United States Patent 3734100

Improved catheter tubes and their method of construction having a comformable balloon cuff of silicone rubber of low hardness, modulus, and stress values, and which results in less pressure necrosis and cuff failure in use. Specific examples include endotracheal tubes, Foley catheters, tracheostomy tubes, urethral catheters, and catheters for use in gastric, esophageal, pharyngeal, nasal, intestinal, rectalcolonic, choledochal, arterial venous, cardiac and endobronchial applications.

Walker, Robert D. (Racine, WI)
Bazell, Seymour (Skokie, IL)
Goldberg, Edward M. (Glencoe, IL)
Ostensen, Ralph G. (Morton Grove, IL)
Application Number:
Publication Date:
Filing Date:
Primary Class:
Other Classes:
International Classes:
A61M16/04; A61M25/00; A61M25/02; (IPC1-7): A61M25/00; A61M16/00
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US Patent References:
3547126CATHETERDecember 1970Birtwell
3481339ENDOTRACHEAL TUBEDecember 1969Puig
3292627CatheterDecember 1966Harautuneian
2308484CatheterJanuary 1943Auzin et al.

Other References:

Cooper et al. Surg, Gyne. & Obstet. December 1969 Vol. 129 pp. 1235-1241.
Primary Examiner:
Truluck, Dalton L.
We claim

1. An improved catheter comprising:

2. An improved catheter as in claim 1 wherein the wall thickness of said cuff is preselected to provide for a predetermined, controlled shape of the cuff when inflated.

3. An improved catheter as in claim 2 wherein said cuff walls are preselected to vary in thickness in cross-section.

4. As improved catheter as in claim 2 wherein said cuff walls are preselected to vary in thickness in an axial direction.

5. An improved catheter as in claim 1 wherein the cross-sectional shape of said body portion is preselected to substantially conform to a body cavity in which said catheter is used.

6. An improved catheter as in claim 5 wherein the wall thickness of said cuff is preselected to provide for a predetermined, controlled shape of the cuff when inflated.

7. An improved catheter as in claim 1 having a plurality of inflation lumens disposed in said body portion walls.

8. An improved catheter as in claim 1 wherein said distal end is adapted for use as an endotracheal tube.

9. An improved catheter as in claim 1 wherein said distal end is adapted for use as a Foley-type catheter.

10. An improved catheter as in claim 1 wherein said Shore A hardness is less than about 25, said tensile strength is in the range of from about 500-600 psi, said elongation is in the range of from about 1,000 to 1,500 percent, and said stress value upon sealing inflation is in the range of from about 15-25 percent.

11. An improved catheter as in claim 1 wherein said main body is a silicon rubber of hardness greater than said cuff.

This invention is directed to improved cuffs for catheters, for example, endotracheal tubes, and to a method of construction of the improved catheters. More particularly, the invention is directed to a special molded silicone rubber conformable cuff having low values of hardness, modulus and stress, the latter expressed as a percentage of the breaking stress of the cuff.


Catheters are extremely important and useful medical tools for the input or withdrawal of fluids from the body of a patient. Generically, catheters are tubular in shape and have a retaining and/or sealing inflatable balloon cuff near the distal (intra corporeal) end of the tube. Often the catheters must remain in place for substantial periods of time. Present catheters have not been entirely satisfactory since they tend to cause tissue necrosis from pressure or biochemical incompatibility of the inflatable balloon cuffs. For example, standard rubber cuffs of endotracheal tubes in place for as little as 72 hours can cause severe pressure necrosis. Latex material is chemically irritating and polyvinylchloride plastic cannot elongate sufficiently to provide adequate balloon volumes, has no memory and prunes upon deflation. A more detailed discussion of the serious aspects of these problems follows, with special emphasis on endotracheal tubes, by way of example.

In cases of patients requiring general inhalation anesthesia, the quickest and easiest way to insure a clear upper airway for ventilation of the lungs is by endotracheal intubation. In the simplest of terms, this involves slipping a tube down to the trachea through the larynx to provide an air passage to the lungs. The patient's head is supported and the neck is slightly flexed on the trunk to provide for a relatively straight-line approach to the larynx. The jaw is kept apart, and the tube is slipped directly down into the trachea. This process can be accomplished in a very few seconds, which in an emergency may be life-saving since the person who cannot breathe adequately will be dead within minutes. This also eliminates obstruction of the breathing passage by vocal cord spasms since the tube is directed through the larynx.

