1. Field of the Invention
This invention relates generally to regional anesthesia and more particularly to a system for positioning a nerve stimulator needle 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.
The nerve stimulator needle was placed within the tissue of the patient'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.
In U.S. Pat. No. 6,533,732, entitled: NERVE STIMULATOR NEEDLE GUIDANCE SYSTEM issued Mar. 18, 2003 to Applicant, there is disclosed a nerve stimulator needle guidance system having a cutaneous electrode with a conductive tip and a bore extending through the electrode. The electrode is coupled to a nerve stimulator to noninvasively locate a target nerve registration point while depressing the patient's dermal layers. Thereafter a nerve stimulator needle is introduced through the bore and into the patient at the located registration point. There is also disclosed, in Applicant's Application No. PCT/US01/32412, published Apr. 25, 2002, Publication No. 02/32289 82 a subcutaneous electrode guidance system for a nerve stimulator needle which utilized a smooth tipped electrode probe for locating the direction of a nerve or nerve plexus relative to a cutaneous introduction point.