Interact CardioVasc Thorac Surg 2006;5:680-682. doi:10.1510/icvts.2006.129999
© 2006 European Association of Cardio-Thoracic Surgery
Work in progress report - Cardiopulmonary bypass |
Preliminary experience with the mini-extracorporeal circulation system (Medtronic resting heart system)
Hiroyuki Kamiya*,
Theo Kofidis,
Axel Haverich and
Uwe Klima
Division of Thoracic and Cardiovascular Surgery, Hannover Medical School, Carl-Neuberg-Strasse 1, 30625 Hannover, Germany
Received 7 February 2006;
received in revised form 24 August 2006;
accepted 25 August 2006
*Corresponding author. Tel.: +49 511 532 6581; fax: +49 511 532 5404.
E-mail address: hkamiya88{at}yahoo.co.jp (H. Kamiya).
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Abstract
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A compact cardiopulmonary bypass (CPB) utilized by closed circuit system with minimized priming volume can be a solution to reduce adverse effects of CPB, and the Resting Heart System (RHS; Medtronic, Inc, Minneapolis, MN, USA) is the newest one on the market. We performed CABG with RHS in 10 patients, and report here our preliminary experiences with RHS in comparison with conventional CPB. Twenty patients who underwent isolated CABG were randomized into two groups; RHS group (n=10) with the use of RHS and Conventional group (n=10) with the use of a conventional CPB. There were no significant differences of preoperative patient characteristics in both groups. The mean number of grafts was 2.7±0.6 and 2.7±0.8 (P=0.38), the mean aortic clamp was 32±11 and 35±11 min (P=0.35), and CPB times were 68±25 and 72±24 min (P=0.82) in RHS and Conventional group, respectively. All patients but one had no complications and survived in both groups. One patient in RHS group died suddenly on the 5th postoperative day after uneventful postoperative course. Postoperative leukocyte count at 6 h after the operation and value of the C-reactive protein were 11200±2310 and 13300±3990/mm3 (P=0.10) and 44.4±9.7 and 65.3±18.5 mg/l (P=0.045) in RHS and Conventional group, respectively. CABG operations could be safely performed using the RHS with a comfort level similar to standard CPB.
Key Words: Cardiopulmonary bypass; Coronary artery bypass grafting; Mini-circuit
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1. Introduction
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Considering the adverse effects of cardiopulmonary bypass (CPB) including inflammatory response, and renal, pulmonary, and neurologic dysfunction, off-pump coronary artery bypass grafting (OPCAB) was recently developed [1,2]. However, the technical difficulties of OPCAB resulting from hemodynamic instability due to cardiac displacement, myocardial ischemia during anastomoses, and incomplete bloodless surgical field have limited its popularization, and coronary artery bypass grafting (CABG) with CPB and cardioplegic arrest is still the standard method of choice in many institutes.
A compact CPB utilized by closed circuit system with minimized priming volume can be a solution to reduce adverse effects of CPB. A limited number of such devices have been commercially available, and the Resting Heart System (RHS; Medtronic, Inc, Minneapolis, MN, USA; Fig. 1) is the newest one on the market. We performed CABG with RHS in 10 patients, and report here our preliminary experiences with RHS in comparison with conventional CPB.
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2. Materials and methods
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In the present study, 20 patients who underwent isolated CABG were randomized into two groups; RHS group (n=10) with the use of RHS and Conventional group (n=10) with the use of a conventional CPB. The aim of this study was explained to all patients and informed consent for this study was obtained from all of them. Patient characteristics in both groups are presented in Table 1. Patients received hydroxyzine (1 mg/kg) for premedication before arrival in the operating room. The anesthesia protocol was similar for all the patients. Anesthesia was induced with intravenous sufentanyl and propofol. Muscle relaxation was achieved with pancuronium. After intubation, anesthesia was maintained with a combination of sufentanyl and propofol. A full dose heparin (3 mg/kg) was given, and the activated clotting time was maintained above 400 s. CABG operations were performed through a median sternotomy and under aortic cross-clamping. Warm hyperkalemic blood cardioplegia was delivered intermittently through an antegrade route. Partial aortic cross-clamping was carried out for proximal anastomoses of vein grafts, if needed.
2.1. The resting heart system
The RHS is an integrated, low-prime arrested semi-closed-loop CPB system, offering minimal air–blood interface and elimination of anti-form agents. The priming volume of this circuit is 990 ml and the membrane surface area for gas exchange is 2.5 m2. Primary blood contact surfaces of this RHS are coated with heparin (BioActive Surface, Carmeda, Stockholm, Sweden) throughout to provide thromboresistance and biocompatibility by mimicking critical characteristics of vascular endothelium, and 150 U/kg dose of intravenous heparin is required to use this system. The RHS can offer blood flow from 1.0 to 6.0 l per minute. A vent circuit is available in the RHS and it was used in this study. The blood from this vent is reinjected into the pump inflow. The absence of cardiotomy reservoirs limits the artificial surface-blood contact that occurs secondary to aspiration of blood. Accordingly, an erythrocyte-scavenging device is necessary when using the RHS. The blood in the pericardial space is aspirated, treated, and reinfused with the erythrocyte-scavenging device. The key of this system lies in its unique technology to detect and remove small air bubbles in the circuit to reduce embolic events. If air is entrained from the right atrium, visual and audible alarms alert the surgical team to the condition so that it can be quickly remedied. Two pairs of ultrasonic fluid sensors in the venous air removal device (VARD) detect air at the inlet of the device. When air enters the VARD through the venous return line, air bubbles are detected and the device exerts evident visual and audible indications while removing the venous air. The air is automatically removed from the VARD until its sensors detect no remaining air/blood mixture in the upper area of the device, and then it returns to normal setting.
