WO2006084874A1

WO2006084874A1 - Guiding device for insertion of probes into or through air-filled hollow spaces

Info

Publication number: WO2006084874A1
Application number: PCT/EP2006/050798
Authority: WO
Inventors: Ralf Schnell
Original assignee: Tracoe Medical Gmbh
Priority date: 2005-02-10
Filing date: 2006-02-09
Publication date: 2006-08-17
Also published as: DE102005006276A1; DE202006020106U1

Abstract

The invention relates to a guiding device for insertion of probes (1) into or through air-filled hollow spaces, especially for insertion of tracheotomy cannulae and/or dilators into the trachea, which consists of an elongate, flexible guiding element that is sufficiently rigid in the longitudinal direction. The aim of the invention is to provide a guiding device for insertion of a probe into or through air-filled hollow spaces that allows to give a feedback to the doctor carrying out the tracheotomy as to the exact position of the tip of the guiding device inside or outside an air-filled or gas-filled body cavity in a rapid and simple manner. For this purpose, at least the distal tip of the guiding device has a sensor element (11) which triggers a visible reaction of an extracorporeal display element upon contact with body tissue.

Description

Guide aid for introducing probes into or through air-filled cavities

The present invention relates to a guide aid for the introduction of probes in or through air-filled cavities, especially on living human or animal body, wherein the guide consists of an elongated, rigid or flexible, but at least in its longitudinal direction sufficiently rigid guide element.

An example of such introducers are puncture devices, cannulas or syringes, or, for example, a so-called "silk-finger wire" for introducing tracheostomy tubes and / or dilators into the trachea of a patient.

Such guide aids have been known in principle for a long time. The state of the art is explained below primarily on the basis of the known tracheotomy procedures and devices, without the invention being restricted to this field.

Tracheostomy is one of the oldest surgical techniques in the history of medicine. The origins of this technique date back to antiquity. In classical tracheotomy, an artificial access to the trachea is created surgically below the larynx, typically between the 1st and 2nd or 2nd and 3rd tracheal ring. In order to maintain this artificial opening for the purpose of ventilation, a so-called tracheal cannula is used. Medical indications, such as The need for long-term ventilation still makes this technique necessary today. As an alternative to surgical technique, minimally invasive puncture techniques have been developed within the last decades. In particular, the percutaneous dilatation stratotomy according to Ciaglia, the dilatation tracheotomy according to Griggs and the translaryngeal tracheotomy according to Fantoni are widely used.

In the percutaneous dilatation tracheotomy according to Ciaglia, the trachea is first punctured at a suitable place with a steel cannula. To ensure that the sensitive tracheal posterior wall is not damaged, this process typically takes place under bronchoscopic monitoring. The correct position of the cannula tip can be checked by aspirating air into an attached, liquid-filled syringe. In the correct position, a sleeve of insulating material, eg of Teflon, placed over the steel cannula is inserted distally into the trachea 1 to 2 cm. After removal of the steel cannula, a J-shaped guidewire (1.3 mm diameter) is advanced through this sheath into the trachea. Thereafter, the sleeve can be removed. Instead, a tubular plastic catheter with safety stop is now pushed over the guidewire for reinforcement. About the armored guidewire are now one or more consecutively so-called - -

Dilators to dilate the puncture opening by means of a rotating movement pushed into the Tracheallumen. Due to the conical shape of the dilators, the tissue expands so that the lubricated wetted tracheal cannula can be inserted over the guidewire using a special obturator. The correct position is checked with the bronchoscope. Then, the guidewire can be removed and a tracheal cannula balloon filled with air to seal the trachea.

If ventilation has been performed through an endotracheal tube inserted through the mouth or nose, it may be removed following secretion aspiration and artificial respiration may be initiated via the tracheal tube.

In the Griggs dilation tracheotomy, pliers are used to dilate the tissue instead of the cone-shaped dilators. In Fantoni translaryngeal tracheostomy, a cannula with a metallic cone tip is inserted orally past the larynx into the trachea using a guidewire. By pulling on the guide wire, the puncture takes place with the help of the metal conical tip located on the cannula out of the interior of the trachea to the outside. The tip is then removed. This is followed by a rotation of the cannula by 180 °.

