Reversal of heparin anticoagulation by recombinant platelet factor 4 in humans

BACKGROUND

Protamine is used to reverse the anticoagulant effects of heparin, but it can have important side effects. Platelet factor 4 (PF4) is a protein found in platelet alpha granules that binds to and thereby neutralizes heparin. We evaluated the safety and effectiveness of intravenous recombinant PF4 to neutralize heparin anticoagulation after cardiac catheterization in a phase 1, open-label trial.

METHODS AND RESULTS

The study group consisted of 18 patients having diagnostic cardiac catheterization. Heparin (5000 U) was given after vascular access was obtained. In the first 12 patients, additional heparin was given at the conclusion of the procedure so that all patients had activated coagulation times > 300 seconds before rPF4 was given. Three patients each received 0.5, 1.0, 2.5, or 5.0 mg/kg rPF4 over a period of 3 minutes at the conclusion of the catheterization procedure. In 6 additional patients, extra heparin was not given at the conclusion of the procedure, and 1.0 mg/kg rPF4 was given. Hemodynamic measurements, cardiac output, and serial blood tests were performed 5, 10, 20, and 30 minutes after rPF4 and then into the next 24 hours. There were no serious side effects in any patient, despite transient rPF4 levels as high as 14,870 ng/mL in the patients receiving 5.0 mg/kg. One patient receiving 2.5 mg/kg had a slight transient rise in liver enzymes possibly related to the rPF4. There were no important hemodynamic effects of rPF4 administration at any dose used. Doses of 2.5 and 5.0 mg/kg were uniformly effective in reversing the anticoagulant effect of heparin. At lower doses, rPF4 neutralized the effects of heparin in most but not all patients. Pharmacokinetic analysis suggested a monophasic and one-compartment clearance of the PF4-heparin complex. No neutralizing factors to rPF4 were detected in the samples collected 7 days after dosing.

CONCLUSIONS

rPF4, in doses ranging from 0.5 to 5.0 mg/kg over 3 minutes, had no serious side effects. Given in sufficient amounts, rPF4 can completely and rapidly reverse the anticoagulant effects of heparin.

Thrombelastography reveals two causes of haemorrhage in HELLP syndrome

We describe the use of thrombelastography in HELLP syndrome (Haemolysis, Elevated Liver Enzymes, Low Platelets). It differentiated between two possible causes of significant haemorrhage and revealed an accompanying underlying fibrinolysis. This allowed specific therapy to be directed at both abnormalities and, we believe, helped prevent this patient from undergoing radical surgery to curb blood loss.

High frequency jet ventilation for severe haemoptysis during extracorporeal circulation

Two patients are described in whom fulminant haemoptysis occurred during extracorporeal circulation. The use of high frequency jet ventilation resulted in a dramatic decrease of blood loss from the tracheal tube, avoiding the need for more aggressive management.

Biocompatibility of heparin-coated membrane oxygenator during cardiopulmonary bypass

The biocompatibility of the cardiopulmonary bypass (CPB) circuit, in which an oxygenator is solely heparinized, was assessed by systemic inflammatory reactions as an indicator during CPB. Fourteen patients, 11 males and 3 females, underwent coronary artery bypass surgery and were randomly divided into 2 groups of 7 patients each. For the heparin-coated oxygenator group (Group H), a heparin-coated membrane oxygenator was used in the CPB circuit, and in the control (Group C) an uncoated membrane oxygenator was employed. Systemic inflammatory reactions, such as platelet activation, prostaglandin production, complement activation, and activated granulocyte released substance, were measured prior to, during, and 6 h after CPB. The number of platelets decreased after protamine administration in both groups (14.5 +/- 4.7 x 10(4)/microliters in Group H and 13.8 +/- 8.7 x 10(4)/microliters in Group C) and returned to baseline levels in Group H while it remained decreased in Group C at 6 h after CPB. The platelet factor 4 level was significantly lower in Group H (181 +/- 40 ng/ml) than in Group C (297 +/- 131 ng/ml) after protamine administration. Thromboxane-B2 (TXB2) rose during CPB in both groups; however, there were significantly different levels of TXB2 between the 2 groups at 60 min after CPB (293 +/- 258 pg/ml in Group H versus 408 +/- 120 pg/ml in Group C) and after protamine administration (259 +/- 122 pg/ml in Group H versus 709 +/- 418 pg/ml in Group C). Plasma concentrations of granulocyte elastase were significantly lower in Group H at 30, 60 and 90 min, immediately after, and post-CPB than those of Group C.(ABSTRACT TRUNCATED AT 250 WORDS)

