Protamine Reversal Of Heparin Anticoagulation Research Articles

Editor's Choice – Protamine Reduces Serious Bleeding Complications Associated with Carotid Endarterectomy in Asymptomatic Patients without Increasing the Risk of Stroke, Myocardial Infarction, or Death in a Large National Analysis

Controversy persists regarding the use of protamine during carotid endarterectomy (CEA), despite real world evidence to support its use. The purpose of this study was to determine the impact of protamine reversal of heparin anticoagulation on the outcome of CEA in the USA. A prospective national registry (Society for Vascular Surgery Vascular Quality Initiative) of 72787 patients undergoing elective asymptomatic CEA by 1879 surgeons from 316 centres in the USA and Canada from 2012 to 2018 was reviewed. Protamine use varied by both surgeon (20% rare use [< 10%], 30% variable use [11%-79%], 50% routine use [> 80% cases]) and geographical region (44% vs. 96%). Temporal trends in protamine use were also determined. End points included post-operative re-operation for bleeding, as well as potential protamine related thrombotic complications, including stroke, death, and myocardial infarction (MI). Predictors of end points were determined by multivariable logistic regression. Propensity matching was additionally used to control for differences between groups. Of the 72787 patients who underwent CEA, 69% received protamine, while 31% did not. Protamine use increased over time from 60% (2012) to 73% (2018). In total, 378 patients (0.7%) in the protamine treated group underwent re-operation for bleeding vs. 342 patients (1.4%) in the untreated cohort (p<.001). Protamine use did not affect the rate of MI (0.7% vs. 0.8%; p=.023), stroke (1.1% vs. 1.0%; p=.20), or in hospital death (0.2% vs. 0.2%; p=0.70) between treated and untreated patients, respectively. On multivariable analysis, protamine use was independently associated with reduced risk of re-operation for bleeding (odds ratio 0.5, 95% confidence interval 0.39-0.55; p<.001). Independent of protamine exposure, the consequences of a return to the operating room (RTOR) for bleeding were statistically significant, with a sevenfold increase in MI (RTOR 4.9% vs. no RTOR 0.7%; p<.001), an eightfold increase in stroke (RTOR 7.2% vs. no RTOR 0.9%; p<.001), and a 13 fold increase in death (RTOR 2.4% vs. no RTOR 0.2%; p<.001). Protamine reduces serious bleeding complications at the time of CEA without increasing the risk of MI, stroke, or death, in this large North American analysis. Based on this and previous regional work regarding protamine use in CEA, it is believed that there is now sufficient evidence to support its routine use, and it should be considered as a benchmark for quality during CEA.

Thrombography Reveals Thrombin Generation Potential Continues to Deteriorate Following Cardiopulmonary Bypass Surgery Despite Adequate Hemostasis

The intrinsic and extrinsic activation pathways of the hemostatic system converge when prothrombin is converted to thrombin. The ability to generate an adequate thrombin burst is the most central aspect of the coagulation cascade. The thrombin-generating potential in patients following cardiopulmonary bypass (CPB) may be indicative of their hemostatic status. In this report, thrombography, a unique technique for directly measuring the potential of patients’ blood samples to generate adequate thrombin bursts, is used to characterize the coagulopathic profile in post-CPB patients. Post-CPB hemostasis is typically achieved with protamine reversal of heparin anticoagulation and occasionally supplemented with blood product component transfusions. In this pilot study, platelet poor plasma samples were derived from 11 primary cardiac surgery patients at five time points: prior to CPB, immediately post-protamine, upon arrival to the intensive care unit (ICU), 3 hours post-ICU admission, and 24 hours after ICU arrival. Thrombography revealed that the Endogenous Thrombin Potential (ETP) was not different between [Baseline] and [PostProtamine] but proceeded to deteriorate in the immediate postoperative period. At the [3HourPostICU] time point, the ETP was significantly lower than the [Baseline] values, 1233 ± 591 versus 595 ± 379 nM.min (mean ± SD; n = 9, p &lt; .005), despite continued adequacy of hemostasis. ETPs returned to baseline values the day after surgery. Transfusions received, conventional blood coagulation testing results, and blood loss volumes are also presented. Despite adequate hemostasis, thrombography reveals an underlying coagulopathic process that could put some cardiac surgical patients at risk for postoperative bleeding. Thrombography is a novel technique that could be developed into a useful tool for perfusionists and physicians to identify coagulopathies and optimize blood management following CPB.

