Note: Descriptions are shown in the official language in which they were submitted.
wo 95/21374 2 1 ~ 7 5 8 2 Pcr/usss/0l424
DUAL SENSOR AIR-IN-I,I~E DETECTOR
Field of the Invention:
S This invention relates to devices for tletecting gas, e.g. air or air bubbles,in fluid con~lucting tubing and in p~rticular in fluid con~llJctin~ tubing
forlTlin~ part of a fluid flow system utili7~ for the intravenous supply of
fluid to a meAiC~l p~ti~l~t
10 Discussion of Bac~ d:
Typically ll~l~a~cl~t walled p.v.c. tubing is employed in systems as last-
mentioned bec~nse it is hygienic and cheap it being common practice to
change and discard the length of tubing in use frequently. A known
15 arrangement for use in clini~l analysis and capable of ~etecting air in
tubing utili7~s a device as illusl,~ted in transverse section in Figure l of
the acco~ yi"g drawings.
R~fç~rin~ to Figure l, the known device inc~ es a body member 1 having
20 a passage 2 p~ing thel~tlllough in which may be ~ccornmodated a length
of tran~ar~nt 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. Fxt~n-lin~ into the body l from its base and
right-hand side (as viewed) l~"peclively are two circular-cylindric~l
25 passages 4 and 5 which are orthogonal to each other and exit via a~l Lul~,s
6, 7 respectively into tubing p~cs~ge 2. ~ oc~t~ in circular cylinclric~l
passage 4 is an infra-red receiver 8 (a phototransistor) which receives
infra-red energy tr~n~mitte~ by an infra-red tr~ lr~ 9 (an LED).
30 In operation the output level of receiver 8 depends upon the nature of the
W O 95/21374 21 5 7~ 82 PCTrUS95101424
i ~ . .. . .
fluid p~ing through the tubing 3 past receiver 8 and tr~n~mitt~-r 9.
Difr~r~ fluids will result in different output levels with a si~nifir~nt
change if a gas, e.g. air, is ~r~selll. For example, in a test a voltmeter 10
co~ P~lecl to the output of a suit~ble ~ietector circuit 11 was found to
S in~ t~ 0.1 volts when the fluid p~sins~ through tubing 3 was ~i~till~A
water; 0.2 volts when the fluid was semi-skimm~l milk; 1.4 volts when
the fluid was a 20% intralipid solution and 4.2 volts when air passed
through.
10 While not a ~ y function of a clinir~l analyzer, a device as shown in
Figure 1 will therefore operate as a detector of air p~in~ through tubing
3. Ho~ t;l, as is l~r~sel-~ed, p.v.c. tubing typically used in a clinir~l
analyzer is small bore thick-walled tubing with an outside ~i~meter of
2.5mm and an inside ~ meter of O.9mm. In the intravenous supply of
15 fluids to a patient however, the standard p.v.c. tubing used is of relatively large bore and thin walled having an outside ~ et~ of 4mm and an
inside rli~mpter of 3.1mm.
EA~1111e11lS have been carried out in con~e~;lion with the det~oction of air-
20 in-line with a device generally as ill~:ilrated in Figure 1, but adapted
ionally to accept the relatively large bore, thin walled tubing
l.~tili7Yl for the intravenous supply of fluid to a patient but the results
achieved were not s~ti~f~ctory~ Particularly bearing in mind the critical
importance of ~et~.cting air-in-line in such applications, the changes that
25 took place in the output of the receiver c~ ,s~onding to receiver 8 in
Figure 1 were inmffici.o.ntly m~rk~l for the device to be regarded as useful
in this connection However, further e~ ..P.nt~tion led to the
intro~uctio~ of an optical spacer between the ll~ c. and the tubing,
and ~e tubing and the receiver and with this, markedly il~roved results
30 were achieved.
