Air detector for thin walled tubes

Abstract: A device for detecting air in large bore thin walled transparent tubing 14 comprises a body 12 providing accommodation for the tubing; an LED 21 in a passage 19 in body 12 for transmitting light energy towards the tubing 14; a phototransistor 20 mounted in an orthogonally extending passage 18 for receiving light transmitted by LED 21 and modified by changes in the constituency of fluid passing through tubing 14, and an optical spacer in the form of a slotted collar 15 of material optically matched to the material of tubing 14 occuping space between LED 21 and the tubing 14 and phototransistor 20.

Description: This invention relates to devices for detecting air, e.g. air bubbles, in fluid conducting tubing and in particular in fluid conducting tubing forming part of a fluid flow system utilised for the intravenous supply of fluid to a medical patient. Typically transparent walled p.v.c. tubing is employed in systems as last-mentioned because it is hygienic and cheap - it being common practice to change and discard the length of tubing in use frequently. One object of the present invention is to provide an improved arrangement for detecting air-in-line in a fluid conducting system as referred to above. A known arrangement for use in clinical analysis and capable of detecting air in tubing utilises a device as illustrated in transverse section in Figure 1 of the accompanying drawings. Referring to Figure 1, the known device comprises a body member 1 having a passage 2 passing therethrough in which may be accommodated a length of transparent walled p.v.c. tubing 3. Passage 2 is open at the top (as viewed) in order that the tubing 3 may readily be slotted into position and of course removed after use. Extending into the body 1 from its base and right-hand side (as viewed) respectively are two circular-cylindrical passages 4 and 5 which are orthogonal to each other and exit via apertures 6,7 respectively into tubing passage 2. Located in circular cylindrical passage 4 is an infra-red receiver 8 (a phototransistor) which receives infrared energy transmitted by an infra-red transmitter 9 (an LED). In operation the output level of receiver 8 depends upon the nature of the fluid passing through the tubing 3 past receiver 8 and transmitter 9. Different fluids will result in different output levels with a significant change if air is present. For example, in a test a voltmeter 10 connected to the output of a suitable detector circuit 11 was found to indicate 0.1 volts when the fluid passing through tubing 3 was distilled water; 0.2 volts when the fluid was semi-skimmed milk; 1.4 volts when the fluid was a 20% intralipid solution and 4.2 volts when air passed through. Whilst not a primary function of a clinical analyser, a device as shown in Figure 1 will therefore operate as a detector of air passing through tubing 3. However, as is represented, p.v.c. tubing typically used in a clinical analyser is small bore thick-walled tubing with an outside diameter of 2.5mm and an inside diameter of 0.9mm. In the intravenous supply of fluids to a patient however the standard p.v.c. tubing used is of relatively large bore and thin walled having an outside diameter of 4mm and an inside diameter of 3.1mm. Experiments have been carried out in connection with the detection of air-in-line with a device generally as illustrated in Figure 1, but adapted dimensionally to accept the relatively large bore, thin walled tubing utilised for the intravenous supply of fluid to a patient but the results achieved were not satisfactory. Particularly bearing in mind the critical importance of detecting "air-in-line"in such applications, the changes that took place in the output of the receiver corresponding to receiver 8 in Figure 1 were insufficiently marked for the device to be regarded as useful in this connection. However, further experimentation led to the introduction of an optical spacer between the transmitter and the tubing and the tubing and the receiver and with this markedly improved results were achieved. WO-A-81/01655 discloses a similar arrangement to that shown in Figure 1 and the precharacterising point of Claim 1 is based on this disclosure. According to this invention, a device for detecting the presence of air in fluid conducting translucent or transparent tubing, comprises a body providing a gap for accommodating said tubing, a light energy transmitter for transmitting light energy towards said gap and a light energy receiver for receiving from said gap light energy transmitted by said transmitter and modified in use by changes in the consistency of fluid passing through said tubing, characterised in that the body includes an optical spacer defining said gap and occupying space between said light energy transmitter and said gap and between said gap and said light energy receiver. Preferably said light energy transmitter and said light energy receiver are operative in the infrared spectrum, and preferably said transmitter is an LED (light emitting diode) and said receiver is a phototransistor. Preferably the body comprises a body member having a passage therethrough for accommodating said tubing and said optical spacer is in the form of a collar within said passage, and said light energy transmitter and said light energy receiver are housed in said body member. Preferably said light energy transmitter and said light energy receiver are located in passages extending through said body member and opening into said tubing accommodating passage. The transmitter and receiver locating passages may open into said tubing accommodating passage via respective apertures. Said apertures may be in an integral wall of said body member, or in plugs inserted in said passages. The apertures may be of different sizes chosen to provide optimum effect in any given device. Commonly, the aperture through which said