I appreciate Dr Burt's interest in the use of the hanging drop technique to identify the epidural space in the thoracic region. While there is a presumption of negative pressure in the thoracic epidural space as a reflection of interpleural pressure, I am not aware of any study which confirms this, nor the effect of spontaneous vs controlled ventilation and explanation of the mechanism of the hanging drop or any other so-called negative pressure technique used to locate the epidural space remains speculative.

I use a lateral approach for insertion of a mid-thoracic epidural, which requires generous infiltration with lidocaine 1% to allow the lamina to be explored with the epidural needle prior to coming off bone into the ligamentum flavum. This allows the lamina to be probed without discomfort to the patient and although the initial injection may be painful very briefly, it is certainly less extensive than the infiltration required for many plastic surgery procedures performed under local anaesthesia. General anaesthesia is certainly not required.

My own practice is to site thoracic epidurals, following explanation, appropriate premedication and (especially) adequate local anaesthesia, in patients who are awake. Apart from potential safety issues in anaesthetised patients, concerns about modification of technique to take account of putative alterations in pressure in the epidural space then become academic.