Original articles 0Springer-Verlag Eur J Cardio-thorac

1992

Surg (1992) 6: 397-402

Biocompatibility of extracorporeal circulation with autooxygenation A. Bochenek I, Z. Religa ‘, F. Kokot ‘, A. M. Wnuk-Wojnar ‘, J. Wojnar 4, R. Wnuk 3, G. Gallert 5, and J. Skiba ’ ’ 1st Clinic of Cardiac Surgery, ’ 1st Cardiologic Clinic, Silesian Medical Academy, Silesian Heart Center, 3 Department of Nephrology, 4 Clinic of Hematology. and ’ Department of Anesthesiology, Silesian Medical Academy, Katowice, Poland

Abstract. Platelet damage, complement activation and neutropenia during cardiopulmonary bypass are the result of blood contact with artificial surfaces, mainly in the oxygenator. To evaluate biocompatlbility of this kind of bypass we compared two techniques of extracorporeal circulation in 40 patients undergoing elective coronary bypass operations. In 20, a standard technique with a bubble oxygenator was used (group l), and in the remaining 20 patients with autooxygenation, the patients’ own lungs were included in the perfusion circuit (group 2). Several blood samples were taken before, during and after perfusion to estimate the corrected platelet numbers and pulmonary leucocyte sequestration in all patients, and additionally in 6 patients from each group, complement C3a and C5a anaphylatoxins were measured (radioimmunoassay). At the end of cardiopulmonary bypass, the decline of platelet number corrected to haematocrit platelet number in group 1 was significantly higher than in group 2 (P < 0.01). There was a significant increase in circulating white blood cells when compared to pre-bypass time in both groups (P < 0.05). However, comparison of differences between leucocyte counts in the blood of the patients’ right and left atia showed enhanced leucocyte sequestration in group 1, 1.46 + 0.5 x 103/mm3 vs only 0.34 f 0.2 x 103/mm3 in group 2. The C3a rose progressively during extracorporeal circulation: in group 1 from 268 + 46 rig/l to 521 + 65 rig/l,,and in group 2 from 244 +, 46 rig/l to 418 +, 34 rig/l (P < 0.05). No characteristic changes in C5a activation were observed in either group. The current study confirms the theoretically better biocompatibility of extracorporeal circulation with the use of the patients’ lungs as compared to an oxygenator. [Eur J Cardio-thorac Surg (1992) 6:397-4021 Key words: Biocompatibility

of extracorporeal

circulation - Complement activation

Efforts to improve haemo- and biocompatibility of cardiopulmonary bypass are aimed mainly at preventing coagulation disorders assessed by the amount of blood loss and the resulting need for blood transfusion. The membrane oxygenator has proved to be less traumatic to platelets. However, no differences have been found between bubble and membrane oxygenators in terms of complement activation and subsequent lung leucocyte sequestration. Since morbidity after cardiopulmonary bypass is considered to be related to complement activation [7,20], its reduction may prove beneficial. A number of approaches can be made to achieve this. The effectiveness of steroid administration as a prophylactic measure against complement activation remains controversial. The authors believe that prevention of the occurrence of Receivedfor publication: August 6, 1991 Accepted for publication: March 17, 1992

complement activation rather than its suppression with steroids is a better approach. Chenoweth demonstrated that complement is activated by the nylon mesh liner of oxygenators and vigorous oxygen bubbling through blood [8, 91. In the present study we evaluated a model wherein the oxygenator was replaced by the patient’s own lungs in the extracorporeal circuit of cardiopulmonary bypass (CPB) during coronary revascularisation. A double pump system for extracorporeal circulation (ECC) was studied by Drew [II], Cass and Ross [6], and Blanc0 [3]. For many years, because of the danger of air embolisation, cardiac surgeons showed very little or no interest in this technique. In the face of the growing number of coronary operations this method was reevaluated by Glenville, Ross and Berglin [2, 161. The autooxygenation method of extracorporeal circulation excludes the oxygenator as a substantial part of the

398 artificial monary

surface bypass

and, thus deleterious may be avoided.

effect of cardiopul-

Material and methods

RA

Patients The study included 40 patients undergoing coronary revascularisation with cardiopulmonary bypass. The patients were randomly assigned to one of two groups according to the type of ECC. All patients were anaesthetized by the same modified form of neuroleptanalgesia and muscle relaxant. Anticoagulation was maintained using heparin; the accelerated clotting time was monitored by Haemochron and maintained above 450 s throughout the bypass.

