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Dr. Ajith Kumar J MD
Dept. of Emergency Medicne
KIMS, Kollam
India
editor@emmedonline.com

correct technique for taking an abg ...

SITE

Radial artery is the commonest site as it easily accessible and more comfortable for patients.
Other common sites are femoral, brachial, dorsalis pedis.

PROCEDURE

Put on protective gloves and sit in a comfortable position facing the patient.
With the patient’s hand supinated and wrist slightly hyperextended, palpate the radial artery. Excessive hyperextension may obliterate the pulse.
Cleanse the skin with an alcohol swab .

With 25 Gauge needle, inject 1% Lidocaine indradermally to raise a wheal at the point where the skin puncture is made.

Use 22 G Needle with 5ml syringe
Wet the needle and syringe with sodium heparin (1000U/ml) . Express all excess solution.
With the needle, enter the artery at an angle of approximate 45 degrees to long axis of the vessel .
Advance the needle into a radial artery until a blood flashback appears, then allow the syringe to fill to appropriate level. DO NOT PULL BACK THE PLUNGER.
Immediately after obtaining the specimen, expel any tiny air bubbles to ensure that the specimen will be anaerobic and then cap the syringe.
Roll the blood sample between both palms for 5 -15 seconds to mix the heparin and blood.

MODIFIED ALLEN’S TEST

The patient’s hand is initially held high with the fist clenched.
Both radial and ulnar arteries are compressed firmly by two thumbs. This allows the blood from hand to be drained.
The hand is lowered and fist is opened (It will appear pale).
The pressure from the ulnar artery is released while radial artery is occluded.
Pink colour should return within 6 seconds indicating that the ulnar artery is patent and superficial palmar arch is intact.
Test is considered abnormal if colour doesn’t returns to normal within 10 seconds.

SAMPLING ERRORS

Inappropriate collection and handling of arterial blood specimen can produce incorrect results.

If ABG specimen is not analyzed within 1 minute of being drawn or not immediately cooled to 2 Degree, the PO2 and pH falls and PCO2 will rise because of cellular respiration and consumption of oxygen by leukocytes, reticulocytes and platelets .

The heparin can decrease the pH if acidic heparin is used and the dismissal of heparin from the syringe is incomplete . It can also dilute the PaCO2, resulting in a falsely low value. The amount heparin used should be minimized and atleast 2ml of blood should be obtained.

Diffusion gas from plastic syringe and consumption of oxygen by leukocytes is a potential source of error that results in low PaO2 when the sample is left for prolonged periods at room temperature.
Air bubbles that exceed 1 to 2% of blood volume can cause a falsely high PaO2 and a falsely low PaCO2. The magnitude of the error depends upon the difference in gas tensions between blood and air. It can decreased by gently tapping on syringe to remove the bubbles after the sample has been withdrawn and analysing the sample as soon as possible.

Complication

Updated on 18/1/2017

Reference

WHO Practice on drawing blood : Best practices in phlebotomy.2010.
Irwin & Rippe’s Intensive Care Medicine.
Importance of correct handling of samples for the results of the blood gas analysis. Harsten A.

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emmedonline
Dr. Ajith Kumar J MD
Dept. of Emergency Medicne
KIMS, Kollam
India
editor@emmedonline.com