What's fishy about protamine? Clinical use, adverse reactions, and potential alternatives

Protamine, a highly basic protein isolated from salmon sperm, is the only clinically available agent to reverse the anticoagulation of unfractionated heparin. Following intravenous administration, protamine binds to heparin in a nonspecific electrostatic interaction to reverse its anticoagulant effects. In clinical use, protamine is routinely administered to reverse high-dose heparin anticoagulation in cardiovascular procedures, including cardiac surgery with cardiopulmonary bypass. Despite the lack of supportive evidence regarding protamine's effectiveness to reverse low-molecular-weight heparin, it is recommended in guidelines with low-quality evidence. Different dosing strategies have been reported for reversing heparin in cardiac surgical patients based on empiric dosing, pharmacokinetics, or point-of-care measurements of heparin levels. Protamine administration is associated with a spectrum of adverse reactions that range from vasodilation to life-threatening cardiopulmonary dysfunction and shock. The life-threatening responses appear to be hypersensitivity reactions due to immunoglobulin E and/or immunoglobulin G antibodies. However, protamine and heparin-protamine complexes can activate complement inflammatory pathways and inhibit other coagulation factors. Although alternative agents for reversing heparin are not currently available for clinical use, additional research continues evaluating novel therapeutic approaches.

Optimal protamine dosing after cardiopulmonary bypass: The PRODOSE adaptive randomised controlled trial

BACKGROUND

The dose of protamine required following cardiopulmonary bypass (CPB) is often determined by the dose of heparin required pre-CPB, expressed as a fixed ratio. Dosing based on mathematical models of heparin clearance is postulated to improve protamine dosing precision and coagulation. We hypothesised that protamine dosing based on a 2-compartment model would improve thromboelastography (TEG) parameters and reduce the dose of protamine administered, relative to a fixed ratio.

METHODS AND FINDINGS

We undertook a 2-stage, adaptive randomised controlled trial, allocating 228 participants to receive protamine dosed according to a mathematical model of heparin clearance or a fixed ratio of 1 mg of protamine for every 100 IU of heparin required to establish anticoagulation pre-CPB. A planned, blinded interim analysis was undertaken after the recruitment of 50% of the study cohort. Following this, the randomisation ratio was adapted from 1:1 to 1:1.33 to increase recruitment to the superior arm while maintaining study power. At the conclusion of trial recruitment, we had randomised 121 patients to the intervention arm and 107 patients to the control arm. The primary endpoint was kaolin TEG r-time measured 3 minutes after protamine administration at the end of CPB. Secondary endpoints included ratio of kaolin TEG r-time pre-CPB to the same metric following protamine administration, requirement for allogeneic red cell transfusion, intercostal catheter drainage at 4 hours postoperatively, and the requirement for reoperation due to bleeding. The trial was listed on a clinical trial registry (ClinicalTrials.gov Identifier: NCT03532594). Participants were recruited between April 2018 and August 2019. Those in the intervention/model group had a shorter mean kaolin r-time (6.58 [SD 2.50] vs. 8.08 [SD 3.98] minutes; p = 0.0016) post-CPB. The post-protamine thromboelastogram of the model group was closer to pre-CPB parameters (median pre-CPB to post-protamine kaolin r-time ratio 0.96 [IQR 0.78-1.14] vs. 0.75 [IQR 0.57-0.99]; p < 0.001). We found no evidence of a difference in median mediastinal/pleural drainage at 4 hours postoperatively (140 [IQR 75-245] vs. 135 [IQR 94-222] mL; p = 0.85) or requirement (as a binary outcome) for packed red blood cell transfusion at 24 hours postoperatively (19 [15.8%] vs. 14 [13.1%] p = 0.69). Those in the model group had a lower median protamine dose (180 [IQR 160-210] vs. 280 [IQR 250-300] mg; p < 0.001). Important limitations of this study include an unblinded design and lack of generalisability to certain populations deliberately excluded from the study (specifically children, patients with a total body weight >120 kg, and patients requiring therapeutic hypothermia to <28°C).

CONCLUSIONS

Using a mathematical model to guide protamine dosing in patients following CPB improved TEG r-time and reduced the dose administered relative to a fixed ratio. No differences were detected in postoperative mediastinal/pleural drainage or red blood cell transfusion requirement in our cohort of low-risk patients.

TRIAL REGISTRATION

ClinicalTrials.gov Unique identifier NCT03532594.

Thrombolysis Following Heparin Reversal With Protamine Sulfate in Acute Ischemic Stroke: Case Series and Literature Review

INTRODUCTION

Administering intravenous IV tissue plasminogen activator (tPA) is the recommended standard of care in acute ischemic stroke (AIS), although it is not recommended to administer intravenous thrombolysis with tPA following heparin reversal with protamine sulfate in patients with AIS.

METHODS

We describe a case series of three patients and the most comprehensive literature review published to date in this specific subset of AIS patients undergoing thrombolysis following heparin reversal with protamine sulfate. The literature review was based on a scoping review methodology performed on four databases; PubMed, CINAHL, Web of Science, and Cochrane Library. All sources were searched from the inauguration of the database until February 2019. A total of six articles involving eight patients were identified.

RESULTS

The primary safety outcome of no symptomatic intracranial hemorrhage (sICH) was met in all eleven patients, although only seven cases had a good functional outcome at 3 months.

CONCLUSIONS

In appropriately selected AIS patients, coagulopathy correction appears to be safe from an sICH standpoint and may be beneficial. However, given the potential for bias with observational databases, case reports and case series, extreme caution is warranted in applying these results to routine clinical practice.

Heparin-protamine balance after neonatal cardiopulmonary bypass surgery

Essentials Heparin-protamine balance (HPB) modulates bleeding after neonatal cardiopulmonary bypass (CPB). HPB was examined in 44 neonates undergoing CPB. Post-operative bleeding occurred in 36% and heparin rebound in 73%. Thrombin-initiated fibrin clot kinetic assay and partial thromboplastin time best assessed HPB.

