Preservation of human platelets with prostaglandin E1 during in vitro simulation of cardiopulmonary bypass

The Effects of Adenosine Upon the Coronary Circulation Studied by Thermography. An Experimental Study

If blood passes through extracorporeal circuits, platelets are activated even if the patient is fully heparinized.1 These activated thrombocytes begin to adhere, cluster, release their granular constituents, and within minutes of the institution of cardio pulmonary bypass a sheath of platelet and fibrin aggregates will line all components of the extracorporeal circuit.2,3,4 This process endangers the patient in two ways: (1) The lining of aggregates on the "down side" to the arterial filter may fragment and cause a shower of microemboli. (2) Intra-bypass platelet aggregation depletes the number of circulating thrombocytes, thus increases the possibility of post-operative bleeding.5,6,7

The effect of oxygenator membranes on blood: a comparison of two oxygenators in open-heart surgery

Open-heart surgery (OHS) requires cardiopulmonary bypass (CPB) in most patients. Membrane oxygenators are a critical component of the CPB system. Despite advancements in CPB technology, injury to blood components during CPB still occurs and may result in complications after surgery. The purpose of the present study was to evaluate the performance of the Medtronic Affinity NT® with Trillium coating and the Cobe Optima XP® oxygenators and compare their influence on blood components.

Two hundred and fifty-six male and female patients scheduled for urgent or elective cardiac surgery with CPB were randomly assigned to either the Affinity NT or the Optima XP oxygenators. Outcomes included platelets, hemoglobin, leukocyte counts, and O2 transfer, measured preoperatively and at 15, 45 and 75 min of CPB time. Blood loss was measured at six and 12 hours postoperatively. A modified intention-to-treat analysis was conducted.

The two groups were similar for age, sex, height, weight, body surface area, and blood components at baseline. There were no differences between the Affinity NT and Optima XP for any outcome measure, although a significant change with time was seen in platelets, hemoglobin, hematocrit and leukocytes, as well as O2transfer for both groups ( p <0.001). The Affinity NT oxygenator had a significantly lower difference in pressure across the membrane ( p <0.001) compared with the Optima XP.

In conclusion, the two oxygenators performed similarly with respect to their impact on blood components, O2transfer, and blood loss postoperatively during OHS with CPB. The Affinity NT had the smaller transmembrane pressure drop of the two.

Ex vivo evaluation of a new neonatal/infant oxygenator: comparison of the Terumo CAPIOX® Baby RX with Dideco Lilliput 1 and Polystan Safe Micro in the piglet model

Objective: A newly developed neonatal and infant oxygenator with a nonheparin biocompatible polymer coating, low priming volume (43 mL), high oxygen transfer, wide operating range (<1.5 L/min) and low pressure drop represents a promising solution for cardiac surgery in neonates and infants. We compared the new CAPIOX® Baby RX, Terumo (BRX) with two commonly used neonatal oxygenators: Dideco Lilliput 1 (DL1) and Polystan Safe Micro (PSM) in a piglet model.

Methods: Fifteen piglets (5.6±1.3 kg) were placed on standardized cardiopulmonary bypass (CPB) for 6 hours using one of the three oxygenators ( n = 5 in each group). After 120 min, the system was cooled to 25°C for 60 min and then returned to normothermia. Arterial and venous blood gas data and temperature were recorded continuously by a CDI500 System (Terumo). Pressure drop, FiO2 and gas flow were recorded. Blood samples were taken before CBP, after 10 min, before and after cooling, and at the end. Total blood counts, thrombin-antithrombin complex and plasma-free haemoglobin (PfHb) were measured.

Results: All oxygenators showed acceptable performance for the duration of CPB. The BRX had lower mean gas flow (0.33±0.05 L/min) and FiO2 (0.43± 0.02%) throughout CPB than the DL1 (1.14±0.25 L/min, p = 0.006 and 0.60±0.02%, p = 0.009, respectively) or the PSM (1.47±0.87 L/min and 0.54±0.08%, p = ns). Pressure drop in the BRX group ranged from 12 to 22 mmHg. This was significantly lower than in the DL1 group (39-65 mmHg, p = 0.005). In the PSM group, values ranged between 24 and 33 mmHg (p = ns). The increase in PfHb at six hours was significantly lower in the BRX (11.3±4.2 ng/dL) versus the DL1 (42.2±6.1 ng/dL, p = 0.004) and the PSM (56.7±15.5 ng/dL, p = 0.045).

Conclusions: The BRX is as safe as the DL1 and the PSM, with superior performance in pressure drop, efficient blood gas management and lower haemolysis. The BRX exhibited the lowest prime, hold-up volume and breakthrough time.

Prostaglandin el attenuates impairment of cellular immunity after cardiopulmonary bypass

OBJECTIVE

It is well documented that cardiopulmonary bypass (CPB) severely impairs cellular immunity. The objective of this study was to investigate the effect of prostaglandin E1 (PGE1) on cellular immunity after CPB.

