Low-volume ultrasound-guided nerve block provides inferior postoperative analgesia compared to a higher-volume landmark technique

Reg Anesth Pain Med. Jul-Aug 2011;36(4):393-8. doi: 10.1097/AAP.0b013e31821e2fb7.

Abstract

Background and objectives: Ultrasound guidance reduces the required local anesthetic volume for successful peripheral nerve blockade, but it is unclear whether this impacts postoperative analgesia. This prospective, randomized, observer-blinded study tested the hypothesis that a low-volume ultrasound-guided ankle block would provide similar analgesia after foot surgery compared with a conventional-volume surface landmark technique.

Methods: A total of 72 patients presenting for elective foot surgery under general anesthesia were randomized to receive a low-volume ultrasound-guided ankle block (n = 37; ropivacaine 0.5% adjacent the anterior/posterior tibial arteries and short saphenous vein; subcutaneous infiltration around the saphenous and superficial peroneal nerves) or conventional-volume surface landmark guided technique (n = 35; 30 mL of ropivacaine 0.5%). Patients received regular postoperative acetaminophen, diclofenac, and rescue tramadol. Assessment was in the recovery room and at 24 hours for pain and tramadol consumption.

Results: Mean (SD) total local anesthetic volume for the low-volume ultrasound group was 16 (2.1) mL. Block success in the recovery room was similar between groups (low-volume ultrasound 89% versus conventional-volume landmark 80%, P = 0.34; however, during the first 24 hours, numerically rated (0-10) "average pain" (median [10-90th percentiles] = 1 [0-4] versus 0 [0-2], P = 0.01), worst pain at rest (1 [0-6] versus 0 [0-2], P = 0.03), and the proportion of patients requiring rescue tramadol (% [95% confidence interval]: 50 [34-46] versus 20 [10-36], P = 0.01) were higher in the low-volume ultrasound group. Numerically rated numbness, weakness, satisfaction, and procedural time were similar between groups.

Conclusions: Low-volume ultrasound-guided ankle block is associated with a high block success rate after foot surgery; however, compared with a conventional volume (surface landmark) technique, the reduced local anesthetic volume marginally compromises postoperative analgesia during the first 24 hours.

Publication types

  • Clinical Trial
  • Comparative Study
  • Randomized Controlled Trial

MeSH terms

  • Adolescent
  • Adult
  • Aged
  • Aged, 80 and over
  • Analgesia / methods*
  • Anesthetics, Local / administration & dosage*
  • Ankle / diagnostic imaging
  • Ankle / surgery
  • Female
  • Humans
  • Male
  • Middle Aged
  • Nerve Block / methods*
  • Pain, Postoperative / diagnostic imaging*
  • Pain, Postoperative / drug therapy*
  • Prospective Studies
  • Ultrasonography, Interventional / methods*

Substances

  • Anesthetics, Local