Surgery – Respiratory method or device – Means for supplying respiratory gas under positive pressure
Patent
1991-11-18
1993-03-23
Millin, V.
Surgery
Respiratory method or device
Means for supplying respiratory gas under positive pressure
12820527, 12820417, A61M 1610
Patent
active
051955270
DESCRIPTION:
BRIEF SUMMARY
This invention relates to an improved respiratory filter included in a respiratory system of the kind used in anaesthesia and/or patient ventilation. Such filters may be used both for bacteriological control and as heat and moisture exchangers.
Such a filter comprises a housing containing a filter medium, with said housing representing an enlargement of the breathing tube in which it is included, and with ports at opposite ends of the housing being fitted to lengths of the tube, usually a flexible, plastics pipe of corrugated construction, passing respectively to and away from the patient. The filter medium spans the housing between the ports so that air and/or other gases inhaled and exhaled by the patient must pass through it. The filter medium employed in one type of such filter in common use comprises a generally rectangular block of corrugated paper. In another such filter in common use the filter medium is a permeable disc held in the housing to be perpendicular to the direction of flow of gases between the ports. The latter type has the advantage of being relatively less bulky than the former, but what both types have in common is that the housing is generally funnel-shaped at its ends where it tapers toward each port from the opposed surface of the filter medium. The empty space thus provided at each end of the filter housing is undesirable not only because it increases the size and bulk of the filter but more significantly because it represents "apparatus dead space" (see e.g. British Standards Institute's, BS 6015:1980) in which exhaled gases can collect so as to be reinspired. Nevertheless substantial "dead space" has been provided because the further the relatively wide surface of the filter member is from each port the more opportunity gases will have to spread from the port before impinging on the filter member. Secondly, if the filter member were too close to each port it would be difficult to breath through the filter and in the case of weak patients e.g. in an intensive care unit it is essential that breathing should be obstructed as little as possible by the filter.
A principal object of the present invention is to provide a filter, included in a breathing system, in which "apparatus dead space" within the filter housing is substantially reduced without the prejudicial consequences to be expected from so doing.
Another problem inherent in the use of such filters is that because only a relatively small, central area of the filter medium is directly opposed to the housing port through which gases flow toward it the gases pass predominately through a central portion of the filter medium and its peripheral portion relatively unused. The solution most commonly employed has been to distance the filter member further from each port to give the gases more room to diverge from the ports, but this makes the filter larger and more bulky and increases "apparatus dead space". Concentration of use of the filter medium to a central area reduces its effectiveness, or at least its effective life.
Another object of the present invention is to provide a smaller, less bulky filter with reduced "apparatus dead space" yet in which the filter medium will be more uniformly employed. for either liquid or gaseous media in which the filter member is enclosed between cover plates continguous therewith each having ribs which define with the filter member a plurality of inlet and outlet passages. A filter of this kind would not be suitable as a respiratory filter because of the resistance it would offer to gases passing through it. This Specification proposes "substantially conical jet spreaders" arranged to deflect the incoming or outgoing medium from the inlet port or to the outlet port.
The arrangement of substantially conical deflectors adjacent the inlet and outlet ports of a respiratory filter would assist in the reduction of "apparatus dead space" but at the expense of unacceptably increasing resistance to flow. Moreover solid deflectors would produce a "shadow" on the central area of the filter member aligned
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Chiu Raleigh W.
Intersurgical Limited
Millin V.
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