METHODS

Patients who underwent elective cardiac surgery were randomly divided into the PGE1 group (n=12) and the control group (n=12). In the PGE1 group, PGE1 was administered at 20 ng/kg/min from just after the induction of anesthesia to the end of surgery. Peripheral blood mononuclear cells (PBMCs) were taken before anesthesia and on postoperative days 1, 3 and 7 (POD 1, POD 3 and POD 7). Proliferation responses of T cells to phytohemagglutinin (PHA) and pure protein derivative (PPD) antigen were measured as indicators of cellular immunity.

RESULTS

PGE1 significantly attenuated the impairment of both PHA and PPD response after cardiac surgery on POD 1 (PHA response, 30 +/- 21% vs. 53 +/- 32%, control vs. PGE, p=0.048; PPD response, 18 +/- 21% vs. 39 +/- 27%, control vs. PGE, p=0.046). The reduced glutathione content of PBMCs in the control group was significantly decreased on POD 1.

CONCLUSION

PGE1 attenuated the impairment of cellular immunity after cardiac surgery with CPB by reducing oxidative stress on PBMCs.

Pharmacologic platelet anesthesia by glycoprotein IIb/IIIa complex antagonist and argatroban during in vitro extracorporeal circulation

OBJECTIVE

Contact between blood and the synthetic surfaces of a cardiopulmonary bypass circuit leads to platelet activation, and resultant platelet dysfunction contributes to postoperative bleeding. We compared the effects of various platelet inhibitors on preservation of platelet function during simulated cardiopulmonary bypass circulation.

METHODS

Fresh human blood was recirculated in an in vitro cardiopulmonary bypass model circuit. We measured various platelet activation markers including expressions of PAC-1 and P-selectin, annexin V binding, and microparticle formations by means of whole-blood flow cytometry.

RESULTS

Two types of glycoprotein IIb/IIIa complex antagonists, peptide-mimetic FK633 and abciximab and prostaglandin E(1), significantly prevented platelet loss and the increase in binding of PAC-1, an antibody specific for fibrinogen receptor on activated platelets, during extracorporeal circulation of heparinized blood. These antagonists significantly suppressed but did not abolish P-selectin expression, annexin V binding, and microparticle formation. Anti-von Willebrand factor monoclonal antibody and aurin tricarboxylic acid (an inhibitor of glycoprotein Ib) had no effect on platelet activation during simulated cardiopulmonary bypass circulation. These data suggest that inhibition of fibrinogen binding glycoprotein IIb/IIIa complex is partly effective in attenuating platelet activation in a heparinized cardiopulmonary bypass model circuit. The direct thrombin inhibitor argatroban prevented platelet loss and expression of P-selectin significantly more than did heparin. A combination of FK633 with argatroban as a substitute for heparin further prevented platelet loss and platelet secretion during simulated cardiopulmonary bypass circulation, although the inhibition of microparticle formation was less.

CONCLUSION

The inhibition of both platelet adhesion and thrombin may be effective to preserve platelet number and function during cardiopulmonary bypass circulation.

Activated neutrophils and platelet microaggregates impede blood filterability through microchannels during simulated extracorporeal circulation

BACKGROUND

Neutrophil sequestration and platelet microaggregates in organ capillaries have been implicated in the inflammatory response associated with cardiopulmonary bypass. We examined the filterability of neutrophils and platelet microaggregates through silicon microchannels during simulated extracorporeal circulation. We hypothesize that blood contact with artificial surfaces over time decreases the ability of neutrophils, platelets, and their aggregates to pass through microchannels.

METHODS

Fresh human blood from donors (n = 9) was recirculated for 120 minutes in a simulated extracorporeal circuit. Blood samples were obtained from a donor at 0, 30, 60, and 120 minutes of recirculation. The microchannel transit time and the flow behavior of blood cells were evaluated by a silicon microchannel array flow analyzer. CD11b, L-selectin, and F-actin of neutrophils were measured by flow cytometry. Neutrophil and platelet counts and platelet aggregation to adenosine diphosphate were measured.

RESULTS

The microchannel transit time was prolonged during recirculation, reaching 185.9% +/- 25.6% of baseline at 120 minutes. The video microscope showed that neutrophils and platelet microaggregates plugged the microchannels. CD11b, L-selectin, and F-actin levels changed significantly by 120 minutes. Platelet counts decreased and platelet aggregability was attenuated.

CONCLUSIONS

Simulated extracorporeal circulation caused a progressive loss in the ability of neutrophils, platelets, and their aggregates to pass through the microchannels independent of neutrophil adhesion molecule expression.

Effects of small doses of prostaglandin E(1) on systemic hemodynamics and jugular venous oxygen saturation during cardiopulmonary bypass

STUDY OBJECTIVE

To examine the effects of small doses of prostaglandin E(1) (PGE(1)) on systemic hemodynamics and cerebral oxygenation during cardiopulmonary bypass(CPB).

DESIGN

Randomized, prospective study.

SETTING

Cardiac surgery at Saitama Cardiovascular and Pulmonary Center.

