WO1999066975A1

WO1999066975A1 - Ventilation catheter

Info

Publication number: WO1999066975A1
Application number: PCT/CA1999/000576
Authority: WO
Inventors: John A. Pacey
Original assignee: Pacey John A
Priority date: 1998-06-24
Filing date: 1999-06-18
Publication date: 1999-12-29

Abstract

The ventilation catheter is embodied in an endotracheal tube (20) that carries an inflatable cuff (34) on its distal end (37). Once the distal end of the cuff (34) is located in the trachea (22) of the patient, the cuff (34) is automatically inflated with the periodic application of inspiratory fluid that is directed into the proximal end (26) of the tube's lumen (38). Substantially all of the inspiratory fluid is diverted through the cuff to inflate the cuff (34) against the wall of the trachea (22). The cuff is partially deflated during the expiratory phase of respiration. The periodic deflation is combined with a tube (20) construction that directs substantially all of the patient's expiratory fluids along a path on the outer surface (39) of the tube wall. This expiratory flow path is effective for moving fluid volumes in amounts sufficient to ensure that the patient's carbon dioxide levels do not increase beyond acceptable levels, even for extended time periods of ventilation. This path is particularly effective for enabling the expiratory fluids to scour away secretions that may collect on the wall of the trachea (22). Dead space in the airway is eliminated. A channel (36) for suction or other instruments is also provided.

Description

VENTILATION CATHETER

Field of the Invention

This invention relates to ventilation catheters, such as those used for intratracheal ventilation.

Background and Summary of the Invention

A patient will sometimes require mechanical ventilation to assist normal respiration. High-pressure ventilation employing jet ventilation systems are often used when the patient undergoes surgery on the airway or larynx. After standard endotracheal ventilation, small-diameter catheters or tubes may be employed in place of the larger ones. These small-diameter tubes are referred to as exchange catheters.

Ventilation through small-diameter tubes, such as those having 2 to 5 millimeters (mm) inside diameters, is often advantageous because such tubes are less obstructive, enable airway surgery, and reduce the risk of trauma to the wall of the trachea or to the vocal cords through which the tube passes.

Ventilation with small-diameter tubes is difficult, however, especially for longer time periods. The difficulty arises primarily because of inadequate pressure development and ventilation volume, which results in gradually increased carbon dioxide levels in the patient's blood. Moreover, adequate inspiratory flow though the small tube is difficult to maintain at reasonable pressure levels. This latter problem may be addressed by use of a tube that has an expanded external cuff on its distal end. The cuff plugs the area of the trachea surrounding the exterior surface of the tube. This results in the development of higher pressure in the trachea, for a given inspiratory flow rate, for more efficient transfer of inspiratory fluids (such as air, oxygen, and water vapor mixtures).

The use of a cuff can cause mucosal and ciliary damage and trauma to the wall of the trachea in instances where the pressure of the cuff against the trachea! wall exceeds, for a significant time period, the intracapillary flow pressure. Cuffs also typically obstruct the trachea completely, thus trapping secretions in the airway proximal and distal to the cuff. These secretions must be removed by frequently introduced suction tubes or the like, which require increased nursing intervention and attendant increase in infection risk.

The present invention is directed to a ventilation catheter that, owing to its small diameter, carries with it the size advantages mentioned above. The catheter is embodied in an endotracheal tube that carries an inflatable cuff on its distal end. Once the distal end of the cuff is located in the trachea of the patient, the cuff is automatically inflated with the periodic application of inspiratory fluid that is directed into the proximal end of the tube's lumen. In this regard, substantially all of the inspiratory fluid is diverted through the cuff to inflate the cuff against the wall of the trachea. From the cuff, the inspiratory fluid passes back into the lumen and out of the distal end of tube. The diversion of inspiratory fluid is preferably combined with flow restriction mechanisms that enhance the cuff inflation.

From the distal end of the tube the inspiratory fluid is passed through an attached cap from where the fluid is expelled into the trachea. The cap is preferably a collapsible member and permits most of the expelled inspiratory fluid to pass through a primary opening in its most distal end. The cap also includes secondary openings that direct in a radial sense some of the inspiratory fluid that is expelled from the cap. This radial or lateral flow of inspiratory fluid has the effect of moving or dislodging any trapped secretions. Other secondary openings serve to further diffuse the fluid flow expelled from the cap to reduce the likelihood of trauma to the tracheal wall, which might otherwise occur if a single jet of inspiratory fluid were expelled against, for example, the carina, at the junction of the trachea and bronchi.

