Surgery – Respiratory method or device – Means for mixing treating agent with respiratory gas
Reexamination Certificate
1999-10-07
2001-10-02
Lewis, Aaron J. (Department: 3761)
Surgery
Respiratory method or device
Means for mixing treating agent with respiratory gas
C128S203140, C128S203250
Reexamination Certificate
active
06295985
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention is directed to an anaesthetic machine for delivering anaesthetic to the airways of a patient, the anaesthetic machine being of the type having a gas flow generator with an inlet and an outlet, and a first system of flow paths connected between this inlet and outlet and a second system of flow paths also connected between this inlet and outlet.
2. Description of the Prior Art
Anaesthetic machines are usually based on a circular (loop) system in which breathing gas is returned to the patient after exhalation. The main reason for this is to minimize the consumption of expensive anaesthetic. Breathing gas is purified in a carbon dioxide absorber. Breathing can either be spontaneous or maintained with gas delivered to the patient in pulses. The pulses are usually generated by a bellows or piston. This kind of anaesthetic machine is usually referred to as a low-flow system. This is because a volume of gas, less than the total volume of gas in the circle system, usually passes every point in the flow paths in every breathing cycle.
European Application 164 500 describes another type of anaesthetic machine. This known anaesthetic machine has a fan to which a first system of flow paths and a second system of flow paths are connected. The first system includes an inspiratory line, a positive pressure reservoir, an inspiratory valve, an expiratory line, a negative pressure reservoir and an expiratory valve. The second system includes a return line between the fan's inlet and outlet and a pressure-controlled valve. A predetermined pressure gradient can be generated by the fan and maintained between the inspiratory section and the expiratory section of the first system. By regulating the inspiratory valve and expiratory valve, the breathing of a patient connected to the known anaesthetic machine can be controlled. If pressure in the expiratory section drops too far, the pressure-controlled valve opens, enabling gas to flow from the inspiratory section to the expiratory section via the second system.
This known anaesthetic machine has a number of disadvantages. For example, it does not allow the patient to breathe spontaneously, since breathing is completely controlled by the inspiratory and expiratory valves. Moreover, this known anaesthetic machine cannot provide all the various kinds of controlled breathing modes. As a result, this known anaesthetic machine has a limited range of use in practice.
European Application 813 883 describes a ventilator, such as one intended for respiratory care in the patient's home. In one embodiment, the ventilator has a gas reservoir with an inlet open to ambient atmosphere, a compressor for generating a flow of gas, a flow splitter that conducts gas, via an inspiratory tube, to a patient or, via a return tube, back to the gas reservoir. Oxygen can be dispensed into the return tube to raise the level of oxygen in the breathing gas.
This known ventilator, however, is not suitable for anaesthesia, mainly because it is open to atmosphere.
SUMMARY OF THE INVENTION
An object of the present invention is to provide an anaesthetic machine that overcomes the aforementioned problems associated with known anaesthetic machine.
The above object is achieved in accordance with the principles of the present invention in an anaesthetic machine having a gas flow generator with an inlet and an outlet and first and second flow path systems connected between the inlet and the outlet, a shunt valve connected at the outlet of the gas flow generator for regulating respective amounts of gas flowing in the first and second systems of flow paths, and a control unit which controls the shunt valve to control the degree of division of the respective amounts flowing into the first and second systems of flow paths.
A number of advantages are achieved when a shunt valve is arranged at a gas flow generator's outlet in order to regulate the amount of gas flowing into the first system of flow paths and the second system of flow paths respectively.
One advantage is that all types of breathing modes can be accommodated, both controlled and assisted breathing. The shunt valve regulates the exact amount of gas needed for the prevailing breathing mode. When a bias flow is allowed to be supplied to the patient, triggering can be obtained for spontaneous breathing.
The patient's expiration is facilitated in an embodiment wherein the fan actively draws gas through the expiratory section of the first system of flow paths. As a result, any carbon dioxide absorber in the system does not pose any resistance to expiration. Filters also can be used in a way that is impossible in low-flow anaesthetic systems.
Another advantage is that gas in the anaesthetic machine can be quickly replaced with a new gas. This is important in the switch to another anaesthetic agent and when the patient is to be awakened from anaesthesia. Gas in the system is appropriately evacuated through an evacuation line. This prevents anaesthetic gas from escaping into the air around the anaesthetic machine.
As used herein, “shunt valve” means any individual component or combination of components that is capable of splitting (in analog or discrete steps) a gas flow into at least two sub-flows.
As used herein, “gas flow generator” means an individual component or combination of components that is capable of generating a flow of gas. Fans, compressors and pumps in particular are examples of such a “gas flow generator.”
In an embodiment wherein a gas reservoir is arranged in the flow paths, gas mixing is improved and made more homogenous in the whole system. The gas reservoir can be a hand ventilator for manual ventilation of the patient.
In another embodiment, the expiratory valve is arranged in the expiratory section of the first system of flow paths. The entire course of respiration can alternatively be regulated by the expiratory valve alone.
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Emtell Par
Kock Mikael
Lewis Aaron J.
Schiff & Hardin & Waite
Siemens Elema AB
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