Findings of the study, “Goal-Directed Perfusion Methodology for Determining Oxygenator Performance during Clinical Cardiopulmonary Bypass,” were published in the June 2017 edition of the Journal of ExtraCorporeal Technology.
During open-heart surgery, a cardiopulmonary bypass circuit often provides circulatory support to patients. This heart-lung machine is composed of various essential devices, one of the most important being the oxygenator. It serves as a temporary substitute for patients’ lungs by delivering oxygen to and extracting carbon dioxide from their blood. The challenge is to replicate the gas exchange characteristics of the lungs.
Historically, oxygenators were all “direct contact” by design, meaning they had no intervening barrier between blood and oxygen. But, over the past several decades, new models have emerged that minimize blood contact with the surface area of the device using semipermeable membranes.
The latest generation of oxygenators also includes integrated rather than external arterial line filters as a means to remove air bubbles. But debate persists among perfusionists—the medical specialists who operate the heart-lung machine—about the safety of the design modification and the possibility of blood clotting the arterial filter that would render the oxygenator dysfunctional.
Recent research suggesting adequate oxygen delivery might help reduce the incidence of postoperative kidney dysfunction has given rise to the practice of goal-directed perfusion focused on oxygen delivery. A research team, led by the Medical Department of SpecialtyCare in Nashville, Tennessee, recently compared three commercially available oxygenators on this basis for all adult patients undergoing cardiac surgery with cardiopulmonary bypass at a single center in the U.S.
For this non-randomized, sequential study, 60 patients were matched for disease state and body size into one of three groups based on oxygenator type. Their surgeries took place between January 2013 and July 2014. Among the exclusion criteria were patients undergoing emergent cardiac surgery, and those with congenital heart disease or preoperative anemia. Included patients were operated on by the same surgical team following standardized protocols and were risk-stratified by commonly accepted methodologies.
The Terumo SX18 oxygenator was used for patients in the first study group, and the patients in two other study groups alternatively had the Terumo FX15 or LivaNova Inspire6F. Only the FX15 had the traditional external arterial line filter.
The primary endpoints were oxygenator performance, including fraction of inspired oxygen and ventilating gas flow. The secondary endpoints were fluid management during and after surgery, transfusion rates, and chest tube drainage. All data were obtained from the Perfusion Electronic Medical Record.
Among the differences between the three study groups was that SX18 patients received significantly more clear fluid and total perfusion volume while on the bypass pump. Volumes were also higher among SX18 patients requiring transfusions of blood plasma and platelets. Relative to FX15, higher volumes were likewise seen for those receiving a red blood cell transfusion postoperatively. Additionally, the SX18 group had the highest postoperative transfusion rates.
Compared to the Inspire6F group, SX18 patients had higher volumes of anticoagulants and red blood cells salvaged throughout their procedure. SX18 patients also had a greater volume of salvaged blood returned to them than patients in the other two study groups, and their urine output was higher.
Compared to the SX18 group, the FX15 group had the highest concentration of red blood cells while on the bypass pump and during the early operative period. FX15 patients also had significantly less total chest tube drainage than SX18 patients.
The Inspire6F had the highest performance for gas transfer relative to the other two oxygenator models.
Clinicians have been slow to embrace oxygenators using integrated arterial line filters in part because of the scarcity of objective research evaluating their gas exchange performance. Decisions about oxygenator technology are therefore based largely on cost rather than value.
The study under discussion brings into question the hoped-for benefit of the dual reservoir feature of the Inspire6F in optimizing “autologous priming.” The latter is a common perfusion practice whereby saline solution in the heart-lung machine gets displaced by patients’ own donated blood before cardiopulmonary bypass begins to lessen the impact on their red blood cell count.
The FX15 and Inspire6F are considered small oxygenators. In a previous study, the FX15 was found to be superior to a similarly sized model when it came to the need for a red blood cell transfusion. The Inspire6F model has also been shown to outperform the FX15 in terms of oxygen transfer but not carbon dioxide removal.
CLINICAL EXCELLENCE IN PRACTICE
Newer generation oxygenators are clinically effective, permitting the safe transfer of gas during cardiopulmonary bypass. The three commercially available oxygenators evaluated exhibit small differences in performance, although the Inspire6F may offer superior oxygen transfer relative to the FX15 and SX18 models.
THE RESEARCH TEAM
At the time of the study, clinicians on the research study team were all affiliated with Pocono Medical Center in East Stroudsburg, Pennsylvania. Three are now full-time members of the SpecialtyCare Medical Department—Alfred H. Stammers, MSA, CCP; Randi Miller, CCP; and Stephen G. Francis, MS, CCP. The other researchers were cardiovascular and thoracic surgeon Laszlo Fuzesi, M.D.; Anthony Nostro, M.D., chief of anesthesiology at Pocono Medical Center; and Eric A. Tesdahl, PhD, senior biostatistician at SpecialtyCare.