Validation of Capnodynamic Assessment of Mixed Venous Oxygen Saturation and Cardiac Output in Anesthetized Children Undergoing Cardiac Catheterization

Background: Mixed venous saturation (SvO2) is an indicator of the balance between oxygen supply and demand in the body's tissues The primary objective of the current study is thus to investigate the agreement and trending ability for capnodynamically derived SvO2 against the gold standard CO-oximetry. The secondary objective is to investigate the agreement and trending ability for capnodynamically derived CO (COEPBF) against the modified CO2-Fick method.

Methods:

The rationale of capnodynamic SvO2 (capno-SvO2) can be briefly described as follows:

The Capno-SvO2 method is based on differential Fick's principle and utilizes a combination of continuous estimation of Effective Pulmonary Blood Flow (COEPBF) and oxygen consumption (VO2) incorporated in a rearranged Fick's equation. COEPBF is estimated by applying a special breathing pattern of variations in I:E relationships (six breaths with normal I:E relations followed by three breaths vid an approximately 2 s expiratory pause). This breathing pattern causes small fluctuations in alveolar CO2 concentration and VCO2, related to the pulmonary blood flow participating in gas exchange which allows for estimation of COEPBF. VO2 can be estimated using continuous volumetric capnography measurement of VCO2 combined with the Respiratory Quotient (RQ).

Modified CO2-Fick: CO estimation using modified CO2-Fick is assessed by incorporating measured CO2 content in mixed venous and arterial blood into the equation below where VCO2 is estimated using volumetric capnography.