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Interact CardioVasc Thorac Surg 2009;8:457-466. doi:10.1510/icvts.2008.200857 © 2009 European Association of Cardio-Thoracic Surgery
Can a mini-bypass circuit improve perfusion in cardiac surgery compared to conventional cardiopulmonary bypass?
a Department of Cardiothoracic Anaesthesia, James Cook University Hospital, Middlesbrough, UK Received 15 December 2008; received in revised form 23 December 2008; accepted 27 December 2008
*Corresponding author. Tel./fax: +447801548122.
A best evidence topic in cardiac surgery was written according to a structured protocol. The question addressed was whether the ‘mini-bypass technique’ can give a reduction in complications after cardiac surgery compared to the conventional cardiopulmonary bypass circuit. Altogether 144 papers were found using the reported search, of which 14 represented the best evidence to answer the clinical question. The authors, journal, date and country of publication, patient group studied, study type, relevant outcomes and results of these papers are tabulated. We conclude that 10 out of these 14 studies show reduced hemodilution, 7 show reduced red blood cell transfusion, 2 show reduced fresh frozen plasma use (one showing increased use), and 2 show reduced platelet use. Three studies show reduced postoperative blood loss, but one shows increased blood loss. Three studies show better renal function. Four studies show a better cardiac index and 2 show shorter intensive care unit stay. One study found an increased minute volume and reduced oxygenation for one hour post-mini-bypass. Six studies find significantly reduced inflammatory markers, and 5 measure superior myocardial protection. There are several anecdotal references to a ‘learning curve’ with this technique but no significant morbidity with complications arising from this were found. Mini-bypass seems to be a promising technique with many documented benefits in studies reporting as many as 1000 patients undergoing this technique.
Key Words: Cardiopulmonary bypass; Mini cardiopulmonary bypass; Cardiac surgery
A best evidence topic was constructed according to a structured protocol. This is fully described in the ICVTS [1].
For [patients undergoing on-pump cardiac surgery] is [minimized extracorporeal circulation (MCPB)] superior to conventional cardiopulmonary bypass (CCPB)] in terms of [complications]?
You have just been to a conference where you have talked to a colleague who told you that they are now using mini-bypass, and it is an excellent technique, and very easy to learn with ‘not many’ technical issues. You are very impressed by his description and resolve to look up the literature prior to discussing this technique with your own institution.
Medline 1950 to August 2008 using the OVID interface. [mini$ CPB.mp OR mini$ extracorporeal.mp OR mini$ bypass.mp OR Mini$ invasive closed.mp OR mini$ invasive cardiopulmonary.mp]. In addition, the reference lists of all relevant papers were searched.
One hundred and forty-four papers were found and from these 14 were selected as representing the best evidence on the topic (Table 1).
The criteria were: randomized studies with sample size >20 patients (per group). Non-randomized studies were included when the sample size was large >150 (total).
Huybregts et al. [2] performed a prospective randomized study (PRCT) between the Synergy mini-bypass system (Cobe) and CCPB (conventional CPB). It is the only study where the two circuits were equal in all their components. They found reduced on-pump hemodilution, reduced transfusion of red blood cells (PRBC), fresh-frozen-plasma (FFP), and platelets (PLT), decreased postoperative bleeding and reduced PLT consumption and activation during CPB. They also found reduced inflammatory response [white cell count (WBC) and interleukin-6] and reduced proximal tubular injury and intestinal tissue injury (  NAG, IFAB). Remadi et al. [3] performed a PRCT in 400 patients who underwent CABG with the mini-bypass system MECC and with CCPB. In the MECC group there was less hemodilution and need for transfusion of PRBC during CPB. Postoperatively there was a lower drop in platelets, lower CRP and troponin T, lower incidence of low cardiac output syndrome and need for inotropic support, lower levels of creatinine and urea and lower incidence of neurological complications. Thirty-day mortality was lower in the MECC group (1.5% vs. 2.5%) but that difference was not significant. They also published a smaller PRCT in 100 aortic valve patients showing similar results between groups [21]. Immer et al. [4] studied patients who underwent CABG with MECC or with CCPB. MECC group had: lower peak values of inflammatory markers (IL-6, SC5b-9 and lactoferrin), lower troponin I (cTnI) levels 6 and 24 h postoperatively, and reduced transfusion of PRBC (9.3% vs. 31.9%) postoperatively. They also found better clinical outcome for MECC: shorter duration of ventilation and reduced ICU and hospital length of stay. Wiesenack et al. [5] found comparative length of ICU stay, total hospital stay and 30-day mortality but MECC group had significantly lower morbidity: lower incidence of myocardial infarction (1.9% vs. 3.3%), AF (12% vs. 33%), renal insufficiency (0.8% vs. 3.1%), stroke (1.0% vs. 3.1%), low cardiac output, respiratory insufficiency. They also observed reduced hemodilution and transfusion of PRBC.