PATIENTS

Forty patients who underwent elective coronary artery bypass surgery.

INTERVENTIONS

The study was performed at the stable CPB period. Patients were randomly divided into four groups: control group (n = 10) received an infusion of saline, PGE(1) 10 group (n = 10) received an infusion of PGE(1) 10 ng/kg/min, PGE(1) 25 group (n = 10) received an infusion of PGE(1) 25 ng/kg/min, and the PGE(1) 50 group (n = 10) received an infusion of PGE(1) 50 ng/kg/min.

MEASUREMENTS

After measuring the baseline partial pressure of the arterial oxygen saturation (SpO(2)), mixed venous oxygen saturation (SvO(2)), and jugular venous oxygen saturation (SjvO(2)), blood gases, and cardiovascular hemodynamic values, PGE(1) was infused intravenously at rate of between 10 and 50 ng/kg/min. PGE(1) infusion continued 30 minutes after the start of drug infusion, and the blood gas analysis and cardiovascular hemodynamic values were simultaneously determined together with the hemodynamic values at 2, 5, 10, 20, and 30 minutes during drug infusion. At 30 minutes after discontinuation of the drug infusion, the blood gas analyses were simultaneously determined together with the hemodynamic values.

MAIN RESULTS

Mean arterial pressure (MAP) in PGE(1) 25 and 50 groups was decreased 20 and 30 minutes after the start of PGE(1) infusion compared with the baseline value (p < 0.05). In contrast, SvOm(2) in PGE(1) 25 and 50 groups was increased 20 and 30 minutes after the start of PGE(1) infusion compared with the baseline value (p < 0.05). There was no change in SjO(2) value despite a decrease in MAP during the study.

CONCLUSIONS

Cerebral oxygenation estimated by SjvO(2) was maintained despite a decrease in MAP during the administration rate of PGE(1) between 10 and 50 ng/kg/min.

Selective blockade of membrane attack complex formation during simulated extracorporeal circulation inhibits platelet but not leukocyte activation

OBJECTIVE

Complement activation is induced by cardiopulmonary bypass, and previous work found that late complement components (C5a, C5b-9) contribute to neutrophil and platelet activation during bypass. In the present study, we blocked C5b-9 formation during extracorporeal recirculation of whole blood to assess whether the membrane attack complex was responsible for both platelet and leukocyte activation.

METHODS

In a simulated extracorporeal model that activates complement (C3a and sC5b-9), platelets (CD62P expression, leukocyte-platelet conjugate formation), and leukocytes (increased CD11b expression and neutrophil elastase), we examined an anti-human C8 monoclonal antibody that inhibits C5b-9 generation for its effects on cellular activation.

RESULTS

Anti-C8 significantly inhibited sC5b-9 formation but did not block C3a generation. Anti-C8 also significantly inhibited the increase in platelet CD62P and monocyte-platelet conjugate formation seen with control circulation. Moreover, compared with control circulation, in which the number of circulating platelets fell by 45%, addition of anti-C8 completely preserved platelet counts. In contrast to blockade of both C5a and sC5b-9 during simulated extracorporeal circulation, neutrophil activation was not inhibited by anti-C8. However, circulating neutrophil and monocyte counts were preserved by addition of anti-C8 to the extracorporeal circuit.

CONCLUSIONS

The membrane attack complex, C5b-9, is the major complement determinant of platelet activation during extracorporeal circulation, whereas C5b-9 blockade has little effect on neutrophil activation. These data also suggest a role for platelet activation or C5b-9 (or both) in the loss of monocytes and neutrophils to the extracorporeal circuit.

Increased anticoagulation during cardiopulmonary bypass by prostaglandin E1

Prostaglandin E1 (PGE1) inhibits tissue factor/factor VIIa-dependent thrombin formation and platelet procoagulant activity. These pathways may trigger thrombin generation during cardiopulmonary bypass (CPB). We hypothesized that the therapeutic combination of PGE1 and heparin increases the degree of anticoagulation as measured by reduced thrombin generation during CPB. Patients undergoing primary coronary artery bypass grafting using CPB were anticoagulated with unfractionated porcine heparin and 12.5 ng x kg(-1) x min(-1) PGE1 (n = 20) or placebo (n = 20). Plasma markers that reflect thrombin generation (prothrombin fragment F1+2, thrombin-antithrombin complex) were determined, and postoperative bleeding was documented. Thrombin generation gradually increased in both groups during and after CPB but was lower in the PGE1 group. After CPB, the difference between mean levels of prothrombin fragment F1+2 was 1.9 nmol/L (95% confidence interval for difference 1.1 to 2.8; P = 0.001). The difference between mean levels of thrombin-antithrombin complex was 43.6 ng/mL (21.2 to 66.1; P = 0.001). A trend in reduced postoperative bleeding was observed in the PGE1 group with a difference of sample means of 183 mL (-5 to 371; P = 0.056). Adding PGE1 to unfractionated heparin enhances anticoagulation during CPB. The results suggest that reduced thrombin generation during surgery may decrease postoperative bleeding.

