Does "Opening the Perineural Space" Before Stimulating Catheter Placement for Continuous Nerve Block Add Value in Clinical Practice?

Introduction: A study using unblinded block performance and subjective outcome measurements suggested that "opening the space" surrounding the femoral nerve with 10 mL dextrose 5% in water (D5W) before catheter placement facilitated placement and improved the quality of the nerve block. We conducted a double-blind, prospectively randomized study to evaluate this suggestion by adding objective measurements to the original subjective measurements. Methods: A Tuohy needle was directed toward the femoral nerve under ultrasound and nerve stimulator guidance. A quadriceps femoris motor response was identified by cephalad patellar movements with a maximum nerve stimulator output of 0.5 mA. The primary anesthesiologist either injected D5W or made no injection through the needle, depending on patient randomization. A second anesthesiologist, unaware of randomization, placed the stimulating perineural catheter. The primary measurement was the procedure time (in seconds) for threading the catheter. Additional measurements included total nerve block time (in minutes), number of attempts passing the catheter, subjective ease of placement by the second anesthesiologist, depth of needle and catheter, minimum stimulating current through needle and catheter, and the quality of the nerve block. Results: Two groups of 35 patients were enrolled. Statistically significant differences were found in the median (5th-95th confidence intervals) catheter threading time (21.0 [9.6-118] and 33.0 [13.4-193] secs in the control and D5W groups, respectively; P = 0.03). Significant difference was also found in the number of attempts at passing the catheter (1 [1-2] and 2 [1-4] in the control and D5W groups, respectively; P = 0.03). Conclusions: The findings of this study do not support the concept that opening the space surrounding the femoral nerve with D5W before femoral catheter placement adds value to perineural catheter placement.