Experience in 2643 Patients

William R. Flinn, MD; Gail P. Sandager, RN, RVT;Michael B. Silva, fr, MD;Marshall E. Benjamin, MD; LeonardJ. Cerullo, MD;Mary Taylor,. RN

¡ "

"Background: Patients who undergo neurosurgical pro- .

cedures are at high risk for perioperativedeep veinthrom:-., '.'. , 'bosis (DVT) and pulmonary emboJis~\Pf),~hic:;~h~ve'

been reported in 6% to 43% of thesépatients.,

,"!i';:,','~

of fue patients. Patients in whom a craniotomy was donehada significantly higher risk for DVT (7.7%, P=.OO6), andpatientswho underwent cervical or lumbar spinal surgicalprocedureshada significantly lower risk (1.5%, P<.OOI).Among those patients in whoma craniotomywas perfo~edlor treatment of a tumor and who had DVT, 87% had ma-li~apt ~~oplasms.. Significant lower -extremityneurómo-tor dvsfunction was present in 69% of all patients with DVT ,

nlng (V~US).

~

The overalllow ,suggesting effective

'~:¡¡f!j¡¡:¡::

(paralysis..malig-spective DVTsurveillance. c,.

SeHing: University-affiliated cornrnunity hospital,

Results: Acute DVT was diagnosed in 147 (5.6%) of fue2643 patients. Eighty-one percent of the patients with acuteDVT were asymptomatic at the time of diagnosis. Deep veinthrombosis developed de nava in the proximal veins in 98%

proximal DVTwere facilitated by prospective VDUS sur-.y~illancei~?t~~!?i pa,~i~nts;" ;i;:;~;:~,~;:~F'¡~;:~;J;J~' :

(Arch Surg. '1996;131:472-480)

c.ESPITE DECADES of mod-

Fromthe Divisions 01 Vascular ern intensive study of

Surgery, Departments 01 .Surgery, University DI t~chmques fo~ preven-Maryland Medical School, non of deep vem throm-Baltimore (Dr Flinn and bosis (DVT) and pulmo-Ms Sandager),and University naiy embolism (PE). fuese entities remain01 Medicine and Dentistry a majar cause of death and morbidity in01 Ne:w Jersey, Ne:wark hospitalized patients.l Estimates sugg~st(Dr Silva); the Depa~ment that at least 260 000 cases of clinically rec-

ognizable venous thromboembolism oc-CUT annually among hospitalized pa-tients in the United States and that PE isthe direct cause of death in more than100000 patients each real and contrib-utes to the deaths of at least another100000 patients.2,3

-,,:,c, ,

,Pátjerits who undergo neurosurgi-cal proced~res are a universally recog-nized high-risk group for perioperative ve-nous thromboembolism. Uncontrolledstudies have documented postoperativeDVT in 29% to 43% of case patients, +6 and

randomized, controlled studies of DVTprophylaxis have reported an average in-cidence of DVT in 24% of control (un-treated) patients.7-13 In addition, PE has

~Ii

P A TIENTS AND METHODS

From 1987 through 1991,a total of2643 patients whowereadmitted to The Chicago (Ill)Neurosurgical Center of Co-lumbus Hospital were entered into a prospective surveil-lance program by using VDUS for the detection of acuteand perioperative DVT. The study group comprised morethan 98% of patients who were admitted to this serviceduring this period, and all patients who were undergo-ing major neurosurgical procedures were included, withthe exceptions noted below. The mean age of thepatients in the study group was 58 years (age range, 18to 92 years) and included 1372 men (51.9°/Ó) and 1271(48.1%) women.

The following surgical and other procedures were per-formed in these patients. Craniotomies were performed in1439 patients (54.4%) for treatment ofneoplasms or ce-rebrovascular disorders (eg, intracranial aneurysms or ar-teriovenous malformations). Ventriculoperitoneal or othershunting procedures were performed in 299 patients(11.3%), and cervical or lumbar spinal surgical proce-dures were performed in 454 patients (17%); this latter fig-ure represents approximately 80% of fue patients who un-derwent spinal surgical procedures during this entire periodoFollowing the initial review of this surveillance programin which no DVTswere detected in 100 patients who un-derwent spinal surgical procedures!8 the protocol was ál-tered to include onlythose patients with other associatedrisk factors (age, >60 years, malignant neoplasms, neuro-motor dysfunction, history ofDVT, etc). There were 119patients (4.5%) who had undergonea varietyof otherneu-rosurgical procedures (eg, stereotactic brain biopsy, cra-nioplasty, management of wounds, etc) and 332 patients(12.6%) who were enrolled in a surveillance programbuthad not undergone any surgical procedures. Thislatter groupincluded patients who were hospitalized with symptom-atic intracranialaneurysms and who received no surgicaltreatment, patients with symptomatic spinal stenosis, pa-tients who were treated with a gamma knife, and patientswho had undergone prior surgical procedures with asso-ciated clinical risk factors for DVT.

