Blood gas and carotid pressure: factors in stroke risk.

The internal carotid back pressure and arterial blood gas measurements have been employed in 269 patients undergoing 332 carotid endarterectomies in an effort to identify individuals at high risk of stroke during surgery. Patients having an internal carotid back pressure less than 25 Torr were operated using an inlying shunt. There were 159 patients having a PaCO2 greater than 45 Torr, 95 individuals with a PaCO2 between 35 to 45 Torr and 78 cases with a PaCO2 less than 35 Torr. The mean internal carotid back pressure was 63 Torr in the hypocarbic group and 45 Torr in the hypercarbic patients which represents a highly significant inverse relationship between PaCO2 and carotid back pressure (P less than 0.0002). There were four neurological deficits following surgery in the hypercarbic group and one each in the normocarbic and hypocarbic groups. These findings suggest a lower stroke incidence in patients having hypocarbic or normocarbic general anesthesia than those receiving hypercarbic general anesthesia. The low overall stroke rate of 2% indicates the safety of selective shunting during carotid endarterectomy.