Ventilator Disconnect Detection via Dynamic Leak Thresholds
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Solution Overview
Problem
Medical ventilators face challenges in accurately detecting patient disconnection due to pressure-dependent elastic leaks, which can lead to nuisance alarms and impaired therapy delivery under acceptable leak conditions.
Innovation Solution
A novel model and algorithm that calculates actual and maximum allowed leakage based on pressure in the ventilation system, allowing for precise determination of ventilator connection state and minimizing false alarms by accounting for both inelastic and elastic leak components.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If the ventilator uses a fixed threshold disconnect alarm, then disconnect detection is simple, but false alarms occur due to pressure-dependent elastic leaks
Solution Approach 1:
The disconnect alarm threshold is made dynamic rather than fixed. The system calculates a time-varying disconnect threshold based on the measured pressure waveform and leak model parameters, allowing the threshold to adapt to changing pressure conditions throughout the breathing cycle. This resolves the contradiction by enabling accurate disconnect detection across varying pressures without requiring complex real-time leak compensation during the alarm evaluation itself.
Solution Approach 2:
The leak model parameters (elastic and inelastic leak coefficients) are determined in advance during a calibration phase or initial operation, before disconnect detection is performed. This preliminary characterization of the system's leak behavior allows the subsequent disconnect alarm to use a simplified comparison against a pre-calculated threshold, avoiding the need for complex real-time leak compensation while maintaining accuracy.
2Reliability
If the ventilator allows leak compensation therapy, then therapy accuracy is improved, but disconnect detection reliability deteriorates
Solution Approach 1:
The system separates the leak compensation function from the disconnect detection function. Leak compensation operates independently to maintain therapy accuracy, while disconnect detection uses a separate mechanism based on comparing measured pressure against a pre-calculated disconnect threshold. This segmentation allows both functions to operate optimally without interfering with each other's accuracy.
Solution Approach 2:
A pre-calculated disconnect threshold acts as an intermediary between the leak compensation therapy and the disconnect detection. This threshold is derived from the leak model but is used independently of real-time leak compensation calculations, serving as a stable reference point that enables reliable disconnect detection even when leak compensation is actively adjusting therapy delivery.
3Ease of operation
If the ventilator uses a simple disconnect alarm, then operation is easy, but nuisance alarms occur under acceptable leak conditions
Solution Approach 1:
The disconnect alarm uses a pressure-dependent threshold rather than a fixed value. The threshold is calculated based on the measured pressure waveform and the characterized leak model parameters, automatically adjusting to account for pressure-dependent elastic leaks. This parameter change maintains operational simplicity while significantly improving alarm reliability by reducing false positives under acceptable leak conditions.
Data Source
AI summary
This disclosure describes systems and methods for detecting disconnect conditions in a ventilator. The disclosure describes a model-based enhancement to conventional disconnect detection. The methods and systems described herein compensate for the additional leakage that occurs due to inelastic and elastic leaks in the ventilation system. One method described includes calculating the actual leakage from the ventilation system including leaks from elastic leakage and inelastic leakage based on measurements of pressure and flow in the ventilation system for a breath and then comparing this leakage to a calculated hypothetical maximum allowable leakage determined based on an operator-selected maximum allowable leakage and the measurements of pressure for the same breath. Disconnection is assumed if the actual leakage is greater than the maximum allowable leakage.