Note: Descriptions are shown in the official language in which they were submitted.
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BACKGROUND OF THE INVENTION
Field of the Invention
This invention relates to an apparatus for acoustically a.nd visually
monitoring the cardiac pulse while simultaneously administering anesthetic
gases to a patient during surgery.
Description of the Prior Art
During operations in which general anesthesia is used, the accepted
practice is to administer the anesthetic gases through a flexible endo-
tracheal tube which ;s inserted through the mouth of the patient and into
the trachea. The early, rudimentary versions of such an endotracheal
tube were greatly improved by the addition of sealing means at the out-
side of the distal end of the tube. The sealing means in most common
usage today comprises an inflatable cuff which can expand into contact
with the interior wall of the trachea. With the trachea thus blocked,
positive control over the administration of anesthesia and of the res-
piration itself is permitted through the respiratory passage in the endo-
tracheal tube.
The administration of anesthesia gases tends to produce a state of
relaxation of muscle tissue. This effect is quite desirable to the surgeon
who must cut into and through such tissue, but is also can have effects
which are not desired. Although some of the undesired effects may not
be evident until the post-operative recovery period, the possibility of
cardiac arrest is typically of utmost concern during the surgery itself.
Since cardiac arrest is an ever-present danger during the condition
of general anesthesia, the cardiac pulse must be ~nonitored carefully and
continually. In fact, in some states there exists practically an absolute
requirement to monitor the actual heart sounds during surgical proce-
dures. In other areas, the amount and type of cardiac monitoring i8 left
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to local or hospital rule, or to the preference of the anesthesiologist.
Sometimes, such monitoring is accomplished acoustically as by taping an
acoustic stethoscope pickup directly to the exterior of ~,he body of the
patient in the region of the chest. Such cardiac monitoring is perhaps
more often accomplished by electrical or electronic means which essentially
monitor motor nerve impulses. The electrical activity thus picked up is
usually converted into audible "beeps" which essentially serve only to
monitor the heart rate, and occasionally the same electrical activity may
be presented for visual observation on an oscilloscope. This direct
technique of electrical monitoring of motor nerve impulses is often remark-
ably less sensitive than acoustic monitoring of the cardiac pulse, and in
addition the audible "beeps" produced by electrical monitoring are far less
informative of the actual activity and condition of the heart than the true
heart sounds available through acoustic monitors. By listening to the
actual heart sounds through acoustic monitoring means the anesthesiologist
can receive the earliest possible indication that the heart is becoming
depressed due to the anesthetic, thus permitting the anesthesiologist to
take early and minimal corrective measures so that there is little or no
impact on the progress of the surgical procedure and no adverse effect
on the patient.
Acoustic monitoring of the heart during surgery has been accom-
plished by using one or more acoustic pickups for stethoscopes taped to
the chest of the patient. However, even undex the best of conclitions,
the heart sounds are attenuated substantially by the body tissue in the
sound path from the heart to the acoustic pickup g and it is often impos-
sible to change the location of the stethoscope acoustic pickup once the
surgical procedure has begun. This type of acoustic monitorin~ on the
outside of the chest wall is particularly clifficult and unsatisfactory for
obese patients, since the excessive amount of body tissue in the sound
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path between the heart and the acoustic pickup often attenuates the heart
sounds to an unusable level.
Although the present invention is gen0rally oriented toward cardiac
monitor;ng during surgery, it is also applicable to the careul monitoring
of the cardiac pulse which may also be required Eor several days after
surgery while the patient is in the intensive care unit. Endotracheal
monitors are well suited to such prolonged use.
The nature of the surgery permitting, one of the preferred cardiac
pulse monitoring methods requires the use of a device known as an " eso-
phageal tube", which~ as its name implies, is inserted in the esophagus of
the patient. Acoustic or electric sensors may be disposed near the distal
end of the esophageal tube to pick up and transmit the cardiac pulse from
the ~;urrounding tissue. Unfortwnately, the amount of various body fluids
in the esophagus can vary drastically during the course of surgery; such
variations not only can affeet the ability to monitor the cardiac pulse
acoustically, but can also create confusing and distracting noise. The
esophageal tube itself must be sealed at its distal end in order to prevent
the entrance of body fluids which may occasionally be present in the
esophagus during surgery. Also, sensors located in the esophagus
cannot always be positioned as close to the heart as is possible with
sensors located at the distal end of an endotraeheal tube. Thus, esoph-
ageal sensors tend to distort the cardiac pulse. A more reliable means of
monitoring the cardiac pulse with greater fidelity is desirable.
