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BACKGROUND OF THE INVENTION
1. Field Of The Invention
The invention relates generally to devices and methods employed to prevent
the accidental implantation of surgical implements used in the course of a
surgical procedure. More specifically, the invention employs an active
surgical implement tagging and detection system, adapted to sense the
presence of retained implements before post-operative suturing takes
place.
2. Description Of The Prior Art
Known prior art devices and methods used to detect retained surgical
implements can generally be classified as "passive" in nature. For
example, X-ray examination has long been advocated as a useful means to
detect the presence and location of radio opaque implements and radio
opaque tags or thread attached to surgical sponges and gauze, or the like.
Representative art disclosing such an approach is U.S. Pat. No. 2,698,270
issued to Mesek and U.S. Pat. No. 3,698,393 granted to Stone. X-ray
examination of patients does provide fairly reliable screening for
retaining articles. However, each screening requires the cumbersome task
of moving the X-ray machine into place over a properly positioned patient,
whose wound has already been sutured to avoid sterility problems. In the
event that a retained implement is discovered, it is necessary to reopen
the wound, remove the implement, and then resuture the wound before the
patient can be released from anesthesia. In view of the foregoing, X-ray
examination for retained surgical implements has not proved practical as a
regular procedure.
Other passive systems proposed preferably use a hand manipulable detector
to sense the presence of metal, magnetized particles, or radioactive
material attached to or associated with the surgical implements. Prior art
from among this group includes U.S. Pat. Nos. 3,097,649; 3,422,816; and
3,587,583. While this approach allows examination of the patient in the
operating room, health hazards are posed by the radioactive material, and
the extraneous metal and magnetic responses present in the operating room
make the other systems less than completely reliable.
More recently, in U.S. Pat. Nos. 4,114,601 and 4,193,405, Abels teaches the
tagging of surgical implements with a small film deposition of ferrite or
other semiconductor material exhibiting gyromagnetic resonance at selected
frequencies. When exposed to electromagnetic radiation at two selected
frequencies, a higher order product frequency is radiated and detected by
an RF receiver. While the Abels device is claimed to work at any
frequency, the proposed range of frequencies discussed in the patents is
4.5-5 Gigahertz. It is well recognized that human tissue is significantly
absorptive of radio frequency energy at this microwave frequency, and even
the 0.5 watt transmitter power range proposed in Abels could present a
health hazard either to the patient or to the administrator of the test.
Consequently, while the "passive" approach is initially appealing in terms
of the simplicity and the diminutive size of the surgical implement tag or
identifier, other problems are posed by the cost, safety and reliability
of the transmission and detection systems used to sense the presence of
passive tags.
SUMMARY OF THE INVENTION
The invention herein is generally active in nature, employing the use of a
miniature, battery powered oscillator attached to each implement and
actuated prior to initial use during the course of the surgical procedure.
The output of the low powered oscillator is coupled to the body fluids and
tissue of the patient by unobtrusive conductors located on the
oscillator's housing or physically integrated with the implement's
structure.
The frequency of the oscillator is selected safely to exceed the normal
physiological signals of the body, so as not to interfere with the usual
electro-cardiograpic monitoring of the patient's condition during surgery.
In the lower range of useful oscillator frequencies, say 4 KHZ, the
patient's body fluids and tissue conduct the oscillator pulses with
reasonable efficiency. Consequently, post-operative detection of the
oscillator's pulses may be effected by momentarily switching the ouput of
the patient's ECG electrodes from the ECG monitor to the pulse detection
system.
The detector employs amplification, filtering, and in some cases, logic
circuitry to produce an output signal in the event that a surgical
implement is retained within the patient's body. The detector's output is
then fed to an alert system, providing visual and aural indications to the
test administrator that corrective action is needed. The use of such low
frequencies is advantageous in that it effectively integrates the
implement tagging and detection system with existing ECG hardware and
associated personnel.
In the event that a tagging oscillator operating at a higher frequency is
employed, say within the range of 1-30 MHZ, the output signal is similarly
coupled to the body fluids and tissue, but the resultant signal is
detected in a somewhat different fashion than just described.
It has been determined that body-coupled radio frequency energy, at least
within in the 1-30 MHZ range, is directly radiated by the patient's body
to a significant extent. Thus, an inductive loop or other wire antenna
passed over the patient's body has proven effective in intercepting the
oscillator's radiated pulses and locating the surgical implement. The low
level output of the inductive loop is fed through amplifier, filtering,
and logic circuitry similar to that employed in the low frequency
detector, and any detected pulses actuated an interconnected alarm or
alert system.
