The use of pressure waves to confirm the correct position of the epidural needle has been described in several domestic species and proposed as a valid alternative to standard methods, namely, control radiographic exam and fluoroscopy. The object of this retrospective clinical study was to evaluate the sensitivity of the epidural pressure waves as a test to verify the correct needle placement in the epidural space in dogs, in order to determine whether this technique could be useful not only in the clinical setting but also when certain knowledge of needle’s tip position is required, for instance when performing clinical research focusing on epidural anaesthesia. Of the 54 client-owned dogs undergoing elective surgeries and enrolled in this retrospective study, only 45% showed epidural pressure waves before and after epidural injection. Twenty-six percent of the animals showed epidural pressure waves only after the injection, whereas 29% of the dogs showed epidural pressure waves neither before nor after injection and were defined as false negatives. Our results show that the epidural pressure wave technique to verify epidural needle position lacks sensitivity, resulting in many false negatives. As a consequence, the applicability of this technique is limited to situations in which precise, exact knowledge of the needle's tip position is not mandatory. 1. Introduction Locoregional anaesthesia is becoming increasingly popular in veterinary medicine. Among the different techniques, epidural administration of local anaesthetics and analgesics is nowadays widely employed in canine clinical patients, especially when performing orthopedic procedures involving the hind limbs [1, 2]. Beside its clinical application, within the last decade, epidural anaesthesia has been the focus of a large number of experimental investigations [3–5]. A proper needle placement into the epidural space is essential to correctly perform the technique and also to forecast the likelihood for the epidural injection to result in successful analgesia. Confirmation of the proper needle positioning is useful in the clinical setting and mandatory when performing clinical studies in which the epidural injection plays a central role. Several techniques have been described to verify the correct needle placement into the epidural space. Traditionally, the “pop sensation,” the “hanging drop” (HD), and the “loss of resistance” techniques have been used in the clinical setting [6–8]. These methods have the advantage of being inexpensive; however, they are based on subjective perceptions, which
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