US3460541A - Endotracheal intubation tubes - Google Patents

Description

G. O. DOHERTY ENDOTRACHEAL INTUBATION TUBES 3 Sheets-Sheet 1 Filed Oct. 6. 1966 n Nam mv'suron o.

GEORGE oonga'rv ATTORNEY G. O. DOHERTY ENDO'I'RACHEAL INTUBATION TUBES Aug. 12,19 9

3 Sheets-Sheet 2 Filed Oct. 6. 1966 INVENTOR GEORGE O. DOHERTY BY I A ATTORNEY Aug. 12, 1969 s. o. DOHERTY ENDOTRACHEAL INTUBATION TUBES- 3 Sheets-Sheet 5 Filed Oct. 6. 1966 "I" l h INVENTOR.

GEORGE .DOHERTY United States Patent Office 3,460,541 Patented Aug. 12, 1969 3,460,541 ENDOTRACHEAL INTUBATION TUBES George 0. Doherty, 2301 River Road, Missoula, Mont. 59801 Continuation-impart of application Ser. No. 437,365,

Mar. 5, 1965. This application Oct. 6, 1966, Ser.

Int. Cl. A61m 16/00, 25/00; F161: 15/14 U.S. Cl. 128-351 9 Claims ABSTRACT OF THE DISCLOSURE An intubation tube including an open-ended flexible tubular conduit having an inflatable cuff on its distal end for engaging a patients tracheal lining. The cuff is inflated through an aperture in the tubular conduit and the aperture is normally covered by a check valve which can be a flap-like element, a collar embracing the flexible conduit, a saddle-like element, or an invaginated sleeve-like extension of one end of the cuff. Other embodiments have distal ends provided with accordion-like pleats or outwardly extending flares in lieu of inflatable cuffs.

This invention relates in general to intubation tubes and, more particularly, to endotracheal tubes.

This application is a continuation-in-part of my copending application Ser. No. 437,365, filed Mar. 5, 1965, now abandoned.

The present invention is directed to endotracheal tubes having expansible distal ends which may be easily enlarged for sealingwise engagement with tracheal lining immediately caudad to the larynx. With the exception of the expansible end portion of the tube, there are no other obstructions either along the exterior or within the interior of the tube, thereby leaving the tube completely clear for the conduct of an operation.

Since it is often desirable during surgical procedures to maintain complete control over the patients breathing, it has been the practice to administer oxygen or anesthetics to the patient through a tube which is inserted through the patients mouth and larynx and into the vestibular portion of the trachea caudad to the sphincter muscles of the larynx. The end of the tube projecting from the patients mouth is connectible to an anesthesia machine which provides a flow of gaseous mixtures.

Several varieties of tubes are available. One type embodies a soft, flexible tube which is diametrally sized to fit past the larynx and into the vestibular portion of the trachea. To retain the tube within the trachea and to provide a seal between the tracheal lining and the walls of the tube, inflatable rubber cuffs or collars were developed. Such cuffs slip over the distal end of the tube and have a thin flexible hose extending from one annular end thereof. The opposite end of the thin flexible hose is provided with a syringe bulb for inflating the cuff. Generally, the cuff is positioned on the intubation tube so that when the latter is fully inserted, the cuff will lie in the trachea beyond the sphincter muscles of the larynx. The small tube, of course, is disposed loosely along the side of the intubation tube, while the bulb is free for squeezing outside the patients mouth. By squeezing the syringe-type bulb, the anesthesiologist can inflate the cuff within the patients trachea and thereby provide a seal between the outer walls of the intubation tube and the encircling tracheal lining. Such cuffs, however, have not proved entirely satisfactory for a number of reasons. Initially, the intubation tube is coated with a lubricant having anesthetic properties to prevent irritation upon insertion and annoyance by its presence. The lubricant occasionally reduces the friction between the cuff and intubation tube to such an extent that the deflated cuff slides upwardly over the tube upon encountering a restricted organ such as the sphincter muscles of the larynx. Additionally, the small air tube leading from the cuff to the syringe type bulb creates an additional irritant, obstructs the anesthesiologists view, becomes twisted and tangled, and often interferes with the conduct of the operation itself. Finally, since the cuff is constructed from rubber, it cannot be adequately sterilized by steam or other high temperature methods. Thus, it is possible for infections such as inflammatory sore throats to be transferred from one patient to another.

