Leukocyte depletion has been implicated in attenuating

Transcription

1 ORIGINAL ARTICLES: CARDIOVASCULAR Leukocyte Depletion During Cardiac Operation: A New Approach Through the Venous Bypass Circuit Y. John Gu, MD, PhD, A. J. de Vries, MD, Paulien Vos, Piet W. Boonstra, MD, PhD, and Willem van Oeveren, PhD Departments of Cardiothoracic Surgery and Anaesthesiology, University Hospital Groningen, Groningen, the Netherlands Background. Leukocyte depletion recently has been introduced for cardiac surgical patients to attenuate leukocyte-mediated inflammation and organ reperfusion injury. We evaluated the feasibility of a new leukocyte depletion method in which systemic leukocyte depletion is achieved through the venous side of the cardiopulmonary bypass circuit under low blood flow. Methods. Forty cardiac surgical patients undergoing cardiopulmonary bypass were allocated randomly to a leukocyte depletion group and a control group. In the depletion group, leukocyte filtration was achieved with two filter sets located between the venous drainage and the venous reservoir. Leukocyte filtration was commenced after the start of rewarming but before the release of the aortic cross-clamp, and it was driven by a spare roller pump of the heart-lung machine. Results. All the episodes of filtration went smoothly within a period of 10 minutes and with a blood flow rate of 400 ml/min. The mean leukocyte removal rate calculated at the end of filtration was 69%. Circulating leukocytes were reduced by 38% in the depletion group compared with the control group at the moment of crossclamp release ( /L versus /L, p < 0.05). The postoperative inflammatory response also was reduced as indicated by less production of interleukin-8 (p < 0.05). Clinically, there was no significant difference between the two groups in postoperative PaO 2 or pulmonary hemodynamics. Conclusions. It is technically feasible to deplete circulating leukocytes through the venous side of the cardiopulmonary bypass circuit with a low blood flow rate. Future studies should focus on the duration and timing of leukocyte depletion to optimize the methodology of leukocyte depletion for cardiac surgical patients. (Ann Thorac Surg 1999;67:604 9) 1999 by The Society of Thoracic Surgeons Leukocyte depletion has been implicated in attenuating the leukocyte-mediated inflammatory response and organ injury in different experimental models of cardiac operations [1 3]. Clinically, at least three types of leukocyte-depleting techniques for cardiac surgical patients have been introduced since the early 1990s: an arterial line filter located on the arterial side of the extracorporeal circuit, a leukocyte-depleting filter for blood cardioplegia, and a transfusion filter for depleting leukocytes from the residual blood in the heart-lung machine at the end of cardiopulmonary bypass (CPB) [4 15]. For systemic leukocyte depletion from the CPB circuit, an arterial line leukocyte-depleting filter is used, usually from the initiation of CPB [6, 8, 11, 14]. The advantage of this method is the combination of the leukocytedepleting filter with the conventional arterial line filter. However, the filter is located on the arterial side of the circuit and thus is confronted with a high rate of blood flow, which may reduce its efficiency [3, 8]. We used a new clinical leukocyte depletion method in which systemic leukocyte depletion is achieved through the venous side of the CPB circuit. Using this approach, Accepted for publication July 13, Address reprint requests to Dr van Oeveren, Blood Interaction Research, Department of Cardiothoracic Surgery, University Hospital Groningen, Bloemsingel 10, 9712 KZ Groningen, the Netherlands. we started the process of leukocyte depletion during the middle period of CPB before the reperfusion phase and with a low rate of blood flow. We evaluated whether this method was technically feasible for depleting circulating leukocytes during CPB, and whether this temporary depletion method would affect patient outcome after cardiac operations. Patients and Methods Patients Forty patients undergoing coronary artery bypass grafting, heart valve replacement, or a combined procedure were included in this study. The patients were allocated randomly to a leukocyte depletion group and a control group. The study protocol was approved by the Medical Ethics Committee of the University Hospital in Groningen, The Netherlands, and informed consent was obtained from all the patients. Patients who had a history of allergy, infection, or preoperative pulmonary dysfunction were not included. The demographic data of the patients in both groups are listed in Table 1. Anesthesia Anesthesia was induced and maintained through the intravenous infusion of sufentanil citrate (1 to 3 g/kg) and midazolam (0.05 to 0.1 mg/kg). Muscle relaxation was 1999 by The Society of Thoracic Surgeons /99/$20.00 Published by Elsevier Science Inc PII S (99)

