cJ2-Review

Graduated compression stockings in the prevention 01 venousthromboembolism

O. Agu, G. Hamilton and D. Baker

University Departrnent of Surgery, Royal Free Hospital, Pond Street, Hampstead, London NW3 2QP, UKCorrespondence fa: Mr O. Agu

Background: Surveys still show a wide variation in routine use of deep vein thrombosis (DVI)prophylaxis despite its established place in current patient management. This article reviews themechanism of action, efficacy and complications of stockings inpreventing Dvr.Methods: Relevant publications indexed in Medline (1966-1998) and the Cochrane database wereidentified. Appropriate articles identified from the reference lists of the above searches were alsoselected and reviewed.Results and conclusion: Graduated compression stockings reduce the overall cross-sectional area ofthe limb, increase the linear velocity of venous flow, reduce venous wall distension and improve valvularfunction. Fifteen randomized controUed trials of graduated compression stockings alone were reviewed.Stockings reduced the relative risk of Dvr by 64 per cent in general surgical patients and 57 per centfoUowing total hip replacement. The effect of stockings was enhanced by combination withpharmacological agents such as heparinj the combination is recommended in patients at moderate orhigh risk of Dvr. Knee-Iength stockings are as effective and should replace above-knee stockings.Complications are cace and avoidable.

Paper accepted 18 April1999 BritishJoumal ofSurgery 1999, 86, 992-1004

Prevention of Jeep vein thrombosis (DVT) in hospitalizedpatients has received considerable attention because of therisk of potentially fatal pulmonary thromboembolism andthe long-term morbidity associated with chronic venousvalvular insufficiency. The result has been a continuingdrop in the incidence and complications of DVTl-5.Without prophylaxis, the risk of DVT ranges from 25 to30 per cent in general surgical patients to 70 per centfollowing some orthopaedic procedures6-9. Prophylaxis,often consisting of a combination of pharmacological andmechanical agents, reduces the risk of DVT by 60-80 percent in general surgical and 50-64 per centin orthopaedic

patientslO-13.Despite the established place of prophylaxis in current

patientmanagement, more episodes ofvenous thromboem-bolism are reported in clinical practice than would beexpected. Surveys show a wide variation in routine use ofDVT prophylaxisl4-17. This variation mar represent a lagbetween intended and actual implemented prophylaxis.There appears to be a shortfall in awareness of themechanism of action and efficacy, especially of mechanical

agents. Violation of established protocols, which marinvolve up to 30 per cent of patients, has also beenreported 18.

Graduated compression stockings are the most widelyused mechanical antithrombotic agents. Theyare of provenefficacy in general surgical patients 11. However, the case forstockings mar not be as convincing in some other surgicalspecialties, especially orthopaedics, where patients are atmuch greater riskl9-21. The value of stockings for obstetric,long-stay general medical and geriatric patients is alsouncleár. Evidence supporting current stocking pressureprofiles, which have been in use for ayer 25 years, needsreappraisal especially in patient groups in which stockingsare not proving as effective. Evidence comparing theefficacy of thigh- versus knee-Iength stockings needsclarification. Although stockingrs are generally regarded assafe, complications occasionaUy occur.

This review considers the current evidence on themechanism of accion, design, efficacy and complicationsassociated with graduated compression stockings in theprevention of venous thromboembolism.

992 British J ouma! oí Surgery 1999, 86, 992-1004 @ 1999 Blackwell Science Ltd

O. Agu, G. Hamilton and D. Baker .Glraduated compression stockings in the prevention of venous thromboembolism 993

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Fig.1 Possible mecharusm of action of graduated compression stocking in preventing deep vein thrombosis

Methods

Relevant publications indexed in Medline (1966-1998)were identified using fue medical subject headings 'stock-ings', 'clothing', 'bandages', 'thrombophlebitis', 'venousthrombosis', 'postoperative complications' and 'throm-bosis/prevention'. The Cochrane database was alsosearched and relevant studies identified. Further articlesidentified from fue reference lists of fue above searches werealso selected and reviewed. Odds ratios of studies reviewedwere combined using fue Mantel-Haenszel i procedure.Number needed to treat was calculated based on a 25 percent risk ofDVT in untreatedgeneral surgical patients and a40 per cent risk following total hip replacement.

