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Arterial line insertion and management

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Invasive lines are often essential to the management of critically ill children, but are associated with significant morbidity so necessity should always be carefully considered and lines should  be removed as soon as they are no longer required.


The risk of thrombotic and thromboembolic events is always present, especially with relatively large cannulae in small vessels (see size guide below).


  • Radial is the preferable line. Never place in an ulnar artery in small children.
  • Remove line if blanching or cyanosis. 


  • If limb remains ischaemic after removal, heparinise unless contraindicated

General size guide

  • <3kg 24 guage
  • 3-50 kg 22 guage
  • ≥ 50 kg 20 guage

Arterial line insertion

  • In neonates with cardiac disease or diaphragmatic hernias consider the underlying anatomy before placing arterial line. For example, pre-ductal (right upper limb) arterial lines are more useful than other sites in infants with diaphragmatic hernia or aortic coarctation.
  • Site preference is 1) radial, 2) femoral, 3) axillary, 4) brachial 
    In cases where a pre-ductal BP/ABG is preferable (coarctation, CDH), discuss with the consultant if unsuccessful at obtaining right radial access and before attempting any other sites. Posterior tibial and dorsalis pedis are rarely used but acceptable, provided both are not attempted in the same limb during the admission.
  • Always use adequate sedation and pain relief (consider use of local anaesthesia).
  • The patient will be hidden by sterile drapes and the operator concentrating on the technical procedure, therefore, ensure appropriate monitoring is in place (HR, pulse oximetry and blood pressure cuff both on a different limb to the artery being cannulated, cycling 3 minutely), before beginning procedure.
  • When arterial lines are inserted in a medical emergency and without proper disinfection, the line should be changed within 48 hours where this is feasible.
  • 2% aqueous chlorhexidine should be used for skin antisepsis.
  • Standard sterile precautions involve the use of sterile gloves and small sterile drape.
  • Always position patient carefully and appropriately before beginning the procedure to maximise the chances of successful insertion.
    For radial lines, this often involves a small roll on the dorsum of the wrist & taping the hand (in full supination) temporarily to the bed. Under and over extension of the wrist are both problematic.
    For femoral lines, this involves no flexion or extension at the hip.
  • For operators used to placing arterial lines in adults, remember flashback will often be significantly slower in small patients (due to cannula diameter & patient blood pressure). In very cyanotic children, flashback will often be dark in colour. If in doubt, transduce the line.

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Document Control

  • Date last published: 07 June 2018
  • Document type: Clinical Guideline
  • Services responsible: Paediatric Intensive Care Unit
  • Author(s): Brent McSharry, Dave Buckley
  • Owner: Brent McSharry
  • Editor: John Beca
  • Review frequency: 2 years