The esophageal tube has the disadvantage of being difficult to locate
properly in some situations. In attempting to properly place the esopha-
geal tube, it is possible for the anesthesiologist to perforate the wall of
the esophagus, resulting in "false passage". Such false passage is more
likely to occur where there is scar tissue in the esophagus or where
there is a congenital pouch in the wall of the esophagus which leads the
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probing tip of the esophageal tube in the wrong direction. Due to the
nature of the tissue involved, false passage is a less signiffcant problem
in the trachea than in the esophagus. Since an endotracheal tube is used
in most cases for the administration of the anesthetic gases, the use of a
separate esophageal tube merely for the purpose of monitoring the cardiac
pulse creates excessive and unnecessary crowding in the area of the
mouth of the patient, and adds unnecessary expense to the surgical
procedure itself. Also, certain forms of radical neck surgery involving
the esophagus would necessary preclude the use of an esophageal stetho-
scope in any form.
Even where esophageal stethoscopes are used routinely, it is difficult
to adequately seal the esophagus to prevent fluids from the digestive
track from moving toward the mouth of the patient during the operation,
De~ending somewhat upon the nature of the surgery and the length of
the operation, these fluids may find their way into the trachea of the
patient, and ultimately into the lungs of the patient Such leakage of
fluids from the esophagus into the trachea can cause aspiration pneu-
monia, which is a problem commonly associated with the use of esophageal
stethoscope tubes.
Current monitoring devices which convert sound into an electrical
signal for transmission to the output means are generally deficient in two
respects. First, the output is often limited to a series of gated tone
bursts commonly known as "beeps". Such a signal provides only an
indication of the carcliac rate, and actually serves to conceal the degree
of depression of the heart during surgery. In those systems where
additional information containing more of the actual heart sound is used,
the deficiency arises from the fact that the output is generally available
only to the anesthesiologist, and not to the surgeons(s) operating on the
patient .
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Therefore, it is an object of this invention to provide an apparatus
which overcomes the aforementioned inadec uacies of the prior art devices
and provides an improvement which is a significant improvemen~ to the
advancement of the prior art.
Another object of this invention i5 to provide a flexible endotracheal
tube with an inflatable cuff suitable for sealing the trachea and having
means for permitting the monitoring of pressure variations within the
inflated cuff.
Another object of this invention is to provide a flexible conduit to
conduct pressure variations from an inflatable cuff on the distal end of an
endotracheal tube to an external monitor connector.
Another object of this invention is to provide a diaphragm-sealed
connector in the pressurization conduit system of an endotracheal tube
having an inflatable cuff so that sounds transmitted through the tracheal
wall to the inflated cuff may be monitored externally while maintaining the
pressure integrity of the inflated cuff and conduit system.
Another object of this invention is to provide an endotracheal cardiac
monitor so that only one tube is required to be inserted into the mouth of
a patient during surgery, thus reducing crowding in the vicinity of the
mouth of the patient, as well as reducing the expense of equipment
required for surgery.
Another object of this invention is to provide an electromechanical
transducer to convert the pressure variations representing heart sounds
into an electrical signal suitable for processing and specific distribution.
Another object of this invention is to provide an output means
wherein the electrical signal representing the heart sounds is displayed
on a video display and on a chart recorder, as well as being made avail-
able as an audio output either to headphones or to a loudspeaker.
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The foregoing has outlined some of the more pertinent objects of the
invention. I'hese objects should be construed to be merely illustrative of
some of the more prominent features and applications of the intencled
invention. Many other beneficial results can be attained by appl-ying the
disclosed invention in a different manner or modifying the invention
within the scope of the disclosure. ~ccordingly, other objects and a
fuller understanding of the invention may be had by referring to the
summary of the invention and the detailed description describing the
preferred embodiment in addition to the scope of the invention defined by
the claims taken in conjunction with the accompanying drawings.
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SUMM~RY OF T~IE INVENTION
The invention is defined by the appended clairns with a specific
embodiment shown in the attached drawings, For the purposes of
summarizing the invention, the invention comprises an apparatus which
permits the administrat;on of anesthetic gases to a patient during surgery
through the use of an endotracheal tube which simultaneously permits the
acoustic monitoring of the cardiac pulse at a location in the trachea close
to the heart L The lnvention comprises a flexible endotracheal tube,
typically made of polyvinylchloride or similar plastic, which terminates at
its proximal end in a standard fitting compatible with anesthesia machines.
