The rectus sheath block: accuracy of local anesthetic placement by trainee anesthesiologists using loss of resistance or ultrasound guidance.

The aim of this study was to compare the accuracy of local anesthetic placement in the rectus sheath block when performed by trainee anesthetists using loss of resistance (LOR) or ultrasound guidance. Eighty-one patients undergoing laparoscopic surgery were randomly assigned to undergo rectus sheath block by either LOR or ultrasound guidance. Trainee anesthesiologists were also randomly assigned to provide the rectus sheath block by LOR or by using ultrasound. The placement of local anesthetic was recorded using ultrasound. The placement of local anesthetic by LOR was accurate in 45% of attempts but was superficial and deep to the rectus sheath in 34% and 21% of punctures, respectively. Accurate placement of local anesthetic within the rectus sheath decreased significantly as body mass index increased. Ultrasound guidance significantly improved the accuracy of needle placement, with 89% of abdominal punctures being correctly placed at the time of first injection of local anesthetic. An additional fascial plane lying at variable distance above the anterior layer of the rectus sheath was commonly observed. Ultrasound guidance improves the accuracy of local anesthetic placement when undertaking the rectus sheath block. An additional fascial plane above the anterior layer of the rectus sheath may be wrongly perceived as the anterior layer of the rectus sheath when the block is undertaken without the aid of ultrasound.