Peripheral lines are commonly placed to provide IV access and to provide a route for IV medication or fluids. However they have a very limited time span before they must be changed due the risk of infection its normally every 72 hrs but can be left in place for a maximum of 120 hrs ( 5 days) providing the site is clean, not red, or feels warm/ hot to touch or painful, after this period the risk of Phlebitis (inflammation of the vein)and infection increases dramatically.
Hoverer with most peripheral lines depending on the drug ( usually antibiotics) or the rate of flow of the fluids they would require changing before that. In addition they may require replacing due to accidental dislodgement and occlusion before the 72hr or 120 hr timescale. Its very important with any peripheral lines to stop any infusion or drug administration if you notice any redness or swelling or if the patient complains of pain. As extravasation ( commonly called tissuing) can be a nasty complication and result in skin sloughing, tissue necrosis, thrombophlebitis, venous thrombosis, or severe consequences including functional impairment, residual scarring and disability.
With regards to Central lines ( which comes in single lumen and multi-lumen) which are commonly place in the neck ( internal or external jugular vein), in the Chest ( either Rt or Lt Subclavian vein) or the groin ( Rt or Lt Femoral vein) or it can be done peripherally in in case of a peripherally inserted central catheter (PICC or PIC line) usually in the ( cephalic vein, basilic vein or brachial vein).
These lines can be left in almost indefinitely. Central lines are need for the administration of certain drugs like inotropes ( adrenaline, noradrenaline, dopamine etc), chemotherapy and TPN but are used for access in difficult to cannulate patients. In addition all fluids, blood and blood products as well as all medication can be administered centrally via the central line. However a chest xray is required to confirm the position of a central line if inserted in the neck or chest.
As liquidsky mentioned a bonus of having a central line in is the ability to monitor the Central Venous Pressure (CVP) normally 2-6 mm Hg, however in my clinical environment we like it to be around 8-12 mm Hg. It is an important tool when assessing right ventricular function and systemic fluid status.