Patent Application
20120017897
The present disclosure relates to a tracheal catheter or tube used for mechanical ventilation of a hospital patient, by insertion of the tube into the trachea of the patient. In particular, the present disclosure relates to a tracheal tube having means to indicate the pressure in the balloon or cuff that occludes the trachea and that is located on the tube.
There are two principal types of tracheal catheters or tubes; the endotracheal tube (ET tube) and the tracheostomy tube (trach tube). The ET tube is inserted through the mouth of a patient and guided past the vocal cords and glottis into the trachea. The trach tube is inserted directly into the trachea through a stoma created in the throat and the tracheal wall by surgical means and enters the trachea below the glottis. Both types of tube have a relatively large main ventilating lumen that delivers the air from a mechanical ventilating device to the lungs. Both types of tubes typically terminate at a position above the carina, anterior to a position between the second and fourth thoracic vertebrae. Gases may then be introduced through the tracheal tube and into the lungs of the patient.
The primary purposes of tracheal intubation are to mechanically ventilate the patient's lungs, when a disease prevents the patient from normal, breathing induced ventilation, and to apply anesthetic gases during surgical intervention. In order to create enough air pressure to accomplish such mechanical ventilation and to prevent escape of gases past the tube, it is necessary to seal the passageway around the tracheal tube. A seal may be produced by the use of an inflatable cuff or balloon formed integrally with and surrounding the tracheal tube. When the tracheal tube has been introduced into the patient's trachea, the inflatable cuff will normally be located a few centimeters above the carina and within the tube-like trachea
The inflatable cuff is then inflated so as to engage the wall of the trachea and thereby seal the trachea and prevent gases being introduced through the tracheal tube from simply turning back up around the tube and passing out of the patients mouth and nose.
The proper inflation of the cuff is quite important. Under-inflation can allow secretions which would normally be directed away from the trachea and into the digestive system to instead follow the path of the ET tube and flow around the inflatable cuff of the tracheal tube downward into the lungs. These contaminated secretions may result in the patient developing ventilator acquired pneumonia or VAP, a major problem in modern medical treatment. Under inflation can also be a cause of poor air sealing allowing air to leak upwardly past the cuff, reducing the effectiveness of the ventilator. Under-inflation of the cuff is, however, less common than over-inflation.
Over-inflation of the inflatable cuff is more common and can result in compression of the tissue in the wall of the trachea, possibly resulting in stenosis. If the cuff on the trachael tube is inflated to a pressure greater than about 40 cmH2O , the capillary perfusion pressure of the trachea is exceeded. It is then possible to develop mucosal ischemia, chondritis, granulation tissue and, finally, scar and contraction of scar and fibrosis tissue, which leads to the stenosis. High-volume low-pressure cuffs have a much lower rate of tracheal stenosis than the low-volume high pressure cuffs used previously, but any low-pressure cuff can be easily converted to a high pressure cuff by over-inflation.
Current methods of determining inflatable cuff pressure are quite haphazard. A common method is for the medical professional to feel the pressure of the pilot balloon, located on the proximal end of the tube, between his forefinger and thumb. Considering the thickness of the pilot balloon and the limitation of the human hand to feel such subtle differences in pressure, this is of relatively limited utility. Some physicians count the number of times they pump the inflation device for the cuff, though the differences in size of the trachea from patient to patient makes this method unreliable at producing a safe pressure as well.
Current methods also include devices that attach to the inflation line of the cuff and provide information related to the cuff pressure. These have varying forms that range from fairly complex dial gages to more simple bellows or spring/rolling diaphragm type configurations. These devices tend to be on the bulky side such that they are not amenable to be readily used for continuous cuff pressure monitoring. Moreover, these approaches require direct access to the inflation line thus creating a new potential failure mode for the cuff to deflate if there is an accidental leak in the connections.
Use of the pilot balloon as a cuff pressure estimation site has also been identified previously. Clip-on pressure gages that provide either a numerical value or a qualitative estimate of the pressure have been discussed. However, the challenge and potential error introduced by the pilot balloon material on the accuracy and sensitivity of cuff pressure estimation has not been recognized previously.
What is needed is a tracheal catheter having an indicator of pressure so that the user knows how high the pressure is in the cuff, or at least that the pressure in the cuff does not exceed safe limits.
The present disclosure improves upon a cuffed tracheal catheter by providing an indicator for the pressure in the cuff. The pressure indicator may be attached to the proximal end of the cuff inflation lumen. The pressure indicator uses an indicator balloon that inflates and deflates in response to the pressure in the inflatable cuff. The balloon as described here may have walls that may or may not stretch. The walls of the balloon may be heterogeneous in the sense that some parts of it may be rigid while others flexible. The balloon is desirably in fluid communication with the tracheal tube cuff. An indicator needle is desirably in mechanical communication with the balloon and moves in response to the inflation and deflation of the balloon, thus showing the state of inflation of the cuff.
Other objects, advantages and applications of the present disclosure will be made clear by the following detailed description of a preferred embodiment of the disclosure and the accompanying drawings wherein reference numerals refer to like or equivalent structures.
Reference will now be made to the drawings in which the various elements of the present disclosure will be given numeral designations and in which the disclosure will be discussed so as to enable one skilled in the art to make and use the disclosure. It is to be understood that the following description is only exemplary of the principles of the present disclosure, and should not be viewed as narrowing the pending claims. In particular, though most references herein are to an ET tube since the problem of cuff overpressure is greater when using ET tubes, these teachings apply equally to trach tubes. Those skilled in the art will appreciate that aspects of the various embodiments discussed may be interchanged and modified without departing from the scope and spirit of the disclosure.
