Catheters are an invaluable way of delivering life-saving drugs and nutrition directly to the blood vessels near the heart, but guiding the devices through veins can be tricky. A doctor in Boston is developing a catheter fitted with a light that’s visible outside the body so that it’s easier for medical professionals to get it in place.
Farhad Imam, a newborn-intensive-care physician at Children’s Hospital Boston, says that his transilluminating catheter could be useful in outpatient, wilderness, and military settings, where there isn’t the luxury of using fluoroscopy or ultrasound to track the device’s movement.
More generally, the transilluminating catheter could reduce the need for reinsertions and repeated x-rays to check the instrument’s positioning, Imam says.
Imam designed his catheter with babies in mind, knowing that it would be relatively easy for light to shine through their thin skin. However, he thinks that it will also work in adults.
Imam has tested the catheter in rabbits and patented it, and he’s now gearing up for human trials, which he expects to begin in 2009. He’s working with a catheter manufacturer and an optics company to produce a variety of prototypes.
“The reason why we’re so excited about this technology is, it’s simple, it’s intuitive in the sense that you can see it with your own eyes, and you don’t need an extra pair of hands to hold something,” Imam says.
Central venous catheters, which feed into the sizeable veins leading to the heart, are commonly used in intensive care and during cancer treatment. They’re needed to administer potent drugs like chemotherapeutic agents that have to be diluted in the rush of blood flowing through a large vein; to treat patients whose peripheral veins have collapsed and can’t be accessed with an intravenous line; and to administer long courses of antibiotics, pain relievers, and nutrition, which can’t be given through peripheral intravenous lines that must be replaced every few days and are easily dislodged.
Some central catheters are inserted directly into the chest during a surgical procedure, but increasingly, variants called peripherally inserted central catheters (PICCs) are being used. They consist of a long, flexible tube that’s inserted in a small vein in the arm or ankle, then carefully threaded up into the chest until it reaches the large vessels that deliver torrents of blood to the heart.
PICCs can be guided into place using fluoroscopy or ultrasound to trace the path of the catheter in real time, but that requires pricey equipment and specially trained personnel, and, in the case of fluoroscopy, it exposes the patient to radiation. Magnetic probes have also been developed, but they require calibration and an extra hand. Such methods “all make it harder to do something that’s already hard to do on its own,” Imam says.
A simpler, although not as accurate, method that can be performed at the bedside is to first measure the distance the PICC will travel using external landmarks like the shoulder and clavicle, then insert a PICC to that predetermined length and check its positioning with an x-ray.
However, “using external landmarks is never necessarily a completely accurate reflection of what the body looks like,” says David Rodeberg, a surgeon in the Division of Pediatric General and Thoracic Surgery at Children’s Hospital of Pittsburgh of UPMC, who wasn’t involved in Imam’s work.
The process often needs to be repeated because PICCs can get stuck or flip around and end up directed toward the head rather than the heart. Imam says that between a third and half of PICCs that are placed without the help of ultrasound or fluoroscopy need to be readjusted or reinserted. Misdirected catheters can damage veins and allow toxic drugs to leak into the surrounding tissue. In rare cases, if a catheter is pushed too far into the heart, it can trigger an irregular heartbeat or other serious problems.
Imam came up with the idea of a light-guided catheter five years ago, when he was an intern at Children’s Hospital Boston, where PICCs are commonly used in babies, and he “saw a few of these end up in the wrong place.
For his first prototype, Imam attached the light from a laser pointer to the tip of a PICC. He is now investigating different wavelengths of visible light, focusing on red, which penetrates tissue well, and green, which is easy to see, and he’s considering using a flashing light to make the catheter even more visible. One of the prototypes that’s being developed is outfitted with lights all along the catheter line so that when it’s inserted, “you can see essentially a dashed line moving forward.” Tests on rabbits indicate that the glow shows the catheter’s position to within millimeters. The realm of accuracy needed for a catheter insertion, Imam says, is about a centimeter.
A three-to-five-milliwatt light in a vein less than a centimeter under the skin was easily seen outside the body during Imam’s tests in a dimly lit room. PICCs often get stuck or are misdirected in these shallow veins.Imam says that he’s now working on solutions to that problem. Ideally, the catheter will still be visible as it travels deeper within the chest, toward the heart.
“If it will actually show you where it is when you go up into the chest, that’s a fascinating idea,” says David Gaieski, an attending physician in the emergency department at the Hospital of the University of Pennsylvania, who was not involved in the work.
Amy Kyes, manager for the Infusion Clinic and Vascular Access Team at Froedtert Hospital, in Wisconsin, says that while light would be useful to more accurately track the path of a catheter, she thinks that x-ray checks will still be necessary to confirm placement because “not everybody is built the same. I can only imagine that we’ll still have the radiology piece because of people’s different anatomy.”
Imam hopes that he can develop a catheter that’s visible throughout its journey toward the heart, but “there’s certainly nothing wrong with using this technology in combination with other probe technology,” he says.
At the very least, Imam says, a transilluminating catheter could be inserted without the need for fluoroscopy or ultrasound, make bedside placements more accurate, and cut down on the number of x-rays required.