The distal end of the endotracheal tube is open, and a respiratory
passage within the endotracheal tube provides fluid communication between
the anesthesia machine and the patient's trachea.
Disposed near the distal end of the endotracheal tube is an inflatable
cuff. In use, the endotracheal tube is typically inserted while the cuff is
deflated. The cuff is adapted so that when it is inflated, it expands and
comes into contact with the inner wall of the trachea. Not only does I:his
serve to gently center the distal end of the endotracheal tube so as to
minimize irritation of the trachea of the patient, but it also serves to seal
the trachea, thus providing positive control over the administration of
anesthetic gases and of the respiration process of the patient during
surgery .
Inflation of the inflatable cuff is accomplished through a separate
conduit which is in fluid communication with the interior of the inflatable
cuff. Near its proximal end, the flexible inflation conduit branches into
two other conduits, both of which are in fluid communication with one
another and therefore with the interior of the inflatable cuff. The prox-
imal end of the first branch of the flexible inflation conduit terminates in
an inflation connector through which the fluid is initially pumped to
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pressurize the conduit and thereby inflate the cuff. This inflation con-
nector often contains a valve means such as a spring loaded check valve
to preserve the pressure integrity of ~he conduit and inflatable c-uff
system .
The second branch at the proximal end of the flexible conduit ter-
minates in a monitor connector. This connector inclucles a sealing dia
phragm which serves to preserve the pressure integrity of the cwff
inflation system while simultaneously permitting acoustic energy in the
form of cardiac pulses to be transmitted out of the apparatus and into the
desired monitorin~ device,
The acoustic energy of the cardiac pulse is sensed by an electro-
mechanical transducer such as a piezo electric microphone housed within a
transducer connector mated with the monitor connector. The transducer
converts the sound energy into an electrical signal which is used to drive
the output means comprising, in general, a signal processor, a Yisual
display, a chart recorder and one or more forms of audio output.
In use, the inflatable cuff is pressuri~ed or expanded by a fluid,
either gaseous or liquid, after the endotracheal tube is inserted into the
patient to the desired depth. When the inflatable cuf contacts and
conforms to the inner wall of the trachea, it also acoustically couples the
cardiac pulse from the surrounding tissue which is in close proximity to
the heart and permits the propagation of the acoustic cardiac pulse
through the fluid inflating medium. The propagation of that acoustic
energy is guided through the flexible conduit until it reaches the dia-
phragm at the monitor connector, where it is available for monitoring by
the desired device. The flexible conduits presently used for pressuriza-
tion typically have internal diameters on the order of one millimeter or
less. The flexible conduits used in this apparatus may be slightly larger
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in internal diameter in order to transmit the heart sounds with a minimum
of attenuation of the acoustic energy.
The foregoing has outlined rather broadly the more pertinent and
important features of the present invention in order that the detailed
description of the invention that follows may be better understood so that
the present contribution to the art can be more fully appreciated. Addi-
tional features of the invention will be described hereinafter which form
the subject of the claims of the invention. It should be appreciated by
those skilled in the art that the conception and the specific embodiment
disclosed may be readily utili~ed as a basis for modifying or designing
other structures for carrying out the same purposes of the present
invention. It should also be reali~ed by those skilled in the art that
such equivalent constructions do not depart from the spirit and scope of
the invention as set forth in the appended claims.
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The monitor of the invention shares some characteristics
with the apparatus shown in U.S.Patent No. 4,383,534 (PETERS, 17
May 19~3). In P~TERS, however, the inflatable cuff follows the
general teaching for constructing cuffs, which is khat the cuf f`
should be short, to minimize possible sources of irritatiorl in
the region of contact. In the invention, the cuff is lon~, This
means that there is a good deal of fluid contained within the
cuff, which ensures a faithful trans~ittal of trachea-borne
sounds into the cuff. The material of the cuff is soft and
pliable, which gives an excellent conformability of the cuff to
the trachea, yet with little risk of irritation. This may be
contrasted ~ith prior art devices where the cuff has been short:
in those cases, the pressure to which the cuff was inflated had
to be quite high, to get a good sound connection, and hence the
cuff had to be of a stiffer material to prevent it from
ballooning under the pressure.
Another distinction over PETERS is that in the monitor
of the invention the tube along which the sounds are transmitted
is acoustically separate from the tube that conducts the air and
anaesthetic gases into the lungs. Hence the trachea-borne heart
sounds can be listened to with little interference from the
sounds in the breathing tube.