Protamine reduces bleeding complications associated with carotid endarterectomy without increasing the risk of stroke

Controversy persists regarding the use of protamine during carotid endarterectomy (CEA) based on prior conflicting reports documenting both reduced bleeding as well as increased stroke risk. The purpose of this study was to determine the effect of protamine reversal of heparin anticoagulation on the outcome of CEA in a contemporary multistate registry. We reviewed a prospective regional registry of 4587 CEAs in 4311 patients performed by 66 surgeons from 11 centers in Northern New England from 2003-2008. Protamine use varied by surgeon (38% routine use, 44% rare use, 18% selective use). Endpoints were postoperative bleeding requiring reoperation as well as potential thrombotic complications, including stroke, death, and myocardial infarction (MI). Predictors of endpoints were determined by multivariate logistic regression after associated variables were identified by univariate analysis. Of the 4587 CEAs performed, 46% utilized protamine, while 54% did not. Fourteen patients (0.64%) in the protamine-treated group required reoperation for bleeding compared with 42 patients (1.66%) in the untreated cohort (P = .001). Protamine use did not affect the rate of MI (1.1% vs 0.91%, P = .51), stroke (0.78% vs 1.15%, P = .2), or death (0.23% vs 0.32%, P = .57) between treated and untreated patients, respectively. By multivariate analysis, protamine (odds ratio [OR] 0.32, 95% confidence interval [CI], 0.17-0.63; P = .001) and patch angioplasty (OR 0.46, 95% CI, 0.26-0.81; P = .007) were independently associated with diminished reoperation for bleeding. A single center was associated with a significantly higher rate of reoperation for bleeding (OR 6.47, 95% CI, 3.02-13.9; P < .001). Independent of protamine use, consequences of reoperation for bleeding were significant, with a four-fold increase in MI, a seven-fold increase in stroke, and a 30-fold increase in death. Protamine reduced serious bleeding requiring reoperation during CEA without increasing the risk of MI, stroke, or death, in this large, contemporary registry. In light of significant complications referable to bleeding, liberal use of protamine during CEA appears warranted.

SS31. Protamine Reduces Bleeding Complications Associated With Carotid Endarterectomy Without Increasing the Risk of Stroke

Controversy exists about whether protamine given during carotid endarterectomy (CEA) prevents bleeding or increases thrombotic complications such as stroke or myocardial infarction (MI). The purpose of this study was to determine the effect of protamine reversal of heparin anticoagulation on the outcome of CEA. A prospective regional registry in Northern New England of 4,712 patients undergoing CEA by 66 surgeons from 11 centers from 2003-2008, was reviewed. Protamine use varied by surgeon (38% routine use, 44% rare use, 18% variable use). The primary endpoint was postoperative bleeding requiring reoperation. Secondary endpoints included stroke, death and MI. Predictors of endpoints were determined by univariate analysis using Pearson chi-square (Fisher's exact correction) and multivariate logistic regression. Among 4712 patients undergoing CEA, 46% received protamine while 54% did not. Patients who did not receive protamine had a 2.6-fold increase in reoperation for bleeding (Table). Protamine use did not affect the rate of stroke, death, or MI. By multivariate analysis, protamine reduced bleeding complications after accounting for other potential predictors of bleeding including center variation, surgical technique, and antiplatelet therapy; (OR 0.43, 95% CI 0.18-0.98, P<.05). Consequences of reoperation for bleeding were a 7-fold increase in stroke, a 30-fold increase in death and a 4-fold increase in MI.Tabled 1NReoperation For bleedingStrokeDeathMIProtamine218014 (0.64%)17 (0.78%)5 (0.23%)24 (1.1%)No Protamine253242 (1.66%)29 (1.15%)8 (0.32%)23 (0.91%)Chi-squareP=0.001P=0.20P=0.57P=0.51 Open table in a new tab Protamine reduces serious bleeding complications during CEA without increasing the risk of stroke, death, or MI. Thus, protamine is both safe and beneficial during CEA as practiced in this large, prospective registry. In light of substantial complications referable to bleeding, liberal use of protamine during CEA appears warranted.