The cuff of the present invention is partially deflated during the expiratory phase of respiration. This deflation reduces the potential for mucosal, ciliary, and tracheal wall trauma mentioned above. The periodically deflating cuff is combined with a tube construction that directs substantially all of the patient's expiratory fluids along the outer surface of the tube wall. In other words, the expiratory fluid moves through the annular space between the tube and the tracheal wall. This expiratory flow path is effective for moving fluid volumes in amounts sufficient to ensure that the patient's carbon dioxide levels do not increase beyond acceptable levels, even for extended time periods of ventilation. Moreover, this path is particularly effective for enabling the expiratory fluids to scour away secretions that may collect on the wall of the trachea. Dead space in the airway is eliminated.

The preferred embodiment of the cap helps to control expiratory fluid flow into the annular expiratory flow path just mentioned. In this regard, the cap is collapsible so that expiratory fluid flow is restricted from passing back into the lumen of the tube. Moreover, in a preferred embodiment, the lumen of the tube is occluded to prevent fluid flow in the direction from the distal end toward the proximal end of the tube. Transition to a non-ventilated state is enhanced by application of suction to completely deflate the cuff.

The cuff of the present invention is configured to have something of a conical shape whereby the proximal end of the cuff is wider than a distal end of the cuff. As a result, pressure applied to the outside of the proximal end of the cuff tends to push that end of the cuff away from the outer surface of the tube to close the space between the outer surface of the tube and the tacheal wall. Such pressure may arise from the presence of gastric liquids that may reflux from time to time through the patient's esophagus. Thus, as respects unwanted fluid movement along the outside of the tube toward the cuff, the cuff acts like a one-way valve, preventing such movement.

The distal side of the cone-shaped cuff tapers in the direction toward the most distal end of the cuff. As a result, expiratory fluid encounters a generally inclined surface of the cuff. The fluid applies pressure to that surface, which tends to collapse the deflated cuff toward the tube so that the annular, expiratory flow path is made contiguous with the distal and proximal sides of the cuff. To the extent that the cuff does not collapse, the expiratory flow area is diminished along the length of the cuff as compared with the area of the path away from the cuff. This area reduction has the effect of increasing the velocity of the expiratory fluid as it moves along the cuff for scouring away (toward the proximal end of the tube) secretions that may have accumulated in the vicinity of the cuff. This accumulation is attributable, in part, to the lateral flow provided by the secondary openings as mentioned above. In short, the combination of the lateral flow and expiratory flow path provide effective clearing of secretions that accumulate distal to the cuff.

The preferred embodiment of the invention is also provided with a channel. The channel accommodates capnography function, a suction catheter or bronchoscope. The channel may terminate on the proximal side of the cuff and include holes for suction to remove material that may be refluxed as mentioned above, or to remove secretions that may remain after being moved to the proximal side of the cuff via the expiratory flow through the path just mentioned. It will also remove expired samples for capnographic analysis as required to ensure adequate ventilation.

Other advantages and features of the present invention will become clear upon study of the following portion of this specification and drawings. Brief Description of the Drawings

Fig. 1 is a diagram showing a ventilation catheter formed in accordance with the present invention, the catheter being intubated so that its distal end resides in the trachea of a human patient.

Fig. 2 is a side view of the catheter of the present invention.

Fig. 3 is an enlarged view of the distal end of the catheter, which end carries an inflatable cuff.

Fig. 4 in an enlarged, cross sectional view of the distal end of the tube taken along line 4-4 of Fig. 3.

Fig. 5 is a view taken along line 5-5 of Fig. 3, showing the cuff in a deflated position.

Fig. 6 is a view similar to Fig. 5 but showing the collapse of the cuff when suction is applied to the tube lumen.

Fig. 7 is a side view of an alternative embodiment of a ventilation catheter formed in accordance with the present invention.

Fig. 8 is a view similar to Fig. 5 but relating to the embodiment of Fig. 7.

