VV ECMO Cardiac Output Assessment Using Oxygen Saturation Shifts
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Solution Overview
Problem
Current methods for measuring cardiac output in patients undergoing veno-venous extracorporeal membrane oxygenation (VV ECMO) are invasive and often inaccurate, especially in the presence of recirculation, which can lead to missed diagnoses of cardiac insufficiency and potential life-threatening situations.
Innovation Solution
A non-invasive method and apparatus that measures cardiac output by monitoring blood flow rates and oxygen saturations in a veno-venous extracorporeal circuit, adjusting flow rates to account for recirculation, and using mass balance equations to calculate cardiac output based on measured parameters.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If pulmonary artery thermodilution or transpulmonary thermodilution is used to measure cardiac output, then measurement can be performed, but the method is invasive and often inaccurate especially at high recirculation levels
Solution Approach 1:
The patent uses oxygen saturation as an intermediary parameter to indirectly measure cardiac output. Instead of directly measuring blood flow through invasive catheters, the system measures oxygen saturation in the blood before and after the extracorporeal circuit, using oxygen as a tracer substance to calculate cardiac output through mass balance equations. This eliminates the need for invasive pulmonary artery catheterization while maintaining measurement capability.
Solution Approach 2:
The patent replaces the mechanical invasive measurement system (thermodilution catheters requiring pulmonary artery access) with a non-invasive optical measurement system (oximetry). The system substitutes mechanical intrusion into the cardiovascular system with optical detection of oxygen saturation, thereby eliminating invasive procedures while enabling continuous cardiac output monitoring in VV ECMO patients.
2Reliability
If standard cardiac output measurement methods are used in VV ECMO, then measurement is possible, but recirculation causes misleading results and cardiac insufficiency may be missed
Solution Approach 1:
The patent implements a feedback mechanism by continuously monitoring oxygen saturation levels and using this information to calculate and update cardiac output estimates in real-time. The system measures oxygen saturation before and after the extracorporeal circuit, feeds this data into mass balance equations, and generates continuous cardiac output measurements that account for recirculation effects. This feedback loop enables reliable detection of cardiac insufficiency despite the presence of recirculation.
Solution Approach 2:
The patent changes the measurement parameter from direct blood flow measurement (which is confounded by recirculation) to oxygen saturation measurement (which remains accurate despite recirculation). By measuring oxygen content rather than flow velocity or volume directly, the system transforms a problematic measurement into a reliable one, as oxygen saturation reflects actual oxygen delivery to tissues regardless of recirculation patterns.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
Provides accurate and non-invasive cardiac output measurements, reducing the risk of missed cardiac insufficiency diagnoses and enabling timely interventions.
Implementation Method 1
passing the withdrawn blood through the access line and the blood oxygenator to form oxygenated blood
Data Source
AI summary
A system for calculating cardiac output of a patient on an extracorporeal blood oxygenation circuit includes measuring first oxygenated blood flow rate by a pump in the extracorporeal circuit and a corresponding arterial oxygen saturation and recirculation in the extracorporeal circuit, then changing the pump flow rate, such as decreased, to produce a corresponding change in arterial oxygen saturation (wherein such change is outside of normal operating variances or drift), which change in the arterial oxygen saturation and recirculation are measured. From the first flow rate and the second flow rate along with the corresponding measured recirculation and the arterial oxygen saturation, the CO of the patient can be calculated, without reliance upon a measure of venous oxygen saturation. The system also includes an accommodation of oxygenation by the lungs of the patient during the extracorporeal blood oxygenation.