Coronary artery bypass grafting with a minimized cardiopulmonary bypass circuit: a prospective, randomized trial

Coronary artery bypass grafting with a minimized cardiopulmonarybypass circuit: A prospective, randomized trial Marc P. Sakwa, MD,Robert W. Emery, Francis L. Shannon, Jeffrey M. Altshuler, MD,Dawn Mitchell, RN, Objective: The study was designed to determine differences in blood loss and transfusion associated with a min-imized cardiopulmonary bypass circuit versus a standard bypass circuit.
Methods: From February 2005 through April 2006, 199 patients were randomized to undergo coronary arterybypass grafting with a standard cardiopulmonary bypass circuit (Medtronic, Inc., Minneapolis, Minn) or a min-imized bypass circuit, the Medtronic Resting Heart Circuit. Laboratory perimeters (hemoglobin and plateletcount), were measured at baseline, after initiation of cardiopulmonary bypass, and on intensive care unit admis-sion. Lowest values recorded were noted. Blood administration was controlled by study-specific protocol orders,(transfusion for hemoglobin<8mg%). Patient demographic data were retrieved from the Society of Thoracic Sur-geons database. Blood product administration was recorded during hospital admission, and chest tube drainage astotal output collected from operating room to discontinuation. Continuous variables were tested with a Wilcoxinrank test, and categoric variables with X2 and Fisher’s exact tests.
Results: Hematocrit, equivalent at baseline, was higher in minimized circuit cohort at lowest point during cario-pulmonary bypass (31.5% Æ 3.9% vs. 25.5% Æ 3.7%), after protamine (31.6% Æ 3.9% vs 29.2% Æ 3.7%), and onintensive care unit arrival (35.2% Æ 4.1% vs 31.8% Æ 3.5%, P < .001). Similarly, platelet count was higher inminimized circuit group on intensive care unit arrival, as was lowest platelet count recorded (170 3 103 Æ 48cells/mm3 vs 107 3 103 Æ 28 cells/mm3, P<.0001). Time to extubation was shorter in minimized circuit group(848 Æ 737 minutes vs. 526 Æ 282 minutes, (P<.01), and total chest tube drainage was lower (1124 Æ 647 mL vs.
506 Æ 214 mL, P<.01). Fewer red blood cells (148 vs 19 units) were given in minimized circuit group (P<.0001).
Conclusions: A minimized cardiopulmonary bypass circuit provides less hemodilution, platelet consumption,chest tube output and lower post-operative blood loss than standard cardiopulmonary bypass. Red blood cellusage was also less. All differences are advantageous.
Since its introduction in the 1950s, cardiopulmonary bypass some of these concerns, surgeons initially began doing cor- (CPB) has allowed the development of heart surgery, which onary artery bypass grafting (CABG) procedures without the has become the most common of surgical procedures per- use of CPB (off-pump CABG, or OPCDuring the formed on a global basis.Even though CPB has been 1990s, OPCAB became popular; because of the technical used in millions of cases during the past 56 years, there difficulties encountered in this procedure, however, as well are still unsolved problems, many of which have been eluci- as a questionable effect on long-term graft patency, OPCAB dated in the past decade. These problems include but are not is currently performed in fewer of 25% of CABG proce- limited to hemodilution, complement and white cell activa- dures.A further means of combating the side effects of tion with systemic inflammatory response, platelet activa- CPB has been the development of minimized circuits.
