Preparation of Heparin and Its Use in the First Clinical Cases

Minimum protamine dose required to neutralize heparin in cardiac surgery: a single-centre, prospective, observational cohort study

PURPOSE

Excess protamine contributes to coagulopathy following cardiopulmonary bypass (CPB) and may increase blood loss and transfusion requirements. The primary aim of this study was to find the least amount of protamine necessary to neutralize residual heparin following CPB using the gold standard assays of anti-IIa and anti-Xa activity. Secondary objectives were to evaluate whether the post-CPB activated clotting time could be used as a surrogate marker for quantifying heparin neutralization.

METHODS

Twenty-eight consecutive patients undergoing elective cardiac surgery were enrolled. Protamine administration was standardized through an infusion pump at 25 mg·min-1. Blood samples were withdrawn prior to and following administration of 150, 200, 250, and 300 mg protamine and analyzed for activated clotting time and anti-IIa and -Xa activity.

RESULTS

Following a mean (standard deviation) cumulative heparin dose of 67,700 (19,400) units and a CPB duration of 113 (71) min, protamine requirements varied widely. Eight out of 25 (32%) patients showed complete neutralization of anti-IIa and -Xa activity at the first sampling point (150 mg protamine; protamine:heparin ratio, 0.3 [0.1]). A protamine:heparin ratio of 0.5 (0.2) was sufficient for heparin neutralization in > 90% of patients. After CPB, a low to mid-range activated clotting time correlated well with anti-IIa and -Xa activity.

CONCLUSIONS

The protamine:heparin ratio required to neutralize residual unfractionated heparin (UFH) following CPB is variable. A protamine:heparin ratio of 0.3 was sufficient to neutralize UFH in some patients, while a ratio of 0.5 is sufficient to neutralize both residual anti-IIa and -Xa activity in most patients. Larger studies are necessary to confirm these findings and evaluate their clinical implications.

STUDY REGISTRATION

ClinicalTrials.gov (NCT03787641); registered 26 December 2018.

How blood met plastics, plant and animal extracts: Material encounters between medicine and industry in the twentieth century

Twentieth-century medicine saw the remarkable rise of complex machines and infrastructures to process blood for medical purposes, such as transfusion, dialysis, and cardiac surgery. Instead of attributing these developments to technological ingenuity, this article argues for the primacy of material encounters as a promising focal point of medical historiography. In fact, blood's special properties consistently clashed with most materials used in medical practice, provoking a series of material exchanges. Drawing on a combination of epistemological and network approaches, three exemplary cases are presented to examine blood's encounters with plastics, plant and animal extracts: William M. Bayliss's (1860-1926) injections of dissolved gum acacia to expand diminished blood volume; Charles H. Best's (1899-1978) production of the anticoagulant heparin from animal organs; and the preservation of fragile blood cells by silicone coatings inside of John H. Gibbon Jr.'s (1903-1973) heart-lung machine. The case studies demonstrate how the complementarity of blood and these materials produced hybridizations between medicine and a range of industrial branches, from colonial forestry and meatpacking to commercial chemistry. In this light, the paper concludes by discussing the dependencies of today's healthcare environments on globally distributed, capitalistically appropriated resources in the face of crises like the COVID-19 pandemic.

The History and Innovations of Blood Vessel Anastomosis

Surgical technique and technology frequently coevolve. The brief history of blood vessel anastomosis is full of famous names. While the techniques pioneered by these surgeons have been well described, the technology that facilitated their advancements and their inventors deserve recognition. The mass production of laboratory microscopes in the mid-1800s allowed for an explosion of interest in tissue histology. This improved understanding of vascular physiology and thrombosis laid the groundwork for Carrel and Guthrie to report some of the first successful vascular anastomoses. In 1916, McLean discovered heparin. Twenty-four years later, Gordon Murray found that it could prevent thrombosis when performing end-to-end anastomosis. These discoveries paved the way for the first-in-human kidney transplantations. Otolaryngologists Nylen and Holmgren were the first to bring the laboratory microscope into the operating room, but Jacobson was the first to apply these techniques to microvascular anastomosis. His first successful attempt in 1960 and the subsequent development of microsurgical tools allowed for an explosion of interest in microsurgery, and several decades of innovation followed. Today, new advancements promise to make microvascular and vascular surgery faster, cheaper, and safer for patients. The future of surgery will always be inextricably tied to the creativity and vision of its innovators.

