Instrument and method for delivery of anaesthetic drug

A needle and catheter system, including components, is provided such that the position of an epidural needle may be identified after insertion into the body of a patient by electrically stimulating and thus locating a specific nerve.When a specific nerve is located, the catheter is inserted through the needle to a point slightly beyond the distal tip of the needle. The catheter tip may then be manipulated and the optimum position for the catheter tip determined by applying an electrical voltage through the helical wire to the proximal tip of the helical wire, this electrical stimulation being utilized in locating the specific location of the catheter tip within the nerve. Once optimum placement is achieved, the catheter is utilized for continuous administration of anaesthetic. A catheter adapter is utilized to allow easy access to the catheter and introduction of fluid into the nerve of the patient through the catheter tip. The catheter and catheter adapter are also provided with components so that the catheter adapter can be in place for during electrical stimulation of the target nerve.

BACKGROUND OF THE INVENTION

This invention relates to medical-surgical method of utilizing medical-surgical instruments for delivery of an anaesthetic drug. The invention is more particularly concerned with instruments and methods for use in the delivery of an anaesthetic for use as a nerve block.

A nerve block may be achieved through the administration of variable quantities of an anaesthetic agent to the plexus of a nerve. Since the nerve plexus is a very fragile structure, not capable of simple repair or reconstruction, it is crucial to do as little damage as possible in locating the point at which the plexus may be contacted.

It has been proposed to use a needle to locate the nerve in the usual way, and then to insert anaesthetic through the needle so that it emerges from the tip of the needle and contacts the nerve. An alternative procedure involves the proper positioning of the needle and the introduction of an epidural catheter through the needle. Once properly placed adjacent the nerve and into the plexus sheath of the patient, the epidural catheter may then be used to deliver variable amounts of anaesthetic for use as a nerve block.

It has also been proposed that an integral conductive wire be contained in the catheter, through which an electrical current may be applied to determine-correct positioning of the catheter once it has been inserted through the needle. An electrical impulse sent through the conductive wire is utilized in determining proper placement of the tip of the catheter and, thus, the point at which the anaesthetic will be delivered.

Certain disadvantages exist with regard to the above referenced methods and the apparatus available to accomplish such methods. Most important among these is a danger associated with the uncertainty regarding the position of the needle tip. Such uncertainty could lead to nerve damage in manipulating the tip of the needle without knowing its position relative to nerves in the patient's body. One reason for this uncertainty can be related to leakage of electricity. Placement of the catheter can have similar difficulties. In addition, the integral conductive wire in the catheter can be difficult to utilize effectively, as it is not rigidly attached to the remainder of the catheter apparatus. The catheter itself can also be unwieldy as it is usually of a very small diameter.

BRIEF SUMMARY OF THE INVENTION

In accordance with the present invention, a catheter system is provided comprising: (a) a needle; (b) a catheter provided with an electrically conductive wire; and (c) a multipurpose connector provided with a structure able to make electrical contact with the conductive wire contained in the catheter.

The needle has a distal end and a proximal end. The distal end of the needle terminates in a beveled aperture having a sharp tip adapted for insertion into a nerve sheath of a patient so as to abut the nerve plexus. Contained in the needle and co-terminus therewith at the distal end is a removable stylet utilized in easing insertion of the needle into the patient. The proximal end of the needle is provided with a hub portion used for gripping the needle as well as for accessing the central bore of the needle. The needle, being of metal construction, is electrically conductive along its entire length. A non-conductive material may be used to coat the outer surface of the needle, leaving exposed portions of the proximal and distal ends of the needle, such that electrical voltage is not expended in unnecessary places.

The catheter is adapted for insertion through the hub portion and within and through the needle, with the distal end of the catheter capable of protruding out of the needle's distal end. The catheter is formed primarily of a thermoplastic or related material which covers a tightly wound helical wire. The helical wire extends beyond the sheath material of the catheter at both the proximal and distal ends thereof. The helix formed by the wire leaves the center of the catheter structure available as a conduit. This central conduit of the catheter allows for administration of anaesthetic to the proximal end of the catheter.

The multipurpose connector allows the proximal end of the catheter to be inserted therein. Once inserted therein, the multipurpose connector may be manipulated to rigidly capture the proximal end of the catheter. The structure of the multipurpose connector allows the proximal end of the catheter to be accessed by a syringe or other apparatus for injecting fluid through the catheter. The multipurpose connector is also provided with electrical connections which electrically contact the helical wire of the catheter. These electrical contacts allow the helical wire of the catheter to be accessed despite the presence of the multipurpose connector over the distal end of the catheter and, thus, the protruding proximal end of the helical wire.

