Diagnostic anesthesia is an essential part of most lameness examinations for horses, but interpretation of diagnostic anesthesia is often confusing when a nerve block results in only amelioration rather than resolution of lameness. When that happens, clinicians must decide whether the improvement in lameness was caused by incomplete resolution of signs of pain originating from 1 site in the blocked portion of the limb or the presence of painful lesions at other sites in the unblocked portion of the limb, which necessitates further investigation. Results of recent studies1,2 suggest that poor efficacy of the local anesthetic used for a nerve block should also be considered as a cause of incomplete resolution of lameness during diagnostic anesthesia. The use of a local anesthetic that is highly efficacious for pain desensitization in a nerve block should facilitate interpretation of diagnostic anesthesia results because it would eliminate poor anesthetic potency as a possible cause of incomplete resolution of lameness. The use of local anesthetics that produce an insufficient duration of analgesia can also interfere with interpretation of diagnostic anesthesia results, especially when multiple sites of pain contribute to the lameness and multiple nerve blocks have to be serially administered. In horses, use of a local anesthetic that has a sufficient duration of analgesia is also important for desensitization of a surgical site for standing surgery.
In human medicine, it is well established that the addition of epinephrine to a local anesthetic solution prolongs the analgesic effect by counteracting the vasodilatory effects that most local anesthetics have on neural vasculature, which slows the clearance of the local anesthetic from the injection site.3–6 A notable exception is ropivacaine, which is a local anesthetic with intrinsic vasoconstrictive properties.7 Epinephrine can also intensify the analgesic effect of a nerve block.3,5,6
The purpose of the study reported here was to determine whether the addition of epinephrine to a lidocaine solution would prolong and intensify the analgesic effect of lidocaine when the combination was administered as a PDNB in horses with signs of pain isolated to a foot. Our hypothesis was that the addition of epinephrine to a lidocaine solution would prolong and intensify the analgesic effect of lidocaine.
No third-party funding or support was received in connection with this study or the writing or publication of the manuscript. The authors declare that there were no conflicts of interest.
The authors thank Britta Fischer for technical assistance.
Maximum head height
Minumum head height
Mechanical nociceptive threshold
Palmar digital nerve block
Lidocaine hydrochloride 2%, Hospira Inc, Lake Forest, Ill.
STATA, version 8.1, Stata Corp, College Station, Tex.
Lidocaine hydrochloride 1%, Hospira Inc, Lake Forest, Ill.
Epinephrine (1:1,000), Hospira Inc, Lake Forest, Ill.
Equinosis LLC, Columbia, Mo.
Keegan KG, Department of Veterinary Medicine and Surgery, College of Veterinary Medicine, University of Missouri, Columbia, Mo: Personal communication, 2017.
Force Ten FDX Compact Digital Force Gage, Wagner Instruments, Greenwich, Conn.
SAS, version 9.1, SAS Institute Inc, Cary, NC.
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