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Ann Thorac Surg 2007;83:586-591
© 2007 The Society of Thoracic Surgeons
a Department of Cardiac Surgery, San Raffaele Hospital, Milan, Italy
b Department of Cardiac Anesthesiology, San Raffaele Hospital, Milan, Italy
Accepted for publication September 11, 2006.
* Address correspondence to Dr Verzini, Department of Cardiac Surgery, San Raffaele Hospital, Via Olgettina, 60 20100 Milan, Italy (Email: verzini.alessandro{at}hsr.it).
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Abstract |
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METHODS: Forty consecutive patients undergoing isolated aortic valve replacement at a single institution were randomly assigned to either miniaturized closed circuit cardiopulmonary bypass with the Maquet-Cardiopulmonary (Rastatt, Germany) minimal extracorporeal circulation (MECC) system (study group B, n = 17) or standard cardiopulmonary bypass (control group A, n = 23). The MECC system is a low priming circuit without blood-air interface. Technical feasibility, in particular the potential entry of air in the circuit, and clinical results were prospectively evaluated.
RESULTS: Demographic characteristics and surgical data were similar in both groups. Patients in the study group showed reduced chest tube drainage (217 ± 62 mL vs 420 ± 219 mL, p < 0.05) and blood transfusion requirements (5.1% vs 43.4%, p < 0.02) compared with patients in the control group. Moreover, the study group showed significantly higher time course of hematocrit at all time points during the operation and longer hospital stay (p < 0.02) than the control group; similarly, in the study group patients’ platelet count in intensive care unit admission was significantly higher than the control group (140 ± 29 x 109/L vs 119 ± 37 x 109/L, p < 0.05). Peak postoperative troponin C release was significantly lower in the study group (4.74 ± 2.82 vs 8.43 ± 6.25 ng/dL, p < 0.033). One patient undergoing the MECC system operation showed a major neurologic event on postoperative day four, which was probably secondary to severe aortic calcification.
CONCLUSIONS: The MECC system is suitable for aortic valve replacement and provides better clinical results than standard cardiopulmonary bypass as regards blood transfusion requirements, platelets consumption, and myocardial damage.
Despite advances in perfusion, anesthesiologic procedures, and surgical techniques, cardiopulmonary bypass (CPB) is still reported to induce inflammatory reactions that may lead to postoperative morbidity [1]. In coronary artery bypass grafting (CABG) procedures, the off-pump technique [2, 3] is used to prevent CPB-induced inflammatory response but in open heart surgery this is still an outstanding problem. Cardiac surgery and CPB trigger a systemic inflammatory response largely caused by the contact of blood with foreign surfaces and recirculation of activated shed mediastinal blood [3, 4].
A novel technique based on minimal extracorporeal circulation (MECC) was successfully used in CABG to minimize the detrimental effects of extracorporeal circulation [5–8]. Minimal extracorporeal circulation was shown to provide hemodynamic stability, together with an extensive biocompatibility ensured by the complete coating of the CPB system, lines, and cannulae [9, 10]. The aim of this study was to evaluate the feasibility and safety of the MECC system for aortic valve replacement versus standard CPB.
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Material and Methods |
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All patients underwent preoperative angiogram and transesophageal echocardiography (TEE) to confirm the absence of interatrial or interventricular defect. Patients’ preoperative characteristics in both groups are summarized in Table 1.
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Shed mediastinal blood suction and left heart venting were actively performed with two separated roller pumps. Additionally, blood was aspirated from the operative field with a vacuum suction device, processed in a cell saver (Compact-A; Dideco), and then reinfused into the patient after chest closure.
A standard single left ventricular vent was placed through the right superior pulmonary vein.
In group B a totally coated closed circuit with a centrifugal pump was used (Rotaflow centrifugal pump and Quadrox D membrane oxygenator; Maquet-Cardiopulmonary, Rastatt, Germany). In this group a dedicated circuit was created to obtain complete air-blood separation. The circuit was primed with Ringer’s lactate solution 500 mL (group A). A double vent was used; the first one was placed through the right superior pulmonary vein and the second one through the pulmonary artery. No venous open reservoir was used. The left vent was used only when the heart was completely closed while the right vent was used during the cross-clamp time. The left and right heart blood was withdrawn by the left vent and the right vent and collected into a cell-saver and a vacuum bag, respectively. Then it was directly reinfused into the patient through the venous cannula. All lines and cannulae were treated with Bioline (Bioline Jostra AG, Hirrlingen, Germany) coating (Fig 1).
