Aortic Surgery Using Total Miniaturized Cardiopulmonary Bypass

Aortic Surgery Using Total Miniaturized Cardiopulmonary Bypass Richard W. Issitt, BSc(Hons), John W. Mulholland, BEng, Martin D. Oliver, BMedSci, Gemma J. Yarham, BSc(Hons), Philippa J. Borra, FRCA, Paul Morrison, FRCA, Ioannis Dimarakis, MD, and Jon R. Anderson, FRCS(CTh) Departments of Clinical Perfusion Science, Anesthesia, and Cardiac Surgery, Hammersmith Hospital, London Perfusion Science, London, United Kingdom Purpose. Few centers have attempted aortic surgery using miniaturized cardiopulmonary bypass (MCPB) systems due to concerns of air handling. The extra corporeal circuit optimized (ECCO) total MCPB system uses a venous air removal device and a parallel soft-shell reservoir that allows for venting of the heart. At our institution, total MCPB is used for all coronary artery bypass graft patients. Our objective was to assess the suitability of the ECCO total MCPB system during aortic surgery. Description. Fifty consecutive and unselected aortic procedures using the ECCO system were undertaken. Surgical feasibility, air removal ability, and blood transfusion requirements were audited to determine the efficacy of this technique. Evaluation. The bypass time was 81.6 28.0 minutes and the ischemic time was 56.7 18.9 minutes. Total MCPB handled 1,910 404 ml of vented blood with 96 venous air removal device activations noted. The blood product transfusion rate was 12%, which was below the surgical transfusion rate for our unit. There were no complications. Conclusions. Aortic surgery can be undertaken safely and effectively using the ECCO total MCPB system. (Ann Thorac Surg 2008;86:627 31) 2008 by The Society of Thoracic Surgeons Technology onventional cardiopulmonary bypass (CCPB) is C associated with increased activation of inflammatory factors, hemodilution, and gaseous microemboli [1]. Miniaturized cardiopulmonary bypass (MCPB) can reduce these deleterious effects [2]. Total miniaturized cardiopulmonary bypass (TMCPB) delivers two major advantages in comparison with CCPB (ie, reduced prime volume and a more physiologic surface). Total from the chest and pleural cavities) is returned to the cell-saving device. This eliminates the need for defoamers and further reduces the surface area of the circuit, while enabling the entire circuit to be biocompatibly coated. These factors all reduce the activation of inflammatory markers [2]. The low priming volume reduces hemodilution and translates into a reduction in transfusion requirements [3]. Apart from the financial implications of using less donated blood, MCPB has the added advantages of a significantly the clinical benefits are seen in the reduction of risks decreased nonphysiologic surface area, 55.4% less than associated with homologous blood transfusion [4]. 2 the standard circuit for our unit (containing a 1.8 m oxygenator), due to the type of oxygenator and lack oftechnique a venous reservoir in the arterial and venous loop. The oxygenator uses the entire fiber bundle to deliver Until recently a major cause for concern when using efficient gas exchange while minimizing the surface MCPB was the lack of an automated air removal device exposure interaction. Kinetic venous drainage provides more accurate control in comparison with stan- [5]. We have previously reported that this concern is addressed by the extracorporeal circulation optimized dard venous drainage. Vented blood is returned to the (ECCO) TMCPB system, which incorporates an automated venous air removal device (VARD) [6, 7]. At this system while the cavity blood (ie, the blood coming institution, TMCPB is used for all cardiopulmonary Accepted for publication March 7, 2008. bypass graft (CABG) patients. The next step was to assess its suitability in patients undergoing aortic surgery using an audit of practice looking at the safety and Address correspondence to Dr Mulholland, Department of Clinical Perfusion Science, Cardiac Theatres, 2nd Floor, Block A, Hammersmith Hospital, 150 Du Cane Rd, London, W12 0HS, United Kingdom; e-mail: applicability of the next generation cardiopulmonary john@londonperfusionscience.com. bypass. 2008 by The Society of Thoracic Surgeons 0003-4975/08/$34.00 Published by Elsevier Inc doi:10.1016/j.athoracsur.2008.03.015

