WO1999011314A1

WO1999011314A1 - Catheter with localization apparatus and method of localization

Info

Publication number: WO1999011314A1
Application number: PCT/US1998/018073
Authority: WO
Inventors: Randolph B. Lipscher; David F. Prelewitz; Antoun Ayeta
Original assignee: Emtek, Inc.
Priority date: 1997-09-02
Filing date: 1998-08-31
Publication date: 1999-03-11
Also published as: AU9040898A

Abstract

A positioning element is used in combination with a catheter for localizing the position of the catheter within a body. The positioning element identifies the position of the catheter by emission of energy , reflection of the energy, and reception of the reflected energy. A catheter includes a flexible tube having a proximal end and a distal end. The flexible tube is employed by insertion into a body. A reflector is affixed to the flexible tube at a measured location between the proximal end and the distal end. The reflector indicates the position of the flexible tube within the body relative to a position on a skin surface of the body.

Description

CATHETER WITH LOCALIZATION APPARATUS AND METHOD OF LOCALIZATION

TECHNICAL FIELD

The present invention relates to a medical catheter device. More specifically, the invention relates to a catheter including a localization apparatus for ensuring proper placement and positioning of the catheter within a patient.

BACKGROUND ART

Correct placement of catheters is critical in medicine. Catheters deliver oxygen, medication, and fluids. Examples of catheters currently in use are intravenous catheters, nasogastric catheters, and endotracheal tubes. When catheters function correctly they can deliver a substances like oxygen to the lungs (endotracheal tube), food to the gut (nasogastric tube), or fluids and medications to the venous system (large bore intravenous catheters). When catheters are placed in the body an X-Ray is typically taken to ensure that the catheters are placed in the proper position. A catheter that is poorly positioned may lead to morbidity or death. For example, if the nasogastric tube is not positioned correctly in the stomach, the patient may aspirate undigested food and develop pneumonia.

Endotracheal tubes are catheter devices in which proper positioning is highly critical. A five minute episode of endotracheal tube malpositioning may lead to death.

Airway management is fundamental to medicine. Definitive airway control is provided by endotracheal intubation. In endotracheal intubation, a balloon-tipped, large gauge, catheter is introduced past the vocal cords and secured by expanding the balloon. In an adult, the tip of a properly positioned endotracheal tube is located about 5 to 7 cm into the trachea, approximately the trachea midpoint.

Currently endotracheal tubes are routinely positioned by anesthesiologists in the operating theater, placed by emergency department physicians in the emergency department, positioned by intensive care unit (ICU) physicians in the ICU, and inserted by paramedics skilled in critical care interventions in the pre-hospital setting. Despite the ubiquitous and routine use of endotracheal tubes to oxygenate and ventilate patients, misplacement of the endotracheal tube remains a serious problem with life-threatening consequences.

Significant morbidity and mortality occurs not infrequently as a consequence of misplacement of the endotracheal tube into the esophagus, and misplacement or migration of the tube into the right main bronchus. Dislodgement of an endotracheal tube as a result of patient movement, malpositioning the tube in either the pharynx or bronchus.

A review of various anesthetic-related morbidity and mortality statistics indicates that unrecognized esophageal intubation remains a problem, even among anesthesiologists. An analysis of anesthetic accidents in the United Kingdom from 1970 to 1978, for example, revealed that nearly half the cases resulting in death or cerebral damage were caused by inadvertent placement of the endotracheal tube into the esophagus. Another review of anesthesia-related medical liability claims in the United Kingdom from 1977 to 1982 listed esophageal intubation as a main cause of accidents leading to death or neurologic damage. A review of malpractice claims brought against Washington state anesthesiologists from 1971-1982 concludes that esophageal intubation figured prominently among complications resulting in cardiac arrest, brain damage, and death.

In a retrospective study of 100 emergency patients, Bissinger et al ("Unrecognized Endobronchial Intubation in Emergency Patients," Annals of Emergency Medicine, 1989, Vol. 18, No. 8, pp. 853-855) concluded that "inadvertent endobronchial intubation was not recognized by the physician or the admitting anesthesiologist in 7 percent of the reviewed cases, and endotracheal malpositioning of the tip near the carina (2 cm or less) occurred in another 13 percent". Furthermore, Bissinger stated, "Evaluation of the depth of tube insertion with the aid of common clinical techniques is particularly unreliable in the case of thoracic trauma, aspiration, or previously existing pulmonary disease."

Malpositioning of the endotracheal tube within the airway following intubation can result in serious complications, particularly in the critically ill patient requiring emergency intubation. Endobronchial placement of the endotracheal tube leads to atelectasis of the nonventilated lung and to decreased oxygenation. The lung that is ventilated may become hyperventilated, causing barotrauma and hypotension. If respiratory function of an endobronchially-incubated patient is already impaired by additional damage such as lung contusion, hemothorax, pneumothorax, shock, or the like, systemic hypoxemia rapidly develops and cannot be satisfactory compensated by higher concentrations of inspirator/ oxygen.

Endobronchially intubated patients with chest injuries, aspiration, or both are at high risk of acute posttraumatic respiratory insufficiency. In the presence of injury or shock, hypoxemia, hypercapnia, hypotension, and rising intracranial pressure can lead to reduction of intracerebral compliance and, due to resulting ischemia, result in additional secondary brain damage.

Placement of the endotracheal tube too high in the airway increases the likelihood of accidental extubation, resultant hypoxemia and hypoventilation. A properly positioned endotracheal tube has a tip that is located substantially at the midpoint of the trachea, generally between 2 and 6 cm above the carina when the patient's head is in a neutral position.

