U.S. patent application number 10/033387 was filed with the patent office on 2002-05-09 for oral/nasal cannula.
Invention is credited to Brown, Sanford, Colman, Joshua L., Levitsky, Gershon.
Application Number | 20020055685 10/033387 |
Document ID | / |
Family ID | 11071162 |
Filed Date | 2002-05-09 |
United States Patent
Application |
20020055685 |
Kind Code |
A1 |
Levitsky, Gershon ; et
al. |
May 9, 2002 |
Oral/nasal cannula
Abstract
A nasal/oral cannula for the collection of exhaled gases from
the nostrils of a patient, made up of two nasal prongs for
insertion into the patient's nostrils and a collection tube for the
collection of the exhaled gases, the nasal prongs and the
collection tube being connected at a single junction, such that the
exhaled gases flow freely from the nasal prongs to the collection
tube. An oral prong can also be provided, whose end is placed near
the oral cavity of the patient, the oral prong too being connected
at the single junction of the nasal prongs and the collection
tube.
Inventors: |
Levitsky, Gershon;
(Jerusalem, IL) ; Colman, Joshua L.; (Jerusalem,
IL) ; Brown, Sanford; (Jerusalem, IL) |
Correspondence
Address: |
MORGAN & FINNEGAN, L.L.P.
345 Park Avenue
New York
NY
10154-0053
US
|
Family ID: |
11071162 |
Appl. No.: |
10/033387 |
Filed: |
December 26, 2001 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
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10033387 |
Dec 26, 2001 |
|
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09239119 |
Jan 28, 1999 |
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Current U.S.
Class: |
600/543 ;
128/207.18; 600/529 |
Current CPC
Class: |
A61M 2210/0625 20130101;
A61M 16/0666 20130101; A61B 5/0836 20130101; A61B 5/682 20130101;
A61M 16/0833 20140204; A61B 5/097 20130101; A61B 5/6819 20130101;
A61M 16/0672 20140204; A61B 5/083 20130101; A61M 2230/432 20130101;
A61M 16/085 20140204 |
Class at
Publication: |
600/543 ;
128/207.18; 600/529 |
International
Class: |
A62B 007/00; A61M
015/08; A61B 005/08; B65D 081/00 |
Claims
1. A nasal cannula for collection of exhaled gases from a patient
having nostrils, comprising: two nasal prongs for insertion into
the nostrils of the patient; and a collection tube for the
collection of the exhaled gases from the patient, said nasal prongs
and said collection tube being connected at a single junction, such
that the exhaled gases flow freely from said nasal prongs to said
collection tube.
2. The cannula of claim 1, wherein said nasal prongs are joined in
an arc substantially before being connected to said junction.
3. The cannula of claim 1, wherein said collection tube delivers
said exhaled gases to a capnograph for gas analysis.
4. An oral/nasal cannula for collection of exhaled gases from a
patient having nostrils and an oral cavity, comprising: two nasal
prongs form insertion into the nostrils of the patient; an oral
prong for placement near the oral cavity of the patient; and a
collection tube for the collection of the exhaled gases from the
patient, said nasal prongs, said oral prong and said collection
tube being connected at a single junction substantially near the
nostrils of the patient, such that the exhaled gases flow freely
from said nasal prongs and said oral prong to said collection
tube.
5. The cannula of claim 4, wherein said oral prong features a
distal portion, said distal portion being bent at an angle such
that it is placed near the oral cavity of the patient,
substantially in parallel to the orally exhaled air stream.
6. The cannula of claim 5, wherein said distal portion features a
cap, said cap being attached to said distal portion, and said cap
being made of a substantially hydrophilic material, such that said
cap absorbs condensation from said distal portion.
7. The cannula of claim 4, wherein said nasal prongs are joined in
an arc substantially before being connected to said junction.
8. The cannula of claim 4, wherein said collection tube delivers
said exhaled gases to a capnograph for gas analysis.
9. The cannula of claim 1, and further comprising: at least one
oxygen tube for delivery of oxygen, said at least one oxygen tube
being located near the nostrils of the patient; and two oxygen
inlets connected to said at least one oxygen tube and being
disposed such that said oxygen flows from said at least one oxygen
tube through said oxygen inlets into the nostrils of the
patient.
10. The cannula of claim 9, wherein said at least one oxygen tube
includes a centrally located input, substantially equidistant from
said two oxygen inlets for receiving oxygen.
11. The cannula of claim 9 wherein said at least one oxygen tube
comprises two oxygen tubes, one disposed on each side of said two
oxygen inlets.
12. The cannula of claim 9, wherein said oxygen inlets are
holes.
13. The cannula of claim 4, and further comprising: at least one
oxygen tube for delivery of oxygen, said at least one oxygen tube
being located near the nostrils of the patient; and two oxygen
inlets connected to said at least one oxygen tube and being
disposed such that said oxygen flows from said at least one oxygen
tube through said oxygen inlets into the nostrils of the
patient.
14. The cannula of claim 13 wherein said at least one oxygen tube
includes a centrally located input, substantially equidistant from
said two oxygen inlets for receiving oxygen.
15. The cannula of claim 13 wherein said at least one oxygen tube
comprises two oxygen tubes, one disposed on each side of said two
oxygen inlets.
16. The cannula of claim 13 wherein said oxygen inlets are
holes.
17. The cannula of claim 12, wherein said holes include a screen
constructed of a material selected from at least one of the group
consisting of a hydrophobic porous material, a wide mesh and a
netting.
18. The cannula of claim 16, wherein said holes include a screen
constructed of a material selected from at least one of the group
consisting of a hydrophobic porous material, a wide mesh and a
netting.