While uncuffed tubes have been used, they do not seal off the trachea from the digestive tract and aspirate. Further, they do not provide a closed system and positive pressure ventilation. Endotracheal tubes having an expansible cuff which effectively seals off the trachea, retains the tube in place, and provides a passage therethrough, have been used for some time. Once in place, a cuff-type endotracheal tube provides the following advantages. A clear upper airway is insured. Aspiration of blood, mucus and vomitus into the lungs is prevented. Resistance to air flow and thus the oxygen consuming work of breathing is reduced. An Ambu bag or a positive-pressure respirator may be employed to assist ventilation. The excessive secretions causing lower airway obstruction can be easily removed by direct aspiration. Inhalation anesthesia can also be given easily, if required. Use of the cuff provides a closed system such that oxygen or other gases can be given in a controlled and measured manner and that carbon dioxide can be removed under controlled circumstances.

Recent reports have clearly established the relationship between the use of cuffed endotracheal tubes and subsequent occurrence of various types of tracheal injury, including tracheal stenosis, tracheal malacia, or tracheo-esophageal fistula at the cuff site. Tracheal stenosis is the more frequent of these complications, and has been estimated to occur in up to 15 percent of the patients whose survive prolonged ventilatory assistance by means of the tubes. The tracheal injury is due to pathologic evolution of necrosis as a result of the pressure at the site of contact between the balloon cuff and the tracheal wall. Present expansible cuffs or balloons require sufficiently high pressure that the tender mucosal membrane is severely injured by prolonged contact therewith. Several techniques have been developed in clinical practice to reduce the hazard of the tracheal injury. These include careful inflation of the cuff with a volume of air just sufficient to provide a seal with the tracheal wall. However, since the tubes are frequently subjected to forces of mechanical aspirating equipment, movement of the patient and the like, the amount of pressure must be sufficient so that the seal between the outer balloon wall and the trachea is sufficiently secured to resist such forces. This unfortunately results in necrosis-causing cuff pressures. The second technique involves hourly deflation of the cuff for 5 minutes, and a third method involves alternating the site of contact with the tracheal wall by use of double-cuffed tubes which are periodically and alternately inflated and deflated.

Recent studies of Bryant et al. (Journal of American Medical Association, Volume 215, No. 4, pages 625-628, "Reappraisal of Tracheal Injury from Cuffed Tracheostomy Tubes") indicates that such widely practiced techniques of hourly deflation of the balloon cuffs fail to protect the trachea from significant injury. In addition, the contour deformity or out-of-roundness of the trachea, low compliance and high intra-cuff pressures characteristic of presently used balloons and accidental over-inflation of the cuffs are the principal causes of tracheal injury.

The method of alternating cuff sites also fails to prevent significant injury. Indeed, because the cuffs extend over a greater length of the tube, the injury is also more extensive and makes the operative repair of tracheal stenosis or tracheal-esophageal fistula more difficult. The above authors devised a "minimal" leak technique, in which the balloons were first inflated to a no-leak position and then a sufficient amount of inflation air was withdrawn until an audible leak occurred with each inspiration. While this reduced the hazard of excessive cuff inflation, it does not prevent rotation, slipping or leakage of the tube, and may also permit a certain amount of aspiration of fluids into the lungs.

Still another approach to stenosis problems was reported by Arens et al. in the Journal of Thoracic and Cardiovascular Surgery, Volume 58, No. 6, December 1969, "Volume-Limited Intermittent Cuff Inflation for Long-Term Respiratory Assistance." This involves the use of endotracheal intubation with polyvinyl-cuffed endotracheal tubes using Bird respirators. The cuff is inflated periodically, timed to be inflated to a volume at which the cuffs would not leak at the peak of inspiration. This provides a preset volume-limited intermittent cuff inflator for use in both pressure-limited and volume-limited ventilation. The clinical and experimental evidence reveals that such intermittently inflated cuffs produce less tracheal damage than does a cuff that is constantly inflated. While there were no evidences of severe errosion of the trachea or dilation, a majority of the subjects had up to moderate effects.