Reversal of post-reperfusion coagulopathy by protamine sulphate in orthotopic liver transplantation

We report details of two liver transplant procedures in which post-reperfusion coagulopathy was reversed by administration of protamine sulphate. Both procedures were uncomplicated until about 30 min after reperfusion of the graft, when the cut surfaces began to ooze blood. Failure of coagulation was confirmed by thrombelastography and in both cases routine coagulation tests revealed a prolonged kaolin cephalin clotting time (KCT). A heparin-like effect was suspected. Protamine sulphate 50 mg was given i.v., resulting in cessation of bleeding and normalization of the thrombelastogram and KCT.

Peri-operative anticoagulant effects of heparinization for carotid endarterectomy

The question of whether or not to reverse heparin following carotid endarterectomy is a topic of debate. The potential reduction of the risk of thrombosis at the endarterectomy site with non-reversal has to be measured against a potential increase in the risk of wound haematoma. This study prospectively followed activated clotting time (ACT) of 42 consecutive patients undergoing carotid endarterectomy. A standard heparin dose of 100 units/kg was used, and heparin reversal was employed only if the wound appeared excessively haemorrhagic at the procedure's completion. Heparin was reversed in 11 patients. Following heparin administration, ACT increased to a mean 2.72 +/- 0.09 times baseline (range 1.84-4.07), and fell with time, until at 3 h after heparin administration mean ACT in the non-reversed patients was 1.48 +/- 0.03 times baseline (range 1.1-2.03). There was one postoperative neurological event (2%), a contralateral hemisphere stroke. No patient developed a frank wound haematoma requiring evacuation, although three patients (7% of the total study group, 9% of patients not receiving heparin reversal) developed neck swelling and symptoms of airway compromise, and were intubated. Measurements of ACT suggest that a heparin dose of 100 units/kg achieves an adequate anticoagulant level in the operative and early postoperative phase, when thrombosis is most likely to occur, and is not associated with an increased risk of wound haematoma. If heparin is to be selectively reversed in patients felt to be at high risk of postoperative haematoma, the decision should be based on an objective measurement such as ACT, and not the surgeon's impression of wound haemostasis.

Inhibition of inflammatory angiogenesis in rats by loco-regional administration of hydrocortisone and protamine

We have studied the antiangiogenetic effects of hydrocortisone and protamine given intra-arterially. The cornea of male, Sprague-Dawley rats were cauterized with silver nitrate. The following treatments were given: 30 micrograms hydrocortisone topical (t.p.), b.i.d., 50 mg/kg/day intraperitoneally (i.p.) or intra-arterially (i.a.), 10 mg/kg/day protamine i.p. or i.a. Saline was administered to the control groups. In separate experiments we also evaluated the anti-inflammatory effects of hydrocortisone, i.p., on the cauterized corneas. Five days after cauterization, the animals were killed, exsanguinated and India ink was injected to show the network of neovessels. The percentage area of the cornea covered by neovessels was measured morphometrically and evaluated statistically. Hydrocortisone t.p. (-84%), i.a. (-60%) and protamine i.a. (-44%) significantly inhibited angiogenesis in the cauterized cornea. Either drugs, i.p., had any antiangiogenetic effects, but hydrocortisone significantly reduced cell infiltration of the corneas. The results suggest that locoregional administration of antiangiogenetic drugs might be clinically useful.