19. The cannula of claim 9, wherein said inlets are oxygen prongs
for insertion into the nostrils of the patient.
20. The cannula of claim 13, wherein said inlets are oxygen prongs
for insertion into the nostrils of the patient.
21. The cannula of claim 19, wherein said oxygen prongs are formed
of a substantially hydrophobic porous material, such that said
oxygen prongs are permeable to gases.
22. The cannula of claim 20, wherein said oxygen prongs are formed
of a substantially hydrophobic porous material, such that said
oxygen prongs are permeable to gases.
23. A method of collecting exhaled gases from a patient having
nostrils, the method comprising the steps of: (a) providing a
cannula featuring: two nasal prongs for insertion into the nostrils
of the patient; and a collection tube for collecting the exhaled
gases from the patient, said nasal prongs, and said collection tube
being connected at a single junction substantially near the
nostrils of the patient, such that the exhaled gases flow freely
from said nasal prongs to said collection tube; (b) inserting said
nasal prongs into the nostrils of the patient; (c) attaching said
collection tube to a conduit for conducting gas; (d) connecting
said conduit to a gas analyzer; and (e) applying a force at said
gas analyzer, such that the exhaled gases flowing through the
cannula moves from said collection tube to said gas analyzer.
24. A method of collecting exhaled gases from a patient having
nostrils and an oral cavity, the method comprising the steps of:
(a) providing a cannula featuring: two nasal prongs for insertion
into the nostrils of the patient; an oral prong for placement near
the oral cavity of the patient; and a collection tube for
collecting the exhaled gases from the patient, said nasal prongs,
said oral prong and said collection tube being connected at a
single junction substantially near the nostrils of the patient,
such that the exhaled gases flow freely from said nasal prongs and
said oral prong to said collection tube; (b) inserting said nasal
prongs into the nostrils of the patient; (c) placing said oral
prong near the oral cavity of the patient; (d) attaching said
collection tube to a conduit for conducting gas; (e) connecting
said conduit to a gas analyzer; and (f) applying a force at said
gas analyzer, such that the exhaled gases flowing through the
cannula move from said collection tube to said gas analyzer.
25. A cannula for collection of exhaled gases from a patient and
for delivery of oxygen to a patient having nostrils and an oral
cavity, comprising: (a) two nasal prongs for insertion into the
nostrils of the patient; (b) a collection tube for the collection
of the exhaled gases from the patient, said nasal prongs, and said
collection tube being connected at a single junction, such that the
exhaled gases flow freely from said nasal prongs to said collection
tube; (c) an oxygen tube for delivery of oxygen, said oxygen tube
being located near the nostrils of the patient; and (d) two oxygen
inlets connected to said oxygen tube and being disposed such that
said oxygen flows from said oxygen tube into the nostrils of the
patient.
26. The cannula of claim 25 and also comprising an oral prong for
placement near the oral cavity of the patient, said oral prong also
being connected at the single junction of said nasal prongs and
said collection tube.
27. The cannula of claim 25, wherein said oxygen inlets are
holes.
28. The cannula of claim 26, wherein said oxygen inlets are holes.
Description
FIELD AND BACKGROUND OF THE INVENTION
[0001] The present invention relates to a nasal cannula and to an
oral/nasal cannula, and, more particularly, to a nasal cannula and
an oral/nasal cannula which permits both delivery of oxygen and
accurate sampling of carbon dioxide.
[0002] For purposes of description, the discussion herein is
focused on cannulas for use with human patients, it being
understood that the present invention is not limited in scope only
to use with patients and can beneficially be used in various other
contexts.
[0003] Different types of oral/nasal cannulas are used to deliver
oxygen to hospital patients who require assistance to breathe
properly, to collect carbon dioxide samples from patients to
monitor respiration, or to perform both functions. Such cannulas
are used when direct ventilation is not provided. The term
"oral/nasal" refers to the adaptable configuration of such cannulas
which can be in close proximity to the oral cavity or inserted into
the nasal cavity of the patient. In either arrangement, a
sidestream of the patient's exhaled breath flows through the
cannula to a gas analyzer to be analyzed. The results of this
non-invasive analysis provide an indication of the patient's
condition, such as the state of the patient's pulmonary perfusion,
respiratory system and metabolism.
[0004] The accuracy of this non-invasive of exhaled gases depends
on the ability of a sampling system to move a gas sample from the
patient to the gas anaylzer while maintaining a smooth, laminar
flow of gases, such that there are as few alterations to the
waveform and response time of the concentration of the gases as
possible. The Waveform of the concentration of the gas is critical
for accurate analysis. As the gas mixture travels from the patient
to the gas analyzer, the concentration of the gases can be affected
by nixing of the component gases, which reduces the accuracy of the
analysis of the sample by the gas analyzer, and reduces the amount
of information obtained from that analysis.
[0005] Prior art nasal or oral/nasal cannulas unfortunately have
caused significant alteraitions to these important features of the
internal structure of the stream of exhaled gases. Such alterations
have especially arisen as the result of attempts to combine the
delivery of oxygen with the sampling of the exhaled breath of the
patient. For example, the simplest nasal cannula design, consisting
of a tube with two double hollow prongs for insertion into the
nostrils, allows significant mixing of the oxygen which is
delivered from the end of one tube, and the exhaled breath which is
collected from the end of the second tube. Such mixing occurs when
oxygen is delivered in a stream with strong force, so that the
oxygen stream penetrates deeply into the nasal cavity even during
expiration, thereby artifactually altering the composition of the
exhaled gases.