Mechanism

The mechanism of action of compression stockings inpreventing venous thrombosis remains unclear and isprobably multifactorial (Fig. 1). Compression stockingsachieve their effect by affecting the three classical aetiolo-gical factors described by Virchow (1856), namely stasis,endothelial damage and hypercoagulability. A decrease inthe luminal diameter of the vein appears to play the key Tole;

Effect oí externa! compression on venous function

External compression reduces the overall cross-sectionalarea of the lower limb and increases the linear velocity ofblood flow within the veins22-27. An external pressure of15 mmHg results in a 20 per cent reduction in the venouscross-sectional area and a si~ficant increase in thevelocityof flow in both superficial and deep venous systems28.Increased velocity of tlow reduces venous stasis anddecreases the risk of thrombus formation by reducingvenous wall distension, local contact time and the concen-tration of coagulation reactants. Compression stockingsalso improve evacuation of incompetent and incompletelyemptied valvular cusps29. Stasis within these cusps isassociated with the initiation of venous thrombosis3o.Stockings have also been shown to enhance venous functionby improving coaptation of valvular cusps, again reducingretlux-related stasis and the risk of thrombosis, especially inpatients with valvular insufficiency31.

Postoperative DVT is associated with intraoperativesystemic venodilatation affecting both lower and upperlimbs32.33. Passive venodilatation stretches the endotheliumbeyond the support of the tUnica media. The resultingintimal tears have been demonstrated on electron micro-

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994 Graduated compression stockings in the prevention of venous thromboembolism .O. Agu, G. Harnilton and D. Baker

Tubigrip (Seton Health Group, Oldham, UK) is probablyinappropriate, as the latter is unlikely to deliver uniformcompression with increasing proximallower limb circum-ference. Instead, a reverse compression gradient or tourni-quet effect is to be expected.

The design of the majority of stockings in current use isbased on a pressure profile of 18, 14,8,10, 8mmHg fromankle to thigh as recommended by Sigel et al.42 andLawrence and Kakkar43, and confirmed by clinical trials incomparison to untreated controls44.45. Although 30 mmHgat the ankle had a greater effect on velocity of flow than18 mmHg, the latter was deemed safer, being less likely tocompromise subcutaneous oxygenation 43.46. Sparrowetal!7 showed that the efficiency of stockings correlatedclosely with changes in calf compression if ank1e compres-sion was held constant; higher calf compression was moreeffective. Varying ankle compression and ankle-calf gra-dient were not as important. A profile of 16.8, 14.5 and64 mmHg at the ankle, calf and thigh respectively provedmost effective. Although the 18 to 8 mmHg pressure profileis effective, it mar not necessarily represent the best profileor be ideal in all clinical situations in which stockings areneeded for Dvr prophylaxis. Further studies are needed todetermine the optimal profile in different clinical situations.These studies would require a large number of subjects, awide variety of pressure profiles and postures, and should bebased on the effect of stockings on both venodilatation andvelocity of venous outflow.

scopy in canine models. Intimal tears predispose to DVT byexposing thrombogenic subendothelial collagen, in thepresence of venous stasis, to activated platelets, clottingfactors and other thrombogenic products oftissue injuo/4.Venodilatation in excess of 20 per cent of resting diameterhas been shown to be associated with an increased risk ofDVT32. Coleridge Smith et al.35 demonstrated a median 48(interquartile range 26-53) per cent reduction in thediameter of gastrocnemius veins during operation in

patients wearing graduated compression stockings. Addi-tionally, in the same study, in contrast to the control group,no venous distension occurred during operation in patients