It is therefore an object of the present invention to provide a needle and catheter system including components, such that the position of an epidural needle may be identified by electrically stimulating and thus locating a specific nerve. When a specific nerve is located, the catheter is inserted through the needle to a point slightly beyond the distal tip of the needle. The catheter tip may then be manipulated and the optimum position for the catheter tip determined by applying an electrical voltage through the helical wire to the proximal tip of the helical wire, this electrical stimulation being utilized in locating the specific location of the catheter tip within the nerve. Once optimum placement is achieved, the catheter is utilized for continuous administration of anaesthetic.

Some of the objects of the invention having been stated above, other objects will become evident as the description proceeds below, when taken in connection with the accompanying drawings as best described below.

DETAILED DESCRIPTION OF THE INVENTION

Referring first toFIG. 1, there is shown relevant portions of a human body10containing a nerve12located subcutaneous to adjacent neck portion14. In this example of use, a needle assembly16has been inserted into a specific point in the neck14of the human body10for the purpose of locating the nerve12. The needle assembly16comprises a needle18and a central stylet20which extend coaxially of one another. The needle18is a metal needle which is joined at its rear end to a hub22of a plastic material. The needle18is hollow and projects about 95 mm forwardly of the hub22.

The needle18has three portions along its length. The major portion of the needle is the central portion24thereof. This central portion24of the needle is wrapped on the outside surface thereof in an insulating coating26which will not conduct electricity. This coating26is shown inFIG. 1as being divided into sections of alternating color28and30. Each of these sections is of a known, specific, length. Such colored sectioning enables the user to determine the extent of penetration of the tip32of the needle18.

The remaining two portions of the needle18are the distal end34and the proximal end36. At its proximal end36, the needle18extends within the hub22where it is secured, such as by molding the hub around the needle. Between the insulating coating26of the central portion of the needle24and the plastic hub22the proximal end36of the needle18is exposed such that electrical contact with the remainder of the needle may be achieved by contact with the exposed proximal end36. The bore through the needle38opens into an axially-aligned bore40through the hub22of the same diameter as the needle bore38. The rear end of the bore42is enlarged and tapered to provide a female Luer opening44for use in receiving the stylet20and stylet hub21. The hub22is provided with an axially-extending slot or keyway25formed in the outer surface of the hub, on that side of the hub to which the tip32of the needle18is inclined.

As shown inFIG. 1C, the forward 5 mm or so31of the needle18is bent downwardly at an angle of about 20°, the distal end34of the needle being cut such that it makes an angle θ of about 10° with the axis of the major part of the needle. This inclined end of the needle provides it with a tip32constituting a sharp point that readily pierces body tissue. The distal end34of the needle is not covered by any electrically insulating material and is in electrical contact, by way of the covered central portion24, with the proximal end36of the needle. The insulating coating26prevents the flow of electricity radially out of the central portion24of the needle, but allows the flow of electricity axially along the length of the needle18.

As best exemplified inFIG. 1D, the inner stylet20is formed of a solid metal needle. The distal tip45of the stylet20is cut to have the same sharp tip angle θ as the tip32of the needle. Joined to the proximal end of the stylet20is a stylet hub21of plastic material. The stylet20is smaller in diameter than the outer needle18and is straight along its entire length. The connector46of the stylet hub21which grasps the stylet20is of generally cylindrical shape. The forward end of the connector46has a Luer taper48that is dimensioned to fit within the Luer-tapered opening44in the needle hub22. A short peg or key50of rectangular section is provided along the lower side of the stylet hub21, as viewed in FIG.1. The peg50extends axially of the stylet hub21, being spaced outwardly by a small gap from its Luer-tapered section48. The peg50is aligned with respect to the stylet hub21and stylet20such that, when the peg is engaged in the slot25of the needle hub22, the plane of the inclined tip45of the stylet20lies in the same plane as the inclined tip34of the needle. The combined sharp tips of the needle and stylet readily pierces body tissue while the stylet, occupying the center bore38of the needle, prevents any tissue from entering the needle bore38.

Also shown inFIG. 1is an electrical connector52, which may be in the form of an alligator clip which conveys electrical impulses from an anaesthetic nerve stimulator17to the proximal end of the needle36.

FIG. 1Ais an end on view of the tip of the needle assembly16, showing the inclined tip of the needle32the inclined tip45of the stylet20. Also shown is the insulating coating26.FIG. 1Bis a detail of the needle18of the needle assembly, with the stylet20removed and only showing a small portion of the hub22. In addition, the needle18ofFIG. 1has been sectioned along section line1B of FIG.1A.FIG. 1Bshows the relationship of the insulating coating26(of exaggerated thickness) to the various portions of the needle18.

