[Coronary circulation and myocardial oxygen balance in anesthesia]

It is generally believed that in patients with impaired coronary reserve an imbalance between myocardial O2-demand and O2-supply is the main cause of myocardial ischaemia. However, clinical experience as well as recent experimental results indicate that this global view may not always explain the occurrence of regional myocardial ischaemia. It was therefore investigated whether in patients before and after induction of anaesthesia as well as during sternotomy metabolic indices of ischaemia, i.e. lactate and/or hypoxanthine release into the coronary sinus, are related to global indices of myocardial O2-balance. It was found that neither myocardial O2-demand or O2-supply nor O2-balance correlated with myocardial ischaemic events. Conversely it was observed that in contrast to expectations lactate and/or hypoxanthine release occurred more often in conjunction with high values of coronary venous oxygen saturation than with low values. Since coronary venous oxygen saturation can be considered as a physiological index of global myocardial O2-balance, the data of the present investigation suggest that during anaesthesia a global imbalance between myocardial oxygen supply and demand is not the main cause of myocardial ischaemia. Thus, regional factors seem to be more important for initiation of myocardial ischaemic events than global O2-balance.