METHOD AND APPARATUS FOR DELIVERING A FLUID TO A PATIENT

Abstract

The present invention relates to a method and apparatus for delivering medicated fluid or anaesthetic to a patient. An issue, particularly with small patients, is the issue of dead space in an anaesthetic circuit which can lead to hypoxia and difficulty with achieving anaesthesia. An apparatus in accordance with the present invention minimises or eliminates dead space by introducing fresh gas (e.g. containing anaesthetic) proximal to a respiratory opening of the subject's respiratory tract, and inducing a fluid flow to reduce re-breathing of fluid exhausted from the respiratory tract.

Claims

1. An apparatus for facilitating delivery of a fluid to a respiratory tract of a human or animal subject weighing up to 15 kilograms, the apparatus comprising: a substantially conical elongate enclosure having a first end having a width sufficient to fit over and seal around a respiratory opening of the subject, and a second end that is narrower than the first end in which is formed an outlet; and an inlet arranged peripherally in the first end to enable introduction of fresh fluid into the first end of the enclosure at the periphery of the enclosure at a positive pressure with respect to the outlet to induce unidirectional fluid flow through the enclosure from the first end to the second end past the respiratory opening of the patient to the outlet in a direction of exhalation fluid flow from the patient, whereby expelled gases are removed from the second end of the enclosure by the unidirectional fluid flow to reduce re-breathing of fluid exhausted from the respiratory tract.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0030] Features and advantages of the present invention will become apparent from the following description of embodiments thereof, by way of example only, with reference to the accompanying drawings, in which:

[0031] FIG. 1 is a diagram of a prior art anaesthetic circuit for the delivery of anaesthetic to a subject;

[0032] FIG. 2 is a diagram of an alternative prior art anaesthetic circuit;

[0033] FIG. 3 is a diagram of an anaesthetic circuit including an apparatus in accordance with an embodiment of the present invention;

[0034] FIG. 4 is a drawing of an apparatus in accordance with an embodiment of the present invention;

[0035] FIG. 5 is a side view of an apparatus in accordance with an embodiment of the present invention;

[0036] FIG. 6 is a back view of the embodiment of FIG. 5;

[0037] FIG. 7 is an underneath view of the embodiment of FIG. 5;

[0038] FIG. 8 is a cross sectional view of the embodiment of FIG. 5, and

[0039] FIG. 9 is a perspective view on a smaller scale of the embodiment of FIG. 5.

DETAILED DESCRIPTION OF EMBODIMENTS

[0040] Referring to FIG. 1, a prior art anaesthetic circuit of the non-re-breathing type is shown. Such non-re-breathing circuits are often used to anaesthetise animals, particularly small animals, and also children and infant human subjects. The anaesthetic circuit is designated generally be reference numeral 1.

[0041] The anaesthetic circuit 1 includes a means of providing oxygen, in this case being a gas cylinder 2 containing oxygen. A regulator 3 is provided to regulate the pressure of the oxygen supply and a flow meter 4 provides an indication of the gas flow. A vaporiser 5 is provided for the introduction of anaesthetic (and perhaps other medicinal gases) to the gas flow. A tube 6 having a central lumen 7 extends from the vaporiser into a further tube 8 providing a further lumen 9 surrounding the tube 6. A mask 10 is provided connected to corrugated tube 8. The lumens 7 of the tube 6 and 9 of the corrugated tube 8 open into an interior space 11 of the mask 10. A reservoir bag 12 is provided connected to the distal end 13 of the corrugated tube 8 and has outlet 14 which proceeds to a Scavenging Interface (not shown).

[0042] The apparatus of FIG. 1 is a standard type of non-re-breathing anaesthetic circuit which is well known and, with variations, finds wide application.