[0006] However, attempts to prevent mixing between delivered oxygen
and exhaled gases have resulted in other alterations to the exhaled
gases. For example, one type of prior art nasal cannula (Salter
Labs. Arvin, Calif. USA) consists of a tube with two openings at
either end, and two hollow prongs projecting pendicularly from the
center of the tube with a partition between them. Oxygen enters the
tube from one end and exhaled breath leaves the tube from the other
end. The two hollow prongs are inserted into the nasal cavity of a
patient, one prong in each nostril, so that oxygen could be
delivered to, and exhaled breath collected from, the patient.
Unfortunately, the reliance of this cannula on a single nasal prong
for collection of exhaled gases does not prevent the strong flow of
delivered oxygen from the other nostril mixing with exhaled gases
deep in the nasal cavity, above the nasal septum. Such mixing of
delivered oxygen with exhaled gases reduces the accuracy of gas
analysis.
[0007] In addition, this type of cannula usually has significant
"void volume", or space in which mixing of gases, and concurrent
alteration of the gas waveform, can occur. Such space is often
referred to as "void volume" because it is not part of the pathway
for the flow of gases and hence is unproductive. For example, void
volume arises in this cannula between the septum dividing the main
tube and the junction of each prong with that tube. The presence of
such void volume is a significant hindrance to the accurate
analysis of exhaled gases. Thus, this prior art nasal cannula has a
reduced efficiency for the collection of exhaled gases for
analysis.
[0008] Another design for a nasal cannula (Hospitak Lindenhurst,
N.Y., (USA) has two parallel overlapping tubes, one for delivering
oxygen and one for receiving exhaled gases. The tube which receives
exhaled gases has two nasal prongs, while the tube which delivers
oxygen has two holes parallel to these prongs. Both tubes have two
holes, such that the gases can flow freely from the prongs to the
holes. This configuration allows delivered oxygen to easily mix
with expired gases, even at the end of the expiration period,
thereby reducing the accuracy of the gas analysis.
[0009] U.S. Pat. No. 5,046,491 discloses another type of nasal
cannula which also includes a first tube with two double nasal
prongs and a septum placed between the prongs. One prong delivers
oxygen and the second prong collects exhaled gases. A second tube
is attached to the first tube and has two holes which are placed in
or near the oral cavity of the patient for collecting exhaled
breath. One problem with this cannula is that the exhaled gases are
collected through two outputs, which are then connected to two
separate tubes. These separate tubes then join together before
delivering the gases to the capnograph. If gases are not flowing at
exactly the same rate through both tubes, for example due to
condensation, then the waveform of the gas concentration is altered
and the results of the analysis are affected. In addition, this
cannula has significant void volume because of the large dimension
of the tubes and because there are two outputs for collecting the
exhaled gases. The large void volume also causes mixing of the
gases. Thus, the cannula of U.S. Pat. No. 5,046,491 does not solve
the prior art problems for accurate gas analysis by nasal
cannulas.
[0010] Furthermore, none of these prior art cannulas is a true
oral/nasal cannula which can be placed in either the oral or nasal
cavities of the patient interchangeably. Such prior art oral/nasal
cannulas, which are described below in the "Description of the
Preferred Embodiments", also have significant problems regarding
the collection of gases for accurate analysis, but offer the
desirable feature of flexibility concerning the respiratory cavity
from which exhaled gases are collected. Patients often alternately
exhale through the nasal cavity and the oral cavity. The advantage
of the oral/nasal cannula is that exhaled gases can be
automatically collected from either cavity. The disadvantage is
that many prior art oral/nasal cannulas are susceptible to the
intake of ambient air through that portion of the cannula which is
not receiving exhaled air. For example, if the patient exhales
through the oral cavity, ambient air can be sucked into the cannula
through the opening provided for the nasal cavity. Such ambient air
can dilute the concentration of gas in the exhaled breath of the
patient, thus giving misleading results for the gas analysis.
[0011] Hereinafter, the term "respiratory cavity" refers to the
oral cavity, the nasal cavity, or both cavities, of a patient.
[0012] In addition, the effectiveness of oxygen delivery by a
cannula is determined by two principles, neither of which is
completely fulfilled by prior art cannlulas. The first principle is
that the distribution of the delivered oxygen stream should be
equal between the two nostrils of the patient. In most prior art
cannulas, one nostril receives 1.2-2.0 times as much oxygen as the
other. However, an equal distribution of oxygen is preferable for
the following reasons. First, if one of the nostrils is blocked,
the second will continue to deliver oxygen. Second, even flow rates
for both nostrils will not cause the patient to feel excess
pressure in one nostril, even at high flow rates for the delivered
oxygen. Third, producing even flow rates through the presence of
oxygen "clouds" near the nostrils of the patient will cause such
"clouds" to be the same size at both nostrils, and will permit the
more effective use of ambient oxygen present near the nostrils
before the inspiration phase.
[0013] The second principle is that the oxygen stream should be
delivered at a relatively slow rate, rather than being forced into
the nostrils at a high rate, for the following reasons. First, an
oxygen stream which is delivered at a slows rate will not penetrate
deeply into the nostrils of the patient and so will not be
collected during the exhalation phase, thereby preventing
distortion of the carbon dioxide measurements because of dilution
of the exhaled gases. Second, the patient will feel more
comfortable since the oxygen stream will not be so forceful.
[0014] If both principles are fulfilled, then oxygen delivery and
analysis of exhaled gases will be optimized. Unfortunately, many
prior art cannulas fail to implement these principles and are thus
lacking in this respect.
