Effects of Prostacyclin Infusion on Platelet Activation and Postoperative Blood Loss in Coronary Bypass

Effects of Prostacyclin Infusion on Platelet Activation and Postoperative Blood Loss in Coronary Bypass Claes Aren, M.D., Kurt Feddersen, M.D., and Kjell Ridegran, M.D. ABSTRACT The effects of infusion of prostacyclin were studied in 41 patients undergoing aortocoronary bypass. Twenty-three patients received heparin (2 mg per kilogram of body weight) and prostacyclin (50 ng per kilogram per minute) during cardiopulmonary bypass (CPB). Eighteen patients received heparin (3 mg per kilogram). One hour after CPB, the platelet count was 98 * 16% of the value obtained before CPB in the prostacyclin group and 73 * 18% in the control group (p < 0.001). The plasma level of platelet factor 4 rose only initially during CPB in the prostacyclin group, but increased continuously in the control group; at 90 minutes of CPB it was 92 * 35 ng per milliliter and 376 * 119 ng per milliliter, respectively (p < 0.001). Beta-thromboglobulin showed a similar pattern. Postoperative chest drainage was 386? 87 ml in the prostacyclin group and 596 -+ 342 ml in the control group (p < 0.05). Blood transfused during and five days after operation was 1,359 * 751 ml in the prostacyclin group and 2,047 * 915 ml in the control group (p < 0.05). During cardiopulmonary bypass (CPB) the blood is exposed to the artificial surfaces of the extracorporeal circuit, including the blood-gas interface in the bubble oxygenator. Such exposure leads to activation of the platelets followed by morphological changes, release of substances from subcellular granules, and formation of platelet aggregates. Platelet aggregates are removed from the circulation [l], and the remaining circulating platelets often demonstrate impaired function [2]. This disturbance of platelet function may contribute to postoperative hemorrhage. From the Departments of Thoracic Surgery and Anesthesiology, Sahlgrenska sjukhuset, Goteborg, Sweden. Accepted for publication Sept 28, 1982. Address reprint requests to Dr. Ridegran, Department of Thoracic Surgery, Sahlgrenska sjukhuset, S-413 45 Goteborg, Sweden. Inhibition by pharmacological means of platelet activation during CPB might protect the platelets and leave their hemostatic capacity intact for use after bypass. For this purpose, prostacyclin may be the best platelet inhibitor yet discovered. Also, it is rapidly broken down in vivo and its effects on the platelets are shortlived. We and others [3-51 have shown that infusion of prostacyclin reduces the decrease in platelet count during CPB. Platelet activation is accompanied by release of two platelet-specific proteins, platelet factor 4 and beta-thromboglobulin, into the plasma [6]. The plasma levels of these two proteins may thus be used as indicators of platelet activation. We decided to study whether infusion of prostacyclin results in less platelet activation as measured by the release of platelet factor 4 and beta-thromboglobulin and whether this would be accompanied by a reduction in postoperative blood loss. We found that infusion of prostacyclin during CPB significantly inhibited the increases in plasma of the two platelet-specific proteins, and reduced postoperative blood loss and the amount of blood and blood products needed for transfusion. The study was approved by the Ethics Committee of the Sahlgrenska sjukhuset. Material and Methods The investigation comprised 41 patients (numbered 9 through 49 in our ongoing studies) who underwent aortocoronary bypass during the period October, 1980, to January, 1982 (Table l). No patients were studied between February and September, 1981, because of the unavailability of prostacyclin. No patient had taken any drug known to affect platelet function within five days prior to operation. The patients were randomly divided into two groups. Eighteen patients received heparin, 3 mg per kilogram of body weight, before CPB and served as a control group. Twenty-three pa- 49

