Significance of the whole blood activated clotting time in cardiopulmonary bypass

Recent publications have described a poor correlation between whole blood activated clotting time (WBACT) values and plasma heparin levels during cardiopulmonary bypass (CPB). A prospective, controlled study was undertaken to investigate the variables which may influence the WBACT in this situation. Antithrombin III levels over a range of 35-93 u/dl did not influence either the WBACT value or plasma heparin level. However, reduced platelet function following infusion of prostacyclin (10 ng/kg/min prior to CPB and 20 ng/kg/min thereafter); platelet number (range 63-287 X 10(9)/l) and packed cell volume (range 16-30%) were found to correlate with the WBACT. It is concluded that in addition to the circulating plasma heparin level, the wide variations in platelet number, platelet function and packed cell volume which are frequently observed during cardiopulmonary bypass may also influence the WBACT value.     

Heparin dosing and monitoring for cardiopulmonary bypass. A comparison of techniques with measurement of subclinical plasma coagulation

Subclinical plasma coagulation during cardiopulmonary bypass has been associated with marked platelet and clotting factor consumption in monkeys. To better define subclinical coagulation in man, we measured plasma fibrinopeptide A concentrations before, during, and after cardiopulmonary bypass. Patients were assigned to one of three groups of heparin management: group 1 (n = 10)--initial heparin dose 300 IU/kg, with supplemental heparin if the activated coagulation time fell below 400 seconds; group 2 (n = 6)--initial heparin dose 250 IU/kg, with supplemental heparin if activated coagulation time was less than 400 seconds; and group 3 (n = 5)--initial heparin dose 350 to 400 IU/kg, with supplemental heparin if whole blood heparin concentration was less than or equal to 4.1 IU/ml. Activated coagulation time and heparin concentration were measured every 30 minutes during cardiopulmonary bypass, and fibrinopeptide A was measured at hypothermia, normothermia, and whenever activated coagulation time was less than 400 seconds. Quantitative and qualitative blood clotting competence was assessed after cardiopulmonary bypass, including mediastinal drainage for the first 24 hours. Fibrinopeptide A values were markedly elevated during cardiopulmonary bypass but were well below the levels present before and after cardiopulmonary bypass. Fibrinopeptide A correlated inversely with heparin concentration during cardiopulmonary bypass (r = -0.46, p = 0.03), but higher fibrinopeptide A levels during cardiopulmonary bypass did not correlate with post-cardiopulmonary bypass coagulopathy. Group 3 patients received the highest heparin doses (p less than 0.05) and had the greatest postoperative blood loss (p less than 0.05). Protamine dose and heparin concentration during cardiopulmonary bypass correlated best with postoperative mediastinal drainage. Our findings support the following conclusions: (1) compensated subclinical plasma coagulation activity occurs during cardiopulmonary bypass despite activated coagulation time greater than 400 seconds or heparin concentration greater than or equal to 4.1 IU/ml; (2) post-cardiopulmonary bypass mediastinal drainage correlates strongly with increased heparin concentration during cardiopulmonary bypass (p less than 0.05) and protamine dose (p less than 0.05); and (3) during cardiopulmonary bypass at both normothermia and hypothermia, activated coagulation times greater than 350 seconds result in acceptable fibrinopeptide A levels and post-cardiopulmonary bypass blood clotting.     

Heparin Monitoring and Neutralization during Cardiopulmonary Bypass Using a Rapid Plasma Separator and a Fluorometric Assay

Avoidance of over- or underheparinization during cardiopulmonary bypass (CPB) is crucial in preventing bleeding or clotting. Currently no completely satisfactory method is available for measuring heparin levels—a method that would be rapid, inexpensive, specific, and reproducible. We combined the use of two devices, a rapid plasma separator and a fluorometric heparin assay system, in an attempt to satisfy these requirements in 15 patients having CPB during cardiac surgical procedures. The first instrument separates plasma from whole blood using a pneumatic filtration principle, while the heparin assay system measures the effect of heparin on thrombin conversion of a synthetic fluorogenic substrate. Accurate plasma heparin levels can be generated in less than five minutes, and the assays are inexpensive and easy to perform. Performing heparin assays at critical intervals during CPB allowed desired heparin levels to be maintained and the protamine dose for heparin neutralization to be reduced to a minimum. In addition, studies for heparin rebound revealed negligible rebound up to six hours postoperatively despite the reduced doses of protamine. There were no hemorrhagic or clotting complications in the series.     

