Preoperative prediction of postoperative deep vein thrombosis

Body mass index as a correlate of postoperative complications and resource utilization

PURPOSE

To describe the relationship of body mass index (BMI) with postoperative complications and resource utilization.

PATIENTS AND METHODS

Two thousand nine hundred and sixty-four patients 50 years or older undergoing elective noncardiac surgery with an expected length of stay > or = 2 days were enrolled in a prospective cohort study to measure major cardiac complications, noncardiac complications, length of stay, and costs. The setting was an urban teaching hospital. A preoperative history, physical, electrocardiogram (ECG), and chart review were performed by study personnel. Postoperative complications were detected by ECGs, creatine kinase and creatine kinase MB levels, and daily chart review. Total costs were obtained from the hospital's computerized database.

RESULTS

Complication rates were not different among BMI groups (underweight < 20, normal 20 to 29, overweight 30 to 34, most overweight > 34), but patients with BMI 30 to 34 and > 34 who underwent abdominal or gynecologic procedures had significantly higher wound infection rates (11% each) than normal weight patients (4.7%) or the underweight (0%). After adjusting for age, race, gender, smoking history, comorbid diseases, procedure type, and insurance status, there were nonsignificant trends toward increased resource utilization by the most overweight patients (BMI > 34). These patients stayed 0.8 days longer (P = 0.13) and had total costs that were $843 higher (P = 0.17) than patients of normal weight (BMI 20 to 29). The underweight patients stayed 0.9 days longer (P = 0.23) and had total costs that were $3,150 higher (P = 0.04) than patients of normal weight. Quadratic models to test for a U-shaped relationship found no correlation between BMI and length of stay, but did find that BMI was significantly correlated with total costs (P = 0.04). This relationship persisted when patients who had complications were excluded from the analysis.

CONCLUSIONS

Overall, BMI was not significantly correlated with postoperative complications or length of stay. However, overweight patients who underwent abdominal or gynecologic procedures had higher wound infection rates, and patients with the highest and lowest BMIs had significantly higher adjusted total costs.

An ultrasound study of gestational and postural changes in the deep venous system of the leg in pregnancy

OBJECTIVE

To investigate gestational and postural changes in diameter and blood flow in the proximal deep leg veins during pregnancy.

DESIGN

A longitudinal, prospective observational study.

SETTING

The ultrasound department of a teaching maternity hospital.

POPULATION

Twenty-four healthy women with uncomplicated singleton pregnancies.

METHODS

Real-time and duplex Doppler ultrasound assessments of the vessel diameter, flow velocity and respiratory flow fluctuation in the proximal deep leg veins of women serially measured from the first trimester of pregnancy to six weeks postnatally.

MAIN OUTCOME MEASURES

The effects of increasing gestation and the adoption of the left lateral position on the above parameters.

RESULTS

An increase in vessel diameter and a fall in flow velocity with increasing gestation was observed. However, no change in venous flow variation was observed. Delivery had reverse effects. Flow velocity was slower in the left than right legs, but on adoption of the left lateral position an increase in flow velocity and venous flow variation was observed in both legs during pregnancy.

CONCLUSIONS

These data are consistent with the observed increase in incidence and pattern of deep venous thrombosis in pregnancy and may aid interpretation of duplex Doppler ultrasound examinations for deep venous thrombosis in pregnancy. Postural changes should be part of this evaluation. The gravid uterus may not be the sole cause for postural changes in deep venous flow velocity.

Nursing assessment of clients at risk of deep vein thrombosis (DVT): the Autar DVT scale

Deep vein thrombosis (DVT) poses a threat to hospitalized clients' recovery. It is preventable and the cost of treating this problem is considerably more than that of preventative practices. Accurate DVT risk assessment facilitates the application of the most appropriate venous thromboprophylaxis. Founded on Virchow's triad of risk factors in the genesis of deep vein thrombosis, the Autar DVT scale was developed as a predictive index. The DVT scale is composed of the following seven risk categories: increasing age, build and body mass index (BMI), immobility, special DVT risk, trauma, surgery and high risk disease. The DVT scale was tested on two trauma wards and the study was essentially a data generating exercise. Clinical data were gathered on 21 clients to validate the reliability, sensitivity and specificity of the DVT scale. Pearson moment correlation coefficient (r) and total percentage agreement (T%) measurement yielded a value of r at 0.98 and a T% ranging between 70% and 87% respectively for both reliability studies. Predictive validity of the scale calculated from a threshold score of 16 achieved 100% sensitivity and 81% specificity. The Autar DVT scale has produced some interesting results and holds considerable promise as a predictive index. However, as this was a small study further testing in diverse clinical areas of a large client population is recommended.

