# Patent

## Title
Method and system for determining placement of a tracheal tube in a subject

## Abstract

According to various embodiments, a tracheal tube may employ optical sensing techniques for determining a distance between the inserted tube and an anatomical structure, such as a carina. The distance information may provide an indication as to whether or not the tracheal tube is properly placed within the trachea. The optical techniques may include backscattered intensity measurements.

## Background
BACKGROUND
The present disclosure relates generally to medical devices and, more particularly, to airway devices, such as tracheal tubes.
This section is intended to introduce the reader to aspects of the art that may be related to various aspects of the present disclosure, which are described and/or claimed below. This discussion is believed to be helpful in providing the reader with background information to facilitate a better understanding of the various aspects of the present disclosure. Accordingly, it should be understood that these statements are to be read in this light, and not as admissions of prior art.
In the course of treating a patient, a tube or other medical device may be used to control the flow of air, food, fluids, or other substances into the patient. For example, tracheal tubes may be used to control the flow of air or other gases through a patient's trachea. Such tracheal tubes may include endotracheal (ET) tubes, tracheotomy tubes, or transtracheal tubes. In many instances, it is desirable to provide a seal between the outside of the tube or device and the interior of the passage in which the tube or device is inserted. In this way, substances can only flow through the passage via the tube or other medical device, allowing a medical practitioner to maintain control over the type and amount of substances flowing into and out of the patient.
For example, a patient may be intubated when an endotracheal tube is inserted through the patient's mouth and into the trachea. Often, such intubation procedures may be performed during medical emergencies or during critical care situations. As such, healthcare providers may balance a desire for speed of intubation with a desire for accurate placement of the tube within the trachea. However, proper placement of a tracheal tube may be complex. In certain situations, placement may be aided with visualization of the trachea performed during laryngoscopy. During an intubation procedure, a practitioner may employ a lighted laryngoscope during introduction of the endotracheal tube. However, often the visualization of the trachea is poor because of patient secretions that may obscure the laryngoscope. In addition, such visualization during introduction of the tube may not account for ongoing changes in the tube's position within the trachea that may occur when a patient coughs, which may dislodge a tube from its desired location, or when a patient is jostled or moved within a care setting, which may change the position or angle of the tube within the trachea.



BRIEF DESCRIPTION OF THE DRAWINGS
Advantages of the disclosure may become apparent upon reading the following detailed description and upon reference to the drawings in which:
FIG. 1 illustrates an exemplary system including an endotracheal tube with a coherent light source and detector according to embodiments;
FIG. 2A is a schematic diagram of optical sensing components including a beam splitter that may be coupled to a tracheal tube according to embodiments;
FIG. 2B is a schematic diagram of an alternative arrangement of optical sensing components including a beam splitter that may be coupled to a tracheal tube according to embodiments;
FIG. 2C is a schematic diagram of optical sensing components including an optical coupler that may be coupled to a tracheal tube according to embodiments;
FIG. 2D is a schematic diagram of optical sensing components including a multi-port circulator that may be coupled to a tracheal tube according to embodiments;
FIG. 3 is a flow diagram of a method of operating a tracheal tube according to embodiments;
FIG. 4 is a perspective view of an exemplary endotracheal tube of FIG. 3; and
FIG. 5 is a perspective view of an exemplary distal tip of a tracheal tube with embedded optical fibers for that may be coupled to a light source and photodetector.



