Surgery – Respiratory method or device – Means for supplying respiratory gas under positive pressure
Reexamination Certificate
1999-06-15
2001-07-03
Dawson, Glenn K. (Department: 3761)
Surgery
Respiratory method or device
Means for supplying respiratory gas under positive pressure
C128S204210, C128S204220
Reexamination Certificate
active
06253765
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a method for determining the volume of a tubing system connected to a ventilator and to a patient. The present invention also relates to a method for determining an elastic volume of a tubing system connected to a ventilator and to a patient. The present invention also relates to a breathing apparatus system intended for use in the respiratory care of a patient and including a ventilator and a tubing system.
2. Description of the Prior Art
The ability to determine and/or regulate the amount of breathing gas supplied to a patient is important in respiratory care. Determined and/or regulated volume is usually stipulated in volume per breath (tidal volume) or average volume received per unit of time (minute volume) Breathing gas is usually supplied to the patient by a ventilator and a tubing system. Since gases are compressible (elastic), the volume of gas in the tubing system must be taken into account. As a rule, the tubing system is also elastic, so the actual volume in the tubing system can vary with the pressure. Studies have shown that the mechanical elastic volume can constitute 25-40% of the total elastic volume.
Testing a breathing apparatus system (e.g. a ventilator and tubing system) before the patient is hooked up to it is common. Compensation for the elastic volume can then be made by an operator. This is particularly important when a specific tidal volume must be supplied to the patient in each breath.
It would be advantageous if these measurements also could be performed while the patient is connected to the breathing apparatus system for respiratory care, since conditions could change in the course of treatment. Changes might develop especially in peripheral devices, which constitute dead space for the system, such as humidifiers, dehumidifiers and nebulizers.
A major problem is to exclude the patient from volume determinations. Determinations would be erroneous if the patient's airways and lungs were allowed to interact with the tubing system during a volume determination.
Another problem is to establish total elastic volume in an effective fashion.
SUMMARY OF THE INVENTION
An object of the present invention is to provide a method for determining only the volume of a tubing system while a patient is connected to it.
Another object of the invention is to provide a method for determining the total elastic volume of a tubing system while the patient is connected to it.
Yet another object of the invention is to provide a breathing apparatus system in which the volume of the tubing system and the elastic volume of the tubing system can be established while the patient is connected to the tubing system.
The inventive methods and apparatus are based on the recognition that in the breathing or respiratory cycle there are (brief) periods when the flow of breathing gas to or from the patient is zero or close to zero. By utilizing these periods in the method according to the invention, the patient can be excluded from the volume determinations. Since the flow is zero, there is no interaction with the patient's lungs, nor will the additional supply of a gas for measuring the volume of the tubing system involve the patient in the measurement as long as the pressure in the tubing system is not affected. In the method according to the invention, an additional gas is supplied to the inlet of the tubing system at a predetermined flow rate, preferably at a constant rate. When this additional gas reaches the outlet of the tubing system, the volume of supplied additional gas can be calculated with a time integral of flow. The supplied volume of additional gas corresponds to the volume of the tubing system.
In an alternative embodiment of the inventive method, when the flow of breathing gas to or from the patient is virtually zero, such as during an inspiratory pause or during an expiratory pause, a predetermined flow of a first gas is added to the tubing system while maintaining constant pressure in the tubing system, a determination is made of when the first gas starts flowing out of the tubing system, the outflow of the first gas from the tubing system is measured, a predetermined flow of a second gas is then added to the tubing system while maintaining constant pressure in the tubing system, a determination is made of when the second gas starts flowing out of the tubing system, and a determination is then made of the out flowing first gas, this volume constituting the volume of the tubing system.
In principle, the only difference is that in the alternative method the volume of additional gas flowing out of the tubing system is determined after the tubing system has been filled with the additional gas.
Both methods can naturally be utilized at the same time by first determining the supplied volume and then determining the outflow volume. This then provides an additional check to show that the patient was not involved in the measurement in any way and that there was no leakage or the like.
In principle, the first additional gas supplied can be breathing gas but with a differing composition than is used, e.g. 5-10% more oxygen, or breathing gas containing some trace gas or a completely different gas mixture that is harmless to the patient, e.g. helium.
It is fully sufficient for only the very first part of the supplied additional gas to contain e.g. a trace gas or different composition. The trace gas (or different composition) only serves as a marker of the “column of air” introduced into the tubing system. Such a gas marker is sufficient, regardless of whether the volume is determined from the supplied volume or the outflow volume. Otherwise just breathing gas can be used. The risk of the patient inspiring anything other than breathing gas is then greatly reduced.
All the additional gas supplied during a determination of volume, however, can naturally have the same composition.
In a method for determining the elastic volume of a tubing system is achieved according to the invention, the volume of the system is measured at two different pressures, and the mechanical elastic volume is determined as the difference between the volumes found at the two different pressures.
Performing these measurements in the final phase of inspiration and final phase of expiration, respectively, is particularly important, since the pressure difference is then greatest while flow is at a minimum. Flow can even be zero, in the inspiratory pause and expiratory pause respectively.
In instances in which a continuous bias flow is used, this flow can either be compensated for in determinations or utilized when the gas/gases used in the determination is/are supplied.
In a breathing apparatus according to the present invention, including a ventilator and a tubing system, the ventilator has an inspiratory valve, an expiratory valve, at least one flow meter, at least one pressure meter, at least one gas meter, and a control unit which determines the volume of the tubing system according to one of the above-described embodiments of the inventive method.
Using the volume of the tubing system determined in accordance with the inventive method, the inventive breathing apparatus can undertake automatic determination of a factor for compensating for the volume of the tubing system in the volume of gas which is supplied to the patient for respiratory purposes.
REFERENCES:
patent: 3729000 (1973-04-01), Bell
patent: 3923056 (1975-12-01), Bingmann et al.
patent: 4819629 (1989-04-01), Jonson
patent: 5738090 (1998-04-01), Lachmann et al.
patent: 0 791 327 (1997-08-01), None
Hognelid Kurt
Skog Goran
Dawson Glenn K.
Patel Mital
Schiff & Hardin & Waite
Siemens Elema AB
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