Protamine sulfate and vancomycin are synergistic against Staphylococcus epidermidis prosthesis infection in vivo

We have previously demonstrated that the quaternary amine, protamine sulfate (PS), is bactericidal against Staphylococcus epidermidis. In an attempt to decrease genitourinary prosthesis infection rates, we examined the ability of PS as a wound irrigant to inhibit Staphylococcus epidermidis viability. Eighty-seven Sprague-Dawley rats were studied by implanting a sterile silicone pellet in their dorsum. The pellet was inoculated with Staphylococcus epidermidis and the rats were divided into four groups based on the wound irrigant employed after inoculation: (1) control (sterile water) (2) vancomycin; (3) PS; (4) vancomycin + PS. All rats received perioperative and daily intramuscular vancomycin, and the pellets were explanted on postoperative day 28 and cultured. The infection rates were: (1) control 77%, (2) vancomycin 50%, (3) protamine sulfate 67%, and (4) protamine sulfate and vancomycin 19%. The differences between (2) vancomycin versus (4) vancomycin + PS and (3) PS versus (4) vancomycin + PS were significant (p = 0.05 and p < 0.005). The data suggest that PS potentiates vancomycin as a wound irrigant in prosthesis implantation.

Anticoagulation and hemostasis in cardiac surgical patients

Optimizing anticoagulation and hemostasis during cardiopulmonary bypass and perioperatively helps to ensure the best possible clinical outcome. This article reviews the pharmacology of unfractionated and low-molecular weight heparin, aprotinin, desmopressin, dextran, antiplatelet agents, warfarin, and direct thrombin inhibitors. Their use is discussed in the context of coronary artery surgery, valvular surgery, and mechanical cardiac support devices, as well as in the management of acute ischemic syndromes, atrial fibrillation, and prevention and treatment of venous thromboembolism. Progress in the development and utilization of these anticoagulants and antiplatelet agents has supported the major advances that have been achieved in cardiac surgery.

Safe use of heparin-coated bypass circuits incorporating a pump-oxygenator

Durable, covalently bonded, heparin-coated cardiopulmonary bypass (CPB) circuits with oxygenators have been developed. Proposed advantages of heparin-coated CPB circuits include improved biocompatibility and thromboresistance. The purpose of this study was to evaluate our experience with heparin-coated CPB circuits in 20 patients. Heparin was given to maintain an activated clotting time equal to or greater than 200 seconds, while flow rates were kept equal to or greater than 2 L/min. Indications for use of this circuit included recent stroke, posttraumatic injuries, recent gastrointestinal bleeding, protamine allergies, combined cardiac and noncardiac procedures, and ventricular assist. Mean heparin dosage was 0.50 +/- 0.18 mg/kg and protamine dosage was 57.14 +/- 39.36 mg. Postoperative blood loss and transfusion requirements were minimal. Postoperative complement levels of C3a and C5a were normal, suggesting excellent biocompatibility. There were no deaths or perioperative complications. Heparin-coated CPB circuits using a pump oxygenator can be used safely with low-dose heparin administration in select patients requiring CPB.

The effect of an intraoperative treatment algorithm on physicians' transfusion practice in cardiac surgery

BACKGROUND

Inappropriate transfusion in cardiac surgery may, in part, be due to empiric transfusion therapy instituted in the absence of timely laboratory data. Therefore, the effect of a transfusion decision algorithm based on intraoperative coagulation monitoring of physicians' transfusion practice and the transfusion outcome was evaluated.

STUDY DESIGN AND METHODS

In a randomized, controlled trial, cardiac surgical patients determined to have microvascular bleeding at the cessation of cardiopulmonary bypass were assigned to algorithm (A) or standard (S) therapy. Group A was treated with plasma and platelet therapy according to a transfusion algorithm based on on-site coagulation data available within 4 minutes. For Group S, the use of laboratory-based data and the decision to transfuse blood components were at physician discretion.

RESULTS

Sixty-six patients were entered into the study (Group A, n = 30; Group S, n = 36). Other than the fact that there were significantly more female patients in Group S than in Group A, no differences between cohorts in regard to perioperative risk factors for blood transfusion needs were identified. Therefore, gender was factored in as a covariate in the statistical analysis. Group A patients received fewer hemostatic blood component units (p = 0.008) and had fewer total donor exposures (p = 0.007) during the entire hospitalization period. Linear regression analysis of the differences in slopes in Groups A and S for the relationships between the red cell volume lost and the red cell volume transfused (p < 0.03), non-red cell units transfused (p < 0.0001), and total number of blood components transfused (p < 0.0001) demonstrated that physicians' transfusion practice was significantly altered by the use of a transfusion algorithm with on-site coagulation data, independent of surgical blood losses.