Purification of the human fibroblast growth factor 2 using novel animal-component free materials

This paper analyzes the use of animal-component free chromatographic materials for the efficient purification of the human fibroblast growth factor 2 (hFGF-2). hFGF-2 is produced in Escherichia coli and purified via three different chromatography steps, which include a strong cation exchange chromatography as a capture step, followed by heparin affinity chromatography and an anion exchange chromatography as a polishing step. The affinity chromatography step is based on the animal-derived material heparin. Chemically produced ligands provide a viable alternative to animal-derived components in production processes, since they are characterized by a defined structure which leads to reproducible results and a broad range of applications. The alternative ligands can be assigned to adsorber of the mixed-mode chromatography (MMC) and pseudo-affinity chromatography. Eight different animal-component free materials used as adsorbers in MMC or pseudo-affinity chromatography were tested as a substitute for heparin. The MMCs were cation exchangers characterized with further functional residues. The ligands of the pseudo-affinity chromatography were heparin-like ligands which are based on heparin's molecular structure. The alternative methods were tested as a capture step and in combination with another chromatographic step in the purification procedure of hFGF-2. In each downstream step purity, recovery and yield were analysed and compared to the conventional downstream process. Two types of MMC - the column Foresight^TM Nuvia^TM cPrime^TM from Bio-Rad Laboratories and the column HiTrap^TM Capto^TM MMC from GE Healthcare Life Sciences - can be regarded as effective animal-component free alternatives to the heparin - based adsorber.

A Century of Heparin

The year 2018 was the centennial of the naming of heparin by Emmett Holt and William Howell and the 102nd anniversary of Jay McLean's discovery of an anticoagulant heparphosphatide at Johns Hopkins Hospital in Baltimore. This article discusses recently discovered historical artifacts that shed new light on heparin's christening, including McLean's unpublished letter written in 1950 that represents one of the most complete accounts of heparin's discovery before his untimely death. In addition, the article describes the finding of a plaque dedicated to McLean and explores the circumstances of its removal from public display, as learned from interviews with present and former staff members.

Heparin: role in protein purification and substitution with animal-component free material

Heparin is a highly sulfated polysaccharide which belongs to the family of glycosaminoglycans. It is involved in various important biological activities. The major biological purpose is the inhibition of the coagulation cascade to maintain the blood flow in the vasculature. These properties are employed in several therapeutic drugs. Heparin’s activities are associated with its interaction to various proteins. To date, the structural heparin-protein interactions are not completely understood. This review gives a general overview of specific patterns and functional groups which are involved in the heparin-protein binding. An understanding of the heparin-protein interactions at the molecular level is not only advantageous in the therapeutic application but also in biotechnological application of heparin for downstreaming. This review focuses on the heparin affinity chromatography. Diverse recombinant proteins can be successfully purified by this method. While effective, it is disadvantageous that heparin is an animal-derived material. Animal-based components carry the risk of contamination. Therefore, they are liable to strict quality controls and the validation of effective good manufacturing practice (GMP) implementation. Hence, adequate alternatives to animal-derived components are needed. This review examines strategies to avoid these disadvantages. Thereby, alternatives for the provision of heparin such as chemical synthesized heparin, chemoenzymatic heparin, and bioengineered heparin are discussed. Moreover, the usage of other chromatographic systems mimetic the heparin effect is reviewed.