The practice of alternating two cuffs at different levels results in a larger area of stenosis because the width of each cuff is relatively narrow. High pressures are required to inflate a narrow cuff, and thus the lateral pressure on the tracheal mucosa is also greater. If the lateral pressure due to cuffs approximates or is greater than the capillary blood pressure in tissues, ischemia may readily be produced, especially when a patient is in hypotensive shock. Ischemic damage results in weakness of the tracheal wall, dilation, fibrosis, and finally, tracheal stenosis.

Still another suggestion to the problems of trauma connected with pressure necrosis due to the cuff has been that of Drs. Kamen and Wilkinson. Their measurements show that with standard cuffed endotracheal tubes presently in use, for example, a No. 34 red rubber endotracheal tube show intra-cuff levels of 280 mm. Hg and at the tracheal wall, that is between the cuff and the trachea, as high as 200 mm. Hg. Kamen and Wilkinson devised a latex cuff in which the intra-cuff space was filled with a polyurethane foam. This cuff operates in a manner the reverse of the usual cuff, that is, the cuff is always in the extended shape with the latex sheath stretched over the ball of polyurethane foam through which the tube extends. In order to insert the Kamen tube, the pilot tube is attached to a vacuum, and the low pressure draws out some of the air in the polyurethane foam cells. The pilot tube is then pinched shut and the cuff in the relatively deflated form is then inserted through the larynx into the trachea.

However, the Kamen construction has two very serious drawbacks. First, the deflated size of the cuff is substantially larger than the tube itself in view of the fact that the nature of the polyurethane foam prevents all of the cells from being open. Thus, it cannot be entirely evacuated, and the deflated volume is physically larger than the standard latex or polyvinylchloride empty balloon. Secondly, the endotracheal tube can become trapped in the patient and impossible to remove other than by surgical procedures when the external pilot tube becomes blocked, clogged, cut or separated from the latex sheath. In short, the polyurethane foam acts as a physical spring exerting an outward pressure against the latex sheath, and the spring must be collapsed by the vacuum. In addition, the ability to collapse the polyurethane foam depends upon the integrity of the latex sheath. Where the integrity is disrupted or broken, it will be impossible to pull sufficient vacuum through the pilot tube to collapse the polyurethane foam to a diameter small enough to be able to remove the endotracheal tube through the larynx. Likewise, in field emergency situations, where no vacuum creating source is available, such tubes cannot be used. In contrast, the cuffs of our tubes can be breath inflated if necessary. While the Kamen polyurethane foam filled sheath type of cuff does have the advantage of relatively low pressure exerted between the cuff and the tracheal wall, the danger of impossibility of removal is a serious drawback. From the point of view of safety, it is far better if a rupture of the cuff causes deflation and a loss of securing pressure, rather than leading to impossibility of removal.

Another type of cuffed catheter is a Foley type urethral retention catheter. This urethral retention catheter is utilized for prolonged or chronic bladder drainage. The catheter is retained within the bladder by inflating the cuff. This prohibits it from being withdrawn through the urethra. The inflated cuff may cause undesirable pressure against the bladder wall or urethra. These problems are further complicated in cases involving an enlarged prostrate. As in the endotracheal tube, the cuff pressures and conformability are significant.

A recent attempt to adapt silicone rubber to use in Foley-type catheters, U.S. Pat. No. 3,547,126, follows the prior art of having a balloon substantially round in cross section of a relatively hard silicone rubber. The inflation pressures, and predictably the pressure necrosis, is not appreciably different from the standard rubber latex, or polyvinylchloride cuffs. In addition, the non-conformable round balloon shape provides only for point contact (in cross section) with the interior of the bladder.

Finally, the wall thickness of latex, rubber or silicone cuffs constructed by the common dip coating process is, practically speaking, impossible of reproducible, controlled thickness. Manufacturing rejects and unexpected "bulge" failures are relatively high.



It is among the objects of this invention to provide improved cuffed catheter tubes such as endotracheal tubes, Foley-type urethral retention catheters, urethral catheters, and catheters for use in gastric, esophageal, pharyngeal, nasal, intestinal, rectal-colonic, choledochal, arterial, venous, cardiac, endobronchial and tracheostomy applications, which have a low-pressure conformable cuff of physio-logically compatible material.