IMPLICATIONS

Cardiopulmonary bypass is associated with extensive thrombin generation even in the presence of clinically sufficient heparin anticoagulation. The addition of prostaglandin E1 to heparin enhances the degree of anticoagulation as measured by reduced thrombin formation during cardiopulmonary bypass.

Platelets and cardiopulmonary bypass

Exposure of blood to an extracorporeal circulation, such as CPB, causes a variety of physiological responses. Haematological derangements are just one of many potential dangers to the patient who undergoes CPB. The paradox of CPB-related problems with the haematological system is that there are some factors tipping the balance towards a bleeding tendency, and others that favour a prothrombotic state. Both of these issues must be dealt with independently to create the safest environment for surgery. It has been demonstrated that platelets play a key role in both haemostatic dysfunction and thrombotic complications of CPB. Much has been achieved, both clinically and in the laboratory, in the understanding of the precise role platelets play in these events, but the exact mechanisms involved have yet to be completely identified. As research progresses, our understanding will increase, but until then clinical practice must be dictated by the current evidence available.

Right coronary autoregulation in conscious, chronically instrumented dogs

Right coronary (RC) autoregulation and right ventricular (RV) function were assessed in conscious dogs, chronically instrumented to measure RC flow and RC pressure (RCP) as a hydraulic occluder on the RC was inflated. Dogs were then anesthetized, and RC autoregulation and RV function were again assessed. In the conscious state, moderate RC autoregulation was present with closed loop gains (Gc) of 0.59-0.27 as RCP was reduced from 100 to 40 mmHg. In the anesthetized state, Gc was not significantly less than in the conscious state at RCP >50 mmHg. The range and potency of RV autoregulation were greater in both groups than for previously reported findings in anesthetized dogs with RC perfused by an extracorporeal system. RV contractile function was well maintained in conscious and anesthetized dogs at RCP >45 mmHg. We conclude the following: 1) modest RC autoregulation is present in the conscious dog, 2) anesthesia limits the range but not the degree of RC autoregulation, 3) extracorporeal perfusion systems appear to depress RC autoregulation, and 4) RV contractile function remains constant in both conscious and anesthetized dogs until RCP falls below 50 mmHg.

Anticoagulation with prostaglandin E1 and unfractionated heparin during continuous venovenous hemofiltration

OBJECTIVE

To determine the effect of two doses of prostaglandin E1 (PGE1, alprostadil) combined with unfractionated heparin on the hemofilter life-span and the coagulation profile during continuous venovenous hemofiltration.

DESIGN

Prospective, randomized, controlled trial.

SETTING

Intensive care unit at a university-affiliated hospital.

PATIENTS

Twenty-four critically ill, mechanically ventilated patients with postoperative acute renal failure who require continuous venovenous hemofiltration.

INTERVENTIONS

The patients were anticoagulated with 5 ng/kg/min PGE1 and 6 IU/kg/hr heparin or 20 ng/kg/min PGE1 and 6 IU/kg/hr heparin, injected into the extracorporeal circuit before the hemofilter.

MEASUREMENTS AND MAIN RESULTS

The life-span of 43 hemofilters was evaluated. They were used until extracorporeal line pressure exceeded 250 mm Hg, ultrafiltration rate decreased to 16 mL/min, or grossly visible extracorporeal clotting occurred. Blood was sampled from the afferent (prefilter) and efferent (postfilter) lines of the extracorporeal circuit. Platelet counts, in vitro platelet function, plasma concentrations of platelet factor 4, prothrombin fragment F1+2, thrombin-antithrombin complex, routine plasma coagulation tests, and hemodynamic profile were determined before and during hemofiltration. Hemofilter usage was significantly longer in patients anticoagulated with 20 ng/kg/min PGE1 (32 +/- 3 [SEM] hrs) than with 5 ng/kg/min PGE1 (22 +/- 3 hrs). In vitro bleeding parameters were significantly prolonged in postfilter blood in patients receiving 20 ng/kg/min PGE1. Prefilter, there was no antiplatelet activity in either group and platelet counts remained stable. No intra- or intergroup differences in plasma coagulation profile or hemodynamic parameters were detected.

CONCLUSION

Extracorporeal administration of PGE1, combined with low-dose heparinization, inhibits platelet reactivity and preserves hemofilter life dose-dependently.