2 Ann Thorac Surg GU ET AL 1999;67:604 9 LEUKODEPLETION THROUGH A VENOUS CPB CIRCUIT 605 Table 1. Patient Demographic Information Characteristic Study Group a Leukodepletion Control p Value Age (y) Sex Male Female Height (cm) Weight (kg) Body surface area (m 2 ) CPB time (min) Cross-clamp time (min) a Values are means plus or minus standard deviation unless otherwise indicated. CPB cardiopulmonary bypass. achieved with pancuronium bromide (100 to 140 g/kg). Cefamandole (2 g) and dexamethasone (1 mg/kg) were administered after the induction of anesthesia. Anticoagulation was achieved through the intravenous administration of bovine lung heparin (300 IU/kg) about 5 minutes before the start of CPB. Cardiopulmonary Bypass The CPB circuit consisted of roller pumps (Stöckert Instrumentation, Munich, Germany) and a microporous polypropylene membrane oxygenator (CML Excel; Cobe Laboratories Inc, Lakewood, CO), and it was primed with 1,500 ml of Ringer s lactate solution plus 500 ml of 10% hydroxyethyl starch solution (Fresenius, Bad Homburg, Germany). Myocardial preservation during aortic crossclamping was achieved with 1LofSt. Thomas cardioplegia solution (4 C) infused into the aortic root. During CPB, moderate hypothermia was applied with a pump flow of 2.4 L min 1 m 2. Anticoagulation during CPB was monitored with the celite-activated clotting time (International Technidyne Co, Edison, NJ). After CPB, 3 mg/kg of protamine chloride was administered to neutralize the effect of heparin. Leukocyte Depletion Method Leukocyte depletion during CPB was achieved with the use of two Pall Duplex filter sets (J1647G; Pall Biomedical, Portsmouth, United Kingdom) equivalent to four transfusion leukocyte-depleting filters, as reported previously [13]. The filtration circuit was located between the venous drainage and the venous reservoir and was driven by a separate roller pump (Fig 1). Leukocyte depletion was performed during CPB after the start of rewarming but before the release of the aortic cross-clamp. For each filter set, 2,000 ml of the CPB perfusate was filtered at a flow rate of 400 ml/min. The total blood volume for filtration was 4,000 ml, and the entire filtration procedure was completed within 10 minutes. Efficiency of Leukocyte Removal by Filters At the end of each filtration period, blood samples were taken from the inlet and outlet of each filter set. Leukocytes, granulocytes, lymphocytes, and platelets were counted by an electronic cell counter (Cell-Dyn 610; Sequoia Turner, Mountain View, CA). The cell removal rate was calculated according the following fomula: (1 count outlet /count inlet ) 100. Efficiency of Leukocyte Removal in Patients Blood samples from patients were taken from the radial arterial catheter before operation, at several points during CPB, at the end of CPB, at the end of operation during skin closure, 1 hour and 3 hours after transfer to the intensive care unit, and at 6 am the next morning in the intensive care unit. Circulating leukocytes were counted by the Cell-Dyn electronic counter. Further, levels of inflammatory mediators were determined mainly during the postoperative course in 10 patients in each group. For these tests, leukocyte activation was indicated by elastase activity determined by an enzyme immunoassay (Kordia, Leiden, the Netherlands) and the soluble form of l- selectin (R & D Systems Europe, Abingdon, United Kingdom). Cytokine release was indicated by levels of interleukin-8 (Amersham International Inc, Buckinghamshire, United Kingdom). Clinically, pulmonary gas exchange function was determined by the partial arterial oxygen pressure (Pao 2 ) standardized at a 40% fraction of the inspired oxygen. Postoperative intubation time and blood loss were recorded from the intensive care data sheet. Length of stay in the intensive care unit and in the hospital were obtained from hospital registration records. Fig 1. Leukocyte depletion through the venous side of the cardiopulmonary bypass (CPB) circuit. The leukocyte-depleting filter is located between the venous drainage and the venous reservoir, with a side-line circuit driven by a separate roller pump with a low rate of blood flow.