VENOUS THROMBOSIS PROPHYLAXIS

AII patients in this study had bilateral knee-Iength elasticcompression stockings applied. lntermittent mechanicalcompression was also performed in all patients by using acalf-length single-chamber device. lntermittent pneu-matic calf compression was begun preoperatively andcontinued intraoperativelyand postoperatively until thepatient was fully ambulatory or until discharge in thosepatients with sustained lower-extremity neuromotordysfunction. AII patient caTe was conducted in dedicatedneurosurgical intensivecare afeas and wards where per-sonnel were specifically instructed about the program ofprophylaxis and surveillance: Compliance was moni-tored under the direction of a dedicated clinical nursespecialist (M.T.).

3 and 70 Repeated VDUS was perfonned thereafter at weeklyintervals until discharge in patients ""ho remained immo-bilized or who had sigriíficant lower-extremity neuromo-tor dysfunction. Additional scans were perfonnedat the re-quest ofthe managing physicians ifpátients exhib\tedsignificant clinical changeso The: protocol for YDUSsur-veillance generally remained consistent throughout theperiod of this report, with the exception of patients whohad undergone lumbosacral or cervical spinal proce-dures and who had their VDUS surveill~nce protocolaltered significantly following preliminary data analysisin November 19880 As noted above, onlypatients whohad undergone spinal surgical procedures and who wereat a higher risk were enrolled in surveillance, and scanswere performed 1 week postoperatively or prior to dis-chargeo

The technique for performance ofVDUS has becomestandardized, and its details have been thoroughly de-scribed in other reportso29.JO Venous duplex ultrasound scan-ning in this study was perfQnned from the conflueri.ce ofthe tibial veins to the common femoral vein at the ingui-nal ligamento Longitudinal and transverse Bcmodeimages, combined with pulsed wave Doppler or color Dop-pler assessments, were obtained from the popliteal, super-ficial femoral, Jeep femoral, and common lemotal veins.Scanning was carned centrally into the iliac veins and venacava when it was clinically indicated, but lt was not per-fonned routinely. Scanning of the calf veins was not rou-tinely perfonned as a part of this protocolo Patients wereexamined in the vascular laboratory when possible, but mostexaminations in this study were conducted at the bedsideoVenous duplex ultrasound scanning was perfonned witha variety of commerciallyava\lable ultrasound u~i~allfroma single manufacturer (Advance T echnology Labora-tories, BothelWash).

The VDUS giagnostic criterialoracute DVT have alsobecome standardiZed,29,,30 and these criteria' w~reapplieathroughoutthe stUdyo Prior to theiri.ltiation ofthissurveil.: '.'lance program, the diagnostic accuracyofVDUS foracute 'proximal DVT (94%) in ourvascular laboratory had beendetermined by comparison with findings from conttastphlebograms.zB Most of theDVTs inthis stUdy were,diag-nosed by using direct visualiZation of di,c;;cr~,teho~oge-neous echogenic intraluminal-fillingdefec~o}~othe~ ~es,an echolucent clot produced distended,iI:!c~Q~pressiblevenous segments. An accurate diagnosis Wás faci4tat~ in',', "many cases by comparison with prior normal preóperativeor interval scans. ,,""

Acure DVTs, diagnosed in ~~isstiidy;were;classi-fied by their anatomic location...Eárly'~ri.jri:this stUdy; itwas recognized that an isolated.~o~iñ(jn'.femoral veinthrombosis was a characteristicfindingin patients in thesurveillance protocol, and thesepatients wereemp\ri-cally given a sepa.rate~l~s?:\f\~ati,°..njp~his ,r~pqrtoThrombi i~ the ~9,~onfemor~ly~i~thatextendedanydistanceabove the inguinalligament were classified asillofemoral: '" 'é. '.'.'" 'o ",-;- to

that-",

(emoral vein2nd thrombi

that were ldentlfied belowthe popliteal were termed cal(vein thrombi.

VENOUS DUPLEX ULTRASOUND SCANNING

Venous duplex ultrasound scans were perfonned on bothlegs of all patients preoperatively and on postoperative days Continued on next page

ARCH 5URGNOlI31. MAY 1996473

ning24.26 in symptomatic patients. Barnes et ap7 alsodemonstrated that the diagnostic accuracy ofVDUS wasequivalent to that of contrast phlebography for proxi-mal DVT (above the calf level) in a prospective study ofasymptomatic high~risk patients who had undergone jointreplacement procedures. In most hospital settings, thistechnique has supplanted phlebography for the initial di-agnosis of DVT o

The present repon details an extended experience withVDUS surveillance for the detection of acute and periop-erative DVT in patients who underwent neurosurgical pro-cedureso The goals of this repon were to examine fue ef-ficacy of DVT prophylaxis in these patients and to identifysubgroups of patients who were at a higher risk and thusallow fue continued modification of such a surveillanceprogramo Another goal was to compare fuese summary ob-servations with fmdings in a preliminary report28 that con-tained far fewer patients with DVT to determine thevalidity of OUT original observations and conclusionso

been implicated in up to 3% of ~ostoperativedeaths re-lated

ACUTE DVT

:Ac~_t~:p,VT was diagnosed in 147 oÍ, the 2643 patients,~hound~rwent neurosurgical procedures and who were

;;entered into !:he surveillance program for an oyerall in-'cidence of 5.6%. The mean age oÍ, patients who had acute'DVTwas 60 years (age ran~e, 21 to 87 years) , which was

programprevalence groupo .