Detailed Description of Preferred Embodiments

With particular reference to Figs. 1 and 2, a preferred embodiment of the ventilation catheter formed in accordance with the present invention comprises an elongated tube 20 that, during use, extends into the trachea 22 of a patient 24 to provide ventilation.

The tube is preferably made of a soft, clear plastic, and has a proximal end 26 to which may be connected a conventional adapter 28. The adapter is the terminal part of a delivery conduit 30 of a conventional ventilation system 32. That system is controllable for delivering inspiratory fluid (air/oxygen mixtures, with or without added water vapor) at pre-selected flow rates. The inspiratory fluid is thus delivered to the proximal end of the tube 26 into the lumen 38 of the tube at a pressure of about 20 mmHg for a selected period of time, after which the system is vented in a way to drop the pressure in the system to about 6 mmHg during the expiratory phase of the ventilation cycle.

In a preferred embodiment, this ventilation cycle uses a relatively high inspiratory/expiratory phase duration ratio, exceeding 1 :1 and as high as 1 :4. During the expiratory phase, a continuous minimal inflow of inspiratory fluid is maintained as discussed more below.

The tube 20 is supplemented with a channel 36 that is integrally formed with or attached to the tube 20. The channel facilitates the use of suction or instrumentation such as a bronchoscope, as described more fully below.

In a preferred embodiment, the proximal end 26 of the tube 20 is enlarged to have thicker walls than the remaining portion of the tube so as to provide a relatively stiffer portion of the tube as an aid to intubation. It is contemplated, however, that a uniform diameter tube 20 will also suffice. A guide rod 21 (Fig. 3) fits inside the tube and bears against a later described diverter wall 44. The guide rod facilitates correct placement of the tube and is removed once placement is complete.

With reference to Figs. 1-3, the tube 20 carries on its distal end 37 an inflatable cuff 34 that is made of a thin film of substantially impermeable plastic. The edges of the cuff are bonded to the outer surface of the tube 20. The cuff 34 is inflated during the inspiratory phase of the ventilation cycle so that it bears against the tracheal wall 40, thereby to plug the annular passageway 42 that is defined between the outer surface 39 of the tube and the tracheal wall 40.

The inflation of the cuff takes place as a result of diversion of the inspiratory fluid that is provided to the tube lumen 38. In this regard, the distal end of the tube lumen is occluded with a diverter 44 comprising a disc-shaped plug. The diverter forces the inspiratory fluid from the lumen 38 to move through a pair of entry ports 50 that are formed through the wall of the tube 20. These ports 50 are in fluid communication with the interior of the cuff 34. Thus, the inspiratory fluid that is diverted through the ports 50 inflates the cuff to its fully inflated orientation (see Fig. 3) such that it bears against the tracheal wall. The nature of the flow into and through the cuff is turbulent, thereby enhancing the pressure applied by the cuff. Inspiratory fluid escapes from the inflated cuff through an exit port 52 that is formed through the wall of the tube 20 in the distal end of the cuff. This exit port 52 is located in the tube lumen 38 such that the diverter 44 is between the entry ports 50 and the exit port 52. Consequently, in this embodiment, all of the inspiratory fluid is diverted through the cuff before passing through the exit port 52. It is noteworthy here that although two entry ports 50 and one exit port 52 have been depicted, more or fewer of each type of port could be used. From the exit port 52, the inspiratory fluid is expelled from the distal end of the tube, through a resilient cap 54.

In order to enhance the inflation pressure developed in the cuff 34 for a given inspiratory flow, the portion of the lumen 38 of the tube distal to the exit port 52 may be configured to have a flow restriction feature in the nature of a reduced diameter portion, shown in dashed lines 41 in Fig. 4. The restriction dimensions are selected to provide the desired cuff-to-tracheal-wall pressure for a given inspiratory flow rate, tube outside diameter, etc.

The cap 54 is a flexible, synthetic rubber or plastic member that is attached as by bonding or thermoplastic welding to the distal end of the tube. The cap includes a primary opening 56 aligned coaxially with the distal end of the tube. The primary opening 56 is sized so that most of the inspiratory fluid that is expelled through the cap passes through that opening, generally directed toward the carina, at the junction of the trachea and bronchi. In order to reduce the chance of damaging the tissue near the cap 54, the inspiratory flow that is expelled from the cap is diffused by the incorporation of secondary openings 58 formed in the cap, spaced from the most distal end of the cap. As a result, the inspiratory fluid that flows through these openings moves generally radially outwardly from the long axis of the cap so that it does not impinge on the same region in the trachea as does the flow through the primary opening 56.

