VALIDATION OF MYOCARDIAL OXYGEN-DEMAND INDEXES IN PATIENTS AWAKE AND DURING ANESTHESIA

An important guideline for anesthesia in patients with ischemic heart disease is the effect on myocardial oxygen demand. Therefore, this investigation evaluated commonly used myocardial oxygen demand formulas for clinical application. The study was performed on patients undergoing coronary bypass surgery (n = 62). Measurements of standard hemodynamics were obtained before and after induction of anesthesia, as well as during sternotomy and after surgery. Coronary blood flow was determined by the argon wash-in technique. In 15 patients, a left ventricular tip manometer was used to accurately assess the first derivative of left ventricular pressure time course. The following indices of left ventricular oxygen demand were calculated: 1) rate pressure product (RPP); 2) tension time index (TTI); 3) pressure work index (PWI) according to the methods of Rooke; and 4) additive parameter (E(g)), according to the methods of Bretschneider. All hemodynamic indices of myocardial oxygen demand showed moderate correlation with myocardial oxygen uptake (MV(O2)) (RPP: r = 0.77; TTI: r = 0.79; PWI: r = 0.79; E(g): r = 0.71). On the average, PWI and E(g) led to an underestimation of MV(O2) in patients. The constants of the PWI and E(g) formulas, which have been developed based on animal experiments, therefore are not directly applicable to clinical conditions. New constants have been derived for PWI by multiple linear regression analysis of the data in the current investigation. The PWI formula thereby was modified for clinical application (PWI(mod) = K1 P(syst) HR + K2 [0.9 P(syst) + 0.2 P(diast)] CI; K1 = 8.37 . 10(-4), K2 = 8.0 . 10(-6); where P(syst) = systolic blood pressure, HR = heart rate; P(diast) = diastolic blood pressure, and CI = cardiac index) and retrospectively showed reasonably good correlation with MV(O2) (r = 0.84) in patients. The 95% limits of agreement between MV(O2) and PWI(mod) were +/- 3.96 ml . min-1 100 g-1. The authors conclude from the current investigation that hemodynamic indices of myocardial oxygen demand derived from animal experiments cannot be applied to humans without modification.