SUMMARY

Background Neonates undergoing cardiopulmonary bypass (CPB) are at risk of excessive bleeding. Blood is anticoagulated with heparin during CPB. Heparin activity is reversed with protamine at the end of CPB. Paradoxically, protamine also inhibits blood coagulation when it is dosed in excess of heparin. Objectives To evaluate heparin-protamine balance in neonates undergoing CPB by using research and clinical assays, and to determine its association with postoperative bleeding. Patients/Methods Neonates undergoing CPB in the first 30 days of life were studied. Blood samples were obtained during and after surgery. Heparin-protamine balance was assessed with calibrated automated thrombography, thrombin-initiated fibrin clot kinetic assay (TFCK), activated partial thromboplastin time (APTT), anti-FXa activity, and thromboelastometry. Excessive postoperative bleeding was determined by measurement of chest tube output or the development of cardiac tamponade. Results and Conclusions Of 44 neonates enrolled, 16 (36%) had excessive postoperative bleeding. The TFCK value was increased. By heparin in neonatal blood samples, but was only minimally altered by excess protamine. Therefore, it reliably measured heparin in samples containing a wide range of heparin and protamine concentrations. The APTT most closely correlated with TFCK results, whereas anti-FXa and thromboelastometry assays were less correlative. The TFCK and APTT assay also consistently detected postoperative heparin rebound, providing an important continued role for these long-established coagulation tests in the management of postoperative bleeding in neonates requiring cardiac surgical repair. None of the coagulation tests predicted the neonates who experienced postoperative bleeding, reflecting the multifactorial causes of bleeding in this population.

Use of epoprostenol to treat severe pulmonary vasoconstriction induced by protamine in cardiac surgery

Since there were a few articles to report the treatment of severe pulmonary vasoconstriction induced by protamine in cardiac surgery, we described the use of epoprostenol to reverse this condition.A total of 5 cases of severe pulmonary vasoconstriction induced by protamine in cardiac surgery were reviewed. The demographic, clinical data and treatment process were obtained. All the patients were followed up.Severe pulmonary vasoconstriction was occurred 4 to 10 minutes after protamine infusion. The primary sign was sudden hypotension, the pulmonary artery pressure was increased gradually, the arterial oxygen partial pressure was decreased in all the patients. Epoprostenol was infused via pulmonary artery catheter at dosage of 20 to 40 ng/kg·min in all the patients, 2 patients were underwent re-cardiac pulmonary bypass assistance. The hemodynamic instability status lasted 40 to 65 minutes respectively. All the patients were recovered uneventfully.All physicians should alert to the incidence of severe pulmonary vasoconstriction induced by protamine in cardiac surgery. Use epoprostenol through pulmonary artery catheter could treat pulmonary artery vasoconstriction effectively and safely.

Glycosaminoglycan Neutralization in Coagulation Control

The glycosaminoglycans (GAGs) heparan sulfate, dermatan sulfate, and heparin are important anticoagulants that inhibit clot formation through interactions with antithrombin and heparin cofactor II. Unfractionated heparin, low-molecular-weight heparin, and heparin-derived drugs are often the main treatments used clinically to handle coagulatory disorders. A wide range of proteins have been reported to bind and neutralize these GAGs to promote clot formation. Such neutralizing proteins are involved in a variety of other physiological processes, including inflammation, transport, and signaling. It is clear that these interactions are important for the control of normal coagulation and influence the efficacy of heparin and heparin-based therapeutics. In addition to neutralization, the anticoagulant activities of GAGs may also be regulated through reduced synthesis or by degradation. In this review, we describe GAG neutralization, the proteins involved, and the molecular processes that contribute to the regulation of anticoagulant GAG activity.

Intraoperative medications associated with hemodynamically significant anaphylaxis

STUDY OBJECTIVE

To facilitate the identification of drugs and patient factors associated with hemodynamically significant anaphylaxis.

DESIGN

Using an existing database containing complete perioperative records, instances of hemodynamically significant anaphylaxis were identified using a physiologic and treatment-based screening algorithm. All cases were manually reviewed by 2 clinicians, with a third adjudicating disagreements, and confirmed cases were matched 3:1 with control cases. Intraoperative medications given in instances of hemodynamically significant anaphylaxis and patient risk factors were compared with control cases.

SETTING

University of Michigan Hospital, a large, tertiary care hospital.

PATIENTS

All adult patients undergoing surgery between January 1, 2004, and January 5, 2015.

INTERVENTIONS

None.

MEASUREMENTS

Incidence of hemodynamically significant anaphylaxis during anesthesia. Patient risk factors and intraoperative medications associated with hemodynamically significant anaphylaxis.

MAIN RESULTS

Hemodynamically significant anaphylaxis occurred in 55 of 461 986 cases (1 in 8400). Hemodynamically significant anaphylaxis occurred in 52 patients, with 1 patient experiencing 3 instances and another patient 2 instances. Only 1 drug was associated with an increased risk of hemodynamically significant anaphylaxis: protamine (odds ratio, 11.78; 95% confidence interval, 1.40-99.26; P=.0233). No category of drugs was associated with increased risk. Of patient risk factors, only personal history of anaphylaxis was associated with an increased risk (odds ratio, 77.1; 95% confidence interval, 10.46-567.69; P=<.0001). Postoperative follow-up and evaluation of patients were low at our institution. A serum tryptase level was sent in only 49% of cases, and 41% of levels were positive, an overall positive rate of 20% of cases. Following instances of hemodynamically significant anaphylaxis, only 29% of patients were seen and evaluated by an allergist at our institution.

CONCLUSIONS

Hemodynamically significant anaphylaxis is a rare complication of anesthesia, with an incidence consistent with the existing literature. Contrary to most existing literature, only protamine was associated with increased risk. A personal history of anaphylaxis appears to best predict risk of hemodynamically significant anaphylaxis.

