Arterial Puncture for Blood Gas Analysis

Abstract

Puncture of the radial artery is the preferred method of obtaining an arterial blood sample for blood gas analysis. The chief indication for blood gas analysis is the need to obtain values for the partial pressures of oxygen and carbon dioxide and for arterial pH. This information is needed in assessing a patient with acute, severe respiratory distress. Measurements of arterial pH and the partial pressures of carbon dioxide and oxygen provide accurate information on the status of acid–base balance and gas exchange. Another indication for arterial blood gas sampling is the need to perform CO-oximetry in order to assess for methemoglobinemia and carboxyhemoglobinemia. Contraindications Radial arterial puncture is contraindicated in the presence of a known deficiency of collateral circulation to the distal upper extremity. A modified Allen test can be performed to assess the adequacy of the collateral circulation of the radial artery by the ulnar artery (Fig. 1). To perform the test, occlude both the ulnar and radial arteries. Instruct the patient to make a fist to drain the blood from the hand; this should be done for approximately 30 seconds. Instruct the patient to unclench the fist. The patient’s palm should appear blanched or pale. Now, release pressure only from the ulnar artery. Adequate collateral circulation is indicated by the return of normal color within 10 seconds. 1 There is no agreement as to whether the Allen test can accurately predict the risk of rare ischemic complications. 2 On the basis of current evidence, its use can be neither refuted nor supported. Alternative techniques to measure collateral circulation of the forearm include color Doppler studies of flow, plethysmography, and magnetic resonance imaging. 3 These methods are more often used in assessing the radial artery for more invasive procedures, such as arterial harvesting for coronary bypass. Radial arterial puncture should not be performed in patients with an overlying skin infection. In patients who are taking anticoagulants or in those with coagulopathies, it should be performed only if absolutely necessary, because of the increased risk of bleeding and hematoma formation. Preparation Standard kits for sampling arterial blood gas are readily available and should contain a syringe, a small 23-to-25-gauge needle (either with a rubber stopper used to remove the needle from the syringe or with an attached safety cap), and a syringe cap containing dry lithium heparin or sodium heparin. The concentration of hepa