DETAILED DESCRIPTION OF SPECIFIC EMBODIMENTS
One or more specific embodiments of the present disclosure will be described below. In an effort to provide a concise description of these embodiments, not all features of an actual implementation are described in the specification. It should be appreciated that in the development of any such actual implementation, as in any engineering or design project, numerous implementation-specific decisions must be made to achieve the developers' specific goals, such as compliance with system-related and business-related constraints, which may vary from one implementation to another. Moreover, it should be appreciated that such a development effort might be complex and time consuming, but would nevertheless be a routine undertaking of design, fabrication, and manufacture for those of ordinary skill having the benefit of this disclosure.
A tracheal tube may be used to seal a patient's airway and provide positive pressure to the lungs when properly inserted into a patient's trachea. Positioning the tracheal tube at a desired position within the trachea, for example during endotracheal intubation, may improve the performance of the tracheal tube and reduce clinical complications. In particular, the distal inserted end of the endotracheal tube may be positioned in the patient's trachea at a location substantially between the patient's vocal cords and carina. If the tube cuff is not inserted far enough past the vocal cords, for example, the tube may become more easily dislodged. If the tube is inserted too far into the trachea, such as past the carina, then the tube may only function to adequately ventilate one of the lungs, rather than both. Thus, proper placement of the distal tip of the tube may result in improved ventilation to the patient.
Provided herein are tracheal tubes and systems for facilitating proper placement of the tracheal tube relative to certain anatomical structures in and around the patient's airway and trachea. Such tracheal tubes may include assemblies for shining light into the trachea and detecting the returned light. The intensity of the detected light may be affected by its interaction with an anatomical structure. Accordingly, information related to the intensity of the detected light may be used to determine a distance from the tube to the anatomical structure in question. In certain embodiments, a distance from the distal end of the tracheal tube to the carina may be determined. A healthcare provider may then use the information about the location of the tracheal tube relative to the carina to determine whether the tube is properly placed or whether the position of the tube should be adjusted.
In certain embodiments, the disclosed tracheal tubes, systems, and methods may be used in conjunction with any appropriate medical device, including without limitation a feeding tube, an endotracheal tube, a tracheotomy tube, a circuit, an airway accessory, a connector, an adapter, a filter, a humidifier, a nebulizer, nasal cannula, or a supraglottic mask/tube. The present techniques may also be used to monitor any patient benefiting from mechanical ventilation, e.g., positive pressure ventilation. Further, the devices and techniques provided herein may be used to monitor a human patient, such as a trauma victim, an intubated patient, a patient with a tracheotomy, an anesthetized patient, a cardiac arrest victim, a patient suffering from airway obstruction, or a patient suffering from respiratory failure.
FIG. 1 shows an exemplary tracheal tube system 10 that has been inserted into a patient's trachea. The system 10 includes a tracheal tube 12, shown here as endotracheal tube, with an inflatable balloon cuff 14 that may be inflated to form a seal against tracheal walls 16. The tracheal tube 12 may also include one or more optical fibers 18 that are associated with the tube 12. The optical source fiber 18 may be configured to pass light from a source 24 through a distal end 27 of the endotracheal tube and into a patient's trachea such that a portion of the emitted light may interact with a carina 28. The emitted light may be transferred back through the optical fiber 18, which may be coupled to a light detector 26.
The system 10 may also include devices that facilitate positive pressure ventilation of a patient, such as a ventilator 22, which may include any ventilator, such as those available from Nellcor Puritan Bennett LLC. The system may also include a monitor 30 that may be configured to implement embodiments of the present disclosure. The monitor 30 may be a stand-alone device or may be coupled to another patient monitor or to the ventilator 22. The monitor 30 may include a microprocessor 32 coupled to an internal bus 34 and a display 36.
The monitor 30 may include certain elements for controlling the light source 24 and the light detector 26. The monitor 30 may drive light from source 24, which in turn may be carried by optical fiber 18. The light may pass into the tissue, where it may be variously scattered, absorbed, and/or reflected and then detected by detector 26. A time processing unit (TPU) 38 may provide timing control signals to light drive circuitry 40, which controls when the light source 24 is activated, and if multiple light sources 24 are used, the multiplexed timing for the different light sources. TPU 38 may also control the gating-in of signals from detector 26.
In an embodiment, the monitor 30 may be configured to receive signals from the detector 26 and store the signals in a mass storage device 42, such as a RAM, ROM, optical storage device, flash memory device, hardware storage device, magnetic storage device, or any other suitable device permitting memory storage. The signals may be accessed and operated according to microprocessor 32 instructions. In certain embodiments, the signals may be related to a placement of the tracheal tube 12 within the patient's trachea and may be processed by the monitor 30 to indicate whether the tracheal tube 12 is properly placed. The monitor 30 may be configured to provide an indication about the placement of the tracheal tube 12 within the patient's trachea, such as an audio alarm, visual alarm or a display message if the tracheal tube 12 is too far or too close to certain anatomical structures, such as the carina 28, or outside of a predetermined placement range. In an embodiment, based at least in part upon the received signals corresponding to the light received through optical fiber 18, microprocessor 32 may calculate a placement parameter of the endotracheal tube 12 using various algorithms. In an embodiment, the placement parameter may relate to a distance 44 between the distal end 27 of the tube 12 and the carina 28 or other anatomical structure.
FIGS. 2A-D are schematic representations of optical sensor arrangements that may be incorporated into system 10 for analyzing placement of a tracheal tube 12 within a patient's trachea. From the change in intensity of the returned light beam 48 after its interaction with the carina 28 or any other anatomical feature of interest, the distance 44 to the carina 28 may be estimated, as discussed in more detail below. In embodiments, such arrangements may involve measuring the intensity of the emitted light 46 to generate a reference intensity measurement to which changes in the intensity of the returned light beam 48 may be compared. A calculated return distance, R, may be equal to the distance 44 (i.e., the distance between the distal end 27 and the carina 28).
