Management of heparin therapy: Controlled prospective trial

Experience with the management of deep vein thrombosis in patients with spinal cord injury. Part II: a critical evaluation of the anticoagulant therapy

Eight acute spinal injury patients with deep vein thrombosis and/or pulmonary emboli are presented witn an in-depth analysis and management of anticoagulation therapy. Special considerations for acute spinal cord injury patients with regards to prophylactic and therapeutic anticoagulation by heparin and coumadin are discussed. There was a wide variation in the requirement of heparin and/or coumadin to maintain effective coagulability which could only be elicited by frequent laboratory monitoring. Inadequate dose and shorter duration of administration of anticoagulant resulted in recurrence of thromboembolism in three out of eight patients in the present series. Haemorrhagic complications were minor and easily manageable. Co-trimoxazole potentiation of coumadin action occurred in two of our patients and it requires special mention as the drug is used increasingly in the treatment of urinary tract infections.

Prophylaxis of venous thromboembolism: analysis of cost effectiveness

The rapidly expanding literature regarding prevention of venous thromboembolism is confusing and contradictory, but, when analysed in the aggregate, the collective experience permits a judgment about the relative efficacy of different prophylactic regimens in specific patient populations, who vary in the risk factors predisposing them to thromboembolism. The dollar cost of the several approaches to prevention and their consequences should also be a matter of concern. Efficacy and dollar cost together determine cost effectiveness, which provides a practical guide to selection of the prophylactic approach appropriate to an individual patient.

Heparin bleeding due to qualitative platelet dysfunction

On two separate occasions, a 26-year-old white woman bled from arterial puncture wounds while receiving heparin for thromboembolic disease. Bleeding time was prolonged after heparin administration at the time that she was ill and bled, and when she was re-challenged 2 years later. Heparin may produce bleeding as a result of a qualitative platelet dysfunction.

Heparin therapy: a randomized prospective study

Eighty patients were assigned randomly either to continuous or to intermittent heparin therapy, with control by the Lee-White Clotting Time (LWCT). Major bleeding complications occurred in 7.5 per cent and minor complications in 18 per cent of the entire group. The incidence of major bleeding complications in the continuous group (5 per cent) did not differ significantly from the incidence in the intermittent group (10 per cent). In contrast, bleeding complications were significantly more frequent in patients with soft-tissue trauma due to such procedures as thoracenteses and cut-downs, vascular damage due to other causes, and LWCTs over 35 minutes for 2 consecutive days. The incidence of bleeding complications appear to be the same in patients receiving intermittent as in those receiving continuous heparin therapy. Thoracenteses, cut-downs, and other forms of soft-tissue injury predispose to bleeding complications while laboratory monitoring with the LWCT may help to reduce bleeding complications.

Antithrombotic therapy. Rationale and application

Arterial thrombosis and venous thrombosis differ in pathogenesis, morphology, and response to antithrombotic therapy. Antiplatelet therapy usually is aimed at arterial thrombi, in whose formation platelet-mediated reactions predominate, while anticoagulant therapy is effective against venous thrombi, in whose formation coagulation predominates.

Prophylaxis and therapy of venous thromboembolism

Heparin is an anticoagulant drug which is used for the prophylaxis and treatment of venous thromboembolism and for the treatment of some cases of arterial thromboembolism. Venous thromboembolism is the commonest preventable cause of death in hospitalized patients, and the best approach to reduce its morbidity and mortality is the use of safe, effective, prophylaxis in patients at high risk. The use of low doses of heparin given s.c. (5000 units, 8 hourly)) has been shown in prospective clinical trials to be effective prophylaxis against venous thrombosis and nonfatal and fatal pulmonary embolism in patients undergoing general abdominothoracic surgery, without producing dangerous bleeding. Low-dose heparin, however, is not totally effective in patients undergoing hip surgery and suprapubic prostatectomy. The lack of benefit in these patients may be related to the intensity of the provocation to thrombosis. The use of heparin in large doses to treat thrombosis is associated with hemorrhagic complications in up to 30% of patients. There is evidence that continuous i.v. heparin is associated with fewer hemorrhagic complications than intermittent i.v. heparin, but the frequency is not related to the dose or to the use of laboratory monitoring. Hemorrhagic complications occur more frequently in elderly patients and in females and is more common following surgical operations. The frequency of recurrent venous thromboembolism is low in patients on therapeutic doses of heparin, and there is no difference in the frequency of recurrence in patients receiving heparin by continuous i.v. or intermittent i.v. administration.