50 The Annals of Thoracic Surgery Vol 36 No 1 July 1983 Table 1. Data on the Two Groups of Patients" Variable Control Group Prostacyclin Group Mentwomen 1711 2211 Age (yr) 56? 9 56? 8 Weight (kg) 82? 10 78 f 10 Peripheral anastomoses 3.6 * 0.8 3.5? 1.1 CPB (min) 132? 25 134? 30 End of CPB to sternum closure (min) 83 f 19 82 f 10 "Where applicable, data are shown as mean k standard deviation. CPB = cardiopulmonary bypass. tients received heparin, 2 mg per kilogram, before CPB and prostacyclin, 50 ng per kilogram per minute in the extracorporeal circuit, from the start of CPB until 10 minutes before its termination. Prostacyclin (Cyclo-Prostin, synthesized by the Upjohn Company and formulated by the Wellcome Foundation) was dissolved in a glycine buffer, ph 10.5. Anesthesia was initiated with thiopental, administered intravenously, and maintained with fentanyl, also given intravenously, and inhalation of oxygen plus nitrous oxide. Extracorporeal circulation was by roller pump and a Polystan VT 7000 bubble oxygenator in the first 20 patients and a Harvey H-1500 bubble oxygenator in the last 21 patients. Priming was with Ringer's acetate, to which was added 75 mg of heparin. There was no arterial line filter. Cardiotomy suction was used freely. A Polystan 444 cardiotomy reservoir, containing a 40 p filter, was used. Hypothermia to 28 C was induced, and the blood flow at this temperature was reduced to 40 to 45 ml per kilogram per minute. Anticoagulation was checked intraoperatively by the activated clotting time using a Hemochron.* The same device was used in all patients. If the activated clotting time was less than 350 seconds, small additional doses of heparin were given. After CPB was terminated, protamine chloride was given to both groups in a 1:l ratio to injected heparin. Seventy-five percent of this dose was given shortly after discontinuance of bypass and the remainder, after *International Technidyne Corp., Metuchen, NJ transfusion of all blood from the extracorporeal circuit. Blood samples were drawn by direct needle puncture of a peripheral vein before initiation of anesthesia and by puncture of the right atrial appendage before arid 60 minutes after CPB. Samples were taken from the venous line of the extracorporeal circuit after 10 and 30 minutes of bypass and then at.30-minute intervals. Measurements were made of hematocrit, platelet count in whole blood," activated clotting time (Hemochron), and heparin by a chromogenic substrate method [7, 81. In the last 16 patients of the series, 9 in the prostacyclin group and 7 in the control group, measurements were also made of platelet factor 4 and beta-thromboglobulin in plasma. For these determinations. 4.5 ml blood was drawn into siliconized glass tubest containing 0.5 ml of a solution of 3.3 gm of sodium ethylenediaminetetraacetate, 180 mg of theophylline, and 0.33 pg of prostaglandin El per 100 ml of distilled water, p1-i 7.3. The samples were stored immediately on ice and centrifuged at 4 C and 2,000 x g within two hours. The supernatant was then frozen and stored at - 20 C until analysis. Commercially available radioimmunoassay kits were used for measurements of platelet factor 4$ and beta-thromboglobulin. The drainage from the chest tubes was measured from the end of the operation to 6:OO A.M. the following day. It was collected in a bottle containing 100 ml of 0.1% chlorhexidine solution. The hemoglobin concentration of the bottle content was deterinined, and a recalculation of the drainage volume, for a common hemoglobin value of 100 gm per liter, was performed. In order to standardize the surgical procedure, all patients were operated on by the same two surgeons (K. R. and C. A.). The period of surgical hemostasis, i.e., from the end of CPB to closure of the sternum, was determined (see Table 1). Because of the blood sampling protocol, this period could not be less than 60 minutes. *Ultra-Flo 100; Clay Adam. Division of Becton, Dickinson & Company, Parsippany, NJ. 'Venoject; Kimble-Terumo Inc., Elkton, MD. iabbott Laboratories Diaanostic - Division, Abbott Park, N Chicago, IL. Amenham International Limited, Amersham, UK