[0015] There is thus a widely recognized need for, and it would be
highly advantageous to have, a cannula which does not alter the gas
waveform, which does not easily become blocked or clogged, which
has minimal added void volume, and which can deliver oxygen without
disturbing the waveform of exhaled gases, yet which has the
flexibility and adaptability of an oral/nasal cannula.
SUMMARY OF THE INVENTION
[0016] According to the present invention there is provided a nasal
cannula for collection of exhaled gases from a patient having
nostrils, comprising (a) two nasal prongs for insertion into the
nostrils of the patient; and (b) a collection tube for the
collection of the exhaled gases from the patient, the nasal prongs
and the collection tube being connected at a single junction, such
that the exhaled gases flow freely from the nasal prongs to the
collection tube. Preferably, the collection tube is a single
collection tube. Also preferably, the nasal prongs are joined in an
are substantially before being connected to the junction.
Preferably, the collection tube delivers the exhaled gases to a
capnograph for gas analysis.
[0017] According to another embodiment of the present invention,
there is provided a cannula for collection of exhaled gases from a
patient having nostrils and an oral cavity, including: (a) two
nasal prongs for insertion into the nostrils of the patient; (b) an
oral prong for being located proximately to the oral cavity of the
patient; and (c) a collection tube for the collection of the
exhaled gases from the patient, the nasal prongs, the oral prong
and the collection tube being connected at a single junction
located substantially near the nostrils of the patient, such that
the exhaled gases flow freely from the nasal prongs and the oral
prong to the collection tube. Preferably, the collection tube is a
single collection tube. Also preferably, the oral prong features a
distal portion, the distal portion being bent at an angle. More
preferably, the angle is about 90 degrees, such that the distal
portion is located proximately to the oral cavity of the patient.
Most preferably, the distal portion features a cap, the cap being
attached to the distal portion, and the cap being made of a
substantially hydrophilic material, such that the cap absorbs
condensation from the distal portion. Also preferably, the nasal
prongs are joined in an arc substantially before being connected to
the junction. Preferably, the collection tube delivers the exhaled
gases to a capnograph for gas analysis.
[0018] According to preferred embodiments of the present invention,
the cannula further includes (d) an oxygen tube for delivery of
oxygen, the oxygen tube being located near the nostrils of the
patient; and (e) two oxygen inlets connected to the oxygen tube and
being disposed such that the oxygen flows from the oxygen tube into
the nostrils of the patient.
[0019] Preferably, the oxygen tube is located either above or below
the nostrils of the patient. Also preferably, the oxygen tube
includes a centrally located input for receiving oxygen being
placed substantially equidistant from both oxygen inlets.
Preferably, the oxygen inlets are holes. More preferably, the holes
have an first diameter at an inner surface of the oxygen tube and
the holes have a second diameter at an outer surface of the oxygen
tube, the first diameter being smaller than the second diameter.
Most preferably, the oxygen tube features a screen, the screen
being placed within the oxygen tube such that the oxygen flows from
the oxygen tube through the screen. Preferably, the screen is
constructed of a material selected from the group consisting of a
hydrophobic porous material, a wide mesh and a netting.
[0020] Alternatively and preferably, the inlets are oxygen prongs
for being inserted into the nostrils 0f the patient. More
preferably, the oxygen prongs are substantially shorter in length
than the nasal prongs, such that the nasal prongs extend farther
into the nostrils than the oxygen prongs. Also more preferably, the
oxygen prongs are formed of a substantially porous material, such
that the oxygen prongs are permeable to gases. Most preferably, the
oxygen prongs are formed from an inner cylinder and an outer
cylinder, both cylinders being made from the substantially
hydrophobic porous material, and the inner cylinder being
substantially shorter in length than the outer cylinder.
[0021] According to other preferred embodiments of the present
invention, at least a portion of the oxygen tube is formed from a
substantially porous material such that the at least a portion of
the oxygen tube is permeable to gases. More preferably, the at
least a portion of the oxygen tube is located substantially between
the oxygen prongs.
[0022] According to another embodiment of the present invention,
there is provided a method of using the cannula of claim 1 for
collecting the exhaled gases from patient, including: (a) inserting
the nasal prongs into the nostrils of the patient: (b) attaching
the collection tube to a conduit for conducting gas; (c) connecting
the conduit to a gas analyzer; and (d) applying a force at the gas
analyzer such that the exhaled gases flowing through the cannula
moves from the collection tube to the gas analyzer.
[0023] According to yet another embodiment of the present
invention, there is provided a cannula for collection of exhaled
gases from a patient and for delivery of oxygen to a patient, the
patient having nostrils and an oral cavity, including: (a) two
nasal prongs for insertion into the nostrils of the patient; (b) an
oral prong for being located proximately to the oral cavity of the
patient; (c) a collection tube for the collection of the exhaled
gases from the patient, the nasal prongs, the oral prong and the
collection tube being connected at a single junction, such that the
exhaled gases flow freely from the nasal prongs and the oral prong
to the collection tube; (d) an oxygen tube for delivery of oxygen,
the oxygen tube being located near the nostrils of the patient; and
(e) two oxygen inlets connected to the oxygen tube and being
disposed such that the oxygen flows from said oxygen tube into the
nostrils of the patient.
[0024] Hereinafter, the term "attached" is defined as connected to,
or integrally formed with. Hereinafter, the term "connected" is
defined as communicating with. Hereinafter, the term "prong" refers
to a hollow tube with two openings, one at each end of the
tube.