transmitter communicates will be of smaller cross-sectional area than the aperture through which said receiver communicates. In one embodiment of the invention wherein said apertures are of circular cross-section, the diameter of the aperture through which said transmitter communicates is at least half the diameter of the aperture through which said receiver communicates. Preferably said transmitter and receiver are spaced around said tubing accommodating passage with their principle optic axes in the same transverse plane. Preferably again said transmitter and receiver are arranged with their principle optic axes orthogonal one to the other. Where the said axis lie in the same transverse plane it may be found that satisfactory results are obtained with the optic axes at some angle one to the other other than 90° but it is believed that optimum results are obtained when the axes are orthogonal one to the other. Again, spacing the transmitter and receiver along the length of the tubing accommodating passage may be found to give satisfactory results, but it is believed that arranging the transmitter and receiver such that their principle optic axes are spaced around the tubing accommodating passage is believed to provide optimum results. The tubing used in the intravenous supply of fluids to a patient is of course of circular cross-section and normally therefore said tubing accommodating passage is of circular cross-section. Typically the diameter of said tubing accommodating passage and the outer diameter of said collar will be between twice and three times the outside diameter of said tubing. In a preferred embodiment the diameter of said tubing accommodating passage and the outer diameter of said collar are 2.5 times the outer diameter of said tubing. Preferably said transmitter and receiver are discrete devices and preferably an LED (light emitting diode) and a phototransistor respectively. Normally such components are generally circular-cylindrical in overall outline and accordingly said transmitter and receiver passages are normally circularly cylindrical. In order to simplify the insertion and removal of said tubing, preferably said collar has a linearly extending slot through which said tubing may be slotted into said gap. The width of said slot and the width of said gap are not necessarily similarly dimensioned but it is convenient that that should substantially be so. The material chosen for said optical spacer should be a reasonable match optically to the material of said tubing. Preferably said material is acrylic. It should be noticed that whilst a device in accordance with the present invention is primarily intended to operate with tubing which is relatively large bored thin-walled tubing as used in the intravenous supply of fluids to a patient, it may be operable using small bore thick-walled tubing as used in clinical analysis although, as previously mentioned, the known device shown in Figure 1 operates satisfactorily with such tubing. The invention is further described with reference to Figure 2 of the accompanying drawing which shows a transverse section through one device in accordance with the present invention for detecting the presence of air in tubing forming part of a fluid flow system for the intravenous supply of fluid to a medical patient. Referring to Figure 2, the device consists of a body including a body member 12 having a passage 13 passing therethrough in which may be accommodated a length of transparent big bore thin-walled p.v.c. tubing 14. Tubing 14 has an internal diameter of 3.0mm and an outside diameter of 4.1mm. Passage 13 is of diameter 10mm. The body includes a spacer located within said passage 13, the spacer being in the form of a collar 15 of material chosen to be a good optical match with the material of the tubing 14. In this case the material of the collar 15 is acrylic. The collar 15 defines a gap 16, which receives the tubing and the collar surrounds the gap 16 and the tubing 14, save for a slot 17, aligned with the gap 16 and of width sufficient for the tubing 14 to pass through to the gap 16. The slot 17 has a similar width to the gap 16 and extends longitudinally through the top (as viewed) of the passage 13. The slot 17 enables the tubing 14 readily to be slotted into position in the gap 16 and removed after use. Extending into the body member 12 from its base and right-hand side (as viewed) respectively are two circular-cylindrical passages 18 and 19 in which are located respectively an infra-red receiver 20 in the form of a phototransistor and an infra-red transmitter 21 in the form of an LED. Circular-cylindrical passages 18,19 are orthogonal to each other and exit via apertures 22,23 respectively into tubing passage 13. The openings of apertures 22,23 in tubing passage 13 are covered by the outer surface of the collar 15. In this particular example the receiver and transmitter apertures 22,23 are not of the same diameter. The diameter of transmitter aperture 23 is one half that of receiver aperture 22. With an arrangement as described above and utilising for infra-red transmitter 21 a type TSTS 7202 LED and for infra-red receiver 20 a type BPW 77B and with receiver and transmitter apertures of diameter 3.0mm and 1.5mm respectively, a test corresponding to that described earlier in reference to Figure 1 provided an indication of 0.3 volts when the fluid passage through tubing 14 was distilled water; 1.2 volts when the fluid was semi-skimmed milk; 1.2 volts when the fluid was a 20% intralipid solution and 4.0 volts when air passed through. It will be recalled that with an arrangement generally as illustrated in Figure 1 but adapted dimensionally to accept relatively large bore, thin-walled tubing such as tubing 14 in Figure 2 in contrast provided a change in output in the presence of air which was insufficiently marked to be useful in the terms of "air-in-line" detection.