51 Aren, Feddersen, and Ridegran: Effects of Prostacyclin Infusion in Coronary Bypass Records were kept of transfusions of blood and blood products during operation, from the end of operation to 6:OO A.M. the following day, and postoperatively including the fifth postoperative day. A systolic arterial blood pressure of less than 100 mm Hg together with a low pulmonary capillary wedge pressure or diastolic pulmonary pressure was considered an indication for volume substitution with whole blood or plasma. A hemoglobin concentration of less than 100 gm per liter was considered an indication for transfusion of packed red cells. Infusion of crystalloid solutions, including the priming solution, was measured and urinary output determined during and after operation until 6:OO A.M. the following day. All data are reported as mean 2 standard deviation. Significance testing was by the twotailed Mann-Whitney test. A p value less than 0.05 was considered to indicate a significant difference. Results One patient in the control group had a myocardial infarction on the fourth postoperative day and died. There were no hospital deaths in the group given prostacyclin. The platelet count, corrected for hematocrit, was significantly higher in the prostacyclin group than in the control group from 60 minutes of bypass onward (Fig 1). Sixty minutes following CPB, the platelet count was 73 5 18% of the value obtained before bypass in the control group compared with 98 t 16% in the prostacyclin group. The plasma levels of platelet factor 4 and betathromboglobulin did not change significantly during the period before the induction of anesthesia to immediately before the start of CPB. During CPB there was a continuous rise in the levels of platelet factor 4 and beta-thromboglobulin in the control group (Figs 2, 3). In contrast, there was only an initial, small increase in the levels in the prostacyclin group. Sixty minutes after CPB, platelet factor 4, but not beta-thromboglobulin, had returned to levels similar to those measured before bypass in both groups. Concentration of heparin decreased slightly in both groups during CPB (Fig 4). The need for 6W- 500- PTC % of pre-cpb value * t * x* *** *** *** 120 J I T (I/ 20.,.,.,,, ~ PRE 10 30 60 90 120mln 60 min CPB of CPB after CPB Fig 1. Platelet count (PTC), corrected for hemodilufion, during and an hour after cardiopulmonay bypass (CPB) Data are shown as mean? standard deviation. (0 = control group; 0 = prostacyclin group; * = p < 0.05; *** = p < 0.002.) 1 \ PRE PRE 10 30 60 90 ANEST CPE I I 120rnm of CPE 60mm after CPE Fig 2. Concentration of plasma platelet factor 4 (PF 4) before anesthesia (PRE ANEST), before start of cardiopulmonary bypass (PRE CPB), during CPB, and an hour after CPB. Data are shown as mean? standard deviation. (0 = control group; o = prostacyclin group; * = p < 0.05; ** = p < 0.02; *** = p < 0.001.) supplementary heparin was greater in the control group in which 12 out of 18 patients received extra heparin. In comparison, only 2 out of 23 patients in the prostacyclin group required additional heparin. Activated clotting time was greatly prolonged in the prostacyclin group in comparison with the control group early during CPB. However, the difference disappeared after two hours of CPB (Fig 5).

