Bi-level charge pulse apparatus to facilitate nerve location during peripheral nerve block procedures

An electrolocation apparatus is provided for locating a nerve to which anesthesia may be delivered. The apparatus includes a needle assembly having an electrically conductive needle cannula non-conductive tube secured over the needle cannula, and a conductive plating on the tube. The conductors are connected to a stimulator that generates alternating high and low charge pulses with a constant low current level. The high charge pulses generate noticeable muscle twitches immediately after insertion of the needle into the patient. Muscle twitches responsive to the high charge pulses will peak in magnitude, and muscle twitches responsive to the low charge pulses will become observable as the needle approaches the targeted nerve, and will be indistinguishable from the muscle twitches responsive to the high charge pulses when the needle is in a position for administration of anesthetic.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
The subject invention relates to an apparatus for efficiently locating a 
nerve and for subsequently delivering an anesthetic to the nerve. 
2. Description of the Prior Art 
Many medical procedures require a patient to be at least locally 
anesthetized. A regional anesthesia or nerve block offers advantages over 
general anesthesia for many medical procedures. For example, a regional 
anesthesia or nerve block typically is less traumatic to the patient 
undergoing surgery and often permits a shorter post-operative recovery. 
A regional anesthesia or nerve block necessarily requires location of the 
nerve to which anesthetic agent will be administered. The prior art 
includes methods for locating the nerve. In most such prior art methods, 
the doctor typically uses general knowledge of physical anatomy to 
approximately locate the targeted nerve. In accordance with one prior art 
method, an electrically conductive pad is positioned on the skin on a 
portion of the patient's body at some distance from the targeted nerve. 
For example, if the targeted nerve is in the shoulder, the electrically 
conductive pad may be secured to a distal portion of the arm. The 
electrically conductive pad is connected by a wire to a prior art 
stimulator box that is capable of generating electrical current, as 
explained further herein. An electrically insulated needle cannula with an 
uninsulated conductive tip is then urged through the skin and subcutaneous 
tissue in the general direction of the nerve to be anesthetized. The prior 
art needle is connected by a wire to the prior art electrical stimulator 
box. 
The prior art stimulator box is electrically powered and is operative to 
produce an adjustable current pulse for a duration of approximately 
100-200 microseconds ("uS"). The current pulse is set initially to a level 
of approximately 1.0-5.0 milliamps ("mA"). This current level typically is 
sufficient to stimulate the targeted nerve when the needle has been placed 
into the tissue in the approximate area of the targeted nerve. The 
stimulation will cause a noticeable muscle twitch on areas of the body 
controlled by the targeted nerve (e.g., the fingers). The current then is 
decreased slowly until the twitching disappears. The prior art needle then 
is advanced slowly toward the targeted nerve until the twitching 
reappears. This iterative procedure continues until the prior art needle 
is able to generate noticeable muscle twitches at a current level of 
approximately 0.2-0.3 milliamps. At this point, the prior art needle is 
considered to be sufficiently close to the targeted nerve for 
administration of the anesthetic agent. The anesthetic agent then is 
delivered directly through the needle while the needle continues to 
produce the current pulses. Cessation of the muscle twitch typically is 
considered to indicate successful location of the nerve. 
The prior art electrolocation procedure is intended to ensure accurate 
placement of a needle for delivery of anesthetic. However, the prior art 
device and the prior art procedure for electrolocation of a targeted nerve 
have several drawbacks. For example, the prior art electrolocation device, 
including the stimulator box, is a fairly large, costly and reusable piece 
of equipment that is not easily sterilized. Thus, there are problems with 
using the prior art electrolocation device in the sterile environment of 
an operating room. It is typically necessary to employ two technicians for 
carrying out this prior art procedure, namely a first technician operating 
under sterile conditions and manipulating the needle, and a second 
technician spaced from the first technician and operating under 
non-sterile conditions to incrementally decrease the current level. The 
use of two technicians necessarily requires fairly high costs and requires 
considerable coordination and communication between the two technicians. 
