ARTERIAL BLOOD SAMPLING & PERIPHERAL ARTERIAL LINE CANNULATION

ARTERIAL BLOOD SAMPLING & PERIPHERAL ARTERIAL LINE CANNULATION


Preparation :

• Topical anaesthetic (TA)
• Alcohol swab
• Needle size 27
• Catheter size 25
• Heparinised saline in 5cc syringe, T-connector
• Heparinised saline (1 u/ml) for infusion

Indications :

1. Arterial blood gases
2. Invasive blood pressure monitoring
3. Frequent blood taking

Complications :

1. Arteriospasm which may lead to ischaemia and gangrene.
2. Neonates especially – digital and limb ischaemia which can lead to partial and complete limb loss.

Procedure :

1. Check the ulnar collateral circulation by modified Allen test.
2. The radial pulse is identified. Other sites that can be used are posterior tibial and dorsalis pedis artery.
3. A topical anaesthetic may be applied half an hour before procedure.
4. Clean the skin with alcohol swab.
5. Dorsiflex the wrist slightly. Puncture the skin and advance the catheter in the same direction as the radial artery at a 30-40 degrees angle.
6. The catheter is advanced a few millimetres further when blood appears at the hub, then withdraw the needle while advancing the catheter.
7. Aspirate to ensure good flow, then flush with heparinised saline.
8. Peripheral artery successfully cannulated.

• Ensure that the arterial line is functioning. The arterial pulsation is usually obvious in the tubing.
• Connect to T-connector and 3-way stop-cock to a syringe pump.
• Label the arterial line and the time of the setting.

9. Run the heparinised saline at an appropriate rate:

• 0.5 to 1.0 mL per hour for neonates.
• 1.0 mL (preferred) or even up till 3.0 mL per hour for invasive BP line (to avoid backflow in bigger paediatrics patients).

10. Immobilize the joint above and below the site of catheter insertion with restraining board and adhesive tape.


Precaution - Prevention of digital & limb ischaemia :

1. AVOID end arteries e.g. brachial (in cubital fossa) and temporal artery (side of head) in babies (BEWARE - both these arteries can be accidentally cannulated and mistaken as ‘veins’).

2. Test for collateral circulation

• If a radial artery is chosen, please perform Allen’s test (to confirm the ulnar artery collateral is intact) before cannulation.
• If either the posterior tibial or dorsalis pedis artery on one foot is chosen, ensure that these 2 arteries are palpable before cannulation.

3. Circulation chart
Perform observation and record circulation of distal limb every hour in the NICU
and PICU, and whenever necessary to detect for signs of ischaemia, namely:

• colour - pale, blue, mottled
• cold, clammy skin
• capillary refill > 2 seconds

4. Treatment of digital / limb ischaemia

• This is difficult as the artery involved is of small calibre.
• Refer vascular surgeon if available / orthopaedic surgeon.
• May consider warming the contralateral unaffected leg to induce reflex vasodilatation if part of one leg is affected (see section on UAC).
• Anticoagulant drugs and thrombolytic agents are unlikely to be beneficial.

5. Reminder

• Prevention of limb ischaemia is of utmost importance.
• Early detection of ischaemia is very important in order to avoid irreversible ischaemia.
• If the patient is in shock, the risk of limb ischaemia is greater.
• Small and preterm babies are at greater risk for ischaemia.
• The risk of limb ischemia is greater with fast infusion rate (e.g. > 1 ml per hour).
• No fluid or medication other than heparinized saline can be given through arterial line. This mistake can occur if the line is not properly labelled, or even wrongly labelled and presumed to be a venous line.