Marked alterations in the endotracheal tube position occur with changes in head position so that the location of the endotracheal tube is very significant after intubation. Flexion of the neck from the neutral position can result in the tip of the endotracheal tube moving as much as 3 cm closer to the carina, while extension can displace the tube up to the 5 cm farther than the carina. Lateral movement of the neck can cause the tip of the endotracheal tube to move 2 cm from the carina. Such changes of head position are typical with normal patient movement in the ICU, emergency department, and in the prehospital setting. Therefore, endotracheal intubation in patients outside the operating theater significantly risks the occurrence of mispositionings that are undetected by clinical evaluation.

Malpositioning is a commonly occurring problem that is not easily detected by routine clinical assessment, but only by chest radiograph. Patients may be extubated during movement to a hospital, and the extubation may well not be discovered until the patient arrives at the hospital, potentially leading to long periods of anoxia and possibly devastating sequela.

Several techniques, methods and devices are conventionally known and available that attempt, with varying degrees of success, to distinguish a suitable tracheal positioning of the endotracheal tube from a malpositioned esophageal positioning.

A first conventional endotracheal tube localization method involves direct visualization of the vocal cords and visual monitoring as the tube is passed into the trachea. The visual method is considered by many to be the "gold standard" for correct tube placement and remains one of the most reliable signs. Unfortunately, visual inspection is impossible to achieve in some patients. A further problem is that, even after visualization of the cords and visual monitoring of tube placement, the tube may be inadvertently withdrawn from the trachea prior to or during securing of the tube. The tube may also be unsuitably withdrawn during a change of positioning of the patient into a lateral or prone position. For example, mere flexion or extension of the neck can change the position of the endotracheal tube as much as 5 cm, resulting in inadvertent extubation.

A second common conventional endotracheal tube localization method involves observation of symmetric bilateral movements of the chest wall during ventilation. However, conditions in which ventilation is more than usually dependent on diaphragmatic movement make assessment of proper tube position by chest expansion difficult. In an obese patient, or in a patient with large breasts, a barrel chest from lung disease, or other conditions that result in a rigid chest wall, chest movement can be difficult to evaluate. More importantly, movement of the chest wall simulating ventilation of the lungs can be seen even if the endotracheal tube is malpositioned in the esophagus.

A third conventional endotracheal tube localization method involves monitoring of breathing sounds.

The presence of bilateral breath sounds upon apical and/or midaxillary auscultation of the lungs apparently provides strong reassurance of proper tube position. However, even experienced clinicians have mistakenly confused esophageal ventilation with normal breathing sounds. Air passing through the esophagus may resemble course or tubular breath sounds. Furthermore, with mechanical or hand ventilation, gas flows tend to be faster, tidal volumes larger, and distribution different from what is observed with spontaneous respiration. Breath sounds are more predominantly bronchial and may differ in quality, depending on whether the chest is auscultated over the midline or laterally. Therefore sounds produced by air movement through an esophageal tube may be mistaken as breath sounds.

A fourth conventional endotracheal tube localization method involves analysis of chest radiographs. Chest radiography to verify proper tube position is time consuming and expensive, yet still not fail-safe. Chest radiographs in an intensive care unit (ICU) are commonly used to confirm the position of the tracheal tube. Chest radiographs are generally considered undesirable because of the large number of radiographs that are acquired over time to ensure detection of movement of the endotracheal tube potentially resulting in excessive irradiation during ventilatory support. A substantial disadvantage of current radiographic procedures is a failure to provide real time information about tube position due to the interval required to set up the X-ray apparatus, develop radiographic film, and return the film to medical personnel. Furthermore, X-ray methods are expensive and entail the risk of inadvertent exposure to medical personnel.

A fifth conventional endotracheal tube localization method involves monitoring of breathing sounds using a video stethoscope. Lung ventilation is monitored by intraoperative use of a video stethoscope device that includes a small plastic electrocardiographic electrode casing fitted with a microphone and placed on the skin overlying each hemithorax. By displaying the sound from each microphone on an oscilloscope screen in an X-Y format, distinct visual patterns are produced by esophageal, right mainstem bronchial, and normal tracheal intubation. The video stethoscope, although apparently reliable, is relatively awkward and time-consuming to use.

A sixth conventional endotracheal tube localization method involves visual monitoring of the trachea using a fiber optic bronchoscope. Visualization of the tracheal rings and carina by fiber optic bronchoscopy reliable detects tracheal tube placement. However, the fiber optic bronchoscope instrument is relatively expensive, prone to breakage, and the method is unwieldy for routine usage.

A seventh conventional endotracheal tube localization method is pulse oximetry. Pulse oximetry is useful in many situations but may indicate esophageal intubation too late for suitable intervention for several reasons. Apparently normal functioning of a ventilator is sometimes observed even when connected to an esophageal tube, delaying recognition of tube misplacement.

A seventh conventional endotracheal tube localization method is capnometry. In the operating theater, the most reliable and simple determination of proper tube placement involves capnometry, the measurement of carbon dioxide concentration during the respiratory cycle. Carbon dioxide concentration is displayed as a wave form on a screen which is monitored by an anesthesiologist. The reliability of the carbon dioxide monitoring is based on the assumption that C0₂ is reliably detected in patients with an intact pulmonary circulation whose trachea is incubated, whereas no C0₂ is present in gases exiting from an esophageal tube. In the emergency setting, however, capnometry is unwieldy and expensive.

