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288 • VENOUS THROMBOEMBOLISM
37.
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DIAGNOSIS OF DEEP VENOUS THROMBOSIS
David A. Frankel and Warner P. Bundens
BACKGROUND
Patients with one or more of Virchow’s triad of stasis, hypercoagulability, or vein wall abnormalities are susceptible to
1
thrombosis.
Lower limb deep venous thrombosis (DVT)
is a common and potentially serious problem. Over ve
million occur in the United States annually, and approxi-
2,3
mately 10% become pulmonary emboli.
of pulmonary emboli originate from lower limb DVTs.
Ninety percent
4,5
Furthermore, DVT can also result in permanent venous
obstruction, that is, chronic DVT, and/or damage to venous
valves leading to postphlebitic chronic venous insu ciency.
Timely and accurate diagnosis can aid signi cantly in the
reduction of morbidity and mortality.
e clinical presentation of DVT can range from silent,
with no symptoms or physical ndings, to phlegmasia
cerula dolens and venous gangrene. However, the sensitivity and speci city of symptoms and physical ndings such
as pain, tenderness, swelling, redness, or a positive Homan’s
sign range from 30 to 80%. e clinical diagnosis of DVT is
not reliable with an overall accuracy of only approximately
6–10
50%.
us, when DVT is suspected or it is part of a differential diagnosis, an accurate and objective test that can
rule in or rule out DVT is indicated.
ough this chapter is devoted to the diagnosis of
thrombosis in the deep leg veins, one should keep DVT
in mind when seeing a patient with super cial thrombophlebitis. e clinical diagnosis of thrombophlebitis of a
super cial vein is accurate. One should be aware, however,
that multiple studies have shown that approximately 20%
11–16
of patients will also have an occult DVT.
e extent of
thrombus in super cial veins usually extends further than
is evident clinically, and in up to one-third of cases the
thrombus will eventually extend into the deep system via
17–19
the saphenofemoral junction or communicating veins.
e traditional “gold standard” of objective testing is
ascending contrast phlebography. Compared with autopsy
20
ndings it has a 97% sensitivity and 95% speci city.
e
test, however, is costly, invasive, uncomfortable, and associated with de nite risks. One of the “particularly unwelcome”
complications is a 2 to 3% risk of the contrast agents actu-
9
ally causing DVT.
For decades, trends have been toward
less invasive and in the case of ultrasonography, less expensive methods of studying patients suspected of having DVT.
For years, radioactive brinogen scanning and impedance
plethysmography were widely used but were supplanted by
duplex ultrasonography as scanners became widely available
and multiple studies showed acceptable accuracy. Currently,
duplex ultrasonography is still the most commonly used
method of testing for lower limb DVT, though other methodologies are being increasingly used in selected settings.
DUPLEX ULTRASONOGRAPHY
e combination of B-mode imaging and the pulse Doppler
into one instrument, the Duplex, was originally done as
an aid to arterial diagnosis. It soon became evident that it
could also be used for venous investigations of both obstruction and re ux. Since 1990s the hardware technology has
improved the quality of the B-mode imaging dramatically.
Color-coded ow displays as well as “power Doppler” are
now available in most instruments. ese two modes are
o en helpful for locating veins and outlining intraluminal
defects.
e possible duplex ndings with a lower limb DVT are
listed in Table37.1. Virtually all vascular labs use the rst
criteria, the inability to collapse a vein with probe pressure
(Figures37.1 and 37.2), as the primary diagnostic method.
21
Some use only this nding.
Meta-analysis has shown this
sign to be 95% sensitive and 98% speci c for proximal leg
DVTs. When all the criteria of Table37.1 are used the sen-
22
sitivity is 98% and speci city94%.
Although the accuracy of this noninvasive, readily
available, and relatively low cost test is impressive, one
should realize most data re ect ndings in patients with
femoral and/or popliteal vein disease. e majority of
patients with symptomatic DVTs have thrombus in these
23,24
veins.