Heparin at physiological concentration can enhance PEG-free in vitro infection with human hepatitis B virus

Hepatitis B virus (HBV) is a blood-borne pathogen responsible for chronic hepatitis, cirrhosis, and liver cancer. The mechanism of HBV entry into hepatocytes remains to be investigated. Recently, sodium taurocholate cotransporting polypeptide (NTCP) was discovered as a major HBV receptor based on an in vitro infection system using NTCP-reconstituted HepG2 cells. However, this infection system relies on the compound polyethylene glycol (4% PEG), which is not physiologically relevant to human infection. High concentration of heparin has been commonly used as an inhibitor control for in vitro infection in the field. Surprisingly, we found that heparin at physiological concentration can enhance HBV infection in a PreS1-peptide sensitive, NTCP-dependent manner in both HepaRG and HepG2-NTCP-AS cells. O-sulfation of heparin is more important for the infection enhancement than N-sulfation. This system based on the HepG2-NTCP-AS cells can support in vitro infection with HBV genotypes B and C, as well as using serum samples from HBeAg positive and negative chronic carriers. In summary, our study provides a PEG-free infection system closely resembling human natural infection. In addition, it points to a future research direction for heparin and heparin-binding host factor(s) in the blood, which are potentially involved in viral entry. To our knowledge, this is the first soluble and circulatory host factor which can enhance HBV in vitro infection.

History of Cardiovascular Surgery at Toronto General Hospital

The Division of Cardiovascular Surgery at Toronto General Hospital has enjoyed an enviable history of academic achievement and clinical success. The foundations of this success are innovation, creativity and excellence in patient care, which continue to influence the current members of the division.

A bio-enabled maximally mild layer-by-layer Kapton surface modification approach for the fabrication of all-inkjet-printed flexible electronic devices

A bio-enabled, environmentally-friendly, and maximally mild layer-by-layer approach has been developed to surface modify inherently hydrophobic Kapton HN substrates to allow for great printability of both water- and organic solvent-based inks thus facilitating the full-inkjet-printing of flexible electronic devices. Different from the traditional Kapton surface modification approaches which are structure-compromising and use harsh conditions to target, and oxidize and/or remove part of, the surface polyimide of Kapton, the present Kapton surface modification approach targeted the surface electric charges borne by its additive particles, and was not only the first to utilize environmentally-friendly clinical biomolecules to build up a thin film of protamine-heparin complex on Kapton, but also the first to be conducted under minimally destructive and maximally mild conditions. Besides, for electrically charged ink particles, the present surface modification method can enhance the uniformity of the inkjet-printed films by reducing the “coffee ring effect”. As a proof-of-concept demonstration, reduced graphene oxide-based gas sensors, which were flexible, ultra-lightweight, and miniature-sized, were fully-inkjet-printed on surface modified Kapton HN films and tested for their sensitivity to dimethyl methylphosphonate (a nerve agent simulant). Such fabricated sensors survived a Scotch-tape peel test and were found insensitive to repeated bending to a small 0.5 cm radius.

The long path to NOAC

The discovery of anticoagulant drugs occurred at a time when the process of blood coagulation only had been roughly described and their mode of action was unknown. Nevertheless, heparin – which was discovered 100 years ago – and warfarin – which was developed in the 1920s – had taken off on a triumphal course which is unique in medical history. The synthesis of anticoagulants with targeted mode of action was only achieved at the end of the last century, e. g. the inhibitor of factor Xa fondaparinux or the recombinant production of the direct thrombin inhibitor hirudin, closely followed by the synthesis of the direct oral inhibitors of factor Xa and thrombin. These compounds had been clinically developed in the early 21st century and meanwhile, they have become available for several indications. Dabigatran is the only thrombin inhibitor and rivaroxaban, apixaban and edoxaban are the three factor Xa inhibitors which entered the market and have started replacing the conventional anticoagulants for treatment of venous thromboembolic complications and for prevention of stroke in patients with atrial fibrillation. They have several characteristics in common such as a reproducible bioavailability, much shorter halflives than vitamin K antagonists, low interaction with other drugs, fixed dosing regimens without the necessity for routine coagulation controls and a better risk-/benefit profile than conventional anticoagulants. However, there are differences between the various compounds with regard to metabolism, renal elimination and the various dosing regimens which definitely need to be considered when prescribed to various patient populations.

Anticoagulation strategies and difficulties in neonatal and paediatric extracorporeal membrane oxygenation (ECMO)

Objective:

The aim of this review is to highlight an emerging problem with anticoagulation-related complications in neonatal and paediatric ECMO, to explore for flaws in the currently recommended anticoagulation management responsible for these problems and to discuss possible strategies mitigating further escalation of the issue.