It should be understood that the depicted embodiments are exemplary, and the relationships between the optical components may vary. In particular, in embodiments in which optical fibers 18 are employed, the spatial relationships between light source 24, detector(s) 26, and beam splitter 50 (or optical coupler or multi-port circulator) may be altered. FIG. 2A depicts an embodiment in which one optical fiber 18a is dedicated to transmit light 46 and a second optical fiber 18b is dedicated to collect the returned light 48. In embodiments, optical fibers 18a and 18b may be part of a single fiber bundle. As shown, the emitted light 46 is split at beam splitter 50 so that a portion of the light, light beam 46a, is directed towards a detector 26a, which may then generate a reference signal related to the intensity of the emitted light 46. The light beam 46 may pass through the airway until the light interacts with an anatomical tissue structure, such as a carina 28. The returned light beam 48 may be collected optical fiber 18b and detected by light detector 26 to generate light intensity signals that may be analyzed by monitor 30.
In one implementation, a single fiber 18 may be used to emit light and return the light that is reflected/scattered by an anatomical structure. In FIG. 2B, a light beam 46 from source 24 may be emitted and split at beam splitter 50 so that a portion of the light, light beam 46a, is directed towards a detector 26a, which may then generate a reference signal related to the intensity of the emitted light. The rest of the light beam 46 may be emitted from the distal end 27 of tube 12. As noted, light from source 24 may be transmitted through optical fiber 18 and the returned light beam 48 may pass through the same fiber 18. In an alternative embodiment, shown in FIG. 2C, instead of a beam splitter 50, a 2×2 optical coupler 54 may be used to split off a portion of light, light beam 46a, to impinge a detector 26a and generate a reference intensity signal. FIG. 2D depicts an embodiment in which a multi-port circulator 56 may allow an arrangement in which a single detector may be used to detect the return beam 48.
The signal generated at one or more detectors 26 may be communicated to the monitor 30. The incoming signals may include an emitted light intensity signal from the detector 26, which may be a measure of the intensity of the emitted light beam 46. The incoming signals may also include an intensity signal of the returned light beam 48. The monitor 30 may control the light source 24 and light detector 26. The TPU 38 may control the gating of signals from one or more light detectors 26 in conjunction with the light drive circuitry 40. In embodiments, the monitor 30 may control a switch from emitting light to detecting light within the optical fiber 18.
In embodiments, the intensity of the emitted light beam 46 may be estimated or determined without splitting a portion. For example, light source 24 may be factory calibrated such that the intensity is known. The intensity value may be stored as a calibration factor by the monitor 30 or by a separate encoder associated with the light source 24 that may be accessed and read by the monitor 30.
The light source 24 and a detector 26 may be of any suitable type. For example, the light source 24 may be one or more light emitting diodes adapted to transmit one or more wavelengths of light, for example in the red to infrared range, and the detector 26 may be one or more photodetectors (e.g., photodiodes) selected to receive light in the range or ranges emitted from the light source 24. A light source 24 may be a coherent light source, such as a laser diode or a vertical cavity surface emitting laser (VCSEL). The light source 24 may include a broadband or “white light” source, in which case the detector could include any of a variety of elements for selecting specific wavelengths, such as reflective or refractive elements or interferometers. It should be understood that, as used herein, the term “light” may refer to one or more of ultrasound, radio, microwave, millimeter wave, infrared, visible, ultraviolet, gamma ray or X-ray electromagnetic radiation, and may also include any wavelength within the radio, microwave, infrared, visible, ultraviolet, or X-ray spectra.
In embodiments, the light source 24 and detector 26 may be directly coupled to the distal end 27 of the tracheal tube 12, such that the light does not first pass through an optical fiber 18 before being emitted or detected. In such an embodiment, any distance between the light source 24 and detector 26 may be accounted for by measuring intensity profile of the returned light.
FIG. 3 is a process flow diagram illustrating a method in accordance with some embodiments. The method is generally indicated by reference number 64 and includes various steps or actions represented by blocks. It should be noted that the method 64 may be performed as an automated procedure by a system, such as system 10. Further, certain steps or portions of the method may be performed by separate devices. For example, a first portion of the method 64 may be performed by a light source 24 and light detector 26, while a second portion of the method 64 may be performed by a monitor 30. In certain embodiments, the method 64 may be performed continuously or intermittently for long-term patient monitoring or at any appropriate interval depending on the particular situation of the intubated patient. Further, the steps of method 64 may be performed during insertion of the tracheal tube 12 into the patient.
According to an embodiment, the method 64 begins with emitting light, at step 66 from a light source 24, which in embodiments may be coupled to one or more optical fibers 18. The emitted light beam 46 is transmitted through fiber 18, which is associated with tube 12 that is inserted into a patient's airway. The portion of the emitted light is split at step 68 into an intensity reference light beam 52. The rest of the beam 46 may exit the distal end 27 of the tube 12 before interacting with anatomical structures in the patient. The returned light beam 48 that is returned through optical fiber 18 and received by the detector 26 at step 70 may carry information about the relative position of the tube 12 and the anatomical structure that is carried in the sample signal, generated at step 72. The intensity of the returned light beam 48, Ir, at the detector 26, may be used to calculate a placement parameter. At step 74, the intensity reference beam is detected by the detector 26 to generate the intensity reference signal, Io, at step 76.
A monitor 30 may perform analysis of the sample signal and the reference signal at step 78. In embodiments, the monitor may amplify and/or filter one or both of the sample signal and the reference signal prior to the analysis. A monitor 30 may determine a placement parameter at step 80 to determine if this the distance 44 between the distal end 27 and the carina 28 associated with a desirable placement of the tracheal tube 12. In one embodiment, the analysis may include determining the distance 44, or R, between the distal end 27 to the carina 28, which in embodiments may be determined by the following equation:

