Venepuncture and venous access

Published on 09/04/2015 by admin

Filed under Hematology, Oncology and Palliative Medicine

Last modified 22/04/2025

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Venepuncture and venous access

Obtaining a sample of venous blood from a patient is the most commonly performed practical procedure in haematology. The technique is apparently straightforward but poorly performed venepuncture can both upset the patient and compromise the quality of the sample. Gaining venous access for the delivery of fluids, blood or drugs is also fundamental to good haematological practice. This section is an overview of venepuncture and venous cannulation. These skills are best learnt by practice with expert supervision.

Taking a venous blood specimen (venepuncture)

The patient should be the correct patient – check their identity! Most serious haemolytic transfusion reactions arise from careless identification of patients and incorrect form labelling. Patients should sit or lie comfortably in such a way that no serious injury could result from a faint. The operator washes his hands and wears plastic gloves – insist on gloves that fit properly. The procedure is explained to the patient and the necessary consent obtained. The presence of a little transient pain when the needle is inserted should be acknowledged but not exaggerated.

Under normal circumstances blood is most easily taken from a vein in the antecubital fossa; the median cubital vein is preferred (Figs 52.1 and 52.2). It is considerate to ask whether the patient is left- or right-handed and then to choose the non-dominant arm. A tourniquet is applied well proximal to the site. This should cause distension of the veins but not discomfort. Gentle palpation is the best method of identifying a vein and checking its patency. If a suitable vein proves elusive it may help to gently tap the area or to warm the arm in water. The skin over the chosen vein is thoroughly cleaned with antiseptic solution. Usually a 21- or 22-gauge needle is used but a smaller size (e.g. 23) can be used where the veins are fragile, or in children. The syringe should be adequate for the sample – where larger blood samples necessitate more than one syringe a ‘butterfly needle’ may be preferred to a conventional venepuncture needle. The needle is inserted bevel uppermost along the line of the vein at an angle of around 20°. There is a distinctive ‘give’ as the vein is entered. Blood is aspirated into the syringe slowly to avoid haemolysis. The tourniquet is released and the needle withdrawn after a dry swab has been held to the site. Pressure should be applied by the patient or an assistant with the arm held straight or slightly elevated. The needle is removed from the syringe – not resheathed – and placed directly into a sharps container. The specimen is expelled gently from the syringe into the relevant bottles. Mixing with anticoagulant is best achieved by gently inverting the bottle several times – violent shaking will damage the sample. An adhesive plaster can be applied to the venepuncture site (check for allergy) when bleeding has stopped.

Fig 52.1 Veins at the antecubital fossa.
The median cubital vein is preferred for routine venepuncture.

Fig 52.2 Taking blood from a vein in the antecubital fossa.

The above describes the procedure for a conventional needle and syringe. Increasingly, venepuncture is performed using closed evacuated container systems where a double-ended venepuncture needle is screwed into a holder and the evacuated tube inserted into the holder following entry of the vein. Blood is automatically aspirated into the tube as the vacuum is released. It is important to understand how the system works before undertaking venepuncture.

Venous access

Peripheral venous cannulation

Almost all haematology patients admitted to hospital require a drip to infuse fluids, blood products or drugs. Before inserting a cannula into a vein, an appropriate giving set should be prepared in accordance with instructions and the bag or bottle containing the infusion fluid inverted and hung on the drip stand. The set should be properly primed and all bubbles excluded. The operator must wash hands and wear gloves. It is vital to ensure that the patient is comfortable and fully understands the procedure and that necessary consent is obtained. The choice of cannula depends both on the quality of the veins and the duration and type of infusion. For short-term infusions or small veins a winged metal cannula (butterfly needle) is often suitable. In other circumstances a larger gauge plastic cannula is used (Fig 52.3). In adults, 18–20-gauge catheters provide good flow rates without too much discomfort for the patient.

Fig 52.3 A large gauge plastic cannula.

The best site is the non-dominant forearm or the dorsum of the hand. The antecubital fossa is best avoided as it is uncomfortable to have the elbow immobilised. A tourniquet is applied and the skin cleaned as for venepuncture. The skin at the site may be stretched slightly to immobilise the vein. The cannula assembly (metal needle and surrounding plastic cannula) is introduced through the skin and into the vein. Once blood enters the cannula chamber or is easily drawn into a syringe, the tourniquet is released and the metal needle withdrawn from the plastic cannula which may be advanced further into the vein. The pre-prepared giving set is attached to the cannula and fluid allowed to enter the vein while the insertion site is carefully inspected for possible extravasation. The needle is promptly disposed of in a sharps receptacle. To minimise the chance of the drip being infected or dislodged the site is protected with a sterile dressing and the cannula secured with a bandage or adhesive tape.

The most common problem is failure to locate a vein in the favoured sites. A more experienced operator may be successful. Where problems persist in experienced hands, other veins such as those in the region of the ankle or the subclavian, jugular or saphenous veins may be cannulated. Regular inspection of the drip site and careful hygiene will minimise the chance of infection. Where there is local inflammation or an otherwise unexplained bacteraemia, the cannula should be removed and another site used.

Central venous cannulation

Insertion of wide-lumen silicon rubber catheters (generally referred to as Hickman catheters) is routinely undertaken in clinical haematology where recurrent intravenous access is required. Examples include:

patients with haematological malignancy receiving intensive chemotherapy

patients with thalassaemia having regular blood transfusions

children with haemophilia A on prophylactic factor VIII treatment.

The catheter is normally inserted into the subclavian vein and the location of the distal tip checked on X-ray (Fig 52.4). The proximal end of the catheter can be tunnelled under the skin with an exit site on the anterior chest wall. A catheter cuff within the tunnel promotes the formation of fibrous tissue which helps secure the device. The procedure is usually performed in the operating theatre by a surgeon or anaesthetist. Once in place the catheter may be used for several months. Strict aseptic technique is necessary as infection with coagulase-negative staphylococci is the most common complication.