In some cases the thrombus may also involve the
iliac or calf veins. Duplex examination may not detect
289
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Table37.1 DUPLEX FINDINGS OF LOWERLIMBDVT
MODE FINDING IMPLICATION
B-Mode Image Unable to coapt vein
Pulse Doppler No spontaneous ow Occlusive thrombus
Color Flow
or Power
Doppler
Combined Increased ow
Figure37.1 Duplex of normal femoral vein. Vein can be completely
collapsed with probe pressure.
walls with probe
pressure
Visible thrombus rombus, possibly old
Vein enlarged Acute thrombus
No augmentation of
ow with distal
limb compression
No ow variation
with respiration
Intraluminal defect Nonocclusive thrombus
velocity and size of
surrounding veins
Intraluminal thrombus
Obstruction distal to
probe
Obstruction proximal
to probe
Being used as
collaterals
the full extent of thrombosis in these instances, but at
least the diagnosis of DVT will be made and, presumably,
appropriate treatment given. One must realize, however,
that isolated calf vein DVT are common and isolated
iliac thrombi do occur. Duplex is not as accurate in these
instances. In a study of postoperative orthopedic patients,
24% of the symptomatic and 88% of the asymptomatic
patients had isolated calf thrombi. In the symptomatic
group, duplex imaging was 85% sensitive and 86% speci c,
but in the asymptomatic group sensitivity was 16% and
25
speci city99%.
Isolated iliac vein thrombosis is o en reported as being
rare. However, most series from which data comes do not
include patients who are at increased risk for this problem
(i.e., those who are pregnant or have pelvic conditions such
as tumors, trauma, or recent surgery). e true incidence of
isolated pelvic vein thrombosis is unknown but probably
higher than previous estimates. Most vascular labs do not
routinely scan iliac veins as part of a lower extremity DVT
study. ose that do nd the study unsatisfactory because of
26
excessive bowel gas in 20% of patients.
e primary sign
used in the leg, the ability to coapt vein walls with probe
pressure, is usually not possible. Many labs use indirect signs
such as lack of ow variation with respiration in the proximal femoral (“common femoral”) vein, or a 50% increase in
proximal femoral vein diameter with the Valsalva maneuver.
e accuracy of these methods varies greatly in the litera-
27–30
ture.
Magnetic resonance venography is a more reliable
diagnostic modality in these patients.
In addition to the ability to diagnose the presence of
a deep vein thrombosis, duplex ultrasonography usually
provides information as whether the thrombus is acute or
chronic. Criteria are listed in Table37.2. e nding of a
partially compressible thrombus is the most common reliable sign of an acute DVT, as “free oating” thrombi (i.e.,
thrombi that appear to be moving within the vein lumen)
are only occasionally seen. Many clinicians use the criteria
Figure37.2 Duplex of acute femoral vein DVT. Vein cannot be collapsed
with probe pressure. Also note, vein is enlarged, thrombus is echolucent
and is partially compressible, which are signs of acute thrombus.
Table37.2 DUPLEX CRITERIA FOR DIFFERENTIATING
ACUTE VERSUS CHRONIC THROMBUS.
CHARACTERISTIC ACUTE CHRONIC
Degree of
Occlusion
Free Floating Free ++++ Stationary +
Clot Compressibility So ++++ Firm +
Surface Character Smooth ++ Irregular ++
Echogenicity Faint or None ++ Bright ++
Homogeneity Homogen. ++ Heterogen. ++
Collaterals Absent + Present ++
Recanalization Absent + Present ++++
++++=Diagnostic +++=Good ++=Fair +=Poor
M o d i ed from Karkow, Ruo , Cranley, B-Mode Imaging. In:Kempczinski RF,
Yao JS, eds. Practical noninvasive vascular diagnosis . Chicago:Year Book Medical
Publishers.1982.
