The type of tourniquet used to target antibiotics directly at localized infections in horses, typically in the joints of the lower limbs, affects the success of the technique, the researchers report.
The use of analgesia is also linked to the success of the technique, known as regional intravenous limb infusion.
It is widely used in equine medicine to treat lower limb infections, including joints affected by synovial sepsis.
The procedure is generally considered successful if the maximum antibiotic concentration in the sampled joint structure is at least 8 to 10 times the minimum concentration required to inhibit bacterial growth.
Despite extensive experimentation and widespread clinical use, the optimal technique for performing successful infusion remains unclear.
Researchers Laurel Redding, Elizabeth Elzer and Kyla Ortved set out in their study to examine the effects that different infusion techniques have on the success of the procedure.
They searched for horse studies related to regional limb infusions published between 1990 and 2021. Their search identified 158 peer-reviewed publications, 36 of which were deemed suitable for their analysis.
Overall, individual studies contained outcomes measured for between 1 and 8 different combinations of infusion techniques, for a total of 123 permutations of dose, route, location, and time across all studies.
Analysis variables included sampled joint structure, antibiotic dose, tourniquet location, duration of tourniquet, general anesthesia versus standing sedation, infusion volume, type of tourniquet, and simultaneous use of local analgesia.
Final modeling showed that tourniquet type and concurrent use of local analgesia were the two most important variables associated with joint-related antibiotic concentrations.
Pneumatic tourniquets were associated with lower antibiotic concentrations than wide rubber tourniquets, and pneumatic tourniquets with pressures greater than 400 mm Hg were the least effective in achieving peak antibiotic concentrations 10 or more times the concentration minimal to inhibit bacterial growth.
“One of the suggested benefits of pneumatic tourniquets is the ability to normalize pressure between horses, while the benefits of rubber tourniquets include less risk of pressure loss associated with leaking or bursting of pneumatic tourniquets” , the trio reported in the open-access journal. PLOS ONE.
“Clinically, wide rubber tourniquets are economical, easy to use, and accessible, and their effectiveness is clearly supported by the current literature.”
Regional limb perfusion was first performed under general anesthesia to limit animal movement. However, its clinical use is much simpler and more accessible using standing sedation.
The analysis showed that the procedure, whether performed under general anesthesia or standing sedation, achieved similar joint concentrations of antibiotics.
“Nevertheless, the movement of the sedated horse while standing was cited as a plausible reason for the infusion failure,” they said.
In their study, they found that the simultaneous use of local analgesia, either by nerve blocks or by the addition of a local anesthetic to the perfusate, was strongly associated with obtaining high peaks of concentrations of antibiotics in joint structures.
They noted that pain associated with tourniquet is a reported complication of use in human medicine. Using analgesia alongside limb perfusion appears helpful in limiting animal discomfort and subsequent movement, thereby decreasing the risk of tourniquet failure, they said.
Based on their analysis, concurrent analgesia appears to be particularly important in the treatment of resistant bacterial infections.
Parameters that were not statistically significantly associated with higher joint concentrations of antibiotics included duration of infusion, distance from withers to joint, whether the horse was standing or under general anesthesia, and dose of antibiotics. ‘antibiotic.
Therapeutic concentrations of antibiotics were reached in synovial fluid at 10 minutes, 15 minutes, 20 minutes, 30 minutes, and 45 minutes after tourniquet application in various studies. The average time to peak concentration in studies was 29 minutes, although the authors noted that it is not possible to determine exactly when because samples are only taken at predetermined times.
When using the technique to treat infections, it may be advisable to leave a tourniquet in place for 30 minutes when possible to achieve the highest possible antibiotic concentration. However, the individual horse’s behavior, movement and response to sedation during the procedure can be unpredictable and shorter times may be required.
The study team noted that therapeutic concentrations of antibiotics in synovial fluid were achieved using doses ranging from 2% to 91% of the recommended systemic dose.
Some researchers and clinicians have recommended performing a regional limb infusion with one-third of the systemic dose of the desired antibiotic, while others have suggested administering the full systemic dose by infusion without simultaneous systemic administration.
The lack of statistical significance of dose on peak antibiotic concentrations in current research may have been influenced by the small number of studies evaluating high doses, they said.
In conclusion, the researchers stated that there were considerable differences in technique between the studies. However, their work had allowed them to focus on the parameters that most affected joint concentrations of antibiotics, the most important of which appear to be the type of tourniquet and the administration of analgesia with the antibiotic.
“Our results suggest that wide rubber tourniquets and concomitant local analgesia should be strongly considered for use in regional limb perfusion. Our results also indicate that adequate therapeutic concentrations can often be achieved through a variety of techniques for susceptible but non-resistant pathogens.
Redding and Ortved are at the University of Pennsylvania School of Veterinary Medicine; Elzer is with Rood and Riddle Equine Hospital in Saratoga Springs, New York.
Redding LE, Elzer EJ, Ortved KF (2022) Effects of regional limb perfusion technique on target site achieved antibiotic concentrations: a meta-analysis. PLoS ONE 17(4): e0265971. https://doi.org/10.1371/journal.pone.0265971