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

The research explores the efficacy of an acoustic device in correctly identifying the extradural space in horses for anesthetic administration. The investigators claim positive results in nine out of twelve horses, with the device being able to clearly differentiate between successful and unsuccessful attempts at puncture.

Methods

• The study involved twelve healthy adult horses, each weighing between 434 and 640 kg. These horses were sedated and placed in stocks.
• A caudal extradural anesthesia was administered using 2% lidocaine.
• An 18 gauge Tuohy needle, connected to an acoustic device through an electronic pressure transducer, was used for the extradural puncture. This setup allowed recording of the extradural pressure profile and converting the changes in pressure into an audible signal.
• Extradural needle advancement was halted and the local anesthetic was administered when a sharp decrease in sound pitch occurred or a ‘pop’ sensation was felt.
• The correct placement of the needle was evaluated clinically by assessing the degree of extradural anesthesia using needle prick stimuli, loss of tail tone, and the occurrence of localized sweating.

Results

• The acoustic device successfully detected correct extradural space needle placement in nine out of twelve horses.
• In successful punctures, the pitch of the audible signal first increased and then abruptly changed to a constant low-pitched sound.
• In the three unsuccessful punctures, only a slight decrease in pitch was observed. This indicates the ability of the device to differentiate between successful and unsuccessful extradural needle placements.
• In five of the nine horses in which the extradural puncture was successful, a ‘pop’ was clearly distinguished. However, in four other horses, this ‘pop’ was absent despite successful needle placement, suggesting that a ‘pop’ sensation is not a definitive indicator of correct needle placement.

Conclusions

• The acoustic device proved valuable in identifying successful or unsuccessful extradural needle placements in horses.
• While the pitch change in the audible signal served as a good indicator of correct placement, the ‘pop’ sensation was not consistently reliable.
• The findings suggest potential for the use of similar acoustic devices in improving the accuracy of extradural anesthesia administration in horses and potentially other large animals.