A comparison of three techniques (local anesthetic deposited circumferential to vs. above vs. below the nerve) for ultrasound guided femoral nerve block

Abstract

Background: Fractured neck of femur generally requires operative fixation and is a common cause of admission to hospital. The combination of femoral nerve block and spinal anesthesia is a common anesthetic technique used to facilitate the surgical procedure. The optimal disposition of local anesthetic (LA) relative the femoral nerve (FN) has not been defined. Our hypothesis was: that the deposition of LA relative to the FN influences the quality of analgesia for positioning of the patient for performance of spinal anesthesia. The primary outcome was verbal rating (VRS) pain scores 0-10 assessed immediately after positioning the patient to perform spinal anesthesia.

Methods: With Institutional ethical approval and having obtained written informed consent from each, 52 patients were studied. The study was registered with ClinicalTrials.gov (NCT01527812). Patients were randomly allocated to undergo to one of three groups namely: intention to deposit lidocaine 2% (15 ml) i. above (Group A), ii. below (Group B), iii. circumferential (Group C) to the FN. A blinded observer assessed i. the sensory nerve block (cold) in the areas of the terminal branches of the FN and ii. VRS pain scores on passive movement from block completion at 5 minutes intervals for 30 minutes. Immediately after positioning the patient for spinal anesthesia, VRS pain scores were recorded.

Results: Pain VRS scores during positioning were similar in the three groups [Above group/Below group/Circumferential group: 2(0-9)/0(0-10)/3(0-10), median(range), p:0.32]. The block was deemed to have failed in 20%, 47% and 12% in the Above group, Below group and Circumferential group respectively. The median number of needle passes was greater in the Circumferential group compared with the Above group (p:0.009). Patient satisfaction was greatest in the Circumferential group [mean satisfaction scores were 83.5(19.8)/88.1(20.5)/93.8(12.3), [mean(SD), p=0.04] in the Above, Below and Circumferential groups respectively.

Conclusions: We conclude that there is no clinical advantage to attempting to deposit LA circumferential to the femoral nerve (relative to depositing LA either above or below the nerve), during femoral nerve block in this setting.

Figure 1

Composite figure of the femoral nerve block. Representative images depicting the anatomy: fascia iliaca (light brown lines), femoral artery (red), femoral nerve (yellow), needle (arrow) and local anesthetic (blue) position in Group A, B and C.

Figure 2

Enrollment.

Figure 3

VAS pain scores on positioning for spinal anesthesia. VRS median pain scores at positioning to perform spinal anesthesia in Group A /Group B /Group C: 2.5(0–9)/3.2(0–10)/4.7(0–10), median(range) Kruskal-Wallis test p: 0.43) The box-and-whiskers plots show maximum and minimum values and 90th percentiles, lower and upper quartiles and the median (horizontal bar) for each group.

Figure 4

Number of needle passes. Boxplot showing distributions within each group of number of needle passes during ultrasound guided FNB. The median number of needle passes was statistically significantly higher in the Group C compared with the Group A (2.0 vs. 1.0, Mann–Whitney U between Groups C vs. A, p = 0.009). The Group B median was also higher than the group A median i.e. 1.5 but this was not significant.