Pathophysiology of fibrinolysis

The observed association between abnormal fibrinolysis and a tendency toward bleeding or thrombosis demonstrates the (patho)physiological importance of the fibrinolytic system. Deficient fibrinolysis represents an important haemostatic abnormality associated with thrombosis. A decreased fibrinolytic activity may be due to a defective synthesis and/or release of tissue-type plasminogen activator (t-PA) from the vessel wall, to a deficiency or functional defect in the plasminogen or fibrinogen molecule or more frequently to increased levels of t-PA inhibitor. Alternatively, excessive fibrinolysis due to increased levels of t-PA, to alpha 2-antiplasmin deficiency or to plasminogen activator inhibitor-1 (PAI-1) deficiency, may result in bleeding tendency.

Continuous wave venous Doppler examination for pretreatment diagnosis of varicose and telangiectatic veins

BACKGROUND

Doppler examination of varicosities is an essential part of accurate venous diagnosis prior to treatment. Doppler examination is the most fundamental of diagnostic techniques and must be familiar to all dermatologic surgeons treating the venous system of the leg. Those physicians presently concentrating primarily on telangiectasia will find their ability to judge when treatment will be effective greatly enhanced by Doppler-assisted diagnosis.

OBJECTIVE

To describe the indications, basic principles, and a detailed, logical, rapid protocol for venous continuous wave Doppler examination.

CONCLUSION

Continuous wave Doppler examination is a rapid, precise method to determine sources of reverse physiologic flow (reflux) prior to treatment of varicose and telangiectatic leg veins. Doppler-assisted mapping of physiologic abnormalities of the venous system should be the second step following physical examination.

Diagnosis and treatment of varicose veins: a review

Varicose veins are superficial vessels that are abnormally twisted, lengthened, or dilated and are usually caused by inefficient or defective valves within the vein. They represent a medical condition accompanied by symptoms deserving treatment. Varicose veins are a manifestation of venous disease that may precede later severe complications. Varicosities cause cutaneous disease in addition to complications specific to the venous system. This article reviews the epidemiology, adverse sequelae, anatomy, pathophysiology, evaluation, and treatment of varicose veins.

Red blood cell aggregability in patients with a history of leg vein thrombosis: influence of post-thrombotic treatment

Reversible aggregation of red blood cells (RBC) plays an important role in determining blood flow properties, and it is this aggregation which increases blood viscosity at low shear rates. The structure and sites of venous thrombi, as well as the fact that stasis is a major predisposing factor in venous thrombosis, suggest a strong association between vein thrombosis, slow blood flow and increased blood viscosity. RBC aggregation and disaggregation were measured (SEFAM erythroaggregameter, France) in 54 patients with a history of unexplained leg vein thrombosis. Results were compared to those of controls classified according to age. Increased RBC aggregability was observed in 41% of the patients, and the mean values indicated a significant elevation of RBC aggregability in patients when compared with controls (P < 0.05). Subgroups were compared to study the influence of thrombus recurrence and thrombosis type (deep versus superficial vein thrombosis) on the aggregation parameters. No significant difference was found between these subgroups. The use of compression stockings and veinotropic drugs tended to reduce the abnormalities in RBC aggregability (P < 0.05). An increase in RBC aggregability and in the shear resistance of RBC aggregates, by predisposing to circulatory stasis, is likely to contribute to the evolution and complications of leg vein thrombosis.

Fibrinolysis and thrombosis

In conclusion, venous and arterial thrombi contain significant amounts of fibrin. There is evidence that defective fibrinolytic mechanisms may participate in their genesis or persistence in the body. Some evidence suggests that defective fibrinolysis may presage and predict both arterial and venous thrombi; this is stronger evidence of a causal link with thrombosis. Thrombi protect themselves from lysis by incorporating inhibitors (plasminogen activator inhibitor-1 and alpha 2-antiplasmin) in their structure. Fibrinolytic mechanisms may play a role in the genesis or development of atherosclerotic lesions, in addition to thrombosis. Thrombolytic agents lyse both arterial and venous thrombi when administered shortly after their development. If it proves possible in future to enhance natural fibrinolytic mechanisms and to sustain this enhancement by pharmacological or other means, the interesting prospect of harnessing the fibrinolytic system to prevent thrombus formation, as well as to treat it, will arise.

The use of thromboembolic prophylaxis in oral and maxillofacial surgery

OBJECTIVES

To investigate the use of thromboembolic prophylaxis in oral and maxillofacial surgery.

DESIGN

Postal questionnaire.

SETTING

Oral and maxillofacial surgery departments in the UK.

SUBJECTS

Consultant Oral and Maxillofacial surgeons as listed in the BAOMS Handbook of Hospitals, Oral and Maxillofacial Surgery.

MAIN OUTCOME MEASURES

Factors used in the decision to use thromboembolic prophylaxis and the methods of prophylaxis used.