wo 95/21374 2 1 5 7 5 8 2 PCT/US95/01424
Such an optical spacer is known from EP-A-0481656, which discloses a
deYice for ~let~cting the presence of air in liquid con~lucting, tr~n~lu~ent
or ttar,s~alenl tubing, the device co~ ing a passage for ~ccol.. odating
of said tubing, a l~ er for tr~n~mitting radiation (in this case, light)
5 towards said passage; a receiver for receiving radiation from said passage
which has passed through the tubing, the receiver being operable to
produce an output signal (i) when air is plcsenl in the tubing and/or (ii)
when the dilution ratio of the liquid in the tubing is below a first
predet~lnlil.ed threshold; and proces~ing means. The ~loces~ g means
10 proc~es said output signal to provide an in-lic~tion that air is ~l-,se-ll inthe tubing. Hence, the device tends to make a false detection that air is
present in in~t~nces define~ in (ii) above.
Claim 1 relates to an improvement of the device of EP-A-0481656,
15 wherein the improvement comprises means for eli...i..A~ false ~let.~ctionc
made by the receiver, that gas is present in the tubing, and comrrising
means (iii) a second receiver for receiving from said p~S~ge r~ tion
which has passed through said tubing, the second receiver being operable
to produce an output signal when gas is ~reselll in the tubing, the second
20 receiver m~king false detections under lirrt;lc;nt liquid conditions from the
first receiver, and (iv) proces~in~ means opelati~ely connPct~ to both
receivers to receive said output signals to provide an intlic~tion that gas is
present in the tubing only when the output signals from both receivers are
Se,.l~.
Preferably the tl~s~ lfr and receivers are respectively a light energy
tr~..~...;l~er and light energy receivers and are all o~e,~livt; in the infra-red
spectrum, and preferably the tr~n~mitter is a LED (light emitting diode)
and the receivers are phototr~n~i~tors.
WO95/21374 21 5 75 8 ~ PCT/US95/01424
Preferably, the device includes an optical spacer defining said passage and
occupying space between said passage and said tr~ncmi~ter and between
said p~cs~Ee and said receivers, the optical spacer comrri~ing a cylindrical
C1~P~I~P~I~ having a ~iP-lectric co":i~nL g1eater than that of air, said tubing
S passage e~rtPnrling along a lon~itl~lin~l axis of the cylintlTic~l eltoment for
~coInmodating said tubing in intim~te contact with said cylin~ iC~l n
ÇlF .~F.I~t
r~ bly,the optical spacer is in the form of a collar ~u11o.~ linE the
10 tubing, the L~ and the receivers being housed in the body.
P~,f~ly the tr~ and the receivers are located in passages
ekl~ndillg through the body and opening towards the tubing
acco."lllodating passage.
1~ Normally the ~.~....Il~,r and receiver locating passages open lo~ r~s the
tubing accommodaLillg passage via respective apc1~u,es. The a~11u,~s
may be in fixed walls, integral wi~ the body, which otherwise close the
passages or in plugs ins~l~d in the passages otherwise to close the same.
20 The a~JG~ Lur1s may be of dirr~ sizes chosen to provide o~Li",ulll effect
in any given device. Commonly, the a~e1lu,~, through which the
lln.-~ ,r co.. ~ ir-~tes will be of smaller cross-sectional area than the
a~1Lu~Gs through which the receivers comm-lni~te. In one embo~imt~-nt
wherein the ~c.lLIrcs are of circular cross-section, the diameter of the
25 apc1lu-e through which the tr~ncmitter communicates is at least
approxim~t~ly half the diameter of the ~C1lu1Gs through which the
receivers communic~t~.
P~ bly the lr~..s..~;tl.,r and receivers are spaced around the tubing
30 accomlllodating passage, prl_fGr~ly with their principle optical axis in the
WO 95/21374 2 1 5 7 ~ 8 2 PCT/US9~/01424
same transverse plane. Preferably again the receivers are arranged with
their prinriple optic axes orthogonal one to the other. Where the axes lie
in the same transverse plane it may be found that s~ticf~r-tory results are
obtained with the optic axes at some relative angle other than 90 but it
5 is believed that o~Li--,u-l- results are obtai,lcd when the axes are orthogonal
one to the other. Again, spacing the LIA~ and receivers along the
length of the tubing accommodating passage may be found to give
s~ticf~rtory results but arranging the l~ ;ller and receivers such that
their l";,lr;ple optic axes are spaced around ~e tubing accommodating
10 passage is believed to provide optimum results. The tubing used in the
illLIa~,.,.lOus supply of fluids to a patient is of course of circular cross-
section and therefore for this application the tubing accommodating
passage is normally of circular cross-section.