In manufacturing a tracheal tube, the main cannula is generally extruded by conventional means. As it is extruded in a never ending tube, the cannula is generally given three lumens; the main respiratory lumen, a cuff inflation lumen, and a suction lumen, separated by internal walls. There may be more lumens extruded into the cannula for additional functions and the suction lumen is sometimes dispensed with, but the three recited are the most common. These lumens extruded into the cannula extend the entire length of the cannula. Once the cannula is cut to the proper length, the cuff inflation port and the suction port are located and “skived” or cut out, a technique that is well known to those skilled in the art. This allows liquid communication of each lumen (suction and inflation) through the wall of the cannula to its respective port, opening into the space outside the cannula. The remaining distal portion of the cuff inflation and suction lumens are then blocked below the skived port, generally with a sealing plug. The respiratory lumen extends the entire length of the cannula and is not skived out. The cuff is then attached to the cannula, usually adhesively, in a location over the inflation port.
Turning to the drawings,
During the insertion of the tube 10, the cuff 12 is at least partially collapsed. Once properly in place, the cuff 12 may be inflated via the inflation lumen 30 and cuff inflation port(s) 31 formed in or otherwise associated with the cannula 16. The inflation lumen 30 may be coupled to an inflation line 32 with the pilot balloon 33 and terminating at its proximal end in a fitting 34 that allows inflation of the cuff 12 via the inflation lumen 30 and cuff inflation port(s) 31. The cuff 12, inflation lumen 30, inflation line 32 and pilot balloon 33 are thus in fluid communication.
While the balloon 42 shown in
The indicator needle 44 is desirably constructed of an elastic polymer with little or no plastic deformation or creep over the range of strains that occur over the relevant pressure range and time scales of use. One end of the needle 44 may be attached to the frame 41 and the other end is unattached. The unattached end of the needle 44 may be inflexible and colored or shaped to provide visual clarity for the indicator portion of the needle. The attached end is either hinged or held fixed directly to the frame 41. If the attached end is hinged, the needle is preferably rigid while if the attached end is fixed, the needle is preferably flexible. This will ensure one degree of freedom in deflection of the needle tip that can then be robustly translated into a pressure value.
If the indictor is attached to the frame through the use of a hinge, a restorative force must be provided by, for example, a spring, weight or other means known in the art, to move the needle towards its starting point (e.g. downward) as the pressure in the balloon decreases.
If the attached end is fixed directly to the frame without a hinge, the proper choice of materials will provide a restorative force so that the needle 44 will bend upwardly in response to increased pressure (and therefore size) of the balloon 42 and will return to a lower position should the balloon 42 pressure decrease. In another embodiment, as the indicator balloon inflates it pushes against a fixed support structure that holds the indicator needle as well.
The indicator balloon 42 is desirably made from a thin and compliant material so that it can respond quickly to changes in the cuff pressure and be minimally isolating between the internal pressure and ambient. Exemplary materials include soft, pliable polymers such as polyethylene teraphthalate (PET), low-density polyethylene (LDPE), polyvinyl chloride (PVC), polyurethane (PU), polyolefin or polydimethylsiloxane (PDMS) polymers. The balloon 42 should be very thin; with a thickness on the order of 25 microns or less, e.g. 20 microns, 15 microns, 10 microns or even as low as 5 microns in thickness, though at least 1 micron. The balloon should be able to indicate changes in the system pressure at quite low pressures, as a low pressure cuff desirably operates at an inflation pressure of about 25 to 30 cmH2O or less. Very thin balloons, for examples those described in U.S. Pat. Nos. 6,802,317 and 6,526,977, can successfully operate at even lower pressures, such as 20 cmH2O, 15 cmH2O or even less. An appropriate range for an indicator balloon would be, for example, from 0 to 70 cmH2O or more desirably from 15 to 45 cmH2O.
The inflation of the indicator balloon has two phases. The balloons are manufactured to have a specified shape when the balloon material is unstretched. In a blow mold process for example a tube of the given raw material is placed into a cavity mold that has the designed balloon shape. The tube is heated above its softening point and inflated. The balloon mold is cooled and the newly formed balloon material solidifies into this designed shape (with some small changes as it cools). The first phase of the inflation of the balloon occurs as the incoming air re-inflates the balloon to this original shape. In this phase the balloon material undergoes very little if any stretching while it inflates. In this phase the air pressure is reshaping, unfurling or “filling out” the balloon only and not stretching the wall of the balloon. The second phase occurs after the balloon reaches the initial balloon shape. Adding pressure to the balloon after it has reached this shape will cause additional change in shape but will also cause the walls of the balloon to stretch. A pressure indicator can be constructed to make use of balloon deformation in either phase of the inflation. The non-linear behavior of the second phase inflation and the complexities of the shape/pressure behavior at the transition from one phase to the other results in desirably using the first phase in the practice of the disclosed pressure indicator.
The indicator embodiment shown in
Other arrangements are included in the spirit and scope of the disclosure. As used herein and in the claims, the term “comprising” is inclusive or open-ended and does not exclude additional unrecited elements, compositional components, or method steps.
While various patents have been incorporated herein by reference, to the extent there is any inconsistency between incorporated material and that of the written specification, the written specification shall control. In addition, while the disclosure has been described in detail with respect to specific embodiments thereof, it will be apparent to those skilled in the art that various alterations, modifications and other changes may be made to the disclosure without departing from the spirit and scope of the present disclosure. It is therefore intended that the claims cover all such modifications, alterations and other changes encompassed by the appended claims.
