[Continuous Fick cardiac output measurement during inhalation anesthesia]

A computer based system that continuously monitors cardiac output (CO) and the other hemodynamic variables has been developed. Fick CO was calculated every 10 sec on breath by breath basis. The arterio-venous oxygen content difference was measured by a combination of a pulse oximeter and a fiberoptic oximeter. Oxygen consumption was calculated by a direct measurement of respiratory gas exchange: airway flow was obtained from a Servo 900C ventilator and the instantaneous oxygen concentration was measured with a paramagnetic oxygen sensor. This system enabled us to use inhalation anesthetics which were avoided during Fick CO measurement with a zirconium oxygen sensor. Fick CO was compared to electromagnetic CO (EMCO) in 5 dogs anesthetized with enflurane. A total of 198 simultaneous data of CO measurements had a range from 0.5 to 2 l/min. Simultaneous measurements of Fick CO and EMCO showed a good correlation (r = 0.97), and a regression equation was: Y = X + 0.029. Fick CO was compared with cardiac output measured by a conventional thermodilution method (TDCO) in 12 patients anesthetized with either enflurane or isoflurane. A total of 207 simultaneous CO measurements ranged from 3 to 10.2 l/min. Regression analysis of 207 paired Fick CO and TDCO values showed a good correlation (r = 0.94), and a regression equation (Fick CO = TDCO-0.28). The "limits of agreement" (mean difference +/- 2 SD of bias) were within +/- 1.12 l/min, which could be acceptable for clinical settings. When hemodynamic states were abruptly changed by an intravenous administration of isoproterenol, Fick CO reached 90% of EMCO change within 30 sec. The author concludes that this system provides virtually continuous hemodynamic analyses and facilitates more sophisticated circulatory control of the patients within a limited fluctuation.