Multiple preoperative and intraoperative factors predict early fistula thrombosis in the Hemodialysis Fistula Maturation Study

OBJECTIVE

Early thrombosis (ET) contributes to autogenous arteriovenous fistula (AVF) failure. We studied patients undergoing AVF placement in the Hemodialysis Fistula Maturation Study, a prospective, observational cohort study, using a nested case-control analysis to identify preoperative and intraoperative predictors of ET.

METHODS

ET cases were compared with controls, who were matched for gender, age, diabetes, dialysis status, and surgeon fistula volume. ET was defined as thrombosis diagnosed by physical examination or ultrasound within 18 days of AVF creation. Conditional logistic regression models were fit to identify risk factors for ET.

RESULTS

Thirty-two ET cases (5.3%) occurred among 602 study participants; 198 controls were matched. ET was associated with female gender (odds ratio [OR], 2.75; 95% confidence interval [CI], 1.19-6.38; P = .018), fistula location (forearm vs upper arm; OR, 2.76; 95% CI, 1.05-7.23; P = .039), feeding artery (radial vs brachial; OR, 2.64; 95% CI, 1.03-6.77; P = .043) and arterial diameter (OR, 1.52; 95% CI, 1.02-2.26; P = .039, per mm smaller). The draining vein diameter was nonlinearly associated with ET, with highest risk in 2- to 3-mm veins. Surprisingly, ET risk was lower in diabetics (OR, 0.19; 95% CI, 0.07-0.47; P = .0004), lower with less nitroglycerin-mediated brachial artery dilation (OR, 0.42; 95% CI, 0.20-1.92; P = .029 for each 10% lower) and higher with lower carotid-femoral pulse wave velocity (OR, 1.49; 95% CI, 1.02-2.20; P = .041, for each m/s lower). Intraoperative protamine use was associated with a higher ET risk (OR, 3.26; 95% CI, 1.28-∞; P = .038). Surgeon's intraoperative perceptions were associated with ET: surgeons' greater concern about maturation success (likely, marginal, unlikely) was associated with higher thrombosis risk (OR, 8.09; 95% CI, 4.03-∞; P < .0001, per category change), as were absence vs presence of intraoperative thrill (OR, 21.0; 95% CI, 5.07-∞; P = .0001) and surgeons' reported frustration during surgery (OR, 6.85; 95% CI, 2.70-∞; P = .0004). Decreased extent of intraoperative thrill (proximal, mid or distal third of the forearm or upper arm, based on AVF placement) was also associated with ET (OR, 2.91; 95% CI, 1.31-∞; P = .007, per diminished level). Oral antithrombotic medication use was not significantly associated with ET.

CONCLUSIONS

ET was found to be associated with female gender, forearm AVF, smaller arterial size, draining vein diameter of 2 to 3 mm, and protamine use. Paradoxically, diabetes and stiff, noncompliant feeding arteries were associated with a lower frequency of ET. Absent or attenuated intraoperative thrill, and both surgeon frustration and concern about successful maturation during surgery, were correlated strongly with ET.

[Case of bronchial obstruction by thrombosis after cardiopulmonary bypass]

A 78-year-old man underwent total arch replacement for an aortic arch aneurysm under cardiopulmonary bypass. After protamine sulfate administration, his peak inspiratory pressure suddenly rose, and his arterial oxygen saturation dropped. We checked his bronchus with a bronchoscope and found that his left main bronchus was blocked by a large thrombus. We tried to remove the thromus with suction via the bronchoscope channel, but it was too large to pick out. We had no way to perform this removal, and we called a respiratory specialist who performed the removal. The size, shape and time of onset suggested that the thrombus had been formed by residual blood left after administration of protamine. This case indicated that residual blood in the bronchus should be cheeked carefully after cardiopulmonary bypass.

[Severe shock after protamine infusion in a neonate undergoing cardio pulmonary bypass]

Shock after protamine infusion are rare. We report here the case of a 6-day-old boy having presented severe and recurring hypotensions after protamine infusions during cardiac surgery under cardio pulmonary bypass. The physiopathology of these reactions is complex and, in the presented case, involved mechanism may not be anaphylactic.

Methylene blue to treat vasoplegia due to a severe protamine reaction: a case report

Protamine sulfate is used during coronary artery bypass graft surgery to reverse the anticoagulating effects of heparin. Vasoplegic syndrome is a state of endothelial dysregulation that produces profound vasodilatation that is refractory to vasopressors. This syndrome leads to systemic hypoperfusion and may progress to death. Up to 27% of patients after cardiac bypass may experience vasoplegia. Symptoms of vasoplegia may also be present in many different clinical settings. This case report describes a 57-year-old woman who after cardiac bypass experienced a severe protamine reaction with profound hypotension, which was unresponsive to volume resuscitation and vasopressor therapy. A dramatic increase in blood pressure resulted almost immediately after administration of methylene blue. This patient had no prior risk factors for a protamine reaction other than her current cardiac surgery. A review of the pathophysiologic characteristics associated with vasoplegia and the pharmacodynamics of methylene blue will potentially enable anesthesia providers to utilize this lifesaving drug when needed.

Acute thrombosis of drug eluting stent following protamine: a case report

Reversal of anticoagulant effect of heparin to treat coronary perforation after bare metal stent implantation is an accepted practice. However this practice may not be safe following drug eluting stent implantation. We report a case of acute stent thrombosis following protamine administration for coronary perforation after drug eluting stent implantation.

Protamine-associated hypotension in patients on hemodialysis: retrospective study and prevalence of antiprotamine antibodies

AIMS

Protamine, when administered to neutralize heparin in cardiovascular surgery, is associated with occasionally severe antigen-antibody reactions associated with substantial morbidity and mortality. The objective of this study is to investigate whether patients on hemodialysis are more susceptible to the protamine adverse effects.