Rapid disappearance of protamine in adults undergoing cardiac operation with cardiopulmonary bypass

BACKGROUND: Despite long use of protamine in cardiac operations, neither protamine concentrations nor pharmacokinetics have been reported in patients. METHODS: Twenty-eight patients (age, 26 to 80 years) undergoing various cardiac surgical procedures gave their consent to receive 250 mg of protamine sulfate administered intravenously by an infusion pump during 5 minutes. Protamine was administered at the usual intraoperative time after separation from cardiopulmonary bypass for reversal of heparin. Timed arterial blood samples were obtained after protamine infusion. Blood plasma was subjected to solid-phase extraction and high-performance liquid chromatography. Total (free + heparin-bound) protamine concentration versus time data were subjected to pharmacokinetic modeling. RESULTS: Twenty-six patients completed the study. Total plasma protamine concentrations declined rapidly. Model-independent pharmacokinetic analysis revealed median (range) values as follows: volume of distribution, 5.4 L (0.82 to 34 L); clearance, 1.4 L/min (0.61 to 3.8 L/min); and half-life, 4.5 min (1.9 to 18 min). Schwarz-Bayesian criterion identified a two-compartment exponential model with adjustment for weight in the central compartment volume of distribution as performing better than other compartmental or Michaelis-Menten models. CONCLUSIONS: Protamine has a very short (approximately 5 minutes) half-life after a single 250-mg dose in adult patients. This short half-life could underlie recurrent anticoagulation after initial apparent reversal of heparin.     

体外循环中肝素、鱼精蛋白对血小板的激活及抑肽酶的抑制作用

目的研究在体外循环中肝素化及鱼精蛋白中和时血小板的激活以及应用抑肽酶对这种激活的抑制作用。方法２０例心脏瓣膜置换术患者随机等分为两组：对照组和抑肽酶组，分别于肝素化及应用鱼精蛋白前后检测血小板胞浆游离钙浓度，磷脂酶Ａ２活性及血浆血栓素水平。结果上述指标在肝素化及鱼精蛋白中和后均显著升高，其中鱼精蛋白中和时升高幅度更大，应用抑肽酶对肝素及鱼精蛋白所引起的上述改变均有显著抑制作用。结论抑肽酶对肝素和鱼精蛋白所致的血小板激活有显著抑制作用，这可能与抑肽酶在体外循环中的止血作用有关。     

Response to heparinization in adults and children undergoing cardiac operations.

The activated clotting time is an unreliable index of anticoagulation status during cardiopulmonary bypass procedures. However, modern instrumentation (Hemotec Hepcon HMS) now allows the monitoring of free heparin levels via automated protamine titration. In the present study, the standard procedure of anticoagulation at Killingbeck Hospital, Leeds, was investigated. Twenty-two pediatric patients and 20 adult patients undergoing open heart procedures involving cardiopulmonary bypass were given empirical doses of heparin (3 mg/kg body weight bolus), and activated clotting time was maintained at a level greater than 450 seconds using the Hemochron Timer. Heparin neutralization was performed at the termination of the bypass period using an empirical equivalent (3 mg/kg) of protamine sulfate. Mean free heparin concentration (+/- standard deviation) fell from 2.26 (+/- 0.45) mg/kg to 1.39 (+/- 0.34) mg/kg over the period 10 to 40 minutes on bypass in children. In adults, free heparin level declined from 2.56 (+/- 0.58) mg/kg to 1.81 (+/- 0.58) mg/kg over the same period. The biological half-life for heparin was 60 minutes in adults and 35 minutes in pediatric patients. Empirical protamine dosing resulted in excess protamine administration when compared with Hepcon titrated dose requirements: for children: median (range), 80 (12 to 350) versus 33 (12 to 97) mg, p less than 0.001; and for adults: 350 (200 to 500) versus 130 (61 to 237) mg, p less than 0.001. In conclusion, empirical heparin administration (3 mg/kg) does not result in "steady-state" anticoagulation during cardiopulmonary bypass, and empirical administration of protamine takes no account of interindividual differences in heparin sensitivity and biological half-life, which may be assessed using the Hepcon HMS.     

