Arterial puncture or arterial blood gas sampling is a necessary procedure in the evaluation of any critically ill patient, especially those with significant respiratory distress or compromise. The ability to measure (and interpret) pH, PCO₂, and PO₂ in these patients is an essential skill for the pediatric hospitalist. Although the procedure itself is similar to venipuncture or phlebotomy, there are significant potential complications that all people who perform the procedure must be aware of.

Arterial puncture is performed for limited sampling and is a routine procedure in the management of critically ill and injured children.¹ Arterial blood gas sampling provides information about lung ventilation through the interpretation of PCO₂ and information about tissue oxygenation through the interpretation of PO₂ for patients with respiratory distress and/or cardiovascular compromise, and is often needed to clarify abnormal capnography or pulse oximetry readings. Quantification of the levels of dyshemoglobins such as carboxyhemoglobin and methemoglobin may be obtained as well. Acid–base problems are associated with a number of diseases, such as diabetic ketoacidosis, shock, severe dehydration, metabolic diseases, and certain toxic ingestions. These conditions are often diagnosed by, or treatment decisions are based on, the interpretation of arterial pH, PCO₂, and bicarbonate (HCO₃) levels.

Collateral circulation of the hand must be assessed when attempting radial artery puncture or catheterization. The Allen test is a simple procedure that has demonstrated consistent and valid results in the assessment of collateral blood flow to the hand.^2,3 It is performed by placing pressure to occlude the radial and ulnar arteries simultaneously for 20 seconds at the wrist. During that time, the patient’s hand is elevated above the level of the heart while making a tight fist. The clenched fist is released, and one observes the hand become pale from decreased circulation. After the hand blanches white, one releases pressure over the ulnar artery while retaining pressure over the radial artery. If the patient has adequate collateral circulation, the hand should flush or become pink again as a sign of restored circulation within 5 to 7 seconds. Arterial puncture should not be attempted at that site if return of perfusion takes longer, indicating inadequate collateral circulation. In a young, difficult, or unconscious patient, a modified Allen test can be performed (Figure 190-1).

Extra precautions should be taken when performing arterial blood sampling on patients receiving anticoagulants or those with bleeding disorders. Arterial access should be avoided when the patient has an infection or burn of the overlying skin puncture site.