BRIEF DESCRIPTION OF THE DRAWINGS
[0025] The invention is herein described, by way of example only,
with reference to the accompanying drawings, wherein:
[0026] FIG. 1 is an illustrative prior art oral/nasal carbon
dioxide cannula.
[0027] FIG. 2 is an illustrative prior art double nasal
oxygen/carbon dioxide cannula for oxygen delivery and collection of
exhaled gases;
[0028] FIG. 3 is a second illustrative prior art divided nasal
oxygen/carbon dioxide cannula for oxygen delivery and collection of
exhaled gases;
[0029] FIG. 4 is an illustrative oral/nasal cannula for the
collection of exhaled gases according to the present invention;
[0030] FIGS. 5A-5C are cross-sectional views of the cannula of FIG.
4 according to the present invention;
[0031] FIGS. 6A and 6B show cross-sectional views of a second
illustrative embodiment of an oral/nasal cannula according to the
present invention;
[0032] FIGS. 7A and 7B show portions of the oral/nasal cannula of
FIGS. 6A and 6B in more detail, with the preferred addition of a
porous screen to the oxygen tube according to the present
invention;
[0033] FIGS. 8A and 8B show detailed cross-sectional views of
portions of a third embodiment of an oral/nasal cannula with porous
oxygen delivery tubes according to the present invention; and
[0034] FIG. 9A shows a prior art cannula for oxygen delivery, and
FIGS. 9B-9C show a cannula with equal oxygen delivery to each
nostril according to the present invention.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0035] The present invention is of a cannula which can effectively
be used to collect samples of gas without reducing the accuracy of
the analysis of the collected gas, and which is less likely to
become blocked by condensed moisture, or by liquid or solid
material, or their mixtures thereof, such as mucous or saliva.
Specifically, the present invention has two prongs for insertion
into the nostrils of a patient. These two prongs are joined outside
the nasal cavity to a single output tube for collection of the
exhaled gases. According to preferred embodiments of the present
invention, a second tube is attached to the two prongs, which is
parallel to the nasal prongs, for placement of the distal end of
the tube near the oral cavity of the patient, thereby providing an
oral/nasal cannula. According to other preferred embodiments of the
present invention, an additional tube is provided for the delivery
of oxygen, the additional tube having two additional prongs for
insertion into the nostrils of the patient, and the additional tube
being perpendicular to the additional nasal prongs.
[0036] The principles and operation of an airway adapter according
to the present invention may be better understood with reference to
the drawings and the accompanying description.
[0037] Referring now to the drawings, FIG. 1 shows a prior art
oral/nasal carbon dioxide cannula. A cannula 10 has two nasal
prongs 12 for insertion into the nostrils of a patient (not shown).
Nasal prongs 12 are connected to a first side 14 of a hollow tube
16. Hollow tube 16 is substantially perpendicular to nasal prongs
12. Two oral prongs 18 are also connected to a second side 20 of
tube 16 in a substantially perpendicular orientation, such that gas
flow from nasal prongs 12 to oral prongs 18 through tube 16 is
substantially free and unimpeded. Tube 16 also has two holes 22,
one at each end of tube 16, for connection to one of a plurality of
connectors 24. Each connector 24 is attached to a gas line (not
shown) which is then connected to a Y-connector 26. Y-connector 26
is attached to a line which leads to a capnograph (not shown).
Thus, cannula 10 is suitable only for collection of exhaled gases
for analysis.
[0038] Prior art cannula 10 unfortunately has a significant void
volume 28 (also designated as V.sub.o) between nasal prongs 12,
within which gases do not properly circulate. Two smaller void
volumes 30 (also designated as V.sub.1 and V.sub.2) are also
present parallel to nasal prongs 12 and oral prongs 18. Such void
volumes 28 and 30, and especially the larger void volume 28, permit
the mixing of exhaled gases from a currently exhaled breath with
previously exhaled breaths, thereby increasing the response time,
altering the waveform and introducing an artifact into the gas
analysis. Furthermore, the separation of the exhaled gases into two
streams from nasal prongs 12 by tube 16, the later reintegration of
the two streams at Y-connector 26 and the subsequent great distance
of about 0.5 m between tube 16 and Y-connector 26, also increases
the response time if there is even a slight difference in the flow
rated of the gases between tubes 16. Such separation potentially
also results in two streams having different flow properties. For
example, if one tube 16 accumulated more condensed water than the
other, the corresponding stream of exhaled gases would have a lower
flow rate, thereby altering the waveform of the gas concentrations
and increasing the response time for gases in that tube 16. Thus,
prior art cannula 10 cannot provide completely accurate collection
of gases for analysis.
[0039] FIG. 2 shows an exemplary prior art double oxygen/carbon
dioxide nasal cannula for the collection of exhaled gases and the
delivery of oxygen. A prior art nasal cannula 32 again has a first
pair of nasal prongs 34 for insertion into nostrils 36 of a
patient. First nasal prongs 34 are again connected to a first
hollow tube 38. First hollow tube 38 is again substantially
perpendicular to first nasal prongs 34. In additions, nasal cannula
32 has a second pair of nasal prongs 40 for insertion into nostrils
36. Second nasal prongs 40 are attached to a second hollows tube 42
in a substantially perpendicular orientation. First nasal prongs 34
and first hollow tube 38 are intended for the collection of exhaled
gases from the patient, in a substantially similar configuration as
that shown in FIG. 1. Second nasal prongs 40 and second hollow tube
42 are intended to deliver oxygen to the patient, so that nasal
cannula 32 is capable of simultaneous oxygen delivery and gas
collection.