Second, the prior art electrolocation device does not provide a definitive 
indication of when the needle is properly positioned for injecting the 
anesthetic. The attending physician must rely upon judgment and experience 
to determine when the needle is in the optimum position. 
Third, the considerable distance between the insulated needle and the prior 
art conductive pad requires the generation of a relatively high voltage to 
achieve the desired current level. A voltage of at least 25 volts ("V") is 
common in the prior art electrolocation apparatus. These relatively high 
voltage levels limit the use of the prior art apparatus. For example, the 
high voltage levels can affect the performance of pacemakers and other 
implanted electronic devices. Hence, the prior art electrolocation device 
generally cannot be used on patients with implanted electronics. 
Additionally, the relatively high energy creates the risk of arcing. Hence 
the prior art electrolocation apparatus cannot be employed in many 
surgical environments, such as those where oxygen is being used, due to 
the risk of fire or explosion. The high current levels may also create the 
potential for tissue damage in proximity to the needle. 
SUMMARY OF THE INVENTION 
The subject invention is directed to an electrolocation apparatus for 
accurately and efficiently locating a nerve to which an anesthetic agent 
may be administered. The apparatus employs sufficiently low energy levels 
to avoid potential tissue damage and to permit use of the apparatus in 
situations where a patient has an implanted electronic device. The 
apparatus also is sufficiently small and inexpensive to be manufactured 
for single use and can be made sufficiently sterile for use in the sterile 
field of an operating room. Furthermore the apparatus can be used by only 
a single technician. 
As noted above, the voltage required for an electrolocation apparatus is a 
function of the distance between two conductors and the contact resistance 
to the patient. To substantially minimize the distance, the subject 
invention provides both conductors on the needle cannula. More 
particularly, the electrolocation apparatus of the subject invention may 
employ a needle assembly having a pair of coaxially disposed conductors. 
An inner conductor of the pair of coaxial conductors may be defined by the 
needle. A non-conductive sheath or tube may then be mounted over the inner 
conductor and may be plated, coated, coextruded or otherwise provided with 
an electrically conductive material, which functions as the outer 
conductor. A bevel or chamfer may be defined at the distal end of the 
non-conductive tube. The bevel may be defined by a non-conductive adhesive 
at the distal end of the tube. The beveled adhesive functions to hold the 
tube in place and also facilitates entry of the needle assembly into the 
patient. The spacing between the conductors of the electrolocation device 
is defined by the distance from the distal edge of the bevel to the 
conductive sheath, which preferably is slightly more than 1.0 millimeter 
("mm"). In view of this very small distance, a very low voltage can be 
used to generate the required current. It is believed by the inventors 
herein that this aspect of the invention makes the subject electrolocation 
apparatus suitable for use with patients having implanted electronic 
devices, such as pacemakers. Furthermore, the low energy level permits the 
subject electrolocation apparatus to be used in virtually all operating 
room environments, including those where prior art electrolocation 
apparatus had created the potential for combustion. Additionally the low 
voltage permits simple electronic circuitry that can be provided 
conveniently in a small package. 
As noted above, the prior art electrolocation device had required two 
technicians, namely a first technician to carefully manipulate the needle 
and a second technician to carefully vary the current level. The subject 
electrolocation apparatus employs entirely different structure that 
operates under entirely different principles, and enables use of the 
subject electrolocation apparatus by a single technician. The 
electrolocation apparatus takes advantage of the determination that the 
threshold electrical parameter for generating a muscle twitch is measured 
more accurately in terms of electrical charge rather than electrical 
current. Electrical charge is the product of current and time, and charge 
can be varied by changing either the current level or the time duration. 
In a first preferred embodiment, the subject electrolocation apparatus 
generates constant current pulses; however, the sequential pulses 
alternate between a relatively long duration and a relatively short 
duration. In this manner, sequential constant current pulses alternate 
between the relative high charge and a relatively low charge. In a second 
embodiment, the electrolocation apparatus is operative to alternately 
deliver relatively high current pulses (e.g., 0.5 mA) and relatively low 
current pulses (e.g., 0.1-0.2 mA). Each pulse may be of the same duration 
(e.g., 0.1-0.2 milliseconds ("mS") and the pulses may be generated at 
uniform intervals (e.g., 0.25-2.0 seconds). 