The management of anticoagulation during noncardiac operations in patients with prosthetic heart valves. A prospective study

Based on previous thromboembolic complications associated with the interruption of anticoagulation during subsequent noncardiac operations in patients with nonbiological mitral prostheses, a protocol was developed for this high risk group. We report the successful management of 26 such operations in which anticoagulation was interrupted for 12 hours and then rapidly restored by means of heparin in the postoperative period. Since an earlier study suggested no adverse effect from the interruption of chronic anticoagulants for three to five days among patients with isolated aortic valve prostheses, simple interruption was again employed during 16 subsequent noncardiac operative procedures in this group with no complications. There were three episodes of hemorrhage observed in patients receiving therapeutic doses of heparin postoperatively, but only one required blood replacement.

The origin of thrombi in the deep veins of the lower limb: a venographic study

A series of 952 patients was examined by ascending venography; 812 with clinically diagnosed deep vein thrombosis (DVT) (group 1) and 140 with clinical features suggestive of pulmonary embolism (group 2). Thrombus was demonstrated in 401 (49.4 per cent) of group 1 and in 74 (53 per cent) of group 2 patients. A total of 535 limbs contained thrombus. In 493 (92 per cent) thrombus was present in the calf with either no further clot, or clot in continuity with that in more proximal veins. In the remaining 42 legs (8 per cent) thrombus either originated from multiple discontinuous sites in the legs and pelvis, or in proximal major veins without concomitant calf involvement. The clinical implications of these findings are discussed.

Bedside monitoring of heparin therapy

Continuous infusion heparin therapy was monitored in twenty-five patients with simultaneously performed activated partial thromboplastin times and activated clotting times. These data were then compared by means of the coefficient of correlation. Significant correlation is demonstrated between the APTT and ACT in 88 per cent of cases.

Heparin pharmacokinetics: increased requirements in pulmonary embolism

Heparin disappearance after injection and plasma levels during continuous infusion were studied in normal subjects and patients with thrombophlebitis, pulmonary embolism, renal failure, and liver failure. Heparin removal in normal subjects after 75 u/kg was nearly linear with a clearance of 0.64 ml/min/kg, SD +/- 0.11. Clearance varied inversely with dose. Heparin clearance in pulmonary embolism (0.80 ml/min/kg +/- 0.23) was significantly accelerated compared both to normals (P less than 0.005) and to thrombophlebitis patients (0.55 ml/min/kg +/- 0.19, P less than 0.01); the disappearance was more curvilinear in thrombophlebitis and pulmonary embolism than in normal subjects (P less than 0.025). Continuous infusion heparin requirements were greater in pulmonary embolism than in thrombophlebitis, in accordance with pharmacokinetic predictions. The pattern and rate of disappearance in renal disease was similar to normal subjects; in liver disease clearance was accelerated (0.86 ml/min/kg +/- 0.28) and disappearance curvilinear. Because of accelerated clearance, the initial dose of heparin in pulmonary embolism should be greater (25 u/kg/h) than in thrombophlebitis (10-15 u/kg/h). Variability within patient groups necessitates some laboratory control of dosage.

Consumption coagulopathy associated with intrauterine fetal death: the role of heparin therapy

A gravida with intrauterine fetal death who developed progressive chronic consumption coagulopathy was treated with heparin. When serial fibrinogen levels fell below 100 mg% and the prothrombin time was significantly prolonged, intravenously injected heparin corrected hypofibrinogenemia. A safe delivery followed administration of oxytocin. The authors emphasize the infrequent need for heparin therapy in the majority of cases of the intrauterine fetal death syndrome. Therapeutic guidelines for its use in selected cases are reviewed.

Pulmonary embolism

It is reasonable to conclude by considering an approach to the diagnosis and treatment of pulmonary embolism. When the diagnosis is suspect, and in the absence of contraindications, or hemodynamic instability, treatment with heparin may be begun and an arterial blood gas and perfusion lung scan obtained. If the Pao2 and perfusion scan are normal, it is unlikely that significant pulmonary embolism has occurred. The presence of a perfusion scan defect and hypoxemia should suggest that a ventilation scan and/or evaluation for deep vein thrombosis is performed. A ventilation scan which shows absence of ventilation in areas where there is a perfusion defect, or failure to demonstrate deep vein disease, strongly mitigate against the diagnosis of pulmonary embolism. If the diagnosis is in doubt, pulmonary angiography should be performed. If the patient presents in shock, an angiogram should be performed, while heparin is administered and supportive measures are begun. If anticoagulants are contraindicated, or if re-embolization occurs after adequate anticoagulant therapy, consideration should be given to placement of a transcaval umbrella filter.