Data Sources:

Pertinent neonatal and paediatric literature on the topic of interest and international Extracorporeal Life Support Organisation (ELSO) registry data request.

Conclusions:

The international ELSO registry data reveals increasing rates of anticoagulation-related complications during neonatal and paediatric ECMO worldwide. The causes are multifactorial and the proposed solution to the problem is to match anticoagulation management to the pathophysiological complexity of haemostasis on ECMO.

Curious stories surrounding the discovery and development of conventional antithrombotics

Die Entdeckung eines therapeutischen Effektes war früher meist ein Zufallsereignis. Vielfach war der Weg bis zur Anwendung lang und steinig und nicht selten von merkwürdigen Geschichten begleitet, so bei den Antithrombotika Heparin, Aspirin und Warfarin.

Heparin: Wem gebührt die Anerkennung als Entdecker? Dem Studenten Jay McLean, der neben den gesuchten thromboplastisch wirksamen Cephalin-Komponenten zufällig eine gerinnungshemmende Komponente fand? Oder seinem Chef, der die „zufällige Entdeckung“ McLeans später aufgriff und eben-falls gerinnungshemmende Komponenten isolierte, die sich jedoch chemisch von den McLean´schen unterschieden und zur Ausgangssubstanz des heutigen Heparins wurden?

Aspirin: Als schmerz- und fiebersenkendes Mittel längst bekannt, erfuhr es eine zweite Karriere in der kardiovaskulären Medizin. Erst 1967 erkannte man, dass die Plättchenaktivität inhibiert wird. Die zweite Karriere begann mit der Zulassung für TIA und Herzinfarkt anfangs 1980. Bis dato unbekannt war die Geschichte des Dr. Craven, der bereits 1950 in „obskuren“ Zeitschriften seine Beobachtung publizierte, dass alle seine unter Aspirin stehenden Patienten von Herzinfarkt verschont blieben.

Warfarin:Um 1920 starben tausende Rinder in Nordamerika an inneren Blutungen. Die Ursache fand man im Verzehr des gelagerten „sweet clover“. Erst nach Jahren hatte man die Erklärung: die Umwandlung des ungiftigen Coumarin im Heu in das gerinnungshemmende Dicoumarol durch Pilzinfektion. Bald folgte die Synthese und damit auch der klinische Einsatz als Antithrombotikum. Viel größeren Erfolg aber hatte die Substanz als Rattengift mit dem Namen Warfarin. Die erneute Anwendung beim Menschen erfolgte erst wieder, nachdem ein Soldat seinen Suizidver-such durch Vitamin K-Gabe überstanden hatte.

Isolation of low-molecular-weight heparin/heparan sulfate from marine sources

The glycosaminoglycan (heparin and heparan sulfate) are polyanionic sulfated polysaccharides mostly recognized for its anticoagulant activity. In many countries, low-molecular-weight heparins have replaced the unfractionated heparin, owing to its high bioavailability, half-life, and less adverse effect. The low-molecular-weight heparins differ in mode of preparation (chemical or enzymatic synthesis and chromatography fractionations) and as a consequence in molecular weight distribution, chemical structure, and pharmacological activities. Bovine and porcine body parts are at present used for manufacturing of commercial heparins, and the appearance of mad cow disease and Creutzfeldt-Jakob disease in humans has limited the use of bovine heparin. Consequently, marine organisms come across the new resource for the production of low-molecular-weight heparin and heparan sulfate. The importance of this chapter suggests that the low-molecular-weight heparin and heparan sulfate from marine species could be alternative sources for commercial heparin.

Systematic review on heparin-induced thrombocytopenia in children: a call to action

BACKGROUND

Heparin-induced thrombocytopenia (HIT) has increasingly been reported in children as an indication for use of new alternative anticoagulant drugs (NAADs).

OBJECTIVES

To systematically review the literature regarding: (i) the incidence and prevalence of seroconversion and HIT and (ii) the clinical/laboratory findings and management of HIT in children.