[0040] Unfortunately, prior art nasal cannula 32 also permits the
mixing of delivered oxygen and exhaled gases between first nasal
prongs 34 and second nasal prongs 40 in nostrils 36, thereby
diluting the true concentration of expired analysis of expired
gases.
[0041] Also, the efficiency of oxygen delivery by prior art nasal
cannula 32 is not sufficient because the oxygen flow rate varies
between nasal prongs 40. Specifically, nasal prong 40 which is
closer to the input of hollow tube 42 will have a higher flow rate
than the other nasal prong 40. In addition, the strong oxygen
stream into the nostrils creates discomfort for the patient, the
alleviation of which is especially important for long term oxygen
delivery.
[0042] FIG. 3 shows a second exemplary prior art divided
oxygen/carbon dioxide nasal cannula for the simultaneous delivery
of oxygen and collection of exhaled gases. A prior art nasal
cannula 44 has a single tube 46 for both delivery of oxygen and
collection of gases. Tube 46 has two nasal prongs 48 and 50 for
insertion into nostrils 52 of a patient. Oxygen is delivered
through nasal prong 48 and exhaled gases are collected from nasal
prong 50. A septum 54 is present inside tube 46 between nasal prong
48 and nasal prong 50 to separate the delivered oxygen from the
exhaled gases. However, particularly forceful streams of delivered
oxygen can pass from nasal prong 48, penetrate deeply into nostrils
52, entering nasal prong 50 and dilute the true concentration of
exhaled carbon dioxide. Furthermore, a significant void volume 56
is present between septum 54 and nasal prong 50, both increasing
the response time and mixing the exhaled gases, which also reduce
the accuracy of the analysis of the exhaled gases. Thus, prior art
nasal cannula 44 is still not able to collect gases for a
completely accurate analysis. In addition, the strong oxygen stream
into the nostrils creates discomfort for the patient, the
alleviation of which is especially important for long term oxygen
delivery.
[0043] FIG. 4 shows a schematic illustration of an exemplary novel
oral/nasal carbon dioxide cannula for collection of exhaled gases
according to the present invention. An oral/nasal cannula 58 also
has a pair of nasal prongs 60 for insertion into the nostrils 62 of
a patient. Cannula 58 preferably features an oral prong 64 for
placement near the oral cavity of the patient (not shown) to form
an oral/nasal cannula. If oral prong 64 is absent, then cannula 58
is a nasal cannula according to the present invention. Cannula 58
also has a collection tube 66 for collection of the exhaled gases
for analysis by a capnograph (not shown). Nasal prongs 60, oral
prong 64 and collection tube 66 meet at a single junction 68, which
is preferably minimized to reduce void volume. Hereinafter, the
term "single junction" refers to the joining of nasal prongs 60,
oral prong 64 and collection tube 66 at least in close proximity,
and preferably at exactly one junction.
[0044] At the very least, having the single junction 68 between all
portions of oral/nasal cannula 58 significantly reduces the void
volume, thereby reducing mixing of the gases and maintaining the
response time. In addition, having the single collection tube 66,
rather than two such tubes as in prior art cannulas. eliminates the
division of the stream of exhaled gases as well as reducing the
amount of void volume created.
[0045] A cross-sectional view of the oral/nasal cannula of FIG. 4
is shown in FIG. 5A-5C, clearly illustrating the small void volume
created within the cannula. FIG. 5A shows a front cross-sectional
view of oral/nasal cannula 58. As clearly shown in the
illustration, nasal prongs 60, oral prong 64 and collection tube 66
all meet at a single small junction 68 with a minimum void volume.
In practice, the void volume can be almost completely eliminated
through this configuration, because there are no poorly ventilated
areas within oral/nasal cannula 58. As shown in the illustration, a
portion 70 of collection tube 66 does extend past nasal prongs 60
opposite to the collection point. However, portion 70 is blocked
and is only intended to permit the attachment of a symmetrical loop
which extends around the head of the patient (not shown).
[0046] FIG. 5B shows a side cross-sectional view of the connection
between one nasal prong 60 and oral prong 64. Preferably, a distal
end 72 of oral prong 64 is bent, more preferably at approximately a
90 degree angle from the remainder of oral prong 64, so as to be
substantially parallel to the direction of flow of orally exhaled
gases from the patient. Such an orientation both provides optimal
response time for gas analysis and promotes self-clearing of
condensation from oral/nasal cannula 58. Furthermore, preferably
nasal prongs 60 are joined in an are, so that condensation tends to
move into oral prong 64 under dynamic pressure of the nasal
exhalation of gases by the patient.
[0047] The structure of oral/nasal cannula 58 is designed to
eliminate one significant problem with certain prior art oral/nasal
cannulas, which is the susceptibility of these prior art cannulas
to the intake of ambient air through that portion of the cannula
which is not receiving exhaled air. For example, if the patient
exhales through the nasal cavity, ambient air can be sucked into
the prior art cannula through the opening provided for the nasal
cavity. Such ambient air can dilute the concentration of gas in the
exhaled breath of the patient, thus giving misleading results for
the gas analysis. The structure of oral/nasal cannula 58 reduces or
eliminates this problem with the presence of single small junction
68, and the bending of distal end 72 of oral prong 64. The
resultant structure substantially prevents ambient air from
entering the portion of cannula 58 which is not directly receiving
exhaled air from the patient.
[0048] Also preferably, nasal prongs 60 and oral prong 64 have an
optimal diameter, sufficiently large to promote rapid and easy
removal of condensation from the interior of nasal cannula 58, yet
not so large as to increase the response time. For this
configuration, an optimal diameter for both nasal prongs 60 and
oral prong 64 is in a range of from about 1.6 mm to about 2.0
mm.