628 ISSITT ET AL Ann Thorac Surg TOTAL MINIATURIZED CARDIOPULMONARY BYPASS 2008;86:627 31 Table 1. Patient, Clinical, and Procedural Data of the Patient Group a Patient Data Age (yrs) 67.7 ( 15.9) Sex Male 34 Female 16 Diagnosis (No. of patients) Isolated aortic valve stenosis 22 Isolated aortic valve regurgitation 9 Aortic valve stenosis and ischemic heart 13 disease Aortic valve regurgitation and ventricular 1 septal defect Aortic and mitral valve regurgitation 1 Aortic valve regurgitation and dilated 4 aortic root Ventricular function (No. of patients) Good (ejection fraction 50%) 29 Moderate (ejection fraction, 30% 50%) 13 Poor (ejection fraction 30%) 8 Body surface area (m 2 ) 1.85 ( 0.24) Calculated flow at normothermia (L/min) 4.44 Calculated flow at planned hypothermia 3.70 32 C (L/min) Average flow obtained on bypass (L/min) 4.21 ( 0.52) Duration of bypass (mins) 81.6 ( 28.0) Duration of X-clamp (mins) 56.7 ( 18.9) Base excess on bypass 1.57 ( 2.1) Number of times SSR air removed to cell 5.5 ( 2.2) saver (per case) VARD activations (per case) 3.3 ( 1.9) Vent blood returned to the SSR (ml) 1910 ( 404) Overall postoperative fluid balance (ml) 1387 ( 240) No. of patients returning to operating room 1 Total No. of blood products transfused 14 Intensive Care Unit stay (d) 1.8 ( 1.3) a Values are given as mean ( standard deviation). SSR soft-shell reservoir; Clinical Experience VARD venous air removal device. Fifty consecutive and unselected patients underwent elective aortic surgery using TMCPB by a single surgeon. Excluding factors included reoperation and emergency surgery. Of the 50 patients, 31 underwent isolated aortic valve replacement (6 through a mini-sternotomy), 13 underwent aortic valve replacement and CABG, 4 underwent aortic root replacement, 1 underwent aortic valve replacement with closure of the ventricular septal defect, and 1 underwent aortic valve replacement and mitral valve annuloplasty. Table 1 presents patient, clinical, and procedural data of the patient group. The board chairperson of our institution s ethics committee approved this retrospective study and waived the need for patient consent. Induction of anesthesia was achieved using etomidate, midazolam, and pancuronium, and this was maintained with a mixture of propofol and remifentanil. Blood gas analysis and activated clotting time were checked every 20 to 30 minutes with a minimum activated clotting time of 480 seconds maintained during bypass. A cardiac index of 2.4 L/m 2 /min was used to determine each patient s target normothermic cardiac output, although during cardiopulmonary bypass a minimum cardiac index of 2 L/m 2 /min was deemed acceptable as the patients were to undergo mild hypothermia (32 C). Total Miniaturized Cardiopulmonary Bypass The extracorporeal circulation optimized TMCPB system (Sorin Group Italia, Mirandola, Italy) was used (Fig 1). This consisted of a centrifugal pump (Revolution Cardiopulmonary Bypass; Stöckert, Munchen, Germany), a 1.1 m 2 hollow fiber oxygenator (Eos [Sorin Group, Mirandola, Italy]), a low prime arterial filter (D733 low prime arterial filter [Sorin Group]), a 0.5 m pre-bypass filter within the arterial-venous sash (Siever [Sorin Group Italia]), an intermittently isolated soft-shell reservoir (SSR) running parallel to the systemic circulation, a cell-saving device (Dideco Electa [Sorin Group]), and 3/8 arterial and venous lines. Attached to the SSR are two 1/4 polyvinylchloride lines