Prospective surveillance 'stúdies todetect 'DVT"inhigh-risk patlent groups have used invasive and nóriin.;;vasive diagnostictechniques,asw~ll as coffibinationsofbotho Contrast phlebography háS been the' dia~ostic stan~.

o o é.' ",;i ",., """Cclara to WhlCh other techmques have been tompar~d,'but,. "0.",, .' c.,.",o.the c~mplexit~, risk, ~iscq~f~r!'o~?g,.'~?~l;~f:R~~ebó::'grams make thlS techmque: u~reallStiCf~r r,epet~tl,~t;:e.~7¡aminationso Decades ago, iodine 125~labeled fibri~o7gen uptake tests were used effectively for the diagnosisof DVT in prospective surveillancestudieso16-1B How-ever, these examinations were more accurate for the di-agnosis of inconsequential calf vein thromboses than forclinically relevant proximal iliofemoral DVT, and this tech-Dique is no longer used since the pooled-plasma prod-uct is unavailableo Physiologic noninvasive tests (eg, im-pedance plethysmography) were very accurate for thediagnosis of proximal symptomatic DVT ,19-21 and thesetests could be easily repeated al intervals without risk tothe patientso However, the diagnostic accuracy of im-pedance plethysmography was compromised when it wasused in prospective screening of asymptomatic high-risk patients!2,23

Venous duplex ultrasouI:ld scanning(VDUS) hasbecome the most universally accepted noninvasive tech-Dique for the diagnosis oflower-extremity DVTo This tech-Dique allows accurate, direct imaging of venous anatomyand, like contrast phlebography, direct visualization ofin situ venous thromboses. Unlike phlebography, VDUScan be repeated at inteivals; thus, it issuitable for pro-spective surveillance studies. The diagnostic accuracy ofVDUS for detection of acute DVT has been extensively'studied, and most well-designed comparisons with con-trast phlebograms have reported sensitivities and speci-

.:ficities in excess of 90% for duplex ultrasound scan-

1), lsolated'in 40

patients,(27.2%),iliofemoral DVTs were seen in 5patients,¡andcalfvein thrombosis was detected in 3

patients.Deep vein thrombosis was diagnosed in asymptom-

atic patients as ihe result of the scheduled surveillancescan in 120 (81.6%) of 147 patients. AIl DVTs in theseasymptdmaticpatients were proximal DVTs (femoro-popliteal y~i~, ~5 patients; common femoral veins, 35patient?;).The remaining 27 cases of acute DVT were di-agnosed by VDUS that was requested outside the usualsurveillance intervals based on patients' symptoms or theirchanging clinical conditions. Preoperative DVTs were di-agnosed in 27 patients (18.4% ofDVTs), and the remain-ing 120 cases of DVT werediagnosed postoperatively.Twenty-three of the 27 patients with preoperative DVTshad been transferred from another inpatient facility; 25patients with preoperative DVTs (92.6%) were asymp-toma tic at the time of their initial surveillance scan.Figure 2 is a graphic representation of fue occurrenceof symptomatic and asymptomatic DVTs at different timeintervals during the surveillance programo

A cranibtomy had been performed in 111 of fue 147patients who had acute DVT. Acraniotomy had been per-formed for treatment of a tumor in 86 patients (58.5%of DV'fs) (Figure 3), and for neurovascular disorders

Femoropopliteal Vein, 67.3%

4%

Common femoral Vein. 27.2'1.

Figure 1. The anatomic distribution of deep vein thrombosis diagnosed byvenous duplex ultrasound scanning in 147 patients in this series. Isolatedthrombi often developed spontaneously in the common femoral vein in thissurveiffance group and have been classified separately here.

Figure 3. Surgical and other treatments in patients in whom acure deepvein thrombosis developed in this series. More than 75% of patients withdeep vein thrombosis had undergone a craniotomy for treatment of tumoror neurovascular disorders. Only 4.8% of deep vein thromboses occurredin patients who underwent surgical procedures on the cervical or lumbar(GIL) spine.40

30..E.,~"-"c5 20ci

z

~o 10

~

oPreoperative 3 7 14 21 >21

Day

Figure 2. The time course of deep vein thrombosis (DVT) diagnosedduring survei/lance. Dveral/, 81% of patients with DVT were asymptomatic.More than 75% of al/ DVTs werediagnosed by dar 14, and 90% of thesewere asymptomatic. (Symptomatic patients here have been grouped withthe closest survei/lance interval for comparison.)

