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C HAP TE R 6 / Hematopoiesis, Coagulation, and Bleeding 151

Table 6-9 ■ “4Ts” SCORING SYSTEM FOR ESTIMATING PRETEST PROBABILITY FOR HIT POINTS (0, 1, OR 2 FOR EACH OF
FOUR CATEGORIES; MAXIMUM SCORE 8)
Date 2 1 0
Thrombocytopenia score 50% platelet decrease to 30% to 50% platelet count decrease 30% platelet decrease or nadir
9
9
____ nadir 20 10 /L (or 50% directly resulting from 10 10 /L
9
surgery) or nadir (10 to 19) 10 /L
Timing of platelet count Day 5 to 10 onset or 1 day Consistent with day 5 to 10 decrease, Platelet count decrease 4 days
decrease, thrombosis, or (with recent heparin exposure but not clear (e.g., missing platelet without recent heparin exposure
other sequelae (first day within 5 to 30 days) counts), or 1 day (heparin exposure
of heparin course day 0) within past 31 to 100 days) or platelet
score _____ decrease after day 10
Thrombosis (including Proven new thrombosis or skin Progressive or recurrent thrombosis, or None
adrenal infarction) or other necrosis (at injection site) or erythematous skin lesions (at injection
sequelae (e.g., skin lesions) post IV heparin bolus sites), or suspected thrombosis
score ___ anaphylactoid reaction (not proven)
OTher cause for No explanation for platelet count Possible other cause is evident Definite other cause is present
thrombocytopenia score decrease is evident
_____
Total score ____ (pretest probability score: 6 to 8 high; 4 and 5 intermediate; 0 to 3 low)
Changes to score can occur, based upon new information (e.g., further decrease in platelets, new thrombosis).
Warkentin, T. (2007). Heparin-induced thrombocytopenia. Hematology/Oncology Clinics of North America, 21(4): 589–607.

treatment of HIT: danaparoid, lepirudin, and argatroban (see Nursing Interventions
Table 6-7). Bivalirudin and fondaparnux are used for treating This clinicopathological syndrome requires the most astute obser-
31
HIT but their use is not supported by controlled studies. Dana- vational and correlation skills of a nurse. A high index of suspicion
paroid is an indirect inhibitor of factor Xa and thrombin. Arga- is needed especially with postoperative surgical patients who are
troban is a direct thrombin inhibitor. Lepirudin is a recombinant receiving prophylactic doses of unfractionated heparin for at least
hirudin and has high affinity binding to two sites on thrombin. 31 5 days. 32 A thorough history of the patient’s possible exposure to
All three approved nonheparin anticoagulants can be adminis- heparin, including 100 days before the event, must be obtained.
tered intravenously. Hirudin is the most potent natural thrombin Platelet count should be measured promptly in these patient pop-
inhibitor that is found in the salivary gland of the medicinal leech ulations and monitored closely. ACCP guideline 20 recommend at
and lepirudin is a derivative of hirudin using recombinant DNA least every other day platelet count monitoring in high risk pa-
therapy. Dosing recommendations for these drugs can be found in tients until day 14 or stopping heparin (whichever comes first).
Table 6-7. A baseline aPTT should be obtained before the start of Similar monitoring during the use of therapeutic unfractionated
therapy. Infusion doses of these drugs are maintained to achieve heparin should also be followed. 35
an aPTT 1.5 to 2.5 times the normal value, similar to the goal of A decreasing platelet count should cause suspicion and the
heparin therapy. The aPTT is usually sampled every 6 hours, but search for possible thrombosis formation should begin. Vigilant
31
with lepirudin, the aPTT should be drawn every 4 hours. Dana- physical assessment of extremities for any evidence of embolic
paroid monitoring utilizes antifactor Xa levels with a therapeutic events such as erythema, asymmetrical edema of the extremities,
target range of 0.5 to 0.8 anti-Xa U/mL. 31 and/or tenderness is critical. The “6 Ps” should provide guidelines
Warkentin 31 summarized the principles of HIT when it for monitoring limb perfusion. 24 Early observation of limb com-
is strongly suspected or has been confirmed. It is important to promise may allow appropriate vascular intervention, which could
(1) stop all heparin including LMWH and heparin administered avert amputation. Further evaluation and observation of all body
as flushes and (2) start alternative nonheparin anticoagulantion. systems, especially neurological, pulmonary, and cardiac, may re-
Evidence supports the use of the three approved nonheparin anti- veal early signs and symptoms of embolic events. If the patient
coagulants described previously. Warfarin is contraindicated in the displays any sign of restlessness or agitation, physiological factors
acute phase of HIT due to the risk of warfarin necrosis manifested such as hypoxemia should be the first consideration. Monitoring
by venous limb gangrene or classic skin necrosis. 31 Warfarin can oxygenation using pulse oximetry will give some estimate of oxy-
also prolong the aPTT values, which could lead to underdosing of genation that can be confirmed with an ABG. If gas exchange is
the direct thrombin inhibitors. 31 Prophylactic platelet transfu- adequate and restlessness and agitation persist, neurological causes
sions should not be given. Diagnostic laboratory testing should must be considered and sedation should be avoided unless indi-
include EIA testing, which can rule in or out the HIT diagnosis cated. Respiratory distress with tachypnea, dyspnea on exertion,
in 80% to 90% of cases in the appropriate clinical context. prolonged expiratory time as well as restlessness, and agitation
Platelet activation assays should be used with the remaining per- could be indications of pulmonary emboli. The patient’s heart
centage of patients. 31 Finally, duplex ultrasonography should be rate, rhythm, and blood pressure should be continually monitored
performed to investigate for lower limb DVT. 31 For patients with for any changes. Hemodynamic monitoring may be used and
a history of HIT who have an important indication for heparin, variations in indices may indicate cardiac failure, myocardial in-
it is recommended that sufficient time has elapsed since the farction, or pulmonary complications such as PE depending on
episode (more than 2 to 3 months) to ensure that the antibodies the situation and the primary disorder. Gastrointestinal dysfunc-
are no longer present. 31 tion can present with a wide range of signs and symptoms from