End-tidal Gas Estimation for Non-intubated Patients
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Solution Overview
Problem
Conventional end-tidal gas measurement techniques lack reliability and accuracy in non-intubated patients, particularly in using end-tidal CO2 as a surrogate for arterial CO2, due to unclear definitions and inconsistent relationships between end-tidal and arterial gas values, especially in unstable ventilatory patterns.
Innovation Solution
A method and apparatus that measure and report end-tidal gas values by determining the greater of either the maximum gas concentration during a breath or the previous breath's value decreased by a maximum allowable percent change, utilizing a differential pressure flowmeter, gas sensors, and processing units to provide reliable end-tidal gas values, and indicating reliability through decision support systems.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If conventional end-tidal gas measurement techniques are used in non-intubated patients, then the measurement process is simple and non-invasive, but the reliability and accuracy of end-tidal CO2 as a surrogate for arterial CO2 deteriorates
Solution Approach 1:
The system incorporates a feedback mechanism by comparing the measured end-tidal CO2 value against an expected physiological range and adjusting the reported value accordingly. The processor analyzes the relationship between end-tidal and arterial CO2 over time and uses this feedback to improve the accuracy of end-tidal CO2 as a surrogate measurement, resolving the contradiction between non-invasive simplicity and measurement reliability
Solution Approach 2:
The patent changes the parameter representation by reporting not just the raw end-tidal CO2 value but also the difference between end-tidal and arterial CO2 values. This parameter transformation allows the system to maintain the simplicity of non-invasive measurement while providing corrected values that reflect the actual arterial CO2 status, thereby improving reliability without sacrificing ease of operation
2Measurement precision
If the maximum gas concentration during a breath is reported, then the measurement captures the peak value, but it may overestimate the true end-tidal gas value in unstable ventilatory patterns
Solution Approach 1:
The system applies partial action by reporting a corrected end-tidal value that is less than or equal to the maximum observed concentration. Instead of always reporting the peak value, the system selectively reports corrected values when physiological conditions indicate that the maximum would overestimate the true end-tidal value, thus achieving reliable measurements without completely discarding the peak information
Solution Approach 2:
The processor performs preliminary analysis of the breath waveform and physiological parameters before finalizing the reported end-tidal value. By预先 evaluating whether the maximum concentration represents a true end-tidal value or an artifact, the system can apply appropriate corrections in advance, ensuring both precision in capturing peak values and reliability in the final reported measurement
3Productivity
If end-tidal gas values are used to estimate arterial gas values, then arterial blood sampling can be reduced, but the accuracy of the estimation deteriorates without proper correction methods
Solution Approach 1:
The patent introduces an intermediary computational model that bridges end-tidal CO2 measurements and arterial CO2 estimation. This intermediary processing layer uses the relationship between end-tidal and arterial CO2 values, along with physiological parameters, to generate accurate arterial gas estimates from non-invasive measurements, thereby maintaining productivity through reduced blood sampling while preserving measurement precision through mathematical correction
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
This approach enhances the reliability of end-tidal gas measurements, allowing for more accurate estimation of arterial CO2 levels, reducing the need for arterial blood sampling and enabling more effective closed-loop ventilation control, while improving the accuracy and safety of capnometry in non-intubated patients.
Implementation Method 1
a source that emits infrared radiation having an absorption band for carbon dioxide. The infrared radiation is usually transmitted along a path that is normal to the flow path of the gas stream being analyzed. Photodetectors are arranged to receive and measure the transmitted radiation that has passed through the gas in the gas stream. Carbon dioxide within the sample gas absorbs this radiation at some wavelengths
Data Source
AI summary
An apparatus and method of using an end-tidal gas value taken from an non-intubated patient that includes measuring a plurality of gas concentration values, determining an end-tidal gas value from the gas concentration values, and reporting the end-tidal gas value for a breath as the greater of either: (a) a maximum gas concentration values observed during such a breath, or (b) the end-tidal gas value reported for a previous breath decreased by a maximum allowable breath-to-breath percent change.