CORRESPONDENCE |
Regional cerebral oximetry after oxygen administration
* E-mail: abaraka{at}aub.edu.lbEditor—We read with interest the report of Stoneham and Martin1 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.2 Cerebral spectroscopy, whilst having limitations in terms of absolute measurement,3 may give continuous noninvasive assessments of the cerebral oxygen supply–demand balance.4
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 
up to 80.2 (9.7)%. The 8% increase of 
after 100% oxygenation matches the increase of the total oxygen content as calculated by Stoneham and Martin.1 The subsequent induction of general anaesthesia resulted in a further increase in 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 
, 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.
Beirut, Lebanon
References
1 Stoneham MD, Martin T. Increased oxygen administration during awake carotid surgery can reverse neurological deficit following carotid cross-clamping. Br J Anaesth 2005; 94: 582–5
2 Ohnishi Y, Hayashi Y, Shimizu J, Koyama Y, Kuro M. Brain monitoring with near infrared spectroscopy during carotid endarterectomy. Masui 1996; 45: 1420–3[Medline]
3 Pattinson K, Clutton-Brock T, Imray C. Validity of near-infrared cerebral spectroscopy. Anaesthesia 2004; 59: 507–8[CrossRef][Web of Science][Medline]
4 Imray CH, Thacker AJ, Mead MK. Oxygen administration can reverse neurological deficit following carotid cross-clamping. Br J Anaesth 2005; 95: 274–5
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