An eighth conventional endotracheal tube localization method is measurement of colorimetric end tidal C0₂. Colorimetric end tidal C0₂ (ETC0 ) is measured using a calorimetric device that is attached to endotracheal tubes to continuously monitor ETC0₂ tension. The calorimetric device is a plastic, disposable unit that enables the user to estimate ETC0 tension by comparing a calorimetric membrane with a calibration color band. The calorimetric membrane changes color in response to ETC0 tension. Several difficulties are associated with the use of ETC0 to determine tube placement in emergency intubation including high price and limited shelf life. The calorimetric device also fails to achieve real time determination of tube placement. Furthermore, ETC0₂ does not distinguish between correct placement of endotracheal tube, intrabronchial intubation, and endotracheal tube movement into the oropharynx.

A ninth conventional endotracheal tube localization method is the usage of a self- inflating bulb in a suction esophageal detection device to differentiate esophageal from tracheal intubation. Usage of the self- inflating bulb is based on the principle that the trachea is held open by rigid cartilaginous rings while the esophagus readily collapses when a negative pressure is applied to the esophagus lumen. The self-inflating bulb is connected to the endotracheal tube and the bulb compressed. Refilling of the bulb is instantaneous if the tube is in the trachea. In contrast, if the tube is in the esophagus, compression of the bulb remains collapsed on release of pressure. Despite the efficiency of the esophageal detector device and the self- inflating bulb in differentiating esophageal from tracheal intubation, the technique may produce a false negative result if, for example, the tube is in the trachea but gas is not aspirated by the syringe or the bulb does not reinflate. Furthermore, the suction device does not produce a real-time determination of tube placement and does not distinguish between 1) correct placement of breathing tube in the trachea, 2) breathing tube in the bronchus, or 3) breathing tube in the oropharynx.

A tenth conventional endotracheal tube localization method is usage of a nonradiographic, noninvasive technique to determine tracheal tube location. A technique proposed by Cullen, et al. (Anesthesiology, 1975, Vol. 43, pp. 596-599), involves electromagnetic sensing to detect a circumferential foil marker band fused into the endotracheal tube a the proximal cuff tube injunction. A hand-held pocket battery powered detector is utilized to detect and locate the foil marker with respect to external landmarks of the neck. The detection system uses a differential mutual sensing scheme to measure the distance of the magnetic band placed on the endotracheal tube and accurately determine tube position. Although preclinical trials of a prototype device have been carried out for a pediatric population (McCormick et al., IEEE/Eiqhth Annual Conference of the Engineering in Medicine and Biology Society proceedings, 1986, pp. 140-143), the technique is not widely accepted in hospitals. The lack of acceptance probably reflects the difficulty of detecting a stationary magnetic field.

An eleventh conventional endotracheal tube localization method is taught by Mansfield, et al., IEEE Transactions on Biomedical Engineering, 1993, Vol. 40, No. 12, pp. 1330-1335). Mansfield describes an instrument that determines the position of endotracheal tubes by differentiating the acoustical properties of the trachea and bronchus. An incident audible sound pulse is introduced into the proximal endotracheal tube and is detected as it travels down the endotracheal tube via a miniature microphone located in the wall of the tube. This pulse is emitted from the tube tip into the airways and a microphone detects a reflected acoustic signal from the airways. A well-defined reflection arises from the point where the total cross-sectional area of the airway increases rapidly. The difference in timing between the detection of the incident pulse and the reflection is used to determine endotracheal tube position or movement. The reflection is not observed if the endotracheal tube is placed in the esophagus. The device discriminates by cross-sectional area between the trachea and the bronchus and insures an adequate fit between the endotracheal tube and the trachea. The method relies on sound wave generation and may not be useful in conditions of pulmonary edema, trauma, or in other conditions.

A twelfth conventional endotracheal tube localization method is orotracheal intubation using transillumination. Transillumination involves introducing a flexible lighted stylet into the trachea. Intratracheal placement of the stylet light gives off an intense, circumscribed glow in the region of the laryngeal prominence and the suprasternal notch, which is indicative of correct tracheal tube. If esophageal placement occurs, the light is usually not visible or is perceived as dull and diffuse. Although the lighted stylet is useful under certain circumstances, the technique does not produce good results in bright sunlight or in bloody situations including trauma, and is not useful for real-time determination of tube placement.

A thirteenth conventional endotracheal tube localization method is taught by Gravenstien et al in U.S. Patent Number 5,560,351, entitled "Method and Apparatus for Determining Endotracheal Tube Position". The technique involves application of a light source to the skin surface of the neck and directed into the neck. A stylet or modified endotracheal tube with an energy-sensing device is then passed into the trachea. When an energy-generating element directly opposes the energy-sensing element, a beeper sounds and the "correct" placement of the endotracheal tube is assured. A difficulty with the localization technique is that an endotracheal tube is significantly modified to include the energy-sensing device, a costly process. Furthermore the endotracheal tube is fitted with either a fiber-optic or sensing device that introduces an energy source into the trachea (i.e. a wire or a fiber optic).

While the preceding discussion details difficulties that arise due to malpositioning of endotracheal tubes, such difficulties are generalized to any catheters for which proper positioning is essential to proper function.

What is needed is an effective, reliable, convenient, and cost-effective apparatus and operating technique for determining positioning of a catheter in the body.

DISCLOSURE OF INVENTION

It has been discovered that a positioning element is used in combination with a catheter for localizing the position of the catheter within a body. The positioning element identifies the position of the catheter by emission of energy, reflection of the energy, and reception of the reflected energy.

In accordance with an embodiment of the present invention, a catheter includes a flexible tube having a proximal end and a distal end. The flexible tube is employed by insertion into a body. A reflector is affixed to the flexible tube at a measured location between the proximal end and the distal end. The reflector indicates the position of the flexible tube within the body relative to a position on a skin surface of the body.