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BRIEF DESCRIPTION OF TE~E DRAWINGS
-
For a fuller understanding of the nature and objects of the inven-
tion, reference should be had to the following detailecl description taken
in connection with the accompanying drawings in which:
Fig. 1 is an elevational view of the endotracheal tube showing the
cuff inflated within the trachea;
Fig. 2 is an enlarged cross-sectional view of the endotracheal tube
taken on the line 2-2 of Fig. l;
Fig. 3 is an enlarged sectional view of the monitor connector de-
picted in Fig. l;
Fig. 4 is an enlarged sectional view of the transducer connector;
and
Fig. 5 is partially exploded block diagram of the endotracheal tube
and connecting devices including the output means.
Similar reference characters refer to similar parts throughout the
several views of the drawings.
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DETAILED DESCRIPTION
Fig. 1 is an elevational view of the endotracheal cardiac monitor 10
in which the predominant structure is a hollow, flexible tube 12 con-
structed of polyvinylchloride or similar material. The tube is open at its
distal end 14, which is often bias-cut as shown in Fig. 1. An aperture
15 is located in the wall of tube 12 on the side opposite the bias cut at
the distal end of tube 12 in order to preclude accidental blockage of tube
12 after insertion into the trachea of a patient. The proximal end 16 of
the endotracheal tube 12 is attached by friction, welding, adhesive or
similar means to a rigid anesthetic connector 18 which permits connection
to an anesthesia machine (not shown). Attached to the side of the endo-
tracheal tube 12 from near the distal end 14 of said tube and running
along said tube for most of its length is another, smaller flexible conduit
20O In some embodiments, this conduit 20 may be extruded integrally
with the wall of the tube 12. The distal end 22 of the conduit 20 is
located pro~imally of the distal end 14 of tube 12.
An inflatable sleeve or cuff 24 made of material such as latex, com-
pletely surrounds the distal end 14 of endotracheal tube 12. The distal
end 26 of the inflatable cuff Z4 is attached and hermetically sealed to the
outer circumference of the distal end of endotracheal tube 12. Similarly,
the proximal end 28 of the cuff 24 is attached and hermetically sealed to
the periphery of the endotracheal tube 12 and conduit 20. The distal end
22 of conduit 20 is located between the distal end 26 and the proximal end
28 of cuff 24. Conduit 20 is hollow and the distal end 22 of conduit 20 is
open and in communication with the volume enclosed by inflatable cuff 24.
As shown in Fig. 1, the flexible cuff 24 is inflated and has ex-
pancled to contact and conform to the inside of the trachea wall 30.
The proximal end of hollow conduit 20 terminates in a standard tee
fitting 32. Other embodiments of this connector, such as a Y connector,
,
11
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may also be used~ The tee connector 32 is attached to and communicates
with another hollow conduit 34, the proximal end of which terminates in
the inflation connector 36 which may contain valve means such as spring-
loaded check valve, not shown in the drawings. Tee connector 32 is also
attached to and communicates with another hollow conduit 38 which termi~
nates in monitor connector 40.
Fig. 2 is a cross-sectional view of endotracheal tube 12 taken along
lines 2-2 as indicated in Fig. 1. The inner surface 46 of endotracheal
tube 12 defines respiratory passage 42, The relatively thick wall of
endotracheal tube 12 has an outer surface 44 to which is attached the
inflatable cuff 24. As shown in Fig. 2, conduit 20 is also a tube con-
taining pressurization passage ~8. Adhesive fillets 50 are depicted in
Fig. 2 as the means for attaching conduit 20 to endotracheal tube 12.
Other means may also be used, or the conduit may be integrally formed
with tube 12. 1'he inflatable cuff 24 is attached to the adhesive fillets 50
and conduit ZO as well as to the outer surface 44 of endotracheal tube 12
in such a manner ~s to forrn a hermetic seal.
Fig. 3 shows a sectional view of monitor connector 40 which is
located on the proximal end of hollow conduit 38, the distal end of which
is connected to tee connector 32. The hollow interior of conduit 2
communicate~ with that of conduit 34 connected to the inflation connector
36 as well as to the sound passage 52 within conduit 38. Inside monitor
connector 40, internal sound passage 54 expands until it terminates at
diaphragm 56, which serves to maintain the pressure integrity of conduits
20, 34 alld 38, as well as cuff 24 while transmitting sound from sound
passages 52 and 54 to sound passage 58. Monitor connector 40 terminates
in a surface 6û suitable for connection to a stethoscope or other device
such as a microphone and amplifier for the purpose of monitoring
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acoustically or visually (as on an oscilloscope) the sound pulses from
within the sound conduit.