RESULTS

The response rate was 73%. Previous thromboembolism (85% of respondents), prolonged immobilisation (79%) and length or magnitude of operation (78% and 74%) were the most commonly used risk factors, in the decision to use prophylaxis against DVT. Pre-operative trauma, cardiovascular disease and varicose veins were the risk factors most infrequently used. No forms of prophylaxis were used by 18% of respondents, with the remaining respondents using a variety of methods. The most widely used methods were graduated elastic compression stockings (74%) and low dose subcutaneous heparin (73%).

CONCLUSION

The majority of known risk factors were taken into account when considering the use of prophylaxis against DVT. The methods of thromboembolic prophylaxis used in oral and maxillofacial surgery are considered to provide a satisfactory degree of protection, in moderate and low risk patient groups.

Persistent hypercoagulation associated with heterotopic ossification in patients with spinal cord injury long after injury has occurred

Three patients are presented with traumatic spinal cord injury (SCI) complicated by acute heterotopic ossification (HO), and concurrent deep vein thrombosis 15 months, 18 months and 22 years after SCI, accompanied by persistent hypercoagulation. The diagnosis of HO preceded deep vein thrombosis in all three patients. All were treated with etidronate disodium and therapeutic heparin followed by oral anticoagulation. As these patients were not acutely injured, the questions arose as to what predisposed them to deep vein thrombosis and when was the appropriate time to discontinue anticoagulation. Over a course of 3 years following deep vein thrombosis, these patients were monitored for evidence of hypercoagulation by D-dimer assay, plasma fibrinogen estimation, and rate of whole blood clotting by Sonoclot coagulation analyzer. The activity of acute HO was assessed by three-phase bone scan. A steady state of hypercoagulation, reflected by an increase in all three parameters, ran parallel to the extent of acute HO for the entire observation period. Moreover, hypercoagulation was persistently greater during increased acute HO activity even when the warfarin-induced prothrombin time ratio was 1.2-1.5. In addition, as acute heterotopic ossification activity decreased, the test values returned to near normal during warfarin therapy.(ABSTRACT TRUNCATED AT 250 WORDS)

Postoperative venous thromboembolism and brain tumors: Part I. Clinical profile

Forty-six patients who underwent surgery for brain tumors were studied prospectively with 125I labeled Fibrinogen leg scans to detect postoperative venous thrombosis. The incidence of thrombosis was 72% for meningioma patients, 60% for glioblastoma patients, and 20% for brain metastasis patients. Correlation between the occurrence of venous thrombosis and the various clinical factors thought to be responsible for the high incidence of thrombosis generally failed to show statistical significance. This finding, along with the marked variation in the incidence of venous thrombosis between the different brain tumor groups, strongly suggests that biological factors play a more important role than clinical factors in determining which brain tumor patient will suffer a postoperative thrombotic event.

Statistical methods in diagnosis

Motivations are presented for exploring formal statistical methods for use in medical diagnosis and the advantages and disadvantages are discussed. A brief review is presented of classical linear discriminant analysis, quadratic discriminant analysis, logistic regression, nearest neighbour and kernel methods, recursive partitioning methods, the independence model, regularized discriminant analysis, structured conditional probability distributions, methods for categorical data, and other methods. Criteria on which a choice might be made are presented and methods for assessing diagnostic performance are outlined. Particular applications of screening and chromosome analysis are used as illustrations and available software is described.

The role of fibrinolytic factors in ischaemia

The fibrinolytic system is an enzymatic cascade system whose activation leads to formation of a trypsin-like serine protease, plasmin, which splits insoluble fibrin into soluble degradation products. It is believed that the main function of fibrinolysis is defence against thrombotic occlusion of vessels and dissolution of thrombi once they are formed (thrombolysis). The authors review the recent literature providing evidence that fibrinolysis plays a role in the pathogenesis of vascular occlusions. From earlier studies based on global assay methods it is known that fibrinolysis is depressed in patients with vascular occlusions. Selective assay methods show that almost invariably the fibrinolytic activity of these patients is depressed either following increased levels of fibrinolytic inhibitors (mainly plasminogen activator inhibitor 1 or PAI-1) and/or decreased levels of a plasminogen activator (tissue plasminogen activator or t-PA). In a few cases the molecule of plasminogen shows a conformational abnormality making it less susceptible to conversion to plasmin. In the last decade numerous studies have been published showing a connection between a depressed fibrinolysis and venous thrombosis. In patients with coronary artery occlusion fibrinolysis is depressed mainly because of increased levels of PAI-1. Hypertriglyceridaemia seems to aggravate the defective fibrinolysis. There is also evidence of a decreased fibrinolysis in patients with peripheral ischaemic diseases. A depressed fibrinolysis has also been documented in states predisposing to vascular occlusions. Thus two levels of t-PA/increased levels of PAI-1 have been found in obesity, diabetes mellitus, postoperative states, SLE, malignancies, and miscellaneous diseases often complicated with thrombosis such as Behçet's syndrome. In pregnancy fibrinolysis is depressed because of the presence in blood of PIA-2, an inhibitor of plasminogen activators secreted by the placenta.

