Abstract:
A target nerve or nerve plexus registration point is percutaneously located using a cutaneous nerve stimulator electrode to elicit response. The electrode includes a tip at the end of a coaxial cylindrical body. A central bore extends through the electrode and carries a nerve stimulator needle. The needle is inserted at the located registration point with the needle path being mechanically guided by the bore, thereby avoiding errant needle passes. A peripheral flange of the body serves as a depth guide in assuring appropriate depression of epidural layers for electrical conductivity and for fixation of the nerve. A nerve stimulator current generator supplies both the percutaneous electrode and the nerve stimulator needle and includes multiple outputs as well as base and variable current setting levels as appropriate for each aspect of the technique and for the specific nerve or nerve plexuses being treated.

Description:
RELATED APPLICATIONS 
     This application claims the benefit of U.S. Provisional Application No. 60/241,141 filed Oct. 17, 2000. 
    
    
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     This invention relates generally to regional anesthesia and more particularly to an apparatus and procedure for nerve stimulator needle guidance in conjunction with various procedures, such as, the administration of an anesthetic blockade, neuro monitoring, electromyography and therapeutic intervention. 
     2. Antecedents of the Invention 
     The field of regional anesthesia relates to the practice of administering anesthesia to a specific body region during surgery, for the relief of postoperative pain, and for extended relief of trauma or chronic pain. Often, regional anesthesia has been found to be preferable to general anesthesia because of increased safety, the availability of postoperative pain control and decreased anesthetic costs. 
     Regional anesthesia delivery techniques strove to optimize administration of a local anesthetic in close proximity to a target or nerve plexus so as to establish a neural blockade. Successful administration of regional anesthesia was dependent upon the accurate placement of the anesthetic in relation to the target nerve or nerves. 
     Various techniques have been employed to assist in placement of an administration needle in close proximity to the target nerve which was not externally visible. One of the traditional methods of needle placement involved eliciting paresthesia. Among the disadvantages of this technique was the lack of accurate patient responses amongst patients who were disoriented and/or sedated. 
     A prevalent technique employed the use of nerve stimulators electrically coupled to a nerve stimulator needle. Such method was premised upon the phenomenon that an electrical pulse is capable of stimulating a motor nerve fiber to contract an innervated muscle or cause paraesthesia, in the case of sensory nerve stimulation. 
     Nerve stimulators generally comprised a power supply, a pulse generating circuit and current adjusting means, e.g. the DIGISTIM III nerve stimulator sold by Neuro Technology Inc. of Houston, Tex., coupled to insulated or uninsulated anesthesia needles. U.S. Pat. No. 4,515,168, issued to CHESTER illustrates a nerve stimulator which mounts directly upon a syringe and needle. 
     Suggested improvements in techniques of utilizing nerve stimulator needles have been exemplified by the patents to GRIFFITH (U.S. Pat. No. 5,853,373), HADZIC (U.S. Pat. No. 5,830,151), RAYMOND (U.S. Pat. No. 5,248,153) and CHESTER (U.S. Pat. No. 4,515,168), which were directed to avoiding the requirement for the presence of an assistant in order to reduce the current levels as the needle was advanced toward the target nerve or nerve plexus. 
     The nerve stimulator needle, e.g. a CONTIPLEX nerve block set sold by B. Braun Medical, Inc. of Bethlehem, Pa., was placed within the tissue of the patient&#39;s body in the vicinity of the nerve to be blocked and then advanced until stimulation of the target nerve was achieved as determined by visually detecting muscle contractions or by eliciting a report that the patient felt the stimulus in response to the current flow through the stimulator needle. 
     The current supplied by the nerve stimulator was reduced as the nerve stimulator needle was further advanced, until stimulation of the target nerve was achieved using a reduced current level associated with a prescribed distance between the needle tip and the target nerve. 
     Thereafter, a portion of the anesthetic dose was administered through the needle to terminate the response to the nerve stimulation current. If the response was terminated by the initial administration, the needle was deemed to be properly positioned in proximity to the target nerve and the remaining dose of anesthetic was administered. 
     It should be understood, however, that the initial placement of the needle was dependent upon anatomic landmarks. Since anatomic landmarks varied from patient to patient, they constituted only an approximate starting zone or region to guide needle insertion. Successful administration was often dependent upon the skill and experience of the anesthesiologist. Multiple needle passes were required when the initial needle placement was not directly registered over the target nerve or nerve plexus or when the angle of introduction was anatomically incorrect. 
