Oct 15, 2017
Lasers are machines that amplify light waves then shoot them out as narrow, intense beams. They are used everywhere today. Lasers read CDs and bar codes, guide missiles, cut through steel, precisely measure distances, entertain people and do a thousand other things. Lasers are used in several applications in urology. Most relevant to our discussion today is that we use lasers to break up kidney stones. L.A.S.E.R. is an acronym for light amplification by stimulated emission of radiation. A laser’s light is different from regular light and has three properties. A laser’s light is coherent, collimated, and monochromatic. The idea and concept of the laser traces itself back to Albert Einstein in 1917, but it wasn’t until May 16, 1960 that the first laser was actually built and fired in a laboratory at the Hughes Aircraft Company by Dr. Theodore Maiman. Dr. Maiman, who was trained in both engineering and physics bested many other scientists working at other prestigious institutions such as IBM, Bell Laboratories, and MIT. One of his breakthroughs was the use of artificial rubies as the active medium, persisting when other scientists had given up on the ruby due to failed calculations. Another breakthrough was the use of a flash bulb to stimulate the ruby rather than continuous light. On July 7, 1960 Dr. Maiman’s laser was introduced to the world at a news conference in Manhattan, New York. When introducing the laser at the press conference Dr. Maiman was prescient but also humble about his new invention. “A laser is a solution seeking a problem,” he said. In urology, the laser solution has discovered a long standing medical problem in urinary stone disease. The history of lithotomy (treatment and removal of urinary stones) dates back to antiquity. The treatment of stones, which at the time most commonly occurred in the bladder, was very dangerous, often lethal. As such, it led to the development of the lithotomist, who opened the urinary tract and removed stones directly. Recognition of this unique set of skills earned a distinction in the Hippocratic oath, written by Hippocrates around 400 B.C. and still recited by graduating medical students: “I will not cut for the stone, but will leave this to be done by practitioners of this work…” Today, “cutting for stone,” has been replaced by minimally invasive techniques. We have discussed the shock wave lithotripsy in episode 30 and the percutaneous nephrolithotomy in episode 34. In today’s episode, I want to discuss the third in the trio of options to treat kidney stone disease that has eliminated our need to “cut for stone.” In this episode, we are discussing ureteroscopy, taking a small scope into the ureter to remove a stone. While this is the third option we are discussing it is the most common way to treat kidney stones in our specialty today. Here is some simple urinary anatomy. The kidney filters blood to make urine. Urine drains from the kidney into a collecting system consisting of individual renal calyces draining into a common, funnel shaped renal pelvis. The renal pelvis tapers into a narrow, long, muscular tube called the ureter that peristalsis and “milks” the urine into the bladder. The bladder stores urine, fills, and empties through the urethra. If you are a man your urethra travels through the prostate and the penis. The female urethra is much shorter. When urine is concentrated the minerals in the urine will form crystals. When the crystals layer on top of one another they will form a kidney stone. When a stone chooses to try to come out it must travel through the ureter into the bladder and out through the urethra. The ureter is the narrowest part of the urinary tract. When a stone is too large to pass through the narrow ureter it will get stuck as it tries to come out. The analogy I use is let’s say you have a strawberry milkshake, the kind where they used real strawberries. I used to love those as a kid. But if there are strawberry chunks they get stuck in the straw. Maybe with some real sucking power you can get a small chunk all the way through the straw but if the chunk is too big you just can’t suck hard enough. That’s like a stone that won’t pass. In episode 7 we learned how a young Lyndon Johnson, the future President, had a stone stuck in his ureter during a campaign for the U.S. Senate and how doctors at the Mayo Clinic would perform a risky “blind basket” technique that allowed him to continue his campaign and win the Senate seat. Although we continue to basket stones to remove them we now we have advanced technology to actually get into the ureter and actually see what we are doing. We call this ureteroscopy. A ureteroscope is an endoscope designed to visualize and work within the ureter. We use both semi-rigid scopes as well as flexible scopes. The rigid scopes give us access just to the lower part of the ureter. Flexible scopes allow us to access all the way back into the kidney and have active deflection on the end of the scope that will allow us to see into all of the calyces within the collecting system. Once we perform ureteroscopy if the stone is small enough we are able to extract it using baskets, thin wire instruments that trap a stone so we can pull it out. But for stones too large to just pull out we have to use form of lithotripsy to break up the stone. These day we use a holmium laser to break the stone up into fragments small enough for us to remove safely. Advances in ureteroscopy and laser technology in stone care parallels my time in urology. It was in the late 1990’s and early 2000’s, while I was a resident and early on in my practice that ureteroscopes could routinely access and treat stones in the kidney and the laser technology to break up the stones was readily available. In fact, when I first moved to St Paul, MN in 2000 to start my practice we did not have lasers in the hospital at all times but they were brought in on special occasions. A doctor would have to order it well ahead of time. Now almost all of our hospitals have a laser available where we can use the technology even on the weekends or in the evenings. When I started my practice, along with other younger surgeons I began to order the laser routinely and it quickly became obvious it would be economical for the hospital to buy a laser. Because this was brand new in the hospital this was a big deal, and introducing the technology in a safe manner was paramount. Lasers can do damage to your eyes. This is not a joke. When we first brought the technology into the the hospital we had to educate physicians and staff about laser safety to make sure we all understood the potential harm of the laser. So it was that one Saturday morning my partners and I all gathered for