52 The Annals of Thoracic Surgery Vol 36 No 1 July 1983 R-TG ng ml-1 * *** *** *** *** ACT sec,ooo] 1 800-600 - LOO - 200 - - I, I t, 1 PRE PRE 10 30 60 90 120min 60mm ANEST CPB of CPB afiercpb Fig 3. Concentration of plasma beta-thromboglobulin (p- TG) before anesthesia (PRE ANEST), before start of cardiopulmonary bypass (PRE CPB), during CPB, and an hour after CPB. Data are shown as mean * standard deviation. (0 = control group; o = prostacyclin group; * = p < 0.05; *** = p < 0.001.) - I PRE 10 30 60 90 120 rnm 60 rnm CPB of CPB aftercpb Fig 5. Activated clotting time (ACT) before cardiopulmonay bypass (PRE CPB), during CPB, and an hour after CPB. Data are shown as mean * standard deviation. (0 = control group; 0 = prostacyclin group.) HEPARIN A IU ml-1 tion of the drainage volumes to a common hemoglobin concentration of 100 gm per liter yielded 163 * 63 ml in the prostacyclin group and 380 k 280 ml in the control group (p < 0.05), a savings of 57%. The patients in the prostacyclin group received significantly less blood and blood products than those in the control group early postoperatively, as well as totally during and after operation (Table 2). The infusion of crystalloid solutions (including the priming and cardioplegic solutions) during operation and up to 6:OO A.M. the following 10 30 60 90 day was 8.6 f 2.3 liters in the control group and of CPB after CPB Fig 4. Plasma concentration of heparin during cardiopulmonay bypass (CPB) and an hour after CPB. Data are shown as mean f standard deviation. (0 = control group; o = prostacyclin group.) 7.6 & 1.7 liters in the prostacyclin group. The urinary output during; this period was 5.5 -+ 1.5 liters in the control group and 3.8 f 1.0 liters in the group given prostacyclin. Chest drainage from the end of operation to 6:OO A.M. the following day was 386? 87 ml in the prostacyclin group compared with 596 & 342 ml in the control group (p < 0.05), a savings of 35%. One patient in the control group was reoperated on for bleeding. Only the chest drainage up to reoperation (1,475 ml) was included in the chest drainage calculation for the control group. No surgical explanation for the bleeding was found at exploration. Recalcula- Comment During CPB there usually occurs a drop in platelet count [2] and a release of constituents from subcellular platelet granules [9]. In the present study, infusion of prostacyclin significantly reduced the drop in platelet count and the release of platelet factor 4 and betathromboglobulin. This demonstrates an inhibitory effect on platelet activation by prostacyclin during CPB. To achieve maximum platelet inhibition at the start of CPB, it might be advantageous to begin the infusion of prostacyclin early in the operation. This might also counteract the

53 Aren, Feddersen, and Rbdegran: Effects of Prostacyclin Infusion in Coronary Bypass Table 2. Intraoperative and Postoperative Transfusions Control Group Prostacyclin Group Period (ml) (ml) Significance During operation End of operation to day 1 Days 1-5 Total 625 * 601 1,076 1?1 525 332? 397 2,047 * 915 adata are shown as mean? standard deviation. NS = not significant. 294 1?1 553 530 & 495 535? 555 1,359 1?1 751 NS p < 0.01 NS p < 0.05 platelet aggregation induced by heparin itself [lo]. Such a protocol has been used [3, 11, 121, but the drop in platelet count early during CPB still occurred. However, the dosages of prostacyclin utilized during CPB in these studies were only 20 to 25 ng per kilogram per minute. Inconsistent protection of the platelet count has been reported with infusions of up to 20 ng per kilogram per minute [ 131. The heparin-sparing effect of prostacyclin was confirmed in this study. We [4] suggested in a previous report that this effect might be due to inhibition of the release of the antiheparin factor platelet factor 4, which was confirmed in the present study. However, the activated clotting time, which is strongly affected by prostacyclin j4], was used as the guide for heparin supplementation. This is the major explanation for the heparin-sparing effect. In our study, the pharmacological inhibition of platelets during CPB was associated with beneficial clinical effects. Chest drainage from the end of the operation to 6:OO A.M. the next day was lower and also varied less in the prostacyclin group than in the control group. Since the chest drainage is composed of both blood and tissue fluid, we measured its hemoglobin concentration. When the drained volume was recalculated