Iloprost and echistatin protect platelets during simulated extracorporeal circulation

Temporary, reversible inhibition of platelets during cardiopulmonary bypass is an attractive strategy to protect platelets and normalize postoperative bleeding times. Iloprost, an analogue of prostacyclin, and the disintegrins reversibly inhibit platelets by different mechanisms. We tested the hypothesis that reduced doses of iloprost and either echistatin, a natural disintegrin, or RO43-5054, a peptidomimetic, in combination provide better platelet protection than any drug alone during simulated extracorporeal circulation. Thirty-five recirculation studies using fresh, heparinized human blood in an extracorporeal perfusion circuit that contained a 0.45-m2 spiral coil membrane oxygenator were performed. Iloprost, but neither echistatin nor RO43-5054, increased platelet cyclic adenosine monophosphate. Combinations of iloprost and either fibrinogen receptor antagonist at reduced doses submaximally increased platelet cyclic adenosine monophosphate. Platelet adhesion and release of beta-thromboglobulin antigen was completely inhibited by combinations of the two classes of drugs, but only partially inhibited by each drug alone. Combinations of drugs also completely inhibited platelet aggregation to adenosine diphosphate; these platelets retained full sensitivity to adenosine diphosphate after 90 minutes of recirculation when drugs were removed by gel filtration. We conclude that combinations of iloprost and a fibrinogen receptor antagonist at doses that are unlikely to produce clinical side effects completely inhibit platelet activation and preserve platelet function during in vitro extracorporeal circulation.

The effect of prostaglandin E1 during cardiopulmonary bypass on renal function after cardiac surgery

We have evaluated the effect of prostaglandin E1 (PGE1) on renal function after cardiac surgery with cardiopulmonary bypass in 20 patients, ten of whom received 0.02 microgram.kg-1.min-1 of PGE1 by infusion into the oxygenator during bypass; ten patients served as controls. Serum beta 2-microglobulin fell significantly and urine beta 2-microglobulin increased significantly after surgery in both groups. Urine N-acetyl-beta-D-glucosaminidase was high after surgery in both groups, but it was significantly lower in the PGE1 group. Free water clearance fell significantly on the 1st, 3rd, and 5th postoperative days compared with preoperative values in the control but not in the PGE1 group. These results suggest that PGE1 may prevent renal dysfunction after cardiopulmonary bypass.

Cyclosporin A augments human platelet sensitivity to aggregating agents by increasing fibrinogen receptor availability

Clinical use of cyclosporin A (CsA) has been associated with platelet hypersensitivity and an increased incidence of thrombotic and vasoactive events. The purpose of this study was (1) to confirm that CsA enhances platelet sensitivity to the soluble agonists, adenosine diphosphate (ADP) and epinephrine (EPI), and (2) to determine if this enhancement is mediated by alteration in the availability of platelet surface fibrinogen receptors, a final mediator of platelet activation. Mean log dose of ADP required to achieve complete second-wave platelet aggregation in vitro decreased from 1.90 to 1.49 microM (n = 19, paired t test, P less than 0.05) and 2.86 to 2.11 microM (n = 16, P less than 0.05) following a 15-min and 3-hr incubation in the absence (saline) and presence of CsA (1000 ng/ml), respectively. At the threshold dose of ADP, concurrent thromboxane B2 levels at 15 min were 245 +/- 44 ng/ml (n = 12, saline) and 265 +/- 54 ng/ml (n = 9, CsA; P greater than 0.05). At 3 hr respective levels were 333 +/- 57 and 442 +/- 81 ng/ml (P greater than 0.05). Similar results were obtained with EPI. The number of fibrinogen binding sites in response to 50 microM ADP was determined in washed platelets in the absence and presence of CsA by radioligand binding. In 6 of 7 volunteers, CsA increased fibrinogen receptors from 26,635 +/- 4841 to 35,925 +/- 7290 sites/platelet (means +/- SEM; P less than 0.05). No change in receptor affinity was noted. In conclusion, cyclosporine does augment platelet reactivity.(ABSTRACT TRUNCATED AT 250 WORDS)

Blood coagulation and autologous blood transfusion in cardiac surgery

STUDY OBJECTIVE

To review the basic pathophysiology of altered coagulation associated with cardiopulmonary bypass and autologous blood transfusion in cardiac surgery.

DESIGN

Review of rational use of heparin, mechanisms and treatment of coagulation disorders, and autologous blood transfusion.

SETTING

Cardiac surgery in community and academic hospitals.

PATIENTS

Adult cardiac surgical patients.

MAIN RESULTS

Heparin is most commonly used for anticoagulation during cardiopulmonary bypass. Although activated clotting time is widely used to assess heparin-induced anticoagulation, the minimum time to prevent clotting during cardiopulmonary bypass remains unclear. Activated clotting time is affected by many factors other than heparin, such as antithrombin III, blood temperature, platelet count, and age. The rational use of activated clotting time still must be defined. The frequency of abnormal bleeding after cardiopulmonary bypass is significant. Although inadequate surgical hemostasis is the most frequent cause of bleeding, altered coagulation often is present. A decreased number of functional platelets is one of the important causes of bleeding diathesis. Platelet dysfunction is induced by perioperative medication such as aspirin. Cardiopulmonary bypass decreases functional platelets by degranulation, fragmentation, and loss of fibrinogen receptors. Medications such as prostacyclin and iloprost may be useful to protect these platelets. Desmopressin increases factor VIII:C and von Willebrand's factor, leading to a decrease in bleeding time. Desmopressin may be useful to decrease blood loss in repeat cardiac operations, complex cardiac surgery, and abnormal postoperative bleeding. Patients undergoing coronary artery bypass grafting immediately after streptokinase infusion also are at risk for abnormal bleeding. Transfusion of fresh-frozen plasma and cryoprecipitate may be necessary. Autologous blood transfusion is cost-effective and the safest way to avoid or decrease homologous blood transfusion. Predonation, intraoperative salvage, and postoperative salvage are encouraged. Erythropoietin may be useful in increasing the amount of predonation red cells.

