Anesthesia (8)

The effects of the single or multiple injection technique on the onset time of femoral nerve blocks with 0.75% ropivacaine. (University of Milan and IRCCS San Raffaele Hospital, Milan, Italy) Anesth Analg 2000;91:181–184. This study evaluated the effect of the injection technique on the onset time and efficacy of femoral nerve block performed with 0.75% ropivacaine. A total of 30 patients undergoing arthroscopic knee surgery were randomly allocated to receive femoral nerve blocakade with 0.75% ropivacaine by using either a single injection (Single group, n = 15) or multiple injection (Multiple group, n = 15). Nerve blocks were placed by using a short‐beveled, Teflon‐coated, stimulating needle. The stimulation frequency was set at 2 Hz, and the intensity of the stimulating current, initially set at 1 mA, was gradually decreased to <0.5 mA after each muscular twitch was observed. In the Single group, 12 mL of 0.75% ropivacaine was slowly injected, as soon as the first muscular twitch was observed. In the Multiple group, the stimulating needle was inserted and redirected, eliciting each of the following muscular twitches: contraction of vastus medialis, vastus intermedius, and vastus lateralis. At each muscular twitch, 4 mL of the study solution was injected. Placing the block required 4.2 ± 1.7 min in the Multiple group and 3.4 ± 2.2 min in the Single group ( P = 0.02). Onset of nerve block required 10 ± 3.7 min in the Multiple group and 30 ± 11 min in the Single group ( P < 0.0005). Propofol sedation was never required to complete surgery; although 0.1 mg fentanyl at trocar insertion was required in 2 patients of the Multiple group (13%) and 9 patients of the Single group (60%) ( P = 0.02). Conclude that searching for multiple muscular twitches shortened the onset time and improved the quality of femoral nerve block performed with small volumes of 0.75% ropivacaine. Comment by Octavio Calvillo, MD, PhD. This study is concerned with the onset of femoral nerve block utilizing 0.75% ropivacaine in 2 groups of 15 patients undergoing arthroscopic knee surgery. The optimal site for injection was identified by the electrically evoked muscular twitch at the quadriceps. In 1 group, 12 mL of 0.75% ropivacaine was injected as soon as a muscle twitch was evoked. In the second group, 4 mL of local anesthetic was injected only after a specific response was elicited at the vastus medialis, vastus intermedius, and vastus laterallis. Onset of the nerve block required 10 ± 3.7 min. in the multiple injection group, whereas in the single group, onset of the nerve block took 30 ± 11 min. The authors concluded that searching for multiple twitches shortened the surgical anesthesia and improved the quality of neural blockade.