Near-infrared spectroscopy assessed cerebral oxygenation during open abdominal aortic aneurysm repair: relation to end-tidal CO₂ tension

During open abdominal aortic aneurism (AAA) repair cerebral blood flow is challenged. Clamping of the aorta may lead to unintended hyperventilation as metabolism is reduced by perfusion of a smaller part of the body and reperfusion of the aorta releases vasodilatory substances including CO₂. We intend to adjust ventilation according end-tidal CO₂ tension (EtCO₂) and here evaluated to what extent that strategy maintains frontal lobe oxygenation (S_cO₂) as determined by near infrared spectroscopy. For 44 patients [5 women, aged 70 (48–83) years] S_cO₂, mean arterial pressure (MAP), EtCO₂, and ventilation were obtained retrospectively from the anesthetic charts. By clamping the aorta, S_cO₂ and EtCO₂ were kept stable by reducing ventilation (median, −0.8 l min⁻¹; interquartile range, −1.1 to −0.4; P < 0.001). During reperfusion of the aorta a reduction in MAP by 8 mmHg (−15 to −1; P < 0.001) did not prevent an increase in S_cO₂ by 2 % (−1 to 4; P < 0.001) as EtCO₂ increased 0.5 kPa (0.1–1.0; P < 0.001) despite an increase in ventilation by 1.8 l min⁻¹ (0.9–2.7; P < 0.001). Changes in S_cO₂ related to those in EtCO₂ (r = 0.41; P = 0.0001) and cerebral deoxygenation (−15 %) was noted in three patients while cerebral hyperoxygenation (+15 %) manifests in one patient. Thus changes in ScO₂ were kept within acceptable limits (±15 %) in 91 % of the patients. For the majority of the patients undergoing AAA repair S_cO₂ was kept within reasonable limits by reducing ventilation by approximately 1 l min⁻¹ upon clamping of the aorta and increasing ventilation by approximately 2 l min⁻¹ when the lower body is reperfused.