CONCLUSION

The use of algorithms by transfusion decision makers can serve as an effective physician education intervention.

Alternative perioperative anticoagulation monitoring during cardiopulmonary bypass in aprotinin-treated patients

Monitoring of anticoagulation during cardiopulmonary bypass by means of the activated coagulation time (ACT) has become questionable due to the prolongation in the clotting time of patients receiving aprotinin. Because the celite-based ACT only indicates intrinsic coagulation, and sufficient anticoagulation is needed to also prevent extrinsic coagulation, the ACT may not be reliable. Three different clotting times, the celite-based ACT, the kaolin-based activated coagulation time (AKT) and the high-dose thrombin time (HITT), were compared in a prospective, double-blind, placebo-controlled study of 20 patients who were to undergo cardiopulmonary bypass. As expected, neither the kaolin-based assay nor the high-dose thrombin time was influenced by aprotinin, whereas the celite-based ACT was significantly prolonged in aprotinin-treated patients as compared to control patients (P < 0.05). This study confirms that both kaolin-based and thrombin-based tests provide a reliable means of determining the degree of heparinization in the presence of aprotinin during cardiopulmonary bypass.

Low-molecular-weight heparin (Fragmin) versus heparin for anticoagulation during cardiopulmonary bypass in open heart surgery, using a pig model

Fragmin and heparin were studied in pigs during 120 min of cardiopulmonary bypass (CPB) and up to 240 min postoperatively, with respect to clotting, bleeding and the effects of protamine. Thirty-three pigs received bolus injections of 300 IU/kg with or without additional dosage during CPB and with or without subsequent protamine sulphate. Doses of Fragmin 60% higher were necessary to prevent clotting. These had 100% higher anti-FXa levels but about 50% shorter activated coagulation time (ACT) compared with heparin. Anti-FXa increased with cumulative doses of heparin and Fragmin but ACT and activated partial thromboplastin time (aPTT) did not, indicating a larger loss of thrombin inhibition compared with anti-FXa in both drugs during CPB. Thrombin inhibition was crucial for prevention of clotting. Protamine efficiently normalized ACT in the Fragmin group but left a residual 20% anti-FXa, which did not increase the bleeding tendency. Fragmin could adequately be monitored with ACT and would be a safe alternative to heparin in CPB.

ATP reduces blood loss produced by heparin in cardiopulmonary bypass operations

It was previously shown that topical application of heparin produces enhanced bleeding from small vessels and capillaries. Adenosine triphosphate at low concentrations is able to dislodge heparin bound to a receptor, counteracting its antihemostatic activity. These results led us to measure the amounts of heparin remaining in the blood after protamine neutralization of the patients subjected to cardiopulmonary bypass operation and to test the topical application of the nucleotide. Adenosine triphosphate at a concentration of 10(-4) mol/L significantly reduces the blood volume (p < 0.005) oozed from the thoracic cavity of the patients (mean, 288 +/- 188 mL) when compared with controls (mean, 564 +/- 288 mL). Adenosine triphosphate at 5 x 10(-5) mol/L reduces the blood loss to a mean of 370 +/- 155 mL in the patients tested (p < 0.08). About 10% of heparin of low molecular weight (< or = 6.0 Kda), which is also found in the oozed blood, is not neutralized by protamine. We suggest that the excessive blood loss of the patients is probably produced by low molecular weight heparins in the commercial preparations that are not neutralized by protamine.

Heparin and protamine use in peripheral vascular surgery: a comparison between surgeons of the Society for Vascular Surgery and the European Society for Vascular Surgery