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Anesthesia Management
All patients received standard premedication (morphine 0.1 mg/kg intramuscularly, scopolamine 0.25 mg intramuscularly, diazepam 5 to 10 mg orally) one hour before surgery. Induction of anesthesia was performed with fentanyl-propofol and orotracheal intubation facilitated with pancuronium (0.1 mg/kg) in both groups. Anesthesia was then maintained with propofol (2 to 3 mg/kg/hour), isoflurane (end-tidal concentration <1 minimal alveolar concentration) and additional doses of fentanyl up to 20 µg/kg.
High systemic vascular resistances, which condition decreased pump flow, were treated with sodium nitroprusside. Insufficient venous return was managed using fluid infusion, small doses of vasoconstrictors, the Trendelenburg position, and by checking if the venous cannula position was appropriate. Prior to institution of CPB, patients received intravenous porcine heparin (300 IU/kg of body weight) and additional doses were administered during CPB (5,000 IU) if necessary, to maintain the activated clotting time greater than 480 seconds (ACT II; Medtronic, Minneapolis, MN). After CPB termination and surgical hemostasis, heparin was neutralized with protamine sulfate (1:1 ratio). All patients received intraoperative infusion of tranexamic acid (1g in 20 minutes before skin incision, followed by a continuous infusion of 400 mg/hour until completion of surgery) according to our institutional protocol. At the end of surgery patients were maintained sedated, mechanically ventilated, and transferred to the intensive care unit (ICU). Extubation and discharge from ICU were performed according to clinical criteria. Intraoperative and postoperative criteria for allogenic transfusions were standardized; hematocrit value less than 25%.
Statistical Analysis
Variables are reported as mean ± SD. Baseline characteristics and outcome were compared using the 
2 analysis for continuous categoric data and the Student t test for continuous variables. Differences were considered significant only with a p value less than 0.05.
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Results |
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Comment |
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Marked hemostasis and inflammation abnormalities are induced by cardiac surgery with CPB. These phenomena are caused by the contact of blood with the large nonendothelial surfaces of the extracorporeal circuit, the release of tissue factor due to surgical trauma, the reinfusion of tissue factor and activated coagulation factors with mediastinal shed blood, the shear forces generated by cardiotomy suction, and the mechanical alteration of corpuscular blood elements due to mechanical propelling devices [13–15]. Sequelae include thromboembolism, inflammation, hemorrhage, blood transfusion requirements, and eventually, organ damage and death.
Cardiopulmonary bypass makes the patient sick; however, it does not make him as sick as it was formerly thought. Indeed, intensity of coagulation and inflammatory responses to extracorporeal circulation are affected by many variables, which largely influence postoperative morbidity. Some of these variables are beyond the clinician’s control (eg, patient characteristics) while others can be manipulated by the clinician and this contributes to increasing clinical evidence [16, 17]. It is suggested that the amount of circulating thrombin and the severity of coagulopathy associated with CPB are substantially decreased by the fact that blood from the operative field is not added to the perfusion circuit, which is obtained by using a closed system. Besides its effects on coagulation and hemolysis, the recirculation of aspirated blood contaminated by tissue contact also decreased mean arterial pressure as a result of prostacyclin and prostaglandin E2 release [18].
Other detrimental effects of shed blood have been identified as induced by lipid microembolization [19], activated complement [20], or cytokine release by pooled leukocytes [21]. The important sequelae of increased postoperative blood loss caused by activation of fibrinolysis and platelet dysfunction in shed blood have already been demonstrated [22]. Therefore, avoidance of shed blood recirculation has been proposed to minimize these effects during conventional CPB. Unfortunately, the amount of blood drained from the operative field can be high, especially in valve procedures; therefore, a considerable loss of autologous blood occurs. To solve this problem, a shed blood separation system was developed. The separated shed blood can be processed in a cell saver to retrieve red blood cells for subsequent administration while potentially detrimental humoral factors are eliminated [23, 24]. Nevertheless, this is not a quick procedure and it might compromise patients’ safety because sustained hypoperfusion or low hematocrit level might ensue. A miniaturized circuit is an avenue out of this dilemma as the degree of hemodilution is decreased and therefore there is no compelling need to reinfuse the patient’s own blood.