Claims: A device for detecting the presence of air in fluid conducting translucent or transparent tubing (14), comprising a body (12,15) providing a gap (16) for accommodating said tubing, a light energy transmitter (21) for transmitting light energy towards said gap (16) and a light energy receiver (20) for receiving from said gap light energy transmitted by said transmitter and modified in use by changes in the consistency of fluid passing through said tubing, characterised in that the body includes an optical spacer (15) defining said gap and occupying space between said light energy transmitter (21) and said gap (16) and between said gap (16) and said light energy receiver (20). A device as claimed in Claim 1 and wherein said light energy transmitter (21) and said light energy receiver (20) are operative in the infra-red spectrum. A device as claimed in Claim 1 or 2 and wherein said transmitter is an LED and said receiver is a phototransistor. A device as claimed in Claim 1 or 2 wherein the body comprises a body member (12) having a passage (13) therethrough for accommodating said tubing, said optical spacer (15) is in the form of a collar within said passage, and said light energy transmitter (21) and said light energy receiver (20) are housed in said body member (12). A device as claimed in Claim 4, wherein said light energy transmitter (21) and said light energy receiver (20) are located in passages (19,18) extending through said body member (12) and opening into said tubing accommodating passage (13). A device as claimed in Claim 5, wherein said transmitter and receiver passages (19,18) open into said tubing accommodating passage (13) via respective apertures (23,22). A device as claimed in Claim 6, wherein said apertures (23,22) are in a wall of the body member (12). A device as claimed in Claim 6, wherein said apertures are in plugs inserted in said transmitter and receiver passages (19,18). A device as claimed in Claim 7 or 8, wherein said apertures (23,22) are of different sizes. A device as claimed in Claim 9, wherein said aperture (19) through which said transmitter (21) communicates is of smaller cross-sectional area than the aperture (18) through which said receiver (20) communicates. A device as claimed in Claim 10, wherein said apertures (23,22) are of circular cross-section, with the diameter of the aperture (19) through which said transmitter (21) communicates at least half the diameter of the aperture (18) through which said receiver (20) communicates. A device as claimed in any one of Claims 5 to 11 and wherein said transmitter (21) and receiver (20) are spaced around said tubing accommodating passage (13) with the principle optic axes lying in the same transverse plane. A device as claimed in any one of Claims 5 to 12, wherein said transmitter (21) and receiver (20) are arranged with their principle optic axes orthogonal one to the other. A device as claimed in any of the Claims 5 to 13, wherein said tubing accommodating passage (13) and said optical spacer (15) are of circular cross-section. A device as claimed in any preceding claim, wherein said optical spacer has a linearly extending slot through which said tubing may be slotted into said gap. A device as claimed in any preceding claim, wherein the material of the optical spacer is acrylic. Intravenous fluid supply apparatus comprising a device according to any preceding claim and including translucent or transparent tubing (14) received in the gap (16), the material of the optical spacer (15) being optically matched to the material of the tubing (14). Apparatus as claimed in Claim 17, as appendant to Claim 14, wherein the diameter of said tubing accommodating passage (13) and the outer diameter of the optical spacer are between twice and three times the outside diameter of said tubing. Apparatus as claimed in Claim 18, wherein the diameter of said tubing accommodating passage (13) and the outer diameter of the optical spacer (15) are 2.5 times the outer diameter of said tubing (14).

Inventors: BRUNDLE ALAN, DANBY HAL, BRUNDLE, ALAN, DANBY, HAL
Applicants: BAXTER INT, BAXTER INTERNATIONAL INC.
Application year: 1991
Main classification: A61M5
IPC codes: A61M5, G01N21