Another variety of intubation tube, the Riisch type, employs an inflatable cuff which is built into, and forms a partof the intubation tube at its lower or distal end. The small air tube used to inflate the cuff passes internally through the intubation tube to the portion surrounded by the cuff where it is connected through the wall of the intubation tube to the internal chamber of the cuff. Although the Riisch type endotracheal tube eliminates several of the problems associated with the previously described type, it is not wholly satisfactory. In the first place, the Riisch type tube is comparatively expensive. Secondly, the' previously described problems associated with high temperature sterilization are also encountered with the Riisch type tube. Finally, the internally disposed air tube can interfere with the insertion of objects through the intubation tube. This is especially true at the commencement of the operation when the anesthesiologist inserts the intubation tube through the larynx, for in so doing a rigid or semi-rigid stylet is used within the tube to lend rigidity thereto for accuracy of manipulation and direction.

Among the several objects of the present invention may be noted the provision of an endotracheal tube which adapts itself t0 easy placement within the patients trachea; the provision of an endotracheal tube which expands within the trachea so as to form a fluid-tight seal with the encircling tracheal lining; the provision of an endotracheal tube which contains no internal or external obstruction to interfere with the conduct of an operation; the provision of an endotracheal tube which is relatively simple in construction and economical to manufacture; the provision of an endotracheal tube which is completely disposable; and the provision of an endotracheal tube which creates comparatively little irritation when placed within a patients trachea. Other objects and features will be'in part apparent and in part pointed out hereinafter.

The invention accordingly comprises the constructions hereinafter described, the scope of the invention being indicated in the following claims.

In the accompanying drawings, in which several of various possible embodiments of the invention are illustrated,

FIG. 1 is a front elevational view of an endotracheal tube constructed in accordance with and embodying the present invention;

FIG. 2 is a sectional view taken along line 2-2 of FIG. 1;

FIG. 3 is a sectional view taken along line 3-3 of FIG. '2;

FIG. 4 is a fragmentary perspective view partially broken away and in section of a modified form of the present invention;

FIG. 5 is a front elevational view of an endotracheal tube constructed in accordance with and embodying the present invention and showing the outline of the human head, torso, mouth and trachea in broken lines;

FIG. 6 is a fragmented front elevational view of a modified form of the present invention;

FIG. 7 is a fragmented sectional view of the endotracheal tube illustrated in FIG. 6, showing the accordionlike pleats in the extended position;

FIG. 8 is a fragmented front elevational View of another modified form of the present invention;

FIG. 9 is a fragmented front elevational view of the endotracheal tube illustrated in FIG. 8, showing a stylet extending therethrough and being in operative engagement with the folded distal end thereof;

FIG. 10 is a sectional view taken along line 10-10 of FIG. 9;

FIG. 11 is a front elevational view partially broken away of still another modified form of the present invention;

FIG. 12 is a sectional view taken along line 1212 of FIG. 11;

FIG. 13 is an elevational view partially broken away and in section of another modified form of endotracheal tube;

FIG. 14 is a fragmentary perspective view, partially broken away and in section, of the endotracheal tube illustrated in FIG. 13; and

FIG. 15 is a perspective view of a cuff forming part of the present invention and used on the endotracheal tube illustrated in FIG. 13.

Corresponding reference characters indicate corresponding parts throughout the several views of the drawings.