DESIGN/METHODS

MEDLINE and EMBASE databases were searched for studies that reported pediatric cases of HIT. Methodological reliability assessment of studies was performed with the Loney scale.

RESULTS

The incidence of seroconversion in neonates ranged between 0% and 1.7%. There were no cases of neonatal HIT in the included cohorts. The incidence range of seroconversion in the non-neonatal population was 1.3-52%. The incidence of HIT in non-neonates after cardiopulmonary bypass was 0.33% (95%CI, < 0.01-2.04). Whereas more than half of pediatric cases labeled as HIT (30/52) did not include pivotal features of this syndrome, 80% of them received NAADs.

CONCLUSION

The incidence of HIT is likely to have been overestimated in children, leading to potential misuse of NAADs in many cases. Clinical findings and laboratory assessment of pediatric cases are poorly described in the literature at present. Thorough laboratory investigation, proper reporting of cases and adequate design of studies are mandatory to elucidate the clinical/laboratory picture of pediatric HIT.

The heparin recall of 2008

Heparin is one of the oldest drugs still in widespread clinical use. Its discovery in 1916 predates the establishment of the Food and Drug Administration. Since 1935, over 15,000 research papers have been published on the effects of heparin. Because the exact chemical formula of heparin is unknown, synthetic manufacturing has proven difficult. In 2008, a worldwide recall of heparin occurred. Scientists determined that a contaminant known as oversulfated chondroitin sulfate was responsible for the numerous deaths and adverse events. This contaminant was first traced to a chemical plant in Changzou, China. This article will review the discovery of heparin and the adulteration process that jeopardized the world's heparin supply.

History of heparin

The history of heparin is described from its initial discovery in 1916 to recent developments in knowledge of its mechanism of action and clinical use. Commercial production started soon after its discovery, in the 1920s, and improved purification methods led to animal studies and the first clinical trials in the 1930s. Research into heparin's chemical structure proved difficult, with uncertainty about the uronic acid moiety and the N-acetyl content, but the structure of the basic disaccharide unit was established by the 1960s, though knowledge of the heterogeneity and fine structure of heparin chains continued to accumulate over the next 20 years. In 1976, it was found that only one third of heparin chains bound with high affinity to antithrombin, and subsequent studies identified a unique pentasaccharide sequence, which was essential for antithrombin binding and anticoagulant activity - this pentasaccharide was synthesised in 1983. Clinical usage of heparin continued to increase and two major developments were the use of low- dose heparin for prevention of deep vein thrombosis and pulmonary embolism, and the development of low-molecular-weight heparin as a separate drug.

[Dermatologic aspects of anticoagulation]

The coagulation system protects the body from uncontrolled blood loss by means of highly regulated processes. In case of an injury the coagulation system instantly switches from controlled blood flow to acute coagulation and thrombus formation with the goal of stopping the blood loss. Minor changes in this well-maintained equilibrium of coagulation and blood flow tip the balance towards uncontrolled blood loss or even fatal thromboembolic events. Iatrogenic manipulation of this highly regulated system is possible with a variety of therapeutic agents. We review the basics of coagulation physiology and then discuss dermatologically relevant aspects of thrombosis prevention, as well as the use of anticoagulants to treat dermatologic diseases.

The prevention and treatment of venous thromboembolism with LMWHs and new anticoagulants

As the risk factors for thrombosis are becoming better understood, so is the need for anticoagulation. The inherent difficulties with warfarin are such that a low-molecular-weight heparin (LMWH) is often the key therapeutic. However, there are several different species of LMWH available to the practitioner, which leads to the need for an objective guide. New agents are coming onto the marketplace, and these may supersede both warfarin and the heparins. The current report will review the biochemistry and pharmacology of different LWMHs and identify which are more suitable for the different presentations of venous thromboembolism. It will conclude with a brief synopsis of new agents which may supersede warfarin and heparin.

A tale of two anticoagulants: warfarin and heparin

This article relays the story of 3 men, Karl Paul Link, who is the discoverer of warfarin, and William Henry Howell and Jay McLean, who are the discoverers of heparin.

