Use of central venous catheters has become standard in the treatment of many chronic conditions during childhood and for the acute treatment of critically ill infants and children. However, these catheters can be associated with numerous complications, including thrombosis at the tip or in the lumen causing difficulty with its overall function. Even more concerning is the occlusion of large veins into which the catheter is placed, which could predispose patients to pulmonary embolism or postthrombotic syndrome.
Recent research has focused on identifying risk factors for catheter-related thrombosis in children and determining methods for diagnosing deep venous thrombosis associated with a catheter in the upper extremities. Evidence now exists that as many as 50% of children with catheters develop deep venous thrombosis; however, most events are clinically silent. Few clinical trials have studied prevention of catheter-related thrombosis in pediatric patients.
Data regarding incidence, treatment, and long-term outcome of catheter-related thrombosis in children are limited. Although central venous catheters are extremely important in the supportive care of sick children, concerns remain about their immediate and long-term safety.
Abbreviations:LMWH low molecular weight heparin
Central venous catheters have been used in children for the last 20 years. Short-term nontunneled external catheters have made the treatment of critically ill children easier [1–3], and tunneled catheters, either external or implanted, have greatly facilitated the management of chronic conditions such as cancer, hemophilia, renal disease, and cystic fibrosis [1,4,5,6•,7]. A tunneled catheter is imbedded into subcutaneous tissue to be secured for a longer duration. Implanted catheters are tunneled catheter systems accessed through an infusion port located under the skin of the chest wall. Use of central catheters has also allowed patients to receive intravenous medications at home, alleviating the additional stress and cost of hospitalization. Although femoral venous catheterization is common in intensive care units and umbilical catheterization is the primary choice for neonates, most central catheters used on a long-term basis are inserted into the upper venous system (subclavian, brachiocephalic, jugular veins, or superior vena cava [1–5,6•,7].
Central catheters are popular with both patients and physicians and have become standard in the care of children who need long-term intravenous medications, nutrition, or blood products; however, they are associated with diverse complications [1–3,8,9••,10–12,13••,14–17]. At the time of insertion, patients can develop pneumothorax, chylothorax, or arterial puncture [1,2,8]. Later complications can include infection, mechanical breakage, and thrombotic occlusion [9••,10–12,13••,14,15]. The rate of complications varies among the different patient populations in which catheters are used. For instance, infection rates can be as high as 4.3 per 1000 catheter days in children with cancer  and as low as 0.14 per 1000 catheter days in patients with hemophilia . Although the most commonly recognized complication is infection [5,6,10,11], the diagnosis of thrombosis related to a central line is becoming increasingly prevalent.
The clinical presentation and the time to development of thrombosis depend on the reason for and duration of catheter use. In the intensive care setting, complications can be seen within 4 days of insertion , with newborns having the highest rate of symptomatic thrombosis [2,3]. Prospective studies in adult patients with cancer demonstrate radiographic evidence of deep venous thrombosis or occlusion in as many as two thirds of patients with central venous catheters [18,19,20•,21•]. Investigators at the authors' institution recently reported that as many as 50% of childhood cancer patients (12 of 24) and hemophilia patients (10 of 22) had radiographic evidence of catheter-related thrombosis [15,16]. However, the time to development of vessel occlusion in the hemophilia population was much longer than in children with cancer . The potential serious complications of deep venous thrombosis (whether catheter-related or not) include recurrent thrombosis, loss of subsequent intravenous access, pulmonary embolism, postthrombotic syndrome, and death [1,9••,12,13••,21•,22,23]. In children with acute catheter-related thrombosis in the upper or lower venous systems, morbidity from pulmonary embolism or postthrombotic syndrome has been reported by the Canadian Registry of Venous Thromboembolic Complications to be 6.5% to 9.4%, and mortality to be 2.2% [13••,14]. However, these retrospective registry-based data have not been validated, and risk of morbidity has not been defined for specific pediatric populations. A large proportion of catheter-related thrombotic events are clinically silent (ie, patients are asymptomatic), but the long-term outcome of the associated vascular damage and occlusion is not known [13••,14–16,23,24]. It is unclear whether these children will exhibit recanalization of the involved vessel lumen or formation of extensive collateral vessels around the occluded vein.