Correlations between plasma levels of fibrin(ogen) derivatives as quantified by different assays based on monoclonal antibodies

New plasma assays for fibrin(ogen) degradation products have become available which are based upon monoclonal antibodies and can be performed in plasma. In this study we have evaluated four of such specific enzyme immuno assays i.e.: for the total of degradation products of fibrin and of fibrinogen (TDP), fibrin degradation products (D-dimer and FbDP) and fibrinogen degradation products (FgDP) in patients suspected of having deep venous thrombosis of the leg (DVT) and patients with cirrhosis of the liver. DVT was assessed by impedance plethysmography (IPG). In each of the (sub) groups of patients, a very good correlation (0.90 less than r less than 0.98) was observed between the actually measured TDP values and the calculated sum of the separately measured FbDP and FgDP levels. Only 2% (5 patients) of the cases showed a discrepancy of more than a factor two between the found TDP values and the calculated sum of the measured FbDP and FgDP levels. About 90% of the fibrin degradation products were crosslinked. FbDP levels correlated well with the FgDP levels (0.72 less than r less than 0.94) and D-dimer levels (0.82 less than r less than 0.91) in both patients with DVT and cirrhotics. In those patients also a good correlation (0.67 less than r less than 0.83) was observed between FgDP and D-dimer levels, but not in patients suspected of having DVT but with a normal IPG test result. Secondary fibrinolysis appeared to be accompanied by fibrinogenolysis.

Risk prediction in medicine and surgery: ethical and practical considerations

Risk prediction is a subject of increasing clinical interest, and publications in this area are likely to have an important influence on patient care in the near future. A multiplicity of risk prediction systems, many of them computer-based, will raise a number of ethical and practical questions. These questions need to be addressed by the originators of systems, the editors of journals, practising clinicians, and the lay public.

Tissue-type plasminogen activator. A review of its pharmacology and therapeutic use as a thrombolytic agent

Coronary arterial thrombolysis is becoming an established treatment of acute myocardial infarction. If given early enough, it recanalises occluded coronary arteries, salvages myocardial function and reduces mortality. A reduction of mortality in patients with acute myocardial infarction has now been demonstrated for streptokinase, anisoylated plasminogen streptokinase activator complex (APSAC; anistreplase) and recombinant tissue-type plasminogen activator (rt-PA). From the biochemical point of view, rt-PA has several attractive properties. It is similar to or identical with the physiological plasminogen activator in blood, it does not induce an antibody response, and it is more fibrin-specific than most or all other currently known thrombolytic agents. The rate of recanalisation of occluded coronary arteries with rt-PA is about 60 to 80% in non-comparative and placebo-controlled trials. rt-PA was similar in efficacy to urokinase in the only trial to compare the 2 agents. In 2 comparative trials evaluated by meta-analysis, rt-PA appeared more effective than streptokinase for the early recanalisation of occluded arteries. Both agents were comparable in their effects on left ventricular function in 2 comparative trials, but further study is needed to conclusively evaluate this parameter. Moreover, both agents reduce inhospital mortality, but much larger direct comparative trials are required before scientifically valid statements can be made on the relative clinical efficacy of available thrombolytic agents in terms of their effects on both morbidity and mortality. Thus, rt-PA constitutes a notable contribution of recombinant DNA technology to the treatment of thromboembolic disease, the main cause of death and disability in Western societies.

Clinical disorders of fibrinolysis: a critical review

Much progress has recently been made in understanding the biochemistry and physiology of endogenous fibrinolysis. As a result, a better understanding of the mechanisms and clinical consequences of disordered fibrinolysis has emerged. Increased fibrinolytic activity is an uncommon but important cause of hemorrhagic disease. Congenital disorders of fibrinolysis which cause bleeding include increased plasma plasminogen activator activity and deficiency of alpha-2 antiplasmin. Acquired disorders associated with increased fibrinolytic activity and bleeding include liver cirrhosis, amyloidosis, acute promyelocytic leukemia, some solid tumors, and certain snake envenomation syndromes. Increased fibrinolysis is important to recognize because epsilon-aminocaproic acid (EACA) may be required to prevent or control bleeding. Diminished fibrinolytic activity has been associated with a variety of thrombotic disorders, but a direct cause-and-effect relationship has yet to be established. Congenital abnormalities of fibrinolysis associated with thrombosis include plasminogen deficiency, decreased endothelial generation of plasminogen activator activity, and certain abnormal fibrinogens. Thrombosis in these disorders is effectively managed with warfarin. Diminished fibrinolysis has also been reported in "idiopathic" venous thrombosis, oral contraceptive-induced and post-operative venous thrombosis, coronary artery disease, cerebrovascular disease, systemic lupus erythematosus, and thrombotic thrombocytopenic purpura, but the significance of abnormal fibrinolysis in these disorders is uncertain. Large, prospective studies of fibrinolytic variables as risk factors for vascular and thrombotic disease are needed to determine whether pharmacologic augmentation of impaired fibrinolysis could be useful in the prevention or treatment of these disorders.

