Clinical meaning
An arterial line (A-line) is an invasive catheter placed in a peripheral artery (most commonly radial, but also femoral, brachial, or dorsalis pedis) for continuous blood pressure monitoring and frequent arterial blood gas sampling. The radial artery is preferred due to collateral circulation from the ulnar artery (assessed by Allen test before insertion). The arterial waveform displays the cardiac cycle: the upstroke represents ventricular ejection (systole), the dicrotic notch represents aortic valve closure, and the downslope represents diastole. The transducer must be leveled at the phlebostatic axis (4th intercostal space, mid-axillary line) and zeroed to atmospheric pressure for accurate readings. Complications include hemorrhage from disconnection, thrombosis, infection, arterial spasm, and distal ischemia. Never administer medications or fluids through an arterial line, as arterial injection can cause tissue necrosis.
Exam relevance
Risk factors: - Hemodynamic instability requiring continuous BP monitoring - Frequent arterial blood gas sampling needs in respiratory failure - Vasopressor therapy requiring precise titration to MAP goals - Critical care patients with unreliable non-invasive BP readings - Peripheral vascular disease increasing risk of arterial thrombosis