Referring now in more detail and by reference characters to the drawings Which represent practical embodiments of the present invention, A designates an endotracheal tube including a flexible relatively soft tube 1 made of synthetic or natural materials and of sufficient length to extend from the vestibular portion of a patients trachea immediately caudad to the larynx to a terminal point beyond his mouth. Disposed encirclingly around the distal or rear end of tube 1 is an inflatable cuff 2 which is preferably constructed from soft rubber or other suitable flexible material. The annular margins of cuff 2 snugly embrace the wall of tube 1, thereby creating an air chamber 3 between the outer surface of tube 1 and the inner surface of cuff 2. Preferably, at least one of the annular margins of cuff 2 is adhesively or otherwise suitably sealed to the wall of tube 1 to maintain cuff 2 in place. Tube 1 is provided with an aperture 4 which provides communication between the internal bore of tube 1 and air chamber 3. Snugly encircling tube 1 and completely covering aperture 4 is a collar 5 which is preferably made of rubber. A small portion of collar 5 diametrally opposed to aperture 4 is cemented or otherwise securely fastened to tube 1 to prevent longitudinal movement of collar 5 on tube 1, all as best seen in FIGS. 1-3. Thus, collar 5 creates a unidirectional air valve over aperture 4. When the air pressure within tube 1 exceeds the pressure within air chamber 3, the portion of collar 5 surrounding aperture 4 will lift slightly away from aperture 4 and permit air to enter air chamber 3, thereby inflating cuff 2 and causing it to expand radially outward from tube 1. However, if the pressure in air chamber 3 exceeds the pressure in the internal bore of tube 1, collar 5 will be pressed into sealing engagement with the outwardly presented margins of aperture 4, thereby preventing the escape of air or loss of pressure within air chamber 3. In this regard, it should be noted that collar 5 should be constructed so that only a slight increase in pressure within tube 1 will lift it away from aperture 4. Moreover, if one of the annular margins of cuff 2 merely embraces tube 1, but is not in any other way secured thereto, air can escape through that margin when a predetermined pressure is reached. The unattached annular end of cuff 2 is sized so that it will diametrally expand and lift away from tube 1, thereby allowing air to escape, before the pressure in air chamber 3 reaches a point where it creates an outwardly directed force on cuff 2 of sufficient magnitude to injure or unduly annoy the tracheal lining.

Provided for cooperation with tube 1 and for insertion therein is a semi-rigid stylet 6 which is preferably manufactured from copper, brass, or stainless steel wire or from synthetic resin rod-stock. One end of stylet 6 is preferably curved in the provision of an eye 7 for grasping and manipulating it. Provided for snug-fitting placement over stylet 6 is adjustable collar 8 which is preferably fashioned from rubber or cork. Collar 8, being diamettrically greater in size than the internal bore of tube 1, limits the extent to which stylet 6 can be inserted within tube 1.

Before leaving the possession of the manufacturer endotracheal tube A and stylet 6 should be suitably sterilized and cuff 2 should be deflated so that it clings snugly to the wall of tube 1. The manufacturer should then seal the endotracheal tube A and stylet 6 in a sterilized package so that it may be used immediately by a hospital upon removal from the package.

Immediately before the operation, after removal of endotracheal tube A and stylet 6 from the package, tube 1 and cuff 2 are smeared with a lubricant such as Xylocaine jelly which has anesthetic properties to lessen irritation upon placement. Collar 8 is adjusted on stylet 6 to provide an optimum working length and it should never be set so as to permit stylet 6 to extend beyond the distal end of tube 1 where it could scratch or otherwise injure throat tissues. The anesthesiologist then inserts the distal end of tube 1 into the patients mouth and through the larynx, using stylet 6 to both manipulate tube 1 and provide rigidity thereto. It should be noted that the rigidity of tube 1 can further be controlled by either reducing or raising its temperature immediately r before placement. It should be further noted that there is no air tube internally disposed within tube 1 to interfere with the manipulation of stylet 6. Also there is no externally disposed air tube to obstruct the anesthesiologists view or to become twisted and tangled. Finally, after cuff 2 has passed beyond the sphincter muscle of the larynx and entered the vestibular portion of the trachea, the end of tube 1 projecting beyond the mouth is connected to an anesthesia machine, which being conventional in design and operation, is not illustrated or described in further detail.

The anesthesiologist has at his option several methods by which he can in effect create a back pressure in the lungs and thereby increase the pressure within tube 1 to lift collar 5 and inflate cuff 2 until it forms a seal with the encircling tracheal lining. First, the anesthesiologist can manually exert short, quick, vigorous bursts of pressure on the rebreathing bag of the anesthesia machine. Second, he can adjust the machine to create a high flow rate of gases which exceeds the escape rate about endotracheal tube A. Third, he can manually close the patients mouth about the projecting tube 1 and block the nostrils while exerting pressure on the rebreathing bag. When employing either of the first two methods, it may be desirable to initially advance tube 11 into the patients trachea far enough to cause it to impinge against a constrictive area of the trachea or bronchus so as to prevent excessive escape of fluid along the exterior surface of tube A at the outset. After cuff 2 is partially inflated, tube 11 is withdrawn from the constrictive position to a position of optimal function.