BRIEF DESCRIPTION OF DRAWINGS

The present invention may be better understood, and its numerous objects, features, and advantages made apparent to those skilled in the art by referencing the accompanying drawings.

FIGURE 1 is a cross-sectional view of a human patient in combination with a schematic representation of a catheter and localization apparatus according to an embodiment of the present invention.

FIGURE 2 is a schematic block diagram representing an embodiment of the catheter and a localization system for localizing the catheter within a patient.

FIGURE 3 is a cross-sectional view of a human patient in combination with a schematic representation of a catheter and localization apparatus according to another embodiment of the present invention.

FIGURE 4 is a schematic diagram illustrating a catheter localization apparatus including a stylet that is supplied for usage with a catheter.

Usage of the same reference symbols in different drawings indicates similar or identical items.

MODES FOR CARRYING OUT THE INVENTION

Referring to FIGURE 1, a sectional view of the upper part of a human body H having a trachea T extending from a larynx L to the carina C, a bifurcation leading to the bronchi (not shown). An endotracheal catheter 100, which is also called an endotracheal tube, is inserted through an oral cavity O, as shown, or through a nasal cavity N into the trachea T. The endotracheal catheter 100 includes a flexible tube 101 having a distal end 102.

A reflector 103 is attached to the flexible tube 101 near the distal end 102. A combined emitter 105 and receiver 106 are placed in intimate contact with the forward outer skin surface SK at a position on the neck NK in an area above the suprasternal notch S.

During operation of a localization procedure, energy such as light or other energy emission is transmitted from an energy source. In an illustrative embodiment shown in FIGURE 2, the energy source includes two radio frequency sources and associated laser driver circuits 1, and diode laser arrays 2 and 3. The energy source transmits laser light through a coated beam splitter cube 4 and a diffractive optical element 5. Referring again to FIGURE 1, the laser illumination is transmitted to the emitter of the emitter/receiver 105 through an optical fiber 108. The emitter 105 directs light from the skin SK to the deep areas of the body H. Light that encounters the reflector 103 on the endotracheal catheter 100 is reflected back to the skin surface SK and detected by the receiver 106. The receiver 106 includes coated diffractive optical elements 11 shown in FIGURE 2 and a linear detector array 10. A signal is transmitted from the linear array 10 through an optical or electric fiber 12 to a detector driver and pre-amplifier circuit 13. The signal is then directed by a connection 14 to a demodulator and filter circuit 15. The demodulator and filter circuit 15 is connected by a connector 16 to an analog-to-digital converter (ADC) and custom ASIC circuit 17 to a digital display 19 via a connector 18. The digital display 19 displays useful parameters including hemoglobin oxygen saturation, pulse rate and amplitude, chemical concentrations such as solute or gas concentrations in human tissue, endotracheal tube location information, and endotracheal tube patency values.

These parameters are used, for example, to detect and monitor the position of the endotracheal catheter 100 within the body H. In the illustrative example, the endotracheal catheter 100 and emitter/receiver 105 circuitry operate in conjunction to attain reliable airway management in a patient by monitoring the position of an endotracheal tube inserted into a patient's oral cavity O or nasal cavity N. The endotracheal catheter 100 includes a flexible tube 101 extending from external to the patient through an airway opening to the distal end 102 of the endotracheal catheter 100. The reflector 103 is attached to the endotracheal catheter 100 near the distal end 102. Successful intubation involves inserting the flexible tube 101 into the patient's trachea T a suitable distance so that the reflector 103 is positioned substantially at the midpoint of the trachea. The energy or light emitter 105 and receiver 106 is placed in intimate contact with the forward outer skin surface SK of the patient's neck NK at a position at least partially overlying the position of the reflector 103.

The flexible tube 101 extends from the oral cavity O or the nasal cavity N of the patient to the distal end 102 within the trachea T. An energy source, for example a laser source, directs energy illumination into the soft tissue of the neck NK. The light source impinges upon the reflector 103, for example a holographic reflector element, and is redirected back to the surface of the neck NK. The reflected light or other reflected energy is detected at the surface of the neck NK by an energy sensor, the receiver 106, to determine positioning of the reflector 103 and endotracheal catheter 100 by triangulation. The position of the reflector 103 is determined in relationship to the skin surface to advantageously allow real-time adjustment of positioning of the endotracheal catheter 100 to ensure optimal placement.

The system, including the endotracheal catheter 100 and signal handling circuits, differentiates between esophageal and tracheal positioning of the endotracheal catheter 100 based on physical differences in light absorbtion of trachea relative to esophageal tissue. If the endotracheal tube is incorrectly positioned in the esophagous rather than the trachea, light passes through the esophagous into the skin and deep into the body, then is reflected and again passes through the esophagus. Light is strongly absorbed by esophageal tissue, significantly reducing the intensity of signal that is transmitted through the neck tissue. The technique is advantageously an extremely sensitive method for differentiating esophageal intubation from tracheal intubation.

The endotracheal apparatus including the endotracheal catheter 100 and signal handling circuits is advantageously employed even under bloody trauma conditions to ensure that the endotracheal tube is inserted in a proper position in the trachea and not mispositioned into the esophagus.

The endotracheal apparatus also monitors the endotracheal tube to detect possible displacement of the endotracheal catheter 100 that results from head/neck movement or transport of the patient.

A signal reflected by the reflector 103 varies as a function of distance from any arbitrary point on the surface of the reflector 103. When movement of the endotracheal catheter 100 occurs, energy traveling from the exterior of the body H through the skin and deep into the tissue encounters reflections having different properties than reflections that occur when the endotracheal catheter 100 is in an original position. Thus reflection signals that are acquired following movement of the endotracheal catheter 100 are different from the reflection signals acquired prior to the movement. The reflection signals are monitored, stored, and compared over time to detect movement of the endotracheal catheter 100 and to generate an alarm signal to alert hospital personnel of a change in catheter position.

