The effects of gas mixtures comprising supplementary 3% carbon dioxide, 35% oxygen or a combination of 3% CO(2) plus 35% O(2) in ambient air have been compared on arterial blood gases, peripheral and cerebral oxygenation and middle cerebral artery velocity (MCAV) at 150 m and on acute exposure to 3459 m in 12 healthy subjects. Breathing 3% CO(2) or 35% O(2) increased arterial blood oxygen at both altitudes, and the CO(2)/O(2) combination resulted in the most marked rise. MCAV increased on ascent to 3459 m, increasing further with 3% CO(2) and decreasing with 35% O(2) at both altitudes. The CO(2)/O(2) combination resulted in an increase in MCAV at 150 m, but not at 3549 m. Cerebral regional oxygenation fell on ascent to 3459 m. Breathing 3% CO(2) or 35% O(2) increased cerebral oxygenation at both altitudes, and the CO(2)/O(2) combination resulted in the greatest rise at both altitudes. The combination also resulted in significant rises in cutaneous and muscle oxygenation at 3459 m. The key role of carbon dioxide in oxygenation at altitude is confirmed, and the importance of this gas for tissue oxygenation is demonstrated.

Cerebral microemboli were controlled by tirofiban both before and after CEA. Further study is required to compare the relative efficacy of tirofiban and dextran.

TCD-directed Dextran 40 offers a safe approach to high-risk patients before elective carotid endarterectomy, and warrants further study.

Background and Purpose— Cerebral microemboli signals (MES) are associated with increased risk of acute stroke syndromes. We compared the effects on cerebral microemboli after carotid endarterectomy of tirofiban with dextran-40. Methods— We used transcranial Doppler ultrasound to study transient MES acutely after carotid endarterectomy between August 2000 and December 2010 in 128 subjects refractory to preoperative antiplatelet treatment. Antithrombotic treatment was given for MES ≥50 hour −1 (tirofiban: 40 patients [age 74 ± 1 {SEM}, males 27, and white 38]; dextran-40: 34 patients [age 69 ± 2, males 22, white 30]). In 54 patients with MES <50 hour −1 (age 71 ± 1, male 36, white 52), MES were monitored during their spontaneous resolution (controls). Data are median (interquartile range). Results— The time to 50% reduction in MES (tirofiban 23 minutes [15–28]; dextran-56 [43–83]; controls 30 [22–38]; P <0.001, Kruskal-Wallis analysis) and for complete MES resolution (tirofiban 68 minutes [53–94]; dextran-113 [79–146]; controls 53 [49–68]; P <0.001, Kruskal-Wallis analysis) were shorter with tirofiban. The early cardiovascular event rate was similar with tirofiban compared with controls but increased in patients who received dextran. Conclusions— These findings suggest that transcranial Doppler-directed tirofiban therapy is more effective than dextran-40 in suppression of cerebral microemboli after carotid endarterectomy.

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