wearing stockings.Elastic compression mar achieve some of its effects by

altering the balance of coagulation reactants in patients atrisk of thrombosis. Elastic compression in the supinereverse Trendelenburg position has been shown to increasesystemic plasma levels of tissue factor pathway inhibitor(TFPI)36. TFPI is a recently described factor Xa-dependentinhibitor of the tissue factor (extrinsic) coagulation path-way. TFPI is endothelium derived, and increases with shearstress in the upright posture, after extensive exercise andfollowing administration of both unfractionated heparinand low molecular weight heparins (LMWHS)37-41.Increased TFPI in the upright tilt mar be an endothelialresponse to venous stasis and luminal distension to preventlocal thrombosis. Enhancing this TFPI effect by elasticcompression mar represent another mechanism oflocal andsystemic venous thromboprophylaxis.

Efficacy

Results of inicial trials on the value of compression forvenous thromboprophylaxis were equivocal. Wilkins et al.48reported, in a post-mortem study, one non-fatal pulmonaryembolism (PE) in 100 deaths in 2 346 patients with stockingscompared with six PEs (two fatal) in 89 deaths in 2395untreated non-randomized controls. Makin 49 reported a

reduced incidence of clinica1ly diagnosed Dvr withTubigrip. Rosengarten et al.5o and Browse et al. 51 were

unable to demonstrate any difference between stockingsand control using the fibrinogen uptake test. Thesediscrepancies probably resulted from the use of Tubigripfor compression, which exerts non-uniform and potentiallyreverse gradient compression. In addition, the studies usedclinical diagnosis, which is undoubtedly unreliable inpredicting the incidence of Dvr and FE. Subsequentstudies using better stocking design and more reliablediagnostic tools provide a clearer picture.

Design of compression stockings

Compression stockings mar be designed to apply graduatedor uniform compression. Graduated compression refers tothe application of varying degrees of constant compressionto differentsegments of the leg, with pressure being greatestat the ankle and graduallydecreasing proximally. Uniformcompression aims to deliver a similar degree of pressure tothe whole lego Graduated compression has been thefavoured option since Sigel et al.42 demonstrated small butconsistent increases in velocity of flow in the cornmonfemoral vein compared with that obtained with uniformcompression. This conclusion was based on the effect of auniform compression of 11 mmHg in four subjects in asupine position at 150 foot-down tilt. The hydrostaticgradient introduced by this position (about 14 mmHg) isscarcely representative of the patient lying in hospital and islarge enough to affect the validity of their results. \Vhilegraduated compression is of proven efficacy in preventingDVI', evidence to support its superiority over uniformcompression appears inconclusive and needs revalidation.Discrediting uniform compression on the basis of trials of

General surgery

The majority of studies of stockings for the prevention ofvenous thrombosis have been on general surgical patients.

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O. Agu, G. Harnilton and D. Baker .Graduated compression stockings in the prevention of venous thromboembolism 995

Table 1 Results of randomized controlled trials of graduated compression stockings in preventing deep vein thrombosis

Values in parentheses are 'percentages or t95 per cent confidence intervals. j:Based on PEER (patient expected event rate) =0.25. FUT, fibrinogen 1251

uptake test; venography, contrast venography

patients following symptomatic proximal vein thrombosisreported mild to moderate post-thrombotic syndrome in 19patients (20 per cent) wearing stockings compared with 46controls (47 per cent) (P< 0.001). In addition, only 11patients (11 per cent) wearing stockings developed aseverepost-thrombotic syndrome compared with 23 control

patients (23 per cent) (P< 0.001)64.

