Analgesic electrical currents associated with carboxytherapy in women with cellulite: A randomized controlled trial

Pain is considered the main limiting factor in carboxytherapy. Electroanalgesia has gained recognition in the field of dermatology and to date, only transcutaneous electrical nerve stimulation (TENS) has proved to be effective at reducing pain associated with carboxytherapy; however, the effect of medium frequency currents has yet to be investigated.

and has a negative effect on quality of life. 3,[9][10][11][12] It is a structural, hormonally sensitive and biochemical disorder of the subcutaneous tissue that causes topographic changes to the skin surface. 11 In terms of the therapeutic effects of carboxytherapy on cellulite, studies show better local oxygenation, histomorphological changes in adipocytes (average diameter, perimeter, length, width, number, and shape), and reduced thickness of fibrous septa. 5,6,13,14 In regard to clinical practice, there are certain limitations in carboxytherapy application, mainly pain due to the use of needles and the mechanical effect of the gas on skin layers. 15 A variety of resources have been recommended to minimize pain during invasive procedures, with electroanalgesia gaining increasing prominence. [15][16][17][18][19] Electrical currents used for analgesic purposes include the current provided by transcutaneous electrical nerve stimulation (TENS), interferential current (IFC), and Aussie current. [20][21][22] TENS is a form of stimulation aimed primarily at analgesia, typically using a low frequency (1-250 Hz) biphasic pulsed current. 23 IFC consists of two independent medium frequency currents (one of 4000 Hz and the other adjustable to between 4001 Hz and 4250 Hz), which produce a modulated low frequency sinusoidal wave, equivalent to the value of the difference between the frequencies used. 24 Aussie current, also known as a burst modulated alternating current, involves short rectangular bursts and an adjustable carrier frequency of 1 or 4 kHz, with a burst duration of 4 ms recommended for analgesia. [25][26][27] In regard to the applicability of analgesic currents during painful procedures, to date only TENS has been investigated. It has demonstrated efficacy after liposuction, during topical photodynamic therapy (PDT) to treat actinic keratosis, pain associated with changing wound dressings and during carboxytherapy in women with cellulite. 15,19,[28][29][30] With respect to the effects of medium frequency currents, they are believed to stimulate deep tissues and research confirms that they cause less discomfort than low frequency pulsed currents. 23,27,31 Although few studies compare the effects of different analgesic electrical currents, the most recent compared the effect of TENS, IFC, and Aussie current on the pressure pain threshold (PPT) during and after stimulation in healthy individuals and found no significant difference between the currents analyzed. 27,[32][33][34] As such, considering recent evidence on the application of low frequency currents in carboxytherapy-associated pain and the advantages of medium frequency currents, analyzing their effect on controlling acute pain in dermatology is highly relevant. 15 35 The research was carried out at the Medical-Dental Clinic-CIMO (Manaus, state of Amazon, Brazil) from November 2019 to July 2020 and participants were recruited via digital media and advertisements. After screening based on eligibility criteria, the participants included in the study were submitted to the procedures after providing written informed consent.

| Eligibility criteria
Included were women aged between 18 and 49 years with a body mass index of 18.5-39.9 kg/m 2 , no previous experience with carboxytherapy and moderate and/or severe gluteal cellulite. Cellulite severity was evaluated according to the cellulite severity scale (CSS) of Hexsel Dal'Forno & Hexsel. 36 The exclusion criteria were described in the previously published protocol. 35 Women undergoing esthetic treatment who had drunk alcohol or taken analgesics, muscle relaxants or anti-inflammatories in the 24 h before the session were excluded from the study.

| Sample size calculation and randomization
Sample size was calculated considering a difference of two points between groups in the numeric rating scale (NRS) for pain and standard deviation of 1.95, based on data from a previous study on the use of TENS to control pain during carboxytherapy. 15 For a significance level of 0.05 and statistical power of 80%, 25 participants were calculated for each group (75 in total) (Minitab software v.17).
The patients were randomly allocated into three groups: TENS (n = 25), IFC (n = 25), and Aussie current (n = 25). Randomizations for group allocation (TENS, IFC or Aussie) and gluteus laterality (right or left) for intervention application were performed via the website www.rando milis ts.com by a researcher not involved in participant recruitment or data collection. In order to conceal allocation, the sealed opaque envelopes were securely stored by the researcher responsible for randomization and were only opened after cellulite assessment and before carboxytherapy administration by the researcher responsible for the treatment.

