Thursday, January 13, 2005

Kidney Stone Blogging

PanseyI have been working on a posting -- or series of postings -- on medical malpractice, a project which has taken longer than I anticipated. So, in the meantime, I thought I would treat you to some kidney stone blogging.

Say again? Kidney stone blogging.

Management of kidney stones has changed dramatically over the past 20 years. In the past, patients who formed kidney stones often required open surgery, with some active stone formers undergoing multiple open surgical operations. Things began to change in the early 1980s, first with the advent of percutaneous renal surgery -- a precursor of today's laparoscopic procedures. After placing a tube in the kidney using x-ray guidance, fiber-optic scopes were placed into the kidney, and kidney stones could be directly retrieved or fragmented.

The next, and perhaps most important, evolution in surgical technique was ESWL (extracorporeal shockwave lithotripsy). This technique was developed in Germany, after aerospace engineers noticed that a peculiar pitting was occurring on military jet aircraft which broke the sound barrier. Research determined that the sonic wave thus created was focused by condensation on the surface of the jet, creating a pit at the apex of the droplet. As perhaps only the Germans could deduce, this logically led to the use of focused sound waves for kidney stone fragmentation. The concept is not dissimilar to a magnifying glass in the sun. Solar energy, a quite comfortable temperature at the magnifying glass level, is intense enough to start a fire at its focal point. Similarly, soundwave energy at its source is weak, and can pass through water (and therefore human tissue) with virtually no damage, but at the focal point, creates a tremendous pressure wave. Using dual-plane x-ray control (for 3D imaging), the focal point could be directed at an internal kidney stone, and a series of shocks could break it into tiny fragments. This, somewhat amazingly, causes little or no injury to the surrounding kidney tissue.

ESWL, while ideal for stones that are still in the kidney, does not work well for stones that have moved into the ureter -- the thin drainage tube connecting the kidney to the bladder. For such stones, the development of small-caliber, high-quality optical scopes has proved an ideal solution. The scopes are introduced into the ureter by passing them through the lower urinary tract, the urethra and bladder. (This is done under anesthesia, of course, for the squeamish among you -- uncross those legs, now). Stones which are trapped in the ureter, even high above the bladder near the kidney, can be reached with such instruments, in most cases with little difficulty. The challenge then becomes: what do you do with the stone when you finally see it?

If it is tiny, you may be able to grasp it with a wire cage -- called a stone basket -- and extract it. In many cases, however, stones trapped in the ureter are larger, and cannot be removed this way. They must be fragmented.

The answer has been provided through laser technology. Using a tiny fiberoptic fibers -- 350 microns in diameter or less -- passed through the ureteroscope (as these delicate scopes are called), laser energy is used to fragment the stone. Darth Vader, meet Marcus Welby.

There are many different types of lasers used in medicine. Different laser types and wavelengths have markedly different effects on living tissue. Some, like the CO2 laser, work best in air, and are used to vaporize skin lesions, such as warts, with very little deep tissue penetration and virtually no subsequent scarring. Others provide deep thermal energy to destroy tumors or other tissues with minimal effect on the surface. For kidney stone work, a holmium laser in direct contact with the stone is commonly used.

The laser is fired at a very rapid repeating frequency. At the tip of the fiber, which is placed in contact with the stone, the intense light energy vaporizes the water used for irrigation, creating a rapidly-expanding plasma. An intense yet short-radius shockwave results. This has the effect of drilling into the stone, which creates areas of relative weakness and fracture. As a result, the stone breaks into increasingly smaller pieces, which can be extracted or flushed out. Because of the short energy radius, the surrounding tissues are unaffected.

A patient I treated recently shows how extraordinary an advance this is. He was morbidly obese, weighing nearly 400 pounds, a situation which precludes ESWL, as the focal length of the machine is not long enough to reach the stone. He presented with a very large stone just below the kidney, measuring about one-half inch in diameter. The patient also had very poor lung function and was at high risk for general anesthesia, and particularly at high risk for open surgery on the upper abdomen, which can greatly impair lung function. Using the ureteroscope and the laser, I was able to successfully treat his stone without the need for high-risk open surgery. Let's take a virtual walk-through of the procedure (the pictures are a bit grainy because of the low video resolution of the surgical camera).

This image shows the ureteral orifice (the opening in the bladder where the ureter enters, draining one of the kidneys) after the scope has been introduced into the bladder, before entering the ureter:

Ureteral orifice

This image shows the ureter below the stone as seen through the scope. The diameter of the ureter is about 3-4 millimeters:

Ureter below

This image shows the laser fiber in contact with the stone. The fiber is the dark blue linear object on the right, and green spot is the actual laser beam:


This image shows a large fissure created in the stone as it begins to break up:


This image demonstrates how the laser fiber can literally drill a hole through the stone. The central dark spot is actually a narrow cavity created from laser contact:


The patient had an uncomplicated surgery and anesthesia, and was discharged from the hospital several hours after it was completed. Contrast this with an open surgical procedure, which at the very best would have left him hospitalized for nearly a week, with a significant risk of requiring a respirator to support his breathing because of his weight and risk of lung complications secondary to the surgery. He also avoided the need for a long and uncomfortable recovery from a large surgical incision.

Life is good.