     Peripheral nerves have been stimulated with cutaneous electrodes at appropriate landmarks utilizing a coupling gel for monitoring the degree of neuromuscular blockade during general anesthesia when neuromuscular relaxing or paralyzing drugs were intravenously administered. 
     BRIEF SUMMARY OF THE INVENTION 
     A nerve stimulator needle guidance system includes a cutaneous electrode having a conductive tip at the end of a cylindrical body with a bore extending coaxially through the body and tip. 
     The cutaneous electrode is coupled to a nerve stimulator to locate a target nerve registration point while depressing the patient&#39;s dermal layers. Thereafter a nerve stimulator needle, coupled to the nerve stimulator, is introduced into the patient at the located registration point through the bore. Conventional nerve stimulation techniques are employed to properly position the needle tip adjacent to the target nerve for the administration of anesthesia or other treatment. 
     The cutaneous electrode bore serves as a guide for the initial placement of the needle at the registration point and for guidance of the needle travel path toward the target nerve. Maintaining the dermal layers in a depressed or indented state by continued pressure on the cutaneous electrode serves to fix the location of the target nerve. 
     From the foregoing compendium, it will be appreciated that it is an aspect of the present invention to provide a nerve stimulator needle guidance system of the general character described which is not subject to the disadvantages of the antecedents of the invention. 
     It is a feature of the present invention to provide a nerve stimulator needle guidance system of the general character described which simplifies the administration of nerve blockade anesthesia. 
     A consideration of the present invention to provide a nerve stimulator needle guidance system of the general character described which increases the likelihood of the successful administration of regional anesthesia with a single needle pass. 
     A feature of the present invention is to provide a nerve stimulator needle guidance system of the general character described which noninvasively locates the entry point of a nerve stimulator needle. 
     To provide a nerve stimulator needle guidance system of the general character described which is well suited for conventional sterilization techniques is a further consideration of the present invention. 
     An aspect of the present invention is to provide a nerve stimulator needle guidance system of the general character described which decreases the likelihood of anesthesia administration complications resulting from errant needle passes. 
     An additional consideration of the present invention is to provide a nerve stimulator needle guidance system of the general character described with increased nerve block success levels. 
     A further feature of the present invention is to provide a nerve stimulator needle guidance system of the general character described with reduced patient discomfort attributable to multiple needle passes. 
     To provide a nerve stimulator needle guidance system of the general character described with increased safety is a further aspect of the present invention. 
     Yet a further consideration of the present invention is to provide a nerve stimulator needle guidance system of the general character described which minimizes the time required to achieve a nerve blockade. 
     To provide a nerve stimulator needle guidance system of the general character described which is simple to use is a further aspect of the present invention. 
     A still further aspect of the present invention is to provide a nerve stimulator needle guidance system of the general character described which is economically disposable after a single usage. 
     Another feature of the present invention is to provide a nerve stimulator needle guidance system of the general character described which lends itself to economical mass production fabrication. 
     Other aspects, features and considerations of the present invention in part will be obvious and in part will be pointed out hereinafter. 
     With these ends in view, the invention finds embodiment in certain combinations of elements, arrangements of parts and series of steps by which the said aspects, features and considerations and certain other aspects, features and considerations are attained, all with reference to the accompanying drawings and the scope of which will be more particularly pointed out and indicated in the appended claims. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     In the accompanying drawings in which are shown some of the various possible exemplary embodiments of the invention: 
     FIG. 1 is a schematized illustration of a nerve stimulator needle guidance system constructed in accordance with and embodying the invention being employed to locate a target median nerve of a patient and illustrating a cutaneous electrode, a nerve stimulator needle positioned within the bore of the cutaneous electrode and with both being coupled to a nerve stimulator, 
     FIG. 2 is a perspective illustration of the nerve stimulator needle guidance system and showing a cylindrical body and a flange of the cutaneous electrode as well as a nerve stimulator needle positioned within the bore of the cutaneous electrode, 
     FIG. 3 is a front elevational view of the cutaneous electrode and illustrated a hemispherical conductive tip of the electrode positioned beneath the peripheral flange, 
     FIG. 4 is a sectional view through the nerve stimulator needle guidance system and illustrating the technique of employing the nerve stimulator needle guidance system for the purpose of locating a femoral nerve for inguinal perivascular femoral nerve block techniques, and 
     FIG. 5 is a perspective illustration of a further embodiment of the invention wherein the cylindrical body of the cutaneous electrode includes a radial slot and a peripheral indexing scale and with a shaft of the stimulator needle including a radial arm positioned within the slot. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     With reference now in detail to the drawings, wherein like numerals denote like components throughout the various figures, the reference numeral  10  denotes generally a nerve stimulator needle guidance system constructed in accordance with and embodying the invention. The system includes a cutaneous electrode  12  which is employed to locate a target nerve registration point on a patient&#39;s skin and a nerve stimulator needle electrode  14  which is introduced into the patient at the located registration point with both electrodes being coupled to a nerve stimulator  16 . 