15 Typically the outer ~ meter of the optical spacer, when pl~ scnl, will be
bet~ twice and three times the outside rli~metp-r of said tubing. In a
ell~d embo~ f-l-~ the outer rli~met~r of the spacer is 2.5 times the
outer ~ te~ of the tubing. r~ c~c.~bly the l~An~"~ and receivers are
discrete devices and pfc~bly an LED (light emitting diode) and
20 phototli~nc;~ respectively. Norrnally such co,ll~onenls are generally
circular-cylindrical in overall outline and accor~ingly, the tr~ncmit~er and
receiver p~Cc~ges are normally circularly cylintlriç~l. In order to simplify
the insertion and removal of the tubing, ~rcfe~ably the tubing
aCco~ o~ting passage has a linearly e~ct~ ing slot through which the
25 tubing may be slotted.
The m~teri~l chosen for the optical spacer, when present, should have a
~lie~ectric coll~lalll which is an optically reasonable match to the ma~erial
of said tubing. Preferably the material is acrylic.
WO 9St21374 2 1 5 7 ~ ~ 2 ` PCTrUS95/01424
In a preferred embo~limrnt the ll~n~n~ fr projects a light beam to the
fluid con~ucfing tube and ligh~ receivers in the form of a pair of sensors
disposed perpen~lir~ rly to each other o~te in opposite modes such that
if an air bubble is ~r se.,l in the line the ~letector will be able to reliably
5 distinguish this cit~-~tion from the case where there is no air bubble. One
sensor is disposed 90 from the optical axis of the Ll~n~ln;~ while the
other sensor is disposed 180, ie., along the tr~ optical axis.
Light beams projected from the L~ er are incident on the tubing and
are thus reflected or Li~ ...;ll~ d~en~ g upon the ch~r~cterictics of the
10 fluid (eg., the opacity of the Ruid and/or dilution ratio of the fluid) and
also upon the presence or absence of air or air bubbles in the line. The
two ~~ lic~ -ly disposed se.lsols provide oulpuls in~lir~tive of the
amount of light received. A processor determines the presence or absence
of air in the line based on the combination of the o~l~uLs of the two
15 se-~o,~. When the oul~u~ of both SenSGl:j are high, the processor
d~,t~,~...i.-r~ that air is lJr~s~lll in the line, v~l,e.~as if one of the two
sel~ols' outputs is low, the pl~,`ces~ g device deLel.l-i--es that no air is
plese.lt in the line. With this arrange...enl, both sensor outputs are used
in order to del~l,.,ine the presence or absence of air or air bubbles in the
20 fluid con~ucting tubing, thus providing a reliable det~ction ~aLus
regardless of the initial calibration of the sensols and IlA.~ ler.
-
Brief Description of the Drawings
25 Figure 1 is a cross-sectional view of a conventional device for ~et~cting
air in tubing;
Figure 2 is a transverse cross-sectional view of the device ~ close~ in
EP-A-0481656 for ~etecting the presence of air in tubing forming part of
30 a fluid flow system for the intravenous supply of fluid to a m~ic~l
~ 21~7~82 -
WO 95t21374 PCT/US95/01424
p~ti~ nt
Figure 3 shows an arr~ng4...~ of an embodiment according to the ~l. sent
invention wherein a single IIA..~ el and a pair of sensors which are
S provided perpen~lir -l~rly to each other are shown;
.