| Study procedures
Demographic information was collected (age, sex, and race), in addition to gynecological history, engagement in physical activity, and use of medication. Next, a physical examination was conducted to obtain anthropometric measurements (body weight and height) and hip circumference. Participants were instructed to remain standing, wear dark colored swimsuits, and keep their gluteus exposed to enable the evaluation of cellulite severity using the CSS, with scores of five to nine indicating moderate severity and 11-15 severe ( Figure 1A). 36 Next, cellulite was marked with a dermatograph pencil for carboxytherapy. It should be noted that, for cellulite severity assessment (performed by the responsible researcher), intra-rater reliability for the CSS was tested in 17 women not involved in the study, who were recruited and evaluated at 48-h intervals. The intraclass correlation coefficient (ICC 3,3 ) was used and intra-rater reliability was considered excellent (0.933; 95% CI 0.828-0.975).

| Demarcation of gluteal cellulite for carboxytherapy
The gluteal region was demarcated bilaterally with the patient in

| Interventions: Electroanalgesia and carboxytherapy
Patients were positioned in ventral decubitus for the application of carboxytherapy combined with an electrical current. A Neurodyn transcutaneous neuromuscular stimulator (IBRAMED®) was used to supply the electrical currents (TENS, IFC, and Aussie) via four 5 × 9 cm self-adhesive electrodes (Arktus®) positioned in the gluteal region ( Figure 1C), in line with the study protocol. 35 The researcher responsible for carboxytherapy was highly experienced in the technique and followed all the guidelines of the Federal Council of Physiotherapy (COFFITO). An Ares carboxytherapy device (IBRAMED®) was used to supply medicinal CO 2 .
Subcutaneous CO 2 infiltration was performed using disposable 30/13 G insulin needles positioned at 45° with the bevel pointing up, flow rate set at 80 mL/min 6 and 50 mL injected every puncture. 5,6,37 A maximum of two punctures per quadrant was established, totaling a maximum of eight. For data analysis purposes, average pain intensity was measured for all the punctures in each quadrant at the end of the carboxytherapy procedure, followed by average overall intensity for all the quadrants.

| Electroanalgesia parameters
The parameters used were: (1) TENS Group: application of a sym-

| Primary outcome
Assessing pain intensity Pain intensity was assessed using an 11-point numerical rating scale (NRS), where 0 represents "no pain" and 10 "the worst possible pain." 39 The scale was applied verbally, per quadrant, after each carboxytherapy puncture in all three study groups and treatment sessions. The average pain intensity value for all the quadrants was considered for data analysis.

| S TATIS TIC AL ANALYS IS
Statistical analyses were performed in SPSS® software (v.12.0; SPSS Inc.). The demographic and clinical data of the patients were analyzed using descriptive statistics. Data normality was assessed by the Kolmogorov-Smirnov test and average pain intensity and sensory comfort between the groups in the three sessions using analysis of variance (ANOVA) and Tukey's test. It should be noted that data imputation was performed for participants who did not return for the second and third sessions, using the expectation-maximization (EM) algorithm. The Kruskal-Wallis test was applied for intergroup sensory comfort comparison. Data were expressed as mean (SD) for pain intensity and mean (SD), median, minimum and maximum values, and interquartile range for sensory comfort. Significance was set at 5% (p ≤ 0.05).

| RE SULTS
A total of 181 individuals were assessed based on the eligibility criteria, 75 of whom were included and allocated into three groups of 25 participants each. The flow chart of the study is presented in Figure 3 and the demographic characteristics of participants in each group are listed in Table 1.

| Pain intensity
Mean (SD) pain intensity per group in each session is presented in Table 2. There was no significant difference between the TENS, IFC, and Aussie current groups in any of the three intervention sessions (p > 0.05) ( Table 3). For intragroup analysis, pain intensity declined significantly during each session in all three groups (p < 0.05), with an effect size of 0.15-0.43 (Table 4).