PEG-Modified Protamine with Improved Pharmacological/Pharmaceutical Properties as a Potential Protamine Substitute: Synthesis and in Vitro Evaluation

Cardiopulmonary bypass (CPB) procedures are frequently associated with massive inflammatory responses, resulting in a high rate of morbidity and mortality in routine cardiac operations. One recognized attribute of these deleterious responses is the synergic effect of heparin and protamine, which elicit the activation of the complement system in vivo. To circumvent such toxic effects following protamine reversal of heparin anticoagulation in the CPB procedures, we proposed that poly(ethylene glycol) (PEG)-modified protamine could retain the heparin-neutralization ability and yet diminish the induced complement activation by the formed heparin-protamine complexes (HPC), thereby providing highly improved pharmacological properties. PEGylation of protamine was carried out by utilizing N-hydroxysuccinimidyl (NHS) conjugation chemistry. Size exclusion chromatography (SEC), reverse-phase high performance liquid chromatography (RP-HPLC), and matrix-assisted laser desorption mass spectrometry (MALDI-MS) were used to assess the conjugation stiochiometry, the purity of the conjugates, and the site of PEG modification, respectively. The heparin-neutralizing activity was determined by using heparin affinity chromatography and various biological assays including the plasma-activated partial thromboplastin time (aPTT), anti-Xa, and anti-IIa methods. The potency in inducing complement activation was examined in vitro using the CH50 hemolytic assay. The PEG-modified protamine was successfully synthesized with a PEG/protamine stiochiometry of 1:1. Only one conjugation site for PEG that was located at the N-terminal end of protamine was obtained. In the biological evaluations, the PEG-modified protamine displayed a full retention of the heparin-neutralizing ability of protamine and a significantly reduced activity in complement activation following its complexation with heparin. Results from studies of the particle size and zeta potential indicated that the PEG-modified protamine formed substantially smaller aggregates with heparin, rendering them less effective in triggering the size-dependent complement responses. As with protamine, PEG-modified protamine exhibited an enhanced aqueous solubility, therefore attaining significantly improved pharmaceutical properties. These preliminary results suggested that the PEG-modified protamine conjugate might serve as a potential protamine substitute with improved therapeutic and pharmaceutical properties in heparin reversal.

Effects of protamine on nitric oxide level in the pulmonary circulation.

Protamine reversal of heparin anticoagulation often causes systemic hypotension by releasing nitric oxide (NO) from vascular endothelium. We investigated the hypothesis that protamine prevents severe pulmonary vasoconstriction by increasing NO. Twenty patients undergoing elective coronary artery bypass graft surgery were included in the study. Nitrite and nitrate levels--as end-metabolites of NO--were measured in blood samples obtained before and after protamine administration. Mean arterial pressure, heart rate, mean pulmonary artery pressure, central venous pressure and left atrial pressure were noted as hemodynamic data. Nitrite levels were 4.64 +/- 0.67 mumol in the right atrium and 4.84 +/- 0.95 mumol in the left atrium before protamine administration. The difference was insignificant statistically. These measurements were 4.85 +/- 0.92 in the right atrium and 5.28 +/- 0.66 mumol in the left atrium after protamine administration. This increase was significant (p < 0.05). The measurements of nitrate levels were completely parallel with those of nitrite. Mean arterial pressures were 78.9 +/- 7.59 mm-Hg before protamine and 74.1 +/- 8.55 mm-Hg after protamine (p = 0.03). The changes in other hemodynamic parameters were not significant. Protamine augments NO production and prevents the pulmonary circulation from possible vasoconstriction.

