Registered nurse Patrice Arrell was ready with her standardized pre-op checklist when the patient arrived at Chester County Hospital on Tuesday morning for an operation to replace his aching right knee.

She made sure that the staff reviewed the 62-year-old's medical history and pre-admission records, and conducted a slew of routine tests. And Arrell herself put a "compression stocking" on the patient's left leg long before he was wheeled off to the operating room.

The tight-fitting hosiery prevents blood from accumulating in an inactive leg. Confirming that it is used, every time, is one of many steps the hospital has devised to lower the risk of potentially deadly blood clots after surgery.

Reducing complications from medical care is a high priority nationwide. Breaking the process into small steps helps identify where problems are likely to occur.

That's how doctors, nurses, pharmacists and other caregivers in this region have been attacking blood clots and other areas of concern.

The clots, which can lodge in leg veins or travel up to form blockages in the lungs, are a relatively rare complication of surgery. But the problem has grown as hospital patients have become sicker.

In 2006, more than 2,000 surgery patients at hospitals in Philadelphia and its Pennsylvania suburbs developed blood clots. That was 14 cases for every 1,000 of those patients, according to an Inquirer analysis of billing records. A decade earlier, the rate was 9 cases per 1,000 surgical patients.

Richard Egen, the patient at Chester County last week, is a manager at vaccine-maker Sanofi Pasteur. He knows that such clots are a risk of joint-replacement operations. But the severe pain in his right knee had recently made it hard to drive, limited his exercise routine, and interfered with his passion: gardening.

"Obviously, I'm nervous," he says as nurses prepared him for surgery. A blood clot, he adds, "is my major concern."

Chester County Hospital is trying to reduce that risk. Last year, it was one of 13 hospitals that participated in a regional effort to lower the incidence of postsurgical venous thromboembolism (VTE) - blood clots that obstruct flow in vessels of either a leg (deep vein thrombosis) or a lung (pulmonary emboli).

The hospitals were part of a broader quality-improvement campaign by the Partnership for Patient Care, a collaborative of local health-care institutions that also worked to reduce patients' falls in the hospitals and confusion when their prescriptions change.

Every year, local hospitals take on one or more of the partnership's initiatives. The choices for 2008: eliminating wrong-site surgery, standardizing the reporting of falls, and preventing bed sores. The collaborative helps hospitals identify and implement so-called best practices - those known to improve patient outcomes.

"The real purpose of our partnership is to bring those practices to a group of hospitals, and, by working together, everyone can adapt them to what works in their individual setting," says Kate Flynn, president of the Health Care Improvement Foundation, which helps lead the effort.

All the hospital systems in Southeastern Pennsylvania took part in at least one of last year's quality-improvement initiatives, and detailed surveys conducted at the start and end of the six-month programs suggest increased use of the best practices.

A true measure of success - actual data on, say, how many patients develop blood clots after surgery - isn't yet available.

Meanwhile, the day-to-day challenge is making sure that the correct actions are taken with every patient before, during and after surgery.

Various national and state campaigns to reduce the risk of blood clots and other complications are keeping the pressure on.

"Setting up systems to ensure delivery of the prophylaxis is key for hospitals," says Geno Merli, chief medical officer at Thomas Jefferson University Hospital and an expert on VTE. "It needs to become foolproof."

An estimated 600,000 Americans a year develop blood clots, and up to a third of them die. Surgery patients make up a very small percentage of the total. Most get the condition after spending many hours without movement - often on long plane rides, as Vice President Cheney had when he developed a clot a year ago.

Trauma and cancer patients are also at high risk of developing such clots. Age is a factor, too, although young people should still take precautions, says John Blebea, chief of vascular surgery at Temple University Health System.

"I was recently on a medical exchange program to China, and every two hours I got up and walked up and down the aisles," he says.

Surgery increases the risk substantially, even in otherwise healthy people. Former Phillies manager and current Boston Red Sox skipper Terry Francona developed a clot in his leg after arthroscopic knee surgery in 2002.

An operation essentially causes trauma to the body, putting the blood in what is called hypercoagulation. Surgery also leaves patients immobile for extended periods of time, slowing blood flow. Both promote clots.

Reducing those risks was already a hospital-wide goal when Egen arrived in West Chester for his knee replacement operation.

After he was wheeled into the operating room, Egen's left foot was wrapped in a mechanism that attaches to an air-pump. This would stimulate blood flow in that leg during the operation on the other.

Every three seconds, the foot pump pressed and released Egen's left foot, as orthopedic surgeon John Benner drilled and sawed, then finally hammered the new right knee in place.

An hour and 45 minutes after the initial incision, Benner's still groggy patient was moved into the recovery room.

As Egen was settled in, registered nurse Betty Blow ran through her post-op checklist. She made sure to attach a pump to his right foot, so both feet would be compressed, one after the other, forcing blood to flow more regularly through extremities that normally are exercised by the leg muscles.

Working on Egen, Blow was cheery, but diligent. She knows the damage a blood clot can do. When Blow was 8 years old, her best friend's mother died of a pulmonary embolism following a hysterectomy.

"I can remember to this day the look on my friend's face," she says.

Egen was transferred from recovery to his own room - and still the nurses, doctors and others weren't finished lowering his risk of a clot.

At 9 the next morning, Egen got his first dose of a blood thinner. Both foot pumps continued to alternate pressure from side to side, helping his blood move along and hindering its tendency to clump together.

At 1:30 p.m., a physical therapist came to the room for Egen's first session. Steadying himself on a walker, Egen moved from the bed to a chair for his therapy.

With each step, the man with the brand new knee reduced his chances of developing a blood clot.