Referring next toFIG. 2, there is shown a catheter assembly54. The catheter assembly54is of a diameter which allows the assembly to be inserted through the needle assembly16and into the body of the patient. The catheter assembly54comprising a sheath56formed from a thermoplastic or similar material. A helical coil of wire58, best shown inFIG. 3, possesses three portions. A proximal portion60, a central portion62and a distal portion64. For its entire length, the helical wire58defines a central bore66through which a liquid may freely pass.

The central portion62of the helical wire58is completely covered by the catheter sheath56and constitutes the vast majority of the total length of the catheter assembly54. The proximal portion60of the helical wire has no distinguishing features except that it is short relative to the central portion of the remainder of the catheter assembly54and is not covered by the catheter sheath. The proximal portion of helical wire is left exposed so that it, and therefore the entire wire helix58, may be electrically contacted, as will be discussed relative to other structures.

The distal portion64of the helical wire, which is also short relative to the remainder of the catheter assembly54and not covered by the catheter sheath56, has several features associated therewith. Where the helical wire58exits the catheter sheath56at the distal end thereof, the helix maintains the tightly wound nature of the proximal60and central62portions of the wire. This tight helix continues for a short distance along the distal portion before the helix opens up considerably at an open helix portion68. The open helix portion68continues for several revolutions of the helix, before the structure returns for the tightly wound end70of the distal portion64. Attached to the distal end of the tightly wound end portion is a wire helix tip72which is a piece of rounded metal.

Referring next toFIG. 4, there is shown a catheter adapter74. Accessing the central bore66of the catheter assembly54would be nearly impossible given the diameter of this structure. This being the case, a catheter adapter74is needed to provide access to the central bore66of the catheter assembly54for various delivery vehicles, e.g. a syringe, for the controlled delivery of fluid through the catheter.

The main constituents of the catheter adapter are the rear body76, the front body78and the holding hub80. The rear body78has a central flange82. From the rear face84of the central flange82extends a connection cylinder86having a threaded outer surface88and a hollow central bore90. The function of this cylinder is to facilitate luer attachment of apparatus for controlled delivery of fluid to the catheter assembly54. The end cap92provided with the catheter adapter74is primarily for sterility purposes, and is simply removed after the catheter adapter74is attached to the catheter assembly54. The central flange has, at its center, a bore93passing completely therethrough such that the rear face84and front face94are in fluid communication.

From the front face94of the central flange84extends an operating cylinder96. Where the operating cylinder96is connected to the front face94of the central flange84, it is of a certain diameter95. Along the length of the operating cylinder, the diameter of the operating cylinder is reduced by a taper98. The remainder of the operating cylinder is of this reduced diameter99to the distal end100of the operating cylinder. The operating cylinder96has a central bore102which extends along the entire length thereof. Axial slots104extend from the distal end100of the operating cylinder, nearly the length thereof, i.e. the slot ends106extend nearly to the juncture of the operating cylinder96and the front face94of the central flange82. Contained in and extending most of the length of the central bore102of the operating cylinder96is an elongated rubber gasket105.

The front body78of the catheter adapter has a structure similar in geometry to the central flange84of the rear body76, this structure is called the rear flange110. The rear flange110has extending from the front face112thereof a front cylinder114. The front cylinder114has an essentially constant outside diameter extending from the front face112of the rear flange110to the distal end116of the front cylinder. A central bore118is provided in the front cylinder114, extending the entire length thereof. This central bore118has several different diameter changes along its length. At the entry portion of the central bore120on the rear face122of the rear flange, the diameter of the bore is slightly larger that the diameter95of the operating cylinder96where it is connected to the front face94of the central flange84. Along the length of the central bore120the inside diameter is reduced by a taper123which is a mirror image of taper98on the operating cylinder. These mirror image structures thus allow sliding contact between the outer surface of the operating cylinder96and the central bore120of the front body78.

The holding hub80is a generally tubular body provided with a cylindrical recess126formed in the rear face128thereof. The distal end100of the operating cylinder96is matingly engageable with the cylindrical recess128of the holding hub80and is rigidly attached thereto. The diameter of the central bore120of the front body78is, from the front face thereof94to a depth less than the length of the holding hub, slightly greater than the diameter of the holding hub. The rigid connection between the holding hub80and the distal end100of the operating cylinder holds these two structures in slidable relationship with the front body78.