     It should be noted that the cutaneous electrode  12  generally comprises a non-conductive body  18 , depicted in the figures as having a cylindrical shape, in an exemplary configuration. A transverse flange  20  projects laterally from the lower end of the body  18  and a generally hemispherical electrically conductive tip  22  is positioned below the flange  20  and in registration with the body  18 . A bore  24  extends coaxially through both the body and the conductive tip and an electrical lead  26  couples the conductive tip to the nerve stimulator  16 . 
     The nerve stimulator needle  14  is of generally conventional configuration and includes a needle shaft  27  which may be coated with a nonconductive material, except for the tip portion thereof. At the proximal end of the shaft  27  is a connector block  28  from which an electrical lead  30  extends to electrically couple the nerve stimulator needle  14  to the nerve stimulator  16 . A conventional Luer fitting  32  may be mounted to the connector block to couple the needle bore to a conventional syringe  34 . 
     With reference to FIG. 1, the nerve stimulator  16  includes known pulse generating and adjustable current control circuits such as those employed in the DIGISTIM III, supra or those disclosed in U.S. Pat. No. 4,515,168, incorporated herein by reference. Multiple base current setting levels and outputs are provided, however. One output terminal  36  is provided for the cutaneous electrode  12  and another output terminal  38  is provided for the nerve stimulator needle  14 , with the respective electrical leads  26 ,  30  being coupled to their associated terminals. 
     The nerve stimulator  16  also includes a ground terminal  40  to which is coupled a ground output lead  42 , the end of which is electrically coupled to the patient in a conventional manner. 
     A base level output current setting control  44  is operable to adjust to the optimal initial or base level currents and current ratios through the terminals  36 ,  38  suitable for employment in conjunction with a specified target nerve or nerve plexus. 
     For each of the various target nerves, e.g. femoral nerve, popliteal fossa approach to sciatic nerve, mid-humeral approach to median nerve, ulnar nerve, sciatic nerve, interscalene brachial plexus approach to C 5  and C 6  nerve roots, etc., optimal initial or base level current flow through the cutaneous electrode terminal  36  and the stimulator needle terminal  38  are provided. 
     The cutaneous electrode current flow may be within an overall range of 2-10 mA, for example, and nerve stimulator needle current flow may be within an overall range of 0.3-3.0 mA, for example. By way of further example, minimum cutaneous electrical current for location of the femoral nerve may be achieved at 5 mA while the minimum stimulator needle current flow may be at 0.5 mA. 
     The nerve stimulator  16  also includes a variable current adjustment control  46  and an output selector switch  48  for selecting either the cutaneous electrode terminal  36  or the nerve stimulator needle terminal  38 . Also provided is a display  50  for quantitatively indicating current flow through the active terminal or other data. 
     It should be understood that the nerve stimulator needle guidance system  10  may be utilized with a conventional nerve stimulator having, for example, a single output and with operating room personnel disconnecting the cutaneous electrode lead  26  and connecting the nerve stimulator needle lead  30  after the target point has been cutaneously located. It should be appreciated that the output will simultaneously be adjusted to a reduced level upon introduction of the nerve stimulator needle into the patient. 
     It is also possible to practice the invention utilizing two separate nerve stimulators, one coupled to the cutaneous electrode and the other coupled to the nerve stimulator needle. 
     FIG. 4 illustrates, in an exemplary manner, the implementation of the present invention in the administration of a nerve block to a patient&#39;s femoral nerve  52 . Initially, as under conventional practice, the patient receives prescribed amounts of intravenous sedatives in accordance with conventional routines for nerve location utilizing nerve stimulators. 