[0043] In this prior art circuit, the mask shown 10 is of the type which is mainly used for relatively small animals (under 30 kilograms and even under 10 kilograms and 5 kilograms). The mask 10 forms an enclosure which encloses an opening to the respiratory tract of the animal, in this case it fits over the nose and the mouth, referenced by reference numeral 15. A flexible gasket 16 borders a forward opening 17 of the mask 10 to provide tight seal of the enclosure 11 with the nose/mouth of the subject. The mask has a single opening 18 at a part of the mask distal from the opening 16, the opening 18 arranged to allow the passage of inspired and expired gases (indicated by arrow 19 and arrow 20, respectively).

[0044] In operation, fresh gas including anaesthetic (and any other required medicated gases) is introduced by line 6 into the space 11 within the mask 10, via opening 18. Exhaled gases travel via the opening 18 and a lumen 9 of the corrugated tube 8 to the Scavaging Interface.

[0045] Dead space 11 within the mask 10 comprises anaesthetic dead space. Dead space constitutes extra volume that the subject must inspire before they inspire fresh gas. Particularly for small animals and small humans, the volume 11 in this dead space can become critical. For example, for a small subject having a small tidal volume, any additional machine volume can significantly affect the composition of the gas being breathed using these types of circuits. Hyperventilation and hypoxia are common problems. Also a common problem, is difficulty in inducing anaesthesia because of the inability to deliver the required dosage of anaesthesia.

[0046] Attempts have been made to overcome this problem by designing very small volume masks in order to reduce the dead space to as little as possible. These small volume masks have to fit tightly and are often very uncomfortable and cause stress to the subject. Further, different ranges of different sizes of masks need to be designed for different sizes of subject.

[0047] Even where masks are designed to minimise volume, there is still sufficient machine dead space to cause the problems discussed above.

[0048] Referring to FIG. 2, an alternative prior art anaesthetic circuit is illustrated. This is a re-breathing type circuit where oxygen/air may be re-breathed after it has been scrubbed of carbon dioxide. Components which are the same as the components of the FIG. 1 system have been given the same reference numerals and no further description will be given. The system includes anaesthesia lines 25 & 26 which form a Y connection 27 with the distal opening 18 of the mask 10. Fresh gas flow comes down line 25 from the vaporiser 5, in the direction of arrow 8. Exhaust gas flow travels up the other arm of the Y, line 26, in the direction of arrow 29. Scrubber 30 removes carbon dioxide from the exhaust gas and it re-enters the line 25 at the other side of the scrubber 30.

[0049] With this type of circuit there is even more machine dead space. As well as the dead space volume in enclosure 11 of the mask, there is also an extra dead space volume c where the arms 25, 26 of the Y connect, being volume 31 distal to the opening 18 of the mask 10.

[0050] An embodiment of the present invention will now be described with reference to FIG. 3.

[0051] An apparatus in accordance with an embodiment of the present invention is designated by reference numeral 40. The apparatus includes an inlet 41 for introducing fluid proximal to a respiratory opening 42 of a human or animal subject, and is arranged to facilitate the induction of a fluid flow which operates to reduce re-breathing of fluid exhausted from the respiratory opening 42. In this embodiment the induced flow is uni-directional, past the respiratory opening 42, as indicated by arrows 43, and out of a further opening, outlet 44 from the apparatus 40, the outlet 44 being distal to the proximal inlet 41.

[0052] The induced fluid flow 43 results in what otherwise might have been dead space within the apparatus 40 being eliminated or reduced for the purposes of the subject breathing in fluid.

[0053] In more detail, in this embodiment, the apparatus 40 is a mask including an opening 45 for receiving the subject's nose or mouth, or nose and mouth and also including a gasket 46 to provide at least a loose seal about the subject. Note that the gasket 45 may not be required in some cases.

[0054] The mask 40 includes the inlet 41 which is proximal to the opening 45 and an outlet 44 which is distal from the proximal inlet. The outlet 44 together with the inlet 41 provides a pathway for gas flow impelled by positive pressure at the inlet 41 compared to the outlet 44.

[0055] In this embodiment, the apparatus 40 is shown connected to a length of corrugated tubing then a re-breathing bag and scavenging interface. Instead of the position in the prior art where the fresh gas enters through the distal opening of the mask, however, in this arrangement fresh gas enters via the proximal inlet 41 and exhaust gas is expired through the distal outlet 44.