that act as an aortic root vent and the left ventricular vent. Myocardial protection was achieved using cold (4 to 1 ratio) blood-cardioplegia mix (Martindale Pharmaceuticals, Romford, UK) through a cardioplegia delivery device (MYOtherm XP [Medtronic, Kerkrade, the Netherlands]) into the coronary ostia. Continuous in-line monitoring was carried out using the CDI500 (Terumo Cardiovascular, Tustin, CA). A second bubble detector (Bubble Detector [Stöckert, Munchen, Germany]), linked to the electronic arterial clamp was used on the outlet of the VARD. The VARD is shown in Figure 2. Venous air (including micro-air and air introduced from the cardiopulmonary bypass sample port) is detected using an ultrasonic bubble detector, which triggers a roller pump that draws the air off the top of a side entry 120- m filter. The side entry creates centrifugal flow, which collects air at the top center of the filter housing. The pump is set at 300 ml/min and runs for 5 seconds post-detection, removing the air. Importantly, any blood that is removed along with the air is instantly available for return to the systemic system. A 29-French Optiflow venous cannula (Sorin Group), a 24-French soft-flow DLP curved tip arterial cannula, and either a 16-French DLP aortic root cannula or a 12-French DLP high-flow coronary artery ostial cannula (Medtronic) were used depending on the presence of aortic regurgitation. The system was primed using 1,000 ml of heparinized (10 IU/mL) Hartmann s solution. Once the air was completely removed, excess prime was removed from the circuit, and bypass was initiated as previously described [8]. Results Total miniaturized cardiopulmonary bypass was conducted in 50 patients undergoing aortic surgery. Bypass times were 81.6 28.0 minutes with ischemic times of 56.7 18.9 minutes. During bypass, the average base

Ann Thorac Surg ISSITT ET AL 2008;86:627 31 TOTAL MINIATURIZED CARDIOPULMONARY BYPASS 629 Fig 1. Schematic and flowchart of the extracorporeal circuit optimized (ECCO) total miniaturized cardiopulmonary bypass system. (a) A 29- French OptiFlow venous cannula (Sorin Group, Mirandola, Italy); (b) venous air removal device; (c) centrifugal pump; (d) heat exchange, and oxygenator module; (e) arterial line filter; and (f) parallel soft-shell reservoir. excess was 1.6 2.1 mmol/l. The average cardiac index achieved on bypass was 2.3 0.3L/min/m 2. Final blood gas analysis on bypass for all patients revealed hemoglobin of 9.7 1.7 g/dl. Subsequent analysis showed hemoglobin of 10.2 1.5 g/dl at day 4 postoperatively (Table 2). Fourteen units of blood products were transfused to 6 patients giving a transfusion rate of 12% and an average of 0.28 units per patient. The length of patient stay in the cardiac intensive care unit was 1.8 1.3 days. The incidence of air introduced to the SSR through the vent was 5.5 2.2 times per patient. During 50 operations, TMCPB handled 1,910 404 ml of vented blood. Table 2. Preoperative and Postoperative Hematological Parameters a Hematological Measurements Preoperatively Postoperatively White cell count ( 10 9 /L) 6.9 ( 1.7) 8.49 ( 2.02) Polymorphonucleocytes 4.5 ( 1.6) 6.3 ( 1.7) ( 10 9 /L) Hemoglobin (g/dl) 13.1 ( 2.0) 10.2 ( 1.5) Hematocrit ratio 0.4 ( 0.05) 0.3 ( 0.04) Platelets count ( 10 9 /L) 231.9 ( 59.1) 183.5 ( 64.5) Prothrombin time (secs) 10.9 ( 0.6) 10.9 ( 0.6) Activated partial 26.7 ( 2.7) 32.8 ( 7.6) thromboplastin time (secs) Thrombin time (secs) 13.6 ( 1.0) 12.1 ( 1.8) Fibrinogen (g/dl) 3.7 ( 0.9) 4.9 ( 1.1) Creatinine ( mol/l) 114.9 ( 87.9) 127.8 ( 79.4) Urea (mmol/l) 6.9 ( 3.2) 9.2 ( 5.6) Albumin (g/l) 39.1 ( 4.0) 22.2 ( 3.9) Total protein ( g/l) 71.9 ( 6.1) 50.9 ( 4.9) Fig 2. Schematic of the venous air removal device. a Values are given as mean ( standard deviation). Preoperative and postoperative data taken 1 day before and 4 days after operation, respectively.