Specific aspects of the invention's construction and operational features,
including variations thereof, will be described more fully in the drawings
and detailed description of the preferred embodiment to follow.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a schematic diagram of a typical low frequency tagging
oscillator, operating at approximately 4 KHZ;
FIG. 2 is a perspective view of a surgical sponge, a corner portion thereof
being broken away to reveal the tagging oscillator and associated output
electrodes;
FIG. 3 is a longitudinal, cross-sectional view of the tagging oscillator
taken to an enlarged scale, showing the inner details and the pull ring
switch prior to actuation;
FIG. 4 is a schematic diagram of a saline fluid actuated switch and
associated battery power supply;
FIG. 5 is a perspective view of an alternative housing, or package, for the
tagging oscillator, showing the pin acutation switch in a withdrawn
position;
FIG. 6 is a block diagram of a low frequency detection and alert system,
shown in combination with a mode switcher, test oscillator, and a
conventional ECG electrode and monitoring system;
FIG. 7 is a schematic diagram of a typical high frequency tagging
oscillator, operating at approximately 1 MHZ; and,
FIG. 8 is a block diagram of a high frequency detection and alert system.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT
Turning now to FIG. 1, a low frequency tagging oscillator 11 is shown. The
oscillator 11 is of conventional design, employing the widely used 555
timer chip, IC 1. R1, R2, and C1, are valued respectively at 11 K ohm, 11
K ohm, and 0.005 uF, providing a characteristic oscillator output
frequency of approximately 4 KHZ. The oscillator's frequency is not
critical per se, but extremely low frequencies, especially those below 100
HZ, should be avoided. Since the body's normal physiological signals are
within this extremely low frequency range and are being monitored by ECG
equipment during surgery, interference with ECG monitoring can only be
avoided by selecting an oscillator frequency safely above 100 HZ.
It is proves desirable to raise the oscillator's frequency into the
Megahertz range, an alternate oscillator and detection system may be
employed, and such a high frequency system will be described in detail
following the present discussion of the low frequency system.
Typically, the battery B1, and the entire circuitry of the oscillator 11,
with the possible exception of the switch S1, are enclosed within a
plastic or elastomeric housing or container 14 (see FIGS. 2 and 3). By
sealing the oscillator circuity within such a container, reliable
operation of the circuit will be ensured despite immersion in body fluids,
handling during surgical procedures, and subjection to electrocautery
activity in the immediate area. So enclosed, the external dimensions of
the oscillator package would typically assume the compact figures of 0.5
cm.times.1 cm.times.2 cm.
The output electrodes 12 and 13 are constructed from an electrically
conductive material, and extend exteriorly from the housing 14. Depending
upon the particular housing design or implement to be tagged, the output
electrodes 12 and 13 can assume a variety of configurations. The tagged
item in FIG. 2 is a surgical sponge 16, or gauze, including a loop 17 to
facilitate removal of the sponge from the patient's body. Utilizing the
loop 17 to good advantage, the output electrode 13 is readily wound around
or intertwined with a portion of the loop, providing ready exposure to the
patient's body fluids and tissue. The other electrode 12 extends within
the body of the sponge 16, again providing good coupling to the patient's
body, particularly when the sponge is fluid saturated. The generally
saline character of internal body fluid enhances the coupling of the
oscillator signal to the patient's body. However, since the power levels
are extremely low and the frequency is far removed from the potentially
dangerous microwave region, no safety hazard is posed either to the
patient or to the surgical team.
Actuating switch S1 is connected in series with battery B1, providing low
voltage power to the oscillator 11 prior to the initial use of the sponge
16. The actuating switch S1 can variously be adapted to suit the nature
and size of the surgical implement in connection with which it is used.
Considering the first, the actuating switch S1 disclosed in FIG. 3, a pair
of inwardly spring biased terminals 18 and 19 is shown separated by a
non-conductive tab 21. A small pull ring 22 is attached to the tab 21 by
means of a short piece of cord 23, or string. The ring 22 extends
exteriorly from the sponge 16, for ready access. The tab 21 is removed by
grasping and pulling on the ring 22, allowing terminals 18 and 19 to
interconnect, thereby applying actuating power to the oscillator 11.