A novel protamine variant reversal of heparin anticoagulation in human blood in vitro

Purpose: Protamine reversal of heparin anticoagulation during cardiovascular surgery may cause severe hypotension and pulmonary hypertension. A novel protamine variant, [+18RGD], has been developed that effectively reverses heparin anticoagulation without toxicity in canine experiments. Heretofore, human studies have not been undertaken. This investigation hypothesized that [+18RGD] would effectively reverse heparin anticoagulation of human blood in vitro. Methods: Fifty patients who underwent anticoagulation therapy during vascular surgery had blood sampled at baseline and 30 minutes after receiving heparin (150 IU/kg). Activated clotting times were used to define specific quantities of [+18RGD] or protamine necessary to completely reverse heparin anticoagulation in the blood sample of each patient. These defined amounts of [+18RGD] or protamine were then administered to the heparinized blood samples, and percent reversals of activated partial thromboplastin time, thrombin clotting time, and antifactor Xa/IIa levels were determined. In addition, platelet aggregation assays, as well as platelet and white blood cell counts were performed. Results: [+18RGD] and protamine were equivalent in reversing heparin as assessed by thrombin clotting time, antifactor Xa, antifactor IIa levels, and white blood cell changes. [+18RGD], when compared with protamine, was superior in this regard, as assessed by activated partial thromboplastin time (94.5 ± 1.0 vs 86.5 ± 1.3%δ, respectively; p < 0.001) and platelet declines (–3.9 ± 2.9 vs –12.8 ± 3.4 per mm 3, respectively; p = 0.048). Platelet aggregation was also decreased for [+18RGD] compared with protamine (23.6 ± 1.5 vs 28.5 ± 1.9%, respectively; p = 0.048). Conclusions: [+18RGD] was as effective as protamine for in vitro reversal of heparin anticoagulation by most coagulation assays, was statistically more effective at reversal than protamine by aPTT assay, and was associated with lesser platelet reductions than protamine. [+18RGD], if less toxic than protamine in human beings, would allow for effective clinical reversal of heparin anticoagulation. (J Vasc Surg 1997;26:1043-8.)

Involvement of Fibrinogen in Protamine-Induced Pulmonary Hypertension

Protamine reversal of heparin anticoagulation occasionally results in pulmonary hypertension as well as systemic hypotension. To examine the contribution of blood components to this induction of pulmonary hypertension, we developed an isolated rat lung perfusion model and perfused heparinized plasma, heparinized serum, and Hepes (4% bovine serum albumin, 20 mMN-2-hydroxyethylpiperazine-N′-2-ethanesulfonic acid, 5 mM glucose, in warm physiological saline) buffer solution with or without fibrinogen. Perfusion with heparinized plasma and Hepes buffer solution with fibrinogen caused pulmonary hypertension; perfusion with heparinized serum or Hepes buffer solution without fibrinogen did not, suggesting that fibrinogen is involved in the induction of pulmonary hypertension. We also labeled protamine with125I and compared the amounts of protamine accumulating in the lung with different concentrations of fibrinogen. The amount of protamine trapped in the lung increased according to the concentration of fibrinogen. Fibrinogen may accelerate the reaction between pulmonary endothelial cells and protamine or protamine–heparin complexes. In the mechanism of protamine-induced pulmonary hypertension, fibrinogen, as well as heparin and protamine, may be an essential component.

24.2 Protamine variant reversal of heparin anticoagulation in human blood in vitro

Purpose: Protamine reversal of heparin anticoagulation during cardiovascular surgery may cause severe hypotension and pulmonary hypertension. A novel protamine variant, [ + 18RGD ], has been developed that effectively reverses heparin anticoagulation without toxicity in canine experiments. Heretofore, human studies have not been undertaken. This investigation hypothesized that [+ 18RGD] would effectively reverse heparin anticoagulation of human blood in vitro. Methods: Fifty patients who underwent anticoagulation therapy during vascular surgery had blood sampled at baseline and 30 minutes after receiving heparin (150 IU/kg). Activated dotting times were used to define specific quantities of [ + 18RGD] or protamine necessary to completely reverse heparin anticoagulation in the blood sample of each patient. These defined amounts of [+18RGD] or protamine were then administered to the heparinized blood samples, and percent reversals of activated partial thromboplastin time, thrombin clotting time, and antifactor Xa/IIa levels were determined. In addition, platelet aggregation assays, as well as platelet and white blood cell counts were performed. Results: [+ 18RGD] and protamine were equivalent in reversing heparin as assessed by thrombin dotting time, antifactor Xa, antifactor IIa levels, and white blood cell changes. [ + 18RGD], when compared with protamine, was superior in this regard, as assessed by activated partial thromboplastin time (94.5 + 1.0 vs 86.5 + 1.3%zi, respectively; p < 0.001) and platelet declines (-3.9 - 2.9 vs -12.8 + 3.4 per mm 3, respectively; p = 0.048). Platelet aggregation was also decreased for [ +18RGD] compared with protamine (23.6 + 1.5 vs 28.5 + 1.9%, respectively; p = 0.048). Conclusions: [+18RGD] was as effective as protamine for in vitro reversal of heparin anticoagulation by most coagulation assays, was statistically more effective at reversal than protamine by aPTT assay, and was associated with lesser platelet reductions than protamine. [+18RGD], if less toxic than protamine in human beings, would allow for effective clinical reversal of heparin anticoagulation. (J Vasc Surg 1997;26:1043-8.)