Lack of correlation between activated clotting time and plasma heparin during cardiopulmonary bypass.

The activated clotting time (ACT) with a Hemochron system for determining heparin requirements during cardiopulmonary bypass surgery, (CPB) accompanied by hemodilution and hypothermia was evaluated using plasma heparin levels as a standard. In 28 patients who were administered a standard heparin regimen (300 units/kg prebypass, 8000 units in the pump prime and 100 units/kg hourly during CPB) mean prebypass plasma heparin was 4 units/ml, and ACT was 493 seconds. During CPB mean plasma heparin decreased significantly (p < 0.001) to 3.1 units/ml, whereas mean ACT increased significantly (p < 0.001) to 674 seconds. The mean protamine requirement predicted from ACT was significantly higher (43%) than predicted from plasma heparin levels or actual protamine administered. The ACT neither accurately reflected plasma heparin during CPB nor predicted protamine requirements. The fixed-dose regimen employed, however, prevented both intraoperative thrombosis, assessed clinically in all patients, and clotting on six arterial line filters, as determined by scanning EM, despite wide variations in ACT and plasma heparin levels during surgery.     

Comparison of two protocols for heparin neutralization by protamine after cardiopulmonary bypass

Twenty patients undergoing cardiac operations were randomly assigned to two protocols for heparin neutralization by protamine after cardiopulmonary bypass. In all patients protamine chloride was given at a ratio of 1 unit of protamine to 1 unit of injected heparin. In Group I (10 patients) all protamine was infused within 10 minutes after termination of cardiopulmonary bypass. Group II (10 patients) received 75% of the calculated protamine dose within 10 minutes after termination of bypass and the remainder after transfusion of all blood in the heart-lung machine. Plasma heparin levels were significantly lower in Group II 5 minutes after transfusion of all blood in the heart-lung machine and were 0.13 units/ml (standard deviation 0.04) in Group I and 0.06 units/ml (standard deviation 0.05) in Group II (p less than 0.001) 60 minutes after bypass. Activated partial thromboplastin time mirrored the changes in plasma heparin, whereas activated clotting time (Hemochron) was too insensitive to detect these low plasma heparin levels. We conclude that the two-dose protocol resulted in more complete heparin neutralization than the one-dose protocol.     

Fresh frozen plasma: a solution to heparin resistance during cardiopulmonary bypass

The reasons for the highly variable response of patients to heparin remain incompletely understood. Empirical maintenance of the activated clotting time (ACT) at levels of 400 to 480 seconds appears to be safe for cardiopulmonary bypass (CPB). For patients with ACT responses lower than predicted for initial heparin doses, titration with additional heparin has been customary. In 44 patients undergoing cardiopulmonary bypass, 20 patients were identified as having initial ACTs of 300 seconds or less after receiving 300 units per kilogram of heparin. In 11 of them, ACTs were titrated to 400 to 480 seconds with additional heparin. Nine were given 2 units of fresh frozen plasma shortly after institution of CPB. In this group, there was significant augmentation of the ACT immediately after infusion of plasma. No differences in total heparin dosages given during CPB were found between 24 control patients with initially acceptable ACTs and the group receiving fresh frozen plasma. In contrast, more heparin was necessary in the patients with a low ACT titrated with heparin alone. Data also indicated that protamine sulfate requirements were substantially lower after administration of plasma than were those in either the control or the heparin-titrated, low ACT group. Fresh frozen plasma appears to "normalize" the heparin-ACT dose-response curve in heparin-resistant patients and to lessen total heparin requirements during CPB.     

Clinical role of blood heparin level monitoring during open heart surgery.