METHOD

First, a retrospective analysis of a protamine-associated hypotension episode (PAHE) in 239 patients undergoing coronary artery bypass grafting surgery was performed for the incidence study in the period of 1999 to 2005. Second, an ELISA determination of serum anti-protamine IgG antibody in 255 serum samples from individuals without previous surgical histories was conducted for prevalence survey. In both studies, patients on HD were matched for age with non HD patients.

RESULTS

The highest incidence (57%) of PAHE occurred in patients on hemodialysis using of M-insulin (a mixed type of insulin aspart 30%, insulin aspart protamine 70%) formulation, and this group also exhibited a high anti-protamine IgG antibody titer in serum (odds ratio: 18.31).

CONCLUSIONS

A substantial proportion of patients on hemodialysis are at high risk of acquiring protamine adverse effects, but definite conclusion about the association between uremia and PAHE, however, still needs to be made with caution.

Life threatening protamine reaction during bypass surgery--a case report

An anaphylactic reaction to protamine sulphate during cardiac surgery is a rare but known entity. Preoperative prediction and outcome of such a reaction is still unclear. We report a case of severe anaphylactic reaction to protamine sulphate in a diabetic while performing beating heart bypass surgery. We also reviewed the literature and discussed the management of such cases.

Increased accuracy in heparin and protamine administration decreases bleeding: a pilot study

Three to 5 percent of the patients undergoing cardiac surgery are reoperated because of bleeding. When a surgical cause can be excluded, heparin/protamine mismatch may be considered. Insufficient reversal of heparin and overdosing of protamine may cause postoperative bleeding. The purpose of the study was to evaluate whether a heparin-protamine titration system, Hemochron RxDx, could reduce postoperative bleeding and blood transfusion. Fifty-three patients were included prospectively over a 6-month period. The test group (RxDx group; 28 patients) received heparin and protamine doses calculated using the Hemochron RxDx system, which performs a baseline activated clotting time (ACT) value together with a heparin response test. An accurate heparin dose was calculated based on the Bull dose/response curve. Protamine doses were calculated by the same method. In the control group (25 patients), heparin was administered based on weight (3.5 mg/kg) and monitored by ACT. Heparin was reversed with protamine (1 mg/l mg of total heparin). Postoperative bleeding was significantly lower in the RxDx group (375 mL; range, 125-700 mL) compared with the control group (600 mL; range, 250-1920 mL; p = .018). A reduced number of patients needed blood transfusions in the RxDx group, although this was not statistically significant (19% vs. 38%, respectively; p = .13). Initial heparin dose was significantly reduced in the RxDx group (250 mg; range, 100-375 mg) compared with the control group (300 mg; range, 200-350 mg; p = .04). The additional heparin during cardiopulmonary bypass (CPB) was significantly lower as well 62 (range, 0-185) vs. 100 mg (range, 0-350 mg); p = .04. Initial protamine dose was reduced in the RxDx group 200 (range, 75-340) vs. 350 mg (range, 200-500 mg); p = .0001. Satisfactory end ACT values were obtained in both groups. Using the Hemochron RxDx, we observed a significant reduction in postoperative blood loss, as well as the amount of heparin and initial doses of protamine used during CPB. Individual patient managed anticoagulation during cardiac surgery using dose/response curve techniques based on in vitro analysis of heparin and protamine seems to reduce bleeding.

Is heparin reversal with protamine after carotid endarterectomy dangerous?

OBJECTIVE

Although systemic heparinisation is routine during CEA, reversal with protamine is controversial with 3 studies suggesting increased peri-operative stroke rates and 3 no effect. None included independent peer-review.

DESIGN

Non-randomised observational study of data derived from a randomised controlled study of anaesthetic technique for CEA.

METHODS

Data on heparin and protamine use and risk factors potentially influencing CEA outcome were collected prospectively. Stroke, death, MI, wound haematoma and re-operation rates were recorded following independent peer-review.

RESULTS

1513/2107 patients received heparin alone (H) and 594/2107 had heparin reversed with protamine (H+P). Risk factors for outcome were similar in both groups. The frequency of outcome events (H v H+P) were: stroke: 67/1513 (4.4%) v 17/594 (2.9%), p=0.098; non stroke or MI death: 10/1513 (0.7%) v 5/594 (0.8%), p=0.657; MI: 6/1513 (0.4%) v 3/594 (0.5%), p=0.718; haematoma: 157/1513 (10.4%) v 44/594 (7.4%), p=0.037; re-operation: 51/1380 (3.7%) v 18/565 (3.2%), p=0.581.

CONCLUSIONS

These results show a non-significant increase in stroke rate in patients receiving heparin alone refuting suggestions that protamine is harmful. Conversely post-operative haematoma was more frequent when protamine was withheld but re-operation rates were no different. Thus protamine use appears safe and should remain a matter for individual surgeon preference.

[Comparison of two schemes of administering the Russian protamine sulfate after extracorporeal circulation in cardiosurgical patients]

The paper presents data of a study comparing two schemes (Scheme 1: a heparin/protamine ratio of 1:2; Scheme 2: a heparin/protamine ratio of 1:3) for administering protamine sulfate to neutralize heparin in patients after extracorporeal circulation. A larger dose of protamine sulfate is shown to induce significant thrombocytic dysfunction, resulting in increased postoperative hemorrhage. To minimize protamine sulfate doses required for neutralization of the anticoagulant effect of heparin is a way of preventing these complications.

