Arterial Puncture Techniques and Blood Component Handling

Arterial puncture is a more complex procedure than venous blood draws, primarily used to obtain arterial blood gas (ABG) samples. ABGs are vital in assessing a patient's respiratory and metabolic status. The most common sites are the radial artery (at the wrist), the brachial artery (in the arm), and the femoral artery (in the groin). The radial artery is preferred due to its accessibility and lower risk of complications. The brachial artery can be used if the radial artery is not accessible. The femoral artery is used as a last resort because of its location, the potential of infection, and the greater difficulty to control bleeding. Before arterial puncture, perform the modified Allen test to assess collateral circulation in the hand. Key risks include hematoma formation, arterial spasm, nerve damage, infection, and, in rare cases, thrombosis. Example: A patient presents with shortness of breath. The physician orders an ABG. After performing the Allen's test and confirming sufficient collateral circulation, the phlebotomist selects the radial artery for puncture.

Patient preparation involves explaining the procedure, obtaining informed consent, and positioning the patient. Palpate the artery to locate the pulse. Clean the site thoroughly with an antiseptic agent (e.g., alcohol wipes), and don gloves. Using a 22-25 gauge needle attached to a heparinized syringe, insert the needle at a 30-45-degree angle (or shallower for femoral) to the artery. Advance the needle slowly until blood pulsates into the syringe. Fill the syringe with the required amount of blood (usually 1-3 mL). Withdraw the needle and immediately apply firm, continuous pressure to the puncture site for 5-10 minutes (or longer for patients on anticoagulants) until bleeding stops. Expel any air bubbles from the syringe, and properly label the specimen. Example: After palpating the radial artery, the phlebotomist inserts the needle. Once blood enters the syringe, the phlebotomist continues until the required blood volume is obtained, and then immediately applies pressure.

After collection, blood is often processed into its components: red blood cells (RBCs), white blood cells (WBCs), platelets, and plasma/serum. Blood is centrifuged to separate these components. Red blood cells settle at the bottom, and the remaining fluid is plasma or serum. Serum is plasma without the clotting factors. Plasma and serum must be stored at the appropriate temperatures to maintain their integrity: Refrigeration (2-8°C) for short-term storage, and freezing (-20°C or colder) for longer-term storage. Specific requirements vary based on the components and tests being performed. Improper handling can lead to hemolysis (destruction of red blood cells), which can affect test results. Example: After centrifugation, the phlebotomist separates the serum for a chemistry panel, storing it in a labeled tube in a refrigerator until testing can be performed.

Blood banking involves the collection, storage, and processing of blood and its components for transfusion. This includes typing and crossmatching to ensure compatibility. Arterial blood gas (ABG) analysis is a critical diagnostic test that measures the levels of oxygen (PaO2), carbon dioxide (PaCO2), and pH in the arterial blood. This information helps clinicians assess the patient's respiratory and metabolic function. Understanding the normal ranges and interpreting ABG results is crucial for proper patient management. Example: An ABG report shows a decreased PaO2 and increased PaCO2, indicating a potential respiratory problem.