CA1209213A - Endotracheal cardiac monitor - Google Patents

Abstract

ENDOTRACHEAL CARDIAC MONITOR

ABSTRACT OF THE DISCLOSURE
A flexible endotracheal tube includes at its distal end an inflatable cuff adapted to monitor acoustically the cardiac pulse. The inflatable cuff, when inflated after insertion of the endotracheal tube into the trachea of the patient, contacts and conforms to the inner wall of the trachea to provide an airtight seal, thereby permitting the administration of anesthetic gases, as well as control and monitoring of the respiratory function through the respiratory passage within the endotracheal tube.
The cardiac pulse is acoustically transmitted from the interior tracheal wall through the inflatable cuff and into the associated inflation conduits, one of which terminates in a monitor connector suitable for monitoring the cardiac pulse. A transducer connector housing an electromechanical transducer mates with the monitor connector and produces an electrical signal which is suitably processed and subsequently used to drive a visual display, a chart recorder, and to provide an audio output.

Description

~2~L3 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 ,. 1 ~ 1%~:~3 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 ~Z~9213 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 ~:~09Z~3 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 .

~2~9Z~3 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.

=~ ~2~9~:~3 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.

- ~L2~2~3 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 ~2092~3 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 9Z~L;3 . .

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.

, ~ g ~LZ~g2~3 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.

~A

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.

ln Z~3 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, , ~2~99;i~

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 ~2~g2~

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 ~2~Z~3 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 ~2~3 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.

Claims (7)

WHAT IS CLAIMED IS

1. A flexible endotracheal tube for insertion through the mouth of a patient into the trachea of the patient, comprising in combination:
means defining a respiratory passage within the endotracheal tube for the administration of anesthetic gases and for the control and monitoring of respiration during surgery;
an inflatable cuff disposed near the distal end of the endotracheal tube, said inflatable cuff being large enough to contact and conform to the interior wall of the trachea;
the proximal and the distal ends of said inflatable cuff both being hermetically sealed to the outside of the endotracheal tube;
flexible conduit means for permitting fluid communication with the interior of said inflatable cuff;
means for permitting the pressurizing of said flexible conduit;
means for permitting the monitoring of pressure variations within said flexible conduit;
where the inflatable cuff is long, to the extent that its area of contact with the interior wall of the trachea is, in substance, large;
where the inflatable cuff is made of soft pliable material, to the extent that the cuff conforms intimately with the interior wall of the trachea when the cuff is inflated to only a small pressure;
and where the flexible conduit means is formed as a structure that is separate from the means defining a respiratory passage, to the extent that the flexible conduit means is, in substance, isolated from the sounds of breathed air passing through the means defining â respiratory passage.

2. An endotracheal tube as described in claim 1, wherein the proximal end of said flexible conduit is connected to a first branch and a second branch, said first branch and said second branch also being flexible conduits; and all of said conduits being in fluid communication with one another and with the interior of said inflatable cuff.

3. An endotracheal tube as described in claim 2, wherein the proximal end of said first branch terminates in an inflation connector; and the proximal end of said second branch terminates in a monitor connector.

4. An endotracheal tube as described in claim 3, wherein said inflation connector comprises a body which includes valve means to preserve pressure integrity in said flexible conduit;
and said monitor connector comprises a body which includes a diaphragm which seals the interior cavity of said monitor connector and preserves pressure integrity in said flexible conduit.

5. An endotracheal cardiac monitor as described in claim 4, wherein said means for permitting the monitoring of pressure variations is an electromechanical transducer.

17 An endotracheal cardiac monitor as described in claim 5, wherein said electromechanical transducer is contained within a transducer connector which permits mating of said transducer connector with said monitor connector;
said electromechanical transducer producing an electrical signal which is a function of said pressure variations; and said electrical signal is used as an input to an output means.

7. An endotracheal cardiac monitor as described in claim 6, wherein said output means comprises a signal processor;
said signal processor performing amplification, filtering and impedence matching functions;
a visual display driven by said signal processor;
audio output means driven by said signal processor; and a chart recorder driven by said signal processor.