Venepuncture complications: haematoma, fainting, nerve injury, and failed draws

Most venepunctures are uneventful. A few are not — and the distance between a complication and a crisis is usually how quickly the phlebotomist recognises what is happening. This guide covers the four complications you will meet most often: the bruise that forms under the skin, the patient who faints, the nerve struck by the needle, and the draw that will not come. Each has a recognisable signature and a structured response.

Haematoma — the most common complication

A haematoma is a collection of blood under the skin, seen as swelling and discolouration around the puncture site. It forms when blood escapes the vein into the surrounding tissue — most often because the needle has passed through the back wall of the vein, or because too little pressure was applied after withdrawal.

The usual causes are:

• The needle penetrating both walls of the vein.
• Inadequate pressure after the needle is removed.
• The patient bending the arm after the draw.
• A fragile or small vein.
• Excessive probing with the needle.

The faint — vasovagal reaction and syncope

A vasovagal reaction is a sudden drop in heart rate and blood pressure, triggered most often by the sight of blood, the anticipation of pain, or prolonged standing. Syncope — the faint itself — is where an untreated reaction ends. It is common, frightening for the patient, and entirely manageable when caught early.

The warning signs come before the faint: pallor, sweating, dizziness, nausea, and a slowing pulse.

If a patient begins to react:

1. Stop the procedure and remove the tourniquet and needle if they are still in place.
2. Lower the head or raise the legs and loosen any tight clothing.
3. Stay with the patient, apply a cool compress to the forehead, and monitor them.
4. Use the recovery position if consciousness is lost, and call for medical help if the episode is severe.

Keep the patient seated or lying and monitored for two to three minutes before they stand again.

Nerve injury — stop the moment it is reported

The median nerve runs close to the basilic vein at the inner edge of the antecubital fossa, which is one reason that vein is a last choice. A nerve injury announces itself with a sharp, electric-shock pain that shoots down the arm, sometimes with numbness, tingling, or weakness in the hand.

A related "blood looks wrong" event is arterial puncture: bright red rather than dark blood, spurting or pulsing with the heartbeat, and a tube that fills unusually fast. Remove the needle immediately and apply firm pressure for at least fifteen minutes.

The failed draw — and the two-attempt rule

A tube that does not fill is a tube the laboratory cannot use. Insufficient sample volume usually comes from one of a small set of causes: a collapsed vein, the needle not quite in the vein, a tube that has lost its vacuum, or blood clotting before the tube is full. A rolling vein is anchored firmly before insertion, not chased once the needle is in.

Recover the draw by repositioning the needle slightly, trying a fresh tube to check the vacuum, lowering the arm below heart level, or asking the patient to make a fist. But know when to stop.

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This guide is a free extract from PhlebMastery's phlebotomy theory course, with content aligned to published WHO guidance. The full treatment — every complication with its figures, procedures, and the incident-reporting that follows — is in Module 9: Complications & Troubleshooting. New here? Start with the free Module 1, or see the whole course — full access is a one-time purchase.