One approach to using the electrolocation device of the subject invention 
may include urging the needle into the patient and toward the targeted 
nerve. The relatively high charge pulses will generate muscle twitches at 
a location distant from the nerve after the skin has been penetrated 
(e.g., when the tip of the needle is about 1.0 cm from the targeted 
nerve). The relatively low charge pulses, however, will not produce a 
sufficient charge to generate muscle twitches at this initial distance. 
The pulses may be separated, for example, by approximately one-half second 
(hereafter, "1/2" or "0.5"second(s)). Thus, the physician initially will 
observe muscle twitches at intervals of approximately one second, 
coinciding with the high charge pulses. 
As the needle is moved toward the targeted nerve, the physician may observe 
a slight increase in the magnitude of the initially observed muscle 
twitches caused by the high charge pulses. Simultaneously, the physician 
will begin to observe small muscle twitches in response to the low charge 
pulse that follows each high charge pulse. Thus, using the preceding 
example, the physician will observe a large twitch in response to a high 
charge pulse followed 0.5 seconds later by a smaller twitch in response to 
a low charge pulse and then followed 0.5 seconds later by another larger 
twitch in response to a high charge pulse. 
Twitches generated in response to the high charge pulses will quickly reach 
a peak, such that further movement of the needle toward the targeted nerve 
will not significantly increase the magnitude or severity of twitches 
resulting from high charge pulses. 
Twitches generated in response to low charge pulses gradually will increase 
in magnitude and intensity as the needle continues to approach the 
targeted nerve. These changes in the magnitude and intensity of the low 
charge twitches will be readily observable by the physician inserting the 
needle. As the tip of the needle approaches the targeted nerve, the major 
and minor twitches will become substantially indistinguishable, and the 
physician will merely observe substantially identical muscle twitches at 
intervals of approximately 0.5 seconds or twice the interval initially 
observed. This will indicate to the physician that the tip of the needle 
is properly positioned for administration of the specified anesthetic. The 
anesthetic agent may then be urged through the needle and to the targeted 
nerve. The anesthetized nerve will then stop twitching, thereby giving the 
physician a clear indication that the targeted nerve has been reached and 
that the anesthetic has had its intended effect. The physician may then 
merely trigger a switch on the small control of the electrolocation 
apparatus to terminate the flow of current to the needle. 
While principally described herein with the concept of generating 
sequentially alternating charge pulses of high and low levels, it will be 
appreciated by the skilled artisan that the construction of the 
electrolocation device and components described herein can be configured 
to produce a repeating pattern of graded charge pulses depending on the 
application desired. For instance, depending upon the anatomy of the 
region surrounding the nerve being sought, it may prove beneficial to have 
a repeating pattern of gradual decrease in charge pulse as the nerve is 
approached, rather than an alternating series of absolute high and low 
level charge pulses as the nerve is approached. That is to say, the 
apparatus and associated compnents can be configured such that rather than 
delivering an alternating series of high and low level charge pulses, it 
will deliver a repeating pattern of graded charge pulses, with the grade 
in each pattern declining from a selected maximum level charge pulse to a 
selected minimum level charge pulse. In this manner, for certain 
anatomies, the practitioner is provided with a greater range of clinical 
observations respective of nerve reaction to the charge pulses, thereby 
providing more accurate knowledge to the practitioner of the location of 
the apparatus to the nerve. Other patterns are also possible.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
An electrolocation apparatus in accordance with the subject invention is 
identified generally by the numeral 10 in FIG. 1. The apparatus 10 
includes a needle assembly 12, a stimulator 14 and a tube 16 for 
delivering a dose of anesthetic through needle assembly 12. 
Needle assembly 12, as shown more clearly in FIG. 2, includes an elongate 
needle cannula 20 having opposed proximal and distal ends 22 and 24 and a 
lumen 26 extending continuously therebetween. Needle cannula 20 is formed 
from an electrically conductive material and preferably stainless steel. 
