Pediatric emergency medicine trisk 2251 2251
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excess prothrombin permit unchecked propagation of the coagulation cascade.
Heterozygosity for factor V Leiden is found in about 5% of the Caucasian population in
the United States, but it is rare in those of African or Asian descent. It carries a two- to
sevenfold increased relative risk of VTE compared with normal individuals, whereas the
relative risk for homozygotes is 80-fold. Homozygous protein C deficiency may cause
widespread thrombosis in the neonatal period leading to purpura fulminans
(hemorrhagic skin necrosis) and cerebral thrombosis.
Clinical Considerations
Clinical Recognition
Thrombosis may manifest as deep venous thrombosis (DVT), pulmonary embolus
(Chapter 99 Pulmonary Emergencies ), stroke, or sinus venous thrombosis (Chapter 118
ENT Emergencies ). History should attempt to identify underlying risk factors.
Carefully review the family history for the occurrence of venous thrombosis or
pulmonary embolus, stroke, myocardial infarction, and recurrent miscarriages. Patients
with homozygous protein C, protein S, or antithrombin typically have a severe clinical
presentation in infancy with purpura fulminans. In the heterozygous state, patients may
present later in life with VTE.
Management/Diagnostic Testing
Clinical features of purpura fulminans in an infant not explained by infection should
prompt consideration for homozygous protein C or protein S deficiency. Administer
FFP (10 to 20 mL/kg q6 to q8 hours) to patients while awaiting the evaluation of these
protein levels. As noted above, levels of these anticoagulants can be difficult to interpret
in infancy (related to developmental hemostasis) and in the setting of acute VTE
(secondary to consumption), so levels drawn from the patient’s parents may be more
informative. For other patients, initiation of treatment should be managed as described
below and a workup for underlying risk factors, including protein levels, can be pursued
at a later point. Consult hematology to tailor the evaluation based on the presentation, as
well as personal and family thrombotic history. Prior to starting anticoagulation therapy,
document the patient’s platelet count, PT, aPTT, renal function, and hepatic function
since these values may be affected by the anticoagulant, and inform bleed risk.
For non–life- or limb-threatening thrombosis, start therapeutic enoxaparin (LMWH)
at a dose of 1 mg/kg SQ q12 hours. Dosing may need to be adjusted in obese patients,
and monitoring levels is imperative. The antifactor Xa assay is used to monitor
treatment with LMWH, 4 hours after the second or third dose. In general, the therapeutic
goal is an antifactor Xa level of 0.5 to 1 unit/mL. Infants up to 2 months of age need a
higher starting dose of 1.5 to 2 mg/kg SQ q12 hours in order to reach the same goal antiXa level. For patients with complex medical issues, renal insufficiency, or increased risk
of bleeding, an individualized anticoagulation plan in consultation with hematology may
be appropriate. Alternatively, IV UFH can be used. Treatment with UFH is usually
