Technique and clinical results of carotid stump back-pressure to determine selective shunting during carotid endarterectomy

Abstract

A method of confirming carotid back pressure accuracy, variability during carotid clamping, and the clinical results with a modified back pressure shunt criterion were evaluated in 665 carotid endarterectomies. Mean arterial pressure, back pressure, and internal jugular vein pressure were measured. Cerebral perfusion pressure (back pressure — jugular vein pressure) and the collateral to hemisphere vascular resistance ratio, (ratio = [arterial pressure — back pressure]/[back pressure — jugular vein pressure]) were calculated. A shunt was used when cerebral perfusion pressure < 18 mm Hg. Back pressure accuracy was confirmed by test occlusion of the internal carotid artery distal to the plaque. Initial back pressure values were falsely high in 83 (12.5%) carotid endarterectomies. The mean SD (n = 665, mm Hg) were arterial pressure = 84.0 ± 9.06, back pressure = 41.0 ± 15.9, jugular vein pressure = 6.2 ± 3.9, cerebral perfusion pressure = 35.1 ± 5.7, and resistance ratio = 1.85 ± 1.44. Perfusion pressure was < 18 mm Hg in 82 (12.3%), of which 74 (11.1%) were shunted, and 8 (1.2%) had perfusion pressure increased ≥ 18 mm Hg during carotid endarterectomy with phenylephrine. Back pressure was <25 mm Hg in 107 (16.1%), ≤25 in 114 (17.1%), and <50 mm Hg in 481 (72.3%). Pressures were continuously monitored during 28 carotid endarterectomies, and all had a positive linear relationship between arterial pressure and back pressure, and minimal variability in the back pressure/arterial pressure and resistance ratios. Only two patients (0.3%) had a new neurologic deficit in the first 12 hours after carotid endarterectomy. Unless confirmation techniques are used, erroneously high carotid stump back pressure measurements may occur in 10% to 15% of carotid endarterectomies, resulting in failure to use a shunt in some depending on the pressure criterion used. Patients with cerebral perfusion pressure ≥18 mm Hg and back pressure ≥25 mm Hg can safely undergo carotid endarterectomy without a shunt.