In use, the catheter adapter74is initially in the configuration shown in FIG.4. In this configuration the proximal end57of the catheter assembly54may be freely inserted and withdrawn from the catheter adapter. The proximal end57of the catheter assembly54may be held in place by sliding the front body78toward the rear body76of the catheter adapter. In sliding these pieces relative to each other, the taper98of the operating cylinder96will be compressed by the taper123of the interior of the front body. The slots104in the operating cylinder96allow this compression to occur. The compression of the operating cylinder results in the compression of the elongated rubber gasket105. This compression of the elongated rubber gasket105results in the rubber gasket fictionally engaging the proximal end57of the catheter assembly54such that the catheter may not be easily removed from the catheter adapter.

An additional structure of the catheter adapter which is of interest is the metal washer130. This metal washer130is disposed about the operating cylinder96adjacent the front face94of the central flange82, and is held in place by nut132. The metal washer130is provided with a tab portion134which extends above the flange portions84and110. This allows electrical contact to be made to the washer by way of the same electrical connector52as was used previously to conduct electricity into the needle assembly16from an anaesthetic nerve stimulator17. As can be seen inFIGS. 5 and 6, a pair of wires138are attached to the metal washer130and extend from the metal washer to the internal bore140of the elongated rubber gasket105. Thus, when the elongated rubber gasket105is compressed about the proximal end of the catheter assembly54and about the exposed helical wire58found at the proximal portion60thereof, electrical contact is made between the pair of wires138and the helical wire58. As a result, electrical contact may be made from the anaesthetic nerve stimulator17, through the catheter adapter74and into the helical wire58of the catheter apparatus54and, thus, to the distal wire helix tip72of the catheter assembly.

The above described apparatus may be used in numerous different medical procedures. The following described medical procedure is one type which utilizes the features embodied in the above described apparatus. The method is drawn to the correct placement of the catheter assembly54and, more particularly, the distal portion64thereof. Once the distal portion64of the catheter assembly54is determined to be in the correct position, a continuous interscalene nerve block may be administered.

The patient is positioned in the dorsal recumbent position with the head slightly in extension and turned somewhat to the opposite side. An assistant applies light traction on the arm with the elbow flexed.

The interscalene groove is easily palpated in this position by the following procedure: First, the posterior edge of the clavicular head of the sternocleidomastoid muscle is located; then the palpating fingers are placed postero-lateral to this muscle to identify the interscalene groove. The external jugular vein almost always lies directly superficial to the interscalene groove and provides a useful additional landmark. Needle entry should be anterior or posterior to the vein. Another constant finding is that the interscalene groove is approximately 3 cm lateral to the most prominent portion of the belly of the sternocleidomastoid muscle at the level of the cricoid cartilage.

The needle assembly16is inserted into the interscalene groove at the level of the cricoid (C6level) and the needle is directed perpendicular to the skin in all the planes. For the placement of the catheter assembly54for this continuous interscalene nerve block technique, the needle assembly16enters the skin at a point approximately halfway between the mastoid and the clavicle, posterior to the posterior border of the clavicular head of the sternocleidomastoid muscle.

The point of needle entry is just caudal to the accessory nerve and just posterior to the anterior border of the posterior triangle of the neck. The accessory nerve can usually be identified by stimulating percutaneously with the electrical connector52of the nerve stimulator17since the nerve runs superficial to the fascial carpet of the posterior triangle of the neck, approximately midway between the clavicle and the mastoid. When the needle tip32is proximate the accessory nerve and voltage from the nerve stimulator17is applied, contractions of the trapezius muscle and elevation of the shoulder girdle will occur. The needle assembly16is directed caudal and parallel to the vertebrae aiming for the interscalene groove with the bevel of the needle assembly16directed laterally (outwards) to avoid possible central (epidural) placement of the catheter.

During insertion of the needle assembly, voltage should be continuously applied to the needle tip32as an aid in navigating the various nerves which may be encountered. The nerves to the levator scapula and rhomboid muscles may be encountered with the needle32tip at an early point. Stimulation of these nerves will also cause movement of the shoulder girdle when stimulated by elevating or rotating the scapula. The phrenic nerve, situated on the belly of the anterior scalene muscle, may be encountered. This causes unmistakable twitching of the ipsilateral diaphragm. All these nerves should be avoided by redirection and/or reinsertion of the needle assembly16as stimulation of these nerves can provide false indications of correct needle placement that will most certainly lead to block failure or phrenic nerve paralysis if local anesthetic agent is injected at this stage.