CONCLUSIONS

Coagulation disorders in cardiac surgery are caused by many factors, such as heparin, platelet dysfunction, and fibrinolysis. Rational use of blood component therapy and medications such as heparin, protamine, and desmopressin are mandatory. Autologous blood transfusion is very useful in decreasing or obviating the use of homologous blood transfusion.

Intraoperative management of patients with heparin-induced thrombocytopenia

For 11 patients with confirmed heparin-induced thrombocytopenia, we used reversible platelet inhibition with iloprost, a stable prostacyclin analogue, to permit safe heparin administration for cardiac (n = 9) or vascular (n = 2) operations. In vitro, iloprost (0.01 mumol/L) prevented both heparin-induced platelet aggregation and 14C-serotonin release in all patients. Therefore, intraoperatively, a continuous infusion of iloprost was started before administration of heparin and was continued until 15 minutes after administration of protamine. For cardiac patients, after heparin administration, the whole blood platelet count did not change (171,000 +/- 29,000/microL versus 174,000 +/- 29,000/microL, mean +/- standard error of the mean); no spontaneous platelet aggregation was observed, and plasma levels of the alpha-granule constituents platelet factor 4 and beta-thromboglobulin increased from 38 +/- 14 and 140 +/- 18 ng/mL to 591 +/- 135 and 235 +/- 48 ng/mL, respectively. Fibrinopeptide A levels actually decreased from 287 +/- 150 to 27 +/- 6 ng/mL. Furthermore, adenosine diphosphate-induced platelet activation was preserved, postoperative bleeding times were unchanged, and no heparin-related deaths occurred. Similar results were obtained in both vascular patients. We conclude that temporary platelet inhibition with iloprost now permits safe heparin administration in all patients with heparin-induced thrombocytopenia who require a cardiac or vascular operation.

Platelet and neutrophil activation in cardiopulmonary bypass

My colleagues and I have employed a simulated extracorporeal circuit to help define blood cell changes during clinical cardiopulmonary bypass. Platelet count decreases sharply due to temporary adhesion to the circuit. Platelets degranulate, synthesize and release thromboxane A2, and lose the ability to aggregate with adenosine diphosphate and epinephrine. These changes are also due to the loss of alpha 2-adrenergic and fibrinogen receptors. The neutrophil count decreases to a lesser extent, but neutrophils also are stimulated to secrete lactoferrin and elastase concomitant with activation of plasma kallikrein. Although lidocaine can inhibit the neutrophil activation and prostacyclin can inhibit the platelet stimulation, prostaglandin E1 appears to prevent both neutrophil and platelet alterations.

Effect of albumin coating on the in vitro blood compatibility of Dacron arterial prostheses

A recirculating in vitro perfusion system was used to assess the effect of albumin precoating on the thrombogenicity of Dacron vascular grafts. A complete analysis of platelet activation was carried out, involving platelet count, release, adhesion and aggregation. Fibrin formation was assessed by measuring fibrinogen levels and fibrinopeptide A production; leucocyte interaction was analysed by measuring total leucocyte count as well as an analysis of cell adhesion to the surface by scanning electron microscopy. The platelet count decreased progressively with perfusion time for Dacron until by 30 min, it had declined to 69% +/- 2% of baseline. The platelet count did not, however, change significantly from baseline when albumin-coated Dacron was tested. Release of platelet factor 4 and beta-thromboglobulin at 180 min for Dacron was 37.8 +/- 29.8 times and 66.9 +/- 18.2 times baseline, respectively, while albumin coating caused significantly less (P less than 0.03) platelet release. Albumin coating diminished coagulation activation and fibrinopeptide A formation. The total leucocyte concentration decreased significantly for Dacron by 180 min, while that for albumin-coated Dacron did not change significantly from baseline levels. Albumin coating produced a film-like covering over the Dacron. For Dacron, there were numerous leucocytes and platelets adherent to the surface, whilst cellular deposition was minimal upon the albumin-coated surface. Thus, albumin coating improved the short-term blood compatibility of Dacron by all of the methods employed in this study.

