Surgical tool with integrated pressure and flow sensors

Details Surgical tool with integrated pressure and flow sensors Surgical tool with integrated pressure and flow sensors

2001-06-08

2004-05-25

Nguyen, Bao-Thuy L. (Department: 1641)

Surgery

Means for introducing or removing material from body for...

Treating material introduced into or removed from body...

C604S067000

Reexamination Certificate

active

06740058

ABSTRACT:

FIELD OF THE INVENTION
This invention pertains generally to the field of surgical instruments and similar devices, to micromechanical systems, and to ultrasonically actuated instruments.
BACKGROUND OF THE INVENTION
Various medical procedures require the injection of material into and/or the removal of material from a patient. For example, medication or other life sustaining fluids may be required to be injected either intravenously or subcutaneously into a patient. Blood and/or other fluids may be required to be removed from a patient for, e.g., testing, and/or to relieve fluid pressure within the patient's body. Sample cells may be required to be removed from, e.g., a tumor, for testing, preferably without requiring highly invasive surgery. Such medical procedures are typically and preferably performed using a surgical device including a hollow needle, or some similar device, with a rigid needle-like structure for passing into tissue and with a fluid flow channel formed therein. For example, a simple hypodermic needle may be used to inject medication into a patient. A hollow needle positioned in a patient may be connected to a fluid supply, such as a bag of saline solution which may, or may not, include additional medications, and an infusion pump employed to pump fluid from the supply through the needle into the patient. More complicated needle-like surgical instruments may be employed to perform more complicated surgical procedures, such as, for example, removing portions of a tumor or other tissue from a patient's body.
An example of a surgical procedure employing a relatively more complicated needle-like surgical tool is phacoemulsification. Phacoemulsification is the predominant method of removing cataracts (a loss of transparency of the lens of the eye) used throughout the world. Phacoemulsification is a method of emulsifying and aspirating a cataract with a low-frequency ultrasonic needle. An exemplary conventional system
10
for performing phacoemulsification is illustrated in FIG.
1
. In such a system
10
, a needle-like ultrasonically driven cutting tool
12
, with a pointed distal end
14
, is provided for cutting and removing a cataract lens. The pointed distal end
14
of the tool
12
penetrates into the eye chamber
16
so as to be positioned in contact with the cataract lens
18
to be cut and removed. The ultrasonic cutting tool
12
is driven longitudinally (e.g., at 40-65 kHz) to fragment the cataracts (deteriorated, cloudy eye lenses) with the hollow vibrating distal tip
14
of the cutter
12
. A double lumen channel may be formed running axially from an aperture at the distal tip
14
of the cutter
12
to a proximal end
20
thereof. For example, the double lumen channel may be formed as an outer lumen channel
22
with an inner lumen channel
24
formed running through the length of the outer lumen channel
22
. During the process of fragmenting the cataract lens
18
, irrigation and aspiration are preferably provided simultaneously through the lumens
22
and
24
. For example, irrigation may be provided as a saline solution, provided from a bottle or bag of saline
26
, through an, e.g., flexible silicone tube
28
, and the outer lumen
22
of the cutting tool
12
to the eye chamber
16
. Irrigation maintains the interior chamber pressure as material and fluid are removed from the eye chamber
16
. Aspiration may be provided, for example, by a peristaltic pump
30
coupled, e.g., by flexible silicone tubing
32
, to the inner lumen
24
at the proximal end
20
of the ultrasonic cutter
12
. Operation of the pump
30
is controlled by a control circuit
34
. Aspiration serves two purposes. It removes the fragments broken from the cataract lens
18
by longitudinal vibration of the ultrasonic cutter tip
14
, and it holds lens particles against the ultrasonic tip
14
to allow efficient fragmentation by pre-stressing the tissue.
Constant pressure monitoring and fluidics control are especially important during aspiration in the phacoemulsification process. If the aperture at the tip
14
of the ultrasonic cutter
12
becomes occluded with tissue fragments, vacuum levels could rise to excessive levels. A sudden release of the occlusion may result in a pressure pulse, which can collapse the anterior chamber
16
of the eye. Thus, it is important to provide feedback to the control circuit
34
of pressure changes in the lumen
24
through which aspiration is performed. In a conventional phacoemulsification system
10
, pressure feedback is provided by a pressure sensor
36
located in a control unit, near the control circuit
34
and peristaltic pump
30
, but removed from the ultrasonic cutter
12
. The pressure sensor
36
is coupled to the ultrasonic cutter
12
via the compliant silicone tubing
32
which couples the pump
30
to the tool. The length of the tubing separating the pressure sensor
36
from the ultrasonic cutter
12
creates a time delay between pressure changes occurring at the tip
14
of the ultrasonic cutter
12
and the detection of such pressure changes by the pressure sensor
36
. This time delay, especially resulting from occlusion of the aperture in the cutting tool tip
14
, between eye pressure transients and the measured pressure, can cause improper feedback control of the pump, with clinically deleterious effects. In addition to the time delay, the silicone tubing
32
connecting the pressure sensor
36
to the ultrasonic cutter
12
can collapse, causing at least temporary complete loss of pressure feedback. Pressure loss along the tubing
32
can also result in inaccurate pressure feedback measurements. What is desired, therefore, is a reliable system and method for measuring pressure and flow changes in, for example, a needle ultrasonic surgical cutter tool employed as part of a phacoemulsification system, and similar needle-like surgical tools employed for injecting fluids into and removing materials from a patient.
Ultrasonically driven surgical tools, and needle-like surgical tools in general, are conventionally manufactured from appropriate metal materials, such as titanium (for ultrasonic tools) or surgical steel. However, it has been determined that such surgical tools may, advantageously, be implemented as micromachined silicon structures. Such silicon surgical tools may be manufactured to have high strength and sharper cutting tips than similar metal tools, thereby providing for easier cutting. Such tools may be manufactured using conventional low-cost micro-mechanical mass (batch processing) fabrication techniques, which makes such tools low-cost and disposable. Micromachined silicon surgical tools also have the advantage of higher maximum achievable stroke velocity and lower heat generation, due to the high thermal conductivity of silicon, thereby resulting in less tissue damage due to friction induced heating of the tool. Furthermore, sensors and control circuits may be integrated directly onto surgical tools fabricated from silicon using conventional micro-mechanical processing techniques, thereby enabling effective closed circuit control of tool operation. Examples of micromachined silicon ultrasonic needle-like surgical tools include the ultrasonically actuated needle pump system described in U.S. patent application Ser. No. 09/617,478, filed Jul. 17, 2000, by Amit Lal, et al., as well as the vibrationally actuated cutting instrument described in U.S. patent application Ser. No. 09/605,323, filed Jun. 28, 2000, by Amit Lal, et al. The latter describes, for example, a strain sensor integrated onto a silicon vibrationally activated cutting tool to provide an output signal that may be used in a feedback loop to control operation of the tool. For example, a signal provided by the strain sensor mounted near the tip of such a tool may be used as a feedback signal to a feedback controller for controlling an electrical power driver that is connected to supply oscillating power to the tool, so as to maintain the amplitude of the vibrations at a selected level to control, e.g., the cutting and pumping ra

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