Orthopaedic surgery

The majority of studies in orthopaedics have includedpatients undergoing elective total hip replacement. Elderlypatients with a fractured hip mar constitute a more idealstudy population as they are often dehydrated, immobileand have a much greater risk of venous thromboembo-lism13. Orthopaedicsurgeons in the UK are more likely touse routine prophylaxis in patients undergoing elective hipreplacement than surgery for hip fracture despite a fivefoldincreased risk of fatal PE in the latter group6S. Theincidence ofDvr exceeds 50 per cent in untreated controls(Toble 2); however, thromboprophylaxis appears to be lesseffective in orthopaedic than in other forms of surgeryl0,70-73. Although the majority of orthopaedic surgeons usepharmacological prophylaxis, the risk ofbleeding leading towound haematoma, infection and implant failure isperceived as unacceptable by a minority74. Physical agentsare safer and more acceptable in this regard7S,76. Examiningthe results of the randomized trials shows a 57 per centoverall relative risk reduction in incidence of Dvrfollowing total hip replacement in patients who used

Table 1 shows the results of randomized controlled trialscomparing the incidence of Ovf in general surgicalpatients. The overall incidence of Ovf was 51 (7 per cent)of 748 in the treatment group compared with 144 (19 percent) of757 in the control group. The summary odds ratiowas 0.31, which translated to a relative risk reduction of 64(95 per cent confidence intervaI53-73) per cent in patients

wearing stockings. Treating eight general surgical patientswith graduated compression stockings prevented theoccurrence of one Ovf. Wells etal.61 reported a 68 percent relative risk reduction of Ovf in general surgicalpatients using stockings. In practice, stockings are oftencombined with pharmacological agents, especially low-clase heparin or LMWH. This combination leads toimproved results (see later).

Oirect evidence of the value of graduated compressionstockings in preventing fatal PE is inconclusive. Numberslimit most trials, as a large sample size would be required toshow a significant reduction because of the low incidence ofFE, particularly as the widespread use of heparin hassubstantially reduced the risk ofDVf and FE. The effect ofstockings in preventing the long-term post-thromboticsequelae ofDVf is easier to demonstrate. Some 60 per centof patients treated for Ovf will have residual venousvalvular insufficiency62 with symptoms ranging from legswelling and discomfort to venous ulcers. Graduatedcompression stockings have been shown to prevent primaryand recurrent Ovf, and decrease the risk and severity of thepost-thrombotic syndrome61.63.64. A recent randomizedclinical trial of the effect of compression stockings in 194

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fficidenceo(dee

p veinJhrombosis'

No. neededtotreatt

R"' fe,erenceYear D1agnos!íc)es! ..,$tocklngs Control

~ ..Oddsratiot

Risk

reductíonit~)

2"' 1 '47' (49)"Of 1.'2601!0137)1201.98(12)3701~Ó3(36}8" '0180 "(,lié)" -1V",110190 (12)-..té, 7201.54';4)'",6óf54{t1.)16f78(9~

1'2o t.8" (1'4), " J1440t757(1~)

~ 0,,3t{0-i2.;CQ-82)

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..0.00(0-0~,55.>0-17(0.0~-86 )-"'0-49(°-02-7.22)

1-]9{0.~2~".39)0,13 ( 0...Oi.;CQ. 1 1)'". ,

0.14 (0'02.;CQ.70}

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51)

General! abdQm.in~l$ yrgs ry

5~ji¡c:I,":,Allan e/aL c cBsrgqvl$lcandLiiidbl~

.,c ss'Wille-jorgen$sn el ~r.Msllbrin g' and Palms~, ,-'c

1976 FUT 110.148(23);

19p F~: 80~70(11)1980 FUT 40!98 (4)

.1983 FUT/venography150.l97 (15)Á' 'o;! =~4 FUT O of80 (O)

1985 FUT/venography 20.186(2)..1986 FUT 10f54i ( 2

),

7of 54 (t;?)1987 FUT/venography 10t78(1L1991 FUT/venography2of 83(2}.

-" "

510\748(7)Total

1984 FUT OOf1~(~)"

40f92 (4) 0."00(0.00-'1 ."32)

1989 FUr/venography-c "7of 80(9)

""16"of81"(2~! O.3~l9;1~1"O9}

996 Graduated compression stockings in the prevention of venous thromboembolism .O. Agu, G. Hamilton and D. Baker

Table 2 Randomized controlled trials of graduated compression stockings for deep vein thrombosis prophylaxis following total hip

replacement

Values in parentheses are 'percentages or t95 per cent confidence intervals. :j:Based on PEER (patient expected event rate) = 04. Venography, contrast

venography; Doppler, Doppler ultrasonography

sion stockings in patients with a fractured hip is still underevaluation.