Nitric oxide inhibition attenuates systemic hypotension produced by protamine

Background: Protamine reversal of heparin anticoagulation often causes systemic hypotension, and in vitro studies suggest that this may be mediated by release of nitric oxide from the endothelium. The present investigations were designed to evaluate the direct myocardial effects of protamine and to determine in vivo whether nitric oxide inhibition can prevent hypotension during protamine infusion. Methods/Results: Protamine sulfate (50 μg/ml) was added to perfusate of eight isolated rabbit heart preparations; in six other preparations, a similar concentration of protamine was added to heparinized (5 U/ml) Krebs perfusate. Left ventricular developed pressure, maximum rate of pressure rise, and heart rate declined significantly ( p < 0.01) in hearts exposed to protamine only (65.0% ± 6.6%, 55.5% ± 6.0%, and 87.6% ± 2.5% of baseline, respectively), whereas protamine added to heparinized perfusate caused little change in developed pressure, maximum rate of pressure rise, and heart rate (85.3% ± 5.4%, 84.9% ± 5.5%, and 98.8% ± 1.6%). To study systemic effects of protamine, we measured hemodynamic parameters in 12 heparinized dogs (150 U/kg). During protamine infusion (1.5 mg/kg intravenously over 30 seconds), mean blood pressure decreased by 46% ± 7% from baseline ( p < 0.05), cardiac output decreased by 38% ± 4% ( p < 0.05), and systemic vascular resistance decreased by 14% ± 9%. After hemodynamic stabilization, N g-monomethyl-f123503d (2 mg/kg), a competitive inhibitor of nitric oxide synthesis, was administered to six dogs, and methylene blue (2 mg/kg), an inhibitor of cyclic guanosine monophosphate synthesis, was administered to the remaining six dogs. After treatment with N g-monomethyl- l-arginine and methylene blue, the second infusion of protamine sulfate caused no significant change in blood pressure or cardiac output. In an additional six dogs, N g-monomethyl- l-arginine pretreatment (5 mg/kg) blocked the effects of the first dose of protamine. The effect of N g-monomethyl- l-arginine could be reversed by the addition of (6 mg/kg) l-arginine but not d-arginine. Conclusions: Protamine-heparin complex does not cause direct myocardial depression but does lead to severe hypotension in vivo. The finding that hypotension can be blocked by inhibitors of the nitric oxide pathway confirms previous in vitro studies indicating that the effects of protamine are mediated, in part, by the vascular endothelium. Further, these studies suggest a novel approach to prevention of hemodynamic complications caused by heparin reversal after cardiopulmonary bypass. (J T HORAC C ARDIOVASC S URG 1996;111:1240-7)