Protamine has been used for neutralizing heparin and its dosage is decided by the initial fixed dose of heparin. Adequate protamine neutralization is very important to reduce complications. To attenuate excess reactions, in particular, whole blood heparin concentration during and after cardiopulmonary bypass was measured using Hepcon, and the efficacy of optimal protamine dose in open heart surgery was evaluated. Twenty patients were randomly divided into two comparable groups, P and C. In the C group, heparin was neutralized with an initial fixed dose of protamine, 1.67 mg protamine per milligram total heparin (n = 8). In the P group, protamine dose was determined for residual heparin concentration (n = 12). In the P group, blood heparin concentrations at 60 minutes after the establishment of cardiopulmonary bypass, just after cardiopulmonary bypass and first protamine administration were 2.35 +/- 0.14, 2.31 +/- 0.17 and 0.13 +/- 0.08 U/ml, respectively. Concentrations reached zero with the second protamine administration. The requirement of transfusion (659 +/- 224 vs. 1559 +/- 323 ml, p = 0.0314), pulmonary vascular resistance index just after the protamine administration (190 +/- 22 vs. 286 +/- 18 dyne.s.cm-5.m2, p = 0.0137) and the IL-8 levels (just after protamine: 26.9 +/- 5.1 vs. 43.5 +/- 5.9 pg/ml, p = 0.0499, 12 hours after cardiopulmonary bypass: 37.1 +/- 12.1 vs. 86.8 +/- 20.0, p = 0.0435) in the P group were significantly lower than those in the C group. These data suggested that heparin level monitoring in whole blood may be useful to determine the optimal dose of protamine resulting in the decrease of a requirement of blood components in open heart surgery and attenuating in transient pulmonary hypertension and excess protamine-induced inflammatory reactions.     

Evaluation of tests used to monitor heparin therapy during extracorporeal circulation.

Two tests, the activated coagulation time test (ACT), and the quantitative protamine titration test (QPT), were examined in detail as representative of a large number of tests potentially useful in determining dose of heparin needed during cardiopulmonary bypass and the dose of protamine needed for reversal of heparin. The variability introduced by the test methods (ACT 6 percent, QPT 8 per cent) was insignificant comparen (greater than 25 per cent) and the variation in plasma volume (14 per cent). Both of these variables affected not only QPT but also any modification of it that measures the level of heparin by titration with protamine solutions. Tests that measure the effect of heparin on the clotting time, of which the ACT is an example, were unaffected by either population variable when used in conjunction with a simply constructed dose-response curve.     

Successful use of a reduced dose of protamine after cardiopulmonary bypass.

The dose of protamine necessary to reverse heparin was examined in 60 patients. Half the patients (controls) received a reversal dose of protamine equal to the entire amount of heparin given them, while half received a reversal dose based on a heparin half-life of 2 hours. Postoperative chest drainage for the first 12 hours and for 48 hours was markedly reduced in patients given the reduced dose of protamine. Platelet counts were higher and postoperative clotting studies varied less from control in patients receiving the smaller dose of protamine. The authors suggest reevaluation of the dose of protamine necessary to reverse the anticoagulant effects of heparin in patients for cardiopulmonary bypass, since larger doses protamine may contribute to the conditions which increase postoperative bleeding.     

Decreased blood loss after cardiopulmonary bypass using heparin-coated circuit and 50% reduction of heparin dose.

In a randomized, double-blind study of patients undergoing elective coronary artery grafting, the effect of heparin-coated circuit combined with 50% reduction of systemic heparin bolus was investigated. Ten patients comprised group HC (heparin-coated) and ten group C (controls). The mean total doses of heparin were 172 IU/kg in group HC and 416 IU/kg in group C and the respective protamine doses were 0.96 and 3.96 mg/kg (both p < 0.001). Activated clotting times during cardiopulmonary bypass were significantly shorter in group HC, and both intra- and postoperative bleeding was significantly less than in group C (7.7 vs. 11.7 ml/kg, p = 0.036, and 6.9 vs. 9.7 ml/kg, p = 0.004). Hemoglobin loss via the drains was 22.5 g in group HC and 43.7 g in group C (p < 0.005). Hemolysis at the end of bypass was significantly greater in group C. Apart from one perioperative myocardial infarction in group HC the postoperative course was uneventful. Use of a heparin-coated circuit is concluded to permit complication-free reduction of heparin and protamine doses and to decrease both intra- and postoperative bleeding, which may favorably influence the outcome of coronary artery grafting.     

Polybrene neutralization as a means of monitoring heparin therapy for extracoporeal cirulation.