Perfusion technique In group I, a standard technique of ECC was used. A Polystan VT 5000 bubble oxygenator connected to a 2000 ml cardiotomy reservoir and a Pall Ultipor arterial filter were used in all patients. To conform with current clinical practice, the blood flow was maintained at 2.4 l/m2 body surface area. The perfusionist was instructed to adjust PaO, to 2Ok3.3 kPa and PaCO, to 5.3kO.7 kPa (alphastat). In group II, the autooxygenation technique described previously by Glenville and Ross [16] was used. The bypass circuit consisted of a Polystan 1500 ml reservoir ’ (892910 Polystan) for each side of the heart joined by the shunt (Fig. 1). The heat exchanger was connected to the left-sided circuit. The circuits were primed with approximately 2 1 of compound sodium lactate. After heparinization, an aortic cannula (6.5 mm internal diameter) was inserted. An angled 36F DLP venous long-term assist cannula was then introduced into the left atrium via a purse string, at the junction of the left superior pulmonary vein and the left atrium. Left heart bypass was then started, and the patient was cooled to 30 “C. During this period a 3/8 basket type cannula was inserted into the right atrium, and subsequently a 6.5 mm (internal diameter) cannula was placed in the main pulmonary artery. The shunt between the two circuits facilitated balancing of the levels in the two reservoirs. The shunt was closed when one of the bypasses had to be stopped. Perfusion was maintained at 2.2 to 2.4 l/min per m2. In both groups, hypothermic potassium cardioplegia was used during aortic cross-clamping for myocardial protection. All distal anastomoses were completed during a single period of clamping. The proximal anastomoses were then made with the aorta unclamped with the heart beating at 32 “C. As soon as the heart contractions were satisfactory the right sided cannula was removed. When the operation was completed and the patient rewarmed, the left-sided bypass could also be discontinued, and procaine was administered in the usual way.

Blood samples

7 Fig. 1. Double reservoir system without oxygenator (autooxygenation). RA = right atrium; PA = pulmonaty artery; LA = left atrium; Ao = aorta

the blood from the right and left atria immediately after ECC (sample 5) to assess pulmonary leucocyte sequestration: this was expressed as a median cell difference (MCD) = total leucocyte count (WBC) in the right atrium minus total WBC in the left atrium. Cell counts were corrected for haemodilution using the following formula: (measured cell count x prebypass haematocrit/haematocrit of test sample). Plasma hemoglobin measurements were made with the use of the cyanmethemoglobin method [I]. Platelet aggregation studies were performed employing a four channel Aggregometer (Helena, UK) according to the method of Born [5]. The platelet function was expressed by the maximum percentage change in the optical density (OD,,% ) of the platelet rich plasma compared to the platelet-poor plasma after addition of ADP. Platelet aggregation was measured in samples 2 and 5. Sample timings were chosen to express only the period when artificial oxygenation or autooxygenation was used. For plasma C3a and C5a evaluation radioimmunoassay kits (Amersham International) were used. The values for C3a and C5a des arg were also corrected for haemodilution. Pre- and postoperative bleeding times (samples l-6) were measured in the volar skin of the forearm (’ Simplate II). Postoperative blood loss through the chest tube drainage and blood transfusions were measured up to 18 h after perfusion. Transfusions of blood and blood products were ordered when hemoglobin concentration dropped below 6.0 mmol/l or when diffuse bleeding persisted. The Student’s t-test or Wilcoxon’s test and 2-factorial analysis of variance (ANNOVA) were used for statistical analyses of differences between the groups. The values of P < 0.05 were considered to be significant.

To evaluate biocompatibility of the two extracorporeal circuits, whole blood samples were withdrawn for hematology and complement studies before, during and after hypothermic ECC at the following times: 1, pre ECC (before heparin); 2, 5 min after institution of ECC; 3, 30 min after sample 2; 4, following removal of aortic clamp; 5, at the end of ECC; 6, 2 h after operation; 7, on the 2nd day; 8, on the 7th day after operation. Sample timings were chosen to coincide with definite phases of the bypass and subsequent surgical events. Complete cell counts including platelets and leucocyte counts were performed using a haematologic cell counter System 8000 (Baker). Complete blood cell and differential counts were made in

There were no significant differences as to anthropometric and bypass data between patients of the two groups (Table 1). All patients survived the operation, and no major complications related to the employed method were observed. There was no prolongation of the operation procedure, and no incidence of air embolism attributable to the autooxygenation technique occurred.

1 Polystan, Copenhagen,

2 General Diagnostic,

Denmark

Results

New Jersey, USA

399 X

1 OOO/ml

Fig. 2. Platelet count during two types of cardiopulmonary bypass. *** P

Biocompatibility of extracorporeal circulation with autooxygenation.

Platelet damage, complement activation and neutropenia during cardiopulmonary bypass are the result of blood contact with artificial surfaces, mainly ...
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