Comparison of three techniques for ultrasound-guided femoral nerve catheter insertion: a randomized, blinded trial

Abstract

Background: Ultrasound guidance for continuous femoral perineural catheters may be supplemented by electrical stimulation through a needle or through a stimulating catheter. The authors tested the primary hypothesis that ultrasound guidance alone is noninferior on both postoperative pain scores and opioid requirement and superior on at least one of the two. Second, the authors compared all interventions on insertion time and incremental cost.

Methods: Patients having knee arthroplasty with femoral nerve catheters were randomly assigned to catheter insertion guided by: (1) ultrasound alone (n = 147); (2) ultrasound and electrical stimulation through the needle (n = 152); or (3) ultrasound and electrical stimulation through both the needle and catheter (n = 138). Noninferiority between any two interventions was defined for pain as not more than 0.5 points worse on a 0 to 10 verbal response scale and for opioid consumption as not more than 25% greater than the mean.

Results: The stimulating needle group was significantly noninferior to the stimulating catheter group (difference [95% CI] in mean verbal response scale pain score [stimulating needle vs. stimulating catheter] of -0.16 [-0.61 to 0.29], P < 0.001; percentage difference in mean IV morphine equivalent dose of -5% [-25 to 21%], P = 0.002) and to ultrasound-only group (difference in mean verbal response scale pain score of -0.28 [-0.72 to 0.16], P < 0.001; percentage difference in mean IV morphine equivalent dose of -2% [-22 to 25%], P = 0.006). In addition, the use of ultrasound alone for femoral nerve catheter insertion was faster and cheaper than the other two methods.

Conclusion: Ultrasound guidance alone without adding either stimulating needle or needle/catheter combination thus seems to be the best approach to femoral perineural catheters.

Fig. 1

Trial diagram.

Fig. 2

Distribution of verbal response scale (VRS) pain scores over postoperative time for each of the three randomized catheter insertion technique groups. Plotted points are proportional in size to the percent of patients within a given group for a given time interval. hr = hour

Fig. 3

Scatterplot of primary outcomes for the enrolled patients. Estimated means for each outcome and corresponding simultaneous 95% confidence intervals are provided by group in the margins. Confidence intervals used a nominal significance criterion of 0.0023, reflecting the Bonferroni correction for six simultaneous estimates and the adjustment for interim monitoring. VRS = verbal response scale

Fig. 4

Results of simultaneous noninferiority hypothesis tests among randomized femoral nerve catheter insertion treatments (SC = stimulating catheter, SN = stimulating needle, and US = ultrasound alone), given as estimates and 95% confidence intervals (confidence intervals adjusted for simultaneous inference and interim monitoring). One treatment (say, SN) was declared noninferior to another treatment (say, US) on mean VRS pain score when the estimated difference in means was significantly less than the pre-specified noninferiority delta of 0.5 points (given as the dashed vertical line). Likewise, SN was declared noninferior to US on mean total IV morphine equivalent dose if the mean for SN was significantly not more than 25% greater than the mean for US. Significant noninferiority (as assessed by the Holm-Bonferroni step-down method) is given by asterisks next to the raw P-values. VRS = verbal response scale

Fig. 5

Results of group sequential monitoring assessing noninferiority on VRS pain score and opioid consumption across the 4 planned interim analyses. Y-axis is the observed z-statistic representing the treatment effect at the given interim analysis or final analysis, while x-axis is the cumulative enrollment over time. Crossing into the blue region indicates a finding of noninferiority of one group over the other, while crossing into the pink region indicates an acceptance of the null hypothesis (i.e., intervention at least “delta” worse than comparator) and no claim of noninferiority. We used the gamma spending function with gamma = −4 for efficacy and −2 for futility, with alpha=0.025 overall for noninferiority and 90% power. Panel A: Stimulating needle (SN) minus stimulating catheter (SC). SN was noninferior to its comparator on both pain and opioid consumption. Panel B: SN minus ultrasound (US). Panel C: SN minus US. SN was noninferior to its comparator on both pain and opioid consumption. Panel C: SC minus US. SC was noninferior to US on pain score, but not on opioid consumption. Superiority tests were done for comparisons in panels A and B but were not significant. SC = stimulating catheter; SN = stimulating needle; US = ultrasound alone; VRS = verbal response scale