title: The use of an acoustic device to identify the extradural space in standing horses.
abstract: OBJECTIVE
  To determine the usefulness of an acoustic device to confirm correct placement of extradural needles in horses.
  
  
  METHODS
  Prospective experimental study.
  
  
  METHODS
  Twelve adult healthy horses weighing between 434 and 640 kg.
  
  
  METHODS
  Horses were sedated, placed in stocks and subjected to caudal extradural anaesthesia using lidocaine 2%. For extradural puncture an 18 gauge Tuohy needle connected to an acoustic device via an electronic pressure transducer was used. This device allowed recording of the extradural pressure profile and the transformation of pressure changes into an audible signal. Extradural needle advancement was stopped and the local anaesthetic administered when either a sharp decrease in sound pitch occurred or a 'pop' sensation was felt. Correct needle placement was assessed clinically by the degree of extradural anaesthesia present using needle prick stimuli, loss of tail tone and occurrence of localized sweating. Descriptive statistical analysis was used for evaluation of the data.
  
  
  RESULTS
  Extradural anaesthesia was successful in nine of 12 horses. In these horses during extradural needle advancement the pitch of the audible signal first increased and abruptly changed to a constant low pitched sound. In the three horses with unsuccessful punctures only a slight decrease of the pitch was noted. A 'pop' was clearly distinguished in five of nine horses with successful extradural puncture. In four horses a 'pop' was not present despite correct extradural needle placement. In three horses with incorrect needle placement a 'pop' was present. In the horses with correct needle positioning the median extradural pressure after the puncture was -0.8 kPa (-6 mmHg).
  
  
  CONCLUSIONS
  The acoustic device is useful to assist in the identification of successful or unsuccessful extradural needle placement in the horse.
authors.affiliation: Division of Anaesthesiology and Perioperative Intensive Care, Clinical Department for Small Animals and Horses, University of Veterinary Medicine, Vienna, Austria. i.iff@liv.ac.uk
authors.forename: Isabelle
authors.initials: I
authors.lastname: Iff
authors.forename: Martina
authors.initials: M
authors.lastname: Mosing
authors.forename: Timo
authors.initials: T
authors.lastname: Lechner
authors.forename: Yves
authors.initials: Y
authors.lastname: Moens
mesh_terms: D000162:Acoustics / Q000295:instrumentation; D000767:Anesthesia, Epidural / Q000379:methods / Q000662:veterinary*; D000818:Animals; D001314:Auscultation / Q000295:instrumentation / Q000662:veterinary*; D006736:Horses / Q000033:anatomy & histology / Q000601:surgery; D006801:Humans; D007268:Injections, Epidural / Q000379:methods / Q000662:veterinary*