Impairment by heparin of primary haemostasis and platelet [14C]5-hydroxytryptamine release

Heparin was administered to 34 normal subjects by intravenous injection (100 mu/kg) and the template bleeding time was significantly increased both 10 min and 120 min following injection. Before heparin the bleeding time was 5-3 +/- 1.0 min (mean +/- 1 SD); 10 min after injection it was 9.8 +/- 5.6 min (P less than 0.001); and 120 min after injection it was 7.2 +/- 3.9 min (P less than 0.001). Increases in the bleeding time were unrelated to changes in platelet count, and independent of heparin's effect on plasma coagulation. In blood drawn 10 min and 120 min following heparin injection, there was significantly less [14C]5-HT released from platelet-rich plasma (PRP) in response to collagen, 0.41 mM epinephrine and 8 micron ADP, although in vitro addition of heparin (0.1 mu/ml, 0.5 mu/ml and 2.5 mu/ml) to baseline PRP of three subjects did not depress [14C]5-HT release. Our experiments suggest that intravenous administration of a therapeutic dose of heparin can cause a significant reversible inpairment of platelet haemostatic properties, possibly by an indirect mechanism.

Haemorrhagic complications of heparin therapy

In a prospective trial 76 patients with venous thromboembolism have received intermittent constant-dosage heparin or continuously infused heparin with laboratory control. Frequencies of bleeding were similar in both groups. 32% of all patients bled, 13% severely. Retroperitoneal haemorrhage occurred in 5 patients. Major spontaneous bleeding was commoner in older patients and minor spontaneous bleeding in women. Bleeding was uncommon during the first 2 days of treatment, and its daily frequency was relatively constant thereafter. 21% of surgical wounds and 7% of arterial and venous puncture sites bled. These preliminary results illustrate the hazards of heparin therapy and suggest that bleeding complications are more closely related to duration of therapy, age, sex, and surgical trauma than to method of administration.

Erysipelas and necrotizing fasciitis

The clinical course of necrotizing fasciitis in 8 patients is compared with observations on 22 other patients with erysipelas. In necrotizing fasciitis the early erythematous areas turn into a dusky blue colour with later vesiculation and formation of bullae. An important finding is a non-pitting oedema extending outside the erythematous patches. The disease often progresses and involves further skin areas proximal to the initial ones. Gangrene tends to follow in multiple sites after the 1st week of illness. Group A streptococci in conjunction with widespread thrombosis and vascular necrosis of the involved skin are two major factors in the pathogenesis of the gangrene. Early debridement and excision of necrotic tissue in combination with large doses of penicillin and cloxacillin are confirmed as mandatory to remove toxaemia and inhibit further necrosis of the skin. In 3 of the 8 patients with necrotizing fasciitis the syndrome of disseminated intravascular coagulation complicated the course of the disease. A promising therapeutic result was seen in 2 further patients exhibiting alarming signs and symptoms of early necrotizing fasciitis; the combination of heparin, given intravenously in therapeutic doses guided by activated partial thromboplastin time studies, and of systemic antibiotics alleviated the symptoms, which vanished within 10 days of the start of treatment.

A miniature syringe pump for continuous administration of drugs and hormones: The Mill Hill infuser

A miniature syringe pump has been developed for intravenous or subcutaneous infusion of the many drugs and hormones which produce better therapeutic responses when continuously delivered at a controlled rate than by repeated separate injections. The infuser uses disposable plastic syringes and is designed for precise tamper-proof delivery of 2 ml/24 h or 2 ml/8 h with quartz-crystal control, unaffected bt the dose-rate can be precisely determined by prescribing solutions of appropriate strength.

The effect of continuous heparin infusion for one year on serum cholesterol and triglyceride concentrations in the dog

Fourteen normal dogs received continuous infusions of intravenous heparin for one year by means of an implantable infusion pump. Heparin wad admistered at an overall mean rate of 666 units/kg/day, a dose sufficient to prolong the Lee-White clotting time to greater than twice normal. Eight control, animals, under the same dietary and activity regimen, received continuous infusions of bacteriostatic water for one year by means of implanted pumps. Serum cholesterol concentrations rose to 50% above control values after one month of heparin infusion, and remained significantly (P less than 0.05) elevated at this level for the remaining 11 months. Serum triglyceride levels were unchanged. A possible mechanism for this elevation resides in the known effect of heparin to increase plasma free fatty acid concentrations by its activation of lipoprotein lipase. These results may have implications for the long-term use of heparin anticoagulation in the treatment of atherosclerotic states in man.