Prostanoid production in varicose veins: evidence for decreased prostacyclin with increased thromboxane A2 and prostaglandin E2 formation

In this study, formation of arachidonic acid-derived prostanoids was investigated in saphenous veins of varicosed and nonvaricosed patients, all undergoing saphenectomy respectively for varicosis or in preparation for coronary bypass operation. Venous production of prostacyclin (PGI2), thromboxane A2 (TXA2) and prostaglandin E2 (PGE2) was assessed by bioassay and/or radioimmunologic assays as appropriate. Fragments of saphenous veins from varicosed patients produced significantly less PGI2 and more TXA2 and PGE2 than those from the control patients. Addition of arachidonic acid to incubation mixtures dose dependently increased release of these prostanoids, but the levels of PGI2 produced were consistently lower in veins from varicosed patients. No differences were found in varicosed patients between various segments of the same vein, no matter whether macroscopically affected or unaffected. These results demonstrate that the cyclooxygenase pathway in the venous wall of subjects with varicosis is shifted toward lesser formation of PGI2 and higher production of proaggregatory and proinflammatory prostanoids such as PGE2 and TXA2. These biochemical changes may be relevant to inflammation and thrombogenesis in varicosis.

The prevalence and pattern of pulmonary thromboembolism in the Chinese in Hong Kong

The prevalence and clinical pattern of pulmonary thromboembolism was studied by a multifaceted approach. This documented the occurrence of pulmonary thromboembolism among the Chinese and confirmed an increasing incidence in Hong Kong, although comparatively it was still much lower (about one-tenth) than that found in western communities. Their clinical pattern, regarding presentation, risk factors, clinical features and response to thrombolytic therapy, conformed well with those reported in the west, but perhaps appeared in a milder form. The strong association of pulmonary thromboembolism with varicose veins and immobilisation would appeal for recommending routine heparinisation in Chinese patients having these combinations. Our findings will stimulate more interest in the comparative study of the haematological profile and the ethnic particulars of the Chinese.

Effect of optimization of hemodynamics on fibrinolytic activity and antithrombotic efficacy of external pneumatic calf compression

External pneumatic calf compression is effective but imperfect for antithrombotic prophylaxis in surgical patients. In preliminary studies, sequential filling of multisegmented leggings with graded pressure decreasing from ankle to knee increased venous flow velocity and wall shear stress, decreased residual venous volume, and enhanced postoperative fibrinolysis more than uniform compression. To determine if improved hemodynamics also increased antithrombotic activity, we performed a prospective randomized trial in neurosurgical patients comparing sequential application of graded pressure with uniform pressure applied to either a segmented bladder or to a single bladder. Deep vein thrombosis was diagnosed by leg scanning and impedance plethysmography and confirmed by phlebography. Venous thrombosis developed in 3 of 45 patients with graded-sequential filling, 6 of 50 with uniform compression-multiple compartments, and 3 of 41 with uniform pressure single bladder (differences not significant). These results suggest either that uniform compression offers all that can be expected of external pneumatic calf compression in prevention of venous thrombosis, or that even if a study with greater statistical power showed graded-sequential filling to be superior, the benefit/cost ratio of the more complex latter system is not likely to be large.

Internal carotid artery occlusion in association with Crohn's disease

A 38-year-old white male with small bowel Crohn's disease presented with an acute right-sided cerebrovascular accident. He died 36 hr later and postmortem revealed thrombosis over the whole length of an otherwise completely normal left internal carotid artery. Histological examination of the artery revealed no abnormalities and in particular no evidence of arteritis. This brings the total number of such cases reported to three, but this is the first with postmortem data. The occurrence of such an event in a young person with normal carotid arteries and no other risk factors would suggest an association with his Crohn's disease, possibly as a result of a coagulation abnormality.