290 • VENOUS THROMBOEMBOLISM
Total ++ Partial ++
of the degree of echogenicity of a thrombus to determine
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age. While the echogenicity of thrombus does increase with
time, it is also dependent on the duplex settings and is only
31–34
a fair indication of age.
Determination of the thrombus age is particularly
important when a clinician is faced with the presentation
of a patient with a past history of DVT who presents with
the complaint of new or increasing leg pain and/or swelling
with no past studies available for comparison. Because 10
to 20% of acute DVTs may become chronic, determining
whether the patient has a new thrombus, or new thrombus
in addition to chronic thrombus or some other cause of the
leg symptoms such as chronic venous insu ciency can be
challenging. When thrombus is found, application of the
Table37.2 age criteria are reliable, but one should realize
there may be both acute and chronic thrombi in conjunction (i.e., “new on old”). In these cases one should look for
partially compressible thrombus (i.e., acute, at either the
proximal or distal ends of the oldDVT).
Duplex examination can also be used to help determine
the cause of leg pain and/or swelling when a DVT is not
found. Intramuscular hematomas sometimes with associated muscle tears, ruptured and unruptured Baker’s cysts,
and venous re ux disease are common causes of symptoms
that may mimic DVT and can o en be identi ed by duplex
ultrasonography if one keeps them inmind.
D D I M E R
Eighty to 90% of all duplex exams ordered are negative
35–37
for DVT.
It would therefore be clinically sensible and
cost-e ective to adopt the use of a blood test to rule in or
rule out DVT and negate the need for more complicated
and expensive testing. Over the last decade, the ability to
detect circulating D-dimer using monoclonal antibody
tests, and red cell and latex agglutination has received considerable attention as a diagnostic adjunct in the detection
of DVT. D-dimers are degradation products that result
from the action of plasmin on cross-linked brin speci cally
in the nal step of thrombus generation. us the presence
of D-dimer is an indication of the initiation of blood clotting. Other conditions that can cause an elevated D-dimer
include infection, in ammation, cancer, vasculitis, pregnancy, trauma, hemorrhage, and postsurgical states.
Several laboratory methods are currently available for
D-dimer testing (Table37.3). ough the enzyme-linked
immunosorbent assay (ELISA) is the most sensitive, it is
also the most expensive and time consuming. e red blood
cell and latex agglutination tests are less expensive and much
quicker, taking minutes as opposed to hours, and are thus
more attractive as clinical tools for management of patients
with suspected DVT. As can be seen from the table, however, the low speci city makes a positive test virtually useless
for ruling inDVT.
Table37.3 SENSITIVITY AND SPECIFICITY OF
DIFFERENT DDIMERTESTS.
METHOD SENSITIVITY % SPECIFICITY %
ELISA 96 39
Red Blood Cell
Agglutination
Latex Agglutination 87 60
Figures represent averages from the literature.
with both possible pulmonary embolism and/orDVT.
88 64
35–38
e results include subjects
A negative test, however, may be a useful aid in ruling
out DVT. Numerous studies have reported sensitivities of
D-dimer but there are limitations to drawing conclusions
from these. Di erent methodologies were used, heterogeneous populations were tested, and many studies combined
patients with pulmonary emboli and/or DVT. Other studies have shown varying sensitivity in relation to the timing
of testing and to the location and or extent of DVT.
38–41
Overall, D-dimer on its own has not proven to be an e ective test to make the diagnosis ofDVT.
In 1999, the American oracic Society recommended
duplex ultrasonography or impedence plethysmography for
42
all patients with suspected DVT,
and in many institutions,
this is current practice. Recent evidence points out that the
use of a D-dimer blood test and a pretest probability score
can safely exclude DVT and obviate the need for further
43,44
diagnostic testing in a large proportion of cases.
e
2006 Institute for Clinical Systems Improvement (ICSI)
reviewed the most recent literature and put forth an algorithm for the diagnosis of DVT. ey rst recommend
determining the clinical pretest probability of DVT using
45
the Wells score (Table37.4)
Table37.4 WELLS SCORE. AMODEL FOR THE
PREDICTION OF THE CLINICAL PRETEST
PROBABILITY OFDVT.