630 ISSITT ET AL Ann Thorac Surg TOTAL MINIATURIZED CARDIOPULMONARY BYPASS 2008;86:627 31 Ninety-six VARD activations were noted from drug injection through the sample ports or from volume addition, while activation due to air entrainment from the venous line occurred 8 times. There were no complications in terms of reported neurologic episodes, hemofiltration requirement, or extended ventilation periods ( 12 hours), and only 1 patient returned to the operating room for postoperative bleeding. Hospital mortality was zero. Comment We have used TMCPB in over 500 CABG patients and have appreciated the technical issues associated with the technique and benefits of TMCPB. We believe that the safety issue regarding air removal had been adequately addressed and that this technique could be applied to patients undergoing aortic surgery. The first 50 patients were analyzed to assess the safety of the technique, any impact on the surgery, air removal ability, postoperative hemoglobin, and transfusion requirements. Total MCPB has a number of advantageous effects (ie, a small prime volume reducing the hemodilution inflammatory activation and reducing the blood-air interface [7]). The use of a centrifugal pump is also associated with less hemolysis. Evidence continues to grow with respect to TMCPB as being a superior technique to CCPB, but many units still only utilize these benefits for CABG. Reduced prime circuits marketed as MCPB systems fail to deliver many of these added advantages over CCPB circuits. In agreement with Perthel and colleagues [3], our group saw a decrease in transfusion products with TMCPB. This is partly due to a low perioperative fluid balance of 1,387 ml, which includes anaesthetic volume, perfusion volume, urine output, and blood loss. Fourteen units of blood products were transfused to 6 patients giving a transfusion rate of 12% and an average of 0.28 units per patient. Although transfusion rates of this study group can not be compared directly with the routine transfusion rates in our unit, as they were not studied concomitantly, it is interesting to note that there is no remarkable change in any of the hematologic measurements both preoperatively and postoperatively. One patient required re-sternotomy and no neurologic episodes (ie, defined as cerebral vascular events or transient ischemic attacks) were reported postoperatively. Neurocognitive testing was not attempted to refine conclusions regarding air embolism, because the aim of the study was to determine if the VARD removed venous air that is normally removed by a hard-shell venous reservoir of CCPB circuit. No patients required hemofiltration or an extended ventilation period. The vent dealt with a considerable volume of blood (1,910 404 ml), the majority of which in an air-free manner reduced blood-air damage. Air collected in the SSR was easily transferred to the reservoir (5.5 2.2 transfers per case; see Table 2) of the cell-saving device. Incidence of air introduced into the SSR (although low) was higher than that seen during CABG surgery due to venting of the open-heart chambers. Nonvent air entrainment into the system was minor and was immediately dealt with by the VARD. Air entrainment was judged on a sliding scale. Major air entrainment was quantified as the complete de-prime of the venous line, moderate air entrainment as the introduction of air from an atrial hole or by the venous pursestrings, and minor air entrainment was the introduction of air from the sample ports. The VARD activations due to air introduction through the sample ports and fluid addition removed air emboli that would not be removed with conventional bypass, which have been previously shown to cause an increase in microemboli delivery to the patient [8 10]. The VARD activations were no more common during aortic surgery than CABG surgery, as the vented blood was directly returned to the SSR. Unlike CCPB, TMCPB does not disguise air that is introduced either from the venous line or the sample ports because of VARD activation. Venting of the heart was a key issue during these operations. The type of vent used was discussed preoperatively to allow maximum benefit while minimizing the entrainment of air. For most cases, a small bore left ventricular vent through the aortic annulus was the most appropriate. It was easy for the surgeon to visualize and provide early communication to the perfusionist. If blood began to impede visibility, then our protocol was to increase the venting speed for a 2-second period to clear the surgical field. The pulmonary artery and the left atrial and apical vents were all assessed. Although the left ventricular vent through the aortic annulus might be thought of as a more difficult and cumbersome venting technique, we found that it reduced air entrainment without any significant interference with the surgical procedure. This technique does not minimize vented blood, which is dictated by the patient, but it does ensure appropriate rather than excessive venting, which should be the standard of care for all cardiopulmonary bypass techniques. Appropriate use of an intracardiac vent and an automated venous air-removal device ensure this surgery can be undertaken safely without the fear of air delivery to the patient and with the added benefits of a total miniature circuit. Further studies are required to assess neurologic function and inflammatory activation, but in this audit of 50 patients undergoing aortic surgery, we demonstrate that with appropriate measures TMCPB can be safely used, and this group of patients can derive the benefits that are seen in CABG patients. Disclosures and Freedom of Investigation The audit was funded institutionally with purchased technology. The authors had full control of the design of the study, methods used, outcome measurements, analysis of data, and production of the written report. We thank Ann Clements, Tom Cumberland, and John Cousins for their technical advice. References 1. Elahi MM, Khan JS, Matata BM. Deleterious effects of cardiopulmonary bypass in coronary artery surgery and

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