In one embodiment, the reflector 103 is a flexible sheet having two sides. One side has an adhering surface that is attached to an outer surface of the flexible tube 101. A second side has a reflective surface directed away from the flexible tube 101.

In another embodiment, the reflector 103 is a flexible sheet having two sides. A first side has an adhering and reflective surface which is attached to an inner surface of the flexible tube 101. The second side has a reflective surface that is directed to the interior of the flexible tube 101.

In a further embodiment, the reflector 103 is formed of a reflective substance, such as a reflective sheet or a dispersion of reflective particles that are mixed or formed into the body of the flexible tube 101.

The reflective substance forms a surface of the flexible tube 101 that is selectively reflective outward from the tube, inward to the interior of the tube, or reflective both to the interior or exterior of the flexible tube 101.

The reflector 103 in various embodiments may have a single reflective surface or a plurality of reflective surfaces. The plurality of reflective surfaces may have a single reflective property or a plurality of reflective properties. In some embodiments, the reflector 103 may have reflective properties that vary as a function of distance from a point on the reflector.

In some embodiments, the reflector 103 has a reflective surface that forms a grid pattern. In other embodiments, the flexible tube 101 may form a grid pattern that affects the reflective properties of the reflector 103. For example, in some embodiments the flexible tube 101 has one or more lines or markings that function as a diffraction grating.

In some embodiments, the reflector 103 includes a holographic surface or element. In other embodiments, the reflector 103 includes a holographic surface or element in combination with a reflective surface such as foil. In some embodiments, a holographic reflector 103 has a holographic surface that varies in reflective characteristics as a function of distance from a point on the hologram.

In some embodiments, the emitter 105 includes an energy emitting element that emits energy such as electromagnetic radiation, sound, pressure, or another energy form. In some embodiments, the emitter 105 includes a plurality of energy emitting elements. In some embodiments, the emitter 105 includes a plurality of energy emitting elements that are formed in an ordered arrangement.

In various embodiments, the emitter 105 includes various types of emitting elements including one or more fiber optic elements, one or more diffractive optical elements, one or more coated beam splitter cubes, or one or more lasers. In other embodiments, the emitter 105 includes one or more light-emitting diodes (LEDs), or incandescent light sources.

In another exemplary embodiment, the emitter 105 includes one or more diode laser arrays. In one specific embodiment, the emitter 105 includes two diode laser arrays, one at 784A and another at 81θA. Another exemplary emitter 105 includes one or more radio frequency (RF) sources with laser driver circuits. The emitter 105 may have one or more power sources.

In some embodiments, the receiver 106 includes one or more optic fibers. In other embodiments, the receiver 106 includes one or more diffractive optical elements. Another embodiment includes a receiver 106 with one or more linear detector arrays. In a specific example, a receiver 106 has a detector array for including wavelength detectors at 784A and 810A.

In a further embodiment, the receiver 106 includes one or more deflector driver and pre-amp circuits. Another exemplary receiver 106 has one or more demodulator and filter circuits. Another embodiment of a receiver 106 includes one or more analog-to-digital converters (ADCs) and custom ASIC circuits. A further embodiment of a receiver 106 includes one or more digital to analog readout screens and alarms.

In an alternative embodiment, a catheter includes a flexible tube and an emitter-receiver affixed to the flexible tube at a measured location on the tube. The emitter-receiver for sends and receives energy signals indicating the position of the flexible tube within the body relative to a position on a skin surface of the body.

In another embodiment of a endotracheal catheter 300 shown in FIGURE 3 in conjunction with FIGURE 2, energy such as light or other energy forms is transmitted by two radio frequency sources and laser driver circuits 1 and diode laser arrays 2 and 3 through a coated beam splitter cube 4 and through the diffractive optical element 5. The light is then transmitted to an internal emitter 303 shown in FIGURE 3 through an optical fiber 307. The internal emitter 303 directs light from deep areas of the body H to the skin SK. Light impinging on the reflector 305 on the skin SK is reflected back to deep part of the body H and is detected by a receiver 313. A suitable receiver 313 is formed by the linear detector array 11 shown in FIGURE 2. The signal is transmitted from the linear array 11 through optical or electric fiber 317 to a detector driver and pre-amp circuit 13. The signal is then directed by the connection 14 to the demodulator and filter circuit 15 which is connected by the connector 16 to the analog-to-digital converter and custom ASIC circuit 17. The signal is applied via the connector 18 to the digital readout 19 to display measured parameters including hemoglobin oxygen saturation, pulse rate and amplitude readings, chemical concentration values, and readings indicative of location of the endotracheal catheter 300.

In some embodiments, the catheter 300 is used to determine the concentration of specific selected molecules such as solutes or gasses in the body tissue. For example, if the illustrative embodiment the surface receiver 313 measures oxygen saturation of hemoglobin and concentration of various solutes in the body by measuring the absorption of light as a function of frequency. In other examples, various solute concentrations or gas concentrations in human tissue are monitored, such as Pa0₂ and blood glucose level.

The catheter 300, by measuring light absorption, advantageously is used for multiple functions including operation as a pulse oximeter or other type of monitor of solute or gas concentration in tissue. The surface receiver 313 monitors energy signals to detect a change in intensity of light which is analyzed to determine hemoglobin oxygen saturation. Functionality of the catheter 300 further extends to determination of pulse rate or other physiological parameters.