Proximal proportions of needle cannula 20 are securely mounted in 
stimulator 14 with proximal and distal ends of needle cannula 20 being on 
opposite sides of stimulator 14. Distal end 24 of needle cannula 20 is 
beveled to a point that facilitates piercing of tissue for accessing the 
targeted nerve. 
Needle assembly 12 further includes a thin walled tube 28 coaxially 
disposed over needle cannula 20. Tube 28 has opposed proximal and distal 
ends 30 and 32 respectively, and is formed from a non-conductive material, 
such as polyimide. Proximal end 30 of tube 28 is disposed in stimulator 14 
as explained further herein. Distal end 32 of tube 28 is spaced proximally 
from bevelled distal end 24 of needle cannula 20. Tube 28 is dimensioned 
to be closely engaged against the outer cylindrical surface of needle 
cannula 20. However, secure retention of tube 28 on needle cannula 20 is 
achieved by a non-conductive epoxy 34 or other such adhesive extending 
between distal end 32 of plastic tube 28 and the outer cylindrical surface 
of needle cannula 20. Epoxy 34 is chamfered to facilitate entry of needle 
assembly 12 into a patient. The chamfer preferably defines a length of 
about 1.0 mm. 
Tube 28 includes a conductive layer 36 on its outer cylindrical surface 
which may be applied by plating or coating. Layer 36 preferably is gold 
and extends continuously from proximal end 30 to distal end 32 of tube 28 
at a thickness of approximately 550 Angstroms. Needle assembly 12 
effectively functions as a pair of coaxial conductors as explained further 
herein. In particular, stainless steel needle cannula 20 functions as an 
inner conductor, while gold layer 36 on tube 28 functions as an outer 
conductor. Tube 28 defines a non-conductive insulating material separating 
the inner and outer conductors defined respectively by stainless steel 
needle cannula 20 and gold layer 36. 
As noted above, stainless steel needle cannula 12 extends continuously 
through stimulator 14, such that proximal end 22 of needle cannula 20 is 
disposed on one side of stimulator 14, while distal end 24 is disposed on 
the opposed side thereof. Proximal end 30 of plastic tube 28 is disposed 
within stimulator 14. As a result, both stainless steel needle cannula 12 
and gold layer 36 are exposed for electrical contact within stimulator 14. 
Stimulator 14 includes a generally rectangular housing 38 which can have 
length and width dimensions, for example, of approximately 0.781 inch and 
a thickness dimension, for example, of approximately 0.375 inch. Housing 
38 can be formed from two molded thermoplastic housing halves 40 and 42 
that are welded or adhered to one another. Top and bottom walls 
respectively may include concave regions to facilitate gripping by the 
digits of the hand. 
Housing 38 performs multiple functions, including providing structural 
support for needle assembly 12, providing a convenient grip for 
manipulation of needle assembly 12 and safely enclosing the electronic 
components of the electrolocation apparatus 10. 
The electronic circuitry of stimulator 14 includes an on/off switch 48 and 
a light emitting diode (LED) 50 both of which are accessible and/or 
visible from the exterior of housing 38. On/off switch 48 functions to 
complete circuitry between a battery and other portions of the circuitry 
as described further below, and optionally may permit switching between 
high and low charge levels. LED 50 is operative to generate a pulse of 
light with each pulse of electrical energy so that the technician or 
attending physician can compare energy pulses with muscle twitches in the 
patient. 
FIG. 3 is representative of circuitry which can be used in stimulator 14. 
As the skilled artisan will appreciate, one way of implementing such 
circuitry is to digitize it, utilizing CMOS technology as active elements. 
Other implementations, such as custom integrated circuits ("ICs") are also 
possible. Here, on/off switch 48 is connected to a three-volt lithium cell 
battery 52. In the off state, the quiescent current is under 1 microamps 
("uA"), providing a battery life in excess of eight years, and thereby 
ensuring adequate shelf life for the electrolocation apparatus 10. In the 
on state, the oscillator and counter described below are enabled, and the 
battery will operate stimulator 14 for approximately 100 hours. 