3 606 GU ET AL Ann Thorac Surg LEUKODEPLETION THROUGH A VENOUS CPB CIRCUIT 1999;67:604 9 Table 2. Rate of Cell Removal by Leukocyte-depleting Filters a Type of Cell No. of Filtration Inlet ( 10 9 /L) Cell Count Outlet ( 10 9 /L) Removal (%) Leukocytes First set ( ) 1.5 ( ) 68.1 ( ) Second set ( ) 1.5 ( ) 69.6 ( ) Average ( ) 1.5 ( ) 68.8 ( ) Granulocytes First set ( ) 1.0 ( ) 73.5 ( ) Second set ( ) 1.0 ( ) 76.0 ( ) Average ( ) 1.0 ( ) 74.7 ( ) Lymphocytes First set ( ) 0.5 ( ) 45.0 (0 85.7) Second set ( ) 0.5 ( ) 49.4 (0 85.7) Average ( ) 0.5 ( ) 47.1 (0 85.7) Platelets First set (59 182) 72 (4 168) 33.7 (0 94.0) Second set (33 178) 74 (27 158) 22.3 (0 40.4) Average (33 182) 73 (4 168) 28.2 (0 94.0) a Blood samples were taken from both the inlet and the outlet of each filter set after the filtration of 2,000 ml of blood during cardiopulmonary bypass. Data are means with range in parentheses. Statistics Data for cell counts are expressed as means with the minimal and maximal counts in parentheses except where otherwise indicated. Data for the inflammatory markers and the postoperative observations are expressed as means plus or minus standard deviation. The Student s t-test or the Mann-Whitney U test was used for comparing differences between the two groups. A p value of less than 0.05 was considered statistically significant. Fig 2. The leukocyte removal rate (efficiency) is similar between the first and second filter sets in individual patients undergoing leukocyte depletion, suggesting that the efficiency of leukocyte depletion during cardiopulmonary bypass is patient-related rather than filter-related. in both the depletion and control groups (Fig 4). After filtration, the count was significantly lower in the depletion group than in the control group at the moment of aortic cross-clamp release ( /L versus /L, p 0.05), reflecting a 38% reduction in circulating leukocytes. After release of the cross-clamp during the reperfusion period, the leukocyte count increased quickly to /L in the depletion group, which Results Leukocyte Removal by Filters The mean overall leukocyte removal rate was 69% as evaluated at the end of filtration (Table 2). Equivalent granulocye, lymphocyte, and platelet removal rates were 75%, 47%, and 28%, respectively. A large variation in the leukocyte removal rate was observed between patients. However, for any one patient, the leukocyte removal rate for the first filter set was similar to the removal rate for the second filter set (r 0.918, p 0.01) (Fig 2). The leukocyte removal rate was positively correlated with the nasopharyngeal temperature during CPB as recorded before the start of filtration (r 0.498, p 0.05) (Fig 3). In addition, the leukocyte removal rate was negatively correlated with the aortic cross-clamp time (r 0.505, p 0.05), but was not correlated with the preoperative soluble l-selectin level (r 0.356) or with the prefiltration systemic leukocyte count (r 0.089). Leukocyte Depletion in Patients Before CPB and before the start of leukocyte filtration during CPB, the circulating leukocyte count was similar Fig 3. Relation between the leukocyte removal rate (data drawn from the first filter set) and the nasopharyngeal temperature recorded before filtration in the 20 patients who underwent leukocyte depletion. A low temperature tended to reduce the efficiency of leukocyte depletion during cardiopulmonary bypass.

