For seven years, Dr. Carl Hasselman has performed orthopedic surgeries on patients at his practice at UPMC St. Margaret in Aspinwall, with several notable interruptions.

He's also served three tours of duty with the Army Reserves, including deployments to Afghanistan and Iraq, where he performed battlefield surgeries on children mangled by land mines, civilians caught in crossfire and soldiers seriously wounded in combat. He's even had to duck gunfire himself.

His experiences represent the disparate lives of doctors who serve in the U.S. Army Reserves or National Guard during times of war.

Now Dr. Hasselman, 44, is preparing to return to duty in September as a member of peacekeeping forces in Bosnia.

The burdens on him and his family are magnified by the strain placed on partners and staff at Three Rivers Orthopedics at St. Margaret. His absence also can create a staffing puzzle for his employer, the University of Pittsburgh Medical Center.

John Galley, UPMC's vice president of compensation, benefits and human resources information systems, said four physicians from the medical system returned recently from active duty. Dr. Hasselman and 13 other doctors still are on active duty with the Army Reserves and National Guard and face future deployment.

"So far we've been able to handle care appropriately when physicians are called up, and we really support doctors and other clinicians when it happens," Mr. Galley said.

Each department at UPMC must deal individually with staffing shortages based on circumstances. Existing staff might be asked to work longer hours or a temporary replacement might be hired, Mr. Galley said.

The burden on UPMC was greater the year after the Sept. 11, 2001, attacks, he said. But now only five to 10 UPMC employees throughout the system are serving in the military, which "is not a big burden from the employment standpoint," he said.

UPMC has more than 48,000 employees, including about 2,000 doctors. Its policy on military service exceeds legal requirements, Mr. Galley said, and provides employees called to duty up to $5,000 a month to offset the difference between military and civilian pay.

"We have the feeling that everyone needs to do his part," he said. "From the broader spectrum of things, doctors are important to the military in healing soldiers. We do our part, regardless of the direct impact on UPMC."

UPMC's policy to support employees serving in the military earned it a Department of Defense certificate of appreciation in March 2007, he said.

Dan Laurent, spokesman for West Penn Allegheny Health System, said six of the health system's physicians have been on active duty at various times since 2002, including two emergency room doctors.

Dr. Hasselman said repeated deployments take a toll on him, his wife, Deirdre, and his career. But the biggest impact is on his four children, who range in age from 2 to 12.

His 12-year-old daughter, Maeve, gets upset when she sees him in uniform, he said, even if he's headed for weekend maneuvers. She fears he'll be gone for months.

In Afghanistan, Dr. Hasselman was assigned to a Combat Army Support Hospital, or CASH.

During the Vietnam War, the military discovered that more lives were saved when doctors were stationed closer to the battlefield. While in Afghanistan, near Kabul, Dr. Hasselman said, he treated many children injured by land mines, along with civilians and soldiers.

Despite the destruction he saw, his first deployment gave him insights into American life by noting the conditions in which people in other countries live.

"It brought home what war really means," he said. "I have my own children, and when you see a child ripped to shreds by a land mine, it really hits home."

Dr. Hasselman said one medical colleague was killed in Afghanistan.

He barely avoided injury in Iraq in 2004 when his convoy was attacked, injuring several colleagues. He was assigned to an 18-member mobile medical team that established an operating room and recovery room inside a tent on the edge of battle.

Their mission was to keep soldiers alive so they would survive the half-hour helicopter transport to a medical facility.

"I saw a lot of bad casualties," Dr. Hasselman said. "Basically it goes from boredom to pure chaos. Sometimes you are playing cards and 10 minutes later you are operating for 24 to 48 hours straight."

In 2006, he returned to active duty, but was sent to Fort Irwin in the Mojave Desert in California to fill in for a deployed surgeon.

In Bosnia, Dr. Hasselman said he will treat injured peacekeepers along with civilians and children who are victims of land mines that still dot the landcape of the European nation long plagued by ethnic conflict.

Now a lieutenant colonel, Dr. Hasselman said he's fulfilling the responsibility he undertook when he "signed the contract on the dotted line with the military" as a means to help defray the costs of his medical-school education.

Some doctors have lost their private practices due to military duty, he said.

"The first couple of times it's a shock," he said of his deployments. "Now you just shrug your shoulders and say, 'Oh, well.'"

Still his pending return to duty will be "disruptive for everybody," including his patients. One unexpected day off for Dr. Hasselman will disrupt the schedules of 45 patients, he said.

"So imagine what three months does," he said. "It's very, very hard, but I'm fortunate to have great partners."