Intravascular lines serve a number of vital functions. They make it possible to give fluids, including glucose and a range of other nutrients, when oral nutrition is impossible or inappropriate. They also make it possible to monitor both arterial and central venous pressure directly and continuously, to collect blood specimens without causing pain or disturbance, and to give drugs reliably and painlessly.

These very real advantages have to be balanced against a range of very real disadvantages. Of these, infection due to localised vasculitis or insidious low-grade septicaemia is perhaps the most common. Vascular thrombosis is a hazard, and thrombi can also shed emboli. Even reactive arterial vasospasm can cause significant ischaemia. Bleeding from an arterial line can cause serious blood loss, life threatening air embolism can occur into any central venous line and fluid extravasation can cause severe ischaemia or chemical tissue damage with subsequent necrosis. Any baby with an intravascular line in place is at risk of sudden fluid overload if steps are not taken to make the unintentional and uncontrolled infusion of more than 30 ml/kg of fluid technically impossible (see the Section on Minimising IV Infusion and Other Drug Hazards). There is also a risk of reactive hypoglycaemia if any glucose infusion is stopped (or the rate changed) too abruptly (see p. 241).

Line care

Thrombosis: Relatively little can be done to reduce the risk of thrombosis. A small amount of heparin (q.v.) may reduce the risk of catheter occlusion, but this has little effect on the formation of mural thrombi. Whether the benefit of full heparinisation outweighs the risk remains unclear. Clinical vigilance can speed the recognition of problems when they occur, and the routine use of a lateral X-ray to identify where any central catheter has lodged can help to ensure that the tip is optimally sited (a lateral X-ray is more easily interpreted than an antero-posterior or AP view). An attempt is usually made to site any central venous catheter in a major vein or at the entrance to the right atrium. The larger the vessel, the less the risk of occlusion (or extravasation), but the greater the hazard should this occur. Similarly, it is standard practice to site any aortic catheter either above the diaphragm (T6) or below the two renal arteries (L4) to minimise the risk of a silent renal or mesenteric artery thrombosis. There is now good evidence that there are fewer recognisable complications associated with high placement (although there may be a marginally increased risk of necrotising enterocolitis). Case controlled studies suggest, however, that intraventricular haemorrhage may be commoner when aortic catheters are positioned above the diaphragm, and when heparin is used to prolong catheter patency. Only a very large properly conducted randomised controlled trial is likely to resolve some of these uncertainties.

Limb ischaemia is usually readily recognised, but by the time it is identified much of the damage has often been done. Thrombosis of the abdominal vessels is often silent, but may be a significant cause of renal hypertension. Central venous thrombosis is also under-diagnosed but can cause a chylous ascites by occluding the exit of the thoracic duct. Occlusion of a small vein is seldom a problem because of the nature of the anastomotic venous plexus, but occlusion of even a small artery can cause severe ischaemia if it is an ‘end-artery’ (i.e. the only vessel supplying a particular area of the body). Even occlusion of the radial artery can sometimes cause vascular compromise if there is no significant terminal anastomosis between the radial and ulnar arteries. Every baby with an intravascular line in place should be examined regularly by the nursing staff for evidence of any of the above complications. There are good grounds for particular vigilance in the first few hours after an arterial line has been sited but, with this one exception, all lines merit equal vigilance. Treatment options are reviewed in a commentary linked to the monograph on the use of alteplase (see p. 68).

Vasospasm: Arteries are particularly likely to go into spasm shortly after cannulation. This may make it necessary to withdraw the catheter, but a single small dose of tolazoline can sometimes correct the acute ‘white leg’ seen after umbilical artery catheterisation, and a continued low-dose infusion may work when a single bolus dose is only transiently effective. Papaverine has also been used experimentally in the same way.

Extravasation: Never give a drug into a drip that has started to ‘tissue’. Delivery cannot be guaranteed once this has happened, and some drugs (as noted in the individual drug monographs) can also cause severe tissue damage. Fluids containing calcium cause particularly severe scaring. Serious damage can also be caused by the fluids used in providing parenteral nutrition. Such problems will only be noticed promptly if every drip is so strapped that the tissue around the cannula tip can be inspected at any time. The best line of management, if extravasation is starting to cause tissue damage, involves early tissue irrigation, as outlined in the monograph on hyaluronidase in p. 258. Hot or cold compresses are of no measurable value. Neither is limb elevation.

Infection: Localised or generalised infection is probably the commonest complication of the use of intravascular lines. Indolent, usually low grade, but occasionally life threatening, blood borne infection (septicaemia) has been reported in more than 20% of all babies with ‘long lines’ in some units. Infection can be devastating in a small baby, and it is a clear indictment of unit policy if the way in which a baby is cared for puts it unnecessarily at increased risk of infection. The risk of such iatrogenic infection can only be minimised by scrupulous attention to hygiene. Inadequate attention to skin sterility (see p. 469) is probably the most common reason why cannulae and catheters have later become colonised. Access should always be achieved using an aseptic approach. A gown, mask and surgical drape should also be used whenever a long line is being inserted. The risk of infection is not reduced by the use of an antiseptic or antibiotic cream. Indeed there is evidence that such use can actually increase the risk of fungal infection. Covering the insertion site with a transparent occlusive dressing helps even though increased humidity under such a dressing can speed the multiplication of skin bacteria. An impregnated chlorhexidine disc may help prevent this.

Infection most frequently enters where the catheter pierces the skin. This is why most infusion-related infections are caused by coagulase-negative Staphylococci and why Broviac® lines that are surgically ‘tunnelled’ under the skin are less prone to infection. Complications, including infection, seem more common in neonates if the line is inserted into an arm rather than a leg. Bacterial colonisation of the catheter hub (where the catheter connects to the giving set) can also be the precursor of overt septicaemia. Stopcocks often become contaminated, but there is no evidence that such contamination causes catheter-related infection. The risk of generalised infection is increased by the use of a long line rather than a short line. Independently of this, parenteral nutrition may, and intralipid certainly does, further increase the risk of systemic infection. Antibiotic treatment for this can, in turn, greatly increase the risk of life-threatening fungal septicaemia. These are strong reasons for avoiding the unnecessary use of long lines and for only using parenteral nutrition when oral feeding is impracticable. Catheters impregnated with an antimicrobial agent have started to become available, but their use is no substitute for proper attention to other aspects of catheter hygiene. Heparin fusions may decrease the risk of thrombosis and infections where use is unavoidable.

It was thought that the risk of infection could be reduced by resiting all infusions at regular intervals, and short cannulas are still often resited in adults once every 2–3 days to reduce the risk of phlebitis and catheter colonisation. There is, as yet, no good evidence that this approach is justified in children. It was also said that fluids and administration sets should be changed daily to minimise the risk of in-use fluid contamination, but this practice is not