Quantitation of platelet preservation with prostanoids during simulated bypass

Extensive blood-synthetic surface interactions during cardiopulmonary bypass produce adverse platelet alterations that can contribute to excessive blood loss following open cardiac surgery. These platelet alterations can be reduced by temporary inhibition of platelet function. In order to define further an optimal method of platelet inhibition during blood-synthetic surface contact, we quantitated platelet functional and structural alterations that occur during simulated extracorporeal circulation (SEC) despite platelet inhibition with Iloprost (ZK) or PGE1. Five-hundred milliliters of fresh heparinized human blood were recirculated for 2 hr in a circuit consisting of silicone rubber components and a spiral coil membrane oxygenator. When blood was recirculated for 2 hr without drug, platelet counts fell significantly to 46 +/- 7% (mean +/- SEM) of initial levels (P less than 0.01); mean platelet volume decreased from 6.90 +/- 0.25 micron3 to 6.05 +/- 0.33 micron3 (P less than 0.01); platelet dispersion increased from 1.73 +/- 0.02 to 2.14 +/- 0.09 (P less than 0.01) and platelets no longer aggregated in response to epinephrine or thrombin. In contrast, when blood was recirculated with either ZK (0.003 microM) or PGE1 (0.3 microM), platelet counts were significantly preserved when compared to blood recirculated without drug (82 +/- 5% and 89 +/- 7%, respectively; P less than 0.01); mean platelet volume did not change; and dispersion only increased from 1.74 +/- 0.02 to 1.85 +/- 0.04 (P less than 0.05). However, following gel filtration, platelets recirculated with PGE1 always responded less than platelets merely incubated with PGE1 when challenged with either epinephrine (50 vs 75%, P less than 0.05) or thrombin (37 vs 65%, P less than 0.05).(ABSTRACT TRUNCATED AT 250 WORDS)

Changes in platelet beta-thromboglobulin, fibrinogen, albumin, 5-hydroxytryptamine, ATP, and ADP during and after surgery with extracorporeal circulation in man

Surgery with extracorporeal circulation (ECC) is associated with transient alterations of platelet function whose pathogenic mechanisms are not completely understood. To define further the platelet abnormalities, we determined the changes in platelet content of several granule-associated substances during and after ECC in patients subjected to aortocoronary bypass surgery. Platelet beta-thromboglobulin (beta-TG) decreased to 79.8% of the preoperative level at the end of ECC (p less than 0.01) and, as expected, did not recover 1 hr after the end of surgery. Platelet fibrinogen and albumin decreased to 67.9% (p less than 0.01) and to 29.8% (p less than 0.01) of baseline, respectively. However, 1 hr after surgery, platelet fibrinogen rose to 92% and albumin to 55.5% of baseline, denoting that during the recovery from ECC, platelets incorporate some plasma proteins. During ECC, platelet 5-hydroxytryptamine (5-HT) and total ATP and ADP decreased to 50.8% (p less than 0.01), 63.2% (p less than 0.01), and 69.9% (p less than 0.01) of their respective preoperative values, indicating dense body release. One hour after surgery, ATP recovered to 83.8%, suggesting that previous depletion compromised also the metabolic pool of adenine nucleotides. In summary, Our results confirm and extend previous observations demonstrating alpha-granule release during ECC. Platelets undergoing ECC can incorporate plasma proteins as evidenced by the rapid increase of platelet fibrinogen and albumin after bypass. Although the mechanisms of this increase and site of storage of the exogenous substances are unknown, this observation justifies further studies to determine if internalization of plasma proteins, especially fibrinogen, may take place in physiological conditions. Dense body depletion with transient storage pool deficiency appears to be a component of the reduced platelet function during ECC. Consumption of metabolic ATP with alteration of platelet energy metabolism may further impair platelet function, contributing to the bleeding episodes observed during surgery with ECC.

Disadvantages of prostacyclin infusion during cardiopulmonary bypass: a double-blind study of 50 patients having coronary revascularization

Prostacyclin (PGI2) has been suggested for use in cardiopulmonary bypass (CPB) because of its positive effects on platelet number and function. Fifty patients who underwent coronary artery bypass grafting using a bubble oxygenator received heparin, 3 mg per kilogram of body weight, and then were randomly assigned to receive PGI2, 25 ng/kg/min, beginning 5 minutes before and until the end of CPB (26 patients) or a placebo (24 patients). Both groups were similar in sex, age, heparin dose, protamine dose, and CPB time. During CPB, mean arterial pressure fell significantly with PGI2 (76 +/- 2 mm Hg to 53 +/- 2 mm Hg; p less than 0.05) and necessitated pressor substances. Platelet counts fell significantly in both groups with the start of CPB, but after 60 minutes were similar in both groups (118 +/- 9 X 10(3) versus 130 +/- 8 X 10(3); not significant [NS]) and were unchanged 3 hours after CPB. Total chest tube output was 647 +/- 51 ml (placebo group) versus 576 +/- 34 ml (PGI2 group) (NS); 18 of the patients given PGI2 required 26 transfusions compared with 16 transfusions in 8 of the patients given a placebo (p less than 0.05). In PGI2 patients, arterial oxygen tension on 100% oxygen fell from 281 +/- 18 mm Hg before CPB to 223 +/- 17 mm Hg immediately after CPB (p less than 0.05). The placebo patients did not show a change in this variable.(ABSTRACT TRUNCATED AT 250 WORDS)