SCORE
1 Active cancer (treatment ongoing or within previous 6months or
palliative)
1 Paralysis, paresis, or recent plaster immobilization of lower
extremity
1 Recently bedridden for more than three days or major surgery
within four weeks
1 Localized tenderness along the distribution of the deep venous
system
1 Entire leg swollen
1 Calf swollen by more than 3cm when compared with
asymptomatic leg (measured 10cm below tibial tuberosity)
1 Pitting edema (greater in the symptomatic leg)
1 Collateral super cial veins (nonvaricose)
-2 Alternative diagnosis as likely or greater than that of DVT
If both legs are symptomatic, score the more severe side.
High risk=scored 3 or more
Moderate risk=1 or 2
Low risk=0 or less
(From Reference 45)
and then using either form
DIAGNOSIS OF DEEP VENOUS THROMBOSIS • 291
(agglutination or ELISA) of D-dimer test to determine
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which patients need to proceed to duplex ultrasonography. All patients with either a moderate or high Wells score
46
should undergo duplex ultrasonography.
e presence of
a DVT, however, cannot be excluded by a negative duplex
in these higher risk patients and a D-dimer test is helpful.
Anegative D-dimer makes DVT very unlikely, whereas a
positive D-dimer then warrants repeat ultrasonography
within 1 week or sooner if symptoms progress.
Conversely, all patients with a low pretest probability undergo D-dimer measurement. ose with a positive
D-dimer are recommended to undergo duplex ultrasonography. ose with a low pretest probability and a negative
D-dimer do not require any further diagnostic testing.
is algorithm is most e ective in the outpatient setting,
as many inpatient conditions will cause D-dimer elevation.
Newer pretest probability scoring algorithms have
been described, including the modi ed Wells score and
47
the Hamilton score,
which stratify patients into only
two groups based on the likelihood of having DVT.
Unfortunately, a standardized algorithm using a single pretest probability scoring system and a single D-dimer assay
has not been developed. e trend, however, is toward
the use of a pretest probability score in combination with
a D-dimer assay to safely rule out DVT and avoid a large
number of unnecessary and costly diagnostic examinations.
MAGNETIC RESONANCE
VENOGRAPHY
e quality of magnetic resonance venography (MRV) has
steadily improved since its introduction in the early 1990s.
It is now a powerful technolog y that is o en used as a “problem solver.” Various techniques are used, including spin
echo and gradient-recalled echo. Intravenous gadolinium
can be used to enhance images and can aid in determination
of the age of the thrombus. Absence of imaging of a vein or
an intraluminal lling defect indicate the presence of DVT.
Examiners must be cognizant, however, of known ow
artifacts that can be mistaken for thrombus. Images can be
viewed in axial, coronal, or sagittal planes, and postprocessing techniques are available that can be used to produce 3D
images with removal of background structures for improved
ease of viewing.
MRV has been shown to highly accurate. Sensitivities
of 97% and speci cities of 100% have been demonstrated
along with excellent interobserver variability for iliac, femo-
48,49
ral, and below knee DVT.
Several authors now consider MRV to be the study of choice for pelvic vein DVT.
Compared with conventional contrast venography it is
not only noninvasive and avoids the use of ionizing radiation, but it also has demonstrated better ability to show
the proximal extent of femoral and iliac vein thrombi. An
added advantage is that it may show underlying pathology
that contributed to the formation of the DVT such as pelvic
masses or le iliac vein compression by the right common
50
iliac artery.
e limitations of MRV include expense and lack of portability and, in some cases, availability. Also, some patients
with implanted metal devices, claustrophobia, and inability
to remain still are not suitable for this exam. Gadolinium
must be used with caution in patients with renal impair-
51
ment due to the risk of nephrogenic systemic brosis.