In a highly advantageous embodiment, two lasers are used to determine the relative absorption of light. Additional lasers may be added in series or parallel to determine the concentration of various solutes or solvents in the blood. The additional lasers may also be used to determine various physiological measurements such as pulse rate, or temperature. The measurement of relative absorption of light and usage of relative absorption measurements to determine chemical concentrations and physiological measurements is well known in the medical arts.

In addition to aiding localization within the body H, the endotracheal catheters 100 and 300 assist in determining the patency of an endotracheal tube by measuring the relative absorption of light reflected after passing through the endotracheal tube.

The patency test is performed by positioning a reflecting element to face the center of the endotracheal tube in a manner not to obscure light entering or exiting the endotracheal tube. One suitable embodiment utilizes a reflector that is wound in a helix or other geometry around the endotracheal tube. Light from an emitter positioned at the skin surface and directed into the body in the direction of the catheter is transmitted across the interior of the endotracheal tube to the reflector and reflected back to a receiver positioned at the skin surface. For a tube that is patent, little attenuation of the light signal occurs.

Attenuation is measured relative to a reference signal such as an emission generated from light reflected from outside the tube. For a tube that is filled with secretions, attenuation of the signal occurs. A diagnostic system that monitors the signal detects the attenuation and automatically notifies an attendant of the need to suction the endotracheal tube. Referring to FIGURE 4, a further embodiment of a catheter localization apparatus includes a stylet 400 that is supplied for usage with a catheter 402. The stylet 400 includes a flexible wire 404 having a proximal end 406 and a distal end 408. The flexible wire 404 is inserted into a lumen 410 of the catheter 402. The catheter is inserted into a body. The stylet 400 includes a positioning element 412 that is affixed to the flexible wire 404 at a measured location 414 between the proximal end 406 and the distal end 408. The positioning element 412 indicates the position of the flexible wire 404 within the lumen 410 of the catheter 402 and within the body relative to a position on a skin surface of the body. In one embodiment, the positioning element 412 is a reflective surface formed on the flexible wire 404. In another embodiment, the positioning element 412 is an energy emitter-receiver coupled to the flexible wire 404. The flexible wire 404 is a conductor for carrying electrical signals to a signal processing device (not shown) that is electrically connected to the stylet 400.

The various described catheters and catheter localization elements are used using numerous processes for identifying the location of the catheter within the body. In some embodiments, energy is emitted from an emitter located at the skin surface of the body, reflected from a reflector placed either on the catheter or on a stylet inserted into the catheter, and detected by a receiver at the skin surface. The reflected energy is monitored to determine a location of the catheter within the body. For example, in some embodiments the reflected energy is measured to localize and monitor a medical device inserted into the body using a triangulation method or by detecting a change in the intensity of a reflected energy source.

In other embodiments, the reflected energy is measured to determine the concentration of solutes or gas within tissue, including blood glucose or Pa0₂ measurements. In some embodiments, two or more wavelengths of light are emitted, reflected from the reflector, received, and analyzed to determine a change in ■ntensity of the light that is correlated to hemoglobin oxygen saturation levels.

In some embodiments, the reflected energy is monitored to determine the patency of the flexible tube. For example, light is transmitted across an internal diameter of a catheter and reflected back to the skin surface to determine flexible tube patency. In another example, energy is transmitted across the internal diameter of the catheter and received by a sensor on the tube or embedded into the tube to determine patency of the flexible tube. In a further example, energy is transmitted across the internal diameter of the catheter and received by a sensor located on a skin surface to determine patency of the flexible tube.

In one embodiment, a plurality of energy sensors or receivers are attached to a flexible tube and an energy emitter is positioned on the skin surface. The intensity of signals received at the individual receivers is compared to allow the tube to be positioned under the sensor with the largest signal.

In another embodiment, a plurality of energy emitters are attached to a flexible tube and an energy receiver is positioned on the skin surface. The intensity of signals received at the receiver is compared while moving the flexible tube to position the tube so that the receiver receives the largest signal. While the invention has been described with reference to various embodiments, it will be understood that these embodiments are illustrative and that the scope of the invention is not limited to them. Many variations, modifications, additions and improvements of the embodiments described are possible. For example, those skilled in the art will readily implementthe steps necessary to provide the structures and methods disclosed herein, and will understand that the process parameters, materials, and dimensions are given by way of example only and can be varied to achieve the desired structure as well as modifϊcationswhich are within the scope of the invention. Variations and modifications of the embodiments disclosed herein may be made based on the description set forth herein, without departing from the scope and spirit of the invention as set forth in the following claims.

For example, numerous varieties of energy sources and energy detectors are suitable for usage in the catheter and in an exterior device used in conjunction with the catheter. The various energy sources and energy detectors are well known to those skilled in relevant arts including the medical device arts. Suitable energy sources include, but are not limited to, electromagnetic radiation, light including monochromatic light and polychromatic light, and sound sources such as magnetic speakers, light-emitting diodes (LEDs), and lasers. Sound sources may generate sound, ultrasound or pressure wave energy. The energy sources emit energy of a suitable wavelength and intensity to be detected by sensors such as ammeters, photovoltaic cells, microphones, and the like after reflection of the energy from a reflector. Suitable reflectors include holographs, reflective surfaces, diffraction gratings, and the like.

Similarly, various types of catheters may be used, including but not limited to endotracheal tubes, nasogastric tubes, infraveneous catheters and intra-arterial catheters. The positioning of an energy source, an energy detector, or a reflector, if utilized, are freely selectable among positioning in or on a catheter that is inserted into the body and positioning exterior to the body. Positioning of endotracheal tubes in useful for differentiating positioning between tracheal positioning and esophageal positioning, and verifying that esophageal intubation has not occurred. Nasogastric tube placement is useful for ensuring correct nasogastric tube placement. Infraveneous catheter placement is useful for verifying correct intravenous line placement including central or peripheral line placement.