It was the intent of this study to document, in general, the patterns and complications of heparin and protamine usage during carotid endarterectomy, aortic and femoral-popliteal-tibial reconstructions for occlusive disease, elective and emergent abdominal aortic aneurysmectomy, thromboembolectomy, and dialysis arteriovenous (AV) fistula placement by surgeons from North America and Europe. All vascular surgeons from the Society for Vascular Surgery (SVS) and the European Society for Vascular Surgery (ESVS) were surveyed by a voluntary, self-reported questionnaire. Six hundred and forty-six completed questionnaires (284 from SVS and 362 from ESVS), representing a 62% response rate, were returned for evaluation. Systemic and regional administration of heparin was common during vascular procedures performed by both SVS and ESVS surgeons. Use of protamine to reverse heparin anticoagulation varied among SVS and ESVS surgeons, respectively, during: carotid endarterectomy (54% vs. 26%, p < 0.01), elective aortic reconstruction for occlusive disease (58% vs. 23%, p < 0.001), elective aortic reconstruction for abdominal aortic aneurysm (63% vs. 27%, p < 0.001), and femoral-popliteal-tibial reconstruction (44% vs. 15%, p < 0.001). Adverse reactions to protamine among the 25,219 and 12,902 cases reported from SVS and ESVS surgeons, respectively, included: hypotension (1209 and 495 cases), pulmonary artery hypertension (65 and eight cases), anaphylaxis (52 and 10 cases), and death (seven and two cases). These adverse responses accounted for 5.3% and 4.0% of the SVS and ESVS cases, respectively. Although this study is subject to the known limitations of a retrospective survey, it is clear that heparin use is common. Protamine reversal of heparin anticoagulation is more common in North America.(ABSTRACT TRUNCATED AT 250 WORDS)

The beneficial effects of aminophylline administration on heparin reversal with protamine

The aim of this study was to demonstrate the beneficial effects of aminophylline on protamine cardiotoxicity. Thirty-four patients were examined, 17 of whom received aminophylline 3 mg/kg before protamine administration, being the study group, while the other 17, being the control group, did not. All cardiac output and biochemical measurements were evaluated 5 min following protamine administration. The cAMP level was 43.4 +/- 3.51 pmol/ml in the study group and 18.7 +/- 2.98 in the control group (P < 0.0001) before protamine administration, while the oxygen extraction rate decreased from 49% to 44 +/- 2% in the control group, and from 51.2% to 47 +/- 3% in the study group (P < 0.03). The N-acetyl glucosaminidase value was 16.9 +/- 13.9 pmol/ml in the study group and 27.8 +/- 1.47 pmol/ml in the control group (P < 0.01), and myocardial lactate extraction was -0.20 +/- 0.03 in the control group and -0.07 +/- 0.07 in the study group (P < 0.001). The left ventricular stroke work index was 28.6 +/- 3.14 gm/m2 in the control group and 37 +/- 6.77 gm/m2 in the study group (P < 0.002). The findings of this study led us to conclude that the adverse effects of heparin neutralization using protamine can be relieved by aminophylline.

Low molecular weight heparin and haemodialysis: neutralization by protaminchloride

Unfractionated heparin (UFH) is the most widely used agent in preventing clot formation in the extracorporeal circuit. The dose of heparin varies and is dependent on biocompatibility of membranes, the construction of the dialyser and the roller pump segment besides the individual patient's sensitivity. The risk of bleeding might be increased in patients with acute renal failure, particularly with multiple organ failure. Alternative strategies were elaborated, one of which is the use of low molecular weight heparin (LMWH). LMWH has a similar antithrombotic activity as UFH but a lower haemorrhagic tendency and a longer plasma half-life in patients with renal insufficiency. Various studies with LMWH--which are only comparable if the same dialyser and equipment are used--clearly show that the anti-factor Xa level must exceed 0.5 U/ml to prevent clot formation. With these levels LMWH is as effective and safe as UFH in inhibiting coagulation during chronic dialysis. Anti-factor Xa levels > 0.5 U/ml will, however, simultaneously increase bleeding tendency, in patients at risk. Therefore, lower doses of LMWH have to be administered to patients with acute renal failure and risk of bleeding. This haemorrhagic tendency may be neutralized by protamine. The present investigation with protamine chloride and different concentrations of LMWH (Clivarin) shows that clotting tests (thrombin time, aPTT) were immediately antagonized. Anti-factor Xa activity was neutralized by only 20-40%. The gradual decline of anti-factor Xa activity thereafter corresponds to the biological half-life of Clivarin. Whether the remaining anti-factor Xa activity is associated with any increased bleeding risk remains to be seen.

