Terumo Cardiovascular Group

Do you know your perfusion circuit's 'net RAP efficiency'?

Sean Murtha, CCP, Director of Perfusion Services at Memorial Regional Hospital and Joe DiMaggio Children's Hospital in Hollywood, Florida, enjoys sharing the results and discoveries of his team's journey to improve patient outcomes. Since 2007, the perfusion team has instituted many changes to reduce donor blood exposure to patients undergoing open heart surgery. Mr. Murtha believes the most significant changes are:

  • selecting the oxygenator membrane and perfusion circuit size based on patient size
  • using a more efficient retrograde autologous prime (RAP) procedure based on a smaller circuit prime volume

Perfusionists recognize that RAP can be more effective with smaller circuits.  Mr. Murtha has developed an awareness of the ratio of circuit prime volume to patient blood volume and how much blood volume is needed for effective RAP. He describes net RAP efficiency as achieving the highest percent RAP efficiency with the lowest percent patient RAP/AAP (antegrade autologous priming) volume. A smaller circuit prime volume makes RAP more efficient and easier to accomplish.

Mr. Murtha's net RAP efficiency formula is: Total RAP/AP Volume divided by Circulating Volume equals Percent RAP Efficiency (higher numbers are most efficient).

New Prescriptive Approach

"Choosing a circuit size in proportion with patient size is more efficient," Mr. Murtha adds. "We see it all the time: the smaller patient can't tolerate a large blood loss during RAP and AAP, and anesthesia just gives back fluids. If anesthesia is not giving fluids back, we maintain higher hematocrit. You can start to see how you can easily reduce hemodilution."

The Memorial Regional Hospital team switched to a low prime volume circuit for patients less than 2.1 M2 — which includes the CAPIOX® FX15 Oxygenator with integrated arterial filter. According to Mr. Murtha, these small patients don't need an oxygenator that flows up to eight liters per minute with its associated high prime volume. In down-sizing the circuit, the perfusion team documented that using RAP and AAP techniques along with the FX15 Oxygenator:

  • decreased circulating prime volume from 1,100 mL to 654 mL — a 41% reduction
  • reduced the patient's exposure to circulating prime volume to 273 mL after RAP/AAP
  • required only 381 mL of the patient's blood volume to achieve an effective RAP/AAP

"We determined 381 mL was our most effective RAP because it's the most volume we can remove from the patient based on our circuit configuration," Mr. Murtha says. "It's about net RAP efficiency, and we now achieve a very high efficiency. It's highly likely perfusionists will find much higher hematocrits by just changing circuit design and techniques to match the patient's size.

Steps to Reduce Blood Transfusions

Prior to selecting the new oxygenator and smaller perfusion circuit, Mr. Murtha had already spent two years analyzing his team's data and making incremental improvements. In 2007, his hospital's Cardiovascular Committee charged the Perfusion and Anesthesia teams with reducing blood transfusions. The clinicians:

  • implemented an evidence-based blood transfusion protocol based on STS (Society of Thoracic Surgeons) recommendations
  • reduced tubing lengths in the perfusion circuit to minimize circuit volume
  • established a protocol to reduce hemodilution involving RAP and AAP techniques

The Cardiovascular Committee held all clinicians accountable to optimize patient care, and therefore Anesthesia became more conservative about giving fluid volume to stabilize the patient. "We tried to set a standard so all anesthesiologists managed the fluid volume in the same way," Mr. Murtha recalls. "With our focus on protocol driven care, everybody became accountable. And everybody got behind it when we started seeing the results."

Mr. Murtha concludes: "You really can optimize cardiac surgery. You just have to start collecting data to see where you're at, and see where you can make your improvements."

For more information:
Visit the Prescriptive Oxygenation webpage
Order the 2010 Optimizing Blood Management CDROM