C O M P U T E R I Z E D
TOMOGRAPHIC VENOGRAPHY
Computerized tomographic venography has many of the
same advantages as MRV when compared with duplex
sonography. It does, however, involve the use of ionizing
radiation and intravenous iodinated contrast agents for
imaging peripheral veins. In imaging peripheral and pelvic
veins, the accurate timing of image acquisition in relation
to contrast injection is o en di cult, and multiple runs
may be necessary to acquire all of the desired veins. In larger
veins one can also be faced with the in ow of noncontrast
blood from a branch vein into a vein with blood containing contrast, which creates a “wash in” artifact that can be
mistaken for thrombus. For these reasons MRV is usually
considered a more appropriate modality when duplex testing is felt to be inadequate. However, some do employ a
technique known as combined computerized tomographic
venography and pulmonary arteriography (CCTVPA).
Computerized tomographic pulmonary arteriography
(CTPA) has become the test of choice in many centers for
suspected pulmonary emboli. Katz etal. reported that by
waiting for 3 to 3.5 min a er the injection of contrast that
is used for CTPA, one can then scan the veins from the
diaphragm to the calves. e scanning can be a survey with
cuts taken every 4cm or a continual helical imaging. e
latter though involves considerably more radiation to the
52
subject.
us, with this technique, one study can not only
answer the question of whether or not there is a pulmonary
embolus and its extent but also o en nd the source of the
embolus and the amount of residual thrombus in the veins.
97% sensitivity and 100% speci city has been reported for
CCTVPA in comparison with ultrasonography, and a large
study has shown that in patients with lower limb DVT 23%
53
extended into the iliac veins or the inferior vena cava.
S U M M A R Y
It is well documented that the clinical diagnosis of lower
limb DVT is unreliable. Fortunately, there are a number
of methodologies available that can objectively rule in or
rule out the presence of DVT with accuracies very close to
the “gold standard” of conventional contrast phlebography.
292 • VENOUS THROMBOEMBOLISM
ey are also less invasive, safer, and usually less costly.
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Duplex utrasonography, with its high accuracy and absent
risk, remains the most common diagnositic modality,
however, the use of a pretest probability score along with
D-dimer measurement can safely obviate the need for this
study in low-risk patients. is new algorithm for diagnosis
is slowly being adopted in practice. is chapter has presented a brief overview of the currently available technologies and diagnostic strategies, which continue to evolve and
improve.
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294 • VENOUS THROMBOEMBOLISM
38.
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THROMBOTIC RISK ASSESSMENT
A HYBRID APPROACH
Joseph A. Caprini
INTRODUCTION
Venous thromboembolism (VTE) is one of the most common, yet highly preventable, causes of in-hospital death. In
response to this problem, the implementation of an appropriate, targeted thromboprophylaxis strategy has been
described as the most important single factor for improving
1
patient safety.
Both medical and surgical patients are at risk
of VTE. It has been calculated that without prophylaxis,
the incidence of hospital-acquired deep venous thrombosis (DVT) is approximately 10 to 40% among medical
patients and general surgery patients, and 40 to 60% fol-
2
lowing major orthopedic surgery.
In patients subjected to
autopsy, approximately 10% of all deaths in the hospital
3
are attributed to pulmonary embolism (PE),
with most
patients who su er a fatal embolus dying within the initial
30-minute period. is small window for e ective treatment, combined with its frequently asymptomatic nature,
explains the high fatality rate associated with this condi-
4
VTE is also responsible for a signi cant number of
tion.
long-term health problems:Prandoni etal. have shown that
30% of patients with symptomatic DVT will su er recur-
5
rent VTE in the 8years following an event,
while almost
a third of patients who su er a DVT will go on to develop
long-term venous insu ciency complications in the lower
leg, also known as “postthrombotic syndrome” (PTS). is
condition may result in chronic leg swelling, discomfort,
dermatitis, and leg ulcers, which can reduce the patient’s
quality of life and have an economic impact frequently over-
6
looked in DVT cost assessment.