Rheology of the absolute polycythaemias

The absolute polycythaemias include all patients who have a raised red cell mass. They may be divided by clinical and laboratory investigation into: primary proliferative polycythaemia (polycythaemia rubra vera), secondary polycythaemias, and idiopathic erythrocytosis. In vitro, the PCV is the single most important determinant of whole blood viscosity with the most marked effects at low shear rates. Yield stress is also dominantly influenced by PCV. Thus in the absolute polycythaemias, from whatever cause, whole blood viscosity and yield stress are high. However, flow conditions in vivo are much more complex than those usually used in in-vitro measurements. Under normal physiological conditions, whole blood viscosity probably does not determine flow in vivo. The observed in-vitro changes are only of relevance in vivo when local or general abnormalities of flow occur. In primary proliferative polycythaemia (PPP) and idiopathic erythrocytosis, presentation with ischaemia or thrombosis (either arterial or venous) is common, and the cerebral circulation is at particular risk. The incidence of vascular occlusion is positively correlated with the PCV. There is an inverse correlation between PCV and cerebral blood flow (CBF), with untreated patients having low CBF values. This is probably a 'physiological' change related to the increased oxygen carrying capacity at high PCV values. However, in many patients, cerebral oxygen carriage actually increases on reduction of the PCV to normal. This explains the improvement in cerebral ischaemic symptoms and mental performance which may be observed following treatment. Platelet contact and adhesion to the vessel wall are increased at high PCV values and, combined with the lower blood flow in both the arteries and veins, tend to favour thrombus formation. Ischaemia causes vessel dilatation but when this is maximal the high whole-blood viscosity demonstrated in vitro is a major determinant of flow. Hence in man and experimental animals, as demonstrated in the brain, the area of ischaemia or non-perfusion following arterial occlusion is greatest at high PCV values. Patients with polycythaemia due to hypoxic lung disease have a poor prognosis. The hypoxic pulmonary vasoconstriction combined with the high blood viscosity causes an increase in pulmonary vessel resistance. PCV reduction of 0.50-0.52 leads to an improvement in work performance and mental alertness, and reduction in pulmonary vascular resistance.(ABSTRACT TRUNCATED AT 400 WORDS)

A prospective study of dextran-induced anaphylactoid reactions in 5745 patients

A prospective study of dextran-induced anaphylactoid reactions (DIAR) in 5745 gynaecological and obstetric patients who received dextran 70 solution intravenously while undergoing major surgery revealed 8 patients who had Grade I or II reactions and 7 patients who had Grade III or IV reactions. The incidence of severe reactions was 1:821 patients treated. The overall incidence of reactions per patient treated was 1:383. One neonatal death followed a dextran-induced cardiac arrest in a woman about to undergo caesarean section. The risks of dextran 70 treatment exceeded the risks of thromboembolism in these patients.

Indicators of depressed fibrinolytic activity in pre-operative prediction of deep venous thrombosis

Euglobulin lysis time (ELT), tissue plasminogen activator (tPA), and the fast-acting inhibitor of tPA, were measured pre-operatively in 128 patients who underwent elective major abdominal surgery. Deep venous thrombosis (DVT) was detected by 125I-labelled fibrinogen scan in 37 patients (29 per cent) after operation. Pre-operatively, there was diminished euglobulin lysis activity (332 +/- 197 versus 255 +/- 156 min, mean +/- s.d.; P less than 0.025), and tissue plasminogen activator activity (4.2 +/- 9.9 versus 7.7 +/- 14.3 milliunits/ml, mean +/- s.d.; P = 0.094) in patients who subsequently developed postoperative DVT compared with those who did not. There was no significant difference between the two groups in the level of inhibition of tissue plasminogen activator (160.6 +/- 75.4 per cent versus 152.5 +/- 77.5 per cent, mean +/- s.d.; n = 47). Stepwise logistic discriminant analysis of the data obtained preoperatively showed that tissue plasminogen activator, a more specific measure of fibrinolytic activity, was a weaker predictor of DVT than euglobulin lysis time. The results confirm other observations which indicate that lowered fibrinolytic activity is a risk factor for postoperative DVT. In addition, they suggest that this is not due entirely to low levels of activity of tissue plasminogen activator in plasma.

Epidemiology and pathogenesis of venous thrombosis

Venous thrombi are intravascular deposits composed predominantly of fibrin and red blood cells with a variable platelet and leukocyte component. They frequently arise in large venous sinuses in the calf, in valve cusp pockets either in the deep veins of the calf or thigh or in venous segments that have been exposed to direct trauma. Venous thrombosis can be produced experimentally by a combination of stasis and systemic hypercoagulability or by stasis and endothelial damage. Thrombosis is augmented if the fibrinolytic mechanism is inhibited or defective. A number of clinical conditions and laboratory abnormalities are associated with and predispose to venous thrombosis and, in many of these, it is possible to identify one or more of the thrombogenic factors discussed. Venous thromboembolism (venous thrombosis and pulmonary embolism) is a serious and potentially fatal disorder that usually complicates the course of sick hospitalized patients, but occasionally affects ambulant and otherwise healthy individuals. Screening studies with iodine-125 fibrinogen leg scanning, impedance plethysmography and perfusion lung scanning have shown that the majority of venous thrombi and pulmonary emboli that occur in hospitalized patients are small and asymptomatic, and it is likely that most are clinically insignificant. In bedridden patients, most thrombi commence in the calf and are asymptomatic. When a calf vein thrombus extends into the proximal venous segment, the risk of clinically significant pulmonary embolism increases. Less is known about the incidence and clinical significance in a nonhospital population; although asymptomatic disease occurs, its frequency is unknown. In contrast to the patients with asymptomatic venous thrombosis, symptomatic patients with venous thrombosis usually have large occulsive thrombi localized in their proximal veins.