As another aspect of this invention, some of the secondary openings are in the form of generally U-shaped slits that serve as one-way valves 60. As best shown in Fig. 4, these valves open in response to the pressure induced during the inspiratory phase of the ventilation cycle. The valves 60 are arranged so that the portion of the inspiratory flow that is expelled through the valves is generally directed radially away from the long axis of the cap 54. This flow, which can be characterized as a lateral flow of inspiratory fluid, has the effect of moving or dislodging tracheal secretions for removal during the expiratory phase as described more below. During the expiratory phase, the valves 60 close as a result of the resiliency of the cap material and diminished fluid pressure inside the cap 54.

It will be appreciated that the plugging effect of the inflated cuff 34, along with the openings arrangement of the cap 54, provides efficient delivery of the inspiratory fluid to the trachea in a manner that diffuses the flow to prevent trauma to tissue and to facilitate removal of secretions in the trachea distal to the cuff. As explained next, the preferred embodiment of the invention is also configured to provide a very effective expiratory phase of the ventilation.

During the expiratory phase, the pressure in the lumen 38 drops to an amount sufficient to enable the cuff 34 to partially deflate. An end view of the deflated position is shown in Fig. 5. This periodic (that is, during each expiratory phase) deflation of the cuff reduces the potential for mucosal, ciliary, and tracheal wall trauma that may otherwise occur if the cuff is maintained in an inflated position against the tracheal wall for an extended period of time.

Also during the expiratory period, and as a result of the pressure drop inside the lumen 38 and connected cap 54, the cap resiles to its normal position whereby opposing inner walls 62 of the cap move together (as shown in dashed lined in Fig. 4). This movement of the cap walls pinches the cap so that expiratory fluid is restricted from moving into the primary 56 and secondary 58 openings of the cap and into the lumen 38 of the tube 20. Consequently, all of the expiratory fluid flow is directed (as shown by the respectively dashed and solid-line arrows 66 in Figs. 4 and 5) through the annular space 42 defined along the outside of the tube between the tube outer surface 39 and the tracheal wall 40.

The restriction of expiratory fluid flow into the lumen of the tube that is effected by the resilient-walled cap 54 may be supplemented with or replaced by other mechanisms. For example, the exit port 52 may be provided with a flap valve 68 that opens in response to sufficient cuff pressure during the inspiratory phase, but closes during the expiratory phase to occlude the port 52 and prevent expiratory fluid flow through the lumen 38 between the port 52 and proximal end 26 of the tube. It is contemplated that the use of a flap valve or similar valving mechanism, will permit the cap 54 to be made so that it remains in the configuration shown in solid lines of Fig. 4, and does not resile into the pinched orientation mentioned above.

The flap valve 68 is normally closed and slightly resists opening. This resistance serves to enhance the pressure increase in the cuff during the inspiratory phase. It will be appreciated that the diverter 44 could also be constructed as a check valve that offers significant resistance to opening in response to inspiratory fluid flow and completely closes during expiratory fluid flow.

As the cuff 34 deflates during the expiratory phase of the ventilation cycle, the annular space or flow path 42 is made contiguous from the distal to the proximal end of the tube. This is best depicted in Fig. 5. In a preferred embodiment, the cuff does not deflate completely against the outer surface 39 of the tube. Rather, the cuff partially deflates, the amount of the deflation depending upon the user's selection of the pressure level that is to be maintained in the ventilation system (thus the cuff) during the expiratory phase. Preferably, the cuff deflates by an amount sufficient to ensure substantially unrestricted expiratory flow along the exterior of the tube 20. This effectively prevents the gradual increase of carbon dioxide levels in the patient's blood.