In the control group, activated shed blood was sucked up from the surgical field into the CPB circuit, whereas in the study group it was washed in a cell saver before reinfusion [25].
The feasibility of this perfusion technique in open heart surgery raises doubts. However, left heart venting through the pulmonary artery trunk allows to avoid blood-air contact; after myocardial reperfusion and aortic cross-clamp release the vent placed through the right superior pulmonary vein can be used with minimal aspiration and reduced blood-air contact, which should not jeopardize the benefits of this technique.
Gaseous microembolization is considered as a main cause of neurologic injury in cardiac surgery, and it is mainly attributed to the CPB system design. On the one side, Liebold and colleagues [26] showed that a closed minimized bypass circuit in CABG patients was associated with a decreased incidence of cerebral microembolization as compared with the traditional open CPB system. They speculated this was mainly due to the closed CPB design, without cardiotomy suction and venous reservoir. Moreover, the use of a membrane oxygenator with a tight hollow fiber membrane was regarded as beneficial. The authors concluded that there was no additional source of microgaseous emboli when kinetic venous drainage was used.
On the other side, Nollert and colleagues [27] reported two dangerous air leaks in their closed CPB circuit and their study was prematurely discontinued because the safety of the system gave cause for concern. However, these adverse events resulted from two preventable mishaps: a leaky atrial purse-string and a defect in the right ventricle unintentionally caused by the preparation of an intramyocardial left anterior descending (coronary artery). The neurologic event that occurred on postoperative day four was not related to the perfusion technique.
Other studies on miniaturized closed system support our findings; Fromes and colleagues [28] showed a reduction of inflammatory response after coronary bypass grafting with total minimal extracorporeal circulation. Nevertheless, no differences regarding clinical outcome were reported.
Remadi and colleagues [29] also prospectively evaluated the MECC system for aortic valve replacement and showed better clinical results with preservation of renal function, decreased cardiac enzyme release, and better platelet count preservation. Their study also showed that hemodilution and blood transfusions could be potentially avoided with this perfusion approach.
Hemodilution is unavoidable in crystalloid prime CPB because of mixing of the crystalloid prime solution with the patient’s blood. Nevertheless, some studies [30, 31] reported adverse effects like excessive hemodilution and subsequent packed RBC transfusion requirements during CPB. The on-pump nadir hematocrit value can widely change according to patient body mass index (or blood volume), and pre-CPB hematocrit level, as well as circuit prime volume [31, 32].
Also, during CPB a lower hematocrit value is a potentially changeable risk factor. Reduced hemodilution and reduced blood transfusion requirements might result from redesigning and using reduced size CPB circuits, that decrease tubing length and diameter and surface coating, as well as from eliminating the cardiotomy reservoir. Miniaturized circuits feature dramatic reduction in pump prime, tip-to-tip coating, and elimination of cardiotomy suction. Our findings awaken the hope that this intervention may effectively minimize some key events of CPB-triggered inflammatory pathways and further improve the safety of aortic valve replacement.
Some limitations to our study should be recognized. First, the sample was not large enough to demonstrate the system safety. Second, the potential clinical results cannot set aside the need for better perfusionist skill and bigger efforts to assure the safety of the procedure.
In conclusion, our study shows that a miniaturized closed CPB circuit can be safely used for aortic valve replacement and this technique entails beneficial effects to the patients’ outcome.
Although we are aware that a sample of 17 patients is too little to provide final results and MECC requires more experience and attention than traditional CEC, we think this technique could be an additional step toward further reduction of surgical injury in selected patients with a high risk of bleeding (eg, patients with cirrhosis, liver disease, and thrombocytopenia). It is speculated that these positive results might be explained by using a totally biocompatible circuit, avoiding shed blood reinfusion and reducing hemodilution and blood transfusion requirements. No apparent device-related adverse events were reported.
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This article has been cited by other articles:
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  R. H. Habib, A. Zacharias, and T. A. Schwann Minimally Invasive Closed Circuit Versus Standard Cardiopulmonary Bypass: Is It Renoprotective? Ann. Thorac. Surg., October 1, 2007; 84(4): 1426 - 1427. [Full Text] [PDF]
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= group A, conventional cardiopulmonary bypass; • = group B, minimal extracorporeal circulation.)