BLOODY TAP

Cannulation of an epidural vessel may occur with either the needle or the catheter during siting of an epidural. Its incidence is uncertain since widely varying figures have been quoted (e.g. 5–45%), possibly related to different methods of locating the epidural space, different needles or different definitions. It is thought to be less likely when the paramedian approach is used, when 5–10 ml fluid is injected before threading the catheter and when smaller needles are used.

Bloody tap is important because if unrecognised, injection of local anaesthetic solution intravenously instead of epidurally may result in systemic toxicity (depending on the drug and dose) as well as not producing a block; and continued bleeding from a punctured vessel (e.g. after the epidural has been resited) may theoretically lead to an epidural haematoma if coagulation is impaired.

Problems/special considerations

Diagnosis is not usually a problem, especially if the needle has punctured a vessel. Puncture of a vessel by the catheter may be marked by discomfort as the vessel wall is pierced. Blood may then be aspirated from the catheter – although this is not always the case, hence the use of a test dose. Similarly, the absence of a bloody tap does not guarantee correct placement of the catheter.

Management options

If blood flows from the needle there is no option other than to remove the needle and reinsert it at a different interspace.