A story about microsurgery in Wednesday's Health section incorrectly described a recent case of hand reattachment surgery as the first in the Washington area. A similar operation took place 10 years ago at the Washington Hospital Center.

Ryan Kahn got to the emergency room about a minute before his left hand.

Less than an hour earlier, nine stories above M Street, on the conctruction site of the new Westin Hotel, Kahn had been cutting trim work with a power saw. It was the 20-year-old carpenter's first morning on the job.

"Pow! Just like that, I looked down and my hand was gone," he recalls. "I couldn't find it at first. I had to look around for it."

When Kahn found his left hand, is was stuck on the 14-inch circular blade of the mitre box saw.

He screamed for help and pulled the severed hand off the saw blade. In the ensuing tumult, a fellow worker managed to find a large red lunch cooler containing some ice. No one wanted to touch the hand. It sat on a sheet of plywood until, finally, a workman picked it up and put it in the cooler.

Above the pain and the panic -- above all else -- Kahn knew he had to get to a hospital fast. Remembering that he had passed a nearby hospital sign on his way to work, he wrapped his bloody left wrist in a jacket and took off down the hall.

The elevator wouldn't come. Kahn flung off his tool belt and raced down the stairs, intercepting the elevator at the seventh floor. He ran two blocks to the hospital, which turned out to be the Columbia Hospital for Women. Hospital attendants couldn't figure out why their visitor was so frantic -- until Kahn pulled the jacket off of what remained of his left arm.

Minutes later, Kahn arrived by ambulance at the emergency room entrance to George Washington University Hospital. Paramedics rushed him into the emergency room, then returned to the ambulance to pick up the cooler containing his hand.

In the past, a patient like Kahn would have been flown by helicopter to Baltimore for replantation surgery. But GW recently set up a microsurgery team, which on Oct. 2, when Kahn arrived, was waiting for its first major replant case.

Joan Grubb, the operating room charge nurse that day, was walking back to her desk when she passed Dr. Mary H. McGrath, director of plastic and reconstructive surgery, racing down the hall.

"This is it," said McGrath.

Ryan Kahn was wheeled into GW's Operating Room 9 around noon. He didn't leave that room until nearly 3 o'clock the next morning, but when he did, his left hand was once again connected to his left wrist. His doctors say it is the first replantation of a severed hand in the Washington area.

The 15-hour operation -- which spanned three nursing shifts -- exemplifies the most dramatic application of microsurgery, a fast-growing medical field in which surgeons repair almost invisibly small structures while looking through a microscope.

Because of microsurgery, Kahn has his hand back -- but it will never be the same again. Two months after the accident, it's still swollen, stiff and sore. With difficulty he can rotate his wrist and curl his fingers, but he cannot yet hold a coffee cup or grip a pencil, and he has no feeling in his fingertips, because the nerves grow back at the rate of about an inch a month.

Whatever sensation he has now in his fingers is what doctors call "referred sensation," caused by movement in the tendons that reach all the way from his wrist to his fingertips.

"Movement in the part he doesn't feel also causes movement in the part he does feel," says Dr. Michael Olding, head of the GW microsurgery team, who operated on Kahn. "It's like biofeedback. It's sort of a training program every time he moves his fingers."

Kahn faces a year or more of physical therapy -- and additional surgery to repair some scarring around the tendons and the nerves. Even then, doctors say, he cannot hope to regain full use of the hand, because nerve regeneration is never complete. The hand is likely to regain much of its strength, but lack some of the complexity of the normal sense of touch.

"Are you left-handed?" Kahn is asked.

"I was," he replies.

Microsurgery -- any surgical operation done under a microscope -- enables surgeons to manipulate tissues too tiny to be seen easily with the naked eye, such as blood vessels, tendons and nerves.

Aside from reattaching limbs and fingers, microsurgery often enables doctors to reconstruct damaged body parts, remove cataracts, and restore fertility by opening tied fallopian tubes or reversing a vasectomy.

"In surgery, for a long time the limiting factor was our ability to see," says Dr. William Shaw, associate professor of plastic surgery at New York University School of Medicine and director of microsurgery and replantation surgery at Bellevue Hospital.

No longer. Today, a 20- or 25-power microscope in the operating room can make a blood vessel the diameter of kite string look like a garden hose. That same blood vessel, if severed, can be spliced with sutures one tenth as thick as a human hair. Reconnecting an artery just 1 millimeter across usually requires eight to 10 stitches around the arterial wall.