The time duration pulse modulation is achieved by a counter 54. Using the 
outputs of the counter 54, it is possible to generate a pulse as short as 
122 uS. Since the outputs of the counter 54 are periodic signals, the 
Timing Selection Gating network 56 selects only one period of the output 
signal and applies it to the current source network 58. In the embodiment 
shown in FIG. 3, the gating network 56 may alternatively enable either one 
of a low charge pulse or one of a high charge pulse. As shown 
schematically in FIG. 5, stimulator 14 is operative to alternately 
generate short and long duration pulses. All of the pulses will be of a 
constant current, but will be of different durations. For example, 
stimulator 14 may be operative to generate a pulse at a current level of 
0.2 mA for 122 uS to produce a relatively low charge of 24.4 nanocoulombs 
("nC"), followed by a current pulse of 0.2 mA for approximately 488 uS to 
produce a relatively high charge of 97 nC. It will be realized by the 
skilled artisan that depending on the components selected to generate the 
pulses, the duration of the pulses may vary within a range of time, for 
example, of about +/-20% of the durations stated herein. Other paired 
pulses of constant current for different durations may be used to produce 
alternating low and high charges. 
The circuit of FIG. 3 also is designed to optionally provide constant 
duration pulses with current amplitude modulation. For example a low 
current pulse of 0.2 mA may be generated for 122 uS to produce a 
relatively low charge of 24.4 nC and may be followed by a high current 
pulse of 0.8 mA for 122 uS to produce a relatively high charge of 97 nC. 
It will be noted that the charges produced by the current level modulation 
option equal the charges produced by the time duration modulation option. 
FIG. 3 is a block diagram of a set of circuit components, in stimulator 14, 
which function to produce appropriate charge pulses across bipolar needle 
12, and FIG. 4 illustrates an example of a combination of operative 
circuit components within the blocks of FIG. 3. As seen in FIG. 3, an 
on/off control 51, actuated by switch 48, has an output that keys an 
oscillator 53 to activate a counter 54, and another output that enables 
and disables the counter 54. A third output is fed to a control circuit 55 
which receives an output from the counter 54 and activates a constant 
current sink 58 coupled to one electrode (20 or 36) of the bipolar needle 
12. Indicator circuitry 57, which drives LED 50, receives inputs from the 
oscillator 53, the counter 54, and the current source V+, which through a 
charge limiter 59 is coupled to the other electrode (36 or 20) of the 
bipolar needle 12. The timing and magnitude of the charge pulses are 
modulated by a Timing Selection Gating component 56 that is coupled to the 
control circuit 55. 
Turning to the circuit details in FIG. 4, the on/off Control 51 may consist 
of the on/off switch 48 which couples the voltage V+ of battery 52 to 
circuitry including a flip-flop A1B and an RC (R1,C3) combination. When 
the apparatus 10 is to be used, the switch 48 is put in the on position 
and stays on to avoid any current surges at the needle. The flip-flop A1B 
controls the timing of the oscillator 53, which may comprise a Schmitt 
trigger A3A, and enables and disables the counter 54, which may be in the 
form of a 12-bit counter A2, and the sink control circuit 55, which may 
comprise a flip-flop A1A. When A1B is ON, output line 12 is low or 0, so 
the reset of counter A2 is off and thus it is free to count, and the reset 
of A1A is off so it is free to change state. Concomitantly, output line 13 
of A1B is high or positive, so that the oscillator A3A operates, e.g., at 
4.096 kilohertz ("kHz"), to cause counter A2 to count, whereupon pin 1 of 
A2 is caused to change state every 1/2 second and pin 15 goes positive 
every 1/2 second. Thus, pin 15 changes state at twice the rate of pin 1. 
When A1B is off, line 13 goes low, stopping the output of A3A, and line 12 
goes high, resetting A2 and A1A. 
When pin 15 of A2 goes positive, the clock signal to A1A causes output line 
1 to go high, by voltage V+, supplying base current to transistor Q3, 
through resistors R4 and R5. Q3 is thereby caused to conduct closing a 
current path for current to flow through the needle 12 from the battery 
V+, across capacitor C4, and through resistor R7 to ground. If the voltage 
at R7 goes above 0.55V, the base of transistor Q2 will be driven through 
resistor R6 to turn Q2 on, which in turn drops the base current to Q3, 
thus maintaining the voltage across R7 at 0.55V. Accordingly, the current 
through the needle 12 is maintained substantially constant. In the event 
of a short or failure in the needle's current path, the capacitor C4 acts 
as a charge limiter by charging to a preselected maximum charge and 
limiting the current level. 