From "spongy" and "cold" hearts to cellular cardiomyoplasty: tales of Canadian contribution to global cardiac surgery

Despite the small size of its population and the number of its cardiac surgeons, Canadians have participated actively in the birth and development of cardiac surgery during the past half century, with pioneers such as Arthur Vineberg and Wilfred Bigelow leading the way. New and innovative cardiac surgical techniques and their scientific bases were developed and shared globally over the years. Canadian surgeons continue to be productive and are contributing to advances in this field at the dawn of the twenty-first century. Some of these efforts and achievements are illustrated in this review.

Fabrication and characterization of heparin functionalized membrane-mimetic assemblies

A membrane-mimetic assembly incorporating surface bound heparin was fabricated as a system to improve the hemocompatibility of blood-contacting devices. As a model system, heparin was chemically modified by end-point conjugation to biotin and immobilized onto membrane-mimetic thin films via biotin-streptavidin interactions. Heparin surface density, determined by radiochemical titration, confirmed that surface density was directly related to the molar concentration of biotinylated lipid within the assembled membrane-mimetic film. The capacity of surface bound heparin to promote ATIII-mediated thrombin inactivation was investigated in a parallel plate flow chamber under simulated venous and arterial wall shear rates of 50 and 500 s(-1), respectively. Significantly, we observed that the rate of thrombin inactivation approached a maximum at a heparin surface concentration greater than 4.4 pmol/cm(2) (61 ng/cm(2)). In the process, mass transport limited regimes were identified for heparin potentiated thrombin inactivation under both simulated venous and arterial conditions.

Heparin-induced thrombocytopenia in the pediatric intensive care unit population

OBJECTIVES

To report the occurrence of heparin-induced thrombocytopenia (HIT), discuss its pathophysiology, and outline an approach to management in the pediatric intensive care unit (ICU) patient.

DESIGN

Retrospective case reports.

SETTING

Pediatric ICU in a tertiary-care center.

PATIENTS AND RESULTS

Two pediatric ICU patients (2 and 6 mos of age) who developed HIT in the pediatric ICU. One was receiving heparin as a flush solution through a central line and the other had full heparinization during cardiopulmonary bypass. Both had received heparin during their neonatal course and developed thrombocytopenia; however, HIT was not considered as a possible diagnosis. HIT was diagnosed using a heparin-induced platelet aggregation study. The thrombocytopenia resolved with the cessation of heparin administration. One of the patients developed a deep vein thrombosis around a femoral venous catheter.

CONCLUSION

Although well described in the adult literature, there have been a limited number of reports of HIT in pediatric-aged patients. Given its potential for morbidity, HIT should be considered in the differential diagnosis of thrombocytopenia in the pediatric ICU patient.

Heparin-protein interactions

Heparin, a sulfated polysaccharide belonging to the family of glycosaminoglycans, has numerous important biological activities, associated with its interaction with diverse proteins. Heparin is widely used as an anticoagulant drug based on its ability to accelerate the rate at which antithrombin inhibits serine proteases in the blood coagulation cascade. Heparin and the structurally related heparan sulfate are complex linear polymers comprised of a mixture of chains of different length, having variable sequences. Heparan sulfate is ubiquitously distributed on the surfaces of animal cells and in the extracellular matrix. It also mediates various physiologic and pathophysiologic processes. Difficulties in evaluating the role of heparin and heparan sulfate in vivo may be partly ascribed to ignorance of the detailed structure and sequence of these polysaccharides. In addition, the understanding of carbohydrate-protein interactions has lagged behind that of the more thoroughly studied protein-protein and protein-nucleic acid interactions. The recent extensive studies on the structural, kinetic, and thermodynamic aspects of the protein binding of heparin and heparan sulfate have led to an improved understanding of heparin-protein interactions. A high degree of specificity could be identified in many of these interactions. An understanding of these interactions at the molecular level is of fundamental importance in the design of new highly specific therapeutic agents. This review focuses on aspects of heparin structure and conformation, which are important for its interactions with proteins. It also describes the interaction of heparin and heparan sulfate with selected families of heparin-binding proteins.