Surgeons repairing blood vessels that small must rely totally on what they see under the microscope, because the nylon suturing thread is so fine it has no "feel." When a microsurgical needle is held up to the light, the suture attached to it is almost invisible and tends to float in the air rather than fall of its own weight.

Microscopes have been around for more than 300 years, but only in this century have doctors used them to operate on patients. In the 1920s, ear, nose and throat specialists began using the microscope to scrape and clean the tiny bones of the middle ear. By the 1950s, eye surgeons were repairing corneas under the microscope.

In the 1960s surgeons began using the microscope to suture severed blood vessels. Several developments made that possible: better anesthesiology, allowing for longer operations; better vascular surgery in general; and improvements in microsurgery equipment -- the microscope itself and other instruments. Needles and sutures posed a particular technological challenge: They had to be sharp enough and fine enough to pierce near-microscopic blood vessel walls with a minimum of damage, yet strong enough not to bend or come apart in surgery.

In 1962, doctors in Boston reattached the severed arm of a 12-year-old boy who had been hit by a train. Three years later, Japanese surgeons successfully replanted a severed thumb -- an even more difficult operation because the blood vessels in a thumb or finger are smaller than those in the arm.

"It was really in the 1970s that replantation began to take hold clinically," says NYU's Shaw. "In the last five years, it has become essentially an established part of surgical practice."

Although replantation remains a highly specialized operation, every major medical center today uses some form of microsurgery.

One of the most important uses is in tissue transfers, called free flaps, in which tissue for reconstruction is transplanted from one part of the body to another in the same patient. Such an operation is sometimes needed in a patient who has lost extensive skin and tissue from an injury, a burn or a tumor removal.

Tissue surrounding a rib, for example, can be transplanted to help rebuild the jaw of a person with mouth cancer. A section of back muscle can be used to cover the ruined lower leg of a motorcycle accident victim and give the exposed bone enough blood supply to heal. A big toe can replace a missing thumb.

Until the 1970s, when surgeons learned to reattach blood vessels, such operations were difficult or impossible. It was necessary to wait until the transplanted tissue had developed its own blood supply in the new location before cutting it off from the old blood supply.

This process often required many operations and awkward positioning of the patient, who might have to stay in a hospital bed for up to six weeks as the tissue graft took hold.

Microsurgery allows a surgeon to cut away the transplantable tissue -- including skin, muscle, nerves, blood vessels and sometimes even bone -- and immediately hook it up to a new blood supply by an artery and a vein.

"What we do in microsurgery," says Olding, head of the GW microsurgery team, "is bring the blood supply along with [the tissue], so it doesn't have to grow its own."

"You wait until the last minute to sever the two blood vessels," says McGrath, "and then you hook up the vein and the artery at the new site. It may only be devascularized [without blood supply] for five minutes."

The steady progress of tissue transfers brings medicine closer to the day when tissue banks are established for transplants of non-essential organs, says NYU's Shaw.

"Then," he says "you could literally talk about a hand bank, a nose bank, a breast bank and so on."

Replantation surgery is the marathon of surgical operations and requires a team effort of many nurses and doctors. One operation in which GW's McGrath participated, on a man who cut off all the fingers of one hand with a bandsaw, took 27 hours. Ryan Kahn's operation took so long that it caused a temporary bald spot where the back of his head rested against the operating table for 15 hours.

Replantation cases, by definition, also occur suddenly and without warning. There is virtually no room for error, no time to waste. The longer it takes to reestablish vital blood supply to the severed part, the less chance it has of surviving. After four hours at room temperature, chances of a severed limb surviving are slim.

Microsurgery requires the delicate touch of a jeweler and the stamina of a distance runner. The operation is a series of critical, painstaking procedures, and no one but the surgeons can really see what's going on under the microscope.

"Once we start the surgery, it's relatively boring for everyone except us," says surgeon Olding.

"Once you look through the microscope," says NYU's Shaw, "it's a different world. It's just like a video game. You don't even think about what you're doing. You just do it.

"It's what I call an 'Alice in Wonderland' world under there."

What Ryan Kahn remembers most about meeting Dr. Olding in the emergency room before his surgery and what the nurses remember most about him after 15 hours in the operating room is the same: Olding's outward calm.

"The coolest dude I know," Kahn says.

Kahn's replantation surgery began as two separate operations. One team of doctors and nurses worked on Kahn himself -- administering anesthesia, cleaning the wrist wound, preparing for possible vein and skin grafts, applying tourniquets, readying the microscope and other instruments. Meanwhile, over to one side of the operating room, microsurgeon Olding worked on the severed hand.

