Children undergoing treatment for cancer will often require repeated blood tests and insertion of cannulas to enable chemotherapy and other drug treatment to be given. Even though doctors and nurses are very experienced at taking blood and inserting cannulae, it can sometimes hurt and is not a pleasant experience for the child.

Many children therefore have a special device called a central line, which is used to take samples of blood and to administer chemotherapy and other drugs (such as antibiotics). It can also be used to give blood or platelet transfusions.

A central line is a fine plastic tube, which is inserted into a vein in the child's chest. This procedure is carried out under a general anaesthetic. When inserting the line, the surgeon makes a small cut into a vein in the neck and feeds the line down towards the heart. The other end is then tunnelled under the skin to emerge on the front of the chest as an external line.

Although inserted in a similar fashion, some lines do not come out through the skin. Instead, the line ends in a reservoir or 'port' that is buried under the skin As nothing comes out through the skin ports can be easier to look after but they still need to be accessed with a needle.

Central lines can remain in place for many months and are a very good way of avoiding the discomfort of repeated injections. However, the main risk associated with central lines is infection. Anytime a foreign body dwells inside the blood vessel, an increased risk of infection exists. Most of these infections are caused by skin bacteria. Attempts will be made to clear the infection with antibiotics, but sometimes the catheter may have to be removed.

Clotting inside the catheter, or outside around the catheter tip, may cause blockage of the catheter lumen or obstruction of the blood vessel the catheter is in. It may be impossible to draw blood from the catheter, or even to flush it or use it for infusion.

Heparin or urokinase may be tried to clear the blockage. Central lines can also slip out or get dislodged but this becomes less likely the longer the duration from insertion.

Your nurses and doctors will advice you on the care for your child's central line.