[0056] Some components of the anaesthetic circuit have been given the same reference numerals as the components of FIGS. 1 & 2. these components are similar and no further description will given. A fresh gas flow tube 47 extends from the vaporiser 5 to the inlet 41 of the mask 40. A corrugated outlet tube 48 is connected between the outlet 44 of the mask 40 and the reservoir bag 12.

[0057] Note that the mask may be separate from the anaesthetic circuit, having connections for the inlet and the outlet 44. Alternatively, it may be integrated with components of the anaesthetic circuit (e.g. inlet line 47 and outlet line 48).

[0058] FIGS. 4 through 9 show in more detail an embodiment of an apparatus in accordance with the present invention. This embodiment is a mask for the delivery of fluid to a subject. Dimensions shown in the drawings are example dimensions only. The mask may be dimensioned and shaped differently.

[0059] The mask 50 defines an enclosure 51 and includes an opening 52 which is arranged to be placed about or over a respiratory opening of a subject. The opening 52 includes a resilient gasket 53. The mask 50 includes an inlet 54 which opens into the enclosure 51 proximal to the opening 52 and in use adjacent to the respiratory opening of the subject. The mask also includes an outlet 55 which is positioned distally of the inlet 54. The mask 50 includes a wall 56 bounding the enclosure 51. The inlet 54 includes a connector piece 57, which may be used to connect to an inlet tube of an anaesthetic circuit, or to another device for providing fluid. The outlet 55 also includes a connector 58 which may be used to connect to the exhaust line of an anaesthetic circuit. From FIG. 8 it can be seen clearly that the proximal end 60 of the inlet 54 opens into the enclosed space 51 proximal to the opening 52.

[0060] The mask 50 can in fact be considered as an integrated anaesthetic circuit in its own right. For small patients, for example, any extra line (e.g. corrugated tubing) on the outlet 55 may not be required. A re-breathing bag and a scavenging circuit could be connected directly to the connector 58. This limb (55, 58) of the mask in fact constitutes an expired limb of the circuit integrated into the apparatus. In embodiments, this limb can be as long and with as much volume as requiredthe tube can be made a metre long, for example. Because of the operation of the apparatus, the volume of this limb does not add to the dead space of the machine. The limb can even be made flexible.

[0061] The apparatus and method of the present invention is not limited to use in anaesthesia. It may also be used for the dispensing of other medicinal fluids, such as pharmaceuticals for treating asthma, for example. The apparatus and method preferably have the advantage that they enable the delivery of an immediate concentration of medicine to the respiratory tract of a subject.

[0062] In anaesthesia, the apparatus and method have particular advantage in small human and animal subjects. Slight positive pressure of gas at the inlet may be required in order to induce unidirectional flow. For a 5 kilogram animal for example, the flow rate may be in order of 3 litres per minute and for a 10 kilogram animal or human in the order of 6 litres per minute. For larger animals the flow rate will need to be greater but, even where there is a lower flow rate, it will still result in at least a reduction of dead space. Significant advantage will be gained as long as the flow rate is higher than the minute ventilation of the subject.

[0063] A further advantage with small animals and small human patients is that it not necessary to make a range of sizes of masks to fit different sizes of patients. One or a few different sizes of masks may be suitable, as dead space is not as big an issue with embodiments of the present invention.

[0064] It will be appreciated by persons skilled in the art that numerous variations and/or modifications may be made to the invention as shown in the specific embodiments without departing from the spirit or scope of the invention as broadly described. The present embodiments are, therefore, to be considered in all respects as illustrative and not restrictive.

[0065] In the claims which follow and in the preceding description of the invention, except where the context requires otherwise due to express language or necessary implication, the word comprise or variations such as comprises or comprising is used in an inclusive sense, i.e. to specify the presence of the stated features but not to preclude the presence or addition of further features in various embodiments of the invention.