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 T₁; Pa_CO2=4.7-5.0 kPa) and hyperventilation (at T₂; Pa_CO2 =3.3-3.7 kPa) were induced and the changes in Sjv_O2 (ΔSjv_O2) and Pa_CO2 (ΔPa_CO2), and ΔSjv_O2/ΔPa_CO2 (CCO₂R) were measured. After normoventilation was re-established (at T₃), milrinone 50 μg kg^-1 was given (at T₄), followed by hyperventilation (at T₅), and ΔSjv_O2, ΔPa_CO2 and CCO₂R were measured. Results. After milrinone administration at normoventilation (T₃ and T₄), 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 (T₁ and T₂), hyperventilation decreased Pa_CO2 and Sjv_O2, and ΔSjv_O2 showed positive linear correlation with ΔPa_CO2. After milrinone administration (T₄ and T₅), hyperventilation decreased Pa_CO2 and Sjv_O2 and ΔSjv_O2 showed positive linear correlation with ΔPa_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.