An infant with an indwelling umbilical artery catheter develops a vasospasm in one leg. The nurse notifies you that another infant with an indwelling umbilical line has no pulses in the lower legs with severely decreased perfusion. Infants are at a high risk for thromboembolism because of their immature hemostatic system and smaller vessel size, and the fact that they require frequent catheter use. The majority of neonatal thromboembolisms are iatrogenic from umbilical artery or venous catheters, indwelling central catheters, and peripheral arterial lines.