page160
thrombus consists of a fibrin web enmeshed with plate-
lets and red cells.
Anticoagulants are of
less use in preventing thrombus
formation in arteries, for in faster-flowing vessels throm-
bi are composed mainly of platelets with little fibrin.
For
the
uses
of
anticoagulants
see
Parenteral
anticoagulants,
below and Oral anticoagulants,
p.
146
Venous thromboembolism
Venous thromboembolism includes deep-vein thrombo-
sis and pulmonary embolism,
and occurs as a result of
thrombus formation in a vein.
Prophylaxis of
venous thromboembolism
All
patients
admitted to hospital
should undergo a risk
assessment for venous thromboembolism on admission.
Patients considered to be at
high risk include those
anticipated to have a substantial
reduction in mobility,
those with obesity, malignant disease, history of venous
thromboembolism,
thrombophilic disorder,
or patients
over
60 years.
Patients with risk factors for bleeding
(e.g.
acute
stroke,
thrombocytopenia,
acquired
or
untreated inherited bleeding disorders)
should only
receive pharmacological
prophylaxis when the risk of
bleeding does not outweigh the risk of
venous throm-
boembolism.
A NICE Guideline
1
provides a full
list of
risk factors,
and gives recommendations for
prophy-
laxis.
A venous
thromboembolism risk
assessment
checklist
is
also available
from the
Department
of
Health (
www.dh.gov.uk).
Patients
scheduled
for
surgery
should
be
offered
mechanical
prophylaxis (e.g.
anti-embolism stockings)
on admission if
appropriate;
prophylaxis should con-
tinue until
the patient is sufficiently mobile.
Choice of
mechanical
prophylaxis will
depend on factors such as
the type of surgery,
suitability for the patient,
and their
condition.
Patients
undergoing general
or
orthopaedic surgery,
who are considered to be at high risk of venous throm-
boembolism (see above), should be offered pharmacol-
ogical prophylaxis. Choice of prophylaxis will depend on
the type of surgery,
suitability for the patient,
and local
policy. A low molecular weight heparin is suitable in all
types of
general
and orthopaedic surgery;
unfractio-
nated heparin is preferred for patients in renal
failure.
Fondaparinux is an option for patients undergoing hip
or knee replacement surgery,
hip fracture surgery,
gas-
tro-intestinal,
bariatric,
or day surgery procedures.
The
oral anticoagulants dabigatran etexilate and rivaroxaban
are indicated for thromboprophylaxis following hip or
knee replacement surgery (see section 2.8.2).
Pharma-
cological
prophylaxis in general surgery should usually
continue for 5–7 days,
or until
sufficient
mobility has
been
re-established.
Pharmacological
prophylaxis
should be extended to 28 days
after
major
cancer
surgery in the abdomen or pelvis.
Hip or knee replace-
ment
surgery,
and hip fracture surgery,
require an
extended
duration
of
pharmacological
prophylaxis,
depending on the preparation used (consult
product
literature).
General
medical
patients who are considered to be at
high risk
of
venous
thromboembolism (see
above)
should
be
offered
pharmacological
prophylaxis
on
admission.
Choice of
prophylaxis will
depend on the
medical
condition,
suitability for the patient,
and local
policy.
Patients should receive either a low molecular
weight
heparin,
unfractionated heparin (if
patient
in
renal failure), or fondaparinux. Prophylaxis should con-
tinue until
the patient is no longer considered to be at
significant
risk of
venous thromboembolism.
Mechan-
ical
prophylaxis (e.g.
anti-embolism stockings)
can be
offered to medical
patients in whom pharmacological
prophylaxis is contra-indicated, and continued until the
patient is sufficiently mobile.
2.8.1
Parenteral anticoagulants
Heparin
Heparin initiates anticoagulation rapidly but has a short
duration of action. It is often referred to as ‘standard’ or
‘unfractionated heparin’ to distinguish it from the low
molecular weight heparins (see p.
141),
which have a
longer
duration of
action.
Although a low molecular
weight
heparin is generally preferred for
routine use,
unfractionated heparin can be used in those at high risk
of bleeding because its effect can be terminated rapidly
by stopping the infusion.
Treatment
For
the initial
treatment
of
deep-vein
thrombosis and pulmonary embolism a low molecular
weight
heparin is
used;
alternatively,
unfractionated
heparin is given as an intravenous loading dose,
fol-
lowed by continuous
intravenous
infusion (using an
infusion pump) or by intermittent subcutaneous injec-
tion.
Intermittent
intravenous
injection of
unfractio-
nated heparin is no longer recommended. An oral anti-
coagulant (usually warfarin,
section 2.8.2) is started at
the same time as
unfractionated or
low molecular
weight heparin (the heparin needs to be continued for
at
least
5 days
and until
the INR has
been in the
therapeutic range for 2 consecutive days).
Laboratory
monitoring for unfractionated heparin,
preferably on a
daily basis,
is essential;
determination of
the activated
partial
thromboplastin time (APTT) is the most widely
used measure (for unfractionated heparin). A low mole-
cular weight heparin or, in some circumstances, unfrac-
tionated heparin is also used in regimens for the man-
agement of
myocardial
infarction and unstable angina
(section 2.10.1).
Prophylaxis
For details on the use of heparins in the
prophylaxis of
venous thromboembolism see section
2.8.
Pregnancy
Heparins are used for the management of
venous thromboembolism in pregnancy because they
do not cross the placenta. Low molecular weight hepar-
ins are preferred because they have a lower
risk of
osteoporosis and of heparin-induced thrombocytopenia.
Low molecular
weight
heparins are eliminated more
rapidly in pregnancy,
requiring alteration of the dosage
regimen for drugs such as dalteparin,
enoxaparin,
and
tinzaparin;
see also under individual
drugs.
Treatment
should be stopped at
the onset
of
labour and advice
sought
from a specialist
on continuing therapy after
birth.
Extracorporeal
circuits
Unfractionated heparin is
also used in the maintenance of extracorporeal circuits
in cardiopulmonary bypass and haemodialysis.
1.
NICE clinical
guideline
92
(January
2010).
Venous
thromboembolism:
reducing the risk
140
2.8.1 Parenteral anticoagulants
BNF 61
2
Cardiovascular system