tion, the need for intensive anticoagulation, systemic organ These circuits minimize foreign surface–blood interaction dysfunction, and the frequent need for blood and blood prod- and are heparinized from tip to tip. The tubing length has ucts to control postbypass bleeding or blood Atrial been shortened to decrease crystalloid prime. Importantly, fibrillation (AF), the most common untoward event after the use of cardiotomy suction is eliminated or minimized, heart surgery, has also been related to CPB.To address and an active air-removal device is added to this closed cir-cuit. To evaluate the potential advantages of a minimizedcircuit relative to a standard CPB (SCPB) unit, a prospective, From the Division of Cardiovascular Surgery, William Beaumont Hospital, Royal Oaks, Mich,a and the Division of Cardiovascular Surgery, St Joseph’s Hospital, Supported by an unrestricted grant from Medtronic Inc to the Beaumont Research Received for publication April 17, 2008; revisions received Aug 4, 2008; accepted for After investigation review board approval was received, 199 patients older than 40 years who were to undergo first-time CABG were randomly Address for reprints: Robert W. Emery, MD, 640 Jackson St, MS: 11503K, St Paul, assigned to the use of a Medtronic Resting Heart (RHC) minimized circuit (Medtronic, Inc, Minneapolis, Minn) or a standard Medtronic CPB circuit (SCBP) at the time of surgical scheduling by means of computer-generated 0022-5223/$36.00Copyright Ó 2009 by The American Association for Thoracic Surgery randomization cards sealed in envelopes. The study was conducted from February 2005 through April 2006. Exclusionary criteria included The Journal of Thoracic and Cardiovascular Surgery c Volume 137, Number 2 CABG ¼ coronary artery bypass graftingCPB coagulopathy (international normalized ratio >2), emergency surgery, andsurgery expected to last longer than 6 hours. Additionally excluded were pa-tients who received 11b/111a platelet inhibitors, clopidogrel, or thrombo-lytic therapy within 5 days of surgery; those who showed evidence ofventricular or aortic aneurysm or ventricular thrombus; and those who re-quired other concomitant therapy. Aprotinin was not used.
Operating personnel could not be blinded to circuit randomization. Ex- tubation was carried out by intensive care unit (ICU) intensivist staff accord-ing to the Beaumont Hospital protocol for all patients undergoing heartsurgery. The ICU physicians were aware that the patients were in theCPB study, but did not know which circuit had been used. The study pa-tients represented fewer than 20% of the heart operations conducted during FIGURE 1. Medtronic Resting Heart circuit (Medtronic, Inc, Minneapolis, Transfusion of red blood cells was controlled intraoperatively and post- operative by a study-specific protocol to administer blood if hemoglobin fell tip to tip with a Carmeda heparin surface. Our circuit included a Trillium- below 8 mg/dL in both groups. There were no protocol violations.
coated (BioInteractions Ltd, Reading, UK) reservoir limited to aortic root Intraoperative fluids were limited by protocol, and perfusion pressure was maintained during retrograde autologous priming (RAP) by pressor ad- Heparin was administered (350 units/kg) to maintain activated clotting ministration. RAP was discontinued if patient hypotension related to hypo- time greater than 400 seconds. Standard aortic and venous cannulations were undertaken, and in the RHC group kinetic assistance was used for ve-nous drainage (40–50 mm Hg suction). After cannulation, RAP was used to displace all but 300 mL of crystalloid prime in the RHC to a bag reservoir, Laboratory parameters recorded included hematocrit on entry to the op- which was separated from the circuit and reinfused to the circuit after CPB, erating room, after the administration of heparin, at its nadir during CPB, displacing blood from the tubing. All salvaged cells were washed and rein- after protamine administration and, on arrival at the ICU. Platelet count fused. In contrast, the Medtronic SCPB circuit, as noted, used the same bio- was measured at baseline, on admission to the ICU, and as the lowest plate- pump and oxygenator but did not have an active air-removal system. The let count recorded during the hospital stay.
SCBP membrane oxygenator and reservoir were Trillium coated. RAP During the hospital stay, the total numbers of units of blood and blood prod- was also used in the SCBP cohort; because of patient hypotension, however, ucts were recorded, and the timing of product administration was noted. Chest only about half of the 1850-mL volume could be displaced.
tube drainage was recorded as total output collected from the operating roomdrainage initiation to chest tube discontinuation, and extubation time was mea- sured from arrival at the ICU until the endotracheal tube was removed.