to a common hemoglobin value of 100 gm per liter, we found that not only was the drained volume lower in the prostacyclin group, but that it also contained less blood than in the control group. A saving of blood on the order of a few hundred milliliters may not seem impressive, but this study was performed with patients undergoing coronary bypass, patients with the fewest problems in terms of bleeding. More pronounced differences might be expected in other categories of patients in whom major bleeding is more commonplace such as those with congenital cyanotic heart disease or those requiring reoperations. Differences in blood loss might be due to surgical technique. In an attempt to reduce such a bias, all patients were operated on by the same two surgeons. The technique used for surgical hemostasis and the time spent on hemostasis were strictly standardized. The amount of blood and blood products transfused intraoperatively and postoperatively was significantly less in the prostacyclin group. It amounted to a savings of 700 ml, which, in fact, is greater than the reduction in chest drainage. Although the water balance was somewhat more positive in the prostacyclin group, this was hardly of a magnitude to explain the difference. Effects on vascular tone by vasoactive substances such as epinephrine, norepinephrine, vasopressin, and angiotensin must also be taken into account. When analyzing the figures in Table 2, it should be noted that 400 to 500 ml of blood was drawn from the patients for all the laboratory tests included in this and coupled studies. The use of an infusion of prostacyclin of 50 ng per kilogram per minute during CPB results in a mean arterial blood pressure of about 30 mm Hg during the first hour of CPB [4]. It might be argued that whatever beneficial effects this infusion may have on postoperative blood loss and blood requirements, such a low blood pressure is too hazardous to justify the use of prostacyclin in this dosage. However, low blood pressure has not been associated with an in-

54 The Annals of Thoracic Surgery Vol 36 No 1 July 1983 creased incidence of postoperative organ dysfunction in the present study or in a previous study by one of us [3]. We conclude that infusion of prostacyclin significantly reduced platelet activation during CPB. This resulted in lower postoperative blood loss and less need for transfusion of blood and blood products. This study was supported by Grant No. B83-17X- 06570-01 from the Swedish Medical Research Council, the Goteborg Medical Society, and the Upjohn Company. References 1. Hope AF, Heyns AduP, Lotter MG, et al: Kinetics and sites of sequestration of indium 111-labeled human platelets during cardiopulmonary bypass. J Thorac Cardiovasc Surg 81:880, 1981 2. Friedenburg WR, Myers WO, Plotka ED, et al: Platelet dysfunction associated with cardiopulmonary bypass. Ann Thorac Surg 25:298, 1978 3. Longmore DB, Bennet G, Hoyle PM, et al: Prostacyclin administration during cardiopulmonary bypass in man. Lancet 1:800, 1981 4. Ridegran K, Aren C, Teger-Nilsson A-C: Prostacyclin infusion during extracorporeal circulation for coronary bypass. J Thorac Cardiovasc Surg 83:205, 1982 5. Ridegran K, Egberg N, Papaconstantinou C: Effects of prostacyclin {during cardiopulmonary bypass in man. Scand J Thorac Cardiovasc Surg 15:263, 1981 6. Niewiarowski S: Proteins secreted by the platelet. Thromb Haemost 38:924, 1977 7. Odegird OR, Lie M, Abildgaard U: Heparin cofactor activity measured with an amidolytic method. Thromb Res 6:287, 1975 8. Teien AN, Lie M, Abildgaard U: Assay of heparin in plasma using a chromogenic substrate for activated factor X. Thromb Res 8:413, 1976 9. Cella G, Vittadello 0, Gallucci V, Girolami A: The release of beta-throntboglobulin and platelet factor 4 during extracorporeal circulation for open heart surgery. Eur J Clin Invest 11:165, 1981 10. Eika C: The platelet aggregating effect of eight commercial heparins. Scand J Haematol 9:480, 1972 11. Bunting S, O Grady I, Fabini JN, et al: Cardiopulmonary bypass in man: effects of prostacyclin. In Lewis PJ, O Grady J (eds): Clinical Pharmacology of Prostacyclin. New York, Raven, 1981, pp 181-193 12. Walker ID, Davidson JF, Faichney A, et al: Prostacyclin in cardiopulmonary bypass surgery. In Lewis PJ, O Grady J (eds): Clinical Pharmacology of Prostacyclin. New York, Raven, 1981, pp 195-199 13. Ridegran K, Papaconstantinou C: Prostacyclin infusion during cardiopulmonary bypass in man. Thromb Res 19:267, 1980