An alternative fluid actuated switch S2, shown in FIG. 4, includes a pair
of conductor plates 24 bridged by a porous wick 26. The spacing of the
plates 24 is such that when the porous wick is immersed within a saline
solution, such as body fluids, a path of sufficiently low resistance is
formed, and the oscillator 11 will begin operating. While any implement
remaining within the body cavity for a prolonged period will be totally
wetted by body fluids, the placement and retention period of a particular
implement prior to wound closure may be such that the wick 26 does not
become adequately saturated. In this event, the oscillator 11 may not be
active during the implement detection period. Accordingly, to ensure
positive actuation in every instance, it may be desirable to dip the wick
26 within a separate saline solution prior to initial use of the tagged
implement.
Once actuated, the tagging oscillator 11 draws continuously upon the
battery B1, for its sole source of power. The drawing current of the
oscillator 11 and the power capacity of the battery B1, are such that
reliable operation of the oscillator should be provided for approximately
ten hours, or so. While ten hours of oscillator operation should be
sufficient for almost all surgical procedures, alternative circuitry for
the oscillator could extend this period substantially. Rather than running
the oscillator continuously, a series of say three to five pulses followed
by a quiescent period of five seconds, or so, would lower the duty cycle
of the oscillator and prolong battery life even further.
Pulsed or gated operation of the tagging oscillator can be accomplished in
a variety of ways. A control, low power oscillator, running at a low
frequency, could be used to switch power on and off to the secondary, or
high power oscillator circuitry. Alternatively, an RC circuit could be
employed in combination with a voltage limiting diode for establishing a
charge/discharge cycle which would pulse the operation of the tagging
oscillator. Thus, while the basic, continuously running oscillator 11 is
shown for illustrative purposes, many variations both in the duration and
pattern of oscillator pulses produced by alternative circuitry are
contemplated, and such circuitry is sufficiently well understood in the
art so as not to require further detailed explanation herein.
Aside from reducing the size and enhancing the life of the battery powering
the tagging oscillator, pulsed oscillator operation provides a further
identifier for the apparatus used to sense the pulses and distinguish them
from extraneous noise. This feature will be discussed more fully in the
explanation of the detector apparatus, to follow herein.
Returning briefly to FIG. 3, the oscillator 11 and the battery B1, are
shown contained within the elongated housing 14. The output electrodes 12
and 13 are flexible wire conductors, extending exteriorly from either end
of the housing 14 physically to integrate with elements of the sponge 16,
as explained previously. While this type of packaging is well suited for a
sponge, other surgical implements may require alternative packaging for
the tagging oscillator and associated components.
FIG. 5 illustrates oscillator, battery, and switch packaged within a
cylindrical capsule 27, constructed from a plastic or elastomeric material
as described before. A wire electrode 28 extends from one end of the
capsule 27, to connect or merge with a physical feature of the tagged
implement. A band electrode 29 extends circumferentially around the
capsule 27, providing the second electrode for coupling the pulsed output
of the internal oscillator and battery (not shown) to the body's fluids
and tissue.
An aperture 31 is provided at the other end of the capsule 27, to
accommodate a non-conductive actuating pin 32. Prior to actuation of the
tagging oscillator, the pin 32 extends interiorly into the capsule 27,
maintaining a pair of spring-biased switch contacts (not shown) in spaced
relation. When it becomes necessary to activate the tagging oscillator, a
knob 33 on the outer end of the pin is grasped, and the pin is withdrawn
from the capsule 27, as shown in FIG. 5. The internal switch contacts are
thereby allowed to spring together, actuating the oscillator.
It is apparent that a second band electrode could be used in lieu of the
wire electrode 28. The second band electrode would extend
circumferentially around the capsule 27 and be spaced from the first band
electrode 29. Such a packaging and electrode combination may be desirable
for tagging an unusually small surgical implement.
Prior to the commencement of surgery, and in any event prior to the use of
a particular surgical implement in the course of surgery, the tagging
oscillator of each implement is actuated. After the surgery has been
completed, but before the post-operative suturing takes place, the patient
is checked for any surgical implements that may have accidentally been
overlooked and retained within the surgical cavity. Accordingly, a
detection system, located outside the body of the patient, is used to
sense and check for oscillator pulses from any such retained implements.
Making reference now to FIG. 6, a pair of electrocardiographic (ECG)
electrodes 34 is generally used in connection with an ECG monitor 36,
during the course of any significant surgical procedure, to observe the
physiological signals of the patient's cardiovascular system. Normal
physiological signals are below 100 HZ, and the monitor 36 is designed to
display such signals on a cathode ray tube 37. The invention herein
contemplates the use of a mode switcher 38 to allow use of the existing
ECG electrodes 34 as sensors for the oscillator detector, generally
designated by reference numeral 39.