[0049] Most preferably, distal end 72 of oral prong 64 features a
porous, hydrophilic cap 74, as shown in cross-section in FIG. 5C.
Porous hydrophilic cap 74 covers distal end 72 and absorbs water
droplets formed from condensation which collects in nasal cannula
58. The particular advantage of cap 74 is that the material of cap
74 preferable attracts water away from oral prong 64, and then
provides a relatively large surface area for evaporation of that
water. Additionally, cap 74 relieves potential patient discomfort
from water dripping from cannula 58 into the mouth of the
patient.
[0050] FIGS. 6A and 6B show cross-sectional views of a second
preferred embodiment of the oral/nasal cannula for oxygen delivery
and gas collection of the present invention. Detailed illustrations
of portions of the cannula of FIGS. 6A and 6B are show in FIGS. 7A
and 7B. FIGS. 7A and 7B also show the preferred addition of a
porous screen to the oxygen tube.
[0051] In this preferred embodiment, as shown in FIG. 6A, an
oral/nasal cannula 76 again has a pair of nasal prongs 78 for
insertion into the nostrils of a patient (not shown). Cannula 76
again preferably features an oral prong 80 for placement near the
oral cavity of the patient (not shown) to form an oral/nasal
cannula. Cannula 76 also has a collection tube 82 for collection of
the exhaled gases for analysis by a capnograph (not shown). Nasal
prongs 78, oral prong 80 and collection tube 82 again meet at a
single junction 84, which is preferably minimized to reduce void
volume.
[0052] Although cannula 76 also features an oxygen tube 86 for
lying near the nostrils of the patient (not shown) and more
preferably above or below the nostrils of the patient,
substantially parallel with the upper lip of the patient (not
shown). oxygen is not delivered through a second set of nasal
prongs. Instead, oxygen tube 86 has two holes 88, through which
oxygen is delivered to the patient. Holes 88 are placed near the
nostrils of the patient yet do not enter the nostrils, thereby
preventing the delivered oxygen from entering as a forceful stream
of gases which dilutes the exhaled gases and reduces the accuracy
of gas analysis.
[0053] FIG. 6B shows a side cross-sectional view of junction 84
between one nasal prong 78 and oral prong 80, as well as a portion
of oxygen tube 86. Oxygen is shown being dispersed from oxygen tube
86 through hole 88.
[0054] FIG. 7A shows holes 88 in more detail. Holes 88 preferably
have a relatively large diameter. Most preferably the diameter of
holes 88 increases from the inner surface of oxygen tube 86 to the
outer surface of oxygen tube 86, in order to reduce the force of
the delivered oxygen stream. Holes 88 have a first smaller diameter
90 at the inner surface of oxygen tube 86, and a second larger
diameter 92 at the outer surface of oxygen tube 86, with the
diameter of holes 88 preferably gradually increasing from the inner
to the outer surface of oxygen tube 86.
[0055] In addition, as shown in FIG. 7A, oxygen tube 86 preferably
features a screen 94 made from a substantially porous material
which is permeable to oxygen, such as a wide mesh, a hydrophobic
porous screen, netting or cotton wool, for example. The advantages
of screen 94 are that the force of the delivered oxygen stream is
reduced and an oxygen "cloud" is created near the nostrils of the
patient. The combination of the dispersion of oxygen through screen
94 and hole 88 is shown in a side cross-sectional view in FIG. 7B,
which also shows junction 84.
[0056] FIGS. 8A and 8B provide a detailed illustration of a portion
of a third embodiment of an oral/nasal cannula according to the
present invention. FIG. 8A shows a portion of an oral/nasal cannula
96, showing a section of a pair of nasal prongs 98 for receiving
exhaled carbon dioxide, an oxygen tube 100 and a pair of second
nasal prongs 102. As clearly illustrated, oxygen is delivered
through oxygen tube 100 and is then dispersed through second nasal
prongs 102.
[0057] Preferably, second nasal prongs 102 are constructed from two
cylinders, in order to ensure that oxygen is delivered to the
nostrils of the patient efficiently, yet is quickly dispersed
within the nasal cavity. The first cylinder is an inner cylinder
104. Preferably made from a substantially porous hydrophobic
material. The material is preferably hydrophobic to prevent
absorption of moisture. Inner cylinder 104 is surrounded by an
outer cylinder 106, also preferably made from a substantially
porous hydrophobic material, such that oxygen is dispersed
throughout the nostrils of the patient, rather than entering the
nasal cavity as a highly pressurized stream of gas.
[0058] FIG. 8B shows a side, cross-sectional view of the portion of
the cannula illustrated in FIG. 8A. A junction 108 between one
nasal prong 98 and an oral prong 110 is shown, as is one second
nasal prong 102 with inner cylinder 104 and outer cylinder 106. The
advantage of constructing second nasal prong 102 from a porous
material is such material would be permeable to oxygen, thereby
allowing oxygen to disperse evenly from second nasal prong 102.
Such dispersion reduces the force of the delivered oxygen
stream.
[0059] FIGS. 9A-9C show a comparison between a prior art oral/nasal
cannula in which oxygen is delivered unequally to the nostrils of
the patient (FIG. 9A), and a oral/nasal cannula according to the
present invention in which oxygen is delivered at equal flow rates
(FIGS. 9B and 9C). FIG. 9A shows a cross-sectional view of the
oxygen-delivery portion of a typical prior art oral/nasal cannula
112. Prior art cannula 112 has an oxygen delivery tube 114 for
delivery oxygen to two outputs 116 and 118. Outputs 116 and 118
could be holes or nasal prongs as shown previously. The problem
with this configuration is that oxygen is not distributed evenly
between both outputs 116 and 118. Output 116, which is closest to
the start of oxygen delivery tube 114, has a greater flow of oxygen
than output 118, as indicated by the arrows. Such a situation
arises because the resistance of outputs 116 and 118 to the flow of
oxygen is much lower than the resistance of the connecting portion
of oxygen delivery tube 114.
