Effects of arterial oxygen tension and cardiac output on venous saturation: a mathematical modeling approach

OBJECTIVES: Hemodynamic support is aimed at providing adequate O2 delivery to the tissues; most interventions target O2 delivery increase. Mixed venous O2 saturation is a frequently used parameter to evaluate the adequacy of O2 delivery. METHODS: We describe a mathematical model to compare the effects of increasing O2 delivery on venous oxygen saturation through increases in the inspired O2 fraction versus increases in cardiac output. The model was created based on the lungs, which were divided into shunted and non-shunted areas, and on seven peripheral compartments, each with normal values of perfusion, optimal oxygen consumption, and critical O2 extraction rate. O2 delivery was increased by changing the inspired fraction of oxygen from 0.21 to 1.0 in steps of 0.1 under conditions of low (2.0 L.min-1) or normal (6.5 L.min-1) cardiac output. The same O2 delivery values were also obtained by maintaining a fixed O2 inspired fraction value of 0.21 while changing cardiac output. RESULTS: Venous oxygen saturation was higher when produced through increases in inspired O2 fraction versus increases in cardiac output, even at the same O2 delivery and consumption values. Specifically, at high inspired O2 fractions, the measured O2 saturation values failed to detect conditions of low oxygen supply. CONCLUSIONS: The mode of O2 delivery optimization, specifically increases in the fraction of inspired oxygen versus increases in cardiac output, can compromise the capability of the "venous O2 saturation" parameter to measure the adequacy of oxygen supply. Consequently, venous saturation at high inspired O2 fractions should be interpreted with caution.

Continuous Cardiac Output by using Arterial Pressure Waveform Analysis and Central Venous Oxygen Saturation during Cardiac Surgery: A case report / 대한마취과학회지

The determination of arterial pressure wave-derived cardiac output (APCO) and central venous O2 saturation (ScvO2) has been introduced as a less invasive procedure for monitoring cardiac function and oxygen delivery. We have used an APCO sensor (FloTracTM) and a monitor for ScvO2 (Vigileo(TM)) in two cases of cardiac valve surgery, where placement of pulmonary artery catheter (PAC) was not applicable due to unfavorable cardiac structure (case 1) and was contraindicated due to an unstable cardiac conduction disorder and arrhythmia (case 2). In case 1, monitoring of APCO was started from the beginning of anesthesia induction and a ScvO2 monitoring central venous catheter was inserted just after anesthesia induction. APCO, ScvO2 and other hemodyanamic information such as arterial BP, CVP, and data obtained from transesophageal echocardiography (TEE) during the pre- cardiopulmonary bypass (CPB) period were measured. APCO and ScvO2 during the post-CPB period showed a reliable correspondence with continuous cardiac output (CCO) and mixed venous O2 saturation (SvO2) as measured by PAC at the end of CPB. In case 2, APCO and ScvO2 were monitored instead of CCO and SvO2. The values of APCO showed a good correlation to intraoperative COs indirectly calculated by the velocity-time integral of the aortic outflow determined in the TEE examination. We experienced that monitoring APCO and ScvO2 is useful for anesthesia management in cardiac valve surgery and can be an alternative to CCO and SvO2 if the placement of PAC and the thermodilution method are not applicable.