R=1⁄2(Io/Ir)1/2,

where  a function of optical properties of the carina surface, Io is the optical intensity of the light beam 46 at the fiber end, and Ir is the received intensity of the returned light beam 48. In one embodiment, R may be the placement parameter. In certain embodiments, a placement parameter may be a ratio of a calculated distance and an empirically derived or clinically measured distance associated with proper tube placement. It should be appreciated that there may be several empirically derived distances, depending on the size, age, or sex of the patient. A placement parameter may also be an average or mean of multiple data points or measurements. A placement parameter may also include a graphical, visual, or audio representation of the tube/anatomical structure distance. For example, a placement parameter associated with proper placement may include green light indicated on a display or a short tone generated by a speaker associated with monitor 30. Similarly, a placement parameter associated with improper placement of the tube 12 may trigger an alarm at step 82, which may include one or more of an audio or visual alarm indication. In one embodiment, the alarm may be triggered if the placement parameter is substantially greater than a predetermined value, substantially less than a predetermined value, or outside of a predetermined range. For example, proper tube placement may involve comparing a measured distance R of the distal end 27 to carina 28 to a predetermined range of 1-5 cm. In an embodiment, the predetermined target distance may differ for adult men, who may have, in an embodiment, a target distance of 3-4 cm, and adult women, for whom the target distance may be 2-3 cm. In other embodiments, the alarm may be triggered if the measured distance R is less than 3 cm, less than 2 cm, or less than 1 cm.