Dose-response effects of heparin and protamine in 34 adult patients undergoing cardiac operations were monitored by an in vitro analysis utilizing hexadimetharine bromide (Polybrene) neutralization. Heparin administered prior to cannulation for cardiopulmonary bypass in a dose of 3.0 mg (300 units) per kilogram of body weight, and 1.5 mg (150 units) per kilogram for each subsequent hour of bypass, routinely produced circulating heparin concentrations greater than 1.0 units per milliliter of plasma. A protamine dose equal to 80% of the total number of milligrams of heparin given resulted in no detectable plasma heparin in 23 of the 34 patients one-half hour after administration. No patient required protamine in an amount greater than the total number of milligrams in the heparin dose to achieve heparin neutralization. Modest postoperative chest tube drainage (mean, 784 ml in 48 hours) in these patients provides clinical support for low-dose protamine administration for heparin neutralization at the conclusion of cardiopulmonary bypass.     

The effects of methylprednisolone on complement, immunoglobulins and pulmonary neutrophil sequestration during cardiopulmonary bypass.

In this study, the authors administered high dose (30 mg/kg body weight i.v.) methylprednisolone before cardiopulmonary bypass to observe the effects on complement, immunoglobulins and pulmonary neutrophil sequestration. Fifty patients undergoing valve replacements were included in this study. Patients were divided into two groups: group I (20 patients) served as control and did not receive methylprednisolone, group II (30 patients) received methylprednisolone. Blood samples for complements (C3c and C4) were taken, before cardiopulmonary bypass, at 5, 10 and 30 min intervals from the end of cardiopulmonary bypass, after reversal of heparin with protamine infusion, and after skin closure. Blood samples for immunoglobulins were taken before cardiopulmonary bypass, 30 min after onset of cardiopulmonary bypass and after skin closure. After onset of cardiopulmonary bypass, all C3c and C4 levels decreased in both groups. There was a significant decrease in C4 levels at end of cardiopulmonary bypass and after protamine infusion in group I compared with group II (P < 0.05). C3c levels in group I decreased significantly compared with group II after 30 min of cardiopulmonary bypass and after protamine infusion (P < 0.05). All immunoglobulin (IgG, IgM, IgA) levels were decreased in both groups, but the decrease in IgG was statistically significant after skin closure in group I compared with group II (P < 0.05). Pulmonary neutrophil sequestration was higher in the control group compared with the methyl-prednisolone group (P < 0.05). In conclusion, methylprednisolone administration before cardiopulmonary bypass may prevent the harmful effects of complement activation, immunoglobulin denaturation and neutrophil sequestration in the pulmonary capillary system.     

Clinical role of blood heparin level monitoring during open heart surgery

Protamine has been used for neutralizing heparin and its dosage is decided by the initial fixed dose of heparin. Adequate protamine neutralization is very important to reduce complications. To attenuate excess reactions, in particular, whole blood heparin concentration during and after cardiopulmonary bypass was measured using Hepcon®, and the efficacy of optimal protamine dose in open heart surgery was evaluated. Twenty patients were randomly divided into two comparable groups, P and C. In the C group, heparin was neutralized with an initial fixed dose of protamine, 1.67 mg protamine per milligram total heparin (n = 8). In the P group, protamine dose was determined for residual heparin concentration (n = 12). In the P group, blood heparin concentrations at 60 minutes after the establishment of cardiopulmonary bypass, just after cardiopulmonary bypass and first protamine administration were 2.35 ± 0.14, 2.31 ± 0.17 and 0.13 ± 0.08 U/ml, respectively. Concentrations reached zero with the second protamine administration. The requirement of transfusion (659 ± 224 vs. 1559 ± 323 ml, p = 0.0314), pulmonary vascular resistance index just after the protamine administration (190 ± 22 vs. 286 ± 18 dyne·s·cm^?5·m², p = 0.0137) and the IL-8 levels (just after protamine: 26.9 ± 5.1 vs. 43.5 ± 5.9 pg/ml, p = 0.0499, 12 hours after cardiopulmonary bypass: 37.1 ± 12.1 vs. 86.8 ± 20.0, p = 0.0435) in the P group were significantly lower than those in the C group. These data suggested that heparin level monitoring in whole blood may be useful to determine the optimal dose of protamine resulting in the decrease of a requirement of blood components in open heart surgery and attenuating in transient pulmonary hypertension and excess protamine-induced inflammatory reactions.     

