Minimal blocking concentrations of bupivacaine and procaine in an exclusively nociceptive system in humans.
OBJECTIVE
Prior to this investigation, there was no approach to compare both the potency of local anesthetics and their time course of action in a reproducible nociceptive system in humans. We tested whether the vascularly isolated vein segment is appropriate for such an approach.


METHODS
In six healthy men, a hand vein segment was vascularly isolated and intraluminally stimulated with electropulses of constant current intensity. The subjects rated pain between threshold and maximally tolerable pain on a visual analogue scale. For determining minimal blocking concentrations (a measure of potency), the vein segment was continuously perfused with Tyrode's solution with increasing concentrations of bupivacaine or procaine for at least 10 minutes each until pain was completely blocked. Subsequently, the respective local anesthetic was rinsed off with Tyrode's solution to determine the time course of recovery.


RESULTS
Both bupivacaine and procaine blocked pain in a concentration-related fashion, the minimal blocking concentrations being 1.6 (0.6-1.9; median and range) mmol/L for bupivacaine and 15.0 (7.5-22.5) mmol/L for procaine. Whereas the onset of block (time of 50% block) did not differ significantly between bupivacaine and procaine [43 s (range, 3-80) vs 53 s (range, 30-115)], local anesthesia lasted significantly longer after application of bupivacaine [278 s (range, 215-325)] than after procaine [183 s (range, 125-225)].


CONCLUSIONS
The vascularly isolated vein segment is well suited to compare in vivo the properties of local anesthetics with a minimally invasive approach at a reproducible nociceptive system in humans.
Holthusen
H
H
Department of Experimental and Clinical Anesthesiology, Heinrich-Heine-University of Düsseldorf, Germany.
Lipfert
P
P
Klement
W
W
D000328:Adult; D000779:Anesthetics, Local / Q000009:adverse effects / Q000493:pharmacokinetics / Q000627:therapeutic use*; D002045:Bupivacaine / Q000009:adverse effects / Q000493:pharmacokinetics / Q000627:therapeutic use*; D004305:Dose-Response Relationship, Drug; D004558:Electric Stimulation; D006801:Humans; D008297:Male; D009619:Nociceptors / Q000187:drug effects* / Q000502:physiology; D010146:Pain / Q000517:prevention & control*; D010147:Pain Measurement / Q000187:drug effects; D017288:Pain Threshold / Q000187:drug effects; D011343:Procaine / Q000009:adverse effects / Q000493:pharmacokinetics / Q000627:therapeutic use*
D000779:Anesthetics, Local; D011343:Procaine; D002045:Bupivacaine