Effects of differing rates of protamine reversal of heparin anticoagulation

Protamine sulfate reversal of heparin anticoagulation may be associated with adverse cardiovascular side effects. The purpose of this study was to determine whether diminished systemic oxygen consumption and hemodynamic changes were more likely to accompany rapid versus slow protamine administration. Fifteen patients undergoing abdominal aortic aneurysm resection in a prospective randomized double-blinded study received intravenous protamine (1.5 mg/kg) rapidly during a 3-minute period (group I, n = 7) or slowly during a 15-minute period (group II, n = 8). Systemic oxygen consumption (VO2) and hemodynamic parameters were assessed for up to 20 minutes after protamine administration began. Blood pressure declines (millimeters of mercury) were greatest in group I with rapid protamine administration (-19 systolic and -9 diastolic) compared with group II with slow protamine administration (-12 systolic and -1 diastolic). Heart rate fell markedly in both groups I and II. Cardiac output (CO) declined in group I at virtually all time periods. Similar CO declines in group II occurred 10 minutes after protamine infusion had begun and persisted for 3 minutes after protamine administration was complete. Maximum VO2 decreases were -16% (60 seconds into protamine infusion) and -13% (1.5 minutes after protamine infusion) in groups I and II, respectively, with statistically significant declines (p < 0.05) occurring only in group I compared with baseline values. Statistically significant differences (p < 0.01), however, were found when mean declines during and after protamine infusion were compared with controls for both CO and VO2 in both groups. Significant declines in systemic VO2 and hemodynamic perturbations accompany protamine reversal of heparin anticoagulation during aortic surgery. Rapid protamine administration increases the magnitude of these adverse responses.

Effective and less toxic reversal of low-molecular weight heparin anticoagulation by a designer variant of protamine

This investigation assessed protamine reversal of heparin anticoagulation by formation of a protamine-heparin alpha-helix by use of a new designer-variant protamine [+18BE] that was made from an existing protamine variant [+18B] whose non-alpha-helix-forming amino acid proline (P) was replaced by an alpha-helix-forming glutamic acid (E). The rate of administration of the new [+18BE] variant protamine on efficacy and toxicity in comparison to that of [+21] standard protamine and [+18B] was also studied. Acetyl-EAA(K2A2K2A)4K2-Amide [+18BE] was administered intravenously in a 1:1 dose to low-molecular-weight heparin (LMWH)-anticoagulated (intravenous 150 IU antifactor Xa/kg) dogs over 10 seconds or 3 minutes (n = 7, each group). Reversal efficacy was documented by measuring activated clotting time, thrombin clotting time, antifactor Xa, and antifactor IIa. Toxicity was defined by measuring systemic blood pressure, heart rate, cardiac output, pulmonary artery pressure, and oxygen consumption. Measurements were made at baseline, after administration of LMWH, before its reversal, and for 30 minutes thereafter. Results were compared with those after LMWH reversal with [+21] standard protamine and the [+18B] variant. A total toxicity score (TTS) was calculated for each compound from maximal declines in blood pressure, heart rate, cardiac output, and oxygen consumption. LMWH anticoagulation reversal was significantly (p < 0.01) less toxic over 10 seconds and 3 minutes with the [+18BE] designer variant (TTS -2.3, -2.2) compared with the [+21] standard protamine (TTS -6.4, -7.2). Percent LMWH reversal at 3 minutes revealed [+18BE] to have antifactor Xa activity as high as 91%, compared with 68% for protamine [+21], when given over 3 minutes (p < 0.05). This investigation documents that a new designer variant of protamine [+18BE] has superior efficacy compared with [+21] standard protamine for reversal of LMWH anticoagulation and that this occurs with a highly favorable toxicity profile.

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)

Catastrophic vasoconstriction after protamine reversal of heparin anticoagulation in the goat.

Catastrophic pulmonary vasoconstriction after protamine reversal of heparin anticoagulation was observed frequently in goats that underwent centrifugal biventricular bypass pump implant. Care should be taken when protamine is used to reverse heparin anticoagulation in goats.

Imaging the ovine heparin-protamine interaction with 111In-protamine

Protamine reversal of heparin anticoagulation occasionally induces the release of thromboxane into plasma with catastrophic pulmonary hypertension. To examine the site of neutralization, we labeled protamine sulfate with 111In and compared activity scans after administration of labeled protamine in unheparinized and heparin-anticoagulated sheep. Protamine administration in sheep without prior heparinization did not cause thromboxane release, pulmonary hypertension, or significant leukopenia, and 111In-protamine was rapidly cleared from the lungs (half time 0.48 +/- 0.08 min). Neutralization of heparin anticoagulation by labeled protamine produced elevated plasma thromboxane, pulmonary vasoconstriction, leukopenia, and prolonged pulmonary clearance of 111In-protamine (half time 3.32 +/- 0.43 min). In rats, protamine reversal of heparin anticoagulation did not induce either thromboxane synthesis or pulmonary hypertension, and 111In-protamine cleared rapidly from the lungs. Thus the ovine heparin-protamine reaction produces concomitant pulmonary sequestration of heparin-protamine complexes, thromboxane release, and pulmonary vasoconstriction; this did not occur in the rat. The lung specificity of the reaction and interspecies differences suggest that ovine pulmonary intravascular macrophages may be activated by heparin-protamine complexes to release thromboxane and provoke acute pulmonary vasoconstriction.