Heparin binding proteins. Contribution to heparin rebound after cardiopulmonary bypass

BACKGROUND

Heparin rebound, the reappearance of anticoagulant activity after adequate neutralization with protamine, can lead to excessive postoperative bleeding after cardiac surgery. We investigated the mechanism of heparin rebound by using chemically modified heparin that lacks anticoagulant activity (low-affinity heparin) but that is able to displace protein-bound anticoagulantly active heparin.

METHODS AND RESULTS

Sixteen patients undergoing elective cardiac surgery were given heparin (400 U/kg) to achieve an activated clotting time (ACT) > 400 seconds. After cardiopulmonary bypass, protamine sulfate was given (by heparin-ACT dose-response curve) to return the ACT to prebypass times (preoperative, 160 +/- 9 seconds; postoperative, 156 +/- 17 seconds). Blood samples were obtained serially for 24 hours and assayed for thrombin clotting time (TCT) and heparin activity using an anti-factor Xa assay. The TCT and anti-factor Xa activity were consistently and abnormally elevated for the first 6 hours after surgery. The anti-factor Xa activity increased fourfold after the addition of low-affinity heparin (essentially free of anti-factor Xa activity), indicating that anticoagulantly active heparin persisted in the circulation after protamine neutralization bound nonspecifically to plasma proteins. Blood loss correlated with postoperative TCTs.

CONCLUSIONS

Our findings demonstrate that heparin anticoagulant activity persists for up to 6 hours after surgery despite apparent protamine neutralization. The observation of the marked increase in plasma anti-factor Xa activity after the addition of low-affinity heparin suggests that after its administration, a large proportion of the heparin binds to plasma proteins and is incompletely removed by protamine. After protamine is cleared, the protein-bound heparin dissociates slowly and binds to anti-thrombin III to produce an anticoagulant effect.

[The effect of protamine on cholesterol, triglycerides and blood serum proteins during the dynamics of experimental hypercholesterolemia]

Content of total proteins, cholesterol, and triglycerides was studied in the blood serum and lipoprotein fractions of rabbits after administration of protamine within 1, 3 and 7 months of hypercholesterolemia development. The protamine effect was accompanied by "equalization" of cholesterol and triglyceride concentrations, as compared with their alteration in hypercholesterolemia, by stabilization of their content in various periods of the disease, but at the higher level than that of intact animals. The phenomenon observed occurred mainly in lipid components of LDL and VLDL subfractions. Analysis of alterations in the content of cholesterol and proteins in HDL and apo B-containing fractions showed that administration of protamine during long-term hypercholesterolemia led to development of antiatherogenic symptoms. Proatherogenic alterations in lipoprotein composition, developed during hypercholesterolemia, appear to be inhibited by protamine.

Histamine release during paediatric cardiopulmonary bypass

Histamine release is part of the general inflammatory response and occurs during surgery and cardiopulmonary bypass (CPB) in adults. Few data are available for children. Histamine release was studied in 23 children undergoing CPB with standard anaesthetic and CPB techniques. Blood sampling was performed in relation to specific anaesthetic and surgical events, e.g., start of CPB, removal of aortic clamps, reventilation of the lungs. Plasma histamine was determined by a single isotope radioenzymatic technique. There was no consistent histamine release in the study population although there was an increase in plasma histamine concentration in some subjects after initiation of CPB (P < 0.05) and on removal of the aortic cross-clamp (P < 0.05). No correlation was demonstrated between histamine concentration and systolic arterial pressure, temperature, duration of CPB or cross-clamp time. Histamine concentration was positively correlated with heart rate.

Effectiveness of nursing involvement in bedside monitoring and control of coagulation status after cardiac surgery

OBJECTIVE

This study explores: (1) the feasibility of involvement of nursing staff in routine bedside testing of activated clotting time and (2) joint implementation with resident medical staff of a preformulated plan for management of mediastinal bleeding after cardiac surgery.

DESIGN

Patients were divided randomly into two groups, an experimental group (n = 108) subjected to ACT testing and management by protocol, and a control group (n = 146) treated by independent medical decisions.

RESULTS

Bleeding, volume of blood replaced, abnormal coagulation profiles and reoperations to control bleeding and its consequences were all reduced in the study group.

