Capnotracking Cardiac Output Monitoring via Venous CO2 Control
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Solution Overview
Problem
Existing methods for determining cardiac output or effective pulmonary blood flow in mechanically ventilated subjects are limited by the need for cyclic ventilation patterns, which can be disrupted during interventions or result in unreliable measurements, making continuous monitoring challenging.
Innovation Solution
A method that maintains a constant level of venous CO2 through active control of mechanical ventilation, allowing changes in cardiac output or EPBF to be determined from changes in alveolar CO2 alone, using a capnotracking technique that adjusts breath duration and volume to keep CO2 levels stable.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional Fick-based methods are used for cardiac output determination, then continuous monitoring is possible during cyclic ventilation, but the method becomes inapplicable when ventilation patterns are interrupted or modified for interventions
Solution Approach 1:
Instead of changing ventilation to measure cardiac output (Fick method), the patent inverts the approach by keeping ventilation constant and measuring how alveolar CO2 changes to determine cardiac output. This allows continuous monitoring without requiring cyclic ventilation changes, making the method adaptable to interrupted or modified ventilation patterns while maintaining measurement reliability
Solution Approach 2:
The patent changes the measured parameter from ventilation changes (Fick method) to alveolar CO2 changes under constant ventilation conditions. By monitoring alveolar CO2 concentration changes while maintaining steady ventilation, the system can determine cardiac output continuously without requiring cyclic ventilation patterns, thus improving adaptability to various clinical situations
2Productivity
If cyclic ventilation patterns are used for Fick-based determination, then breath-by-breath cardiac output can be calculated, but the cyclic pattern must be interrupted for blood gas withdrawal or other interventions
Solution Approach 1:
The patent enables continuous cardiac output determination by monitoring alveolar CO2 changes under constant ventilation conditions. This eliminates the need to interrupt cyclic ventilation patterns for measurements, allowing continuous monitoring to proceed without interruption even during interventions like blood gas withdrawal, thus maintaining productivity while removing the duration limitation
3Measurement precision
If Fick-based methods are employed, then cardiac output can be determined from VCO2 changes, but measurements become unreliable when expired CO2 falls outside the operating range
Solution Approach 1:
Instead of relying on VCO2 changes that may fall outside operating ranges, the patent inverts the approach by maintaining constant ventilation and measuring alveolar CO2 changes. This ensures measurements remain within reliable ranges under varying cardiac output conditions, improving both precision and reliability of cardiac output determination
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
Enables continuous, non-invasive monitoring of cardiac output or EPBF even when conventional Fick-based techniques are not applicable, providing accurate breath-by-breath estimates by controlling mechanical ventilation to prevent changes in venous CO2.
Implementation Method 1
measuring expiratory CO2 of the subject, i.e., the CO2 content of expiration gas expired by the subject
Implementation Method 2
controlling the mechanical ventilation of the subject to keep a level of venous CO2 of the subject substantially constant
Implementation Method 3
Most non-invasive respiratory based methods for determination of cardiac output or EPBF are based on some form of the basic physiological principle known as the Fick principle
Data Source
Figure 1~2
AI summary
The present disclosure relates to a capnotracking method for continuous determination of cardiac output or EPBF of a mechanically ventilated subject (3), comprising the steps of measuring (S1) expiratory CO2 of the subject and determining (S2) a first value of cardiac output or EPBF of the subject at a first point in time. The method further comprises the steps of controlling (S3) the mechanical ventilation of the subject to keep a level of venous CO2 of the subject substantially constant between the first point in time and a second point in time, determining (S4) from the expiratory CO2 measurements a change in alveolar CO2 of the subject between the first and second points in time, and determining (S5) a second and updated value of cardiac output or EPBF of the subject based on the first value and the change in alveolar CO2.