[0060] FIG. 9B shows a cross-sectional view of the oxygen-delivery
portion of a first exemplary oral/nasal cannula 120 according to
the present invention. First cannula 120 has an oxygen delivery
tube 122 for delivery oxygen to two sets of outputs 124 and 126.
Each set of outputs 124 and 126 includes at least two outputs,
although three are shown here for illustrative purposes, without
any intention of being limiting. Again, the outputs could be holes,
holes with a porous screen, or nasal prongs as shown previously.
The advantage of this configuration is that oxygen is distributed
more evenly between both sets outputs 124 and 126. Such a situation
arises because the resistance of both sets of outputs 124 and 126
to the flow of oxygen is much greater than the resistance of the
connecting portion of oxygen deliver tube 122.
[0061] FIG. 9C shows a cross-sectional view of the oxygen-delivery
portion of a second exemplary oral/nasal cannula 128 according to
the present invention. Second cannula 128 has an oxygen delivery
tube 130 for delivery oxygen to two sets of outputs 132 and 134.
Each set of outputs 132 and 134 includes at least one output,
although only one is shown here for illustrative purposes, without
any intention of being limiting. Again, the outputs could be holes,
holes with a porous screen, or nasal prongs as shown previously.
Additionally, oxygen delivery tube 130 features a centrally located
input 136 for the delivery of oxygen. Preferably, centrally located
input 136 is located substantially equidistantly to outputs 132 and
134. The advantage of this configuration is that oxygen is
distributed more evenly between both sets of outputs 132 and 134
even for their relatively lower resistance to air flow in
comparison to the resistance of oxygen delivery tube 130. Such a
situation arises because the resistance of each output 132 and 134
to the flow of oxygen is equal.
TESTING OF THE ORAL/NASAL CANNULA
[0062] The features and embodiments illustrated herein may be
better understood with reference to the experiments described
below. These experiments were conducted on oral/nasal cannulas
according to the present invention, as well as on examples of prior
art cannulas.
[0063] Experimental Methods
[0064] The first test performed was the self-cleaning test.
Self-cleaning is important for preventing the accumulation of
condensed water, which can disturb the sampling of carbon dioxide.
The term "V.sub.ex" is defined as the minimal volume of expired
breath required for self-cleaning of water from the cannula.
[0065] The second test was the response time test, performed in
accordance with Regulation prEN 864:1992 (European Union standard)
for capnography. All measurements were conducted on a capnograph
with low flow rate of 47 ml/min. Response times (in mSec) were
tested for nasal cannula blanks only, nasal cannula systems which
also included the set of sample lines, and the entire capnograph
set which included the nasal cannula system with a typical
capnograph flow system.
[0066] The third test determined the accuracy of measurements of
expired carbon dioxide (EtCO.sub.2). Expired carbon dioxide was
measured both with and without oxygen delivery. In the absence of
oxygen delivery, the alteration to the true EtCO.sub.2 caused by
the influence of the response time was calculated as:
.DELTA.(EtCO.sub.2)=EtCO.sub.2(True value)-EtCO.sub.2(with Entire
Capnograph Set)
[0067] In the presence of oxygen delivery, the alteration to the
true EtCO.sub.2 was calculated as
.DELTA.(EtCO.sub.2)=EtCO.sub.2(Q=0)-EtCO.sub.2(Q.noteq.0)
[0068] The fourth test measured the effectiveness of the delivery
of oxygen according to the flow distribution between the two nasal
cannula oxygen delivery outputs. Oxygen was delivered at the rate
of 8 L/min. The flow of oxygen from each output, given as Q.sub.1
and Q.sub.2, was measured. The efficiency (K.sub.eff) was
determined according to the ratio of Q.sub.1 to Q.sub.2.
[0069] These four tests where performed on several different types
of cannulas. Three types of cannulas were obtained and tested from
Salter Labs (Arvin, Calif., USA): a nasal cannula (catalog number
4000); a dual oral/nasal cannula (catalog number 4001); and divided
oxygen/carbon dioxide nasal cannula (catalog number 4707). Two
types of cannulas were obtained and tested from Hudson (Temecula,
Calif., USA): a nasal cannula (catalog number 1103): and an
oxygen/carbon dioxide nasal cannula (catalog number 1843). An
oral/nasal cannula according to the present invention was also
tested, in the embodiment of an oxygen/carbon dioxide oral/nasal
cannula with inserts of braid or cotton wool for oxygen dispersion
as shown in FIG. 7B. Results for all tests are shown in Table
1.
[0070] Essentially, the cannula of the present invention performed
at least as well as, and in many respects better than, the prior
art cannulas. In particular, the cannula of the present invention
had a much lower response time than any of the other tested prior
art cannulas. For example, without any additional connections, the
cannula of the present invention had a response time of 14, while
those of the cannulas of Hudson were 97 and 47, and those of the
cannulas of Salter Labs were 167, 143 and 239. Thus, clearly the
cannula of the present invention had a far better response time
than these tested cannulas.
[0071] While the invention has been described with respect to a
limited number of embodiments, it will be appreciated that many
variations modifications and other applications of the invention
may be made.
* * * * *