F~gure 4 illu~ les the output of sensor 20a shown in Figure 3;
Figure 5 shows the output of sensor 20b shown in Figure 3;
Figure 6 illu~Llales a graph of the values shown in Table 1 for a Ubest
calibrationn case;
Figure 7 is a graph of the values of Table 1 for the worst case
lS calibration; and
Figure 8 is a circuit diagram illustrating the relationship between the
lln~ and se.-~o~ ~ of Figure 3.
20 Description of the Plerelç~d Embodiments
RP-f~rrinE-now to the drawings, wherein like reference numerals ~esign~te
i~ntic~l or co~ ,yonding parts throughout the several views, and more
partir -l~rly to Figure 2 thereof, a device as ~licçlose~ in EP-A-0481656
inrludes a body member 12 having a tubing accorl.ll,odating passage 13
passing the.Glllrough in which may be accGIIllllodated a length of
Llanspalelll large bore thin-walled p.v.c. tubing 14. Tubing 14 has an
internal di~mçter of 3.0mm and an outside ~ me~ter of 4.1mm. Passage
13 y~ y has a ~ meter equal to lOmm. ~-oc~tçd within passage 13
30 is an optical spacer 15 of material chosen to be a good optical match with
; ~ ~ r ~ ~ ~
WO 95/21374 21 5 7 S 8 2 PCT/US9S/01424
the material of the tubing 14. In this case the material of the optical
spacer 15 is acrylic. The optical spacer 15 sull~ullds the tubing 14 save
for a gap 16 which is of width sufficient for the tubing 14 to pass through.
Gap 16 is ~lign~d with a slot 17, of similar width, e~ten~ling longit~-din~lly
S through the top (as viewed) of the passage 13. The slot 17 and gap 16
enable the tubing 14 to be readily slotted into position and removed after
use. F~cterl~ling into the body 12 from its base and right-hand side (as
viewed) respectively are two circular-cylindrical passages 18 and i9 in
which are located respectively an infra-red receiver 20 in the form of a
10 phototr~n~i~tor and an infra-red tr~n~mitter 21 in the form of an LED.
Circular-cylinrln~l passages 18, 19 are orthogonal to each other and exit
via a~l~ures 22, 23, respectively, into tubing acco,lllllodating passage 13.
The oper~ing~ of a~elLul~s æ, 23 in passage 13 are covered by the outer
s~ re of optical spacer 15. In this particular example the receiver and
15 ~ f a~llur~,s 22, 23 are not of the same ~ mtott r. The fli~meter
of ~ .r a~,lul~, 23 is one-half that of receiver a~cllul~ æ.
With an arrangement as descrihed above and ~Itili7ing for infra-red
tln.lc..-;llef 21 a type TSTS 7202 LED and for infra-red receiver 20 a type
20 BPW 77B and with receiver and tr~t~ er a~ures of rli~m~ottor 3.0mm
and 1.5mm respectively, a test corresponding to that described earlier in
r~f~ ce to Figure 1 provided an indication of 0.3 volts when the fluid
passage through tubing 14 was .listi~ water; 1.2 volts when the fluid
was semi-skimmPA milk; 1.2 volts when the fluid was 20% intralipid
25 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
p1esG.,ce of air which was insufficiently marked to be useful in the terms
30 of "air-in-line" detection.
WO 95/21374 2 1 ~ ~ 5 ~ 2 PCT/US95/01424
An embodiment of the ylese~ll invention will now be described with
reference to Figure 3 of the accompanying drawings. In this embodiment
an additional sensor 20b is provided along the longih-~lin~l axis of
C~ cr 21 at a 90 angle to sensor 20a. As shown in Figure 3,
S inr~ d LED l~ er 21 of type TS 7302, for example, is provided for
projecting a beam of light to fluid con(lucting tubing 14. The
photoll~ tors 20a, 20b of type BPW 77, for e~mrle, also o~ale in
the il~ ;l spectrum wherein sensor 20a is provided at a right angle to
the direction of inr;~en~e of the light beam from the L~ ...;tl~, while
10 sensor 20b is provided along a path parallel to the direction of light beam
inr;denfe, ie., at a 180 angle. A tra..:j~ar~nl optical spacer 15 which
may be of acrylic .~ cl.~l, for example, is also provided within a tubing
accol...uodating passage 13 in the body member 12 for holding the large-
bore thin-walled tubing 14.
