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Pain Research and Treatment
Volume 2014, Article ID 146750, 10 pages
Review Article

Etiology and Use of the “Hanging Drop” Technique: A Review

1Department of Anesthesiology, Memorial Hospital of Rhode Island, Alpert Medical School, Brown University, 111 Brewster Street, Pawtucket, RI 02860, USA
2Department of Anesthesiology, University of Illinois at Chicago College of Medicine, Jesse Brown VA Hospital, 820 S Damen Avenue, Chicago, IL 60612, USA

Received 9 January 2014; Revised 21 March 2014; Accepted 21 March 2014; Published 15 April 2014

Academic Editor: Donald A. Simone

Copyright © 2014 Ludmil Todorov and Timothy VadeBoncouer. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.


Background. The hanging drop (HD) technique presumably relies on the presence of subatmospheric epidural pressure. It is not clear whether this negative pressure is intrinsic or an artifact and how it is affected by body position. There are few data to indicate how often HD is currently being used. Methods. We identified studies that measured subatmospheric pressures and looked at the effect of the sitting position. We also looked at the technique used for cervical and thoracic epidural anesthesia in the last 10 years. Results. Intrinsic subatmospheric pressures were measured in the thoracic and cervical spine. Three trials studied the effect of body position, indicating a higher incidence of subatmospheric pressures when sitting. The results show lower epidural pressure (−10.7 mmHg) with the sitting position. 28.8% of trials of cervical and thoracic epidural anesthesia that documented the technique used, utilized the HD technique. When adjusting for possible bias, the rate of HD use can be as low as 11.7%. Conclusions. Intrinsic negative pressure might be present in the cervical and thoracic epidural space. This effect is more pronounced when sitting. This position might be preferable when using HD. Future studies are needed to compare it with the loss of resistance technique.