FIG. 4 is a perspective view of an exemplary tracheal tube 12 according to certain embodiments. As shown, the tube 12 may include a cuff 14 that may be inflated via inflation lumen 84. The tracheal tube 12 may also include a suction lumen 86 for aspirating secretions that may form above the cuff 14. The tracheal tube 12 may also include a plurality of fiber bundles 88. Each fiber bundle may include one or more optical fibers 18. In embodiments, the transmitting and detecting may also take place within a single fiber. As shown, the fiber bundles 88 may extend through the walls 90 of the tracheal tube 12 such that they are substantially in line with a flow path 92 of the tracheal tube 12. The fibers bundles 88 may include any appropriate optical connector 94 for connecting the fiber bundles 88 to downstream components of the system 10, such as the bean splitter 50 or the light source 24 or light detector 26.
The tube 12 and the cuff 14 may be formed from materials having suitable mechanical properties (such as puncture resistance, pin hole resistance, tensile strength), chemical properties (such as biocompatibility). In one embodiment, the walls of the cuff 14 are made of a polyurethane having suitable mechanical and chemical properties. An example of a suitable polyurethane is Dow Pellethane® 2363-80A. In another embodiment, the walls of the cuff 14 are made of a suitable polyvinyl chloride (PVC). In certain embodiments, the cuff 14 may be generally sized and shaped as a high volume, low pressure cuff that may be designed to be inflated to pressures between about 15 cm H2O and 30 cm H2O. The system 10 may also include a respiratory circuit (not shown) connected to the endotracheal tube 12 that allows one-way flow of expired gases away from the patient and one-way flow of inspired gases towards the patient. The respiratory circuit, including the tube 12, may include standard medical tubing made from suitable materials such as polyurethane, polyvinyl chloride (PVC), polyethylene teraphthalate (PETP), low-density polyethylene (LDPE), polypropylene, silicone, neoprene, polytetrafluoroethylene (PTFE), or polyisoprene.
FIG. 5 is a side view of the distal end 27 of the tracheal tube 12. As shown, the fiber bundles 88 may extend through the walls 90 of the tracheal tube. In certain embodiments, the fiber bundles 88 may be embedded or coextruded within an extruded tracheal tube 12. When the tube 12 is manufactured, the distal end 27 may be cut on a slant to facilitate insertion of the tube 12 in the trachea. After the tube is cut, the fiber bundles 88 may be terminated by any suitable technique.
The fiber bundles 88, or, in some embodiments, individual fibers, may be distributed around the circumference 96 of the tube wall 90. In an embodiment, three optical bundles may be substantially evenly spaced about the circumference 96.
As shown the positioning of the fiber bundles 88 or single fibers may influence the path of the light from the distal end 27 of the tube 12 to the anatomical structure. Arrows 98, 100, and 102 illustrate three different light paths from bundles 88a, 88b, and 88c, respectively, to anatomical structures at or proximate to the carina 28. Arrow 98 has a somewhat shorter path than arrow 100, which is related to its position around the circumference 96 relative to the carina 28, as well as differences in the topography of the carina 28. In addition, slight changes in the angle within the trachea of the distal end 27 of the tube 12 may influence the path of light to and from the fiber bundles 88. In certain embodiments, light detected from all three fiber bundles 88 may be combined or averaged to generate the data used to determine a placement parameter. In addition, the differences in path length between multiple bundles may be used to determine a placement parameter that is indicative of the orientation of the distal end 27 within the trachea. Changes in this orientation (e.g., angular displacement) may indicate a shift in tube placement that may influence cuff pressure and sealing.
In certain embodiments, the fibers or fiber bundles 88 may be formed from materials such as quartz, glass, or a transparent plastic, such as poly(methyl methacrylate) or polystyrene with a fluoropolymer cladding. Examples of optical fibers include single-mode fibers, multi-mode fibers, photonic-crystal fibers, hollow-core fibers, polarization-maintaining fibers and dual-clad fibers. Typical diameters for optical fibers are from 5 to 1,000 micrometers. The optical fiber may be a single-mode fiber or a multi-mode fiber.
While the disclosure may be susceptible to various modifications and alternative forms, specific embodiments have been shown by way of example in the drawings and have been described in detail herein. However, it should be understood that the embodiments provided herein are not intended to be limited to the particular forms disclosed. Indeed, the disclosed embodiments may not only be applied to measurements of tracheal tube placement relative to anatomical structures in the tracheal, but these techniques may also be utilized for the measurement and/or analysis of the placement of other suitable medical devices relative to other anatomical structures. For example, the present techniques may be utilized for the measurement and/or analysis of tracheal tubes relative to tracheal walls or the vocal cords. In addition, the present techniques may be employed in determining appropriate placement of any medical device, such as a stent, catheter, implant, feeding tube, cardiac device, drug delivery device, or pump. Rather, the various embodiments may cover all modifications, equivalents, and alternatives falling within the spirit and scope of the disclosure as defined by the following appended claims.