Claims

WHAT IS CLAIMED IS:

1. A catheter comprising: a flexible tube having a proximal end and a distal end, the flexible tube for insertion into a body; and a reflector affixed to the flexible tube at a measured location between the proximal end and the distal end, the reflector for indicating position of the flexible tube within the body relative to a position on a skin surface of the body.

2. A catheter according to Claim 1 wherein: the catheter is an endotracheal catheter; and the reflector is affixed to the flexible tube at a measured location that is selected to indicate correct endotracheal positioning inside the trachea of the body.

3. A catheter according to Claim 1 wherein: the catheter is an endotracheal catheter; and the reflector is affixed to the flexible tube at a measured location that is selected to indicate incorrect endotracheal positioning when the catheter is positioned inside the esophagus of the body.

4. A catheter according to Claim 1 wherein: the catheter is a nasogastric tube; and the reflector is affixed to the flexible tube at a measured location that is selected to indicate correct nasogastric tube placement inside the body.

5. A catheter according to Claim 1 wherein: the catheter is an intravenous catheter; and the reflector is affixed to the flexible tube at a measured location that is selected to indicate correct central or peripheral intravenous line placement.

6. A catheter according to Claim 1 wherein: the reflector is a flexible sheet having a first side and a second side opposing the first side, the first side having an adhering surface attached to an outer surface of the flexible tube and the second side having a reflective surface directed away from the flexible tube.

7. A catheter according to Claim 1 wherein: the reflector is a flexible sheet having a first side and a second side opposing the first side, the first side having an adhering and reflective surface attached to an inner surface of the flexible tube and the second side having a reflective surface directed to the interior of the flexible tube.

8. A catheter according to Claim 1 wherein: the reflector is a reflective substance formed into the flexible tube so that the flexible tube as a reflective surface selected from reflecting outward from the flexible tube, reflecting to the interior of the flexible tube, and reflected both to the interior and the exterior of the flexible tube.

9. A catheter according to Claim 1 wherein the reflector reflects energy selected from among a plurality of energy forms consisting of monochromatic light, polychromatic light, electromagnetic energy, sound, ultrasound, and pressure waves.

10. A catheter according to Claim 1 wherein: the reflector includes a single reflection surface with a single reflective property.

11. A catheter according to Claim 1 wherein: the reflector includes a plurality of reflection surfaces with a single reflective property.

12. A catheter according to Claim 1 wherein: the reflector includes a plurality of reflection surfaces with a plurality of reflective properties.

13. A catheter according to Claim 1 wherein: the reflector has reflective properties that vary as a function of distance from a point on the reflector.

14. A catheter according to Claim 1 wherein: the reflector has a reflective surface that forms a grid pattern.

15. A catheter according to Claim 1 wherein: the flexible tube forms a grid pattern that affects the reflective properties of the reflector.

16. A catheter according to Claim 1 wherein: the flexible tube has one or more lines or markings that function as a diffraction grating.

17. A catheter according to Claim 1 wherein: the reflector includes a holographic surface or element.

18. A catheter according to Claim 1 wherein: the reflector includes a holographic surface or element in combination with a reflective surface such as foil.

19. A catheter according to Claim 1 wherein: the reflector has a holographic surface that varies in reflective characteristics as a function of distance from a point on the hologram.

20. An apparatus comprising: a catheter including: a flexible tube having a proximal end and a distal end, the flexible tube for insertion into a body; and a reflector affixed to the flexible tube at a measured location between the proximal end and the distal end, the reflector for indicating position of the flexible tube within the body relative to a position on a skin surface of the body; and a monitoring device including: an energy transmitter; an energy receiver; and a signal processor coupled to the energy transmitter and the energy receiver, the signal processor monitoring transmitted signals generated by the transmitter and received signals detected by the energy receiver and generating a diagnostic signal based on the transmitted signals and the received signals.

21. An apparatus according to Claim 20 wherein: the signal processor includes a hemoglobin oxygen saturation monitor.

22. An apparatus according to Claim 20 wherein: the signal processor includes a molecular concentration monitor for measuring solute concentrations or gas concentrations of human tissue.

23. An apparatus according to Claim 22 wherein: the molecular concentration monitor measures Pa0₂ concentration.

24. An apparatus according to Claim 22 wherein: the molecular concentration monitor measures blood glucose concentration.

25. An apparatus according to Claim 20 wherein: the energy transmitter is an emitter that emits energy selected from among a plurality of energy forms consisting of electromagnetic radiation, sound, and pressure.

26. An apparatus according to Claim 20 wherein: the energy transmitter is an emitter that includes a plurality of energy emitting elements.

27. An apparatus according to Claim 20 wherein: the energy transmitter is an emitter that includes a plurality of energy emitting elements that are formed in an ordered arrangement.

28. An apparatus according to Claim 20 wherein: the energy transmitter is an emitter that includes one or more fiber optic elements.

29. An apparatus according to Claim 20 wherein: the energy transmitter is an emitter that includes one or more diffractive optical elements.

30. An apparatus according to Claim 20 wherein: the energy transmitter is an emitter that includes one or more coated beam splitter cubes.

31. An apparatus according to Claim 20 wherein: the energy transmitter is an emitter that includes one or more lasers.

32. An apparatus according to Claim 20 wherein: the energy transmitter is an emitter that includes one or more light-emitting diodes (LEDs).

33. An apparatus according to Claim 20 wherein: the energy transmitter is an emitter that includes one or more incandescent light sources.

34. An apparatus according to Claim 20 wherein: the energy fransmitter is an emitter that includes one or more diode laser arrays.

