An arterial line (A-line) is a thin catheter inserted into an artery, usually the radial artery in the wrist. This device provides highly precise, continuous blood pressure monitoring, which is more accurate than a standard cuff. It also offers direct access for frequent blood sampling. A-lines are used in hospital settings to manage critically ill patients and require strict protocols performed by trained medical professionals.
Why Use an Arterial Line and Necessary Equipment
The primary function of an A-line is to provide a moment-to-moment display of blood pressure, essential when patients receive medications that rapidly affect circulation. For blood collection, the A-line allows frequent sampling for arterial blood gas (ABG) analysis without repeated needle punctures. This access significantly reduces patient discomfort and trauma. Analyzing arterial blood accurately measures oxygen, carbon dioxide, and the body’s pH balance, providing immediate insight into respiratory status.
Before beginning the procedure, the necessary equipment must be assembled to maintain sterility and efficiency. A minimum of two syringes is required: one for collecting the initial waste volume (often 10-milliliters) and a specialized pre-heparinized syringe for the arterial blood gas sample.
Necessary Equipment
The required equipment includes:
- Antiseptic solution, such as a chlorhexidine or alcohol swab.
- Sterile gloves to prevent infection.
- Appropriate laboratory collection tubes.
- A new, sterile cap to seal the sampling port once the procedure is complete.
Detailed Steps for Sample Collection
Begin the procedure with meticulous hand hygiene and donning sterile gloves. The sampling port, typically located on the three-way stopcock closest to the patient, must be thoroughly cleaned with the antiseptic swab. Allow the swabbed area to dry completely according to product guidelines. This prepares the surface for access and minimizes pathogen introduction.
The first step involves manipulating the stopcock, which controls the flow within the system. Rotate the stopcock to close off the flow to the flush solution bag and the pressure transducer. This opens the circuit between the patient’s artery and the sampling port, isolating the sampling area from the continuous flush system.
Waste Volume Collection
Connect the designated waste syringe to the port and withdraw the initial volume of fluid and blood. This creates a “waste volume” containing the colorless flush solution (typically saline) pumped through the line to prevent clotting. Discarding this volume clears the line of dilute fluid that would otherwise contaminate the specimen and lead to inaccurate test results.
The recommended discard volume generally ranges from 3 to 10 milliliters to ensure the removal of the flush solution and residual heparin. Once the waste volume is collected, briefly turn the stopcock to the “off” position for the port. Detach the waste syringe and immediately discard it into a biohazard container, preparing the port for the clean, undiluted blood specimen.
Attach the syringe intended for the lab test, such as the pre-heparinized ABG syringe, firmly to the sampling port. Rotate the stopcock once more to open the pathway. Arterial pressure will push fresh blood into the syringe until the required volume is collected. Once the sample is obtained, close the stopcock to the patient and remove the syringe.
To ensure the integrity of the ABG sample, immediately expel any visible air bubbles from the syringe. Exposure to air can alter the measured oxygen and carbon dioxide levels. Cap the syringe securely to prevent air entry and send it to the laboratory for analysis without delay.
Maintaining Line Patency and Preventing Contamination
After sample collection, return the stopcock to its original monitoring position, re-establishing the connection between the patient, the transducer, and the flush system. Next, activate the in-line flush device. This rapidly pushes solution through the catheter to clear any remaining blood from the stopcock and catheter tip. Flushing maintains patency and prevents blood clot formation inside the catheter.
Clean the sampling port again with an antiseptic swab to remove blood residue, then seal it with a new, sterile, non-vented cap. This prevents infection and ensures the integrity of the closed system. Check all connections throughout the line to confirm they are secure, preventing accidental disconnection, blood loss, or air entry into the artery.
Properly dispose of all used materials, including syringes and wipes, in the appropriate biohazard receptacles. Accurately document the procedure details, including the time the sample was drawn and the patient’s current settings, in the medical record. This provides a complete record of the intervention and ensures continuity of care.