Radially expanding dilator improves surgical access

Sunnyvale, CA--When most people think of surgical access, they think of a scalpel. But early in this century, surgeons began to use minimally invasive (laparoscopic) techniques to perform some basic surgeries. Laparos-copy drastically limits the risk, trauma, and recovery time associated with conventional surgery.

A new access instrument called the Radially Expanding Dilator (R.E.D.) offers potentially dramatic improvements to ordinary laparoscopy. In its first year, the device reduced operating-room and patient-recovery time by as much as 80%.

Laparoscopic procedures generally require one to five trocars to gain access to the abdominal cavity. Each trocar consists of a long, 10-mm-diameter metal tube sharpened at the tip. Surgeons force these through the peritoneum (the membrane that lines the abdominal cavity) into the abdomen, and screw down a fixation sheath to create an airtight seal. They then pass the necessary instruments through the trocars for surgery.

The trocars' large diameter and the screwing-down of the sheath can cause significant tissue trauma. Blood vessels may be cut, the bowel may be injured, and, after removal of the instrument, an incisional hernia may form.

InnerDyne's R.E.D. technology improves this process by reducing the diameter of the initial puncture to that of an 18-gauge needle. Following insertion, the surgeon expands the device radially to 5 to 12 mm in diameter-though dilations of 30 mm or more are possible.

Deceptively simple-looking, the R.E.D. consists of a hypodermic needle encased in a stainless-steel tube or cannula. An ultra-thin sleeve of silicone rubber surrounds the cannula and is the secret to the device's radial expansion.

After the device is inserted into a patient, the surgeon removes the needle and expands the R.E.D. by sliding a dilator-sheath assembly between the silicone rubber and the cannula. The dilator-sheath consists of two tubular plastic components: An inner dilator with a tapered conical tip, and a thin-walled outer sheath. Once the device is fully expanded, the physician removes the dilator and the cannula, leaving the sheath behind. The sheath, surrounded by the silicone rubber, forms the working channel through which surgery takes place.

To prevent the R.E.D. from inadvertently retracting, engineers place a small, torus-shaped balloon at the end of the silicone sleeve. Following initial insertion of the device, surgeons fill the balloon with saline or other fluid via a reflux valve tied to a thin flexible lumen passing longitudinally along the outside of the silicone sleeve.

"The main advantage of this device is that it allows you to do surgeries laparoscopically that could never be done that way before," says Will Dubrul, InnerDyne's application development manager and inventor of the R.E.D. Its smaller initial size means less traumatized tissue and a reduction in the need to cut blood vessels. Radial dilation provides a tight gas seal and eliminates the need for screw-on sheaths. It also naturally puts pressure on (tamponades) the surrounding blood vessels to limit bleeding. "The puncture is so small that after you remove the R.E.D, often you don't need to suture," Dubrul says.

He traces the invention's origin to a development project involving another of the company's products, a thermal ablation (TA) technique for interventional radiologists to treat gall bladders. "Doctors said to me, "while you're working on the TA device, we also need something to get into the gall bladder,'" he says.

With the inspirational seed thus planted, Dubrul began brainstorming different ideas on how to access the human gall bladder. He considered mechanically expanding devices and inflatable balloons, but each had a significant shortcoming. The breakthrough came when Dubrul recalled a physician saying he could, figuratively, insert a 22-gauge (0.028-inch) needle into the body almost anywhere without doing damage. "I thought that if I could make an expanding needle-and "expanding' means "rubber' to me-it would limit tissue damage," he says.

Friction proved to be the design's biggest challenge. Without a good lubricant, sliding the dilator-sheath between the silicone sleeve and the cannula proves impossible. The solution: a Teflon(TM) -based fabric that lines the inside of the rubber.

Though the initial device targeted treatments of the gall bladder, a redesigned model addresses general laparoscopic surgery. And the company believes the R.E.D's unique abilities will allow surgeons to access most any hollow organ-the lungs, pancreas, kidney, stomach, bowels, and gall bladder.

It's a big market. Surgeons currently perform 1.5-million cholecystectomies (gall bladder surgeries) worldwide each year. Roughly 85% of these employ minimally invasive techniques. In all, about 14 million surgeries a year could be performed using R.E.D. technology.

Additional details...Contact Will Dubrul, InnerDyne Medical, 1244 Reamwood Ave., Sunnyvale, CA 94089, (408) 745-6010.

During his fifteen years as a biomedical engineer, Will Dubrul has invented more than 30 products and received nine patents. He traces his interest in medical devices to work he did with paraplegics while still a student at the University of California, Santa Barbara. InnerDyne Medical's first engineer, Dubrul heads the firm's product development and marketing efforts.