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Many hemorrhagic disorders in children are caused by genetic defects, but there exist a number of important acquired conditions that can lead to abnormal coagulation and subsequent bleeding complications. These conditions occur in disparate clinical situations ranging from otherwise healthy-appearing neonates to critically ill children with multiorgan failure. The most important of these conditions are hemorrhagic disorders that result from vitamin K deficiency, liver failure, or disseminated intravascular coagulation (a condition that can lead to both bleeding and thrombosis). Other conditions include acquired platelet dysfunction (see Chapter 435), coagulopathies of hypothermia and extracorporeal life support, and acquired inhibitors to specific coagulation proteins.



Vitamin K deficiency bleeding (VKDB) in the newborn, previously known as hemorrhagic disease of the newborn, is classified as early, classical, or late (Table 433-1). Early-onset occurs in the first 24 hours of life and is due to the cross-placental transfer of compounds that interfere with vitamin K metabolism or function, including some anticonvulsant drugs, antibiotics, antituberculous agents, and vitamin K antagonists. Classical VKDB occurs in the first week of life and is due to a physiological deficiency in vitamin K at birth combined with a lack of vitamin K in breast milk or inadequate feeding. Vitamin K prophylaxis has its biggest impact in preventing this type of bleeding. Late-onset VKDB can occur at any age, although it is classically described as occurring between 2 weeks and 6 months of age. In infants, it is again due to inadequate vitamin K content in breast milk and is thus found almost universally in those exclusively breastfed. In older children (though often in infants as well), additional factors that cause reduced vitamin K intake and absorption are necessary. Some examples of conditions that lead to late-onset vitamin K deficiency are liver or pancreatic disease, both leading to an inability to absorb fat-soluble vitamins; gastrointestinal disorders that affect intestinal flora, because a secondary source of vitamin K is production by intestinal microorganisms; prolonged antibiotic use due to an alteration of intestinal flora; and ingestion (accidental or otherwise) of vitamin K antagonists that, while perhaps not technically causing vitamin K deficiency, can be overcome with vitamin K therapy (see Table 433-1).


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