It is possible to provide a modified endotracheal tube B substantially as shown in FIG. 4. Endotracheal tube B is very similar to endotracheal tube A and includes a soft flexible tube 9, a cuff 10, and an aperture 11. Completely disposed over aperture 11 and having one margin adhesively or otherwise suitably sealed to tube 9 is a flexible saddle 12 preferably made from a thin sheet of soft rubber. Saddle 12 serves the same function as collar 5, that is, it acts as a unidirectional air valve over aperture 11 permitting inflation of cuff 10 when the pressure in tube 9 exceeds the pressure inside culf 10. In other respects endotracheal tube B is identical to endotracheal tube A and is operatively emplaced within the patients trachea in a similar manner.

It is possible to provide another modified endotracheal tube C substantially as shown in FIGS. 6 and 7. Endotracheal tube C includes a flexible soft plastic tube 13, having a distal end portion 14 which is provided with a plurality of annular accordion-like pleats 15. In the contracted position, the position in which tube 13 and pleats 15 are molded, and the position which they normally seek, the outer margins of accordion-like pleats 15 are of such diameter that they will fit snugly against the tracheal lining beyond the larynx. Distal end portion 14 terminates in an aperture 16 which is diametrally smaller than the internal bore of tube 13, and is inwardly flanged to provide an internal annular groove 17.

Provided for cooperation with endotracheal tube 13 is a stylet 18 having an eye 19 at one end for grasping and manipulating it.

Before insertion, tube 13 and distal end portion 14 are lubricated with an anesthetic jelly in a manner similar to that previously described. Stylet 18 is inserted into tube 13 and through distal end 14, where it is received by groove 17 which prevents it from passing through aperture 16, all as best seen in FIG. 7. Further insertion of stylet 18 causes distal end portion 14 to axially extend and concurrently contract in diameter. Distal end portion 14 is extended until the outer margins of accordionlike pleats 15 possess a diameter substantially equal to that of tube 13. The anesthesiologist thereupon inserts distal end portion 14 through the patients larynx and into the vestibular portion of the trachea, and, upon obtaining correct placement, gently removes stylet 18 allowing accordion pleats 15 to longitudinally contract and simultaneously increase in diameter until the outer margins thereof are in contact with the tracheal lining. Thus, a snug-fitting seal is formed between the trachea and endotracheal tube C and an anesthetic can easily be administered therethrough.

It is possible to provide still another modified endotracheal tube D substantially as shown in FIGS. 8-10. Endotracheal tube D includes a flexible soft plastic tube 20 having a flared bell-mouth or funnel-shaped distal end 21. Provided for cooperation with endotracheal tube D and for insertion therein is stylet 22 provided at one end with an eye 23 and a fork 24 at its opposite end. The lateral distance between the furcations of fork 24 is slightly less than double the thickness of the walls of funnelshaped end 21.

To prepare endotracheal tube D for placement within the patients trachea, the anesthesiologist doubles the walls of the funnel-shaped end 21 inwardly in the configuration illustrated in FIGS. 9 and 10 to provide an inwardly presented fold 25. In so doing, the size of funnel-shaped distal end 21 is reduced. The anesthesiologist thereupon engages fold 25 with fork 24 so as to prevent distal end 21 from reverting to its original shape. The walls of tube 20 and distal end 21 are then lubricated in a manner previously described, and funnel-shaped distal end 21 is thereafter inserted through the patients larynx and into the vestibular portion of the trachea.

After obtaining correct placement in the trachea, the anesthesiologist gently removes stylet 22 thereby releasing its grip on fold 25. Distal end 21 thereupon reverts to substantially its original shape and contacts the encircling tracheal lining forming a snug seal therewith.

It is possible to provide still another endotracheal tube E substantially as shown in FIGS. 11 and 12. Endotracheal tube E, like tubes A and B, includes a soft flexible tube provided with an aperture 31 in the distal end wall thereof. Cemented or otherwise suitably sealed to tube 30 at aperture 31 is a valve bushing 32 integrally including a diametrally reduced nose portion 33 which fits snugly within aperture 31 and a diametrally enlarged flange 34. Bushing 32 is preferably formed from a somewhat flexible synthetic resin and is further provided with a concentric bore 35 which extends axially through nose portion 33 and flange 34. Hingedly secured to the outwardly presented face of valve bushing 32 and also formed integral thereto is flipper valve element 36 which is adapted to cover and seal the outwardly presented margins of bore 35, all as best seen in FIG. 12. Encircling the distal end of tube 30 as well as flipper valve element 36 and adhesively or otherwise secured to the wall of tube 30 is inflatable elastomeric cuff 37. Thus, when the pressure in tube 30 exceeds the pressure in cuff 37, it will lift valve element 36 off its seat to permit inflation of cuff 37 However, when the pressure within cuff 37 exceeds that in tube 30, valve element 36 will be pressed into sealing- Wise contact with the outwardly presented margins of bore 35. Em'placement of endotracheal tube E and inflation of cuff 37 is achieved in a manner similar to that described in connection with endotracheal tube A.

