Physicians and surgeons employ procedures involving infusion of a fluid into a body cavity ("irrigation procedures"). Irrigation procedures are often used in conjunction with removal of fluid, unwanted material, diseased tissue, or waste products via aspiration. As used herein, "irrigation procedures" refers to procedures or methods involving delivery of irrigation fluid into a body cavity, regardless of whether aspiration is also performed.
When using irrigation procedures, it is desirable to be able to measure and control the fluid pressure within the body cavity. Lack of control over the internal pressure may impair the effectiveness or ease of the procedure, and in certain cases may result in damage to tissue. The ability to adjust the fluid pressure within the cavity may also be used to control bleeding.
Some examples of irrigation procedures are intraocular surgery, peritoneal dialysis, and removal of diseased spinal disc material. In intraocular surgery, failure to maintain sufficient fluid pressure during an operation may result in collapse of the eyeball with concomitant tissue damage. Conversely, over-pressuring the intraocular region may also result in damage to the sensitive retinal, optic nerve, or corneal tissue. However, it is occasionally desirable to apply controlled high pressure for a brief time period, for example, to staunch bleeding in the intraocular region. If it is necessary or desirable to alter the pressure within the body cavity, the surgeon needs the ability to rapidly alter the pressure to a desired value without significant deviations from that value.
Peritoneal dialysis is used with patients suffering from kidney failure. In peritoneal dialysis, clean fluid is irrigated into the peritoneal (abdominal) cavity and fluid containing waste substances is aspirated out. If abnormally high pressure develops in the peritoneal cavity, mass transfer of waste substances into the dialysis fluid and normal blood flow will likely be disrupted.
Similarly, patients suffering from degenerative lumbar disc disease may have diseased disc tissue removed by irrigation procedures. Surgeons removing this tissue make a small incision through the skin, allowing insertion of a needle-like instrument into the appropriate disc space. The instrument is used to cut away diseased tissue. Irrigation fluid aids in flushing the cut material into an aspiration line. Accurate pressure control is likely to enhance the ease and effectiveness of this procedure.
Attempts to measure and control pressure in irrigation procedures have met with limited success. These attempts have usually related to intraocular surgery. Such surgery involves operations on or within the vitreous cavity or the anterior segment cavity of an eye. As used herein, "anterior segment cavity" means that portion of an eye comprising the anterior chamber and the posterior chamber. Most types of intraocular surgery utilize irrigation procedures. Dedicated surgical machines and highly specialized tools have been developed for such surgery. Cataract surgery (the removal of opacified lens tissue) employs an invasive tool which is used in the anterior segment cavity of an eye. This tool usually contains an irrigation outlet, a mechanical or ultrasonic cutter, and an inlet to an aspiration line, all in close proximity. Alternatively, a separate tool may be used to provide aspiration. Vitrectomy (the excision and removal of tissue from the vitreous) usually involves two invasive tools: an irrigation cannula, which is inserted into the globe and temporarily attached to the sclera, and a cutting/aspiration tool that is manipulated by the surgeon.
One method of controlling pressure within the eye during surgery is disclosed in U.S. Pat. No. 4,041,947 to Weiss, et al. That patent discloses the use of limiting valves external to the eye on the infusion and aspiration lines. These limiting valves are designed to provide pressure relief if either the pressure in the infusion line exceeds a high limit, or if the pressure in the aspiration line exceeds a low limit. This device does provide some ability to maintain pressure within a predetermined range of values, but does not allow the surgeon to accurately know or set the intraocular pressure ("IOP"), nor does it necessary allow rapid correction of over- or under-pressure conditions.
It is possible to directly measure the intraocular pressure ("IOP") in this type of surgery by insertion of a pressure transducer into the eye. U.S. Pat. Nos. 4,548,205, 4,722,350, and 4,841,984 to Armeniades, et al., disclose direct measurement and control of the IOP. A pressure transducer is inserted into the eye as an independent tool or integrated into the cutting tool. Alternatively, a pressure transducer can be integrated into a separate tool that provides infusion or aspiration.
However, there are several problems with tools which provide direct measurement of the IOP. If the pressure transducer is incorporated into the invasive portion of a tool, the tool must be made larger in diameter than is necessary to perform the actual surgery. This approach requires a correspondingly larger incision in the eyeball for tool insertion. Further, integration of a pressure transducer into another tool creates inaccuracies in the pressure readings caused by the proximity of the transducer to the operating infusion line, aspiration line, or surgical tool.
One solution to the size problem is to design a tool with a channel which is inserted into the eye and which provides fluid communication with a pressure transducer outside of the eye. However, this design suffers from the same accuracy problems detailed above, as well as problems caused by debris from the operation clogging the channel. This accuracy problem can be overcome by providing a separate tool that only contains a pressure transducer for insertion into the eye away from the operating tools. However, this approach is disfavored because it requires another incision into the eye.
Similarly, irrigation procedures on other body cavities in which internal fluid pressure must be controlled have characteristic constraints regarding tool size and a need to limit the number of incisions.
It is an object of the invention to provide a device and method for noninvasively measuring internal fluid pressure in a body cavity during irrigation procedures.
It is another object of the invention to provide a control signal for a pressure-generating device, such as a pump, to allow for automatic control of the dynamic internal fluid pressure in a body cavity.