ARTERIAL PUNCTURE (ABG ANALYSIS)
REQUIREMENTS:
Verbal consent, Gauge Piece, Syringe, 23G needle (for radial or brachial artery) OR 21-22G needle (for femoral artery), Sterile gloves, Antiseptic skin solution (generally ethanol is used), cotton, sterile gauze piece
Lithium heparin - 1-2 mL lithium heparin (1000 U/mL) should be aspirated into the syringe through another sterile needle and then pushed out; the plunger should be left depressed to allow the arterial blood flow to fill up the syringe.
For arterial blood gas analysis, when heparin isn't available, do the following:
1) Collect blood in green vacutainer
2) Attach a new needle to the syringe
3) Aspirate blood from the vacutainer
4) Remove any air bubbles
PROCEDURE:
- Take all aseptic precautions.
- First do Allen’s Test if planning to do a radial artery puncture to assess collateral circulation.
i. Firm occlusive pressure is held on both the radial artery and the ulnar artery
ii. (see the first image below).The patient is asked to make a fist and open it, repeatedly till the palmar skin is blanched (see the second image below). Overextension of the hand or wide spreading of the fingers should be avoided, because it may cause false-normal results. The pressure on the ulnar artery is released while occlusion of the radial artery is maintained (see the third image below). The time required for palmar capillary refill is noted. (It should be ≤7 seconds normally).
- Attach the heparinised syringe attached to another sterile 23G needle
- Palpate the location of radial Artery
- Wrist should be positioned in extension
- Clean the puncture site for 30 sec
- Warn the patient for sharp scratch
- Insert the needle at 30- 45°
- Aim towards maximum point if pulsation. Draw the plunger up once blood is seen in the syringe.
- Remove the needle.
- Ask the relative or patient to continue to apply firm pressure over the puncture site for 5 minutes (to ensure haemostasis)
- Recap the needle (not advisable because of the risk of needle-stick injury but done because special ABG syringes and needles are generally not available). For recapping, place the cap of needle over a surface like bed or table and then insert the needle inside the cap. DO NOT pick up the cover of needle to recap it (to prevent needle-stick injury).
**When in doubt if you have had a needle prick or not, remove your gloves and fill it with water and look for any leak. If present, it is likely that you have had a needle prick.
- An abnormal Allen test: Consider attempting to puncture at a different site.
- Local infection or distorted anatomy at the potential puncture site (eg, from previous surgical interventions, congenital or acquired malformations, or burns).
- The presence of arteriovenous fistulas or vascular grafts, in which case arterial vascular puncture should not be attempted.
- Known or suspected severe peripheral vascular disease of the limb involved.
- Severe coagulopathy
- Anticoagulation therapy with warfarin, heparin and derivatives, direct thrombin inhibitors, or factor X inhibitors; aspirin is not a contraindication for arterial vascular sampling in most cases
- Use of thrombolytic agents, such as streptokinase or tissue plasminogen activator.
COMMON SITES FOR ARTERIAL PUNCTURE:
- ABG sampling is usually performed on the radial artery because the superficial anatomic presentation of this vessel makes it easily accessible.
- Other sites include: femoral or brachial artery (present medial to tendon of biceps brachii).
PRACTICAL TIPS & TRICKS:
- If arterial blood flow is not obtained, the operator might slowly pull back the needle; it is possible that the needle has gone through the vessel
- Initial arterial flow may subsequently be lost if the needle moves outside the vessel lumen; reidentification of the arterial pulse, using the nondominant middle and index finger, and repositioning the needle in the direction of the vessel could be attempted; avoid blind movement of the needle while it is inserted deeply in the patient’s body—pull it back to a point just below the skin, and redirect it to the arterial pulse felt with the other hand
- Puncture of venous structures can be identified by lack of pulsatile flow or dark-coloured blood, though arterial blood in severely hypoxemic patients can also have a dark appearance; if venous blood is obtained, removal of the needle from the patient might be necessary to expel the venous blood from the syringe
- Excessive skin and abundant soft tissue may obstruct the puncture site; the operator can use the nondominant hand to smooth the skin, or an assistant can remove the subcutaneous tissue from the puncture site field
- Incomplete dismissal of heparin solution from the syringe could cause falsely low values for the partial pressure of CO; to avoid this, the operator should expel all heparin solution from the syringe before arterial puncture
- Incomplete removal of air bubbles can cause falsely elevated values for the partial pressure of oxygen; to avoid this, the operator should be sure to completely remove air bubbles from the syringe (vented plungers have an advantage over standard syringes in this regard)
- Avoid puncture of the brachial artery or femoral artery in patients with diminished or absent distal pulses; the absence of distal pulses may signal severe peripheral vascular disease.
Written by our guest author - ABHISHEK GANACHARYA
Illustrations by Devi Bavishi