Referring now to FIGS. 13-15, it is possible to provide a further modified form of endotracheal tube F which is also somewhat similar to endotracheal tube A. Endotracheal tube F includes a flexible relatively soft tube or conduit 40 provided near its distal end with a radial aperture 42. Encircling the distal end of tube 40 is an inflatable cuff 44 formed from a soft rubber or other suitable flexible material and having diametrally reduced forward and rear ends 46, 48, respectively, which endwise define an internal fluid chamber 50. The forward end 46 snugly embraces but is not in any other way secured to the outer surface of tube 40, while the opposite or rear end 48 integrally merges into an inwardly extending sleeve 52 which terminates beyond aperture 42 at an arcuate end margin 54. The terminal end of sleeve 52 is further somewhat truncated in the formation of an oblique margin 56 which extends rearwardly from arcuate end margin 54 to a point on tube 40 substantially diametrally opposite aperture 42. Oblique margin 56 reduces the embracive grip of sleeve 52 about tube 40 at aperture 42 and forwardly therebeyond so that when the fluid pressure within tube 40 is increased, the portion of sleeve 52 overlying aperture 42 will lift slightly away from aperture 42 and allow fluid to enter fluid chamber 50 for inflation of cuff 44. The terminal end portion of sleeve 52 serves as a flap-like unidirectional fluid valve. In this connection, it should be noted that the same effect can be achieved by using a full sleeve and providing it with an axially extending slit located diametrally opposite aperture 42.

As will be seen by reference to FIG. 15, cuff 44 prior to placement on tube 40 comprises the diametrally reduced forward end 46, an elongated tubular end portion 58, and an enlarged bulbous intermediate portion 60 which assumes a somewhat bulged or elliptical elevational shape when free of external forces. All of the foregoing are integrally formed by a dipping, molding, or other suitable operation. Elongated end portion 58 is subsequently invaginated so that its terminal end projects into bulbous intermediate portion 60 in the formation of sleeve 52 and diametrally reduced rear annular end 48, the latter of which overlies and embraces the former. In this regard, it should be noted that both forward end 46 and elongated end portion 58 are slightly less in diameter than the diameter of tube 40 so that when cuff 44 is fitted over tube 40 forward end 46 and sleeve 52 will snugly embrace the outer surface thereof. Moreover, rear end 48 will tightly encircle the rear portion of sleeve 52 so as to provide additional assurance against leakage at this point or unauthorized axial movement of cuff 44 on tube 40. If desired, an adhesive can be applied to the inner surface of sleeve 52 to maintain it in place or the same end can be achieved by use of a cinch encircling either diametrally reduced rear end 48 or the portion of sleeve 52 embraced by end 48. It should be noted, however, that the: frictional engagement established is sufficient to maintain cuff 44 in place without the aid of these expedients.

In use, endotracheal tube F, like endotracheal tube A, is inserted through the patients mouth and larynx with cuff 44 completely deflated and adhering to the wall of tube 40, preferably with the aid of a stylet (not shown). When cuff 44 reaches the vestibular portion of the trachea, the outer or proximal end of tube 40 is connected to an anesthesia machine and the pressure within tube 40 is increased slightly above ambient conditions by any of the methods previously described. The pressurized fluid lifts the terminal portion of sleeve 52 away from aperture 42 allowing fluid to flow into air chamber 50 and thereby inflate cuff 44 until it engages the tracheal lining and imposes a fluid barrier within the trachea between the outer surface of tube 40 and the tracheal lining.