4 Ann Thorac Surg GU ET AL 1999;67:604 9 LEUKODEPLETION THROUGH A VENOUS CPB CIRCUIT 607 Table 4. Postoperative Observations a Observation Study Group Leukodepletion Control p Value Pao 2 on arrival in ICU (kpa) Pao 2 at extubation (kpa) Intubation time (h) Urine output (ml/24 h) 2, , Blood loss (ml/24 h) ICU stay (d) Hospital stay (d) a Values are means plus or minus standard deviation. Fig 4. Circulating leukocyte count during cardiopulmonary bypass (CPB) and during the postoperative period in the intensive care unit (ICU) in the leukocyte depletion group and the control group. Data are expressed as means plus or minus the standard error of the mean. The arrow indicates the start of 10 minutes of filtration. T1 before CPB; T2 before filtration; T3 end of filtration; T4 aortic cross-clamp release; T5 5 minutes after clamp release; T6 end of CPB; T7 end of operation; T8 1 hour in ICU; T9 3 hours in ICU; T10 next morning in ICU. *p 0.05 between the two groups. was similar to the count of /L in the control group. Leukocytosis developed in both groups during the postoperative period and lasted until the next morning. Inflammatory Mediators The concentration of interleukin-8 was very low in both the depletion and control groups before CPB. It increased in both groups during CPB and postoperatively in the intensive care unit, but was significantly lower in the depletion group than in the control group ( p 0.05) (Table 3). The level of leukocyte elastase was slightly lower in the depletion group than in the control group during and after CPB. The soluble form of l-selectin was decreased in both groups during and after CPB; there was no significant difference between the two groups. Clinical Observations On arrival in the intensive care unit, the Pao 2 was at 40%, Fio 2 was kilopascal in the depletion group and ICU intensive care unit; kilopascal in the control group; there was no statistical difference between the two groups. In addition, the Pao 2 was similar between the two groups after extubation. Further, there was no statistical difference between the two groups with regard to the intubation time, urine output, blood loss, or intensive care unit or hospital stay (Table 4). Comment kpa kilopascal. Leukocyte depletion is a relatively new technique for attenuating the unwanted inflammatory response in cardiac surgical patients [16 18]. As a systemic approach that targets the circulating leukocytes, the arterial line filter is the only practical method available. Although several studies have suggested that this filter is associated with a reduction in circulating leukocytes [6, 11, 14], it faces a very high rate of blood flow during perfusion. Our current study demonstrated that 10 minutes of leukocyte depletion under a low rate of blood flow, achieved with a duplex filter set located on the venous side of the CPB circuit, resulted in a 38% reduction in circulating leukocytes at the moment of aortic crossclamp release compared with control. It proved technically feasible to locate a leukocyte removal filter between the venous drainage and the venous reservoir. For adequate bodily perfusion during CPB for adult Table 3. Levels of Inflammatory Mediators Before and After Operation a Inflammatory Mediator Before CPB End of CPB 1 Hour in ICU 3 Hours in ICU POD 1 Interleukin-8 (pg/ml) Depletion b Control Elastase (ng/ml) Depletion Control Soluble l-selectin (ng/ml) Depletion Control a Values are means plus or minus standard deviation; b p 0.05 compared with control. CPB cardiopulmonary bypass; ICU intensive care unit; POD postoperative day.