It is another object of this invention to provide a catheter having a special conformable cuff therefor, which overcomes the difficulties described above with respect to the prior art.

It is another object of this invention to provide improved catheters, for example, endotracheal tubes which are simple of construction and operation, and which provide for secure retention and sealing against movement, aspiration or fluids leakage, yet which provide a seal of sufficiently low pressure that tissue damage due to pressure necrosis is reduced.

It is another object of this invention to provide a conformable cuff for catheters generically, which cuff is a physiologically acceptable silicone rubber composition, and which has special properties of low values of hardness, modulus and stress, the latter based on a percentage of the breaking stress, and yet which is tear resistant, extremely soft, easily distensible, and will conform to irregularities in the passage or body cavity in which it is placed.

These and other objects of this invention will become evident from the detailed description which follows.


The detailed description has reference to the following FIGS.:

FIG. 1 is a perspective view of one type of catheter, specifically an endotracheal tube, in accord with the invention.

FIG. 2 is a longitudinal sectional view along the line 2--2 in FIG. 1, showing the cuff in a substantially deflated position.

FIG. 3 is a cross-sectional view along the line 3--3 of FIG. 2.

FIG. 4 is a longitudinal sectional view of the cuff area of the catheter showing it in partially inflated position.

FIG. 5 shows the method of insertion of an endotracheal tube in the trachea of a patient.

FIG. 6 shows one method of inflation of the cuff of the tube in position.

FIG. 7 shows in cross-section another embodiment of the invention where the main tube and cuff walls are of predetermined varying thickness to provide controlled balloon inflation, shape and size.

FIG. 8 shows partly in section the principles of this invention adapted to a Foley-type catheter in the inflated condition in use in the urinary bladder.

FIG. 9 shows, partly in longitudinal section, cuff walls that vary longitudinally in thickness to provide for differential expansion such as shown in FIG. 8.


We have discovered that catheters having conformable cuffs made of a silicone rubber having preselected low values of hardness, modulus, and stress, the latter expressed as a percentage of the breaking stress and which is extremely soft, provide a cuff that is tear resistant, easily distensible, and will permit complete sealing, even over irregularities, with reduced pressure necrosis. We have also found that the basic theory of pressure cuffs of the prior art appears to have been in error. The prior art cuffs specify a balloon material which has a relatively high tensile strength, on the assumption that this will prevent rupture of the balloon cuff under the stress which it encounters in use. In addition, the balloon material has been chosen to have a relatively high hardness and low percentage elongation to provide for sufficient lifetime and mechanical strength against rupture. However, these properties lead to relatively high intra-cuff pressures, a generally spherical balloon shape which is axially centered around the main catheter tube, and requires a relatively high inflation pressure. As a result, the pressure on the tissues contacted by the cuff upon inflation is sufficiently high to cause tissue necrosis.

In contrast, we use an extremely soft, silicone rubber which has a relatively low tensile strength and high elongation. We have discovered that the cuff material should have a definite strain rather than stress value and should be able to assume the given strain value at the lowest possible stress value. The stress value should represent as low a percentage of the breaking stress as possible. In addition, the low value of stress, based on the percentage of the breaking stress, and the softer silicone rubber composition permits the cuff to more completely conform to irregularities of the passage or body cavity, e.g., a trachea, without developing high areas of stress. The conformability allows more equal pressure distribution when the cuff is subjected to pressure variations. This eliminates high point pressure loadings on the tissue. Any type of physiologically compatible plastic or rubber material which meets these criteria may be used. We prefer to use a silicone rubber which meets the above critical parameters. Not only does this rubber have accepted physiological compatability, but it may be compounded and cured to the required degree of softness, low hardness, relatively low tensile strength, and high percentage elongation of breaking stress.


Referring now to the Figures, the following detailed description is made with reference to a specific embodiments of an endotracheal tube and a Foley-type catheter. However, these embodiments are merely illustrative and not limiting of the principles of the invention which may equally be applied to catheters for use in endotracheal tubes, Foley catheters and catheters for use in gastric, esophageal, pharyngeal, nasal, intestinal, rectal-colonic, choledochal, arterial, venous, cardiac, endobronchial and tracheostomy applications.