Safety and efficacy of fixed-dose heparin in carotid endarterectomy

OBJECTIVE

Although fixed dosage of heparin is frequently used during vascular surgery, there are very few studies that document the appropriateness of this type of dosing. We have undertaken a prospective study to determine the physiological response to a fixed dose of heparin, using a conventional measure of anticoagulation, and have correlated this measure with complications.

METHODS

We studied 140 consecutive patients undergoing elective carotid endarterectomy. Serial activated clotting times (ACT values) were obtained in duplicate before administration of heparin, 15 minutes after application of a carotid artery cross-clamp, and 1 hour after administration of 5000 U of heparin by intravenous bolus. Postoperatively, patients were assessed for new neurological deficits (transient ischemic attack and stroke) and neck hematomas. A battery of neuropsychometric tests was performed in 49 patients at baseline and on the day after carotid endarterectomy to identify subtle new neurological deficits.

RESULTS

ACT values were found to be highly reproducible, with less than a 1.5% difference between duplicate baseline samples. Although all patients received 5000 U of heparin, the dose received per kilogram of body weight varied considerably (44-116 U/kg), as did ACT values at both 15 minutes (178-423 s) and 1 hour (173-390 s). Nevertheless, there was a significant correlation between heparin dose per kilogram and ACT values at 15 minutes (r = 0.45) and at 1 hour (r = 0.38) postinfusion, as well as ACT ratios (final ACT/initial ACT) at 15 minutes (r = 0.43) and at 1 hour (r = 0.34) after heparin bolus. Eight patients (5.7%) developed postoperative wound hematomas, one of which (0.7%) required reoperation. No patient had a stroke, but one patient had a transient ischemic attack, and 19 (39%) of 49 patients demonstrated significant early postoperative neuropsychometric deficits. Although the incidence of neck hematoma was not influenced by the heparin dose (P = 0.23), the ACT value at 15 minutes (P = 0.71) or 1 hour (P = 0.61), or the ACT ratio (P = 0.68), the only severe hematoma requiring reoperation occurred when the maximal ACT value was more than 400 seconds. Although performance on neuropsychometric tests did not appear to be statistically influenced by heparin dosing, the ACT value, or the degree of ACT elevation, there was a trend for deficits to be associated with lower heparin doses.

CONCLUSION

Fixed heparin dosing achieves safe and efficacious anticoagulation in the great majority of patients having carotid endarterectomy, with 5000 U expected to result in 15-minute and 1-hour ACT values of 175 to 425 seconds and 170 to 390 seconds, respectively. Although weight-based heparin dosing may reduce the incidence of subtle complications (hematoma formation or decline on neuropsychometric tests) and may result in more predictable 15-minute and 1-hour ACT values (85 U/kg; 225-375 and 200-340 s, respectively), no statistically compelling clinical advantage could be demonstrated. Therefore, either weight-based or fixed dosing is acceptable, with both obviating the need for routine pre-clamp ACT confirmation, thereby saving operative time and expense.

Heparin-bonded circuits: clinical outcomes and costs

The aim of this study was to use meta-analysis to combine the results of numerous studies and examine the impact of heparin-bonded circuits on clinical outcomes and the resulting costs. Heparin-bonded circuits, both ionically and covalently bonded, are examined separately. The results of the study provide evidence that heparin-bonded circuits result in improved clinical outcomes when compared to the identical nonheparin-bonded circuits. These improved clinical outcomes result in subsequent lower costs per patient with their use. However, differences are apparent in the significance and magnitude of these outcomes between ionically and covalently bonded circuits. Covalently bonded circuits provide a greater magnitude and significance of improvement in clinical outcomes than ionically bonded circuits. Total cost savings can be expected to be three times greater with covalently bonded circuits ($3231 versus $1068). It was concluded that the choice regarding the use of a heparin-bonded circuits and the type of heparin-bonded circuit used has the potential to alter clinical outcomes and subsequent costs. Cost consideration cannot be ignored, but clinical benefits should be the main rationale for the choice of cardiopulmonary bypass circuit. This analysis provides evidence that clinical benefits and cost savings can both be derived from use of the same technology-covalently bonded circuits.

