Effects of ultrasound guidance on the minimum effective anaesthetic volume required to block the femoral nerve

• Published in: British journal of anaesthesia : BJA Vol. 98; no. 6; pp. 823 - 827
• Main Authors: Casati, A., Baciarello, M., Cianni, S. Di, Danelli, G., De Marco, G., Leone, S., Rossi, M., Fanelli, G.
• Format: Journal Article
• Language: English
• Published: Oxford Elsevier Ltd 01.06.2007; Oxford University Press; Oxford Publishing Limited (England)
• Subjects: Adolescent; Adult; Aged; Aged, 80 and over; Amides - administration & dosage; anaesthetic techniques; anaesthetic techniques, regional, femoral nerve block; anaesthetics local; anaesthetics local, ropivacaine; Anesthesia; Anesthesia. Intensive care medicine. Transfusions. Cell therapy and gene therapy; Anesthetics, Local - administration & dosage; Arthroscopy; Biological and medical sciences; Double-Blind Method; Drug Administration Schedule; Electric Stimulation; equipment, nerve stimulator, ultrasound; Femoral Nerve - diagnostic imaging; femoral nerve block; Humans; Knee Joint - surgery; Medical sciences; Middle Aged; Nerve Block - methods; nerve stimulator; regional; ropivacaine; Ultrasonography, Interventional - methods; ultrasound; anaesthetic techniques, regional, femoral nerve block; anaesthetics local, ropivacaine; equipment, nerve stimulator, ultrasound; Local anesthetic; Guidance; ropivacaine; equipment; nerve stimulator; regional; Anesthesia; Organic amide; Ropivacaine; anaesthetic techniques; femoral nerve block; anaesthetics local; ultrasound
• ISSN: 0007-0912; 1471-6771
• DOI: 10.1093/bja/aem100

We tested the hypothesis that ultrasound guidance may reduce the minimum effective anaesthetic volume (MEAV50) of ropivacaine 0.5% required to block the femoral nerve compared with nerve stimulation guidance. After standard premedication and sciatic nerve block were given, 60 patients undergoing knee arthroscopy were randomly allocated to receive a femoral nerve block with ropivacaine 0.5% using either nerve stimulation (group NS, n = 30) or ultrasound (group US, n = 30) guidance. The volume of the injected solution was varied for consecutive patients based on an up-and-down staircase method according to the response of the previous patient. The initial volume was 12 ml. A double-blinded observer evaluated the occurrence of complete loss of pinprick sensation in the femoral nerve distribution, with concomitant block of the quadriceps muscle: positive or negative responses within 30 min after the injection determined a 3 ml decrease or increase for the next patient, respectively. The mean (sd) MEAV50 for femoral nerve block was 15 (4) ml (95% CI, 7–23 ml) in group US and 26 (4) ml (95% CI, 19–33 ml) in group NS (P = 0.002). The effective dose in 95% of cases (ED95) calculated with probit transformation and logistic regression analysis was 22 ml (95% CI, 13–36 ml) in group US, and 41 ml (95% CI, fs 24–66 ml) in group NS. Ultrasound guidance provided a 42% reduction in the MEAV of ropivacaine 0.5% required to block the femoral nerve as compared with the nerve stimulation guidance.