     A sterile coupling gel  54  may be applied over the patient&#39;s skin  56  in the appropriate anatomic region prelocated by landmarks. Thereafter, the cutaneous electrode  18 , coupled to the nerve stimulator  16  (illustrated only in FIG. 1) through the lead  26 , is forced against the skin  56  and underlying dermis  58 , compressing subcutaneous fat  60  such that the flange  20  is essentially flush with the skin. In this regard, the flange  20  may be fabricated of a transparent thermoplastic for ease in assuring that the proper tissue depression by the conductive tip  22  has been achieved. 
     The nerve stimulator output, with an initial or base current level set by the control  44  illustrated only in FIG. 1, is moved across the skin to noninvasively elicit responses. By reducing current flow at the control  46 , illustrated only in FIG. 1 the cutaneous electrode  18  locates a point on the skin  56  which is in registration with the target femoral nerve  52 . The registration point is found when it is determined that the appropriate muscle contractions have been elicited with minimum current, that is, maximal motor contractions have been encountered at a minimum current level. 
     The position of the cutaneous electrode is held fast, i.e., is not moved laterally nor is the compressive force released and current flow through the cutaneous electrode is terminated. The shaft  27  of the nerve stimulator needle  14  is then urged through the bore  24  and into the patient while being electrically coupled through the electrical lead  30  to the appropriate output terminal  38  of the nerve stimulator  16  illustrated in FIG.  1 . 
     Utilizing conventional nerve stimulator techniques, the needle  14  is advanced while current flow reduced through adjustment at the control  46  until stimulation of the femoral nerve is achieved utilizing a reduced current level associated with the prescribed distance between the tip of the needle shaft  27  and the target femoral nerve  52 . Maintenance of the compressive force on the cutaneous electrode  18  serves to fix the position of the target nerve while the needle is being advanced. 
     Thereafter, a portion of the anesthetic dose is administered through the needle to terminate response to the stimulation current. If the response terminates with the initial administration, the needle is deemed to be properly positioned for the requisite procedure. 
     With reference now to FIG. 5, wherein an alternate embodiment of the invention is illustrated, it will be noted that like numerals have been employed to denote like components of the previous embodiment, however, bearing the suffix “a”. In the FIG. 5 embodiment, a nerve stimulator needle guidance system  10   a  includes a cutaneous electrode  12   a  and a nerve stimulator needle  14   a  coupled to a nerve stimulator. 
     The cutaneous electrode  12   a  includes a nonconductive body  18   a , illustrated of generally cylindrical configuration, by way of example only and a lower flange  20   a . An electrical lead  26   a  couples a conductive tip, positioned beneath the flange  20   a , to the nerve stimulator. In a manner similar to that with respect to the previous embodiment, the cutaneous electrode  12   a  includes a bore  24   a  extending coaxially through a body  18   a.    
     A planar radial slot  66   a  extends substantially along the entire axial length of the body  18   a  from the upper end thereof and a plurality of indexing marks  68   a  appear as a scale along the length of the body adjacent the slot  66   a.    
     A radial indexing arm  70   a  is fixed to a shaft  27   a  of the needle  14   a  and may be employed, in conjunction with the marks  68   a , to gauge the depth of penetration of the tip of the needle shaft  27   a.    
     The radial arm  70   a  may be of sufficient rigidity to be employed for the purpose of advancing the needle shaft  27   a  into the patient with the anesthesiologist applying a downward force to a portion of the arm  70   a  which projects radially from the slot  66   a.    
     The technique of employing the nerve stimulator needle guidance system  10   a  of the alternate embodiment is substantially identical to that employed in conjunction with the previous embodiment, with the exception, however, of enabling the anesthesiologist to utilize the indexing marks as a depth of penetration gauge and also the utilization of the arm  70   a  for the purpose of advancing the needle shaft into the patient. 
     It should be appreciated that the nerve stimulator needle guidance system of the present invention may be implemented not only for administering an anesthesia blockade but for other medical techniques and practices wherein nerves or a nerve plexus is to be located for treatment such as electromyography, neuro monitoring and therapeutic intervention. 
     Thus it will be seen that there is provided a nerve stimulator needle guidance system which achieves the various aspects, features and considerations of the present invention and which is well adapted to meet the conditions of practical usage. 
     As various possible further embodiments might be made of the present invention and various changes might be made in the illustrative embodiments above set forth, without departing from the spirit of the invention, it is to be understood that all matter herein described or shown in the accompanying drawings is to be interpreted as illustrative and not in a limiting sense.