When the brachial plexus is encountered, definite and unmistakable muscle twitchings should be observed in the biceps and deltoid muscles of which the biceps movements are more easily seen. This is the reason for keeping the elbow slightly flexed during the procedure. If the phrenic nerve is accidentally stimulated the needle assembly16is pulled back slightly and the needle tip32is directed slightly posteriorly until the brachial plexus is encountered. As the needle tip32is advanced further a distinct “pop” or give can be felt followed by an increased intensity of the biceps and deltoid muscle twitchings. This is when the fascia sheath of the brachial plexus is penetrated and the tip of the needle32is now in direct contact with the brachial plexus. The electrical connector52may be removed from the needle18at this time.

The central stylet20is removed from the needle18and the catheter assembly54is fed through the needle18to a point just past the tip of the needle32. Such a placement of the wire helix tip72is far enough so that the metal helical wire58does not make contact with the needle, i.e. the needle tip32is in contact with the catheter sheath56which will not conduct (disperse) electricity.

The catheter adapter74can be attached to the proximal end60of the catheter assembly54at this point, if it has not been attached previously. The electrical connector52of the nerve stimulator17is then clipped to the tab portion134of the metal washer130provided on the catheter adapter74.

The output of the nerve stimulator17can be turned down (typically to approximately 0.5-1.0 mA) as the muscle twitching will increase because all the current is now concentrated in the unsheathed helix tip72of the catheter assembly54. Muscle contractions with a nerve stimulator17output of approximately 0.5 mA provides additional proof of proper placement into the sheath.

Advancement of the catheter helical tip72approximately an additional 1 cm beyond the tip of the needle32down the brachial plexus sheath should not result in a decreasing of the twitching in the biceps and deltoid muscles. Frequently, though, the muscle twitchings do decrease in which case the needle and catheter complex16,54are simultaneously pulled back slightly as a unit, until maximal twitchings are again observed. The catheter54is then again advanced and the above process is repeated until maximal twitchings are observed during catheter54advancement. It is most important for guaranteed successful catheter placement to observe maximal muscle contractions while catheter is being advanced. The catheter54frequently cannot be fed beyond the coracoid process. It should, however, not be forced further as this may lead to nerve damage and, for shoulder surgery, it is not necessary to advance the catheter beyond this point. The needle assembly16may then removed and the catheter securely fixed.

Indwelling interscalene catheters are notorious for falling out or dislodging. To avoid dislodgment after placement of the catheter, the same needle16used to place the catheter, is inserted subcutaneously from just above the suprastenal notch and directed superolaterally, avoiding vascular structures, towards the point of entry of the catheter. The needle assembly16is advanced to exit through the same orifice in the skin as the catheter54and just next to the catheter. The proximal end of the catheter60is fed from the tip of the needle32through the needle18and the needle is removed so that the catheter54is tunneled subcutaneously.

Kinking of the catheter should be avoided as the elbow formed by the catheter disappears under the skin. The catheter is then covered with a transparent dressing.

With the catheter assembly thus firmly in place, anaesthetic may be administered to effectuate a nerve block:1. When a dense motor and sensory block is required:a) Ropivacaine 10 mg/mL (1%). Inject 20 mL as a bolus and then infuse with syringe driver a diluted concentration (5 mg/mL or 0.5%) at 10-20 mL/hour.Orb) Bupivacaine 5 mg/mL (0.5%). Inject 20 mL as a bolus and then infuse a diluted concentration (2.5 mg/mL or 0.25%) at 10-20 mL/hour.2. When sensory block with minimal motor block is required:a) Ropivacaine 2 mg/mL (0.2%). Inject 10-20 mL as a bolus and then infuse the same concentration at 1-10 mL/hour. Continually adjust (titrate) the infusion rate to achieve the desired effect.Orb) Bupivacaine 2.5 mg/mL (0.25%). Inject 10-20 mL as a bolus and the infuse the same concentration at 1-10 mL/hour. Continually adjust (titrate) the infusion rate to achieve the desired effect.3. Patient Controlled Interscalene Nerve Block:Injection if a bolus of 30 mL bupivacaine (0.4%) via an indwelling catheter into the brachial plexus sheath at the level of the interscalene groove followed by a background infusion of bupivacaine 0.15% at a rate of 5 mL/hour and a patient-controlled bolus of 4 mL for patients weighing >65 Kg and 3 mL for patients weighing <65 Kg. A lockout time of 20 minutes was programmed into the PCA device. This seemed successful. Promising preliminary results have been achieved with ropivacaine. It seems that finer adjustment of the block to achieve varying levels and densities of motor and sensory blockade may be possible with ropivacaine.