Normal Saline Versus Heparinized Solution Flush for Maintaining Patency of Peripheral Venous Catheters in Children

The aim of the study is to verify if the periodic flush with normal saline 0.9% NaCl causes a longer or equal duration of patency of peripheral venous catheters, compared with heparin solution 50 U / ml flush, in children from 2 years to 14 years. Only 22 and 24 gauge catheters Will be included in the study.The study will assess in particular: * the difference of permanence in situ of the device * the difference in incidence of complications (in detail: obstruction, phlebitis, thrombocytopenia, systemic anticoagulation) * the difference in costs between use of saline normal saline 0.9% NaCl solution and heparinized 50 U / ml.