Chapter 9. Venepuncture
Background physiology
Before a student attempts to take blood, it is important that she has a basic understanding of the system that transports blood around the body.
Blood vessels
There are three types of blood vessels:
Arteries are large vessels that carry oxygenated blood away from the heart to the tissues. Arterioles are small arteries that deliver blood to the capillaries.
Capillaries are microscopic vessels that connect arterioles and venules. They are so narrow that a red blood cell may have to fold to pass through them (Rankin 2005). They are found close to almost every cell in the body, permitting the exchange of gases, nutrients and waste. Venules (where several capillaries unite) collect blood from capillaries and drain it into veins.
Veins return blood to the heart from the capillary network. They have a thinner vessel wall than arteries and are the vessels from which blood is taken for laboratory analysis.
The veins of the arm are divided into two groups: deep and superficial. The superficial veins which run along the antecubital fossa (inside the elbow) provide the best location for venepuncture.
Changes in pregnancy
During pregnancy there is an increase in blood volume and cardiac output accommodated by a decrease in peripheral resistance (Stables & Rankin 2005). Progesterone relaxes the smooth muscle that surrounds the walls of the veins, leading to vasodilation. Thus pregnant women often have excellent veins for venepuncture purposes.
Venepuncture
Venepuncture generally refers to the activity involving the puncture of a vein with a needle to take a sample of blood for analysis in the laboratory. You may come across the term phlebotomy: phleb = vein and otomy = cut into. It is a procedure that may be undertaken at any point in the childbirth continuum, depending on the condition of the woman; however, there are particular points throughout pregnancy when blood analysis is indicated.
Equipment
There are two main ways in which blood is taken: using a needle and a syringe or using a vacuum system.
Needle and syringe
This system involves the use of a sterile needle and syringe to extract blood from the vein. Sterile, disposable needles are used and the practitioner should check that the seal on the package is unbroken. The size of the syringe should correspond to the amount of blood required and a 21 gauge (green) needle should be used (Johnson & Taylor 2006). The needle should be attached to the syringe, cover intact, before attending to the client to avoid causing unnecessary anxiety. The plunger of the syringe should be withdrawn very slightly as this will enable ‘flash back’ (when blood is seen at the tip of the syringe, confirming that a vein has been punctured) to be observed. When a number of tests are required, it is necessary to transfer blood from the syringe to the individual specimen bottles. This method is potentially hazardous to the practitioner, who may sustain a needle stick injury during the process.
Vacuum system
This system includes a needle that attaches to a disposable plastic cuff into which a pre-vacuumed bottle is connected. When more than one blood sample is required, the needle remains in the vein and bottles are interchanged into the cuff. Blood does not seep out of the cuff during this process as there is a rubber sheath covering the cuff end of the needle that retracts back over the needle when the bottle is removed. The vacuum system has specifically designed needles that have two covered ends. The shortest (white) end is removed first and attached to the plastic cuff, using a screw action. The cover to the sharp end of the needle (green) remains intact until just before venepuncture takes place to keep the needle free from contamination.
Blood bottles
Each individual blood test requires a specific amount of whole blood or serum. Therefore a specific specimen bottle is required for each test. The bottles are colour coded and may contain a medium that enables the blood to be transported to the laboratory in optimum condition for subsequent analysis; for example, to prevent it from clotting. The pre-vacuumed bottles are also primed to take the required amount of blood, and therefore stop filling when an adequate sample has been withdrawn. So, for example, the bottle used to take blood for random blood sugar analysis (RBS) is small and stops filling very quickly, whereas the bottle used for a full blood count (FBC) is larger and fills almost to the top. Blood bottles have an expiry date and this should be checked prior to use.
Alcohol swab
The skin should be thoroughly cleaned prior to puncture and it is recommended that this should be with a 70% alcohol solution and allowed to dry for 30 seconds (Beyea & Nicoll 1996).To prevent re-contamination, the vein should not be palpated after swabbing.
Tourniquet
A tourniquet is an elasticated band used to achieve venous pooling, making the vein distended and more readily targeted. It is applied to the upper arm about 10cm from the antecubital fossa (inside of the elbow). It should not be so tight that it stops arterial blood flow, causing the arm to change colour. The veins can be made more prominent by asking the woman to clench and unclench her fist, as the muscle action will encourage venous return. It is worth spending time locating the most suitable vein rather than literally ‘having a stab at it’. The best vein is not always the largest or most visible. Students can develop the skill of palpating a vein using the pad of the index finger, feeling the springy nature of the vein beneath the skin. The student is advised to become familiar with the various types of tourniquet, ensuring that s/he knows how to release it using one hand. Many commercial companies provide tourniquets to professionals as a means of advertising their products. Ensure that you are not breaking local policy by inadvertently promoting baby milk companies, for example.
Non-sterile gloves
Local policy will probably require you to wear gloves for this procedure to prevent cross infection from client to the practitioner. All body fluids should be regarded as a source of potential infection and direct contact with them should be prevented where possible. Wearing gloves will not prevent needle stick injury, however, and measures should be taken to minimize this risk.
Sharps box
A sharps box is a specially designed repository for contaminated needles and broken glass ampoules. They come in a range of sizes and are located in clinical rooms in hospital and community clinics, in a place that is out of reach to members of the public and especially of small children. You should take a sharps box with you to undertake venepuncture, to avoid the hazard of transporting used needles. The needle should not be removed from the syringe but placed in the sharps box as a unit. It is important that the box does not become over-full as there may be a temptation to apply pressure in order to fit the syringe in the box, potentially resulting in injury from the contents. Never re-sheath a needle as this may result in a needle stick injury.
Additional equipment
You will also need: cotton wool ball (to apply to the puncture site to aid haemostasis), an adhesive dressing (to cover puncture site) and a clean metal or plastic receiver (cardboard trays are not appropriate as they are often re-used but not washable and therefore become a potential source of cross infection).
Procedure
This clinical skill requires considerable dexterity and confidence. It is advisable that the student does not attempt this procedure until she has observed the technique many times. S/he can begin to gain competence by identifying and gathering the necessary equipment and filling out the appropriate laboratory blood forms. S/he can practise identifying suitable veins by applying a tourniquet to fellow students or obliging midwives. Ideally s/he should have the opportunity to practise handling the equipment in a clinical simulation unit, before attempting the procedure on a woman. S/he must work under the direct supervision of a registered midwife until competent and confident. The student must be mindful not to undertake any duty that she is not trained to perform (NMC 2004).
The procedure for taking venous blood from an adult is described using the framework outlined in the introductory chapter. See Box 9.1 for an outline of the procedure for venepuncture.
Box 9.1
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Procedure for venepuncture
■ Consult the client’s plan of care
Rationale To ensure that the client’s condition is monitored effectively
■ Gain verbal consent from the client
Rationale To ensure that the woman understands what the test involves and what the implications of the result might be
■ Discuss the procedure with the client, identify the best arm to use
Rationale To allay fears and correct misconceptions. To identify problems the client may have had with the procedure in the past, involving the client in her care
■ Assess the possibility of confounding factors
Rationale To avoid the possibility of contamination and ensure that the results reflect the true clinical picture
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