The Influence of Inspired Oxygen Fraction and End-Tidal Carbon Dioxide on Post–Cross-Clamp Cerebral Oxygenation During Carotid Endarterectomy Under General Anesthesia


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Abstract

BACKGROUND:Ten to fifteen percent of awake patients develop neurological deficits secondary to cerebral hypoperfusion after carotid artery cross-clamping. The reversal of such deficits by increasing the inspired oxygen fraction (Fio2) has been demonstrated, and regional cerebral oxygenation (rSO2) has been shown to improve during carotid cross-clamping in awake patients by increasing Fio2. Paradoxical improvements in cerebral blood flow during carotid endarterectomy (CEA) at the time of cross-clamping and normalization of post–cross-clamp electroencephalographic abnormalities have been induced by hypocapnia. We performed this study to determine the influence of Fio2 and end-tidal carbon dioxide (Petco2) on rSO2 in patients undergoing CEA with general anesthesia during carotid cross-clamping.METHODS:Twenty patients were recruited. Ten underwent elective shunting. Patients received standardized general anesthesia. rSO2 was measured using the INVOS 5100B monitor (Somanetics Corporation, Troy, MI). After carotid cross-clamping, Fio2 and minute ventilation were sequentially adjusted: 1) Fio2 30%, Petco2 30–35 mm Hg; 2) Fio2 100%, Petco2 30–35 mm Hg; and 3) Fio2 100%, Petco2 40–45 mm Hg. At each point, rSO2 was recorded from both operative and nonoperative sides, and arterial blood gas analysis was performed.RESULTS:Results from shunted and unshunted patients were analyzed separately. Increasing Fio2: Administration of 100% oxygen while maintaining Petco2 in the range 30–35 mm Hg in unshunted patients resulted in an 8% increase (P = 0.008) in rSO2 on the operative side and a 6% increase (P = 0.011) on the nonoperative side compared with an Fio2 of 30%. In shunted patients, administration of 100% oxygen while maintaining the Petco2 in the range 30–35 mm Hg resulted in a 4% increase in rSO2 on both the operative side (P = 0.008) and the nonoperative side (P = 0.011) compared with an Fio2 of 30%. Increasing Petco2: In unshunted patients, there was a 6% (P = 0.008) increase in rSO2 on the operative side and a 5% increase (P = 0.024) on the nonoperative side at Petco2 40–45 mm Hg compared with Petco2 30–35 mm Hg maintaining Fio2 at 100%. In shunted patients, there was a 3% increase (P = 0.018) in rSO2 on the operative side and a 4% increase (P = 0.007) on the nonoperative side at Petco2 40–45 mm Hg compared with Petco2 30–35 mm Hg maintaining Fio2 at 100%.CONCLUSION:rSO2 is reliably improved during carotid cross-clamping by increasing Fio2 in patients undergoing CEA with general anesthesia. Additional improvement in rSO2 may be gained by increasing Petco2.

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