Although these minimally invasive methods have some advantages over traditional surgical techniques, life-threatening injuries to the tracheal posterior wall are the result. Thus it can come by puncture of the Tracheahinterwand to the infection (Mediastinitis) or to the air accumulation in the Mittelfellraum (Mediastinalemphysem). The chance of survival of the affected patients is unfortunately low.

The guidewire, which is also referred to as a "silk-wire wire" in the common usage, consists of one or more thin wire elements which may also have a flat, non-circular cross-section and which are spirally wound with another thin wire already have an insulating sheath, for example made of Teflon or a lacquer, or the entire wrapped wire can have a corresponding outer insulating layer as a whole.

To avoid injury, the guidewire is often J-bent at the patient's end, but is inserted in an elongated form through a puncture cannula in the trachea and the cannula is withdrawn after insertion of the Seidingerdrahtes backwards, the tip of the wire after exiting the front cannula opening again assumes its J-shaped curvature. Nevertheless, it may happen that the wire tip hangs on the trachea inner wall during insertion or further advancement of the guide or Seidinger wire. The tip can then push itself into the tracheal wall under unfortunate conditions. Another risk is when the guidewire kinks. Often, the inner guidewire actually consists of several parallel, flat wire elements with non-circular but flat rectangular - -

Cross section and different length. In the proximal region, these multiple, parallel combined wires give the Seldinger wire a sufficient rigidity so that axial feed forces can also be transmitted through the wire against some resistance. Towards the top, the number of wires is increasingly reduced, i. some of the wires that start together from the proximal end are shorter than others, causing the front part of the Seldinger wire to become increasingly flexible and eventually to have only a few or a single wire at the front, curved tip.

The free ends of the shorter wires, which have a small diameter or consist of very thin flat bands are corresponding sharp or sharp-edged and can at a kinking or sharp bending of the wire in the region of the end of the shorter wires through the spiral wrap pass through the outside and injure the body tissue and in particular the trachea and possibly also act as a guide element, which again leads out of the trachea, especially on the side of the rear wall. If this is not noticed in time, it can lead to the already described life-threatening perforation of the tracheal wall. In the upper area, the attending physician has a good chance of detecting entanglements of the guidewire on the tracheal wall with the aid of a bronchoscope. The farther the tip is pushed towards the lungs, the lower this chance becomes as the view is increasingly obscured. Once the dilator is inserted, there is no way to use the bronchoscope to detect if the tip of the guide wire is touching the trachea.

However, if it goes unnoticed that the guide wire has already penetrated into the tissue, the probability is very high that the dilator will also be pushed into the sensitive tissue in the following operation step, following the guide wire. This life-threatening risk is to be minimized by the present invention.

Also, in the initial puncture of the larynx or the trachea by means of a cannula is in principle the risk to pierce the back wall of the trachea, if not controlled in the meantime, whether the tip of the cannula has already reached the trachea. The above-described method of experimentally aspirating with a syringe partially filled with water to detect the occurrence of air bubbles is relatively complicated and cumbersome as well as the parallel control by means of a bronchoscope.

In other punctures of internal organs, air-filled or gas-filled body cavities may or may occasionally be punctured, and it is often very helpful for the puncture practitioner to know exactly where the tip of a puncture instrument is located, that is, whether it already is or still or not anymore within the gas filled cavity. - -

In view of the above-discussed prior art, the present invention seeks to provide a guide to the introduction of a probe in or through air-filled cavities, with the features mentioned, to the executive doctor in a quick and easy way an accurate feedback on the Position the tip of the guide aid in or outside an air or gas filled body cavity.

This object is achieved in that the distal tip of the guide element has a sensor element which triggers a detectable reaction of an extracorporeal display element upon contact of body tissue.

In this case, the guide aid may consist of the probe itself, which, however, must have a corresponding sensor element at its tip, which triggers a recognizable reaction of an extracorporeal display element upon contact or contact with body tissue. However, the guide aid can also be a separate element from the probe, which merely, as the name implies, serves as an aid to the insertion of the probe by the probe being pushed onto and moved along the guide aid, the term "probe" being in FIG In this case, it should be understood in general terms and includes, for example, dilators for expanding a puncture opening.

Because of the thus triggered, visible (eg visible or audible) reaction of an extracorporeal display element, the surgeon immediately detects the guiding element or the probe inserting into a body whether it is in contact with body tissue with the tip of the probe or guide element or in a body cavity. To stay with the example of tracheostomy, the surgeon recognizes immediately when he reaches the trachea and even if he touches the tracheal back wall if necessary again and he can then by twisting, pulling, pushing or other manipulation at the proximal end of the guide element again this touch and place the guide element in the desired manner in the lumen of the trachea or other body cavity.