[A case of anaphylactic shock in an elderly man following protamine sulfate administration during emergent off-pump coronary artery bypass grafting]

An 80-year-old diabetic man undergoing emergent off-pump coronary artery bypass grafting for acute myocardial infarction developed anaphylactic shock immediately following administering a small dose of protamine sulfate. Preoperative examination revealed atrial fibrillation, severe three-vessel coronary artery disease and impaired left ventricular function with ejection fraction of 40% and severe septal as well as apical hypokinesis and akinesis. After successful completion of coronary bypass grafting, a total of 40 mg of protamine sulfate was given through the central venous line. Three minutes after protamine administration, profound hypotension occurred. Pulmonary artery pressure was low and the left ventricle was almost empty by transesophageal echocardiography. Hypotension was refractory to rapid administration of 2 l of crystalloid and albumin, and repeated administrations of phenylephrine. Blood pressure finally returned towards baseline after infusion of norepinephrine 0.2 microg x kg(-1) x min(-1) and epinephrine 0.1 microg x kg(-1) x min(-1). Hemoconcentration and impaired oxygenation were also noted. The situation suggested anaphylactic shock due to protamine. He had diabetes mellitus for 20 years and been treated by protamine containing insulin. Postoperative interview revealed that the patient had experienced urticaria over the abdominal area with neutral protamine hagedorn (NPH) insulin administration. This history suggested that the patient had been sensitized by protamine before surgery. Although it is rare to experience anaphylactic shock due to protamine, it is important to elicit the detailed allergic history to insulin in diabetic patients. Because anaphylactic shock still carries high mortality even in a patient without cardiac disease, we were lucky to save this elderly patient with acute myocardial infarction and compromised left ventricular function.

Strategies for improving the functionality of an affinity bioreactor

Heparin employed in extracorporeal blood circulation (ECBC) procedures (e.g. open heart operations) often leads to a high incidence of bleeding complications. Protamine employed in heparin neutralization, on the other hand, can cause severe adverse reactions. We previously developed an approach that could prevent both heparin- and protamine-induced toxic side effects concomitantly. This approach consisted of placing a hollow fiber-based bioreactor device containing immobilized protamine (termed a "protamine bioreactor") at the distal end of the ECBC procedure. This protamine bioreactor would remove heparin after heparin served its anticoagulant purpose in the ECBC device, thereby eliminating heparin-induced bleeding risks. In addition, this protamine bioreactor would prevent protamine from entering the patients, thereby aborting any protamine-induced toxic effects. Both in vitro and in vivo studies have successfully demonstrated the feasibility of this approach. Despite promises, early findings also revealed two shortcomings that must be overcome for the protamine bioreactor to be applied clinically. The first drawback was that the cyanate ester linkages, involved in conjugating protamine to the bioreactor device, were unstable and prone to hydrolysis, resulting in the leakage of a significant amount of protamine into circulation during application of the protamine bioreactor. The second deficiency was that the capacity of the protamine bioreactor in heparin removal was rather low, owing to the limited surface area of the hollow fibers for protamine immobilization and subsequently heparin adsorption. In this paper, we present novel strategies to overcome these two limitations. A new conjugation method based on the use of 4-(oxyacetyl)phenoxyacetic acid (OAPA) as the activating reagent was employed to yield stable linkages, via the abundant arginine residues of protamine, onto the hollow fibers. Results showed that while the amount of protamine immobilized on each gram of fibers was relatively comparable between the OAPA and the previous CNBr activation methods (7.45 mg/g versus 7.69 mg/g fibers), there was virtually no detectable leaching of immobilized protamine from the bioreactor by the OAPA method, comparing to 35% leaching of protamine by the previous CNBr method following 72 h of storage of the bioreactor in PBS buffer at 37 degrees C. To improve the capacity and functionality of the protamine bioreactor, two novel approaches were adopted. Long chain and high molecular weight poly-lysine was linked to the hollow fibers, prior to protamine coupling, to create multiple layers of immobilized protamine for subsequent heparin adsorption. In addition, a poly(ethylene glycol) (PEG) chain was inserted between protamine and the hollow fibers to yield a three-dimensional, free dynamic motion for immobilized protamine. Preliminary observations indicated that a four- to five-fold enhancement in heparin adsorption was attained by utilizing each of these new approaches. Aside from their current use, these new strategies can also be employed generically to improve the functionality of any affinity-type bioreactor. Indeed, efforts have been made recently in utilizing these approaches to develop a clinically usable GPIIb/IIIa bioreactor for the treatment of immune thrombocytopenic purpura (ITP)-an autoimmune disease.

A pilot study indicating that bradykinin B2 receptor antagonism attenuates protamine-related hypotension after cardiopulmonary bypass

BACKGROUND

The administration of protamine to patients who received heparin during cardiopulmonary bypass (CPB) induces hypotension. Protamine inhibits the carboxypeptidase N-mediated degradation of bradykinin, a peptide that causes vasodilation and tissue-type plasminogen activator (t-PA) release. This study tests the primary hypothesis that blocking the bradykinin B(2) receptor would attenuate protamine-related hypotension.

METHODS

We conducted a prospective, double-blind, randomized study in 16 adult male patients undergoing elective cardiac surgery requiring CPB and taking an angiotensin-converting enzyme (ACE) inhibitor preoperatively, because ACE inhibition increases bradykinin concentrations during CPB. Subjects were randomized to receive either saline solution (N = 8) or the bradykinin B(2) receptor antagonist HOE 140 (100 mug/kg, N = 8) before the administration of protamine. Mean arterial pressure (MAP) and t-PA activity were measured intraoperatively and before and after protamine administration.

RESULTS

Protamine administration caused a significant increase in bradykinin concentrations in the saline solution group (from 6.0 +/- 1.3 to 10.0 +/- 1.6 fmol/mL, P = .043), as well as the HOE 140 group (from 6.5 +/- 1.8 to 14.3 +/- 4.6 fmol/mL, P = .042). Protamine significantly decreased MAP in the saline solution group (from 69.8 +/- 4.4 mm Hg to a mean individual nadir of 56.1 +/- 2.6 mm Hg, P = .031), but bradykinin receptor antagonism blunted this effect (from 74.3 +/- 3.7 mm Hg to a mean individual nadir of 69.6 +/- 1.2 mm Hg in the HOE 140 group, P = .545). Hence, during protamine infusion, MAP was significantly lower in the saline solution group compared with the HOE 140 group (P = .002). t-PA activity decreased significantly during administration of HOE 140 (from 3.59 +/- 0.31 to 1.67 +/- 0.42 IU/mL, P = .001) but not during saline solution (from 2.12 +/- 0.48 to 1.44 +/- 0.36 IU/mL, P = .214). Similarly, t-PA activity decreased significantly during protamine administration in the HOE 140 group (from 1.67 +/- 0.42 to 0.77 +/- 0.26 IU/mL, P = .038) but not in the saline solution group (from 1.44 +/- 0.36 to 0.99 +/- 0.26 IU/mL, P = .132).

