Measurement of local oxygen parameters for detection of cerebral ischemia.The significance of cerebral "near infrared" spectroscopy (NIRS) and transconjunctival oxygen tension in carotid surgery

The principle of, "selective shunting" during carotid endarterectomy requir es a special concept to monitor neuronal function. The valence of the oxyme tric methods, "near-infrared" spectroscopy (NIRS) and conjunctival oxygen t ension (pcjO(2)) was determined with the reference method somatosensory evo ked potentials (SEP). Methods. In 41 patients undergoing reconstructive surgery on the internal c arotid artery, recordings of the different methods were obtained under cont rol, during carotid occlusion and during reperfusion. Cerebral ischemia was assumed ifa complete loss of SEP appeared and an intraluminal shunt was pl aced. Conjunctival oxygen tension was measured continuously and simultaneou sly on the ipsi- and contralateral eye. Results. In comparison to the reference method (SEP) the sensitivity and sp ecificity of NIRS was 80% and 94%, respectively. The occlusion induced redu ction of NIRS appeared 6.5+/-3.2 min earlier than the corresponding loss of SEP. Biocular determination of conjunctival oxygen tension was not able to detect hypoperfusion dependent ischemia during carotid occlusion. Conclusion. During carotid endarterectomy the measurement of conjunctival o xygen tension is not useful to detect cerebral ischemia. The use of NIPS as a single neuronal monitor is not appropriate to perform,"selective shuntin g". In contrast to SEP, however, NIPS is characterized by its rapid changes immediately following carotid occlusion. This non invasive method is likel y to complete the standard method SEP in a modified monitoring concept of n euronal function during carotid endarterectomy.