In addition to the risk of injury during the initial installation of a tracheostoma, the daily use of a tracheostomy tube involves the risk that the cannula tip rubs against the trachea. Especially in cases where the chosen cannula size is not optimally adapted to the individual anatomy of the patient, constant chafing can lead to serious problems. In principle, the correct cannula position can be determined by means of X-ray images or bronchoscopy. However, since these methods are relatively expensive, this is often omitted. With the help of a special, electrically conductive inner cannula, which is slightly longer than the outer cannula, it can be determined when the tip of the inner cannula touches the trachea. To test this, the special inner cannula is inserted into the external cannula on the patient. Based on measurements of the resistance or current flow between the inner cannula and the patient, for example on the earlobe, it can be determined similarly as described above - -

whether there is contact of the conductive probe to the patient. The patient may even move his neck to determine the position in which the tip of the tracheostomy tube rubs against the trachea. The inner cannula can either consist of conductive material or be conductively coated. Alternatively to the inner cannula, e.g. Also, a conductive obturator (insertion aid) can be used.

In a preferred embodiment of the present invention, the guide aid or probe consists of an electrically conductive material, which has an insulating sheath, wherein at least the distal end of the guide aid or the probe has a free of the insulating sheath portion and wherein this of the insulating Enclosure free portion serves as a sensor element, for example by an electrical resistance or current meter is connected to one of its inputs to the proximal end of the electrically conductive guide member or the electrically conductive probe, while the other input of the current or resistance measuring device connected to an outer body part is.

It is understood that for this purpose also the proximal end of the guide element or the probe must be freed at a suitable location of the insulation in order to be electrically connected to the input of the current or Widerstandsmeßgeräts can.

Such a measuring device usually provides at its two entrances a small DC voltage which is completely harmless to a human being, so that when the distal end of the guide wire freed from the insulation touches any part of the body, in a concrete example the wall of the trachea instead of lying in the open air-isolated lumen of the trachea, the circuit is closed over the patient's body and a current corresponding to the electrical resistance of the body flows. Although this current is also very small, it is noticeably larger than any current that flows without contact of the distal end of the guidewire with the body (ie, when that end is in a - generally gas-filled - cavity) or vice versa in other words, the electrical resistance of the body tissue is considerably smaller than the resistance which exists when, in addition, the insulating air space between the tracheal wall and the distal end of the guide wire is added. In this case, such a current or resistance measuring device can be adjusted so that it emits either an optical signal (for example, a light emitting diode) or an acoustic signal (for example beeping) when the measured current suddenly increases or the resistance suddenly decreases or vice versa.

The executive surgeon may then change the just-initiated movement of the guidewire such that this warning signal disappears. Even when producing the puncture opening for the insertion of a corresponding guide wire, the version according to the invention can already be used for the puncture cannula. For this purpose, the proximal end of the puncture cannula - -

Ie is connected to one input of the current or ohmmeter and the other input is connected, for example via a simple cable clamp, to a body part, e.g. the earlobe of the patient, connected. Upon insertion of the tip of the cannula into the body of the patient, the current or ohmmeter immediately signals a corresponding current or resistance, e.g. by an acoustic or optical signal. However, as soon as the tip of the cannula enters an air or gas filled cavity of the body, e.g. into the trachea of a patient, the signal in question is terminated abruptly, since the cannula except for its tip has an insulating sheath and the tip is now in an insulating cavity. In general, the sheath consists of a thin, adapted to the diameter of the cannula plastic tube, which is pushed over the cannula, so that only the tip remains free, and which is then inserted together with the cannula into the puncture opening.

The puncture cannula may then be withdrawn from the insulative sheath and instead a guidewire or the like is now inserted into the sheath, which, upon exiting the cannula, is displaced further down the lungs in the interior of the trachea to serve as a guidewire for a dilator and / or to serve a later to be inserted tracheostomy cannula. Also, this guide wire, which may be formed in particular as Seidingerdraht, has an insulating sheath, which is missing in the region of the tip of the wire.

In addition, the method or the corresponding elements can also be used to facilitate the puncturing of other body organs.