To the extent that the cuff does not collapse, the area of the expiratory flow path 42 is diminished along the length of the cuff as compared with the area of the path away from the cuff. This area reduction has the effect of increasing the velocity of the expiratory fluid as it moves adjacent to the cuff 34, thereby scouring away (toward the proximal end of the tube) secretions that may have accumulated there. This accumulation is attributable, in part, to the lateral flow provided by the valves 60 as mentioned above. In short, the combination of the lateral flow and the annular, expiratory flow path 42 provides effective clearing of secretions that accumulate distal to the cuff 34. The use of the lateral flow valves, however, is not considered to be critical for this purpose.

As noted earlier, the cuff 34 of the present invention is configured to have something of a conical shape whereby the proximal end 70 of the cuff is wider than a distal end of the cuff. As a result, pressure applied to the outside of the proximal end 70 of the cuff, which end includes a central, generally concave recess 74, tends to push that end of the cuff away from the outer surface of the tube to close the space between the outer surface of the tube and the tracheal wall 40. Such pressure may arise from the presence of gastric liquids or other material 80 (Fig. 3) that may reflux from time to time from the patient's esophagus. Thus, as respects unwanted fluid movement along the outside of the tube toward the cuff 34, the cuff acts as a one-way valve, preventing such movement.

The distal side of the cone-shaped cuff 34 tapers in the direction toward the most distal end of the tube. As a result, expiratory fluid flow 66 encounters a generally inclined surface of the cuff (Fig. 3). That flow fluid applies pressure to that surface, which tends to collapse the deflated cuff toward the tube so that the annular, expiratory flow path 42 (Fig. 5) is made contiguous with the distal and proximal sides of the cuff as discussed above.

The above noted channel 36 preferably terminates in the vicinity of the cuff 34 near the proximal end 70 of the cuff. That terminal end 45 of the channel is open. Suction ports 43 are provided in the channel, as shown in Fig. 2, for removal of secretions that may accumulate in the hypopharynx. Suction applied either directly to the channel 36 or via a separate catheter introduced into the channel is particularly effective for removal of secretions attributable to pulmonary edema, or the refluxed material 80 mentioned above.

In an alternative embodiment, the channel 36 extends through the cuff 34 (the cuff edges being sealed to the exterior of this extension) so that the channel terminates on the distal side of the cuff. This extension is shown in dashed lines in Fig. 3, and the termination of the channel is shown at 47. This embodiment may be adapted to receive a bronchoscope or similar instrument, which can be introduced into the channel, or to provide sensing information to be used for capnography or pressure sensing.

With reference to Fig. 6, it is noted that suction may be applied to the lumen of the tube for collapsing the cuff 34 beyond the amount it would normally collapse as it deflates in the expiratory phase of ventilation. The increase in the flow path 42 that is provided by the application of suction may be required for weaning from ventilation.

Figs. 7 and 8 illustrate an alternative embodiment, whereby components that match the components of the earlier embodiment carry the same reference numbers. In this embodiment the cuff 134 is stiffened with two opposing ribs 99 that can be elongated, thickened strips of the cuff material, extending from the distal to the proximal end of the cuff. These ribs 99 are useful for controlling the configuration of the cuff as it collapses or deflates during the expiratory phase. In this regard, the ribs resist deflation of the cuff during the expiratory phase so that the cuff tends to flatten as shown in Fig. 8. This increases the area of the expiratory flow path 142.

The embodiment of Fig. 8 also includes another channel 100, which is preferably a channel that is dedicated to providing continuous suction. The terminus 145 of this channel 100 as well as the suction ports 143 are located in the hypopharynx, where secretions expelled from the trachea tend to accumulate after being forced through the larynx during the expiratory phase. The continuous suction prevents aspiration of gastric secretions refluxed from the stomach.

While the present invention has been described in terms of preferred embodiments, it will be appreciated by one of ordinary skill that the spirit and scope of the invention is not limited to those embodiments, but extend to the various modifications and equivalents as defined in the appended claims. For example, although the tube is shown intubated through the patient's mouth, the small-diameter tube 20 may be used in cricothyrotomy procedures or tracheostomy. Nasal entry of the tube is also contemplated. Moreover, the small-diameter tube may be used for single-bronchus or single-lung ventilation, or where particularly small or traumatized airways require ventilation. Veterinary uses are also contemplated.