DVT developed. Table 1lists the frequency of neuromo-tor dysfunction among patients who had acute DVTinthe different clinical groups. The presence of.this inde-pendent risk factor was remarkably similar throughoutthe various groups, but itwas particularly notable amongthe otherwise low-risk subgroups. More than 85% ofpatients who had DVT after they underwent spinal sur-gical procedures had neuromotor dysfunction. This wasnot significantly higher than any other clinical group(P=.32) since the case numbers were toa small to c;irawreliable statistical conclusions. Nevertheless, it seems tobe an undeniable clinical observation that these pa-tients were at the highest risk of an otherwise verylow-risk patielit subgroup. '~:,

Table2 liststhe incidence ofDVT in allpatie~tswho were enrolled in the DVT surveillance programineach of the arbitrarily defined clinical treatme~tgroups.Here, as previously detailed in para~aph20fthe "Pa-tients and Methods"section, patientswhó underwent acraniotomy for treatment of a tumor orneurov~cular dis-orders are combined. Also, patients who underwentothersurgical procedures and those who had nonsurgical treat-ments were combined in this analysis, Aéute DVT oc-curred in 7.7% of all patientswhounde~entacrani-otomy. The incidence of DVTwassignificantly higherin the group of patients inwhoma craniotomywas per-formed than in the entirepatient group(P<;OO7). Theincidence of DVT wasstrikinglyhighetinthegroup ofpatients in whoma craniotomy wasperformed thari. infue group of patientS who underwentspinal surgicalpro-cedures (1.5%, P<.OOl)or patients't!ho received other

'ctreatments (2.4%,P<.OOl)~ Patients w~ó~nde~ent spi-nal surgical procedureshad thelowest m<;:lden~e of DVT(1.5%), and thiswasstatisticallysigilificantly lower thanthat in theentirepatient populauón (P<;OOl).

'Contfastphlebography wasperforméd in.lO pa-tientsWjthabnormal findingsfrom VDUS,and it cori-firmed the acute DVT in 8 patients. Chronic postthrom-

,." "boiicchanges, notedóíiYDU5, were confirmed by results

"-',c c ""c""of phlebography in 1 patient. One scan in fue early partofthe experiencedemonstrated a nonocclusive throm-bt,ls in fue commonfemoral vein. Phlebography in this

in 25 patients (17% of DVTs). Acute DVT occurred in18 patients who underwent shunting procedures (12.2%)and in only 7 patients who underwent cervical or lum-bar spinal procedures (4.8%). The remaining 11 cases ofDVT (7.5%) occurred in patients who received othersur-gical or nonsurgical treatments.

Table 1 summarizes the occurrence ofthe majorknown risk factors, malignant neoplasrns, and lower-extremity neuromotor dysfunction in patients who hadacute DVT in this study. Among the 86patients who un-derwent a craniotomy for treatment of a tumor in whomacute DVT developed, 75 (87%) were found to have ma-lignant neoplasms. In the entire group of 147 patientswho had acute DVT, 93 patients were found or knownto have malignant neoplasms (63.3% of all DVTs). Un-derstandably, patients in whom DVT developed follow-ing a craniotomy for neurovasculardisorders, spinal sur-géry, and shunt procedures did not have a high incidenceof malignant neoplasrns (20%, 28.6%,and 16.7%, respec-tively). However, 8 (72. 7%) of 11 patients who had DVTfollowing "other" surgical or nonsu~gical treatments wereknown or found to have malignant neoplasrns.

Lower-extremity neuromotor dysfunction was pres-ent in 101 (68.7%) of1he 147 patients in whom acute

ARCH SURGNOL l3l,MAY 1996.75 \

* OVT indicates deep vein thrombosis; VOUS. venous duplex ultrasound

scanning.t Significantly higher than that for total patient group.:j:Significantly lower than that for total patient group.

* DVT indicates deep vein thrombosis. Patients who underwent "other"surgical procedures and patients who received nonsurgical treatment arecombined.

patient demonstrated a "flow defect" in this anatomic 10-cation, but it was not diagnostic of DVT and no treat-ment was begun; this was initially considered to be a false-positive scan. This patient died sudqenly, and postmortemexamination revealed a PE. In retrospect, this probablyrepresented a false-negatiye phlebogram}~One patientwith acute DVT that was d~gnosed by using VDUS diedof a PE before treatment could be started.

NORMALVDl)S

A segmental, nonfatal PE was diagnosed by using pul-monary arteriography during the period of hospitaliza-tion in 3 (0.12%) of the 2496 patients with normal find-ings from VDUS surveillance. Selective phlebography in1 patientdocuniented thrombus inthe hypogastric veinas a source for aPE (Table3). In the other 2 patients,false-negative scans or a PE arising from a source otherthan the lower extremities was presumed. No patient withnormal VDUS findings during inpatient surveillance diedas the direct result of a PE during the study periodo

Five patients (0.18% of the study group) with nor-mal VDUS findings throughout the surveillance periodsuffered sudden death after discharge from the acute caresetting. Postmortem examination was performed in only1 patient and revealed a PE as a contributing cause ofdeath. However, beca use of the high index of suspicion,the conditions of the other patients wereconsidered torepresent fatal PEsCar this analysis.