Tissue Distribution, Circulating Half-Life, and Excretion of Intravenously Administered Protamine Sulfate

Intravenous protamine reversal of heparin anticoagulation may cause adverse hemodynamic side effects, but little is known about protamine's tissue distribution, circulating half-life (t/2), and excretion. The latter were assessed by examining 125I Bolton-Hunter (125I BH) radiolabeled protamine kinetics in a rat model. Three groups were studied: Group I controls (n = 5) received intravenous 125I BH label alone; Group II (n = 10) received intravenous 125I BH radiolabeled protamine (0.15 mg/100 g); and Group III (n = 10) received intravenous heparin (15 IU/100 g) followed by intravenous 125I BH radiolabeled protamine (0.15 mg/100 g). Five animals in each group were killed at 3 min, and tissue radioactivity was quantitated. An additional five animals each in Groups II and III were followed up for 60 min to determine protamine's circulating t/2 and its renal excretion. The lungs, heart, and kidneys, compared with other organs, retained the most 125I BH radiolabeled protamine per gram tissue at 3 min. Retention of 125I BH radiolabeled protamine (Groups II & III) was greater (p < 0.05, Kruskal-Wallis) than control 125I BH label alone (Group I). Higher tissue 125I activity was observed in Group II than in Group III rats, suggesting that tissue retention of protamine was greater in the absence of prior heparin administration. Circulating t/2 was shorter (18 vs. 24 min) and urinary protamine 125I excretion was higher (34 vs. 24%) in Group III than in Group II, respectively, suggesting more rapid renal clearance of protamine in the presence of heparin.(ABSTRACT TRUNCATED AT 250 WORDS)

Neutrophil Activation Mediates Protamine-Induced Pulmonary Hypertension

Protamine reversal of heparin anticoagulation can cause catastrophic pulmonary hypertension, systemic hypotension, and hypoxemia. This reaction is thought to be associated with pulmonary sequestration of activated neutrophils. To examine whether this reaction could be prevented by blocking neutrophil activation with NPC 15669 (N-(9H-(2,7-dimethylfluorenyl-9-methoxy)carbonyl)-l-leucine), an inhibitor of Mac-1 adhesion molecule up-regulation, we gave 12 piglets a heparin bolus (300 IU/kg iv) followed by protamine (3 mg/kg iv over 90 sec) 15 min later. Six of the piglets received NPC 15669 (10 mg/kg iv bolus, then 6 mg/kg/hr iv infusion) 15 min before the heparin bolus. Two minutes after protamine administration, CD18 (β-sub-unit of Mac-1) expression measured by immunofluorescence flow cytometry increased 128 ± 9% (mean ± SEM) over preprotamine levels in control piglets but remained unchanged in NPC piglets (99 ± 2%, P < 0.05). Fifteen minutes after protamine, lung myeloperoxidase activity, an index of neutrophil degranulation, was significantly lower in the NPC group (87.83 ± 10.04 versus 57.23 ± 2.59 μmol/10 mg; P < 0.005). NPC 15669 also prevented postreversal pulmonary artery hypertension (158 ± 30, 150 ± 20, and 140 ± 13 versus 91 ± 7, 91 ± 18, and 85 ± 9% preprotamine at Minutes 2, 5, and 10; P < 0.05). Systemic arterial pressure, cardiac output, and circulating neutrophil counts were not different between groups. These results demonstrate that (1) neutrophil activation occurs following protamine reversal of heparin anticoagulation and (2) inhibition of neutrophil activation prevents pulmonary hypertension after protamine reversal, suggesting an important role for neutrophils in the adverse pulmonary hypertensive reactions related to protamine reversal of heparin.

Role of platelet-activating factor in the ovine heparin-protamine reaction.