More specifically, the mode switcher 38 would include a normal position for
surgical ECG monitoring and a detect position for directing the output of
the ECG electrodes to the input of the detector 39. It may also be
desirable for the mode switcher 38 to have a third test positon, for
directing the output of a 4 KHZ test oscillator 41 to the input of the
detector 39, to confirm proper operation of the detector 39 before the
post-operative, implement detection procedure begins. Operation of the ECG
system would be unaffected during the detector testing procedure.
Assuming that normal operation of the detector 39 is confirmed, the mode
switcher 38 is switched to the detect position, and the pulses of any
retained tagging oscillators will be routed to the amplifier 42. The
output of the amplifier 42 is conditioned by a bandpass filter 43, having
in this case a center bandpass design frequency of 4 KHZ. The use of a
bandpass filter designed for the frequency of the tagging oscillator
ensures that all extraneous noise, including the body's physiological
signals, will be severely attenuated.
Detection of a signal present at the output of the filter 43 can be
accomplished any number of ways. If the oscillator frequency is within the
audio frequency range, such as here, the signal could be raised by
amplifier 46 to levels necessary to drive a loudspeaker 47. This would
provide a direct aural indication that an implement had been retained, and
that corrective action should be taken to locate the implement.
While such direct detection can easily be accomplished, it may be desirable
to subject the signal to further testing and processing before exploration
for the implement begins. Accordingly, an amplifier/comparator 44 is
provided to reject signals passing through the filter 43 that do not
exceed a predetermined level. If the signal did exceed the predetermined
level, it would then pass to the alarm 48.
In its most basic form, the alarm 48 would provide direct aural and/or
visual indications to the test administrator that an implement search
should be initiated. A latching circuit could also be provided to lock on
the indicators until such time as the latch was reset.
If the tagging oscillator were designed to provide pulsed output, as
previously discussed, the alarm 48 could include counter circuitry to
collect information about the incoming signal during a predetermined test
period. At the end of the period, the counter would be read and compared
to established data for tagging oscillators. If the collected information
and established data correlated, the indicators would be activated.
It would also be possible to eliminate the mode switcher 38, and provide an
independent set of electrodes, attached to the patient's body. However, it
is believed that the dual utilization of the ECG hardware is the preferred
manner of practicing the low frequency version of the invention.
In the event that a higher oscillator frequency is chosen, the tagging and
detection system operates in basically the same fashion, but several
differences in the hardware and detection procedure are noted herein.
Making specific reference to FIG. 7, a high frequency tagging oscillator
49 is shown, utilizing a CMOS "ring oscillator", IC2. Battery B2 and
switch S3 are similar to the battery and switch constructions already
discussed. Capacitor C2, having a value of 0.01 uf, was selected to
provide a characteristic oscillator output frequency of 1 MHZ. The output
of the oscillator is fed to an "antenna", L1. Various configurations of L1
would be useable, ranging from a length of wire wound in serpentine
fashion through or about the implement, to a small coil of wire wound upon
a form. In any event, L1 is effective to couple the output of oscillator
49 into the patient's body tissue and fluids. Again, owing to the very low
output and relatively low RF frequency of the oscillator 49, no health
hazard is posed.
It has been determined that as the frequency of the tagging oscillator is
raised into the RF range (here, 1 MHZ), the output of the oscillator
coupled to the body is radiated by the body, and can therefore be
effectively detected without the need of any direct physical
interconnection.
Accordingly, the high frequency receiver 51, or detector, shown in FIG. 8
employs a loop of wire receiving antenna 52 to sense pulses radiated from
the patient's body. The receiving antenna 52 could vary from a simple
one-turn U-shaped loop or whip, to a multi-turn loop antenna having
directional characteristics. The output of the receiving antenna 52 is fed
to an amplifier 53, a bandpass filter 54, a diode detector and smoothing
network 56, and an alarm 57. It is evident that the comparator, latching,
and counter circuitry previously discussed in connection with the low
frequency detector could be adapted to the receiver 51 to perform
analogous functions. It is contemplated that the entire receiver 51,
including the alarm 57, could be packaged into a hand-held unit, capable
of being passed over the patient's body for ready detection of any tagged
surgical implements.
It will be appreciated that we have provided an active surgical implement
tagging and detection system which is adaptable to a wide variety of
operating room requirements and which provides the necessary levels of
reliability and safety.
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