The timing and form of the current pulses is determined through the use of 
the Timing Selection Gating component 56 which comprises three gates A3B, 
A3C, and A3D that receive inputs from the oscillator A3A and the counter 
A2 and provide an output to flip-flop AlA of the sink control circuit 55. 
Gate A3B controls the short pulses shown in the timing diagram of FIG. 5. 
It will be seen that input pin 10 to counter A2 works on negative pulses 
so that when the output of A3A, on pin 3, goes negative, output pin 15 of 
A2 goes positive driving A1A to turn on the current through the needle 
path as just explained above. The output on pin 3 of A3A is also supplied 
to input pin 6 of gate A3B, the other input pin 5 of which receives the 
output from pin 1 of A2. If the signal on pin 1 and in turn on pin 5 is 
high, A3B can function when pin 6 goes high. If pin 1 is low or at 0, then 
pin 5 is low and A3B cannot function. The operation of A3B can be used to 
control the alternating of the short and long charge pulses. When pin 1 is 
high, the short pulses will be produced. 
More particularly, when pin 3 of A3A goes low, counter 54 will go to its 
next state. Pin 15 goes high so that current begins to flow through the 
needle and pin 1 is high so pin 5 of A3B is high, while pin 6 is low or 0 
along with pin 3. The output of A3B on pin 4 will be 1, which is input on 
pin 13 to gate A3D. With a high input on pin 12, the output of gate A3D, 
on pin 11 will be 0. Now, when oscillator A3A outputs a high on pin 3, the 
counter A2 does not change its state, but pins 5 and 6 of A3B will both be 
high, so that the output on pin 4 will go to 0 causing the input to pin 13 
to be 0. If the input on pin 12 is still high, the output of A3D on pin 11 
goes high. The high signal on pin 11 is coupled through capacitor C2 to 
the reset of flip-flop A1A causing its output on pin 1 to got to 0, 
turning off the constant current sink 58 and the current through the 
needle 12. A short current pulse will then have been produced of 122 uS 
duration. 
To produce the longer pulses, gate A3C is used and gate A3B is disabled. 
Since A3B can only function when pin 1 of A2 is high, the signal on pin 1 
is caused to go low turning A3B off. In this condition the reset function 
of AlA is controlled only by A3C. The output of A3C may be controlled 
according to the pulse ratio table shown adjacent to A3C in FIG. 4. By 
appropriately connecting the A (8) and B (9) inputs of A3C to the listed 
combination of pins of counter A2, the time ratios between the short and 
long pulses shown in the left hand column of the table can be achieved, 
thus accomplishing pulse width modulation of the charge pulses. 
For accomplishing pulse amplitude modulation, the A and B inputs to A3C can 
both be connected to pin 10 of A2 to produce a pulse time ratio of 1 to 1, 
the pulses being of 122 uS. A resistor R10 in the constant current sink 58 
is connected into the circuit between pin 1 of A2 and the emitter of 
transistor Q3 by closing a switch SW1. When pin 1 is high, current flows 
through R1O and resistor R7 to ground. The current in the current path 
through the needle 12 is thus decreased since the voltage across R7 
remains constant and the current through R7 is made up of two sources. 
Consequently, the magnitude of the current pulse across needle 12 becomes 
a comparatively low current pulse. When pin 1 of A2 is low, i.e., goes to 
ground, R1O is configured in parallel with R7 with respect to ground, so 
that the resistance across R7 and R1O drops with respect to the current 
path. Since the voltage of 0.55V is maintained at their junction point, as 
explained above, more current is needed across both resistors. Thus, the 
magnitude of the current pulse across the needle 12 is increased resulting 
in a comparatively high current pulse. Accordingly, pulse amplitude 
modulation can be accomplished with this circuitry. 
