To obtain arterial blood for blood gas measurements.
When blood is needed and venous or capillary blood samples cannot be obtained.
Equipment. A 23- to 27-gauge scalp vein needle or a 23- to 25-gauge venipuncture needle (self-shielding safety type recommended), a 1- or 3-mL syringe, povidone-iodine and alcohol swabs, a 4 × 4 gauze pad, gloves, and 1:1000 heparin.
For a blood gas sample, most hospitals already have 1-mL syringes coated with heparin. If this is not available, draw a small amount of heparin (concentration 1:1000) into the syringe to be used for submitting the blood gas sample and then discard the excess heparin from the syringe. The small amount of heparin coating the syringe is sufficient to prevent coagulation of the sample. Excessive heparin may interfere with laboratory results, causing a falsely low pH and PaCO2. If any other laboratory test is to be performed, do not use heparin.
The radial artery is the most frequently used puncture site and is described here. Alternative sites are the posterior tibial or the dorsalis pedis artery. Femoral arteries should be reserved for emergency situations. Brachial arteries should not be used because there is minimal collateral circulation and a risk of median nerve damage. Temporal arteries should not be used because of the high risk of neurologic complications.
Check for collateral circulation and patency of the ulnar artery by means of the Allen test. Elevate the arm and simultaneously occlude the radial and ulnar arteries at the wrist; rub the palm to cause blanching. Release pressure on the ulnar artery. If normal color returns in the palm in <10 s, adequate collateral circulation from the ulnar artery is present. If normal color does not return for >15 s or does not return at all, the collateral circulation is poor and it is best not to use the radial artery in this arm. The radial and ulnar arteries in the other arm should then be tested for collateral circulation.
Use of topical local anesthetic agents may diminish pain from arterial puncture. Oral sucrose given 2 min prior to the procedure (0.1–1.5 mL of a 24% solution depending on gestational age) and/or pacifier are preferred. (See Chapter 69.)
To obtain the sample, take the patient's hand in your left hand (for a right-handed operator) and extend the wrist. Hyperextension can occlude the vessel. Palpate the radial artery with the index finger of your left hand (Figure 21–1). Transillumination with a high-intensity fiberoptic light or marking the puncture site with a fingernail imprint may be helpful.
Clean the puncture site with a povidone-iodine swab (preferred for blood cultures) and then with an alcohol swab.
Puncture the skin at about a 30-degree angle, and slowly advance the needle with the bevel up until blood appears in the tubing (see Figure 21–1). With arterial blood samples, little aspiration is usually needed to fill the syringe. If there is no return of blood, withdraw the needle slowly because the artery may have been punctured through and through. Using the bevel down ...
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