The minimum effective concentration (MEC90) of bupivacaine for an ultrasound-guided suprainguinal fascia iliaca compartment block for analgesia in knee surgery: a dose-finding study

Abstract

Background: In recent years, the suprainguinal fascia iliaca compartment block (SFICB) has become more common in clinical practice. This assessor-blinded dose-finding study aimed to determine the minimum effective concentration (MEC90, MEC95) of bupivacaine for a single-injection SFICB in patients undergoing arthroscopic anterior cruciate ligament repair.

Methods: This prospective study was conducted at a tertiary hospital (postoperative recovery room and ward). The SFICB was performed as a postsurgical intervention after spinal anesthesia. Seventy patients were allocated using the biased-coin design up-and-down sequential method. The ultrasound-guided SFICB was performed using different bupivacaine concentrations, and standard multimodal analgesia was administered to all patients. Block success was defined as the absence of pain or presence of only tactile sensation during the pinprick test conducted on the anterior and lateral regions of the mid-thigh six hours postoperatively.

Results: According to isotonic regression and bootstrap CIs, the MEC90 value of bupivacaine for a successful SFICB was 0.123% (95% CI [0.098, 0.191]) and the MEC95 value was 0.188% (95% CI [0.113, 0.223]).

Conclusions: Our study showed that the MEC90 and MEC95 values for bupivacaine administered via an SFICB for analgesia were 0.123% and 0.188%, respectively. One advantage of using lower concentrations of bupivacaine is the associated reduction in quadriceps weakness.

Keywords: Analgesia; Bupivacaine; Local anesthetics; Nerve block; Pain management; Regional anesthesia..

Fig. 1.

(A, B) Relevant sonoanatomy for ultrasound-guided suprainguinal fascia iliaca compartment block (SFICB). (A) Natural ultrasound image of the SFICB. (B) Sonoanatomy of the muscles and fascia during an SFICB. The dashed white line represents the fascia iliaca, and the black arrow indicates the deep circumflex iliac artery. SC: subcutaneous tissue, SM: sartorius muscle, IOM: internal oblique muscle, IM: iliacus muscle, IB: iliac bone, LA: local anesthetic.

Fig. 2.

Flowchart of the study.

Fig. 3.

The up-and-down sequence. The black dots represent successful blocks and the white dots represent unsuccessful blocks with varying concentrations of bupivacaine. The horizontal lines represent the calculated minimum effective bupivacaine concentrations. MEC: minimum effective concentration.