# Arterial Blood Sampling

## Overview

This module describes how to obtain an arterial blood sample for blood gas analysis.

## Indications

1. To obtain blood for arterial blood gas analysis (ABG)
2. To obtain blood for investigations if venous sampling has failed

## Contraindications

1. Damaged or infected skin or distorted anatomy at the site

2. AV fistulas or vascular grafts
   AV fistulas or vascular grafts

   An AV fistula is created surgically in renal patients by linking an artery to a vein, causing dilation of the vein for easy access for dialysis. A fistula can be identified by palpating for a thrill over the site. This limb should not be used for routine blood sampling.

   in the limb

3. Severe

   peripheral vascular disease
   peripheral vascular disease

   suggested by a cold, poorly perfused limb with decreased or absent pulses and thin, brittle skin

   in the limb

4. Consider the risks and benefits in patients with coagulopathy or anticoagulation with warfarin or heparin, or recent use of

   thrombolytic
   thrombolytic

   medications used to break up intravascular clots (such as pulmonary embolism or myocardial infarction), including streptokinase, alteplase, or recombinant tissue plasminogen activator (rTPA)

   medication (aspirin is fine)

## Patient information and consent

Always verify your patient’s identity and obtain informed consent before proceeding.

### How do I explain this procedure?

“We need to draw some blood from an artery for testing.”

### What can my patient expect?

“You may feel a sharp sting when I insert the needle. I will only draw a little blood. The test results will come out within a few minutes.”

### What is my patient’s role?

“Let me know if you have any allergies or a bleeding tendency, or use blood thinners. Fearing blood or needles is normal, but tell me if you have fainted from it. Keep as still as possible. If you feel strange sensations or severe pain, tell me immediately. Afterwards, press firmly on the area with cotton wool to prevent bleeding.”

## Preparation

###

### Documentation

1. Patient notes

2. Patient labels

### Equipment

1. Non-sterile gloves

2. Alcohol-based hand rub

3. Sharps container
   Sharps container

   If a sharps container is not within arm's length, use a kidney dish or other hard container to temporarily hold used sharps and to carry them to the sharps container for disposal.

4. Alcohol swab

5. Heparinised syringe OR 2 ml syringe, blunt fill needle and

   heparin
   heparin

   usually in a vial in the fridge

6. Winged set (butterfly needle)

7. Cotton wool and plaster

## Site and Positioning

The preferred site is the radial artery in the wrist. The patient’s arm should be supinated and the wrist dorsiflexed 40°. Before puncturing a radial artery, perform the modified Allen test to see if it is suitable. If neither radial artery is usable, you may use the femoral artery in the groin, or the brachial artery in the upper arm. In these cases the patient should be supine with the leg in neutral, or with the arm supinated and extended respectively.

### Modified Allen Test

1. Ask the patient to make a tight fist.

2. Press firmly
   Press firmly

   on both the radial and ulnar arteries

3. Instruct the patient to open their fist - their hand should be

   pale
   pale

   .

4. Release only the ulnar compression.

5. Colour should return
   Colour should return

   to the entire hand within 15 seconds (positive test).

6. If colour does not return, ulnar circulation to the hand is

   compromised
   compromised

   This is rare, but it may occur in peripheral arterial disease, and sometimes as an anatomical variant.

   and radial artery puncture is contraindicated. Try the other hand, then move to femoral or brachial sites.

## Procedure

Follow medical asepsis with non-sterile gloves.

1. If not using a heparinised syringe,

   heparinise
   heparinise

   Clean the top of the heparin bottle with an alcohol wipe. Pierce the bottle. Holding it upside-down with the needle tip inside the heparin, draw up a small amount (0.2 ml) of heparin and withdraw from the bottle. Pull the plunger back all the way to coat the inside of the syringe with heparin, then push it all the way forward to empty it of excess heparin. Remove the needle and throw it away in a sharps container.

   a syringe.

2. Perform hand hygiene and don gloves.

3. Palpate the position of the arterial pulse with the non-dominant hand. It is useful to make a gentle indentation with your nail to mark this spot or the tip of a needle cap.

4. Clean this area with a swab and allow it to dry. Do not touch this area again. Attach the needle to your syringe.

5. You may wish to palpate again with one finger above and one finger below the puncture site before inserting the needle. Tense the skin by placing the thumb/finger of your non-dominant hand below the puncture site.

6. Insert the needle at a 45° angle with the bevel up. Advance until you enter the artery; you should see blood (flashback) pulsing into the tubing. Withdraw the plunger slowly to fill the syringe. If the flashback does not pulsate, you may have hit a vein — see Troubleshooting.

7. Withdraw the needle and apply firm pressure to the site with a cotton ball. Allow the patient to take this over and continue for 5 minutes.

8. Remove and discard needle in a sharps container.

9. If there is air in the syringe, hold it upright and gently push the plunger to expel the air.

10. Cap the syringe with a stopper.

11. Gently up-end the syringe a few times to mix blood with heparin.

12. Dispose of medical waste safely.

13. Label the syringe with a patient sticker and take it for

    immediate
    immediate

    Often the blood gas machine is in a different part of the ward or hospital. In this case transport the syringe in a kidney dish or other appropriate container rather than by hand or in a pocket.

    analysis.

14. Record completion of the procedure in patient notes.

## Troubleshooting

I have not achieved flashback.

Withdraw until just the tip of the needle is in the puncture site. Make sure you are palpating the pulse, adjust your angle, and try again. If you cannot palpate the pulse anymore, abandon the attempt for now, as there is probably arteriospasm. After

two unsuccessful

two unsuccessful

Multiple attempts will cause pain and frustration and may damage soft tissue/vasculature or distort anatomy, compromising further attempts.

attempts, call a senior for assistance.

I’ve achieved flashback, but it is not pulsatile.

You may have hit a vein. Try re-angling your needle. If still unsuccessful, try again with a new needle and a different entry point. Flashback that appears non-pulsatile may also occur if the patient is in shock, or in cardiac arrest. This may still be arterial blood.

I don’t have a winged set (butterfly needle).

Use a 22 G needle and draw up 2 ml of air into the syringe before entering the artery. The blood should fill the syringe spontaneously in a pulsatile manner.

## Risks

1. Local hematoma, pain, or excessive bleeding at the site

2. Arteriospasm
   Arteriospasm

   Arteriospasm is a transient constriction of the artery. The pulse may be diminished or absent and it may become impossible to draw blood from the artery. This happens more commonly in smaller patients, females, and in more painful or repeated attempts at arterial puncture.

3. Injury to nerves and other local structures

4. Infection at the site

5. Sharps injury to healthcare personnel

6. Vasovagal response (fainting)

## References

1. Brzezinski M, Luisetti T, London MJ. Radial artery cannulation: a comprehensive review of recent anatomic and physiologic investigations. Anesth Analg. 2009 Dec. 109(6):1763-81.
2. WHO Guidelines on Drawing Blood: Best Practices in Phlebotomy. Geneva: World Health Organization; 2010. Available from: https://www.ncbi.nlm.nih.gov/books/NBK138661/
3. Davis MD, Walsh BK, Sittig SE, Restrepo RD. AARC clinical practice guideline: blood gas analysis and hemoximetry: 2013. Respir Care. 2013 Oct;58 (10):1694-703.
4. O’Connell C. Arterial Puncture. In: Essential Clinical Procedures, Third Edition. Philadelphia: Elsevier; 2013. p. 63-70.
5. Dev SP, Hillmer MD, Ferri M. Videos in clinical medicine. Arterial puncture for blood gas analysis. N Engl J Med. 2011;364(5):e7. doi:10.1056/NEJMvcm0803851