmHg is comparable to EEG in predicting need for shunt. There is little published data on the correlation between CO and SP.
Methods: We prospectively evaluated 104 consecutive patients undergoing carotid endarterectomy under general anesthesia between May 2002 and February 2003. Patients were preoperatively connected to INVOS Cerebral Oximeter System (Somanetics Troy,MI) per manufacturer instructions and bilateral awake baseline CO percentage was recorded then monitored continuously through each case. SP and the lowest CO measurement after internal carotid artery clamp placement were recorded.
Results: There were no postoperative strokes. Thirteen patients were excluded because of incomplete data. Six of forty patients who had <10% drop in CO had SP<40. CO with a 15% saturation drop threshold was 76.3% sensitive and 81.1% specific in detecting patients with SP<40. With a threshold of 20% drop, it was 57.9% sensitive and 86.8% specific.(table)
Conclusion: In our series, CO was neither sensitive nor specific in detecting patients with SP<40. Although the role CO should have in carotid endarterectomy is controversial, these data do not support its use as the only monitoring modality during carotid endarterectomy.

CO %Saturation	SP>40	SP<40	Sensitivity	Specificity
>10% Drop	19	32	84.2%	64.2%
>15% Drop	10	39	76.3%	81.1%
>20% Drop	7	22	57.9%	86.8%

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