5 608 GU ET AL Ann Thorac Surg LEUKODEPLETION THROUGH A VENOUS CPB CIRCUIT 1999;67:604 9 patients, a high rate of blood flow (as high as 4,000 ml/min or more) is required on the arterial side of the CPB circuit. Although the arterial line leukocytedepleting filter is designed to accommodate such a high rate of flow, it has been described as relatively inefficient at the beginning of CPB [3]. Using the current method through the venous side of the CPB circuit, the rate of blood flow for leukocyte depletion can be reduced considerably. It is conceivable that a high rate of blood flow exerts a greater hemodynamic force that is likely to propel leukocytes through the filter, whereas a lower rate of blood flow allows a longer contact time between the leukocytes and the filter medium, a mechanism that is known to promote leukocyte adhesion to the filter medium [19]. In this study, the mean leukocyte removal rate was 69% as calculated across the filter at the end of filtration. This filter efficiency was lower than expected; we previously obtained a much higher filter efficiency by filtering the residual blood in the heart-lung machine using a similar rate of blood flow [13]. However, a major difference between the two studies was the method of blood sampling used. In the previous study, a blood sample was taken at the end of filtration from a retention bag containing a mixture of all the filtered blood. The result reflected the average efficiency over the entire period of filtration. In the current study, however, the blood sample was taken at the end of filtration from the outlet of the filtration circuit. This represents the lowest removal rate, because it is known that filtration efficiency can decrease as the volume of blood filtered increases. Therefore, the overall leukocyte removal rate would be higher than estimated. In this study, an interesting phenomenon was noted with regard to the efficiency of leukocyte filters during CPB. Although the leukocyte removal rates were variable between patients, in any individual patient, the leukocyte removal rate of the first filter set bore a close relation to that of the second filter set (Fig 2). This suggests that patient-related factors, rather than varying capacity of the filters, may influence the efficiency of leukocyte depletion during CPB. Several possible factors were investigated. First, temperature may influence leukocyte depletion during CPB, because temperature is known to influence leukocyte adhesion [20, 21]. In this study, a positive correlation was found between the nasopharyngeal temperature before the start of filtration and the efficiency of leukocyte removal, suggesting that hypothermia tends to reduce the efficiency of leukocyte depletion during CPB. Second, medication given before operation may affect leukocyte adhesion (eg, the use of the cyclooxygenase inhibitor, aspirin). However, we could not find a relation between the efficiency of leukocyte depletion and the preoperative use of aspirin or the preoperative concentration of the leukocyte activation marker, soluble l-selectin. Finally, the systemic leukocyte count before filtration seems less likely to play a role in the efficiency of leukocyte removal, because no relation was found between these two variables. Clinically, this temporary filtration protocol did not improve lung function, although a reduced interleukin-8 concentration was observed in patients who underwent leukocyte depletion. The timing of leukocyte filtration in this study may have influenced the overall outcome of systemic leukocyte depletion. Initiating leukocyte depletion before the release of the aortic cross-clamp is theoretically attractive for reducing leukocyte-mediated lung injury during the reperfusion period. However, this attempt is counteracted by concomitant rewarming of the systemic blood, which is known to contribute to systemic leukocytosis. Further, the duration of leukocyte depletion must be considered. The 10-minute filtration protocol used in the current study was chosen based on calculations of filter efficiency from our previous study [13]. A protocol of such short duration apparently is insufficient for targeting the circulating leukocytes during rewarming. However, a longer period of filtration may deplete sufficient leukocytes but be complicated by the potential release of elastase from trapped leukocytes [8]. One possible disadvantage of this method is that a separate filter circuit with a roller pump is required to allow low-flow filtration. However, this is not a practical problem, because most heart-lung machines contain at least one spare pump head and most perfusionists are familiar with the installation of and perfusion with a parallel circuit (eg, a hemofiltration circuit). This method may have an advantage in that the filter and its circuit, like the hemofiltration circuit, can be installed