For example, for some examinations, e.g. Liver or kidney of the human body to be punctured. This is often done under ultrasound control to see if the puncture device has reached the organ in question. However, such ultrasound images are often only low in contrast and above all only two-dimensional, so that it would be helpful to additionally obtain, for example via an electrical signal, the information as to whether the tip of the puncture cannula is within the tissue of the organ of interest or in other regions of the body of the patient. This can be determined, for example, by closely observing the resistance of the body between the puncture tip and the external body contact during the puncture procedure, since this resistance often changes abruptly when puncturing interfaces between muscle or connective tissue and the corresponding organs.

The invention is therefore also applicable to such puncturing methods and devices by simply providing the puncturing element with an insulating sheath and having only at its front end a metallic, exposed tip which serves as an electrical sensor element. - -

In this way, it is possible to insert cannulas, catheters and other probes into the body of a patient with a permanent monitoring of the position of the respective tip without visual inspection, but with a simple visual or audible indication that provides reliable feedback on the type of body tissue or provides a body cavity in which the tip is currently located. In particular, in tracheostomies, with a significantly reduced risk for the patient, it is possible to insert the guidewire into the trachea of a patient sufficiently far enough to be able to manage the further processes, such as, e.g. completing the sliding of dilators on the guide wire, etc.

The further embodiment of the guide aid is described below with reference to guide wires. It is understood, however, that the corresponding features readily on other probes such. B puncture needles and the like, which are in this sense also subject of the present invention.

Conveniently, in the case of a guidewire, the same at its distal end as before bent in a J-shape, because in this way the risk of injury to the trachea in a light touch is practically impossible. In this case, the insulation-free region of the guide wire can be limited to the rearwardly bent leg of the J-shape, with the result that the warning signal does not occur even with light touch the tracheal wall, but only when the guide wire is a little way in depresses the elastically yielding tissue so that a larger portion of the J-shaped end, including a portion of the insulation-free region, makes contact with the body tissue.

An embodiment of the invention is further preferred in which the insulating sheath is formed from a coating adhered to the wire, such as e.g. an insulating paint. Corresponding painted wires are commercially available, but in the particularly preferred embodiment of the invention, a special paint or a special insulating layer is used, which has a significantly lower ductility than the wire itself, such that at a sharp buckling of the wire, the insulating layer in the kink area flakes off or is pierced by a leaking wire tip. In this way, one also recognizes when a possibly sharply bent portion of the wire or an end of a single wire of a plurality of parallel, different lengths of wires, which could also lead to injuries of the tracheal wall, comes into contact with this.

An alternative to the electrical variant guide has a guide element which consists of a (relatively thin) tube, at the distal end of which an inflatable balloon is provided, and on the proximal side a connection for a device for inflating the balloon and a control balloon having. For example, such a tubular guide element could first be inserted into the small initial surgical incision - -

Insert the trachea and inflate the balloon as soon as the distal end of the guide element is inside the trachea. It would be sufficient if, when inflated, the balloon has a diameter of e.g. 2 to 5 mm. When inflating the balloon at the same time the extracorporeal control balloon is inflated, which should also have only a diameter of about 2 to 5 mm. The inflator is then sealed off from the tube, unless it is already sealed against the tubular guide element, as long as it is not actuated.

The balloon at the distal tip of the guide member and the proximal control balloon then communicate with each other via the tubular guide member. Now, if the tubular guide element further inserted into the trachea and thereby pushes the balloon at the top with appropriate pressure to the wall of the trachea, this balloon is pressed and displaced in this way gas in its interior is through the tubular guide element in the control balloon pushed in, so that it inflates accordingly. On the inflation of the control balloon, the surgeon recognizes again that the tip of the guide element bears with corresponding pressure on the wall of the trachea and it can accordingly correct the position of the guide element.

For purposes of the original disclosure, it is to be understood that all such features as will become apparent to those skilled in the art from the present description, drawings, and claims, even though they have been specifically described only in connection with certain further features, both individually and separately any combination with other of the features or feature groups disclosed herein are combinable, unless this has been expressly excluded or technical conditions make such combinations impossible or pointless. On the comprehensive, explicit representation of all conceivable combinations of features is omitted here only for the sake of brevity and readability of the description.

