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Intra-arterial Blood Pressure
| Recording of blood pressure from a peripheral artery allows beat4o-beat monitoring and provides a reliable access site to obtain blood samples to monitor arterial blood gases, pH, and electrolytes and hemoglobin. Although several peripheral arteries are available for cannulation (radial, brachial, femoral, dorsalis pedis, superficial temporal), the radial artery is most commonly selected. Before cannulation, adequacy of collateral flow via the ulnar artery ought to be considered. An Allen test can be performed by simultaneously occluding the radial and ulnar arteries and asking the patient to make a tight fist. This forces blood from the hand and the palmar surface becomes blanched and pale. Pressure over the ulnar artery is then released, and the patient is instructed to open the hand, avoiding hyperextension of the fingers. Return of color to the palmar surface of the hand within 15 seconds is considered to represent adequate collateral blood flow in the hand. Alternatively, a pulse oximeter placed on the thumb can be used instead of skin color to judge the adequacy of perfusion. Traditionally, inadequate collateral ulnar arterial blood flow, as suggested by the Allen test, has been considered a relative contraindication to insertion of a catheter into the corresponding radial artery. Nevertheless, there is evidence that adverse events do not follow cannulation of the radial artery in the presence of an abnormal Alan test. Furthermore, decreased or absent radial arterial blood flow after removal of the catheter (presumably as a result of emboli) is usually of little or no clinical significance. The inescapable conclusion is that radial artery cannulation is a low-risk, high-benefit monitoring technique that deserves frequent use. |
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