Platelet-activating factor (PAF) infusion into sheep, as well as protamine reversal of heparin anticoagulation, causes thromboxane release into plasma, pulmonary hypertension, hypoxemia, and leukopenia. We investigated the possible role of PAF in the heparin-protamine reaction. Intravenous protamine was administered to neutralize heparin anticoagulation in five awake sheep and caused an increase of mean pulmonary arterial pressure from 16.6 +/- 1 (SE) mmHg at base-line to 47 +/- 9 mmHg at 1 min after protamine injection (P < 0.01) because of a 4.5-fold increase of pulmonary vascular resistance. This neutralization reaction induced a 25% reduction of circulating leukocyte count and arterial PO2. Undetectable blood levels of PAF were measured by bioassay and high-performance liquid chromatography during these heparin-protamine reactions. Infusion of BN 52021 (20 mg/kg), a PAF receptor antagonist, before rechallenging the same sheep with heparin and then protamine did not reduce the level of peak pulmonary hypertension or the degree of hypoxemia and leukopenia. We conclude that the leukopenia and thromboxane-mediated pulmonary vasoconstriction occurring after rapid intravascular formation of heparin-protamine complexes in sheep are not due to the release of PAF.

Absence of complement-mediated events after protamine reversal of heparin anticoagulation

Protamine reversal of heparin anticoagulation is associated with adverse hemodynamic effects that may be attenuated with protamine pretreatment (PP). This study assesses the role of complement activation during these phenomena in adult cardiac surgery patients. Sixteen individuals undergoing cardiopulmonary bypass were given intravenous normal saline or protamine (2 mg/kg) as a randomized pretreatment prior to undergoing heparin anticoagulation (400 IU/kg), coronary artery revascularization, and subsequent reversal of the anticoagulated state with protamine (4 mg/kg). Blood pressure, pulmonary artery diastolic pressure (PAD), heart rate, and cardiac output (CO) were measured during and after pretreatment, prior to heparin reversal by protamine, and for 10 min after reversal. Total hemolytic complement (CH50), C3 conversion to C3b, C3a/C5a, platelet count, and white blood cell count (WBC) were also measured at the same time periods. No significant correlation existed between complement activation and hemodynamic events, as might have been evident by decreased CH50, increased C3 conversion to C3b, or elevations in C3a/C5a levels. PP significantly prevented the CO decrease occurring at 1 and 3 min following heparin reversal by protamine (−0.8 and −1.4 liters/min vs 0.1 and −0.2 liters/min, P < 0.05 and P < 0.01, respectively). Reversal hypotension was less with PP, although PAD fell equally in both groups. WBC decreases after heparin reversal were less after PP (−25% vs −7%, P = 0.06). These data support the conclusion that, contrary to earlier reports, adverse hemodynamic and hematologic responses accompanying protamine reversal of heparin anticoagulation do not appear to be correlated with activation of complement. In fact, those patients having the greatest C3a generation exhibited the least hemodynamic changes.

Neutralization of low molecular weight heparin by polybrene prevents thromboxane release and severe pulmonary hypertension in awake sheep : Montalescot G, Zapol WM, Carvalho A, et al Circulation 82:1754–1764, 1990

Protamine reversal of heparin anticoagulation in patients is occasionally associated with life-threatening acute pulmonary hypertension. In a sheep model, we evaluated the effect on this adverse cardiopulmonary reaction of modifying the type of heparin (low molecular weight heparin compared with unfractionated heparin) and the type of heparin antagonist (polybrene compared with protamine). Protamine reversal of low molecular weight heparin (LMWH) and polybrene reversal of unfractionated heparin induced more than a 10-fold increase of plasma thromboxane B2 levels, a threefold increase of pulmonary vascular resistance and pulmonary artery pressure, and a 25% decrease of PaO2. A similar adverse reaction followed protamine reversal of conventional unfractionated heparin. However, with polybrene (1 mg/kg) reversal of LMWH (1 mg/kg), we measured neither pulmonary hypertension (pulmonary artery pressure was 22.6 +/- 3.6 mm Hg at 1 minute after polybrene reversal of LMWH compared with 47.9 +/- 4.2 mm Hg after pro...