Further advantages, features and possible applications of the present invention will become apparent from the following description of a preferred embodiment and the associated figures. Show it:

1 shows schematically a so-called Seldinger wire with a J-shaped bent tip,

FIG. 2 shows a section of a Seldinger wire according to FIG. 1 in an enlarged view,

FIG. 3 shows a further enlarged cross section through such a wire,

Figure 4 shows an insulating introducer for insertion of the Seldinger wire and

5 shows the sleeve of Figure 5 with a puncture cannula. - -

FIG. 1 shows diagrammatically an elongate wire with a J-shaped bent tip 2. The end portion 3, which comprises the tip 2 and is typically several centimeters long, is more flexible than the remainder of the proximal portion of the wire 1.

The proximal section of the wire 1 can be seen again in an enlarged view according to Figure 2. As can be seen, it is a spirally wound tightly with a thin wire or a thin insulating wire core. The outer winding itself either consists of an insulated (eg painted or Teflon-coated) thin wire, or it is applied to the corresponding winding an outer insulating layer, wherein such an additional outer insulating layer can also be applied to an already insulated, spirally rotating wire , An exemplary internal structure of the wire 1 can be seen in the cross-sectional view according to FIG. It is understood that this representation is purely schematic. Accordingly, the wire core consists of a plurality of parallel, flat bands 5, which are wrapped by the already mentioned spirally rotating wire 4 and held together by this. The individual bands, which may also be circular or otherwise, e.g. cylindrical or elliptical cross-section could have different lengths and ends preferably at different positions in the increasingly flexible expectant section 3, so that in the region of the J-shaped curvature, for example, still a single band 5 or wire element is located. This is correspondingly preformed so that it gives the wire end the characteristic J-shape, but the wire has a sufficient elasticity, so that the J-shaped end can be easily bent in the extended state, but again in the force-free state returns to the J-shape shown.

According to the methods mentioned above, a tracheostoma is produced by modern, minimally invasive methods with the aid of a puncture cannula, as shown in FIG. However, the cannula in FIG. 4 is disproportionately large, in particular shown with a disproportionately large diameter. In fact, this diameter is in the range of 2 to 4 mm. The cannula consists of an inner steel cannula 6 with about 1 to 2 mm in diameter and an outer plastic sleeve. 7

The front end of the cannula 6 is chamfered, so that a point for puncturing arises, as is generally known in cannulas, for example for blood sampling.

At the proximal end of the cannula, a flange 8 may be provided which defines the exact location of the tip of the cannula 6 relative to the forward end of the sleeve 7 such that the taper of the cannula tip terminates approximately in the region of the end of the sleeve while the tip itself protruding from the end of the cannula.

To produce a tracheostoma, the cannula 6 with the sleeve 7 pushed in the lower laryngeal region is inserted into the preferably between the second and third cartilage clasp of the throat. - -

stuck into the neck of a patient's head. The proximal end of the cannula is connected via a cable 9 with a resistance measuring device 10, whose second input is connected via a further cable 9 ', for example with a clamp on the earlobe of the patient. When the tip of the cannula 6 touches and penetrates the skin of the patient, the circuit is closed by the meter 10 via the cables 9, 9 ', the cannula 6 and the body of the patient and the meter 10 can measure the measured resistance value of the patient Show body or by an optical and / or acoustic signal (beep) indicate that the resistance has fallen below a predetermined limit, which is preferably also adjustable. This limit is expediently chosen so that it is above the typical resistance of a human body, even if the two measurement points are relatively far apart on the body of the patient.

The cannula is now pushed further and further into the patient's neck until it hits the trachea and enters it. When the tip of the cannula 6 has entered the trachea and even the front end of the sleeve 7 has pierced the wall to the trachea, the resistance is suddenly larger, which can be seen, for example, the silence of a corresponding beeping, because now the over the top of the Cannula 6 made electrical contact is missing after this tip is located in the air-filled cavity of the trachea.

When this condition is reached, the outer sleeve 7 remains in position and the cannula 6 itself is withdrawn from the patient's neck and sleeve 7. Optionally, positioning or fixing aids, e.g. a sliding shield, be attached to the outside of the sleeve 7.

Subsequently, as seen in Figure 5, a so-called Seldinger wire 1 is inserted into the sleeve, wherein during the insertion of this wire, the J-shaped end necessarily has to be stretched straight, but after emerging from the front end of the sleeve again in the mentioned J-shape bends back.

