1. Field of the Invention
The present invention relates to an anesthetic filter arrangement and in particular to a filter arrangement for the re-use of anesthetics in inhalation anaesthesia.
2. Description of the Prior Art
Filter arrangements for the re-use of gaseous anesthetics are well known and are described in, for example U.S. Pat. Nos. 5,044,361 and 5,471,979. These filter arrangements generally have a filter housing in which there are provided openings delimiting a gas flow path through the interior of the housing. Disposed within the gas flow path is a filter element of an adsorption material for the alternate adsorption and desorption of gaseous anesthetic from and into gas passing along the flow path. These filters are placed within gas flow circuits of anesthetic ventilator systems so that anesthetic rich gas which is exhaled by a patient into the gas flow circuit during an expiration phase passes through the filter element along the flow path in one flow direction and so that breathing gas in the gas flow circuit which is to be supplied to the patient during an inspiration phase passes through the filter element along the flow path, usually but not necessarily, in the opposite flow direction. The filter element adsorbs gaseous anesthetic from the exhaled gas then desorbs this adsorbed gaseous anesthetic into the breathing gas.
Such filter arrangements suffer from the disadvantage that their retention properties for the gaseous anesthetic are fixed, dependent on the adsorption and desorption characteristics of the filter element material. Adsorption and desorption of gaseous anesthetic to and from the filter element is then largely controlled by varying the flow of and to a lesser extent the concentration of gaseous anesthetic in gas passing along the gas flow path, through the filter element. However, varying the gas flow and concentration parameters may have undesirable effects on the ventilation of a patient who is connected to an anesthetic ventilator system in which the filter arrangement is disposed.
It is an object of the present invention to provide an anesthetic filter arrangement, as well as an inhalation anesthetic system employing such a filter, wherein the degree of retention of gaseous anesthetic by a filter element can be varied.
The above object is achieved in an embodiment of the present invention directed to an anesthetic filter arrangement wherein a filter housing has openings disposed to delimit a gas flow path in the interior of the housing adapted for passing gas to and from a patient, wherein a filter element, formed of an adsorption material is disposed in the gas flow path for alternatingly adsorbing gaseous anesthetic from and desorbing gaseous anesthetic into gas in the gas flow path, and wherein an energy source is in energy transferring communication with the filter element for supplying energy to the filter element to vary the retention of the gaseous anesthetic by the filter element.
The retention of gaseous anesthetic by the filter element is thus varied through supplying either thermal or vibrational energy, at the element which thereby varies the adsorption and/or desorption of gaseous anesthetic.
The thermal energy may be supplied to the filter element using an energy source formed by a resistive heater element, for example a thin wire, which can be placed in intimate thermal contact with the filter element, for example within the volume of the element material.
Alternatively, the material of the filter element may be electrically conducting, for example activated carbon material, and used as the resistive heater element. This has the advantage that the thermal energy can be evenly distributed throughout the entire volume of the filter element without the need for integrating a separate resistive heater element.
An electromagnetic energy source, such as an infra-red or microwave source may be employed to supply the thermal energy at the element. This has an advantage that the source may be located remote from the filter element which permits the use of a disposable filter element without the need to also dispose of components of the energy source.
A source of vibrational energy, such as an acoustic, preferably ultrasonic, vibrational energy source, may be employed as the energy source. This has the advantage that the vibrational energy can be supplied from outside the filter housing, for example by using vibrational sources detachably mounted to an external surface of the housing. This permits the re-use of the vibrational sources when used with disposable filter elements and housings and also the ready modification of existing filter housings.
The above object is also achieved in accordance with the principles of the present invention in an embodiment directed to an inhalation anesthetic system having a mechanical breathing aid for supplying a breathing gas, including an anesthetic gas, to ventilate a patient, a gas circuit connected to the breathing aid for conducting the breathing gas to the patient during an inspiration phase and for conducting exhaled gas from the patient during an expiration phase, and an anesthetic filter arrangement as described above disposed in the gas circuit, with the aforementioned alternating absorption and desorption of the gaseous anesthetic taking place in the expiration phase and the inspiration phase, respectively.