Regional cerebral oximetry after oxygen administration

Abstract

Editor—We read with interest the report of Stoneham and Martin1Stoneham MD Martin T Increased oxygen administration during awake carotid surgery can reverse neurological deficit following carotid cross-clamping.Br J Anaesth. 2005; 94: 582-585Crossref PubMed Scopus (19) Google Scholar showing that the administration of oxygen 100% can antagonize the neurological deficits after carotid cross-clamping. This was attributed to an increase of the blood oxygen content that could be enough to increase the mitochondrial Po2 above the critical level so that oxidative phosphorylation in ischemic cerebral neurones could restart. Near infrared spectroscopy has been recently used to monitor regional cerebral oximetry (Rso2) during carotid endarterectomy.2Ohnishi Y Hayashi Y Shimizu J Koyama Y Kuro M Brain monitoring with near infrared spectroscopy during carotid endarterectomy.Masui. 1996; 45: 1420-1423PubMed Google Scholar Cerebral spectroscopy, whilst having limitations in terms of absolute measurement,3Pattinson K Clutton-Brock T Imray C Validity of near-infrared cerebral spectroscopy.Anaesthesia. 2004; 59: 507-508Crossref PubMed Scopus (5) Google Scholar may give continuous noninvasive assessments of the cerebral oxygen supply–demand balance.4Imray CH Thacker AJ Mead MK Oxygen administration can reverse neurological deficit following carotid cross-clamping.Br J Anaesth. 2005; 95: 274-275Abstract Full Text Full Text PDF PubMed Scopus (3) Google Scholar We investigated the effect of administration of oxygen 100% with a tight-fitting anaesthetic face mask in six awake patients who were scheduled for coronary artery bypass grafting. The mean (sd) Rso2 in the awake patients during breathing room air was 62 (9.5)%, which increased significantly to 67.8 (10.6)% after oxygenation. After subsequent induction of general anaesthesia using thiopental, fentanyl and rocuronium, there was a further significant increase of RSO2 up to 80.2 (9.7)%. The 8% increase of (R>SO2 after 100% oxygenation matches the increase of the total oxygen content as calculated by Stoneham and Martin.1Stoneham MD Martin T Increased oxygen administration during awake carotid surgery can reverse neurological deficit following carotid cross-clamping.Br J Anaesth. 2005; 94: 582-585Crossref PubMed Scopus (19) Google Scholar The subsequent induction of general anaesthesia resulted in a further increase in RSO2 of about 20%. The combination of an increased oxygen delivery and general anaesthesia, which decreases the cerebral oxygen consumption, has an additive or even a synergistic effect that could have a significant impact on the neurons close to their ischaemic threshold. Our results suggest that breathing oxygen 100% by the awake patients or induction of general anaesthesia using a high FIO2, while monitoring the cerebral oxygen supply–demand by cerebral oximetry can enhance the cerebral oxygen supply–demand balance and may decrease the need for shunting in patients who are liable to develop neurological deficits during carotid endarterectomy.