Altered blood flow in terminal vessels after local application of ropivacaine and prilocaine.
BACKGROUND
Ropivacaine is primarily a local anesthetic, but it also acts as a vasoactive agent. Case reports have described a critical reduction in blood flow when higher concentrations of ropivacaine were used for peripheral-nerve blocks. One hypothesis is that local application of ropivacaine in tissues supplied by end arteries reduces tissue blood flow because of arterial vasoconstriction.


METHODS
Rats were anesthetized by inhalation of isoflurane. The tail vessels were carefully dissected from the ventral side near the radix. Randomly, normal saline, prilocaine 0.5%, prilocaine 0.5% with epinephrine 1:200,000, ropivacaine 0.2%, ropivacaine 0.5%, or ropivacaine 0.75% was applied directly to the artery. Blood flow in the tail was continuously measured by use of laser Doppler flowmetry distal to the surgical site. Changes in temperature in the tail were detected by use of infrared thermography.


RESULTS
Blood flow decreased after the application of ropivacaine at all concentrations in comparison with normal saline (P < .01 at t = 10 minutes, P < .001 at t = 20, 30, and 40 minutes). This effect was most pronounced at t = 30 minutes for ropivacaine 0.5% (with a 64.5% decrease in blood flow). Prilocaine 0.5% with epinephrine 1:200,000 reduced blood flow by up to 44.7% (t = 20 minutes, P < .001). In comparison with the placebo, the application of ropivacaine 0.5% and 0.75%, as well as prilocaine 0.5% with epinephrine 1:200,000, caused a significant reduction in tail temperature (P < .001 at t = 20, 30, and 40 minutes). No alteration in blood flow or temperature was seen after application of prilocaine 0.5%.


CONCLUSIONS
The application of ropivacaine directly to a rat's tail artery diminished blood flow and lowered regional skin temperature. These effects were dose related. The use of ropivacaine at higher concentrations can, therefore, not be recommended if tissues supplied by end arteries might be affected.
Wienzek
Holger
H
Department of Anesthesiology and Intensive-Care Medicine, Muenster University Hospital, Muenster, Germany. wienzek@muenster.de
Freise
Hendrik
H
Giesler
Isabell
I
Van Aken
Hugo K
HK
Sielenkaemper
Andreas W
AW
D000109:Acetylcholine / Q000494:pharmacology; D000577:Amides / Q000494:pharmacology*; D000779:Anesthetics, Local / Q000494:pharmacology*; D000818:Animals; D001158:Arteries / Q000187:drug effects; D001783:Blood Flow Velocity / Q000187:drug effects; D004305:Dose-Response Relationship, Drug; D004837:Epinephrine / Q000494:pharmacology; D006863:Hydrogen-Ion Concentration; D017078:Laser-Doppler Flowmetry; D009599:Nitroprusside / Q000494:pharmacology; D011318:Prilocaine / Q000494:pharmacology*; D051381:Rats; D017207:Rats, Sprague-Dawley; D000077212:Ropivacaine; D012881:Skin Temperature / Q000187:drug effects; D013623:Tail / Q000098:blood supply*; D013817:Thermography; D013997:Time Factors; D014661:Vasoconstriction / Q000187:drug effects*; D014662:Vasoconstrictor Agents / Q000494:pharmacology*; D014664:Vasodilation / Q000187:drug effects; D014665:Vasodilator Agents / Q000494:pharmacology; D014667:Vasopressins / Q000494:pharmacology
D000577:Amides; D000779:Anesthetics, Local; D014662:Vasoconstrictor Agents; D014665:Vasodilator Agents; D011318:Prilocaine; D014667:Vasopressins; D009599:Nitroprusside; D000077212:Ropivacaine; D000109:Acetylcholine; D004837:Epinephrine