An arterial line (A-line) is a specialized, thin catheter inserted directly into one of the body’s arteries. It is routinely used in intensive care units and operating rooms for patients requiring continuous, highly accurate physiological monitoring. The primary function is to provide real-time, beat-to-beat blood pressure readings, offering precision unmatched by a standard arm cuff. The line also serves as a closed access point for taking frequent blood samples, particularly for arterial blood gas analysis, without requiring repeated needle sticks.
Understanding the Arterial Line
The arterial line accesses the high-pressure side of the circulatory system, unlike a standard intravenous (IV) line or a central venous catheter. Arteries carry oxygenated blood away from the heart, resulting in substantially higher pressure than in veins. This pressure difference requires a specialized setup, including a continuous pressurized saline flush system, to prevent blood from clotting within the narrow catheter.
The insertion site is typically the radial artery in the wrist, preferred due to its superficial location and the presence of collateral circulation. Other common sites include the femoral artery in the groin or the brachial artery in the arm. Since the catheter is placed in an artery, it provides access to arterial blood, which is necessary for measuring precise oxygen and carbon dioxide levels in the blood, known as an arterial blood gas (ABG) analysis.
An arterial line is strictly a monitoring and sampling tool, not for administering fluids or medications. Accidental injection of medication into an artery, which feeds oxygen-rich blood directly to tissues, could cause severe harm, including tissue death. The continuous fluid infusion is a slow, pressurized saline solution used only to maintain the catheter’s patency. The real-time waveform display on a bedside monitor allows providers to observe subtle changes in the patient’s hemodynamic status instantly.
Steps for Drawing the Blood Sample
Drawing a sample from an arterial line requires a closed system to maintain sterility and prevent contamination. The process begins by preparing the access port, typically a stopcock or dedicated sampling chamber near the patient. This port must be thoroughly disinfected before any manipulation.
The first step is to clear the line of the continuous flush solution. This is done by withdrawing a specific volume of blood, known as the “waste volume,” into a dedicated syringe or collection chamber. This initial draw is crucial because the flush solution, usually saline, would dilute the sample and lead to inaccurate laboratory results, especially for blood gas values.
Protocols generally require a waste volume of 3 to 10 milliliters to ensure the tubing is filled with undiluted arterial blood. Once the waste volume is secured, the stopcock is repositioned to collect the fresh blood sample into the appropriate laboratory tube or syringe. The blood flows readily due to the high arterial pressure.
After the diagnostic sample is collected, the waste blood is either discarded or re-infused, depending on the system used. Finally, the line must be flushed vigorously with the pressurized saline solution to ensure no residual blood remains in the catheter lumen. This prevents clotting and blockage. Proper function is confirmed by observing a clear, sharp waveform on the monitor.
Risks and Safety Precautions
Drawing blood from an arterial line carries specific risks that require strict adherence to safety protocols. Infection is a concern, which can be local at the insertion site or progress to a systemic bloodstream infection. To mitigate this, providers must use sterile technique during access, including meticulous hand hygiene and disinfection of the needleless port.
Occlusion of the artery, or a blockage, is a potential complication often resulting from a blood clot at the catheter tip. This can impair circulation to the extremity distal to the insertion site, such as the hand if the line is in the radial artery. Staff monitor the limb continuously for signs of poor circulation, including changes in color, temperature, or sensation, to detect this complication early.
The high-pressure arterial system also risks hemorrhage if the line or its connections become compromised or disconnected. A sudden disconnection can result in rapid blood loss, requiring immediate manual pressure and securing the line. Additionally, the pressurized system risks introducing air bubbles into the arterial circulation, potentially causing an air embolism.
Safety measures include securing the line firmly to the patient’s skin to prevent accidental dislodgement. Specialized closed systems are used to minimize the chance of air entry. Staff training focuses on maintaining the integrity of the closed system and confirming the appropriate functioning of the pressure bag and flush device.