FIG. 1 shows a general perspective view of one embodiment of an endotracheal tube illustrating the principles of this invention. At the proximal end of the tube 1 (in the right of FIG. 1) is a pilot tube 2 which connects with a cuff inflation lumen 3 in the wall 4 of the main body 34 of the endotracheal tube. The lumen continues along the length of the tube to an opening 5 beneath the cuff 6. The proximal end also has an adapter means 7 for connection with mechanical or hand aspiration means. The adapter 7 may or may not be used depending upon the medical condition of the patient. The adapter communicates with a central passageway 8, which is a ventilation passageway in the case of an endotracheal tube, and a drainage passageway in the case of a Foley-type catheter (see passage 9 in FIGS. 8 and 9). The tube 1 is preferably made of a silicone rubber which is smooth throughout its entire length. Such tube may be made by an extrusion process in which the lumen 3 is extruded simultaneously with the central passageway 8. The lumen 3 extends distally along the main body under the cuff 6 so that the lumen communicates with opening 5 and the intra-cuff space 11. It is an important aspect of this invention that the cuff silicone rubber material be relatively soft compared to the silicone rubber material used for the tip and shaft. The latter must be relatively hard to facilitate insertion while the cuff silicone rubber material must be relatively soft to provide conformability.

The distal tip 12 of the tube 1 may be bias or diagonal cut as at 13 and chamfered as at 14 so as to prevent tissue trauma upon insertion. In addition, the diagonal cut 13 provides for a tip, oval in cross-section, the leading edge or point of which, 15, is sufficiently small and rounded to provide non-damaging insertion through the larynx, (in the case of an endotracheal tube), or through the sphincter (in the case of a Foley-type catheter). The tip may be integral with or otherwise secured to the main body 34 so it is not pulled off upon withdrawing the catheter from the patient. As shown best in FIGS. 1-4, the proximal and distal edges 16 and 17 of the cuff itself are flush with the outer surface of the tube 18, fit into recess 19 in the tube 1, and at each end abut against shoulders 20 and 21, respectively. The tube 1 thus presentS a smooth, continuous surface which does not have any projecting shoulders which would cause irritation of tissues upon insertion or use.

FIG. 2 shows the cuff in its deflated condition, and FIG. 4 shows the cuff in a partly inflated condition. FIG. 5 illustrates the method of insertion of the tube 1 with the aid of a laryngoscope 22. After the laryngoscope is removed, air is injected into the cuff via pilot tube 2 by means of syringe 23. Upon providing sufficient inflation of the cuff 6', clamp 24 seals off the pilot tube 2 retaining the balloon inflation. Ventilation of the patient's lungs can then proceed through the adapter 7 and central passageway 8.

While the prior art has employed various materials for cuff balloons, such as rubber latex, relatively hard, non-conformable silicone rubber, or polyvinylchloride plastics, we use relatively soft, conformable silicone rubber having a very low durometer and an elongation factor of in the range of from 1000-1500 percent. A cuff balloon made from this material requires much less pressure per unit volumetric expansion than does the above presently used rubber or plastic materials. For example, a typical rubber or polyvinylchloride cuff material has a Shore A hardness on the order of 50, while the physiologically acceptable silicon of our invention should have a hardness on the order of less than about 20-25. The cuff material of our invention should also have a tensile strength, in pounds per square inch, of less than about 700-800, and preferably in the range of 500-700, as compared to the prior art rubber or polyvinylchloride which has a strength of 1,200 psi and greater. Still another parameter critical to our invention is that the percentage elongation capability should be in the range of 1,000-1,500 percent. Prior art materials have had a percentage elongation of from 300-900 percent.

We have also discovered that the stress value must represent as low a percentage of the breaking stress as possible. For example, a typical cuff balloon having a deflated diameter of 0.425 inches will be expanded to the average trachea size of 1.250 inches upon inflation. The maximum extension required is thus 340 percent of the original, or 240 percent elongation as normally calculated. Assuming stress to be directly proportional to strain for typically used rubber cuff compositions, the stress for prior art types of cuff materials having percentage elongation on the order of 600 percent is about 400 psi. For the cuff materials of this invention, having a typical elongation percentage of 1,100, the stress is only 130 psi. This represents a value of 33 percent of the breaking stresses for the prior art material as compared to 22 percent for the material of our cuff. The prior art cuff rubber or plastic material is much nearer its rupture point than the cuff of our invention, and thus is more apt to break under mechanical deformation strains. Thus, this stress value of the cuff should be kept below about 30 percent, and preferably in the range of from 15-25 percent of the breaking stress.

