Background and objectives: Fascia iliac compartment block is widely used as one of the anesthetic techniques used for surgical interventions of the hip, thigh, and knee. The majority of the studies have used fixed volumes of ropivacaine or bupivacaine. The objective of this study was to calculate the effective volume of 0.5% ropivacaine and 0.5% bupivacaine in 50% (EV50%), 95% (EV95), and 99% (EV99) of the cases to achieve fascia iliac compartment block.
Methods: Fifty-one adults scheduled for elective surgical interventions of the hip, femoral diaphysis, and knee underwent fascia iliac compartment block. Patients were randomly assigned to receive either 0.5% ropivacaine (n = 25) or 0.5% bupivacaine (n = 26). The success of the block was defined as a complete sensitive block of the anterior, medial, and lateral regions of the thigh. The volume of the anesthetic was determined by Massey and Dixon's up-and-down method, while the effective volume was calculated by Massey and Dixon's formula (EV50) and by probits regression (EV50, EV95, and EV99).
Results: The volume of anesthetic capable of producing an effective nervous anesthesia in 50% of the cases, calculated by Massey and Dixon formula, were 28.79 mL (CI 95%: 26.31 - 31.5 mL) for ropivacaine, and 29.56 mL (CI 95%: 25.22 - 34.64 mL) for bupivacaine (p = 0.62). The effective volumes of ropivacaine capable of producing a blocking in 50%, 95%, and 99% of the cases were estimated by probits regression as 28.8 mL (27.2 - 30.4), 34.3 mL (32.5 - 37.3), and 36.6 mL (34.3 - 40.5), respectively. The corresponding volumes of bupivacaine were 29.5 mL (28.1 - 31.1), 36.1 mL (33.5 - 38.1), and 37.3 mL (35.1 - 41.3) (p > 0.05).
Conclusions: The volumes of 0.5% ropivacaine and 0.5% bupivacaine with adrenaline 1:200,000 for the fascia iliac block are similar.