The small-diameter tube permits the patient to control the degree of ventilation support provided by the system. For example, in an ambulatory recovery phase of any low-grade form of respiratory insufficiency the patient may select intermittent boosts to the voluntary breathing process. In this application, a brief pulse of suction could be applied to the lumen for completely deflating the cuff against the tube when the ventilation boost is not required. This complete deflation of the cuff would be useful in any weaning situation, or to simplify the removal of the tube.

Claims

1. A ventilation catheter for facilitating the passage of inspiratory fluid and expiratory fluid respectively into and out of a trachea or the like, comprising: a tube having a distal end, a proximal end, an outer surface, and a wall that defines a lumen, the tube also having a proximal port and a distal port, each port formed through the wall near the distal end of the tube; a diverter carried inside the tube near the distal end to restrict inspiratory fluid flow through the lumen toward the distal end of the tube, the diverter being located between the proximal port and the distal port; and an inflatable cuff sealed to the outer surface of the tube and surrounding the proximal and distal ports so that inspiratory fluid forced into the proximal end of the tube is diverted by the diverter through the proximal port to inflate the cuff and escape from the cuff into the lumen through the distal port to be expelled from the distal end of the tube.

2. The catheter of claim 1 further comprising a cap covering the distal end of the tube, the cap having openings therein through which the inspiratory fluid is expelled from the distal end of the tube.

3. The catheter of claim 2 wherein the cap is substantially collapsible thereby to restrict expiratory fluid flow into the tube though the openings in the cap.

4. The catheter of claim 2 wherein some of the openings are arranged so that only a portion of the inspiratory fluid is expelled from the distal end of the cap.

5. The catheter of claim 1 wherein the cuff is debatable, thereby to permit passage of expiratory fluid past the deflated cuff outside of the lumen.

6. The catheter of claim 5 wherein the cuff is generally cone shaped having a proximal end that is wider than a distal end of the cuff such that fluid pressure applied to the proximal end of the cuff tends to force the cuff away from the outer surface of the tube and pressure applied to the distal end of the cuff tends to collapse the cuff toward the tube outer surface.

7. The catheter of claim 1 further comprising a channel carried by the tube and having a bore, the channel having a distal end terminating in the vicinity of the cuff.

8. The catheter of claim 7 wherein the channel distal end terminates at a location that is distal to the cuff.

9. The catheter of claim 7 wherein the channel distal end terminates at a location proximal to the cuff.

10. The catheter of claim 1 further comprising restriction means for restricting inspiratory fluid flow between the distal port and the cap.

11. The catheter of claim 10 wherein the lumen has an internal diameter and wherein the restriction means comprises a reduced diameter portion of the lumen.

12. The catheter of claim 10 wherein the restriction means comprises a flap valve covering the distal port.

13. The catheter of claim 1 wherein the diverter is shaped to completely occlude the lumen.

14. The catheter of claim 1 wherein the diverter is configured as a check valve.

15. The catheter of claim 2 wherein the cap is configured to restrict expiratory fluid flow into the distal end of the tube and wherein the diverter is a flow restricting member for substantially restricting inspiratory fluid flow through the lumen.

16. The catheter of claim 6 wherein the cuff includes rib members that resist deflation of certain parts of the cuff.

17. A method of ventilation to facilitate movement of inspiratory and expiratory fluids, comprising the steps of: inserting a distal end of a tube adjacent to a trachea-like wall, the distal end of the tube having a lumen and carrying an inflatable cuff; directing inspiratory fluid through the lumen and through the cuff and out of the distal end of the tube; deflating the cuff to permit expiratory fluid to move past the cuff; and restricting fluid flow in the lumen so that substantially all of the expiratory fluid is directed between the cuff and the wall.

18. The method of claim 17 wherein the restricting step includes capping the distal end of the tube with a collapsible member having openings formed therethrough.

19. The method of claim 18 including the step of forming at least some of the openings to be one-way valves that restrict flow of expiratory fluid into the cap.

20. The method of claim 17 including the step of directing some of the inspiratory fluid radially out of the distal end of the tube.

21. The method of claim 17 including the step of occluding the lumen near the distal end of the tube.

22. The method of claim 16 including providing means for applying suction adjacent to the tube at a location spaced from the cuff.

23. The method of claim 16 including providing means for sensing the pressure and composition of the expiratory fluid.