The ILAII!I~ and first and second energy receivers are loc~t~A in
respective passages which extend through the body member and open into
the tubing acco-l----ol~ting passage. A~LUrGS 22, 23, 24 are shown
which connect the tubing acco...---odating passage with each of the
20 r~sye~cLi~fe passages provided for the ll~n~...;llPi and receivers. The
a~llules may be of dirr~ L sizes for each of the receivers and
,r or, alternatively, may be the same size for two of these
elPmPntc and of a dirr~,r~ t size for the third cle~..e.lL. Also, the
e~ ~y~lLulG may be of smaller cross-sectional area than the
25 ay~lulG through which light is received by the first and second receivers.
In a yl~rell~d embodiment, the ayel Ll11GS are of circular cross-section with
the ~ meter ofthe a~lL.~ through which the tr~ el Lli~ ...itC light
being aypl~o~ Ately 1.5 times g~akr than the (li~meter of the apertures
through which the first and second receivers con~ icate with the tubing
30 aCconlmo~ting passage. However, the invention is not limited to such a
WO 95/21374 21 5 7 ~ 8 2 PCT/US95/01424 ~
~, i;,; .
circular cross-sectional shape for the ~lur~s. A suitable ~ m~t~r for
the optical spacer is between 2 and 3 times larger than the outer ~ mPter
of the large-bore thin-walled tubing. A preferred outer ~ m~-t~r of the
tubing ~ccommo-l~ting passage is ~ t~ly 2.5 times greater than the
5 outer di~meter of the tubing.
With the arr~n~...e.-~ of the tr~n~mitt~-r and sensors shown in Figure 3,
the voltage oul~uls provided by se-n~ors 20a and 20b are as shown in
Figures 4 and 5. As ~lisc~lssed above, using the output of sensor 20a
10 alone will provide s~ti~f~ctory results provided that the calibration of the
sm;ller and sensor is within a predetermined range. However, as
shown in the worst case calibration illustrated in Figure 7, the output
of sensor 20a at a dilution ration of 9/1 for a 20% intralipid solution may
be equal to the calibrated output of sensor 20a, ie., the air setting value.
15 Since this air setting value may be the same as the output when an air
bubble is ~r,senl in the line, the device shown in Figure 2 of the dl~wings
(which only uses sensor 20) will be unable to distinguish between the
~r~ sence of an air bubble in the line and the case where no air bubble is
~ç~sent. With the device illustrated in Figure 3, on the other hand, even
20 in the worst case calibration situation, the detector will be able to
distinguish between an air bubble and the absence of an air bubble at any
dilution ratio due to the use of the second sensor 20b which operates in an
opposite mode from that of sensor 20a. In other words, at low dilution
ratios such as a~lok;m~tely 10/1, for example, the output of sensor 20b
25 will be low, when the output of sensor 20a is high. Similarly, when the
dilution ratio is high, the output or sensor 20b will be high while the
output of sensor 20a will be low.
It is in~olLallt to note that for either sensor when an air bubble is ~l~,sellt
30 in the line the output of each of the sensors will be high, ie., will be equal
WO 95/21374 215 7 5 8 2 PCT/US95/01424
to the air setting or calibration value. Thus for the situation when an air
bubble is ~l-,senL in the line and the dilution ratio is such that the output
of sensor 20a is subst~nti~lly equal to the output of sensor 20a for the case
when an air bubble is yrcsellt~ the output of sensor 20b will also be high
5 (3 volts) and equal to the air setting value. In this m~nner, the detector
device accor~ling to the ~reSe~lt invention will be able to reliably detect
when an air bubble is in fact ~r~sellt in the fluid con~cting tubing. On
the other hand, if no air bubble or bubbles are ylesen~ the output of
sensor 20a may be high but the output of sensor 20b will be low, thereby
10 inrli~ting that no air bubbles are present.