How much heparin? A simple in vitro test

A simple in vitro test to calculate the dose of heparin required to achieve optimal in vivo anticoagulation during surgery has been assessed in 15 patients who subsequently underwent vascular surgery. Heparin was added to four aliquots of patients blood in vitro to give five solutions with heparin concentrations ranging from 0-0.8 units/ml of plasma. The activated partial thromboblastic times (APTT) of each of these samples was then measured and the natural log (ln) of the APTT calculated. The natural log of the APTT in vitro was then plotted against the in vitro heparin concentration. From this linear correlation the concentration of heparin required to achieve an APTT 2.5 times the normal in vitro (Hc) for the 15 different patients was calculated and ranged from 0.4-0.75 units/ml (median 0.47). Based on an estimate of the plasma volume (PV), the bolus dose of heparin given intravenously to each patient to produce an equivalent anticoagulant response in vivo was calculated (Hc x PB). Heparin boli administered ranged from 1000-2000 units (median 1500). The mean in vivo APTT achieved was 77% of the predicted value (range 62%-123%). Such an estimation of an in vivo response, by means of an in vitro test, should help to more accurately predict the effects of heparin in vivo and individualise anticoagulation dosage.

Antithrombotic therapy in historical perspective

The history of antithrombotic therapy is traced over the past 5 decades, with a focus on the treatment of 2 major disorders: venous thromboembolism and acute myocardial infarction. Five subjects pertinent to clinical management decisions are discussed: (1) theories of thrombosis and coagulation, (2) tests of coagulation, (3) the availability of therapeutic interventions, (4) techniques for the diagnosis of vascular obstruction, and (5) the use and misuse of clinical trials.

Heparin kinetics in vascular surgery

Currently there is little information available about the efficacy of heparin during vascular surgery or of the effects of surgical trauma on heparin kinetics. This study was undertaken to evaluate the kinetics of heparin therapy during vascular surgery. Nine patients undergoing major vascular surgery (one carotid, one common iliac and seven aortic operations) were studied both preoperatively and intra-operatively, each patient acting as his own control. Following determination of control activated partial thromboplastin time (APTT) and plasma heparin levels, heparin (100 u/kg body weight) was administered intravenously. Heparin dosage ranged form 4500 units to 8600 units with a mean dose of 6500 units. Plasma heparin and APTT levels were then measured at 10 minute intervals for 1 hour and 20 minute intervals for a second hour. The mean pre-operative and intra-operative APTT levels at ten minutes attained maximal values of 6.6 +/- 3.7 and 8.8 +/- 1.7 times the control respectively. At the end of 2 hours the mean APTT remained greater than 2.5 times the control in both groups. Mean plasma heparin level was 0.83 +/- 0.04 units at 10 minutes and was almost identical in both groups. Heparin level was not a reliable indicator of anticoagulant effect as most patients achieved the same levels but had markedly differing APTT results. The results of this study suggest that excessive doses of heparin may be used in vascular surgery and that surgical trauma does not significantly alter sensitivity to heparin.(ABSTRACT TRUNCATED AT 250 WORDS)

Heparin-induced thrombocytopenia, thrombosis, and hemorrhage

Sixty-two patients with a heparin-induced thrombocytopenia are reported. Clinical manifestations of this disorder include hemorrhage or, more frequently, thromboembolic events in patients receiving heparin. Laboratory testing has revealed a falling platelet count, increased resistance to heparin, and aggregation of platelets by the patient's plasma when heparin is added. Immunologic testing has demonstrated the presence of a heparin-dependent platelet membrane antibody. The 20 deaths, 52 hemorrhagic and thromboembolic complications, and 21 surgical procedures to manage the complications confirm the seriousness of the disorder. Specific risk factors have not been identified; therefore, all patients receiving heparin should be monitored. If the platelet count falls to less than 100,000/mm3, while the patient is receiving heparin, platelet aggregation testing, using the patient's plasma, is indicated. Management consists of cessation of heparin, platelet anti-aggregating agents, and alternate forms of anticoagulation when indicated.