The use of an acoustic device to identify the extradural space in standing horses.

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.

Clinical results with the acoustic puncture assist device, a new acoustic device to identify the epidural space.

UNLABELLED: Sixty patients scheduled for lumbar epidural anesthesia were included in a study in which we evaluated the efficacy of localizing the epidural space by means of an acoustic signal. A prototype of an acoustic puncture assist device, connected to the epidural needle by an extension tube, generated the pressure needed to perform the epidural puncture and translated this pressure into corresponding acoustic and visible signals. The device frees the anesthesiologist to handle the epidural needle with both hands and to detect the epidural space by means of these signals. In all 60 patients (100%), the epidural space was successfully located by using the acoustic signal. In all cases, this was confirmed by the pressure measurement, which proved to be a reliable indicator for correct identification of the epidural space. We conclude that it is possible to locate the epidural space by means of the acoustic puncture assist device. The method proved to be reliable, safe, and simple in this study. The benefits of this new epidural puncture technique include better needle control, teaching, control of correct catheter placement, and documentation. The last can be an important adjunct to anesthesia practice. IMPLICATIONS: The authors demonstrate that it is possible to identify the epidural space by an acoustic and visible signal. An experimental setup constructed for this purpose makes the epidural puncture procedure audible and visible.