breakfast at the hospital to learn about laser safety. To prove our knowledge and competence in the safe use of the laser we had to use the laser to bust up something. We weren’t going to be allowed to just use the laser for the first time on a patient. So, we put a bunch of eggs in a pan of water. All of my partners and I stood around the pan of eggs, wearing our laser safety goggles taking turns cracking the eggs with the laser, laughing because we were feeling a little silly but, nonetheless, checking off the laser safety box. Such was the introduction of the holmium laser into routine use in St Paul, MN. Different laser mediums (solid, liquid, or gas) emit laser light in different wavelengths. Molecules, proteins, and pigments absorb light only in a specific range of wavelengths. In the real-world application of lasers in medicine different wavelengths of various lasers do different things and may have unique applications. The wavelength determines if the laser can or should be used on the skin, eyes, kidney stones or on some other tissue. The Holmium: yttrium-aluminum-garnet laser (Ho: YAG) is a solid-state, pulsed laser that emits light with a wavelength of 2.1 microns. It can transmit energy through a flexible fiber. Because the wavelength rapidly absorbs in water the power dissipates quickly after it is released through the fiber and can be safely fired near the ureteral wall. The laser energy is able to fragment all stones regardless of composition. Lithotripsy using the holmium laser produces small fragments, a weak shockwave, and less retro-pulsion of the stone fragments than other forms of lithotripsy. All of these factors are important when breaking up a stone stuck in the very narrow, thin-walled ureter or renal pelvis. Accurate fiber contact against a stone is the primary safety factor. A clear visual field is important. Most surgeons will have their preferred settings on the laser machines they are familiar with but in general we start with low-pulse energy and pulse rate and increase as needed. Because we are breaking up the stone while we are observing using ureteroscopy we move the laser over stone surface in a “painting” fashion, creating stress lines that fragment a stone and/or vaporize it. A “snowstorm effect” is created as the stone breaks up because of the small particles created so patience and adequate irrigation is required. Much discussion in our field has centered recently around the technique of stone removal. Historically we would break the stone into fragments, like a rock quarry, and extract the fragments using a stone “basket.” But a “dusting” technique has developed as the lasers have become more powerful and are able to fire at a very high frequency. The current data suggests that basketing rather than dusting is probably a better technique in most cases but urologists should be familiar with all ureteroscopic treatment techniques. Ureteral anatomy, width, the ability to pass an access sheath, the available laser, as well as the stone themselves will mandate one technique over another for any particular patient. As you would expect, short term recovery for this procedure can be uncomfortable. Complications for this procedure also exist. Often urologists will leave a temporary ureteral stent to prevent swelling of the ureter as a result of the procedure. Blood in the urine after the procedure is common. Infections can occur. Perforation of the ureter or long-term damage causing a stricture can also occur but is rare. Regardless of the technique used, the ultimate goal of the procedure should be to leave the patient free of stones. Stone-free is a big deal in the urology world. Residual fragments are likely sources of future stone formation. Crystals form on top of other crystals (listen to episode 3 of this podcast for my rock candy analogy). Residual stones commonly lead to growth, passage, and need for retreatment of more stones in the future. Lastly, surgery to remove a kidney stone is not the end of the relationship with a patient. A patient having ureteroscopy needs follow-up imaging of the kidneys to determine if all of the stones have been removed, whether or not a ureteral stricture (scar) has formed and whether kidney swelling (hydronephrosis) persists after the procedure. Furthermore, as many as 50% of people who have made their first stone will make another within 10 years. If you have ever had a kidney stone there are benefits to dietary counseling, metabolic testing, surveillance imaging, and other practices to prevent and detect stones over the long-term. We have come a long way since Einstein first proposed the laser in 1917, Dr. Theodore Maiman first displayed the laser in 1960, and I was learning laser safety cracking eggs in a hospital basement in 2001. To end this episode, here is a condensed excerpt from the Obituary for Dr Theodore Maiman published in the New York Times May 11, 2007. Theodore Harold Maiman was born in Los Angeles on July 11, 1927, and grew up mainly in Denver. His father, Abraham, was an electrical engineer who worked on inventions, included improvements to the stethoscope. Abraham wanted his son to be a doctor, but Theodore came to feel he had contributed more to medicine with the laser…. Theodore was rambunctious as a boy and aspired to being a comedian, but he was also very good at math. He earned bachelor’s and master’s degrees in engineering physics from the University of Colorado and completed a doctorate in physics at Stanford in 1955…. He went to work for Hughes and after some military contracts fell through, worked on the predecessor to the laser, the maser, which concentrated microwaves, not light… He told his bosses he wanted to make a laser, but they were wary of discouraging reports from other laboratories and said no. They wanted him to work on computers, or “something useful,” his wife said. But he threatened to quit and build a laser in his garage. So, the Hughes executives gave him nine months, $50,000 and an assistant. The assistant was Charles Asawa, who had the idea of illuminating the ruby with a photographic flash, rather than with the movie projector lamp first used. After Dr. Maiman succeeded, a news release predicted that doctors would use lasers to focus on a single human cell. For the rest of his life, Dr. Maiman insisted on emphasizing the laser’s healing possibilities… …Dr. Maiman was twice nominated for the Nobel Prize and won many other awards, including the Japan Prize and the Wolf Prize in Physics. He was inducted into the National Inventors Hall of Fame in 1984, and he published the story of his discovery of the laser in “The Laser Odyssey” (2000). Theodore Harold Maiman died May 5 in Vancouver, British Columbia. He was 79.