Wearing 3-power magnifying eyeglasses, Olding sorted out the blood vessels, nerves and tendons he would need to repair. He "tagged" the key structures with a suture -- one long and one short tie for an artery; two ties of equal length for a vein -- so they could be easily identified later on when swelling and bleeding hindered his view.

As a nurse cleaned the hand with disinfectant, Olding momentarily crossed its index and middle fingers for good luck.

The operating room microscope has two sets of eyepieces, allowing two surgeons to work simultaneously. Olding, assisted by McGrath and chief resident Dr. Robert Dennis, would spend most of the next 12 hours peering at a circle of light focused on Kahn's left wrist and hand.

The first step was to set the broken bones in the wrist. This also would stabilize the hand for the intricate microsurgery to come. The pieces of the large wrist bone were rejoined with three wires threaded through holes drilled in the bone ends. Two long pins, resembling knitting needles, were inserted along the two wrist bones to realign the hand.

Then came the critical challenge: restoring the blood supply to the hand. It would take about five hours to reconnect just two arteries and two veins.

Olding first tried to reconnect the ulnar artery, the main artery in the wrist. Manipulating the microscope's zoom lens with a foot pedal, he meticulously stitched together the two ends of the artery, only to realize that it wasn't working. The reattached artery was under too much tension, like a stretched elastic band, which hampered the blood flow and increased the risk of a blood clot.

The key challenge of replantation is the anastomosis -- the surgical joining of two tubes. The connection must be flawless. The slightest roughness, tension or irregularity could disrupt the blood flow and cause a clot to form.

"There isn't a maybe," says Olding. "There isn't a gray zone. It's either yes, the vessel works -- or no, it doesn't."

Tiny, delicate clamps hold the two ends of the blood vessel in place so they can be joined.

"You can't keep picking it up without destroying it," says McGrath. "It's the consistency of wet Kleenex."

Olding realized he would have to use a short vein graft to bridge the gap between the two ends of the artery and reduce the tension at the splice point.

First, he rejoined the other wrist artery -- the one often checked for a pulse -- sewing it together with an inch-long section of vein taken from the top of Kahn's left foot. The arm tourniquet, which had been tightened to reduce the blood flow and swelling in the wrist, was temporarily loosened.

For the first time since the accident, blood flowed into Kahn's hand.

Olding turned his attention back to the ulnar artery, this time using a vein graft to reconnect it, and repaired the key nerve next to it.

With the two main arteries intact, Olding turned the hand and arm over so that he could reattach the veins on the back of the hand. Again, short sections of vein from the foot were used to bridge the gap caused by the injury.

After nearly six hours of surgery, the tourniquet was released again. Olding pinpricked a fingertip, watched the bright red blood well up, and asked a nurse to jot down the time: 5:45 p.m. "The hand is perfused," he announced to the crowded operating room. It had been eight hours since the accident.

The operation was far from finished. Besides amputating Kahn's hand at the wrist, the saw had sliced down between his thumb and index finger, damaging the thumb and nearly severing the index.

Olding reset and wired the broken thumb and finger bones, before repairing some of the key tendons and nerves. The index finger was getting adequate blood supply from one of its two arteries, so it wasn't necessary to sew the other one back together. Finally, the hand was turned back over, so that more tendons on the palm side, as well as the crucial median nerve, could be repaired.

By now the hand and wrist were so swollen that the surgeons could not close the wound without extra skin. They took a small skin graft from Kahn's right thigh and stapled it into place to help cover the wrist.

Bandaging the hand took nearly an hour. It was coated with disinfectant, bound in gauze and cotton and covered with a cast from the fingertips to the elbow.

"It looked like a big white bonnet," Olding says.

The only break Olding took during the 15-hour operation came after the blood flow had been reestablished in the hand and before work began on the finger and thumb. It lasted 45 minutes -- long enough for him to go to the bathroom, grab a Coke and some potato chips and speak briefly in the waiting room to Patricia Kahn, Ryan's mother. She was not able to get to the hospital from the family's home in Richmond before the operation started, and when she next saw Ryan, he was in the recovery room, eyes still swollen shut from 15 hours of anesthesia.

Ryan Kahn remembers waking up in the recovery room without being able to open his eyes.

"It was like being awake and asleep at the same time," he says.

For a time, even after he was able to open his eyes, Kahn didn't know where he was. He remembers seeing faces all around his bed and hearing a doctor speaking and then the horror of the accident coming back to him -- and finally, the relief of looking over and seeing, at the end of his arm, the huge white bundle of his reconnected hand.