Correlation of carotid artery stump pressure and neurologic changes during 474 carotid endarterectomies performed in awake patients

Abstract

A carotid artery stump pressure (SP) of < 50 mm Hg and abnormal electroencephalography (EEG) changes have been suggested as indications for selective shunting in patients undergoing carotid endarterectomy (CEA) under general anesthesia. We attempted to determine the optimal SP threshold that correlated with neurologic changes in awake patients undergoing CEA using cervical block anesthesia (CBA) and performed a cost comparison with EEG monitoring. Between July 1, 1995, and December 31, 2004, SP was measured during 474 CEAs performed under CBA by inserting a 19-gauge butterfly needle into the common carotid artery. A saline-filled intravenous bag in the patient's contralateral hand was connected to pressure tubing to generate waveforms with hand squeezing that could be visualized on a monitor. Systemic pressure was maintained approximately 10 mm Hg higher than baseline. Accurate SPs were confirmed by the finding of flatline waveforms after internal carotid artery clamping. Selective shunting was performed when neurologic changes occurred (aphasia, inability to squeeze the contralateral hand, decreased consciousness), regardless of SP. During this same period, 142 patients underwent CEA using GA, and SP was also measured. Shunting was necessary because of neurologic changes in 7.2% (34/474) of all CEAs performed using CBA: 0.9% (3/335) with SPs > or = 50 mm Hg systolic vs 1.0% (4/402) with SPs > or = 40 mm Hg systolic, and 22% (31/139) with SPs < 50 mm Hg systolic vs 42% (30/72) with SPs < 40 mm Hg systolic. If these 474 CEAs had been performed using GA, shunts would have been used in 29% (139/474) of patients for a SP < 50 mm Hg systolic vs 15% (72/474) for a SP < 40 mm Hg systolic. In patients not shunted, the perioperative stroke/death rate was 1.2% in patients (4/332) with SPs > or = 50 mm Hg vs 1.0% (4/398) with SPs > or = 40 mm Hg. Three of the four strokes occurred > 24 hours postoperatively and were unrelated to lack of shunting and ischemia. There was no significant difference in the percentage of patients with SPs > or = 50 mm Hg who underwent CEA using CBA (70%, 335/474) vs GA (67%, 96/142) during this time period. At our hospital, charges for SPe measurement, including anesthesia charges and tubing, were 229 dollars per case vs 3439 dollars per case for EEG monitoring. Use of SP measurements in these 474 patients would have resulted in reduced charges of 1,521,540 dollars compared with EEG monitoring if CEA had been performed under GA. Using 40 mm Hg systolic as a threshold, the need for shunting (15%) and the false-negative rate (1.0%) for SP in our series were equivalent to the results of EEG monitoring during CEA reported in the literature. However, charges for SP measurements are dramatically lower compared with EEG monitoring. Our results suggest that a carotid artery SP > or = 40 mm Hg systolic may be considered as an equally reliable but more cost-effective method to predict the need for carotid shunting during CEA under GA compared with EEG monitoring, but further investigation is warranted.