Fig. 4 is a sectional view of the transducer connector generally
denoted as 62. Transducer connector 62 comprises a housing 64, typi-
cally made of plastic or similar material, and is shaped to mate with
monitor connector 40. In the embodiment depicted in Fig. 4, inner sur-
face 66 of connector housing 64 is intended to fit snugly about the outer
surface 60 of monitor connector 40 to permit the joining of monitor con-
nector 40 and transducer connector 62 and to retain that connection
during use of the system. Transducer connector 62 contains an electro-
mechanical transducer 68 such as a piezo electric microphone which gener-
ates an electrical signal which is a function of the sound ~pressure varia-
tions) within sound passage 58 in monitor connector 40. The electrical
signal is transmitted by line 70 to the desired output means.
Fig. ~ is a partially exploded block diagram of the entire endo-
tracheal cardiac monitor system, including the endotracheal tube 10 and
the output means 76. The proximal end of endotracheal tube 10 includes
the anesthetic connector 18 which can be connected to anesthetic tube 72
which communicates with the anesthesia machine (not shown). Inflation of
cuff 24 is accomplished by pressurization through inflation connector 36.
This inflation or pressuri~ation i5 accomplished by pressurization means
74, depicted as a simple syringe in Fig. 5. Monitor ,connector 40 mates
with transducer connector 62 as described in the preceding paragraph.
The electrical signal produced by the transducer housed within trans-
ducer connector 62 is transmitted means of line 70 to the output means
generally denoted as 76. Output means 76 generally comprises a signal
processor 78 which performs such functions as filtering, amplification,
and impedance matching. The output of signal processor 78 is used to
drive visual display 80, and to provide outputs to audio output means ~2
13
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and the chart recorder 84. Although output means 76 is shown as a
single unit in E`ig. 5, it will be appreciated by those skilled in the art
that the various functions depicted may be accomplished by separa~e units
as well as by a single unit, as is well known in the art.
In use9 the distal end 14 of endotracheal tube 12 i6 inserted through
the mouth of the patient and into the trachea to the desired depth.
Monitor connector 40 is attached to the desired acoustic or visual monitor
and inflation connector 36 is attached to the anesthesia machine, not
shown in the drawings, or other apparatus such as a syringe to provide
fluid pressurization of inflatable cuff 24 through conduits 34 and 20.
Although air is the most common pressurization medium, it will be appre-
ciated by those skilled in the art that other fluid media, including li-
quids, may also be used for pressurization and to provide acoustic coup-
ling. As the pressurization medium is pumped into the conduit through
inflation connector 36, which often contains a check valve, the soft
inflatable cuff 24 expands until it comes into contact with the interior wall
30 of the trachea. That point of contact typically is in the proximity of
the heart.
The cardiac pulse is transmitted by tissue and body fluids to the
nearby trachea wall 30. Inflatable cuff 2as, in physical contact with the
interior wall 30 of the trachea, acoustically couples the cardiac pulse to
the fluid pressurization medium within inflatable cuff 24. The cardiac
pulse then propagates in the same pressurization medium from the vicinity
of the inflatable cuff 24 through the hollow, communicating condult 20,
tee 32 and conduit 38 to reach the monitor connector 40. As shown in
Fig. 3, the sound passages 52 and 54 terminate physically at diaphragm
56, which serves to maintain the pressure integrity of the inflation sys-
tem. The cardiac pulse, however, is coupled acoustically through the
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diaphragm 56 and into sound passage 58 which is in communication with
the desired acous~ic or visual monitor.
As discussecl above with respect to Fig. 5, the cardiac pulse rnay be
displayed visually, as on an oscilloscope or a chart recorder, and the
cardiac pulse may also be presented as an audio output which can be
broadcast by means of a loudspeaker or which may be limited to the use
of the anesthesiologist through the use of headphones as is well known in
the art. The use of a loudspeaker, of course, enables the surgeon(s) to
make an evaluation of the heart condition during surgery which is inde-
pendent of that of the anesthesiologist.
The present disclosure includes that contained in the appended
claims as well as that of the foregoing description. Although this inven-
tion has been described in its preferred form with a certain clegree of
particularity, it is understood that the present disclosure of the pre-
ferred form has been made only by way o example and that numerous
changes in the details of construction and the combination and arrange-
ment of parts may be resorted to without departing from the spirit and
scope of the invention.