The results of the experim~nt~l data are shown in the following table.
Table 1
Worst case Best case
Dilution Sensor20a Sensor20b Sensor 20a Sensor20b
Intra 100% 2.04 0.01 1.27 0.01
2:1 2.61 0.02 1.87 0.02
4:1 3.87 0.14 2.44 0.04
8:1 4.15 0.01 2.70 0.1
10:1 3.16 0.24 2.57 0.15
16:1 3.99 0.07 2.53 0.12
20:1 3.55 0.18 2.20 0.22
30:1 2.34 0.52 1.73 0.41
40:1 2.34 0.48 l.SS 0.57
50:1 1.95 0.62 1.30 0.82
60:1 1.81 0.74 1.3i 0.65
70:1 1.55 0.97 1.13 0.84
WO95/21374 21 5 7 5 8 2 PCT/US95/01424
80:1 1.30 1.30 1.08 0.91
90:1 1.10 1.60 0.87 ~ 1.25
100: 1 0.99 2.00 0.70 1 .90
500:1 0.68 4.74 0.46 4.71
1000:1 0.58 4.76 0.48 4.77
The results of the prece~in~ Table 1 are illustrated graphically in figures
6 and 7 of the accol~,pallying drawings. Figure 6 shows the best
calibration results, ie., the calibration of output sensors such that the
10 ou~put of sensor 20a does not intersect the output of sensor 20a for an air
set~in~ ie., 4.0 volts. However, as shown in figure 7, for worst case
calibration the output of sensor 20a at relatively low dilution ratios may
be the same as the output of sensor 20a for the air setting case, and also
the cæe when an air bubble is ~l~se,ll in the fluid line. HoweveL, using
15 the two sensors together, the situation when no air bubble is present can
be eæily deterrnined since the output of sensor 20b will be low at the
point where the output of sensor 20a is close to the air setting value. If,
on the other hand, an air bubble is p~sel-t in the line, both sensors 20a
and 20b will inr~ te high outputs which will never be the case when air
20 is not ~resenl in the line. The results can be summ~rized in the following
table.
Table 2
FLUID SENSOR20a SENSOR 20b
Air High High
Water Low High
Dense Fluid Low or High Low
21~82
WO 95/21374 ~ PCT/US95tO1424
Figure 8 illustrates the circuit diagram arrangement of the tr~nsmitt~r and
. SenSGl~ of Figure 3. As shown, the tr~n~mitttq.r 21 is connected in serie
with a resistor R, equal to 100 ohms in a preferred embodiment, and is
conn~cteA. between a 5 volt source and ground. Also, it should be noted
5 that the angle between the light beams received by sensor 20a and those
received by sensor 20b is equal to 90 since the sensors are at right angles
to each other, and thus the angle illustrated in Figure 8 is not to be
considered the actual angle between sensors 20a and 20b. Output
l~ni~lals 32, 31 of sensols 20a, 20b rGs~ccli~ely~ are connect~A to ground
10 through 200 Kn variable resistors R2, R3, respectively. The outputs of
sensors 20a, 20b are input to a processing device 33 which delel,l,ines the
presence or absence of air in the tubing 14 and oul~uls ~yl~liate signals
to a display device (now shown). Proces.sing device 33 outputs a first
signal when the outputs of sensors 20a and 20b are both high, a second
15 signal when the output of sensor 20a is low and sensor 20b is high
(inAir~ting water or a highly low diluted solution), and a third signal
~I,e~ er the output of sensor 20b is low (indic.~ting a dense fluid at low
dilution). The proc~ssing device 33 may incll~de a microprocessor
o~ali.lg under program control for gcne~ati.lg the ~pr~liate output
20 signals colrespollding to the oul~llls received from the sensors 20a, 20b
thereby inr~ir.~ting the ~l~sence or ~l~se~ce of air in the line.
Alte~ ely, the proces~;ng device 33 may inrluAe discrete logic CilCuilS
for receiving the outputs of the light receivers and generating the requisite
outputs.