35. An apparatus according to Claim 20 wherein: the energy fransmitter is an emitter that includes two diode laser arrays, one at 784A and another at 810A.

36. An apparatus according to Claim 20 wherein: the energy fransmitter is an emitter that includes one or more radio frequency (RF) sources with laser driver circuits.

37. An apparatus according to Claim 20 wherein: the energy fransmitter is an emitter that includes one or more power sources.

38. An apparatus according to Claim 20 wherein: the energy receiver is an emitter that includes one or more optic fibers.

39. An apparatus according to Claim 20 wherein: the energy receiver is an emitter that includes one or more diffractive optical elements.

40. An apparatus according to Claim 20 wherein: the energy receiver is an emitter that includes one or more linear detector arrays.

41. An apparatus according to Claim 20 wherein: the energy receiver is an emitter that includes a plurality of linear detector arrays including wavelength detectors at 784A and 81 OA.

42. An apparatus according to Claim 20 wherein: the energy receiver is an emitter that includes one or more deflector driver and pre-amp circuits.

43. An apparatus according to Claim 20 wherein: the energy receiver is an emitter that includes one or more demodulator and filter circuits.

44. An apparatus according to Claim 20 wherein: the energy receiver is an emitter that includes one or more analog-to-digital converters (ADCs) and custom ASIC circuits.

45. An apparatus according to Claim 20 wherein: the energy receiver is an emitter that includes one or more digital to analog readout screens and alarms.

46. A diagnostic monitoring method comprising: inserting a catheter from exterior to a body to a position inside the body, the catheter including: a flexible tube having a proximal end and a distal end, the flexible tube for insertion into a body; and a positioning element associated to the flexible tube at a measured location between the proximal end and the distal end, the positioning element for indicating position of the flexible tube within the body relative to a position on a skin surface of the body.

47. A method according to Claim 46 further comprising: utilizing a reflector as the positioning element; emitting energy from an emitter at a skin surface of the body; reflecting the emitted energy from the reflector; and receiving the reflected energy at a receiver at the skin surface.

48. A method according to Claim 47 further comprising: analyzing the received reflected energy to determine a location of the flexible tube within the body.

49. A method according to Claim 47 further comprising: analyzing the received reflected energy by triangulation to determine and monitor a location of a medical device within the body.

50. A method according to Claim 47 further comprising: analyzing the received reflected energy by measuring for changes in energy intensity to determine and monitor a location of a medical device within the body.

51. A method according to Claim 47 further comprising: analyzing the received reflected energy to determine gas or solute concentration and properties of tissue including blood glucose or Pa02 measurements.

52. A method according to Claim 46 further comprising: utilizing a reflector as the positioning element; emitting energy of a plurality of wavelengths; reflecting the emitted energy from the reflector; receiving the reflected energy at a receiver; and monitoring the received reflected energy to determine a change in energy intensity that is indicative of hemoglobin oxygen saturation level.

53. A method according to Claim 46 further comprising: utilizing a reflector as the positioning element; emitting energy from one or more energy sources; reflecting the emitted energy from the reflector; receiving the reflected energy at a receiver; and monitoring the received reflected energy to determine patency of the flexible tube.

54. A method according to Claim 53 further comprising: transmitting light across an internal diameter of the flexible tube and reflecting the light to determine patency of the flexible tube.

55. A method according to Claim 53 further comprising: transmitting energy across an internal diameter of the flexible tube and reflecting the energy to a sensor affixed to the flexible tube to determine patency of the flexible tube.

56. A method according to Claim 53 further comprising: transmitting energy across an internal diameter of the flexible tube and reflecting the energy to a sensor on a skin surface of the body to determine patency of the flexible tube.

57. A method according to Claim 46 further comprising: emitting energy from an emitter at a skin surface of the body; receiving emitted energy at a plurality of receivers attached to the flexible tube; comparing the intensity of the received energy; and positioning the tube to attain the largest received energy.

58. A method according to Claim 46 further comprising: emitting energy from a plurality of emitters attached to the flexible tube; receiving emitted energy at a receiver at a skin surface of the body; comparing the intensity of the received energy; and positioning the tube to attain the largest received energy.

59. A stylet for usage with a catheter comprising: a flexible wire having a proximal end and a distal end, the flexible wire for insertion into a lumen of a catheter, the catheter for insertion into a body; and a positioning element affixed to the flexible wire at a measured location between the proximal end and the distal end, the positioning element for indicating position of the flexible wire within the lumen of the catheter and within the body relative to a position on a skin surface of the body.

60. A stylet according to Claim 59 wherein: the positioning element is a reflective surface formed on the flexible wire.

61. A stylet according to Claim 59 wherein: the positioning element is an energy emitter-receiver coupled to the flexible wire.

62. A catheter comprising: a flexible tube having a proximal end and a distal end, the flexible tube for insertion into a body; and an emitter-receiver affixed to the flexible tube at a measured location between the proximal end and the distal end, the emitter-receiver for sending and receiving energy signals indicating position of the flexible tube within the body relative to a position on a skin surface of the body.

63. An apparatus comprising: a catheter including: a flexible tube having a proximal end and a distal end, the flexible tube for insertion into a body; and a reflector affixed to the flexible tube at a measured location between the proximal end and the distal end, the reflector for indicating position of the flexible tube within the body relative to a position on a skin surface of the body; and a monitoring device including: an energy transmitter; an energy receiver; and a signal processor coupled to the energy transmitter and the energy receiver, the signal processor monitoring transmitted signals generated by the transmitter and received signals detected by the energy receiver and generating a diagnostic signal based on the transmitted signals and the received signals.