Increasing the NaCl Concentration of the Preinjected Solution Enhances Monopolar Radiofrequency Lesion Size

Background: The effect of altering the sodium chloride (NaCl) concentration of the preinjected solution on monopolar radiofrequency (RF) lesion characteristics has not been investigated with conventional pain medicine equipment. The purpose of this study was to examine the effects of increasing NaCl concentration on lesion dimensions. Methods: Monopolar RF was performed with ex vivo chicken samples. Fifteen groups were used. Seven groups were used to investigate the preinjection of increasing NaCl concentrations. Two nonionic fluids (water and 5% dextrose in water) were also investigated. One group received no fluid preinjection. Five additional groups received increasing concentrations of NaCl combined with lidocaine. Horizontal diameter, vertical diameter, maximal effective radius, and distal radius of the lesion from the tip of the electrode were each measured in millimeters. The shape (horizontal diameter/vertical diameter) and overall surface area were calculated. Impedance and power values were measured. Results: The addition of NaCl to the injected fluid alters mean lesion attributes beyond that observed with nonionic fluids. All NaCl concentrations 0.7% and above increased the mean surface area over that seen with water by 29% to 154%. Increasing the NaCl concentration from 0.7% NaCl to 23.4% NaCl resulted in a reduction in the impedance and an increase in power (mean watts of 1.4-3.25 W). The addition of lidocaine to NaCl solutions does not significantly alter the mean increases in lesion dimensions and modifications in electrical parameters. Conclusions: Increasing NaCl concentrations significantly increases lesion size. NaCl may produce a larger lesion as a result of reduced impedance surrounding the RF cannula and increased power output. (Reg Anesth Pain Med 2013; 38: 112-123)