Gynaecology, obstetrics and urology

The overall riskofDVT ranges between 4 and 45 percentingynaecological and 8-80 per cent in urological patients9l,the highest risk being after operations for malignancy92.The risk in pregnancy is five times higher than that in non-pregnant age-matched patients. A randomized controlledtria! of the value of stockings in 196 patients undergoingmajar gynaecological surgery showed a significant reduc-tion in venous thrombosis (zero in treated versus 4 per centin controls; P

O. Agu, G. Hamilton and D. Baker .Graduated compression stockings in the prevention 01 venous thromboembolism 997

eight control legs compared with none in legs withstockingslO7. With the exception of this trial and data onstroke patients, no other studies on the efficacy of graduatedcompression stockings in general medical patients werefound. The available data suggest that there is a place forstockings in DVT prophylaxis in medical patients. This isparticularly importantwhen hospitalization is prolonged, inpatients aged ayer 40 years and in the presence of medicalconditions known to predispose to DVT.

Recurrent deep vein thrombosis

Previous DVT is a majar predisposing factor to DVTreCurrencelO8. Belcaro et 01.63 studied the efficacy ofgraduated compression stockings in preventing rerurrentDVT in 224 patients following an episode ofDVT. Threeyears later the reCurrence rate was 46 per cent in untteatedconttols compared with 9, 5 and 2 per cent in patients usingstockings, ibuprofen or stockings and ibuprofen respec-

tively.

pneumatic compression is effective in these patients60.98.99,although its use mar be limited by patient compliance. Theease of application and management of stockings mar be anadvantage. In a recent randomized controlIed trial compar-ing stockings alone versus stockings combined with inter-mittent pneumatic compression, the DVT rate was 9 percent for stockings onIy and 9 per cent for stockings andpneumatic compression, compared with 20 per cent inuntreated controls6O. Stockings alone appeared sufficient.Another multicentre trial showed that LMWH reduced therateofDVTfrom21 percentwithstockingsalone, to 14percent with stockings and nadroparin (relative risk reduction34 per cent; P= 0.018Yoo.

Stockings mar suffice as the sole agent, especialIy wherepharmacological agents are contraindicated. Graduatedcompression stockings combined with LMWH or low-doseheparin should provide adequate DVT prophylaxis inneurological and neurosurgical patients.

Medical

In a study of autopsy-proven PE in 2388 hospital deaths,Sandler and Martin1O1 showed that only 24 per cent of the239 patients who died from PE had undergone recentsurgery. Although the emphasis in the literature is onsurgical patients, DVT is also important in medicalpatientslO2-104. The efficacy of phannacological agents,especially heparin, in preventing DVT in patients withheart failure, myocardial infarction and chest infections hasbeen demonstrated by clínical trialslO5,IO6. In contrast,clínical evidence of the value of mechanical prophylaxis inmedical patients is limited. A recent prospective rando-mized trial of graduated compression stockings in 80patients aged 70 years and above with acute myocardialinfarction, using the fibrinogen uptake test, showed DVT in

Comparison with other prophylactic agents

Graduated compression stockings reduce the risk of DVTby 64 per cent in general surgical patients. Tables 3 and 4show the results of trials that compare the effect of stockingsalone or combined with other prophylactic modalities.Graduated compression stockings combined with low-doseheparin performed better than stockings or heparin alone(Table 3). LMWH combined with stockings was better thanstockings alone (Table4). Compression stockings andpneumatic compression were equally effective (Table 5).Stockings are, however, easier to manage. Either stockingsor pneumatic compression mar be used during operationand postoperative mechanical prophylaxis can be continuedwith stockings alone. In hip replacement, a meta-analysis

