To obtain blood for arterial blood gas measurements.
When blood is needed and venous or capillary blood samples cannot be obtained. Not preferred.
To obtain ammonia levels. Venous blood can be used if it is collected, transported appropriately, and done quickly, but because ammonia levels in peripheral venous blood can be affected by many variables, arterial blood is preferred.
To obtain lactate and pyruvate levels. Free-flowing arterial blood; stasis of blood increases lactate.
To obtain a large quantity of blood that would be difficult to obtain from a peripheral vein.
Sterile gloves, a 23- (preferred for term infants) or 25-gauge (preferred for preterm infants) butterfly needle with extension tubing or venipuncture needle (safety-engineered self-shielding), 1- or 3-mL syringe, povidone-iodine and alcohol swabs, 4 × 4 gauze pad, preheparinized syringes (if not available, use a thin coat of 1:1000 IU/mL heparin in the syringe and plunger to prevent coagulation) or self-contained blood gas kit, high-intensity fiberoptic light for transillumination, Doppler ultrasound, a portable ultrasound (can be useful to locate the artery). Use a cap, mask, sterile gloves, and small sterile drape if obtaining a blood culture.
For a blood gas, most hospitals have kits with 1-mL syringes coated with heparin. If this is not available, draw a small amount of heparin (1:1000) into the blood gas syringe (coat the surfaces and discard excess heparin from the syringe). The small amount of heparin coating the syringe is sufficient to prevent coagulation. Excessive heparin may falsely lower pH and PaCO2. If any other laboratory test is to be performed, use another syringe without heparin. Available arteries to use:
Low-risk preferred sites. Radial, posterior tibial, and dorsalis pedis arteries.
Radial artery. The radial artery is the most frequently used site, is the recommended site, and is described in detail here. The radial artery lies superficially at the underside of the forearm between the radial styloid process and lateral to the flexor carpi radialis tendon. Advantages of the radial artery site include the following: its superficial location is easily accessed, it is easy to palpate and puncture, there are no large veins nearby, there is good collateral circulation, and there are no nerves adjacent to the artery that could be injured.
Posterior tibial artery (preferred second site). The posterior tibial artery lies posterior to the medial malleolus and is in the best position for puncture when the foot is in dorsiflexion. It has good collateral circulation, it is easy to puncture, and there are no large veins nearby.
Dorsalis pedis artery (preferred third site). The dorsalis pedis artery is on the dorsal surface of the midfoot, draw an imaginary vertical line between the first and second toe. It has good collateral circulation, but because it is a small artery, it may be difficult to puncture. If using this artery, do an Allen ...