The interaction between the composition of preinjected fluids and duration of radiofrequency on lesion size.

BACKGROUND: Clinical recommendations for the duration of radiofrequency (RF) delivery have been based on no-fluid design, which may not be representative of clinical practice where fluid preinjection occurs. The purpose of this study was to examine the interaction between the preinjection of fluids of differing compositions and duration of RF on lesion size. The variability of lesion development under different preinjection conditions was also examined across the RF lesion duration. METHODS: Monopolar RF was performed with ex vivo chicken samples for 180 seconds without fluid preinjection or with fluid preinjected. Nonionic and ionic fluids were investigated. Lesion size parameters and and power levels were measured every 10 seconds. The surface area and efficiency index were calculated. RESULTS: The preinjection of specific fluid increased the maximum mean surface area. Lesion growth continued throughout the entire lesion cycle. When all groups were considered together, the largest mean surface area occurred at 180 seconds. The preinjection of specific fluids altered the rate of lesion growth and the time required to achieve maximum lesion size in a fluid-specific manner. Significant variability was documented in the rate and amount of lesion growth under each condition. Extending lesioning time resulted in reduced lesion variability. CONCLUSIONS: Fluid preinjection alters both final lesion size and the time required to achieve maximum lesion size. Extending the duration of RF lesion cycle beyond 90 seconds when fluid is preinjected allows for lesion size to be maximized while limiting lesion size variability, both of which assist in successfully lesioning a targeted nerve.

Investigation of current infection-control practices for ultrasound coupling gel: a survey, microbiological analysis, and examination of practice patterns.

BACKGROUND AND OBJECTIVES: Ultrasound coupling gel may serve as a vector for the spread of bacteria and has been the causative agent for significant health care-associated infections. The purpose of this study was to document existing infection-control procedures and level of contamination present within nonsterile ultrasound gel from several clinical departments at a single institution. A second purpose was to examine the effectiveness of clinician education and manufacturer-based ultrasound additives on ultrasound gel contamination and in vitro bacterial proliferation, respectively. METHODS: Compliance with Health Canada recommended infection-control policies were determined by survey. Contamination of in-use ultrasound gel bottles was determined by inspecting cultures after 72 hours of incubation. After infection-control education, a 28-day interval assessment was used to examine contamination rates in newly provided ultrasound gel. The ability of ultrasound gel containing parabens to prevent bacterial growth was examined in cultures grown with and without ultrasound gel. RESULTS: Practitioners were not compliant with Health Canada recommendations, but the baseline ultrasound gel contamination rate within these departments was only 2.5%. Education in infection control did not improve the contamination rate over 28 days. Contamination was discovered in ultrasound gel supplied directly from the manufacturer. Ultrasound gel suppressed but did not prevent bacterial growth in a species- and time-specific manner. CONCLUSIONS: The source of contamination for in-use ultrasound gel may be of manufacturer or human origin. Because additives to the ultrasound gel are not bactericidal, sterile ultrasound gel should be used for invasive and high-risk cases, and improving infection-control policies is warranted.

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.

The effects of fluid injection on lesion size during bipolar radiofrequency treatment.

BACKGROUND: The effect of preinjected fluid on bipolar radiofrequency (RF) lesion characteristics has not been investigated with conventional pain medicine equipment. The purpose of the present study was to determine the effect of preinjected fluid composition on lesion parameters. METHODS: Bipolar RF lesioning was performed in ex vivo chicken samples without fluid preinjection or with 0.7 mL of fluid injected through the 2 RF cannulas (total volume, 1.4 mL). The preinjected fluids were sterile water, 0.9% NaCl, 3% NaCl, 1% lidocaine, and 6% hydroxyethyl starch (HES). For each condition, RF electrodes were incrementally separated, and the number of trials producing successful lesions was recorded. Maximum and minimum height, length, and depth of the lesions were measured, and volumes of the lesions were calculated. RESULTS: The preinjection of any fluid increased the odds of consistently achieving a continuous lesion between the electrodes that was at least 75% of the maximal height of tissue damaged; 3% NaCl increased the odds of achieving at least 75% maximum height significantly more than any other fluid except for HES. Injection of any fluid containing NaCl (including lidocaine and HES) significantly increased the mean volume of tissue lesioned over that observed with injection of water. CONCLUSIONS: Fluid composition influences success, alters lesion size, and could be an appropriate consideration when selecting treatment parameters for bipolar RF. The enhanced lesion size and improved odds of producing a successful lesion with increasing NaCl concentration suggest a method to enlarge lesion size in a controlled manner.

Contralateral high or a combination of high- and low-frequency transcutaneous electrical nerve stimulation reduces mechanical allodynia and alters dorsal horn neurotransmitter content in neuropathic rats.

UNLABELLED: The purpose of the study was to examine the effect of 3 different application strategies for transcutaneous electrical nerve stimulation (TENS) on neuropathy-induced allodynia and dorsal horn neurotransmitter content. Rats were treated with high-frequency, low-frequency, or a combination of high and low-frequency stimulation. TENS was delivered through self-adhesive electrodes daily for 1 hour to rats with a right-sided chronic constriction injury (CCI). Stimulation was delivered to skin or acupuncture points on the left and mechanical and thermal pain thresholds were assessed in the right hind paw. Neurotransmitter content was assessed bilaterally in the dorsal horn of the spinal cord. Daily, high-frequency or a combination of high- and low-frequency TENS reduced mechanical (P < .001), but not thermal allodynia in the right hind paw when compared with untreated CCI rats. Daily high frequency TENS elevated the dorsal horn synaptosomal content of GABA bilaterally (P < .014) and a combination of high- and low-frequency TENS elevated the dorsal horn content of aspartate (P < .001), glutamate (P < .001) and glycine (P < .001) bilaterally over that seen in untreated CCI rats. The present findings support a contralateral approach to the application of TENS and suggest that distinct strategies for TENS application may differentially alter neurotransmission in the central nervous system. PERSPECTIVE: Because CCI rats are reminiscent of humans with neuropathy, daily high or a combination of high- and low-frequency TENS may reduce mechanical allodynia in humans with neuropathic pain. Because the 2 intervention strategies produce distinctive alterations in spinal cord neurotransmitter content, each may represent a distinctive option for treatment.