Clinically proven methods of prophylaxis have been
shown to prevent a signi cant proportion of clinically signi cant VTE events. Yet despite the publication of regularly
2,7–10
updated consensus guidelines,
VTE prophylaxis is still
under- or inappropriately prescribed in a high proportion of
patients, leaving them at signi cant risk of serious complica-
11,12
tion due to PE or DVT.
E ective VTE risk assessment is therefore critical in targeting and optimizing prophylaxis, and for the subsequent
improvement in patient outcomes. ere is an urgent need
for a clear, easy-to-use risk assessment model based on information in the patient’s medical history and clinical examination. Although there has been, and continues to be, a
great deal of clinical research into VTE, it is unlikely that
there will ever be su cient high-quality clinical evidence to
guide decisions on prophylaxis in every group of patients—
medical and surgical. With each patient representing a
unique clinical situation with their own combination of risk
factors, it can be di cult to determine the level of VTE risk,
and the appropriate intensity of thromboprophylaxis. is
review considers the reasons contributing to underuse of
prophylaxis, and discusses a “hybrid approach” combining
risk assessment scoring with the application of current treatment guidelines. e results of an audit from the author’s
hospital and a real-world case study are also detailed to illustrate key issues.
POOR ADHERENCE TO
PROPHYLAXIS GUIDELINES
Consensus groups such as the American College of Chest
Physicians (ACCP) and the THRIFT Consensus Group
regularly publish guidelines on the prevention and treatment of VTE in both surgical and nonsurgical patients.
2,7–10
While the recommendations from these groups are based
on clinical evidence from trials and meta-analyses that are
strati ed clearly according to patient risk, VTE prophylaxis
11–17
is still suboptimal in many patients,
and the rates of
total and proximal DVT remainhigh.
US surveys of prophylaxis use indicate that the percentage of surgical patients receiving prophylaxis ranges from
38 to 94% depending on the type of procedure.
11,15,18,19
One particular study documenting adherence to the 1995
ACCP guidelines in surgical patients found that 25% of
patients undergoing high-risk major abdominal surgery did
11
not receive any form of VTE prophylaxis.
Furthermore,
in a retrospective analysis by Arnold etal. looking at cases
of VTE in a US cohort of surgical and medical patients, it
was found that one out of six VTE events could have been
295
prevented if physicians had followed the ACCP guide-
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12
Inadequate prophylaxis was most o en attributable
lines.
to the fact that no prophylactic measures were prescribed.
Surprisingly, a tendency has been reported for prophy-
laxis to be administered less frequently with increasing risk
20
Why this occurs is unknown, although it may re ect
level.
physician concerns that the risk of complications due to anticoagulant therapy may be greater in very high-risk patients.
SUBOPTIMAL PROPHYLAXIS
INACTION
e extent of the prophylaxis problem was highlighted in
14
a recent study by the author’s group.
Carried out to test
the performance of current VTE risk assessment, the primary objective was to determine the percentage of a surgical
patient population falling into one of three risk categories
(moderate, high, and highest risk; Table 38.1). e study
also sought to identify whether patients were receiving
appropriate prophylaxis based on their risk level, and to
compare the degree of compliance with prophylaxis guidelines with that found and reported for the same hospital
in 1991. Atotal of 157 patients undergoing neurosurgery,
cardiovascular surgery, general surgery, gynecological surgery, or orthopedic surgery (other than arthroplasty) were
included in the study. Each patient had a detailed preoperative VTE risk assessment, and the type and duration of
prophylaxis prescribed to each patient was recorded and
compared with their individual risk score. In-hospital outcomes for all patients were carefully monitored, and patients
were followed up by telephone a er amonth.
e study found that 19% (30 out of 157)of patients
were not prescribed any prophylactic measures despite the
existence of several risk factors. is was even more surprising considering that the majority of patients were in
the highest risk category, and therefore at greatest need of
prophylaxis. Clinically overt VTE appeared in two out of
seventy-three (2.7%) patients in the highest risk category,
both of whom had not received appropriate prophylaxis,
while a total 57% of patients were shown to have received
inadequate prophylaxis according to the ACCP guidelines.