Platelet damage by protamine and the protective effect of prostacyclin: an experimental study in dogs

Protamine is given after cardiopulmonary bypass to reverse the effect of heparin. However, the adverse effects of an overdose have not been fully evaluated. In this canine study, a standard dose of one bolus of heparin (300 IU per kilogram of body weight) was neutralized by an infusion of protamine hydrochloride in a 1:2 ratio. Platelet number and function were severely reduced by this overdose of protamine, and this finding correlated with a prolongation of the bleeding time. Giving a titrated dose of protamine hydrochloride to reverse heparin activity, measured by the activated clotting time, affected neither platelet number nor function. When prostacyclin (0.5 microgram/kg/min) was infused during administration of an overdose of protamine, platelets again were not affected by the excess of protamine.     

Relationship between granulocyte elastase and C3a under protamine dosing in on-pump cardiac surgery.

OBJECTIVE: The complement cascade and granulocytes are activated in on-pump cardiac surgery. If activation of complement directly regulates granulocytes, granulocyte elastase (GEL) should increase significantly after protamine administration. We examined the effect of protamine on granulocytes by protamine administration and observation of the effect on GEL and C3a. METHODS: Thirty patients who underwent coronary artery bypass grafting were randomly assigned to two groups. In 15 patients, protamine was administered 5 min after the termination of cardiopulmonary bypass, and was administered 35 min after cardiopulmonary bypass in the other 15 patients. All patients were perfused with heparin-coated circuits and received 300 IU/kg heparin and 3 mg/kg protamine. GEL and C3a concentrations were measured at 7 time points. RESULTS: GEL concentrations increased significantly just before aortic declamping and did not increase significantly after protamine administration. C3a concentrations, however, did not increase during cardiopulmonary bypass and did increase significantly after protamine administration. CONCLUSIONS: This study indicates that GEL does not increase after protamine administration and that complement concentration does not directly affect GEL release.     

Propranolol binding in plasma during cardiopulmonary bypass

The effect of cardiopulmonary bypass on the plasma binding of propranolol was examined in seven patients. The fraction of propranolol free in plasma doubled, increasing from 6.6 to 13.5 per cent (P less than 0.001) following the administration of heparin, 400 IU/kg. Once cardiopulmonary bypass was concluded and protamine, 8 mg/kg, given, the free fraction decreased from 13.4 to 8.7 per cent (P less than 0.005). There was a further significant decrease to 6.5 per cent over the next 3.1 hours (SE +/- 0.3). Those alterations in the free fraction, which would result in more drug being available for binding to receptor sites and for exerting its pharmacologic effect, were due principally to the changes in free fatty acid levels produced by heparin and protamine, but also to the hemodilution produced by the pump prime.     

Thrombin Generation During Cardiopulmonary Bypass Using Heparin-Coated or Standard Circuits

For quantitative comparison of thrombin generation during cardiopulmonary bypass (CPB) with heparin-coated vs conventional CPB circuits, thrombin-antithrombin III complex (TAT) and prothrombin fragment 1+2 (F₁₊₂) were analyzed in 20 patients undergoing combined heart valve surgery and coronary artery bypass grafting (CABG), in ten cases with heparin-coated circuits (COMB-HC) and in ten with standard circuits (COMB-C). Extensive thrombin generation was found in both groups, with maximal TAT and F₁₊₂ levels at the end of CPB. Of 15 operations with only CABG, seven were performed with heparin-coated circuits and heparin dose 40% of normal (CABG-HC), and eight with standard circuits and normal heparin doses (CABG-C). TAT was maximal at the end of CPB and F₁₊₂ peaked 3 hours after protamine injection. At the end of CPB both levels were significantly higher in the CABG-HC than in the CABG-C group, though thrombin generation was less than in the COMB groups. The abundant thrombin generation during CPB thus was much more pronounced during complex operations. Use of heparin-coated circuits did not reduce thrombin generation, which was increased by 60% reduction of the systemic heparin dose. The clinical implications are still unknown, as no complications were observed.