Transcutaneous electrical nerve stimulation for the management of neuropathic pain: the effects of frequency and electrode position on prevention of allodynia in a rat model of complex regional pain syndrome type II.

BACKGROUND AND PURPOSE: Complex regional pain syndrome type II (CPSII) is a painful condition that develops following a nerve injury. Although transcutaneous electrical nerve stimulation (TENS) relieves the pain of CPSII, the stimulation parameters that would best prevent the development of the condition are not known. The purpose of this study was to compare the ability of several different stimulation strategies to reduce the development of allodynia. SUBJECTS: Sprague-Dawley rats were used in the study. METHODS: A chronic constriction injury (CCI) to the right sciatic nerve was used to induce allodynia. Two groups of CCI rats received high-frequency TENS to the lumbar paravertebral region with electrodes positioned on the skin overlying either the right or left paraspinal musculature. Two additional groups of CCI rats received low-frequency TENS to acupuncture points in the right or left hind limbs. A fifth group of CCI rats received no TENS intervention. Thermal and mechanical pain thresholds were assessed in the right hind paw before and 12 days after the CCI surgery. The TENS was delivered 1 hour per day beginning on the day of surgery. RESULTS: Daily high-frequency TENS reduced the development of mechanical allodynia in CCI rats, and low-frequency TENS reduced the development of thermal allodynia, but only when TENS was delivered on the left side. DISCUSSION AND CONCLUSION: The results indicate that TENS delivered contralateral to a nerve injury best reduces allodynia development. Comprehensive reduction of allodynia development would require a combination of high- and low-frequency TENS intervention.

The relationship between dorsal horn neurotransmitter content and allodynia in neuropathic rats treated with high-frequency transcutaneous electric nerve stimulation.

OBJECTIVE: To examine the relation between axon terminal neurotransmitter content in the dorsal horn and allodynia in neuropathic rats treated with high-frequency transcutaneous electric nerve stimulation (TENS). DESIGN: A completely randomized experimental design. Two groups of rats received a chronic constriction injury to the right sciatic nerve, and 2 groups did not. The rats were either treated or not treated with TENS. SETTING: Research laboratory. ANIMALS: Adult male Sprague-Dawley rats (150-165g). INTERVENTIONS: TENS was delivered daily for 1 hour to the chronic constriction injury rats or to the uninjured rats through self-adhesive electrodes applied to the skin innervated by the right dorsal rami of lumbar spinal nerves 1 to 6. MAIN OUTCOME MEASURES: Thermal and mechanical pain thresholds were assessed bilaterally in the hind paws of all rats twice before the chronic constriction injury surgery (baseline) and then 12 days after the surgery. An analogous time frame of assessment was used for rats that did not have chronic constriction injury surgery. Thermal and mechanical allodynia were expressed as difference scores between the pain thresholds of the right and left hind paws. These values were normalized to differences that existed between the 2 paws at baseline. The amino acid content of dorsal horn axon terminals was assessed bilaterally with high-pressure liquid chromatography, and values were normalized to wet weight. RESULTS: The mean level of thermal and mechanical allodynia did not differ between the TENS-treated and untreated rats with chronic constriction injury. However, there was a significant relation between the dorsal horn, axon terminal content of glutamate (adjusted R(2)=.45, P<.01) and glycine (adjusted R(2)=.51, P<.005) and the magnitude of mechanical allodynia present in TENS-treated chronic constriction injury rats, but not in any other group. As axon terminal glutamate and glycine decreased in the right dorsal horn and increased in the left, mechanical allodynia was reduced or absent. When this trend was reversed, mechanical allodynia was more severe. Daily TENS also reduced the mean axon terminal content of aspartate, glutamate, and glycine bilaterally in the chronic constriction injury rats from the level observed in untreated neuropathic rats (P<.05). CONCLUSION: The variability in responsiveness of mechanical allodynia to daily TENS treatment in neuropathic rats is related to the axon terminal content of glutamate and glycine in the dorsal horn. These findings may help explain a similar variability in humans when TENS is used to treat neuropathic pain.

Dorsal horn synaptosomal content of aspartate, glutamate, glycine and GABA are differentially altered following chronic constriction injury to the rat sciatic nerve.

The present study directly examined the axon terminal (synaptosomal) level of amino acid neurotransmitters in rats following chronic constriction injury (CCI) to the sciatic nerve. Dorsal horn, synaptosomal content of aspartate (Asp), glutamate (Glu), glycine and gamma-aminobutyric acid (GABA) was assessed in these rats, and in normal age-matched and younger rats. The synaptosomal content of Asp and Glu in CCI rats was increased by 44-46% compared with control rats (P<0.016). The synaptosomal content of GABA in younger rats was 33% lower than that observed in control rats (P<0.005). Altered axon terminal levels of amino acid neurotransmitters accompany the painful symptoms of neuropathy. The lower axon terminal level of GABA in younger rats may help to explain the age-dependency of pain development in animal models of nerve injury.