CONCLUSION

Increased bradykinin contributes to protamine-related hypotension through its B(2) receptor in ACE inhibitor-treated patients.

Protamine after heparin produces hypotension resulting from decreased sympathetic outflow secondary to increased nitric oxide in the central nervous system

To elucidate whether there are linkages among protamine-induced hypotension, nitric oxide (NO), and sympathetic nerve activity, we administered 3 mg/kg protamine sulfate after 300 U/kg heparin after 20 mg/kg of N(G)-nitro-D-arginine methyl ester (D-NAME) or N(G)-nitro-L-arginine methyl ester (L-NAME) as a pretreatment to baroreceptor-denervated rabbits and compared changes in hemodynamic variables and renal sympathetic nerve activity (RSNA). In the D-NAME group, heart rate (HR), mean arterial blood pressure (MAP), and RSNA significantly decreased to 93.7% +/- 0.7%, 75.0% +/- 5.1% and 65.2% +/- 4.6% (mean +/- SE), respectively. In the L-NAME group, the pretreatment of L-NAME significantly inhibited the depressant effects of protamine on these variables. Because the animals were totally baroreceptor-denervated, decreased RSNA was attributable to the central depressant effect of protamine, and decreased sympathetic outflow could have contributed to the reduction of HR and MAP. The depressant effect of protamine on sympathetic outflow was inhibited by the pretreatment with L-NAME, a NO synthase inhibitor, suggesting that decreased sympathetic outflow secondary to a protamine-induced increase in NO concentration in the central nervous system may contribute to protamine-induced cardiovascular depression.

The Importance of Aprotinin and Pentoxifylline in Preventing Leukocyte Sequestration and Lung Injury Caused by Protamine at the End of Cardiopulmonary Bypass Surgery

BACKGROUND

Protamine has adverse effects on pulmonary gas exchange during the postoperative period. The objective of this study was to investigate the importance of aprotinin and pentoxifylline in preventing the leukocyte sequestration and lung injury caused by protamine administered after the termination of cardiopulmonary bypass (CPB).

METHODS

Participants (n = 39) were allocated into three groups at the termination of CPB: Group 1, (control group, n = 16); Group 2 (aprotinin group, n = 12), who received protamine + aprotinin (15,000 IU/kg); and Group 3 (Pentoxifylline group, n = 11), who received protamine + pentoxifylline (10 mg/kg). Leukocyte counts in pulmonary and radial arteries were determined after the termination of CPB and before any drug was given (t1), and 5 minutes (t2), 2 hours (t3), 6 hours (t4) and 12 hours (t5) after the administration of protamine. Alveolar-arterial O2 gradient (A-aO2) and dynamic pulmonary compliance were measured at t1, t2 and t3.

RESULTS

In the control group, an increase in pulmonary leukocyte sequestration was observed 5 minutes and 2 hours after protamine administration, after which this difference disappeared. No significant degree of pulmonary sequestration was detected in any measurements after protamine was administered in the aprotinin and pentoxifylline (PTX) groups. Dynamic lung compliance was 50.1, 45.2 and 47.2 ml/cm H2O in the control group, 49.2, 61.1 and 56.3 ml/cm H2O in the aprotinin group, and 49.5, 54.5 and 50.4 ml/cm H2O in the PTX group. The A-aO2 gradient was 212.2, 263.3 and 254.3 mm Hg in the control group, 209.4, 257.1 and 217.3 mm Hg in the aprotinin group, and 211.3, 260.8 and 219.2 mm Hg in the PTX group.

CONCLUSION

Aprotinin and PTX treatments have favourable effects on lung function by reducing protamine-induced leukocyte sequestration into lungs at the end of CPB.

Role of Endothelin-1 and Thromboxane A2 in the Pulmonary Hypertension Induced by Heparin–Protamine Interaction in Anesthetized Dogs

This study aimed to study the role of thromboxane A2 (TXA2) and endothelin-1 (ET-1) in the pulmonary hypertension induced by interaction of heparin-protamine in anesthetized dogs. The effect of inhaled nitric oxide (NO) was also investigated in this model. Dogs were anesthetized and instrumented for acquisition of mean arterial blood pressure, mean arterial pulmonary pressure (MPAP), and pulmonary pressure gradient (PPG). Cardiac index (CI), heart rate, and index of systemic vascular resistance were also obtained. Intravenous administration of heparin (500 IU/kg) 3 minutes before protamine (10 mg/kg) caused marked pulmonary hypertension, as evaluated by the increase in MPAP and PPG. This was accompanied by systemic hypotension, CI decrease, and tachycardia. Indomethacin (10 mg/kg), dazoxiben (10 mg/kg), or tezosentan (10-mg/kg bolus plus 10-mg/kg/h infusion) significantly reduced the increase in MPAP and PPG, but had no effect on the systemic hypotension. Similar results were obtained with inhaled NO (3 ppm). Plasma TXB2 levels were markedly elevated during the pulmonary hypertension, and this was abolished in indomethacin-treated dogs. Our study shows that interaction of heparin-protamine in anesthetized dogs lead to TXA2- and ET-1-mediated pulmonary hypertension. Drugs that interfere with the synthesis of these mediators as well as inhaled NO may be of beneficial value to control this disorder.