Pulmonary embolism

Contemporary concepts in the diagnosis, treatment and natural history of pulmonary embolism are reviewed, and a practical rationale for investigation and therapy is outlined.

Plasma levels of fibrin fragments in men with myocardial infarction

Degradation products of cross-linked fibrin were measured in the plasma of 30 men who had been discharged from hospital following a myocardial infarct and in 30 age-matched controls selected from a general practice list. Levels were significantly higher in cases than controls, and the direction of the differences was highly consistent in case control pairs. These findings may represent increased thrombogenesis, increased fibrinolysis, or both, in persons who have suffered myocardial infarction.

Venous thrombosis: an overview

Venous thromboembolic disease contributes to morbidity and mortality in certain groups of hospitalized patients, particularly those who have undergone surgery. Although principles of treatment have changed relatively little during the past 20 years, significant advances have been made in the diagnosis of deep vein thrombosis (DVT). Venography, once the only reliable diagnostic technique, has been largely replaced by noninvasive tests: impedance plethysmography, venous Doppler, 125I-radiofibrinogen-uptake test, and phleborheography. Virchow's triad of stasis, vessel injury, and hypercoagulability remains a valid explanation of the pathogenesis of thrombus formation, but laboratory and clinical data have refined our knowledge of how these factors interact to result in clinically significant disease. Knowledge of the natural history of venous thrombosis, plus heightened awareness of the long-term morbidity and expense associated with the postphlebitic syndrome, have led to increased interest in preventing DVT. Clinically and economically, venous thrombosis is best managed by prevention.

Pre-operative identification of patients at high risk of deep venous thrombosis after elective major abdominal surgery

Eighteen items of clinical and laboratory information were measured on the day before operation in 85 patients who underwent elective major abdominal surgery. Postoperatively, deep venous thrombosis (DVT) was detected by 125I-fibrinogen scan in 23 patients. Stepwise logistic discriminant analysis was used to identify factors which predicted DVT. Seven such factors were identified, which were then used to construct a predictive index. In descending order of predictive power, they were: age, euglobulin lysis time (ELT), previous abdominal surgery, varicose veins, antithrombin III concentration, cigarette smoking, and platelet count. Pre-operatively, the predictive index correctly identified 91% of the patients in whom DVT developed, and wrongly allocated to the high-risk group 19% of those in whom it did not. A shortened version of the predictive index based only on age and ELT (I = -11.5 + 0.133 age + 0.006 ELT) was 91% sensitive and 63% specific in the prediction of DVT. In a prospective study of 43 patients, this shortened predictive index correctly identified pre-operatively 93% of patients in whom DVT developed, and wrongly allocated to the high-risk group only 17% of those in whom it did not.

Per- and postoperative changes in coagulation and fibrinolytic variables during abdominal hysterectomy under epidural or general anaesthesia

Blood coagulation and fibrinolysis were studied in 20 premenopausal women undergoing abdominal hysterectomy under general anaesthesia (GA) or high epidural analgesia (EDA). As expected, the adrenocortical stress response was suppressed in the EDA group. The Factor VIII complex (F VIII:C, F VIII R:Ag = von Willebrand factor), known to be related to adrenocortical activity and/or vessel wall reactivity, was found to increase less in the EDA group. With regard to all the other variables analysed there were no significant differences between the groups. With both anaesthetic procedures activation of coagulation could be demonstrated by a decrease in prekallikrein, F X and antithrombin as well as by an increase in fibrinopeptide A levels. A decrease in plasminogen and alpha 2-antiplasmin suggested activation of the fibrinolytic system and a decrease in prekallikrein and kallikrein inhibition activity (C-1-esterase inhibitor) an activation of the kallikrein system. In this study only the differences in F VIII complex could explain the previously reported higher thromboembolic frequency after GA as compared to EDA.

