In the fetus, fibrinogen, factor 5, factor 8, and platelets approach normal levels during the second trimester. Levels of other clotting factors and anticoagulant proteins increase gradually throughout gestation. The premature infant issimultaneously at increased risk of bleeding or clottingcomplications that are exacerbated by many of the medical interventions needed for care and monitoring, especiallyindwelling arterial or venous catheters. Most children attainnormal levels of procoagulant and anticoagulant proteins by1 year of age, although levels of protein C lag and normalize inadolescence.
A detailed family history is crucial for diagnosis of bleeding and thrombotic disorders. Hemophilia is X-linked, and almost all affected children are boys. von Willebrand disease usually is inherited in an autosomal dominant fashion. In the investigation of thrombotic disorders, a personal or family history of blood clots in the legs or lungs, early-onset stroke, or heart attack suggests a hereditary predisposition to thrombosis. The causes of bleeding may be hematologic in origin or due to vascular, nonhematologic causes (Fig. 151-3). Thrombotic disorders can be congenital or acquired (Table 151-1) and frequently present after an initial event (central catheter, trauma, malignancy, infection, pregnancy, treatment with estrogens) provides a nidus for clot formation or a procoagulant stimulus.
Figure 151-1 Diagram of the multiple interactions of the hemostatic mechanism. Solid lines indicate reactions that favor coagulation, and dashed lines indicate reactions that inhibit clotting. Epi, Epinephrine; GAGs, glycosaminoglycans; NO, nitric oxide; PAI, plasminogen activator inhibitor; PGI2, prostaglandin I2 (prostacyclin); TAFI, thrombin-activated fibrinolytic inhibitor; TXA2, thromboxane A2; vWF, von Willebrand factor. (Modified from Scott JP, Montgomery RR: Hemorrhagic and thrombotic diseases. In Kliegman RM, Behrman RE, Jenson HB, Stanton BF, editors: Nelson Textbook of Pediatrics, ed 18, Philadelphia, 2007, Saunders, p 2062.)
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Patients with hemostatic disorders may have complaints ofeither bleeding or clotting. Age at onset of bleeding indicateswhether the problem is congenital or acquired. The sites of bleeding (mucocutaneous or deep) and degree of trauma(spontaneous or significant) required to induce injury suggest the type and severity of the disorder. Certain medications (aspirin and valproic acid) are known to exacerbatepreexisting bleeding disorders by interfering with plateletfunction.
The physical examination should characterize the presence of skin or mucous membrane bleeding and deepersites of hemorrhage into the muscles and joints or internalbleeding sites. The term petechia refers to a non-blanching lesion less than 2 mm in size. Purpura is a group of adjoining petechiae, ecchymoses (bruises) are isolated lesions larger than petechiae, and hematomas are raised, palpable ecchymoses.
The physical examination should also search for manifestations of an underlying disease, lymphadenopathy,hepatosplenomegaly, vasculitic rash, or chronic hepatic orrenal disease. Deep venous thrombi may cause warm, swollen (distended), tender, purplish discolored extremities ororgans or no findings. Arterial clots cause acute, painful,pale, and poorly perfused extremities. Arterial thrombi ofthe internal organs present with signs and symptoms ofinfarction.