There were 199 patients randomly allocated, 97 to SCPB and 102 to Pertinent demographic data, operative data, and postoperative adverse events RHC. Mean age was 67 Æ 10 years (range 39–86 years). Demographic char- were retrieved from the Society of Thoracic Surgeons database collection.
acteristics of the patients are shown in and the operative proceduresare shown in . The left internal thoracic artery was used in all cases.
Proximal and distal anastomoses were conducted under aortic crossclamp The RHC was selected for use after a large experience with routine heart with the heart stilled by the administration of surgeon-specific cardioplegic surgery. A closed circuit (containing an active air-removal device) with solution. There was no 30-day mortality. One SCBP patient was returned to a centrifugal pump and Carmeda-coated (Carmeda AB, Upplands Va¨sby, the operating room for surgical bleeding. One patient in each group required Sweden) high-efficiency oxygenator forms the core of the system ( The tubing consists of a 48 3 0.375-inch arterial line and 84 3 0.375-inchvenous tubing, as opposed to the SCPB circuit, with tubings 80 3 0.375 in- ches and 120 3 0.5 inches, respectively, thus minimizing crystalloid prim- Continuous variables were tested with a Wilcoxon rank test, a nonpara- ing volume to approximately 900 mL versus 1850 mL. Because of the metric approximation of the t test. Categoric variables were examined with shorter tubing length, the circuit has to ‘‘nestle’’ closely to the patient, mak- a c2 test; otherwise, a Fisher exact test was used. Values are expressed as ing the vertical array an important space-saving feature. The RHC is coated The Journal of Thoracic and Cardiovascular Surgery c February 2009 TABLE 1. Demographic characteristics by circuit type TABLE 3. Hematologic parameters by circuit type Data are mean Æ SD. CPB, Cardiopulmonary bypass; SICU, surgical intensive care P not significant for all comparisons.
Several models of minimized CPB circuits have been de- veloped and used on a global basis, although as yet for a mi- CPB times were similar between groups (76 Æ 20 minutes exposure for complete revascularization and, in more than for SCBP and 75 Æ 20 minutes for RHC, P>.05). As shown 1500 cases, found neither systemic injury nor occult air em- in , the hematocrit was significantly higher at all bolism, consistent with other A minimized cir- times after the initiation of CPB with the RHC as opposed cuit has been used in all forms of heart surgery, including to the conventional circuit. Similarly, platelet count was CABG, aortic valve replacement, and robotically enabled higher in patients in whom the RHC was used at all times mitral valve surgery.This randomized trial confirms after baseline. The times to extubation were 848 Æ 737 min- previous non-American studies indicating that less blood utes in the SCBP group and 526 Æ 282 minutes in the administration is needed after minimized circuit use, with RHC group (P < .01). Total chest tube drainage in the less blood loss during the immediate postoperative pe- SCPB group (1124 Æ 647 mL) was greater than that in riod.This is of particular importance because the ad- the RHC group (560 Æ 214 mL (P < .001). In addition to ministration of red blood cells can increase postoperative the blood count being higher in patients in the RHC group, morbidity and mortaliEven after a successful surgical more patients in the SCBP group required the use of red outcome, red blood cell transfusion has also been shown to blood cells, and a greater number of red cell units were given reduce long-term survival.Thus it is important to eliminate both on bypass and during the hospital stay in the SCBP group (The use of platelets in the operating room The salutary effect of the minimized circuit is likely due to (8 vs 3 patients) and in the ICU (4 vs 3 patients) was not sta- several factors. First, hemodilution is minimized by the tistically different (P>.5) for SCBP versus RHC. Similarly, shortened tubing length and the smaller inner diameter of the use of fresh-frozen plasma was minimal, with a total of 5 tubing used, thus not only maintaining a higher hematocrit units versus 1 unit for SCBP and RHC groups, respectively.
