Abstract
Objective
To determine the usefulness of an acoustic device to confirm correct placement of
extradural needles in horses.
Study design
Prospective experimental study.
Animals
Twelve adult healthy horses weighing between 434 and 640 kg.
Materials and 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).
Conclusion and clinical relevance
The acoustic device is useful to assist in the identification of successful or unsuccessful
extradural needle placement in the horse.
Keywords
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Article info
Publication history
Accepted:
May 15,
2009
Received:
February 17,
2009
Identification
Copyright
© 2010 Association of Veterinary Anaesthetists and American College of Veterinary Anesthesia and Analgesia. Published by Elsevier Inc. All rights reserved.