Inhibition of human platelet function by verapamil

We evaluated the ability of the calcium antagonist, verapamil, to alter human platelet function. With the concentrations tested (20 ng to 0.1 mg/ml of whole blood), verapamil inhibited epinephrine-induced aggregation and release of 14C-serotonin; produced a dose-dependent inhibition of 14C-serotonin uptake and prevented aggregation dependent release of thromboxane B2. The action of verapamil could be overcome by higher concentrations of both epinephrine and calcium. Furthermore, verapamil-induced inhibition could be reversed by gel-filtering platelets suggesting that verapamil's anti-platelet activity does not outlast its presence in plasma. Verapamil was relatively ineffective as an inhibitor of ADP-induced aggregation. As with epinephrine-induced platelet activation, the effects of verapamil on ADP-induced 14C-serotonin and thromboxane release correlated with its effects on secondary aggregation. Finally, verapamil failed to alter calcium ionophore-induced platelet aggregation. Thus, verapamil at the concentrations tested, appears to be functioning as a reversible, relatively specific inhibitor of epinephrine-induced platelet activation. Our findings suggest that the actions of verapamil in this regard are complex; there may be competitive inhibition of epinephrine binding as well as a blockade of epinephrine-induced calcium flux.

Platelet-mediated cardiac ischemia

Although platelets have been associated with angina pectoris, myocardial infarction, and sudden death, the platelet's capacity for induction and propagation of cardiac ischemia remains incompletely defined. We therefore evaluated the effects of platelet activation occurring within the coronary circulation and tested the hypothesis that inhibition of platelet function would prevent platelet-induced cardiac ischemia. Human platelets were isolated from blood obtained from normal donors by Sepharose 2B column chromatography, resuspended in Hepes buffer, and added to the perfusate of a Langendorff rabbit heart (platelet counts greater than 10,000/microliters). Without, and with low dose (10 microM) prostaglandin E1 (PGE1), a reversible inhibitor of platelet function, immediate and irreversible global cardiac ischemia, as monitored by NADH fluorescent photography, ensued (N = 4) following platelet activation with thrombin (0.1 to 1 U/ml). Higher concentrations of PGE1 (0.1 to 1 mM, N = 2) or aspirin ingestion (1000 mg taken approximately 12, 4, and 1 hr prior to experiment, N = 2) completely prevented this platelet-induced myocardial ischemia. Aspirin, unlike PGE1, was effective despite its inability to block thrombin-induced platelet aggregation in our in vitro gel-filtered system. We conclude that activation of platelets within the coronary circulation is sufficient for induction of irreversible cardiac ischemia. The efficacy of aspirin, a cyclooxygenase inhibitor, further suggests that the products of arachidonate metabolism (e.g., thromboxanes) have a fundamental role in the genesis of platelet-mediated myocardial ischemia.

Platelets and extracorporeal circulation

Extensive contact between blood and the synthetic surfaces of an extra-corporeal circuit causes thrombocytopenia, release of platelet granular contents, initiation of thromboxane synthesis, disruption of subcellular architecture and loss of platelet sensitivity to standard platelet agonists. All too frequently, these adverse platelet alterations are reflected in a prolongation of the post-operative bleeding time and excessive blood loss which precludes implementation of long-term circulatory assist devices. Unfortunately, a truly biocompatible material does not exist and efficiency of gas transport demands haemodynamic designs which actually promote platelet injury. Although manipulation of surface properties and mechanical improvements in circuitry have managed to reduce platelet-surface interactions, the ultimate potential of these manoeuvres may be limited. Synthetic surfaces and soluble agonists, however, appear to modulate similar pathways suggesting that temporary platelet inhibition might provide significant protection by preserving the morphological and functional integrity of circulating platelets during contact with extracorporeal circuits.

Platelet loss during experimental cardiopulmonary bypass and its prevention with prostacyclin

Prostacyclin (PGI2), a newly discovered short-acting prostaglandin that inhibits platelet aggregation, was evaluated as an agent for prevention of cardiopulmonary bypass-induced thrombocytopenia. Ten adult, splenectomized greyhounds were divided into three treatment groups prior to beginning 120 minutes of partial cardiopulmonary bypass. Group 1 animals received 300 units of heparin per kilogram of body weight, Group 2 animals received 300 units of heparin per kilogram plus PGI2, 1.5 micrograms per minute, and Group 3 animals received 300 units of heparin per kilogram plus PGI2 3.0 micrograms per minute. Bypass and PGI2 infusion were started simultaneously. Mean platelet counts of each group at 5 minutes were approximately 40% of prebypass levels. Additional platelet loss was seen in Groups 1 and 2 at 30, 60, and 120 minutes. However in Group 3, platelet counts at 30 and 60 minutes were essentially unchanged from prebypass levels. At 30, 60, and 120 minutes of cardiopulmonary bypass, the differences between Groups 1 and 3, and 2 and 3 are highly significant (p less than 0.01). We conclude that PGI2 is an effective agent for preserving platelet levels during experimental cardiopulmonary bypass. Furthermore, it is possible that platelet loss during cardiopulmonary bypass may be caused, in part, by an imbalance between PGI2 and thromboxane A2, which results in excessive platelet adhesion and aggregation.