PULMONARY EMBOLISM

A.documented PE occurred in 10 (0.38% of cases) of fue2643 patients in this study. Two patients (,°.07%) suf-

in our original report.28 The present report reviews 7 to8 times more patients and the same additional numbersof patients with acute DVT, and would seem to strengthenthe validity of many of our previous conclusions. How-ever, it also serves to emphasize some of the fundamen-tal issues of DVT surveillance in very high-risk patient

groups.l. Was the system ofDVT prophylaxis successful?

The overall incidence of DVT inthe entire group of pa-tients was 5.6%-similar to the 4.7% incidence in ourinitial reporto This extended experience would certainlyappear to support the efficacy of the DVT prophylaxis(a combination of elastic stockings and pneumatic calfcompression) that was used to treat these patients. Whilevalid statistical comparisons are not possible, it is prob-ablyreasonable to conclude that the obseryed incidenceof 5.6% is significantly lower than the 24% incidence ofDVT in untreated control subjects in previous reports ofDVT prophylaxis in patients who underwent elective neu-rosurgical procedures7-13 and in historic reportsof a 29%to 43% incidence ofDVT in patients who underwent neu-rosurgical procedures when no DVT prophylaxis wasused.4-V While the incidence of 5.6% is similar to the 6%reported by Cerrato et al,7 it appears lower than the 7%to 9%8-13 in other reports of patients who underwent neu-rosurgical procedures in which DVT prophylaxis wasused. These differences (if real) are undoubtedly the resultof the fact that no attempt was made to diagnoseisolated calfvein thrombi in the presentsurveillancestudy.Calf vein thrombi have accounted for the majority of perio-perative DVTs in other reports of patients who under-went neurosurgical procedures7-13 when phlebographywasused for the diagnosis. In a recent report that used phle-bography for diagnosis, Geerts et al30 observed that 69%of.DVTs in trauma patients were calf vein thrombi, andthese thrombi were discovered lto 3 times more fre-quently than proximal DVTs in every clinical subgroupof patients examined. Thus, it is possible that if calf veinthromboses were diagnosed in the present study, the over-all incidence ofDVTs would havebeen 10% to 15%-arange of values that were very similar to those citedabove.8-13

2. Most proximal vein DVTs do not propagate outof the calf but form de novo in the major axial venoussegments. AcuteDVTs were observed from the poplit-eal vein to the common femoral vein in 95% of the pa-

* PE indicates pulmonary embolism; Day, postoperative dar of the fE; plus sign, positive diagnosis of fE; minus sign, not performed; Question mark,diagnosis uncertain (PE presumed); and LE, lower extremity.

tPatient who suffered a fatal PE after diagnosis of deep vein thrombosis but before treatment could be started.:f:Normal venogram resulted in no treatment given.§Extensive normal findings from diagnostic evaluation for thromboembolic comp/ications were found during hospita/ization.

monary arteriogram despite normal serial VDUS. Thesecases (0.07% of patients) could certainly be consideredto represent a PE originating from undiagnosed calf veinthromboses, but the PE in these cases might also haveoriginated from pelvic veins (as demonstrated by phle-bography in 1 patient) or from undiagnosed upper-extremity DVT. Overall, no patient with normal find-ings from VDUS surveillance suffered a fatal PE while heor she was hospitalized. The decision not to perform calfvein scanning as a part of the routine surveillance pro.,tocol did not arrear to compromise either therapeuticdecisions or patient safety in this study. c.;;;

3. Most DVTs in high-risk patients are asymptori1~atic. For decades, it has been recognized that symptOtt1Sor physical findings are unreliable clinical indicators ofacute DVT. However, the magnitude of the problem ofasymptomatic proximal DVT in high.,risk groups is prob-'ably underestimated by most practitioners. Napolitanóet aPI diagnosed asymptomatic major proximal DYTsbyusing VDUS surveillance in 10% of trauma patients whówere treated with standard DVTprophylaxis.BurnsetaJ41 reponed clinicallyoccult DVTs in 21 %of trauma pa-tients who were studied with serial venóusultrasoundscanning. Acute DVT was diagnosed by l.1sing phlebog-raphy in 58% of trauma patientswho did noireceiveDVTprophylaxis in the study by Geerts et al,30and 98.5% ofthese patients had no clinical characteristics of DVT.. Inthe present study, 81.6% of patients withDVT wereasymptomatic at the time~pf diagnosis by using the sur-veillance VDUS,and all had proximal DVTs. It has beenwell recognized that the first manifestation of thrombo-embolicdiseaseinaybe a fatal PE, and reliance on diag-nosiS and treatment of establiShed, symptomatic DVT ex-poses patients to an unacceptable period of risk forembolization of proximal DVTs. OUT data would sug-gest that early diagnosis and treatment of major proxi-mal DVTs reducesthe risk of a PE in hospitalized pa-tients who undergo neurosurgical procedures (0.19% ofall patients in this study); this figure is almost identical