Dramatic post-cardiotomy outcome, due to severe anaphylactic reaction to protamine

Immunologic reactions to protamine sulfate during cardiac surgery are very rare. The frequency and outcome of such adverse reactions is unclear. We report a case of lethal anaphylactic reaction to protamine that occurred in a non-diabetic patient following the uneventful replacement of the ascending aorta. We also briefly review the mechanisms of this adverse reaction and emit some considerations on the management of this situation.

Adverse events after protamine administration following cardiopulmonary bypass in infants and children

We performed this study to determine the incidence of and risk factors for adverse events (AEs) in infants and children after the IV administration of protamine after cardiopulmonary bypass. In a retrospective cohort study, all relevant anesthesia records from a 3-yr period were examined to identify AEs after protamine. The AEs were then grouped into three categories by applying increasingly strict criteria. Among 1249 anesthesia records, there were no documented episodes of isolated or hypotension-associated right-sided cardiac failure or acute pulmonary dysfunction. The incidence of systemic hypotension after protamine was between 1.76% (95% confidence interval [CI], 1.11%-2.65%) and 2.88% (95% CI, 2.03%-3.97%), depending on the strictness of case definition. To identify risk factors, we performed a nested case-control study in which unmatched controls were randomly selected from the parent cohort at a 4:1 ratio to cases. Cases of hypotension after protamine were more likely during operations on girls (odds ratio [OR], 6.47; 95% CI, 1.66-32.8), after larger doses of protamine (OR, 1.88; 95% CI, 1.03-3.63), or after smaller doses of heparin (OR, 0.49; 95% CI, 0.17-0.67).

IMPLICATIONS

Systemic hypotension after protamine administration occurred in 1.76%-2.88% of pediatric patients having cardiac surgery. Female sex, larger protamine dose, and smaller heparin dose were each associated with increased risk. The development of protamine alternatives or prophylactic therapies may be useful for reducing the frequency of these events.

Effect of site of venous protamine administration, previously alleged risk factors, and preoperative use of aspirin on acute protamine-induced pulmonary vasoconstriction

OBJECTIVE

To determine whether the incidence of protamine-induced pulmonary vasoconstriction (PIPV) is influenced by central venous versus peripheral venous infusion of protamine and whether aspirin ingestion within a week of surgery would decrease the incidence of PIPV.

DESIGN

Single-institution, prospective, observational, randomized trial.

SETTING

University teaching hospital.

PARTICIPANTS

One thousand four hundred ninety-seven consecutive patients undergoing cardiopulmonary bypass procedures.

INTERVENTION

Protamine neutralization of heparin by infusion pump via either central venous or peripheral venous route.

MEASUREMENTS AND MAIN RESULTS

Five previously suspected risk factors (valve surgery, prior protamine exposure, history of pulmonary hypertension, fish allergy, and vasectomy), aspirin ingestion within 7 days of surgery, and demographic information were recorded. PIPV was defined as an abrupt increase in mean PA pressure of 7 mmHg or more with associated right ventricular dysfunction as assessed by observation of the right ventricle in the field and regional wall motion abnormality by transesophageal echocardiogram and hypotension (systolic blood pressure < or = 90 mmHg). Data were collected via continuous strip chart recording. A total of 10 patients (0.6%) developed PIPV during protamine infusion. The incidents were similar with respect to the site of venous administration. Prior exposure to protamine was associated with a greater incidence of PIPV (odds ratio 6.9; p < 0.01). Other previously suspected risk factors did not achieve statistical significance. None of the 766 patients who ingested aspirin experienced PIPV as opposed to 10 of the 731 patients who did not ingest aspirin (odds ratio 0.08; p < 0.001).

CONCLUSIONS

Although the site of venous protamine administration does not influence incidence of PIPV, aspirin ingestion within 1 week of surgery may decrease it. These data also confirmed other studies suggesting that previous protamine administration predisposes to this protamine reaction.

A less toxic heparin antagonist--low molecular weight protamine

A new thirteen amino acid peptide, named low molecular weight protamine (LMWP), was obtained through the enzymatic digestion of native protamine. Both in vitro and in vivo results showed that LMWP fully maintained the heparin neutralization function of protamine but had much lower immunogenicity and antigenicity. Unlike protamine, neither LMWP nor LMWP/heparin complexes caused significant blood platelet aggregation in rats. These results suggest that LMWP can be used as a substitute for protamine for developing a new generation of nontoxic heparin antagonists.

[Protamine allergy in heart surgery]

A 68-year-old woman was admitted for open heart surgery. She had no history of allergy, but had suffered acute heart failure after having received protamine twice. Possible predisposition to adverse reactions is discussed and ways of reducing adverse reactions to protamine are suggested.

Mortality and adverse events after protamine administration in patients undergoing cardiopulmonary bypass

We designed this study to determine whether adverse hemodynamic events after a protamine administration increase the risk of in-hospital mortality. Using a retrospective cohort study design, medical and anesthesia records of patients undergoing cardiopulmonary bypass (CPB) at the Hospital of the University of Pennsylvania, Philadelphia, between 1990 and 1994 were reviewed. Adverse events after a protamine administration were determined using strict, predefined criteria, and in-hospital mortality was assessed without knowledge of exposure status. Mortality was more frequent among the 53 patients with adverse events (13.2%) than the 223 patients without events (2.7%; crude odds ratio 5.50; 95% confidence interval, 1.49-20.6). After adjusting for confounders, the odds ratio was 6.98 (95% confidence interval, 1.36-35.9; P = 0.017). Those suffering severe events had the highest mortality (23.5% compared with 8.3% among those with less severe events versus 2.7% among those without any event, P = 0.001 for trend). In addition, the odds ratio was largest when using the strictest definition for protamine-related events. In conclusion, patients undergoing CPB who experience adverse events after a protamine administration have an increased risk of in-hospital mortality. Further studies to confirm these findings and development and testing of protamine alternatives or prophylactic therapies are required to determine if mortality can be reduced.

