ARTERIAL BLOOD GAS USMLE

I. Indications 

A. A sample of arterial blood is used to determine the partial pressure of O2 (pO2), CO2 (pCO2), and the pH of blood. Accurate determination allows for the detec- tion of hypoxia, hypercarbia, and complex acid-base disorders.
 B. Many blood gas analyzers provide additional useful information to the physician, including  electrolytes,  glucose,  lactate,  hemoglobin,  carboxyhemoglobin,  and methemoglobin levels.

II. Contraindications (Relative)

 A. Bleeding diatheses.
B. Possible future use of thrombolytics.
C. Severe peripheral vascular disease.
D. Abnormal skin (burn, dermatitis, infection).

III. Equipment 

A. A commercially available ABG kit includes povidone-iodine or alcohol swab, 3–5 cc syringe (heparinized), 22-gauge needle, gauze pad, collection bag, band-aid, and needle cap .
B. Additional supplies include gloves, lidocaine (1%), a 25- or 27-gauge needle, a folded sheet or “kidney” basin to extend the wrist, and tape.

IV. Procedure:

A. Position the wrist over a folded sheet to extend it approximately 30º.
B. Palpate the radial artery at the proximal flexor crease of the wrist just medial to the
radial styloid and lateral to the flexor carpi radialis tendon.
C. Prepare the skin with a povidone-iodine or alcohol swab.
D. Raise a skin wheal with 1% lidocaine over the site. This has been shown to signifi￾cantly decrease the pain of the procedure and does not affect success rate.
E. Pull the plunger of the heparinized syringe up to 2 cc. (Some ABG kits have syringe
plungers that automatically rise with the pressure of arterial blood, making this step
unnecessary. This added feature helps distinguish arterial blood from venous blood.)
F. Hold the syringe with one hand like a pencil, while the other hand palpates the ra￾dial pulse more proximal to the site of insertion.
G. At a 30–45° angle, and with the bevel of the needle up, insert the needle through
the skin wheal and into the radial artery.
H. Blood flow should be brisk (if arterial). The color of the blood will not accurately
distinguish arterial from venous blood.
I. If blood does not fill the syringe, withdraw the needle to just below the skin sur face and redirect the needle. Movement of the needle at any significant depth
under the skin should be absolutely avoided because it may lacerate the artery.
J. After obtaining blood return, withdraw the needle and apply pressure with gauze
for 5 minutes to prevent hematoma formation. Placing the gauze on the forearm
before the procedure will allow the physician easy access to the gauze.
K. Remove and dispose the needle in a red sharps container.
L. Cap the syringe and carefully expel any air within the syringe.
M. It is necessary to put the sample on ice ONLY if it will take more than 10 minutes
to put the blood into the blood gas analyzer.

Complications:

 Infection, bleeding, neuropathy, pseudoaneurysm, arteriovenous fistula

SOURCE : USMLE