Effect on Neurostimulation of Injectates Used for Perineural Space Expansion Before Placement of a Stimulating Catheter Normal Saline Versus Dextrose 5% in Water

Background and Objectives: We clinically assessed the electro-physiologic effect of dextrose 5% in water (D5W) and of normal saline (NS) used for expansion of the perineural space before placing a stimulating catheter. We questioned if higher current was required with NS but not with D5W, as has been observed experimentally. Methods: This was a prospective randomized double-blind study of ASA I to II patients scheduled for total knee replacement. Patients from 2 hospitals were randomly assigned to receive unidentified injectate D5W (n = 25) or NS (n = 25). The primary outcome was the minimal intensity of stimulation (MIS) recorded before and after 2 and 5 mL of study injectates were flushed through the needle before placing a stimulating catheter for continuous femoral and sciatic nerve blocks. Secondary outcomes included, among other parameters, MIS recorded during placement of stimulating catheters. Results: No difference between groups was found with MIS before injection. However, MIS recorded during neurostimulation via the needle in all blocks was significantly higher after 2 and 5 mL of NS than after D5W In femoral blocks, MIS recorded during placement of catheters was higher during insertion after NS than after D5W but was not different after reaching the final site, regardless of injectate used. In sciatic blocks, MIS was not different during insertion regardless of injectate but was higher after NS than after D5W after reaching the final site. Conclusions: The current needed to electrostimulate the femoral or sciatic nerve was higher after injection of NS than after D5W.