tients in the present reporLThis compares with the 88%incidence of DVTs in the majar axial venous segmentsof the limb in our originalreview. The anatomic classi-fication has been changed somewhat in the present re-port to call attention to the frequently observed occur-rence of focal spontaneous common femoral vein DVTin patients in the surveillance protocol (this was seen in27.2% of aIl DVTs in this series). In a prospective VDUSsurveiIlance program in trauma patients, Napolitano etaPl observed acute DVT in the common femoral veinsin 82.2% of patients. These observations would suggestthat clinically relevant DVTs wiIl be detected by usingsurveiIlance, since it is weIl accepted that most fatal PEsarise from the proximal veins.32.33 The reality of this lat-ter observation was underscored by 1 patient in this se-ries who suffered a fatal PE following VDUS diagnosisof acute DVT before therapy could be started and by an-other patient for whom treatment was withheld based ona normal phlebogram.

As noted above,the scanning protocol for these pa-tients did not include routine examination of calf veins,and it is certain that cases of isolated calf vein thrombo-sis were not diagnosed. Routine calf vein scanning in-creases the technologic complexity of the examinationand roughly doubles the time that is required for testingan individual patient; this would significantly increasethe indirect costs of these examinations (see below). Sev-eral studies have reported the remarkable diagnostic ac-curacy ofVDUS for examination of calf veins,34,35 but mostinvestigators regard calf vein scanning as a continuedsource of diagnostic error !6-38 When extensive DVT ispresent in the calf veins, it wiIl usuaIly be evident dur-ing routine VDUS that does not specificaIly examine thecalf or wiIl produce symptoms that wiIl be suggestiveenough to warrant direct examination as it did in 3 pa-tients in the present study. When DVTs remain con-fined to the calf, they are far less likely to cause a clini-caIly significant PE!2,39.40 However, 2 patients in thepresent series had a PE that was diagnosed by using a pul-

+77

to fue 0.2% incidente ofPEs in trauma patients who weredescribed by Napolitano et apl (in fuese patients, VDUSsurveillance facilitated early diagnosis and treatment ofasymptomatic proximal DVTs).

tistically comparable with phlebography for the detec-tion of proximal DVT. While the diagnostic accuracy ofVDUS in OUT vascular laboratory had been establishedby comparison withphlebograms prior to this study,28this validation had been done largely in symptomatic pa-tients. Thereafter, phlebography was performed in onlyan anecdotal group of patients all within the first year ofthe study; in 1 of these patients, the pblebogram mar havebeen misleading. It should be recognized that the pa-tients who underwent neurosurgical procedures in thisstudy mar represent an "optimal" high-risk group forVDUS surveillance. The baseline or preoperative scanmade difficult anatomic afeas identiflable and made thesubsequent interpretations of changes more reliable. Ac-cess to the lower exttemities of these patients was un-encumbered byfIXation hardware, casts, or traction equip-ment; the limbs of patients could be positioned to optimizeVDUS examination. Finally, there was a single de di-cated team of physicians, nurses, and vascular technolo-gists who closely tracked the surveillance schedule in thesepatients. It seems reasonable to suspect that if a signifi-cant problem with the diagnostic sensitivity ofVDUS ex-isted throughout a study of this magnitude, a much highernumber of fatal and nonfatal PEs would have been ob-served.

It is unquestionable that in the current milieu of cost-containment in health caTe, we must analyze the fiscalritility of protocols, such as this one. Meyer et al46 calledattention to the high cost of the large number of normalVDUSs in asurveillance program ofhigh-risk trauma pa-tients where proximal DVT was detected in only 6% ofthe patientswho they studied; these authors speculatedthat if VDUSwas reserved for only symptomatic high-riskpatients,this would represent a 72% savings in thecost of examinatio_ns;and they noted parenthetically thatthetrue incidence of fatal PE in patients with undiag-nosed, untreated proximal DVT is really unknown. Morerecent prospective studies of trauma patients have diag-nosed proximal DVT in 10% to 18% of patients who wereasymptomatic in 98%to 100%of the cases. If the sort oftherapeutic nihilism suggested by Meyer et al46 is broadlyapplied in the name of cost-containment, then we, asphysicians, have become part of the problem-not partof the solution. While it is unequivocally true that thepatient who dies promptly costs less to caTe for, we donot believe that this particular philosophy of cost-containment should drive diagnostic and therapeutic strat-egies in the new millennium. The results of OUT currentreview suggest that significant modifications can be madein this and any other surveillance program to increaseits effectiveness and reduce costs. Patients who under-went spinal surgical procedures had a significantly lowerrisk ofDVT, especially those patients who underwent op-erations on the cervical spine. We conclude that pro-spective DVT surveillance is not indicated in these pa-tients, with the possible exception o.f those patients withsignificant lower-extremity neuromotor dysfunction ormalignant neoplasms. The same recommendation can alsobe made for patients who undergo neurosurgical proce-dures and miscellaneous procedures or nonsurgical treat-ments. These modifications alone would reduce the cur-rent patient population by one third. Patients in whom