Comparison of these results with our previous thromboprophylaxis audit performed in 1991 (Table38.1) indicates
no improvement in compliance with treatment guidelines;
indeed, in the group at highest risk of VTE, only 30% of
patients received appropriate prophylaxis in 2002 compared with 70% in the same category in1991.
UNDERUSE OF PROPHYLAXIS
WHY IS THERE APROBLEM?
MISCONCEPTION OFRISK
Although the serious implications to health are now well
accepted—both in the short and long term—a large part of
the problem can be attributed to the clinically silent nature
of VTE. For surgical patients there is a low incidence of clinically apparent VTE in the perioperative period, thus it is rare
for an individual surgeon to witness an acute PE or major
DVT event in one of their patients. Studies have shown that
a signi cant proportion of symptomatic thromboembolic
21–23
complications occur a er discharge from hospital,
with
a survey of California orthopedic surgeons nding that 76%
of VTE events were diagnosed following discharge from
hospital a er total hip replacement (THR), and 48% a er
24
total knee replacement (TKR).
e current trend toward
shorter hospital stays serves to accentuate this problem,
whereby the need for and bene ts of thromboprophylaxis
can be di cult to appreciate for a physician who rarely sees
the problem. Extended prophylaxis has value in preventing
not only sudden death but also all of the other complications
of VTE responsible for signi cant morbidity and mortality.
Although the majority of trials in VTE have studied sur-
gical patients, medical patients are also at signi cant risk of
2
thrombotic disease.
fer a fatal PE have recently undergone surgery,
Fewer than a third of patients who suf-
25
and as many
2
Table38.1 ADHERENCE WITH ACCP CONSENSUS GUIDELINES:AN AUDIT OF HOSPITAL PRACTICE
Total (2002) 9/157 (6%) 43/157 (27%) 105/157 (67%)
Prophylaxis guidelines followed 7/9 (78%) 28/43 (65%) 32/105 (30%)
Prophylaxis guidelines not followed 2/9 (22%) 15/43 (35%) 73/105 (70%)
Total (1991) 185/538 (34%) 261/538 (49%) 92/538 (17%)
Prophylaxis guidelines followed 18/185 (10%) 110/261 (42%) 70/92 (76%)
Prophylaxis guidelines not followed 167/185 (90%) 151/261 (58%) 22/92 (24%)
M o d i ed from Reference 14 with permission from Blackwell Publishing.
MODERATE RISK
2 RISK FACTORS
Low
(0–1 risk factors)
296 • VENOUS THROMBOEMBOLISM
HIGH RISK
34 RISK FACTORS
Moderate
(2–4 risk factors)
HIGHEST RISK
5 OR MORE RISK FACTORS
High risk
(more than 4 risk factors)
as one in twenty hospitalized patients with multiple clinical
https://t.me/med1917
26
conditions go on to develop PE.
dence of DVT in medical patients is 10%to 20%,
e average overall inci-
2
but this
rises in certain patient groups. For example, stroke is associated with a 20 to 50% risk of VTE complications without
2
prophylaxis,
of patients with an acute myocardial infarction.
while VTE is thought to occur in 20 to 40%
27
Cancer is
also a well-known thrombotic risk factor due to the hypercoagulable state induced by the malignancy, with treatments for the disease, such as surgery and chemotherapy,
2,28
serving to further compound the risk.
Despite current
guidelines stating that medical patients can be at signi cant
risk of VTE and should receive thromboprophylaxis, a survey from the International Medical Prophylaxis Registry
on Venous romboembolism (IMPROVE) of acutely ill
medical patients recently revealed that fewer than 40% of
13
patients enrolled in the registry received prophylaxis.