While the tube 1 may be round in cross-section as shown in FIG. 3, FIG. 7 shows another embodiment in which the tube is generally a flattened oval in cross-section, more nearly conforming to the actual shape of the human trachea. Thus, the wall 4 of the tube is flattened in a ventral-dorsal direction with the side walls 25,25' being thicker than the ventral wall 26 and the dorsal wall 27. While the central passageway 8 is shown in FIGS. 3 and 7 to be circular, it may also be generally oval and concentric with the outer surface shape 18 (FIG. 7) to provide for walls 4 of substantially equal thickness throughout. However, the increased thickness of the side walls 25, 25' provide for convenient placement of the lumen 3 and the opening 5 into the recess 19 of the tube 1 for placement of the cuff balloon 6.

FIG. 7 also serves to illustrate a still further embodiment wherein the balloon wall itself is of preselected unequal or varying thickness. The ventral portion 28 and the dorsal portion 29 are shown thickened relative to the lateral or side walls 30, 30'. Since the side walls are thinner, the balloon tends to expand unevenly in a controlled fashion with the greater extension in a lateral direction as compared to that along the ventral-dorsal axis of the cuff. While FIG. 3 shows a cuff having even wall thicknesses in conjunction with a generally round tube 4, uneven wall thickness cuffs as in FIG. 7 may also be used in conjunction with tubes round in cross-section. In this particular combination, the predetermined differential thickness of the cuff walls provides for excellent sealing of the tube in the trachea, even where the main body of the tube is round. The differentially expansible wall portions of the cuff compensate for the natural out-of-roundness of the trachea or for tracheal irregularities in the lateral as compared to the ventral-dorsal axial direction. In addition, a plurality of inflation lumens 3 may be used. While one lumen is shown in the side wall 25' in FIG. 7, it should be understood that another inflation lumen communicating with an opening to the intra-cuff space may be placed in the side wall 25.

In preparing the cuff balloon, we prefer to press mold an annular cylinder of silicone rubber to provide cuff balloon material of the specific characteristics described above. The cuff is then placed over an extruded tube having the ventilation and inflation lumens therein, which tube has been incised to provide recess 19 for receiving the balloon, and the opening 5 from the recess to the inflation lumen 3. The proximal and distal margins 16, 17, and transverse edges of the cylindrical balloon cuff are then coated with silicone rubber adhesive and placed in the recess, and the adhesive cured to provide an integral seal between the cuff and the main tube body 34.

FIGS. 8 and 9 show the principles of our invention adapted to use in an improved Foley-type urinary catheter with like parts having the same numbers as in FIGS. 1-5. FIG. 8 shows the cuff 6' in expanded condition within the urinary bladder walls 31. The cuff 6' contacts the wall along region 35 as distinct from typical point (in cross-section) contact of round balloons of the prior art. The special properties of our silicone rubber permits the expanded cuff to conform to the walls of the bladder, thus resulting in a lower perpendicular component of the catheter weight per unit area of the bladder wall. The conformability of our silicone cuff allows spreading the weight over a larger area leading to a lower pressure and less likelihood of severe tissue necrosis. Eye 10 in the rounded distal tip 12 of the main catheter body communicates with drain lumen 9 for removal of urine.

FIG. 9 shows the cuff 6 in normal, uninflated condition. The cuff in longitudinal cross section, i.e., along its axis, is of a predetermined unevenness in thickness, with the distal end 32 being thinner than the proximal end 33. This provides for greater expansion of the balloon at the distal end than the proximal end, with the result that the balloon is generally triangular in shape, as seen in FIG. 8, conforming to the natural shape of the urinary bladder. Thus, by preselected design of wall thickness, the cuffs of our invention may be adapted to any desired body cavity, vessel, tube, orifice or the like. While we have described the invention with respect to several embodiments above, it should be understood that many variations may be made within the spirit of our invention.