Fromes et al. [6] found lower inflammatory reaction (reduced IL-6, TNF Perthel et al. [7] found that MCPB reduces on-pump hemodilution, transfusion requirements and postoperative bleeding. Abdel-Rahman et al. [8] performed a PRCT in CABG operations comparing CorX mini-bypass with CCPB. Hemodilution was greater and Hb values were markedly lower in CCPB group, intraoperative blood loss and FFP transfusion were significantly higher in CorX group. In CorX group pericardial blood was drained exclusively in a cell saver and the amount of retransfused cell-saved blood was also higher. However, the authors observe markedly reduced intraoperative blood loss in the last 50 patients of the CorX group which, as they say, can be explained by the surgeons' learning curve. Markedly reduced inflammatory reaction (p. elastase, complement) and improved myocardial preservation for CorX were found. Marginally longer ventilation times in CorX patients and lower oxygenation index (pO2/FIO2) the 1st hour post CPB (the 3rd hour NS difference), but this did not result in prolonged ICU stay. FEV1 and IVC measured were similar and ICU and hospital length of stay did not differ significantly. Abdel-Rahman et al. [9], in another randomized study found CorX to have a beneficial effect on hemostasis and decreased hemodilution. No difference in transfusion requirements and clinical outcome were found. Beghi et al. [10] found MECC patients to have higher cardiac index and lower SVR and PVR postoperatively and lower plasma-free hemoglobin. Van Boven et al. [11] found reduced PRBC transfusion and milder oxidative stress and alveolar dysfunction for MECC group compared to CCPB. Gerritsen et al. [12] found reduced postoperative mean blood loss and transfusion of RBC and platelets for MECC group than CCPB. Schottler et al. [13] found decreased hemodilution and reduced levels of CK-MB for MCPB. But they observed a higher need for short-term norepinephrine infusion postoperatively for MCPB group. Skrabal et al. [14] found decreased CK-MB and troponin T for MCPB. Initially there were concerns about the possibility of air entering the closed mini-circuit and subsequent air embolism, although no fatal or major episodes have been described by any author.Nollert et al. [15] report that their study was discontinued prematurely because of two cases of air entering the MECC system [(i) around the venous cannula and (ii) accidental tear of right ventricle]. Both incidents were resolved uneventfully but concerns were raised about the safety of the MECC system. Ultrasound controlled air removal devices have been introduced to MCPB [19] and many articles not only confirm the safety of mini circuit but also report superior air elimination compared to standard ECC and reduced cerebral air microembolization [17, 18]. Mulholland and Anderson [16] propose the incorporation of the venous air removal system into conventional CPB circuit. There is only one case report [20] of a severe inflammatory reaction (vasodilatation, bleeding disorder) in a CABG operation with MCPB appearing 10 min after declamping, which though cannot be attributed with certainty to MCPB. The patient was discharged from hospital 6 days later in good condition. Apart from study [2], there are differences between the circuits: cardioplegia, cardiotomy suction/cell saver, tube coating, and type of pump in all these studies.Most studies include only low-risk patients; it would be interesting to see studies comparing MCPB to CCPB in a high-risk patient population. Reported benefits include reduced hemodilution, transfusion, bleeding, ICU stay, and better renal, inflammatory and neurological function in studies up to 1000 patients in size and including 10 PRCTs.There is a learning curve for the best performance of MCPB. Abdel-Rahman et al. [8] report a reduction in intraoperative blood loss after 50 cases with MCPB explained by the surgeons' learning curve. Nevertheless, several thousand cases have been performed with mini-bypass safely and it may be a promising technique for reducing blood loss and transfusion rates.
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Abstract
1. Introduction
and neutrophil elastase release) and less hemodilution when compared to standard CPB.