Effects of milrinone on jugular bulb oxygen saturation and cerebrovascular carbon dioxide reactivity in patients undergoing coronary artery bypass graft surgery

Background. Jugular bulb oxygen saturation (Sjv(o2)) is a surrogate marker for global cerebral oxygenation. The effect of milrinone on Sjv(o2) and the cerebrovascular carbon dioxide reactivity (CCO2R) was investigated. Methods. Thirty patients scheduled for coronary artery bypass graft surgery (CABG) were studied prospectively. After sternotomy, normoventilation (at T-1; Pa-co2=4.7-5.0 kPa) and hyperventilation (at T-2; Pa-co2=3.3-3.7 kPa) were induced and the changes in Sjv(o2) (DeltaSjv(o2)) and Pa-co2 (DeltaPa(co2)), and DeltaSjv(o2)/DeltaPa(co2) (CCO2R) were measured. After normoventilation was re-established (at T-3), milrinone 50 mug kg(-1) was given (at T-4), followed by hyperventilation (at T-5), and DeltaSjv(o2), DeltaPa(co2) and CCO2R were measured. Results. After milrinone administration at normoventilation (T-3 and T-4), cardiac index and mixed venous oxygen saturation increased, while mean arterial pressure and systemic vascular resistance index decreased, without a significant change in Sjv(o2). Before milrinone administration (T-1 and T-2), hyperventilation decreased Pa-co2 and Sjv(o2), and DeltaSjv(o2) showed positive linear correlation with DeltaPa(co2). After milrinone administration (T-4 and T-5), hyperventilation decreased Pa-co2 and Sjv(o2), and DeltaSjv(o2) showed positive linear correlation with DeltaPa(co2). There was no significant difference in CCO2R before and after milrinone administration (13.3 (5.7)% kPa(-1) and 12.3 (3.9)% kPa(-1), respectively). Conclusions. Although milrinone induced significant haemodynamic changes, Sjv(o2) and CCO2R were unchanged during its administration.