Living with prosthetic heart valves. Subsequent noncardiac operations and the risk of thromboembolism or hemorrhage

A total of 111 survivors of prosthetic valve insertion were followed an average of 4 years to assess the risk of thromboembolism or hemorrhage. Non-cloth-covered ball and/or disc valve prostheses were used, and all patients received long-term anticoagulant therapy. During the follow-up period the patients with mitral or combined valve replacement suffered four times more thromboembolic episodes and had a poorer survival rate than the patients with isolated aortic valve replacement. The management of anticoagulation and the complications resulting from 44 subsequent noncardiac operations were analyzed. Anticoagulation was discontinued before 25 noncardiac operations in patients with isolated aortic valve prostheses and there were no perioperative thromboemboli. Ten operations were performed on patients with mitral or combined valve prostheses with cessation of anticoagulation prior to surgery and there were two deaths due to perioperative thromboemboli. Unanticipated hemorrhage was encountered in four of nine patients in whom anticoagulation was maintained during surgery. Cessation of anticoagulation for 3 to 5 days appears safe in patients with aortic prostheses who require subsequent noncardiac operations. The incidence of thromboembolism in patients after mitral or combined valve replacement is high and constitutes a major risk whether or not a subsequent operation is required.

Thrombosis and intravascular coagulation

Stress, including trauma and sepsis, is associated with a state of hypercoagulability. In these circumstances the patient is at risk of generalized or local thrombotic complications. New laboratory investigative procedures facilitate diagnosis and permit improved assessment of therapy, which at present remains of unproven efficacy both in the general and local situation.

Antithrombotic drugs: part I

There are three categories of antithrombotic agents: drugs which prevent fibrin fromation (the anticoagulants and defibrinating enzymes), drugs which prevent platelet adhesion or aggregation (the antiplatelet drugs), and thrombolytic drugs which induce fibrin degradation. Clinical studies have now led to a better understanding of the relative value of these drugs in different thrombotic disorders. In addition, knowledge of the mechanism of action of some of these drugs has recently been much advanced. The anticoagulant drugs in clinical use are heparin and the oral anticoagulants. Heparin is a potent inhibitor of several steps on the intrinsic coagulation pathway through its effect on a plasma cofactor, antithrombin III. its action is immediate, but heparin must be given parenterally. Oral anticoagulants act more slowly, by reducing the hepatic synthesis of biologically active factors II, VII, IX and X, but can be given by mouth. Heparin is therefore most suitable for starting anticoagulant treatment, while oral anticoagulants are generally used for prolonged therapy. The value of the anticoagulants as antithrombotic agents has been best assessed by studying their effectiveness in preventing and treating venous thromboembolic disease. Oral anticoagulants have been repeatedly shown to prevent venous thrombosis and pulmonary embolism in patients at high risk of developing these complications. However, the increased risk of postoperative bleeding has prevented their widespread use for this purpose in surgical patients. Recently, the use of low doses of heparin, given subcutaneously before and after surgery, has been shown to markedly reduce the incidence of venous thrombosis and pulmonary embolism (including fatal pulmonary embolism) after major elective abdominal surgery, and to produce only a slight increase of postoperative bleeding. This represents a major advance in anticoagulant prophylaxis of venous thromboembolism insurgical patients. However, low dose heparin prophylasix is relatively ineffective in patients having hip surgery, and has not been evaluated in patients having other types of orthopaidic surgery. There is direct evidence that antocoagulant therapy prevents death and recurrent embolism in patients who have developed pulmonary embolism, and considerable indirect evidence that it prevents pulmonary embolism, and considerable indirect evidence that it prevents pulmonary embolism (and death from pulmonary embolism) in patients who have venous thrombosis. The incidence of further venous thromboembolism or bleeding during treatment appears to be minimised when heparin is given by continuous intravenous infusion in a dose sufficient to produce a moderate, but no excessive, prolongation of a heparin-sensitive, in vitro coagulation test. The tests most commonly used to monitor heparin therapy was based on either the whole blood clotting time or the activated partial thromboplastin time...