| Sensory comfort
Based on sensory comfort during current application, there was no significant difference between the TENS, IFC, and Aussie current groups (p = 0.502), as shown in Table 5.

| DISCUSS ION
This study is the first randomized controlled trial to compare the an- Our findings are similar to those of Rampazo et al, who conducted the only study to date that investigated the analgesic action of these three electrical currents (TENS, IFC, and Aussie current) in healthy individuals. 32 Other studies, comparing TENS with IFC or TENS with Aussie current, found no significant difference between these electrical currents for cold pain threshold, induced ischemic pain and mechanical pain threshold in healthy individuals. 25,27,41 No comparative studies were identified regarding the effects of IFC and Aussie current. Research comparing TENS with either of the other two techniques corroborates our findings, demonstrating no difference between low and medium frequency currents in healthy individuals. Nevertheless, it should be noted that how pain intensity was assessed differed. In our study, pain was provoked by carboxytherapy, while in the other studies, different painful stimuli were used and the pain threshold was evaluated. Furthermore, in the aforementioned studies, pain was assessed after electrostimulation, whereas in our study, it was evaluated during the carboxytherapy stimulus.
In regard to the mechanism of action of electroanalgesia asso-  15,19 In fact, different studies emphasize that electrode placement plays an important role and seems to be more effective when electrodes are close to the treatment area, enabling the nerve roots to alter nociceptive transmission in the dorsal horn of the spinal cord.
In regard to sensory comfort, there was no difference between TENS, IFC. and Aussie current. It is important to underscore that the values found were close to zero ( TA B L E 5 Sensory comfort assessment in each experimental group using the visual analogue scale.
of deep tissue, since the frequency of alternating currents is inversely proportional to the electrical impedance of the skin. 24 A strength of our research is its innovative approach to controlling acute pain in the field of dermatology and for esthetic purposes. Moreover, it highlights another little explored area of application for electroanalgesia through low and medium frequency currents. The results obtained raise new scientific questions that are expected to prompt further research into the use of these currents during painful procedures, since the pain relief provided could improve patient acceptance of carboxytherapy.
There are also limitations to consider. Given their potential effect on pain, we opted to limit the number of punctures to a maximum Additionally, the nature of the intervention made it impossible to blind the researcher responsible for applying electroanalgesia combined with carboxytherapy.
In terms of prospects, we hope to expand our investigation of electroanalgesic effects associated with carboxytherapy to different areas of the body, for individuals with cellulite and different esthetic dysfunctions, such as stretch marks, localized adiposity, and tissue flaccidity. In addition, we encourage research to control pain using different invasive methods, in order to awaken interest in the use of low and medium frequency electrical currents.
There was no difference between TENS, IFC, and Aussie current in terms of pain associated with three sessions of carboxytherapy in women with gluteal cellulite. Moreover, all the currents studied were considered comfortable.

AUTH O R CO NTR I B UTI O N S
AYS, EPRS, and REL were responsible for conceiving and designing the study. REL is the study coordinator. AYS and EPRS were responsible for data collection, and AYS for data analysis. All the authors contributed to writing the manuscript and approved the final version.

CO N FLI C T O F I NTE R E S T S TATE M E NT
The authors have no relevant affiliations or financial involvement with any organization or entity with a financial interest in or financial conflict with the subject matter or materials discussed in the manuscript. This includes employment, consultancies, honoraria, stock ownership or options, expert testimony, grants or patents received or pending, or royalties. No writing assistance was utilized in the production of this manuscript.

DATA AVA I L A B I L I T Y S TAT E M E N T
The data that support the findings of this study are openly available in Pain Management at https://www.futur emedi cine.com/ doi/10.2217/pmt-2020-0003.

E TH I C S S TATEM ENT
The authors confirm that the ethical policies of the journal, as noted on the journal's author guidelines page, have been adhered to and the appropriate ethical review committee approval has been received.
The guidelines It was approved by the Research Ethics Committee in humans of the Federal University of São Carlos (UFSCar).