Table 3 Venous thromboprophylaxis using graduated compression stockings with and without low-dose heparin

Values in parentheses are percentages. LDH, low-dose heparin; FUT, fibrinogen 125¡ uptake test; Tc-pl, Technetium 99m Tc-plasmin scan for deep vein

thrombosis

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998 Graduated compression stockings in the prevention of venous thromboembolism .O. Agu, G. Hamilton and D. Baker

Table 4 Venous thromboprophylaxis using graduated compression stockings with and without lowmolecular weight heparin

Values in parentheses are percentages. LMWH, low molecular weight heparin

Table 5 Venous thromboprophylaxis using graduated compression stockings and pneumatic compression

Values in parentheses are percentages. .1111n-labelled platelet scan. IPG, impedance plethysmography; FUT, fibrinogen 1251 uptake test

lengili stockings in a randomized trial using the fibrinogenuptake test and found no significant difference in theirability to prevent DVT. Sparrow etol.47 observed that theportion of the stocking above the tibial plateau wasrelatively ineffective in decreasing venous pooling, butappeared to compromise the value of the stocking at lowerlevels. This prompted concern that the thigh- or full-lengilistockings mar actually be inferior to knee-lengili stockings.The above-knee segment of a thigh stocking often rollsclown, either hanging loosely around the knee or exerting agarter-like tourniquet effect121.U3, thus compromising theeffect of the stocking and potentially increasing the risk ofthrombosis. A recent survey of patient compliance showed asignificantly higher number of improperly applied thigh-lengili than knee-lengili stockingsl19. Knee-lengili stock-ings should replace thigh-lengili stockings, being equallyeffective, cheaper, more likely to fit correctly and bettertolerated by patients.

based on 56 trials showed an unadjusted pooled risk of 21per cent for use of stockings compared with 16 per cent forLMWH and 24 per cent for low-dose heparin77. OnlyLMWH and stockings were shown to reduce the risk ofPEin the analysis. Although this agrees with the report byWilkins et al. on the valueof stockings in preventing FE, thefew trials evaluating this suggestion are limited by smaUnumbers.

Graduated compressionstockings alone are effective forthe prevention ofDVf. Their effect is, however, enhancedby pharmacological agents such as low-dose heparin andLMWH. Stockings alone could provide adequate prophy-laxis for patients at low risk ofDVf. Patients at moderate orhigh risk should be managed with stockings combined withLMWH or low-dose heparinl17.118.

Thigh-length verms knee-length stockings

The majorityofstudies on prevention ofvenous thrombosishave been on thigh- or full-length stockings. Thigh- or full-length stockings are more expensive, more difficult to puton and less tolerated than knee-length stockingsl19-121.Lawrence and Kakkar43 found no increase in Jeep venousflow velocity when whole limb compression (18-8 mmHg)was applied compared with below-knee compression (18-14mmHg). Porteous etal.122 compared thigh- and knee-

Customized stockings

Customized stockings, tailored to the patient's leg dimen-sions, are usual1y made from high-modulus yaro withsubstancial variations in the pressure profile with changinglimb circurnference..Johnson etal.124 compared these withcornmercial1y available non-custom low-modulus circular

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O. Agu, G. Hamilton and D. Baker .Gradualed compression slockings in Ihe prevenlion 01 venous Ihromboembolism 999

compression therapy131. Compression stockings for DVTprophylaxis were associated with 38 of the 147 casesreported. Patients with peripheral arterial disease anddiabetics with neuropathy are particularly at risk, and casesresulting in necrosis and amputation have been re-ported132.133. Arterial occlusion, thrombosis and gangreneayer the anterior aspect of the ank1e secondary to thetourniquet effect of multiple layers of rolled clown stockinghave also been reported123.134. It is therefore essential thatsignificant arterial compromise and peripheral neuropathyare excluded before applying stockings. Manufacturersadvise against the use of stockings in patients with anank1e:brachial pressure index less than 0.7. Stockingsshould also be sized and fitted correctly. Legmeasurementsshould be reviewed regularly especially in swollen orswelling legs, as changes in leg girth significantly changethe amount of pressure exerted rendering the stockingineffective or threatening tissue oxygenation. An increase inleg circumference of 5 cm can double the amount ofpressure being applied by a stocking135.