HERE ARE some, aspects of the VDUS sur-veillance protocol ~t were unique to thepopulation of patielits who underwentneurosurgical procedures in ibis study;however, these aspects ar~ generally rel-

evant to an overall consideration of surveillanceofhigh-risk groups. Acute DVT was diagnosed with the use ofthe preoperative or admission VDUSin 27 (18.4%)of the147 patients with DVT. This observation wasclearly theresult of many patients being transferred from other in-patient facilities after a period ofhóspitalization or a priorsurgical procedure. This is a particularlyimportañt ob-servation for this group since without these preliminaryexaminations, many patients might have been taken tosurgery with in situ DVT and a measurableperiod oJ riskfor PE prior to the first postoperative surveillance scan.However, these observations would be irrelevant to sur-veillance of 'otherhigh-riskgroups (ego trauma pa-tients) that would be unlikely to harbor 9ccultDVTpriorto admission. The majority ofacuteDVT;(68:7%) were

,

diagnosed within 14 days postoperatively, and this pe~riod accounted for 75% oJ the asymptomatic:DVTs.Napolitano et al3,l observedlhat 93%of all DVTs that werediscovered by VDUS surveillance weré diagnosed bythefirst 2 scans. After the nrst 2 weeks, the mean occur-rence ofDVT in the presentstuaywas 30 days;and 34.7%of those patients were symptomatic at the time of diag-nosis. These findings wouldsuggest that surveillance pro-grams mar be modified to serve effectively different pa::tient populations at risk and to cover specifically periodsof higher risk.

Venous duplex ultrasound scanning for DVT sur-veillance in high-risk groups has not been universally suc-cessful. Pooled results from 6 studies that screened high-risk patients showed an overall sensitivity of 59% forVDUS although the specificity was 98%.42.43 Davidson etal44teported a sensitivity of only 38% for color Dopplerultrasonography compared with contrast phlebographyfor the detection of proximalleg vein thrombi in pa-tients who underwent hip or knee replacement proce-dures. This latter study is possibly the low watermark forthe diagnostic accuracy ofVDUS and mar be partially ex-plained by the fact that VDUS was being performed at 7different institutions as part of a multi-institutional studyof DVT prophylaxis. Mattos et a.45 stressed the impor-tance of technologic expertise in the performance and in-terpretation ofVDUS, especially in surveillance of asymp-tomatlc patients. They reported a statistically significantincrease in the sensitivity of color-flow duplex scanningfrorn 25%.in the early phase of their surveillance studyto79%{100% sensitivity for proximal DVTs) in the lat-

et ap7 reported an overall

VDUS was sta-

a craniotomy was performed, especially those for malig-nancy, had a significantly higher risk for perioperativeDVT in this study. We would continue to recommendVDUS surveillance of these high-risk patients. A PE oc-curred in only 0.18% of hospitalized patients in this se-ries, and fue only fatal PE in this group occurred in pa-tients in whom VDUS had accuratelydiagnosed DVT.While 1 ofthese deaths was arguably preventable, it islikely that a fatal PE rate of 0.07% among hospitalized,high-risk patients represents an improvement over his-toric observations. One homily with regard to the inter-pretation of statistical significance has been that "to bedifferent, it has to make a difference." We believe thatprospective surveillance for perioperative DVT in pa-tients who underwent neurosurgical procedures in thisstudy made a difference in the occurrence of a fatal PEin these patients.

Prospective surveillance in 2643 patients who under-went neurosurgical procedures by using lower-extremity VDUS diagnosed acure DVT in 5.6% of the pa-tients. Proximal vein Dv1's were diagnosed in 98% of thepatients, and 82% of the patients with DVT were asymp-tomatic at the time of diagnosis. Patients who under-went a craniotomy, especially for malignant neoplasmsor with lower-extremity neuromotor dysfunction, had asignificantly higher risk of DVT. Patients who under-went spinal surgical procedures had a significantly lowerrisk of DVT, and future surveillance is probably not jus-tified in patients who undergo unco~plicated opera-tions on the cervical or lumbar spine. A PE was diag-nosed in 5 hospitalized patients{0.19% of cases) and wasfatal in 2 patients (0.07%). No diagnostic or therapeuticstrategy will eliminate a fatal PE. However, interval sur-veiIlance with the use ofVDUS provides an accurate,. non-invasive, and cost-effective means for diagnosis of DVT;during weIl-de:fined periods of risk, it wiIl significantlyincrease the detection of clinicaIly silent proximal DVTin weIl-defined, high-risk patientgroups and aIlow foreffective treatmenl. Thus, this type of surveiIlance wiIlreduce the incidence of a fatal PE in such patients.