## Claims

1. A method for determining placement of a tracheal tube in a subject comprising:
emitting light from a plurality of optical conductors circumferentially spaced about a beveled distal end of a tracheal tube disposed in a subject, wherein the beveled distal end is slanted relative to a wall of the tracheal tube such that the plurality of optical conductors are different distances from a carina of the subject;
determining an intensity of the emitted light from each of the respective plurality of optical conductors;
receiving returned light from the carina of the subject;
measuring an intensity of the returned light from each of the respective plurality of optical conductors; and
determining a placement parameter reflective of an angular orientation of the beveled distal end relative to the carina based upon a relationship between the intensity of the returned light and the emitted light from each of the respective plurality of optical conductors and a difference in path length between the plurality of optical conductors, wherein the difference in path length is representative of a position of each respective optical conductor about the distal end.

2. The method of claim 1, wherein the intensity of the emitted light is measured by a first photodetector and the intensity of the returned light is measured by a second photodetector.

3. The method of claim 1, wherein the intensity of the emitted light and the intensity of the returned light are measured by a single photodetector.

4. The method of claim 1, wherein the placement parameter is determined based upon an optical parameter of the carina.

5. The method of claim 1, wherein the steps are performed during intubation of the subject.

6. The method of claim 1, wherein the steps are performed after intubation of the subject.

7. A method for determining placement of a tracheal tube in a subject comprising:
emitting light from a plurality of optical conductors circumferentially spaced apart on a beveled distal end of a tracheal tube disposed in a subject, wherein the beveled distal end is slanted relative to a wall of the tracheal tube such that the plurality of optical conductors are different distances from a carina of the subject;
determining an intensity of the emitted light from each of the respective plurality of optical conductors;
receiving returned light from the carina of the subject;
determining an intensity of the returned light from each of the respective plurality of optical conductors; and
determining a placement parameter representative of an orientation of the slanted distal end based upon a difference in path length between the plurality of optical conductors, wherein the difference in path length is representative of a position of each respective optical conductor about the distal end, and an algorithm that implements an equation generally of the form:


R=1⁄2(Io/Ir)1/2,


where R is the placement parameter,  is a function of optical properties of the anatomical structure, Io is the intensity of the emitted light, and Ir is the intensity of the returned light.

8. The method of claim 7, wherein the intensity of the emitted light is measured by a first photodetector and the intensity of the returned light is measured by a second photodetector.

9. The method of claim 7, wherein the intensity of the emitted light and the intensity of the returned light are measured by a single photodetector.

10. The method of claim 7, wherein the steps are performed during intubation of the subject.

11. The method of claim 7, wherein the steps are performed after intubation of the subject.

12. A system for determining placement of a tracheal tube in a subject comprising:
a tracheal tube comprising a plurality of optical conductors circumferentially spaced apart on a beveled distal end of the tracheal tube, wherein the beveled distal end is slanted relative to a gas flow pathway of the tracheal tube;
a light source configured to emit light through each of the respective plurality of optical conductors when the tracheal tube is disposed in the subject;
means for determining intensity of the emitted light from each of the respective plurality of optical conductors;
a photodetector configured to receive returned light emitted from each of the respective plurality of optical conductors after interaction with a carina of the subject and to determine an intensity of the returned light from each of the respective plurality of optical conductors; and
a processor configured to determine an orientation of the beveled distal end of the tracheal tube based upon the intensity of the returned light from each of the respective plurality of optical conductors and a difference in path length between the plurality of optical conductors, wherein the difference in path length is representative of a position of each respective optical conductor about the distal end.

13. The system of claim 12, wherein the means for determining the intensity of the emitted light comprises the photodetector.

14. The system of claim 12, wherein the processor is configured to determine the placement parameter based upon an algorithm that implements an equation generally of the form:


R=1⁄2(Io/Ir)1/2,

where R is the placement parameter,  is a function of optical properties of the anatomical structure, Io is the intensity of the emitted light, and Ir is the intensity of the returned light.