knit stockings, but found no advantage. Non-customizedstockings actually appeared superior in that their lowmodulus allowed for flexibility in the calf diameter withinthe target pressure profile. While commercial non-custo-mized stockings mar be preferable to tailored stockings,studies suggest that they do not always conform to thepressures specified by their manufacturers125,12ó.

There mar be a case for customized stockings in patientswith pronounced calf-ankle disproportion, as in severelipodermatosclerosisl21.

Indications

Patients at risk of Dvr mar be classified into low-,moderate- and high-risk groups based on the aggregate ofpredisposing factors13. Graduated compression stockingsmar be used as sale prophylactic agent in patients at low riskof Dvr. Stockings mar also be used alone in situationswhere pharmacological prophylaxis is contraindicated andfor long-term prevention of recurrence following 3-6 months of anticoagulation for a single episode ofOVfÓ3. Patients at moderate or high risk should bemanaged with stockings in combination with LMWH orlow-dose heparin. Stockings should be applied at least 2 hbefore operation, and continued during and after surgeryuntil the patient is fully mobile. Stockings are particularlybeneficial in the bedridden127. The practice of sittingpatients out of bed early after operation can be hazardous.Sitting with the knees flexed to 900 or more for a patientwith thigh-Iength stockings causes a marked increase inpopliteal-stocking interface pressure. This compromisesthe effect of the stockings and mar jeopardize thrombo-prophylaxis127. The risk of venous thromboembolismsubsists after discharge from hospitaI89.128.129. Stockingsmar potentially be valuable in reducing this risk. With theincreasing ttend towards early discharge from hospital, aproperly conducted randomized controlled trial of the valueof graduated compression stockings following discharge is

necessary.

Conclusions

Graduated compression stockings provide an effective, safe,cheap and convenient means of preventing DVT. Stockingsincrease the linear velocity of venous outflow, prevent stasisand venous distension, and enhance emptying of valvularcusps. Properly used, stockings can reduce the risk of DVTin hospitalized patients by 55-70 per cent. Evidence on thevalue of graduated compression stockings in preventingfatal PE is limited and inconclusive. In combination withLMWH or low-dose heparin, stockings provide adequateprophylaxis for the majority of patients at risk. Knee-Iengthstockings are preferable, being effective and potentiallysuperior to thigh- or full-Iength stockings. Knee-Iengthstockings are cheaper and better tolerated, and shouldreplace thigh- and full-length stockings for DVT prophy-laxis. Continued use of stockings to prevent late venousthrombosis following discharge from hospital mar bebeneficial in patients with poor mobility. The tole ofstockings in preventing DVT recurrence is noteworthy.Attention to the vascular and neurological status of the leg,proper sizing and regular review of the legs should limitthe rafe occurrence of ischaemic complications with

stockings.

Complications

Although graduated compression stockings are relativelysafe, they are not without risk. The main concern isimpairment of subcutaneous tissue oxygenation, especiallyin patients with existing peripheral vascular compromise. Astocking pressure of 10 mmHg produces a 10 per centreduction in cutaneous blood flow, 3 O mmHg a 25 per centdrop and 60 mmHg an 84 per cent drop130. An estimate ofthe hazards of compression treatment of the leg by 154Scottish surgeons showed that at some stage up to one-thirdhad recognized a patient with damage to the leg as a result of

Acknowledgements

The authors are grateful to the Cochrane group, whosedatabase was searched for studies relevant to thisreVIew.

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1000 Graduated compression stockings in the prevention of venous thromboembolism .O. Agu, G. Hamilton and D. Baker

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