This Seldinger wire is then inserted further into the trachea of the patient. During this insertion, it may happen that the wire or its tip does not follow the desired path, but against the wall of the trachea, in particular against the relatively sensitive back wall of the trachea, and this could possibly perforate, if a sufficiently large pressure on the proximal end of the Seldinger wire. In this case, however, due to the elastic yielding of the body tissue and the Trachearückwand also comes from the insulation-free tip 1 1 of the Seldinger wire with the tissue in touch. The proximal end of the Seldinger wire is again connected via the cable 9 with the meter 10, wherein the patient is still connected via the cable 9 'to the other input of the meter 10. If the body tissue is touched by the insulation removed from the body - -

Accordingly, the peak 11 will experience a fall below the resistance limit and the device 10 will indicate this in a corresponding manner (for example, by the mentioned beep). The surgeon may then slightly withdraw the Seldinger wire 1, optionally rotate it and otherwise move it until the resistance is again above the threshold, indicating that the tip 1 1 of the Seldinger wire is not touching any body tissue.

If the Seldinger wire has been inserted sufficiently far into the trachea, the sleeve 7 can be pulled back from the Seldinger wire and instead a so-called dilator is pushed onto the Seldinger wire, which tapers conically at the front end and the serves to expand the initially generated small opening between the cartilage, so that ultimately expands the opening to a diameter on the order of 6 to 14 mm, a tracheotomy cannula with perforated obturator on the wire and then the wire with the Obturator can be removed from the trachea or the tracheostomy cannula again.

In general, the present invention is particularly simple and advantageous applicable to the introduction or implementation of probes or guide aids in or through empty or gas-filled cavities of a body of electrically conductive material, as an electrical resistance between the proximal end of the electrically conductive, but within the probe, which is predominantly insulated from the body, and any outer part of the electrically conductive body, if the insulator-free (distal) tip of the probe enters into or passes through a gas-filled cavity of the body in contact with the electrically conductive material, which the body consists of loses or regains, which can be easily determined with the help of an extracorporeal detection device.

Claims

- PATENT APPLICATIONS

1. Guide to the introduction of probes (1) in or through air-filled cavities, in particular of tracheostomy tubes and / or dilators in the trachea, consisting of an elongated, flexible and longitudinally sufficiently rigid guide element, characterized in that at least the distal tip of the guide element a sensor element (11), which triggers a detectable reaction of an extracorporeal display element upon contact of body tissue.

2. guide aid according to claim 1, characterized in that the guide element has a length-to-diameter ratio of more than 8, in particular of more than 50.

3. Guide aid according to claim 1 or 2, characterized in that the guide element (1) consists of an electrically conductive wire having an insulating sheath, wherein at least a portion (11) of the distal end of the wire of the insulating sheath is free.

4. guide aid according to claim 1 or 2, characterized in that the guide element consists of an electrically conductive cannula (6), which is surrounded by a preferably axially displaceable on the cannula, insulating sleeve (7), so on the cannula (6 ) is positionable that its conductive tip protrudes from the sleeve (7).

5. Guide aid according to one of claims 1 to 4, characterized in that the display element consists of a current or resistance measuring device (10) whose one input to the extracorporeal end of the guide element (1) and whose other input connectable to the body of a patient in whose trachea the guide element (1) is to be inserted.

6. guide aid according to one of claims 3 or 5, characterized in that the wire is bent at its distal end J-shaped.

7. guide aid according to claim 6, characterized in that the insulation-free region is limited to the rearwardly bent leg of the J-shape.

8. guide aid according to one of claims 1 to 3 or 5 to 7, characterized in that the insulation of a coating, such as an insulating paint exists. - -

9. guide aid according to one of claims 3 or 5 to 8, characterized in that the insulating layer has a significantly lower ductility than the wire, such that in a sharp buckling of the wire, the insulation layer peels off in the bending region.

10. guide aid according to claim 1, characterized in that the guide element consists of a tube at its distal end an inflatable balloon is provided, and having on the proximal side a connection for a device for inflating the balloon and a control balloon.

11. Use of a guide aid according to one of claims 1 to 10 in the introduction or passage of a guide element into or through an empty or gas-filled cavity of a body made of an electrically conductive material, wherein the electrical resistance or current flow between a lying outside of the body Detects the end of the guide and an outer part of the body and from this the position of the tip of the guide is derived inside or outside a cavity of the body.