during the operative procedure and after CPB but minimiz- Cell salvage reinfusion was not different between the RHC ing the dilution of coagulation factors. Along with minimiz- and SCBP groups (716 Æ 256 mL and 810 Æ 346 mL, ing the blood–foreign surface interface, the shortened tubing P>.05). Postoperative AF occurred in 16% of the patients, with its tip-to-tip heparin coating also minimizes platelet ac- 14% in the RHC group and 19% in the SCBP group, with tivation. Because of the previously mentioned factor, less in- the difference not reaching significance. Cerebrovascular tensive anticoagulation is necessary during the CPB run, accidents were equally distributed, with 2 events in each enabling better postoperative hemosIn our experi- group, and were all minor, requiring no therapy. There ence, approximately two thirds of the traditional hepariniz- were no postoperative sternal wound complications.
ing dose for the SCPB circuit is used.RAP is also an TABLE 2. Number of grafts per procedure by circuit type The Journal of Thoracic and Cardiovascular Surgery c Volume 137, Number 2 Second, the effect of the minimal circuit volume and ret- rograde autologous priming may be obviated if too much crystalloid volume infusion is administered before and dur-ing the case. In this study, fluid was controlled by protocol, and perfusion pressure was maintained during RAP by pres- Finally, because kinetic assistance is necessary, emptying important factor in red blood cell conservation and minimi- of the heart with decreased perfusion flow can at times be zation of hemodilution; however, RAP was used in all cases difficult. One needs to ensure a complete seal around and in both groups, yet hemoglobin was higher and red blood proper positioning of the venous drainage cannulas to prevent cell use lower with the RHC at all times after the initiation air entering the circuit. and the surgeon must maintain active of CPB. Thus RAP alone cannot explain all the salutary ef- observation on the heart should the right atrium or right fects of the minimized circuit. Finally, because of the mini- ventricle dilate with undrained volume, communicating with mized closed circuit, the heparin coating, and, importantly, the perfusionist to improve drainageThere are specific the decreased air–blood interface, the activation of white instances—including the administration of cardioplegic solu- blood cells releasing inflammatory factors is minimized.
tion, discontinuation of vent drainage, and, importantly, car- Earlier extubation is likely related to less hemodilution and diac manipulation, particularly pulling the heart superiorly white blood cell activation, consequently resulting in less and to the right for access to the circumflex coronary artery system–that can impede venous drainage and lower perfusion Immer and colleaguesfound improved myocardial pro- flows. Drainage issues can also occur with vigorous traction tection in patients undergoing surgery with the minimized on the left atrium during mitral valve surgery. Active commu- circuit as opposed to SCBP. In addition to improved protec- nication among all portions of the surgical team is mandatory.
tion, patients with the minimized circuit had less weight gain, Air entry to the RHC was not encountered. The active air- and the authors believed these facts to be primarily responsi- removal system cleared any air that might enter the venous ble for the lower incidence of postoperative new-onset AF in cannula and obviated, even eliminated, the occult air embo- their minimized circuit patients. Koch and lization that has been seen with SCBP.
found red blood cell transfusion to be associated with an in- In summary, the RHC offers a viable alternative to the creased risk of AF. We found no difference between groups SCPB circuit. It has been associated with less postoperative in the incidence of AF. In patients at higher risk for AF, how- blood loss, lower transfusion rates, and earlier extubation, ever, the impact of a minimized circuit may be more notice- while allowing adequate exposure for cardiac surgical pro- able. Other reports have indicated that the minimized circuit cedures. This was a series of low-risk CABG surgical pa- offers similar decreases in all the previously mentioned pa- tients, and those in populations at higher risk may achieve rameters, which is more similar to OPCAB surgery than to SCBP; however, the use of RHC facilitates complete revas-cularization, especially for complex anatomy or unstable We acknowledge the work of Nicholas A. Tepe, MD, Phillip L.
Robinson, MD, Joseph S. Bassett, MD, Goya V. Raikar, MD, Mark The systemic inflammatory response is the result of the Pica, RN, and Joan Benedetti, RN, without whose efforts the pro-ject would be incomplete.
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The Journal of Thoracic and Cardiovascular Surgery c Volume 137, Number 2

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