IMPLICATIONS

A retrospective cohort study demonstrated an association between adverse events after a protamine administration and increased in-hospital mortality.

A dose-determining trial of heparinase-I (Neutralase) for heparin neutralization in coronary artery surgery

Heparinase-I, a specific heparin-degrading enzyme, may represent an alternative to protamine. We explored the dose of heparinase-I for efficacy and safety in patients undergoing coronary artery surgery. At the conclusion of cardiopulmonary bypass, subjects received 5, 7, or 10 microg/kg of open-label heparinase-I instead of protamine. Activated clotting time (ACT) and its difference from a contemporaneous heparin-free sample (DeltaACT) at 3 min before and 3, 6, and 9 min after heparinase-I determined reversal efficacy. After surgery, we recorded hourly chest tube drainage. Systemic and pulmonary arterial blood pressure and cardiac output measurements before and immediately after heparinase-I were used to evaluate hemodynamic safety. Coagulation measurements included anti-factor Xa and anti-factor IIa activities. Forty-nine patients from seven institutions participated: 12 received 5 microg/kg, 21 received 7 microg/kg, 4 received two doses of 7 microg/kg, 8 received 10 microg/kg, and 4 received two doses of 10 microg/kg. Treatment groups did not differ demographically. Median DeltaACT 9 min later was 11, 7, and 4 s for the 5, 7, and 10 microg/kg groups, respectively. No adverse hemodynamic changes occurred with heparinase-I administration. The authors conclude that heparinase-I effectively restored the ACT after cardiopulmonary bypass. This effect appeared to be dose dependent.

IMPLICATIONS

Heparinase-I (Neutralase(TM)) successfully restored activated coagulation time with no adverse hemodynamic events in patients undergoing coronary artery surgery with cardiopulmonary bypass in an open-label dose-determining trial.

Life threatening cardiopulmonary failure in an infant following protamine reversal of heparin after cardiopulmonary bypass

Life threatening cardiopulmonary failure following protamine reversal of heparin after cardiopulmonary bypass (CPB) was reported to occur in adults but rarely in children. Atrial septal defect closure was performed in a 6-week-old infant erroneously suspected to suffer from right atrial thrombosis in addition. Protamine administration after CPB led to critical pulmonary hypertension and severe haemorrhagic pulmonary oedema resulting in severe hypoxia. Inhaled nitric oxide, together with high frequency oscillation ventilation supplemented by intravenous prostacycline, enabled complete recovery of cardiopulmonary and neurological function. Life threatening cardiovascular compromise after intravenous protamine can occur even in young infants which then require challenging paediatric critical care.

Fatal anaphylactic reaction to protamine after femoropopliteal by-pass surgery

BACKGROUND AND AIMS

Administration of protamine might cause serious complications especially in patients treated preoperatively with NPH insulin.

MATERIAL AND METHODS

A case report.

RESULTS AND CONCLUSION

Administration of protamine sulphate caused fatal anaphylactic reaction to a diabetic patient undergoing femoropopliteal by-pass surgery. Care should be taken when administering protamine to a patient treated preoperatively with NPH insulin and the possibility of an anaphylactid reaction to protamine have to be kept in mind.

[Prevention of negative hemodynamic effects of protamine sulfate by simultaneous infusion of microdoses of adrenaline]

Two groups of coronary patients subjected to revascularization of the myocardium were examined in order to detect the negative hemodynamic effects of protamine sulfate (PS) and the possibility of their correction by simultaneous infusion of adrenaline microdoses. In group 1 (27 pts.) heparin was neutralized by infusion of PS alone (6 mg/kg) and in group 2 (27 pts.) by simultaneous infusion of PS and adrenaline (15 ng/kg/min). The functions of the right and left ventricles were evaluated by catheterization of the pulmonary artery by a Swan-Ganz catheter and transesophageal Doppler echocardiography. These methods provided volume and velocity characteristics of the right and left compartments of the heart. PS deteriorated the systolic function of the right ventricle, particularly in patients with initial dysfunction of the right heart. Infusion of adrenaline simultaneously with PS leveled its negative effects, thus preventing myocardial dysfunction.

Fatal anaphylactoid shock associated with protamine for heparin reversal during anesthesia

A 19-year-old female was scheduled for elective surgery of repair of ventricular septal defect (VSD). She had no known previous food or drug allergy history. She was not previously exposed to protamine and did not have any of the risk factors pointing to protamine hypersensitivity reaction. Unfortunately there were two anaphylactoid shocks occurring during this surgery. One was caused by intravenous (i.v.) administration of antibiotics, and the other happened following i.v. drip of protamine sulfate for reversal of systemic heparinization. She had none of the risk factors suggestive of hypersensitivity to drugs and was therefore considered not at risk for such severe adverse reactions which happened. This article was to discuss the anaphylactoid shock induced by antibiotics and protamine during anesthesia, and the prevention and management of such a reaction.

[Catastrophic pulmonary vasoconstriction associated with protamine reversal of heparin]

Administration of protamine intravenously to neutralize the anticoagulant effects of heparin may be associated with hypotension. These adverse cardiovascular responses to protamine fall into three distinct types: transient hypotension related to rapid drug administration; anaphylactic responses: and catastrophic pulmonary vasoconstriction. We recently observed three patients who had catastrophic pulmonary vasoconstriction, which were treated with the assist circulation and intraaortic balloon pumping. The two patients were survived except one who was dead due to the cerebral ischemic damage which was introduced by delayed establishment of circulatory assist device. We conclude that meticulous longstanding observation of the hemodynamic condition is important after administration of protamine under the unremoved cannulations.

Cardiac surgery in patients with protamine allergy

Intravenous administration of protamine is associated with risk of severe anaphylactic and anaphylactoid reactions. In this review the incidence, pathophysiology, clinical management, and strategies for prevention of protamine reactions are addressed.