CONCLUSION

We concluded that bedside measurement of activated clotting time by nursing staff, associated with therapy based on a flow diagram, enhanced the overall management of early mediastinal bleeding after cardiac surgery as compared with independent management decisions by resident medical staff. In addition, the method provided a sensitive and reliable means of detecting and correcting rebound heparinization in the early postoperative period.

Heparin rebound phenomenon--much ado about nothing?

Significant postoperative bleeding following open-heart surgery is often ascribed to the so-called heparin 'rebound' phenomenon and as such is treated with additional empiric doses of protamine sulphate. However, inappropriate protamine administration has been reported to be associated with acute pulmonary hypertension. The efficacy of heparin reversal was investigated in 42 patients undergoing open-heart surgery. The standard heparin bolus of 3 mg/kg body weight (4.1 IU/ml blood) administered before cardiopulmonary bypass was countered at the end of bypass using an empirical equivalent (3 mg/kg) of protamine. This regimen resulted in complete heparin neutralization (measured by the Hepcon HMS [Hemotec Inc., Englewood, CO, USA]) 15 min after protamine administration in all 42 patients, but heparin levels (0.4 IU/ml) were transiently detectable (duration less than 1 h) in six (14%) of the 42 cases 2 h later. Twenty-four hour postoperative bleeding in these patients did not differ significantly from that seen in patients who did not exhibit heparin rebound. Similarly, the thrombelastographic profiles (at 15 min and 2 h post-operation) and coagulation screen (prothrombin time, activated partial thromboplastin time, activated clotting time and platelets) did not differ significantly from those of non-rebound patients. The significance, if any, of the phenomenon of heparin rebound following cardiac surgery remains to be elucidated, and, until such time, conservative administration of protamine in response to 'rebound' is recommended.

Protamine allergy reactions during cardiac catheterization and cardiac surgery: risk in patients taking protamine-insulin preparations

Protamine insulin use may immunologically sensitize patients to protamine, leading to anaphylactoid reactions upon subsequent exposure to protamine sulfate during cardiac catheterization or cardiovascular surgery. The risk of such reactions in protamine insulin-dependent patients is uncertain. One catheterization study reported a 50-fold greater risk while a second showed no increased risk! To clarify the risk, the records of 7,750 cardiac catheterization procedures between 1984 and 1987 were analyzed for presence of NPH or PZI insulin use, protamine administration, and any complications or adverse reactions. Protamine was administered in 3,341/7,750 procedures (43%), including 171 in diabetics receiving NPH insulin. Adverse reactions to protamine occurred in 2/3, 170 noninsulin patients, 0.06%, and adverse reactions due to probable NPH insulin sensitization occurred in 1/171, 0.6%, of NPH diabetics, p = .034. Meta-analysis of risk showed an odds ratio of 7.96 for the NPH diabetic patients, and combining these results with the other large series in the literature (269 NPH diabetics total) showed an odds ratio of 4.19 compared to a non-NPH insulin group. Meta-analysis of the surgical literature showed the risk in surgical patients to be 2.1% in NPH patients versus 0.12% with no NPH, with an odds ratio of 15.52. The greater incidence in surgical patients may be due to protamine sensitization at prior catheterization and to the larger dose of protamine administered to surgical patients.

Heparin rebound: a comparative study of protamine chloride and protamine sulfate in patients undergoing coronary artery bypass surgery

Heparin rebound has been suggested to occur when protamine sulfate, but not protamine chloride, is used to neutralize heparin. This study was undertaken to compare these two protamine salts in 32 patients undergoing coronary artery bypass surgery. Initial heparin and subsequent protamine doses were determined by constructing a heparin-activated coagulation time response curve. Heparin was neutralized either with protamine sulfate or protamine chloride. The total protamine/heparin dose ratio was 0.71 +/- 0.05 for protamine sulfate and 0.77 +/- 0.07 (mg/100 U) for protamine chloride. The initial neutralization effect, the subsequent behavior of the plasma heparin level, and the various coagulation parameters did not differ significantly between the groups. Two hours after neutralization, a small and temporary increase of plasma heparin level was observed in both groups. The postoperative blood losses were comparable in both groups. Thus, protamine chloride was not a clinically superior antidote to heparin than protamine sulfate. The observed heparin rebound levels were low and clinically insignificant in terms of blood loss, but they were associated with slight changes in coagulation monitoring.