2.2. Conventional CPB
The priming volume amounted to 1540 ml. The line was not coated with heparin. An oxygenator (Medos Hilite 7000, Stolgerg, Germany) and a standard roller pump were included in the set. An arterial filter was used. The intrapericardial suction device was used as usual.
2.3. Statistical analysis
Continuous data are presented as mean±S.D. Unpaired Student's t-test was used for analysis with the assumption of a normal distribution. Further analysis was carried out using a distribution-free test, Mann–Whitney U-test. A P-value of <0.05 was considered a statistically significant difference. Analyses were performed using SPSS software (SPSS Inc, Chicago).
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3. Results
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The mean number of grafts was 2.7±0.6 and 2.7±0.8 (P=0.38), the mean aortic clamp was 32±11 and 35±11 min (P=0.35), and CPB times was 68±25 and 72±24 min (P=0.82) in RHS and Conventional group, respectively. Intraoperative blood transfusion was done when the hematocrit value was under 25%, and it was required in 4 patients of RHS group and 5 patients in Conventional group (P=0.65). Retransfused volume using the erythrocyte-scavenging device was 252±186 ml in the RHS group. One patient who was transferred to the ward on the 1st postoperative day and did well, died suddenly on the 5th postoperative day due to cardiac arrest. The autopsy revealed a severe atherosclerosis of all the vascular system and patent grafts. Atrial fibrillation occurred in 2 patients of RHS group and 3 patients in Conventional group (P=0.61) and was treated with ß-blocker. There was no other complication in both groups. The mean intubation time was 5.9±3.1 and 5.0±3.4 min (P=0.46), and the mean stay of intensive care unit was 16.2±5.0 and 15.8±6.3 h (P=0.45) in RHS and Conventional group, respectively.
Additionally, several biological markers were evaluated (Table 2). The increase of leukocyte count was slightly lower in RHS group (P=0.10), and the C-reactive protein level was significantly lower in RHS group (P=0.045). However, other measured markers (platelet count, creatinine kinase, and creatinine kinase-MB) showed no differences between the groups.
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4. Discussion
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In the present study, we were able to perform CABG operations using the RHS with a comfort level similar to conventional CPB. Although one patient died on the 5th postoperative day after complete uneventful postoperative course, the surgical results were considered to be acceptable in comparison to those with conventional CPB. The lower levels of postoperative leukocyte count and C-reactive protein in patients treated with RHS suggest that RHS can contribute to suppression of the inflammatory syndrome after the use of the CPB.
It has been investigated that factors as follows can reduce CPB-related morbidity; limit hemodilution [3], minimize circuit surface area [4], use a heparin biocompatible surface for circuit blood contacting surfaces [5], reduce shear stress and turbulence [6], use closed-to-air systems to limit an air–blood interface [7]. The RHS consists of a heparin coated closed circuit with minimal priming volume and a centrifugal pump, aiming to achieve those factors. We were able to safely use the RHS in the CABG surgery without any intraoperative problems in this series. This is the first report on the RHS, and clinical effects of the RHS on reducing adverse effects due to CPB should be investigated in further studies. However, it can be assumed at least from this study that it is safe to introduce the RHS in routine clinical settings.
As a similar compact CPB system, the minimal extracorporeal circulation (MECC; Jostra AG, Hirrlinggen, Germany) system has been formerly available on the market. Fromes et al. demonstrated that the MECC system could limit inflammatory reaction including IL-6, TNF- , and elastase release compared to standard CPB system in CABG surgery [8]. Remadi et al. presented lower C-reactive protein and troponin I level in the MECC group compared to the standard CPB group in patients receiving aortic valve replacement, although operative mortality did not differ between the two groups [9]. In the present study, the inflammatory markers (leukocyte counts and C-reactive protein) were lower in RHS group than in Standard group similar to those previous studies with MECC system. However, differing from the MECC system, the RHS has a unique technology to detect and remove small air bubbles in the circuit. The air is automatically removed with the venous air removal device (VARD). Therefore, the RHS may reduce embolic events including neurologic dysfunctions compared to the MECC system, but it should also be investigated in further studies.
In conclusion, we were able to safely perform CABG operations using the RHS with a comfort level similar to standard CPB. It appears that the RHS has potential advantages over conventional CPB, but it should be investigated in further studies.
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Acknowledgements
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We declare that there is no conflict of interest and no source of funding for this work.
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Abstract
1. Introduction