If desired, both pulse width and pulse amplitude modulation can be produced 
by selection of the pulse ratios in the pulse ratio table and the 
switching of resistor R1O into the circuit. 
Lastly, the indicator circuitry 57 is configured to activate whenever a 
pulse has been produced, irrespective of the modulation, and to produce a 
simple on or off indication. Thus, the LED 50 will flash ON upon the 
occurrence of a charge pulse or the buzzer 60 will produce a sound in 
accordance with the timing and state change of the outputs on pin 3 of A3A 
and pin 15 of A2. 
As noted above, proximal end 22 of stainless steel needle cannula 20 
projects entirely through housing 38 of stimulator 14. As shown in FIG. 1, 
proximal end 22 of stainless steel needle cannula 20 is connected to 
flexible tubing 16 which extends to a hub that is connectable to a syringe 
for delivering a selected dose of anesthetic. In an alternate embodiment, 
proximal end 22 of stainless steel needle cannula 20 may be mounted 
directly to a needle hub that is connectable to a syringe for 
administering a selected dose of anesthetic. 
In use, an anesthesiologist or nurse anesthetist inserts the bevelled 
distal tip 24 of stainless steel needle cannula 20 into a patient and 
toward the targeted nerve. No conductive pad and no wires are used. In the 
constant current embodiment described herein, the switch 48 on the 
stimulator 14 is then actuated to generate the low constant current pulses 
of electrical energy. Proper functioning of the electrolocation apparatus 
10 is confirmed by the flashing LED 50 generating a pulse of light 
concurrent with each respective pulse of energy. The respective pulses of 
energy are generated at 1/2 second intervals. The high charge pulses of 
0.2 mA for 488 uS will generate a charge of 97 nC. The low charge pulses 
are of the same 0.2 mA current, but last for only 122 uS and will generate 
a charge of only 24.4 nC. The higher charge pulses of 97 nC will be 
sufficient to generate observable muscle twitches at a substantially 
superficial location after the skin has been penetrated by the gold layer 
34, while the lower charges, pulses of 24.4 nC will not be sufficient to 
initially generate any observable muscle twitches at this distance from 
the nerve. Thus, the anesthesiologist or nurse anesthetist will observe 
muscle twitches at approximately one second intervals coinciding with the 
high charge pulses. 
The needle assembly 12 is urged further toward the targeted nerve. This 
advancement of the needle assembly 12 will show a gradual increase in the 
magnitude of the twitches occurring at one second intervals. However, 
these twitches in response to the high charge will soon peak. The 
anesthesiologist or nurse anesthetist then will observe small magnitude 
muscle twitches between the larger magnitude twitches. Thus, alternating 
small and large magnitude twitches will be readily observable. 
As the needle assembly 12 is further advanced into the patient, the small 
magnitude muscle twitches will increase in magnitude to approach the 
magnitude of the peaked large magnitude muscle twitches generated by the 
high charge pulses. As the distal tip 24 of the stainless steel needle 
cannula 20 nears the targeted nerve, the muscle twitches generated in 
response to the low charge pulses will be substantially indistinguishable 
from the muscle twitches generated in response to the high charge energy 
pulses. Thus, the anesthesiologist or nurse anesthetist will observe 
substantially identical muscle twitches at 0.5 second intervals. This 
readily observable response will indicate to the anesthesiologist or nurse 
anesthetist that the bevelled distal tip of needle cannula 20 is 
sufficiently close to the targeted nerve for administration of the 
anesthetic. The anesthetic is delivered in the conventional manner by 
actuation of the hypodermic syringe communicating with the proximal end 22 
of stainless steel needle cannula 20. 
The exact procedure can be carried out by the alternate embodiment which 
modulates current level. 
While the invention has been described with respect to a preferred 
embodiment, it is apparent that various changes can be made without 
departing from the scope of the invention as defined by the appended 
claims. For example, the stimulator may have switch mechanisms for 
changing the current level or the pulse width to vary the respective 
levels of the charges delivered to the patient. Additionally, other 
indications of pulse generation may be provided, including an audible 
buzzer in place of or in addition to the LED described above.