The fibrinolytic system in man

The fibrinolytic system comprises a proenzyme, plasminogen, which can be activated to the active enzyme plasmin, that will degrade fibrin by different types of plasminogen activators. Inhibition of fibrinolysis may occur at the level of plasmin or at the level of the activators. Fibrinolysis in human blood seems to be regulated by specific molecular interactions between these components. In plasma, normally no systemic plasminogen activation occurs. When fibrin is formed, small amounts of plasminogen activator and plasminogen adsorb to the fibrin, and plasmin is generated in situ. The formed plasmin, which remains transiently complexed to fibrin, is only slowly inactivated by alpha 2-antiplasmin, while plasmin, which is released from digested fibrin, is rapidly and irreversibly neutralized. The fibrinolytic process, thus, seems to be triggered by and confined to fibrin. Thrombus formation may occur as the result of insufficient activation of the fibrinolytic system and (or) the presence of excess inhibitors, while excessive activation and/or deficiency of inhibitors might cause excessive plasmin formation and a bleeding tendency. Evidence obtained in animal models suggests that tissue-type plasminogen activator, obtained by recombinant DNA technology, may constitute a specific clot-selective thrombolytic agent with higher specific activity and fewer side effects than those currently in use.

Clinical efficacy of low molecular weight heparin in postoperative thrombosis prophylaxis

In a randomized controlled clinical trial, the efficacy and safety of two low molecular weight heparin ( LMWH ) fractions in the prophylaxis of deep vein thrombosis (DVT) were assessed. One hundred twenty-six patients undergoing major abdominal surgery received alternatively 2,500 APTT units b.i.d. of two LMWH fractions or 5,000 APTT units b.i.d. of an unfractionated sodium mucosal heparin ( UFH ). LMWH 2 differed from LMWH 1 by presenting a lower mean molecular weight and a higher anti-Xa/APTT ratio in vitro. Patients were randomly allocated to the three groups, and the development of DVT was studied with the 125I-fibrinogen uptake test ( RFUT ). The study was interrupted and the code broken prematurely because of otherwise unexplainable bleeding events. While no thrombosis and no severe bleeding were detected in the UFH group, three (7%) RFUT -positive DVT and two (5%) hemorrhagic complications occurred in the LMWH 1 group. No thrombosis and nine (22%) cases of severe bleeding were observed in the LMWH 2 group. Thus, the latter group differed significantly from the control group with regard to subjective and objective criteria for postoperative bleeding. Although these results do not allow general conclusions as to the value of LMWH fractions in the prevention of DVT, they indicate that these preparations just as ordinary heparin have a limited therapeutic range.

The fibrinolytic system in man

The existence of a system in the human body capable of inducing the dissolution of endogenous pathologically formed thrombi was appreciated in ancient times. Considered in detail in this article are the data that have elucidated the physiologic regulation of which plasmin formation is dependent on, the plasma concentration of plasminogen, availability of activators of plasminogen in the plasma and surrounding tissue environment, the concentration of naturally present inhibitors, and the existence of fibrin in the circulation. Important in this rapidly progressive scientific discipline is consideration of the factors which control the synthesis of the components of this proteolytic enzyme system. Recently abundant information has indicated that this plasminogen-plasmin proteolytic enzyme system can be utilized therapeutically. Knowledge of the mechanisms of this system has permitted identification of agents that can be exogenously administered to releave thrombotic obstruction to blood flow in the venous (pulmonary emboli, deep vein thrombosis) and arterial (peripheral and central vessels) circulatory systems. Particularly important is the demonstration that thrombolytic agents can directly attack and alleviate the immediate cause of acute myocardial infarction. As a result of the innovations in the present decade, it is evident that the plasminogen system can be advantageously employed to reverse the pathologic effects of all thrombotic diseases.

Venous thrombosis in diabetes mellitus

The incidence over 7 days of isotopically-detected calf and popliteal vein thrombosis was determined in a group of 60 diabetic patients admitted to hospital with myocardial infarction, heart failure or stroke, or for abdominal surgery. The result was compared with the incidence in 60 control subjects matched for age, sex and presenting diagnosis. Twenty-one diabetic patients developed positive 125I-fibrinogen scans, compared with 19 control subjects; this difference is not significant. We conclude that diabetes is not associated with an enhanced risk of thrombosis in veins. It is therefore possible that the arterial and capillary abnormalities found in diabetes may arise from mechanisms other than a generalised thrombotic tendency.

Incidence of post-operative deep vein thrombosis in gynaecological oncology

Using 125I-fibrinogen scanning the incidence of post-operative DVT amongst patients with gynaecological malignancy was shown to be 37.9% which is substantially higher than the 10% to 15% expected in a general gynaecological population. Twenty per cent of the total group studied had isotopic evidence of bilateral venous thrombosis post-operatively. The inaccuracy of clinical diagnosis was demonstrated, and also the need to investigate both limbs if thrombosis was suspected. The incidence of post-operative DVT was found to be significantly lower in smokers (11.5%) compared with non-smokers (68.4%) (p less than 0.00025).