Central venous and arterial access in children — formative SAQs

SAQ 1 (10)

A 3-year-old, 14 kg child in septic shock needs central venous access to deliver an adrenaline infusion, and is also thrombocytopenic with a platelet count of 35. You are asked to place the line. [8]

1. State and justify the central venous site you would choose for this child, and explain why the subclavian site is avoided. (4) [3] [8]
2. Outline the steps of the ultrasound-guided Seldinger technique you would perform at your chosen site. (4) [1]
3. Describe how you would confirm correct catheter tip position, and outline your CLABSI prevention bundle. (2) [11] [12]

Model answer

Site choice and why subclavian is avoided. The femoral vein is the first choice for this child. It is fully compressible against the pubic ramus, it is pneumothorax-free, and it can be placed while the child is being resuscitated without turning the head, which suits the emergency setting. The subclavian vein is avoided in a thrombocytopenic child because the subclavian artery lies behind the clavicle and cannot be compressed; a subclavian arterial puncture bleeds invisibly into the chest and can become a haemothorax. The femoral vein lies medial to the femoral artery in the femoral sheath, the NAVL relationship, which makes it ultrasound-friendly and safe. [3] [8]

Ultrasound-guided Seldinger technique. Identify the femoral vein in a short-axis view just below the inguinal ligament, confirming it is the medial, compressible, non-pulsatile structure relative to the artery. Prepare the skin with chlorhexidine and allow it to dry, apply full barrier precautions, and raise a skin wheal with lidocaine 1 per cent (maximum 3 mg/kg without adrenaline). Advance the needle to the vessel under ultrasound, watching the tip enter the lumen, and confirm dark non-pulsatile venous blood. Pass the guidewire through the needle, withdraw the needle, make a small skin nick, dilate the tract, and railroad the catheter over the wire. Remove the wire, aspirate and flush every lumen, secure the line, and confirm the tip. [1]

Tip confirmation and CLABSI bundle. Confirm the tip at the cavoatrial junction on a post-procedure chest radiograph, or by ultrasound-based tip navigation such as the ECHOTIP approach, and exclude a pneumothorax. The CLABSI prevention bundle is full barrier precautions at insertion, chlorhexidine skin antisepsis, a chlorhexidine-impregnated dressing, scrub-the-hub before each access, avoidance of routine flushing, and a daily review of line necessity with prompt removal. [11] [12]

SAQ 2 (10)

A 6-year-old in diabetic ketoacidosis needs an arterial line for frequent blood gas sampling and continuous blood pressure monitoring. The radial site is planned. [5]

1. Describe the Allen test and explain what an abnormal result means for site choice. (3) [5]
2. Outline how you would perform an ultrasound-guided radial arterial cannulation and choose an appropriate cannula gauge. (4) [6]
3. Describe two complications of arterial lines, how you would recognise them, and how you would prevent them. (3) [8]

Model answer

Allen test. Compress both the radial and ulnar arteries at the wrist, ask the child to clench and open the fist to blanch the palm, then release the ulnar artery and watch for reperfusion of the palm within seconds. A brisk flush confirms an intact ulnar collateral supply and makes the radial artery safe to cannulate. A delayed or absent flush indicates poor ulnar collateral flow, and a different arterial site should be chosen because sacrificing the radial artery would risk hand ischaemia. [5]

Ultrasound-guided radial cannulation and gauge. After the Allen test, identify the radial artery in a short-axis view lateral to the flexor carpi radialis tendon, dorsiflex the wrist with ulnar deviation, and approach the artery with an in-plane or out-of-plane needle under ultrasound, using the acoustic-shadowing technique if the vessel is hard to see. A guidewire-assisted or direct cannula technique places a 22 gauge cannula in an older child (24 gauge in an infant). Transduce the line to confirm a crisp arterial waveform and bright pulsatile blood before securing it. [6]

Complications and prevention. First, arterial thrombosis with distal limb ischaemia, recognised by a cold, pale, pulseless hand or foot and a dampened or absent waveform; it is prevented by choosing the smallest effective cannula, confirming collateral flow, checking distal perfusion hourly, and removing the line as soon as it is no longer needed. Second, haematoma at the puncture site, recognised by swelling and bruising; it is prevented by firm proximal pressure after a failed attempt or removal and by correcting any coagulopathy before the procedure. Infection is a lower-rate complication than for central lines but is prevented by the same aseptic discipline. [8]