An instrument for detecting penetration of the epidural space comprises a barrel within which a plunger is urged forwardly by a resilient strap. The barrel has a nose on which a Tuohy needle is mounted. The inner surface of the barrel has a groove that extends along the barrel, being spaced from the...http://www.google.es/patents/US4414983?utm_source=gb-gplus-sharePatente US4414983 - Medico-surgical instruments
