[Measurement of local oxygen parameters for detection of cerebral ischemia. The significance of cerebral near-infrared spectroscopy and transconjunctival oxygen partial pressure in carotid surgery].

UNLABELLED: The principle of, "selective shunting" during carotid endarterectomy requires a special concept to monitor neuronal function. The valence of the oxymetric methods, "near-infrared" spectroscopy (NIRS) and conjunctival oxygen tension (pcjO2) was determined with the reference method somatosensory evoked potentials (SEP).

METHODS

In 41 patients undergoing reconstructive surgery on the internal carotid artery, recordings of the different methods were obtained under control, during carotid occlusion and during reperfusion. Cerebral ischemia was assumed if a complete loss of SEP appeared and an intraluminal shunt was placed. Conjunctival oxygen tension was measured continuously and simultaneously on the ipsi- and contralateral eye.

RESULTS

In comparison to the reference method (SEP) the sensitivity and specificity of NIRS was 80% and 94%, respectively. The occlusion induced reduction 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 oxygen tension is not useful to detect cerebral ischemia. The use of NIRS as a single neuronal monitor is not appropriate to perform, "selective shunting". In contrast to SEP, however, NIRS is characterized by its rapid changes immediately following carotid occlusion. This non invasive method is likely to complete the standard method SEP in a modified monitoring concept of neuronal function during carotid endarterectomy.