Regional anesthesia and pain medicine
-
Reg Anesth Pain Med · May 2011
Randomized Controlled Trial Comparative Study Clinical TrialUltrasound-guided (needle-in-plane) perineural catheter insertion: the effect of catheter-insertion distance on postoperative analgesia.
When using ultrasound guidance to place a perineural catheter for a continuous peripheral nerve block, keeping the needle in plane and nerve in short axis results in a perpendicular needle-to-nerve orientation. Many have opined that when placing a perineural catheter via the needle, the acute angle may result in the catheter bypassing the target nerve when advanced beyond the needle tip. Theoretically, greater catheter tip-to-nerve distances result in less local anesthetic-to-nerve contact during the subsequent perineural infusion, leading to inferior analgesia. Although a potential solution may appear obvious-advancing the catheter tip only to the tip of the needle, leaving the catheter tip at the target nerve-this technique has not been prospectively evaluated. We therefore hypothesized that during needle in-plane ultrasound-guided perineural catheter placement, inserting the catheter a minimum distance (0-1 cm) past the needle tip is associated with improved postoperative analgesia compared with inserting the catheter a more traditional 5 to 6 cm past the needle tip. ⋯ This study did not find evidence to support the hypothesis that, for popliteal-sciatic perineural catheters placed using ultrasound guidance and a needle-in-plane technique, inserting the catheter a minimum distance (0-1 cm) past the needle tip improves (or worsens) postoperative analgesia compared with inserting the catheter a more traditional distance (5-6 cm). Caution is warranted if extrapolating these results to other catheter designs, ultrasound approaches, or anatomic insertion sites.
-
Reg Anesth Pain Med · May 2011
Comparative StudyProlonged cutaneous analgesia with transdermal application of amitriptyline and capsaicin.
Capsaicin selectively binds to TRPV1, the vanilloid subtype 1 of the superfamily of transient receptor potential ion channels, which is highly expressed in pain-transmitting C fibers. Recent reports have demonstrated that the coadministration of capsaicin with a local anesthetic (LA) at the rat sciatic nerve elicits a prolonged nociceptive-selective nerve block, suggesting that activation of the TRPV1 receptor may allow LAs to enter the nerve through the TRPV1 pore. In previous studies, we demonstrated that transdermal amitriptyline achieves clinical analgesic effects and is more potent than lidocaine. Here we examine whether the combined application of amitriptyline and capsaicin as a transdermal patch will produce prolonged cutaneous analgesia compared with amitriptyline alone. ⋯ This study demonstrates that the combined application of amitriptyline and capsaicin results in prolonged cutaneous analgesia compared with amitriptyline alone, suggesting that the activation of the TRPV1 channel by capsaicin facilitates the passage of amitriptyline into nociceptors. This transdermal patch achieves far longer cutaneous analgesia than currently available patch applications such as EMLA cream. The mechanism that underlies the lesser skin irritation noted when amitriptyline is combined with higher doses of capsaicin compared with amitriptyline alone is unclear and may be related to a counteraction of amitriptyline-induced vasoconstriction.