Accepted for publication january 20, 1996.Presented at the 1 03rd Scientific Session of the West-

em Surgical Associatían, Chicago, ni, November 13, 1995.Reprints: William R. Flinn, MD, Division of Vascu-

lar Surgery, University ofMaryland Medical School, 22S Greene St, Room N4E22, Baltimore, MD 21201.

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relates to the fact that they had excluded calf veins in their

imaging protocols?Second, how do the authors know that their DVT surveil-

lance program was responsible for the very low incidence ofPE vs their prophylaxis program?

Third, the authors repon that 69% of the 147 patients withacute DVT had significant lower-extremity neuromotor dys-function, and 63% suffered with malignancy o In additioil to fueserisk factors for venous thrombosis development, were there anyother common causes ofDVT in these patients, such as abnor-malities in coagulation?

FinaIly, although there was a statisticaIly significant dif-ference in the incidence of DVT in craniotomy patients at 7 o 7%vs cervical and lumbar splnal patientsát 1.5%, is only a 7.7%incidence of DVT high enough to justify the added cost orascreening program in this era of cost -containment vsusing someother type of prophylaxis?

Roben Wilson, MD, Detroit, Mich: What son of preop-erative coagulation studies do the authors perform? If they findabnormalities, what changes do they make in their manage-ment? We also know that neurosurgery or brain trauma cancause intravascular coagulation and a tendency to dissemi-nated intravascular coagulation. 1 wonder how much of thatparticular abnormality they saw in these patientso

Dr Flinn: The issue of calf veinthrombosis remains a con-troversial oneo If we 1.ook at prospective studies with veno-graphic control, with the study from Toronto in trauma pa-tients being the best and most recent one, the majority ofDVTsdetected are calf vein DVTs, and so it stands to reason that inour program, therewere a substantial number of isolated calfvein DVTs that were not detected. It was the philosophyof OUTprotocol, early on, that isolated calf vein DVTs were clinicaIlyirrelevant to the outcome of fatal PE,and that is how we pro-ceeded)t seems;based onour long-term results, that this wasa justifiable assumption, but it remains anarea of concem.How-ever; this issue is also relevant to the afea of costo When rou-tine calf vein scanning is performed on every patient, it roughlydoubles the time of the examination and, of course, ult:imatelycontributes to increased indirect costso

Comparing prophylaxiswith surveillance, current stud-ies would indica te, even with good prophylaxis in high-riskgroups, that we wiIl see an incidence of-DVT in the rang~ of5% to 15%0 Prophylaxis clearly provides an increment of im-provement over patients wIthout prophylaxis, and surveil-lance, in the very high-risk groups, wi1.1 provide an additionalincrement of improvemento That is what we are seeing here.What we are struggling with in the framework of the existentdata here is to identify which subpopulations of patients wiIlachieve the additional benefit of surveiIlance and how effec-tive patient se1.ection and intervalstructure wiIl improve the

cost-effectivenessofsurveil1.ance programsoCoagulation abnormalities were not specificaIly studied

in a prospective fashion. Isolated individuals who developedunsuspected DVT had the usual coagulation workupo How-ever, as you can see from the high incidence of malignanciesand lower-extremity paraly~is in patients with DVT, it was feltthat in most of these cases, therewas aclear, predisposing fac-tor to the developmentof the DVT and that funher diagnosticevaluation was unlikely to behelpful.

~

Thomas W. Wakefield,MD, Ann Arbor, Mich: The authors'prospective DVT surveillance protocol for perioperative DVTwas successful in nearly eliminating fatal PE among hospital"'ized neurosurgical patients in their study. By usingpostopera-tive DVT scanning with duplex ultrasound atdays 3and 7 af-leí surgery and scans performed at weekly intervals innonambulatory patients, or for new clinical symptorns sugges-tive ofDVT, onlya 5.6% incidence ofDVT was diagnosed. 'lm-portantly, all patients were treated with prophylaxes with a com-bination of graduated compression stocking and interrnittentmechanicopnéumatic compression devices. Minor segmentalPE occurred in 0.1 % of the total patient population withnormal DVT scans throughout the surveillance protocol, andno patient with a normal scan suffered a fatal pulmonaryembolus. The results of Dr Flinn and bis colleagues areimpressive, and certainly, their close attention to venousthrombosis prophylaxis and diagnosis contributed to theirexcellent results.

First, the incidenceof acute DVT diagnosed in this studywas relatively low at 5.6% compared with that of other studiesthat have described groups of patients undergoing neurosur-gical procedures, even those undergoing prophylaXis. As calfyeinswere notroutinely examined in the study, do theauthor~ feel that their lower incidenceof venoús thrombosis

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