S A F E T Y C O N C E R N S
Another factor underlying the suboptimal use of pharmacological prophylaxis is overestimation of the bleeding risk
associated with anticoagulant prophylaxis. For example,
a survey of orthopedic surgeons in the United Kingdom
found that almost half (48%) had discontinued the use of
low molecular weight heparin (LMWH) for TKR or THR
29
due to concern over bleeding complications.
However,
numerous randomized, placebo-controlled, double-blind
trials and further meta-analyses of prophylaxis with LMWH
and unfractionated heparin (UFH) during major surgery
have demonstrated that both types of heparin prophylaxis
are extremely e ective in preventing VTE at the expense
of no increase, or a very small increase, in the rate of major
30–35
bleeding.
with an increased risk of wound hematomas,
Although LMWH and UFH are associated
30,33,34
major
bleeding complications are extremely uncommon, and the
consequences of VTE are potentially much more severe—
thereby outweighing any justi cation for withholding heparin prophylaxis.
LMWH is at least as safe and e ective as UFH.
31,34,36,37
LMWH has been associated with a lower risk of major bleeding complications; one particular study of patients undergoing abdominal surgery reported a 23% reduction in the
frequency of major bleeding events in patients who received
LMWH compared with UFH, although this di erence was
not signi cant. e study also observed signi cantly fewer
30
severe bleeds and wound hematomas.
LMWH exhibits
minimal binding with plasma proteins, endothelial cells,
and platelet factor IV, providing a more predictable clinical response than UFH as well as reducing the likelihood
of causing heparin-induced thrombocytopenia (HIT).
38,39
With an incidence of 1 to 5%, immune HIT is an uncommon but serious complication of heparin therapy, and is
o en cited as a reason for caution in prescribing heparin
prophylaxis. Of 665 patients who received prophylaxis with
either UFH or LMWH during elective THR, 18 patients
developed HIT, and the majority of these patients were in
39
the UFH group (4.8% versus 0.6%; p < 0.001).
While the bene ts of LMWH thromboprophylaxis have
been shown in numerous studies, suboptimal use may arise
from additional safety concerns combined with a misconception of risk. Clinical issues remain unanswered and may
contribute to physician hesitation to pharmacologic prophylaxis, for example, optimal dosing and the need for monitoring in patients with severe obesity or renal insu ciency.
LACK OF AWARENESS OF THE PROBLEM
Physicians frequently cite informal, retrospective surveys of
their own clinical service or personal experience to explain
40
why they believe the rate of VTE is low.
ere also appears
to be poor awareness of the diverse range of clinical signs
and symptoms that can be attributed to thrombosis and the
fact that these relatively minor symptoms can be extremely
common (Table38.2). Many physicians fail to realize that
what they are seeing may be an indicator of an otherwise
silent thrombotic event requiring further investigation,
which can therefore be attributed to a lack of prophylaxis.
COST OF SUBOPTIMAL PROPHYLAXIS
Pharmacological prophylaxis undoubtedly incurs a signi cant cost, both in terms of the drugs themselves and,
with UFH and oral anticoagulants, an increase in nursing
time and laboratory monitoring. However, the economic
Table38.2 CLINICAL SIGNS, SYMPTOMS, OR EVENTS
THAT MAY BE ASSOCIATED WITH VTE IN CLINICAL
PRACTICE
• Leg pain
• Leg swelling
• Chest pain
• Shortness of breath
• Transient orthostatic hypotension
• Decreased level of consciousness presumed to be narcotic excess
• Fainting spell
• Hypoxia
• Follow-up of patient for readmission or death 90 d postoperatively
• Sudden death
• Death without autopsy
• Postoperative stroke due to patent foramen ovale
• Suspected myocardial infarction
• Failure to thrive, sinking spell, or “the dwindles”
• Postthrombotic syndrome during physical examination of the legs
(standing) 5years postoperatively
• Postoperative pneumonia
37
THROMBOTIC RISK ASSESSMENT:AHYBRID APPROACH • 297
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