At a predetermined pressure forward annular end 46 of cuff 44 will expand to such a point that it will allow fluid to escape along the exterior surface of tube 40 and into the trachea. In other words, forward annular end 46 is sized so that it will lift away from tube 40 and allow fluid to escape when a predetermined pressure within air chamber 50 is reached. This precludes over-inflation of cuff 44 and thereby prevents ischemia or other damage to the encircling tracheal mucosa. This feature also facilitates removal of endotracheal tube F for when withdrawn slightly by a slight pull on tube 40, inflated cuff 44 will engage the diametrally reduced sphincter muscles of the larynx which will squeeze cuff 44, reducing the volume of and causing the pressure in fluid chamber 50 to increase to a point where it lifts annular forward end 46 away from tube 40 and allows fluid to escape. Thus, damage or irritation to the vocal cords upon removal is avoided.

It is readily apparent that endotracheal tubes A, B, C, D, E, and F, being relatively simple in design, are obviously economical to manufacture. Because of the low cost, the hospital can discard the used tubes upon completion of the operation, and it need not worry over transferring infections from one patient to another through reuse of tubes. The tubes, being simple in construction, have few parts which interfere with the conduct of the operation, or obstruct the anesthesiologists view and interfere with his movements. Moreover, the simple construction is adapted to reduce patient irritation to an absolute minimum.

It should be noted that intubation tubes of similar design but differing in size can be constructed for use with varying sized patients as well as for insertion in other body canals.

In view of the above, it will be seen that the several objects of the invention are achieved and other advantageous results attained.

As various changes could be made in the above constructions without departing from the scope of the invention, it is intended that all matter contained in the above description or shown in the accompanying drawings shall be interpreted as illustrative and not in a limiting sense.

What is claimed is:

1. An intubation tube comprising an open-ended flexible tubular conduit provided with a radially extending aperture, an inflatable cuff in sealingwise engagement with the tube at its ends and on each side of the aperture whereby to form a fluid chamber intermediate the walls of the tube and cuff, and a check valve on the tubular conduit and normally covering the aperture, the check valve being oriented so when the pressure of fluid within the tubular conduit increases above that in the chamber the check valve will open and the fluid will flow into the chamber, thereby inflating the cuff.

2. An intubation tube according to claim 1 in which the valve is an expansible collar encircling the tubular conduit and overlying the radial aperture.

3. An intubation tube according to claim 1 and further characterized by a stylet for manipulating the tubular conduit during placement within a body canal.

4. An intubation tube comprising a tubular conduit provided with a substantially radially extending aperture, an inflatable cuff having forward and rear annular ends which embrace the tubular conduit on each side of the aperture so as to form a fluid chamber which communicates with the interior of the tubular conduit through the aperture, and a flexible sleeve embracing the tubular conduit, the sleeve adjoining one of the annular ends of the cuff and extending inwardly therefrom into the chamber to a point beyond the aperture, whereby the sleeve overlies the aperture in the formation of a unidirectional fluid valve.

5. An intubation tube according to claim 4 wherein the sleeve and cuff are formed integral to one another.

6. An intubation tube according to claim 4, wherein one of the annular ends on the cuff merges into the sleeve.

7. An intubation tube according to claim 6 in which the sleeve is an invaginated continuation of the annular end of the cuff into which it merges.

8. An intubation tube according to claim 6 in which the free terminal end of the sleeve within the fluid chamber is truncated in close proximity to but diametrally opposite from the radial aperture in the formation of a rearwardly extending oblique margin whereby the embracive grip of the sleeve on the tubular conduit at the radial aperture is relaxed.

9. An intubation tube according to claim 6 in which the opposite annular end of the cuff lifts away from the exterior surface of the tubular conduit when a predetermined pressure is reached within the fluid chamber so as to allow fluid to escape therefrom whereby to prevent overinfiation of the cuff.

References Cited UNITED STATES PATENTS 249,557 11/1881 Truesdell 137-5253 281,043 7/1883 Finney 128-246 397,060 1/ 1889 Knapp 128-246 504,424 9/ 1893 Pezzer 128-349 1,315,955 9/1919 Gill 137-5253 2,45 8,305 1/ 1949 Saunders 128-348 2,813,531 11/1957 Lee 128-350 2,876,767 3/1959 Wasserman 128-151 OTHER REFERENCES Martinez, An Improved Cuffed Tracheostomy Tube, Jour. Thorac. Surg, vol. 47, #3, March 1964, pp. 404 405.

DALTON L. TRULUCK, Primary Examiner

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