by the perfusionist at any time during CPB without the preinstallation required by the custom packs. We conclude that it is technically feasible to install a leukocyte filter device on the venous side of the CPB circuit that is driven by a separate roller pump using a low rate of blood flow. Ten minutes of leukocyte depletion before the reperfusion phase using this method achieved a 38% reduction in circulating leukocytes. Postoperatively, this temporary leukocyte depletion method resulted in a reduction in interleukin-8 production but not an improvement in lung function. This study poses additional questions about systemic leukocyte depletion during CPB, such as the optimal duration and timing of leukocyte depletion, that need to be explored further to optimize the overall methodology of leukocyte depletion for cardiac surgical patients. We acknowledge the technical support and sponsorship provided by Pall Biomedical UK, and the cooperation of the perfusion staff of the University Hospital in Groningen. References 1. Breda MA, Drinkwater DC, Laks H, et al. Prevention of reperfusion injury in the neonatal heart with leukocytedepleted blood. J Thorac Cardiovasc Surg 1989;97: Bando K, Pillai R, Cameron DE, et al. Leukocyte depletion ameliorates free radical-mediated lung injury after cardiopulmonary bypass. J Thorac Cardiovasc Surg 1990;99: Bolling KS, Halldorsson A, Allen BS, et al. Prevention of the hypoxic reoxygenation injury with the use of a leukocytedepleting filter. J Thorac Cardiovasc Surg 1997;113: Gu YJ, Obster R, Gallandat Huet RCG, Eijgelaar A, van Oeveren W. Leukocyte depletion reduces the postoperative

6 Ann Thorac Surg GU ET AL 1999;67:604 9 LEUKODEPLETION THROUGH A VENOUS CPB CIRCUIT 609 inflammatory response in patients following open-heart surgery. Intensive Care Med 1992;18:(Suppl 1):S Pearl JM, Drinkwater DC, Laks H, Capouya ER, Gates RN. Leukocyte-depleted reperfusion of transplanted human hearts: a randomized, double-blind clinical trial. J Heart Lung Transplant 1992;11: Palanzo DA, Manley NJ, Montesano RM, Yeisley GL, Gordon D. Clinical evaluation of the LeukoGuard (LG-6) arterial line filter for routine open-heart surgery. Perfusion 1993;8: Sawa Y, Matsuda H, Shimazaki Y, et al. Evaluation of leukocyte-depleted terminal blood cardioplegic solution in patients undergoing elective and emergency coronary artery bypass grafting. J Thorac Cardiovasc Surg 1994;108: Mihaljevic T, Tönz M, von Segesser LK, et al. The influence of leukocyte filtration during cardiopulmonary bypass on postoperative lung function. A clinical study. J Thorac Cardiovasc Surg 1995;109: De Vries AJ, Gu YJ, Boonstra PW, van Oeveren W. Transfusion of leucocyte-depleted heart-lung machine blood improves lung function following cardiopulmonary bypass. Br J Anaesth 1995;74(Suppl): Hachida M, Hanayama N, Okamura T, et al. The role of leukocyte depletion in reducing injury to myocardium and lung during cardiopulmonary bypass. ASAIO J 1995;41: M Johnson D, Thomson D, Mycyk T, Burbridge B, Mayers I. Depletion of neutrophils by filter during aortocoronary bypass surgery transiently improves postoperative cardiorespiratory status. Chest 1995;107: Gu YJ, de Vries AJ, Boonstra PW, van Oeveren W. Clinical performance of a high-efficiency rapid flow leucocyte removal filter for leucocyte depletion of heparinized cardiopulmonary bypass perfusate. Perfusion 1995;10: Gu YJ, de Vries AJ, Boonstra PW, van Oeveren W. Leukocyte depletion results in improved lung function and reduced inflammatory response after cardiac surgery. J Thorac Cardiovasc Surg 1996;112: Thurlow PJ, Doolan L, Sharp R, Sullivan M, Smith B, Andersen LW. Laboratory studies of the effect of Pall extracorporeal leucocyte filters LG6 and AV6 on patients undergoing coronary bypass grafts. Perfusion 1996;11: Allen BS, Rahman S, Ilbawi MN, et al. Detrimental effects of cardiopulmonary bypass in cyanotic infants: preventing the reoxygenation injury. Ann Thorac Surg 1997;64: Silvey G, Ammar T, Reich DL, Vele-Cantos F, Joffe D, Ergin AM. Cardiopulmonary bypass for adult patients: a survey of equipment and techniques. J Cardiothorac Vasc Anesth 1995;9: Allen S, Lloyd G, Butz H. Leucocytes and the systemic inflammatory response. J Anästh Intens 1996;5:S Allen SM. Leucocyte depletion in cardiothoracic surgery. Perfusion 1996;11: Steneker I, van Luyn MJA, van Wachem PB, Biewenga J. Electron microscopic examination of white cell-reduction by four different filters. Transfusion 1992;32: Menasché P, Peynet J, Haeffner-Cavaillon N, et al. Influence of temperature on neutrophil trafficing during clinical cardiopulmonary bypass. Circulation 1995;92(Suppl 2): Le Deist F, Menasché P, Kucharski C, Bel A, Piwanica A, Bloch G. Hypothermia during cardiopulmonary bypass delays but does not prevent neutrophil-endothelial cell adhesion. A clinical study. Circulation 1995;92(Suppl 2):354 8.