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Print version ISSN 0034-7094
On-line version ISSN 1806-907X
Rev. Bras. Anestesiol. vol.56 no.6 Campinas Nov./Dec. 2006
Transcutaneous electrical nerve stimulation in the relief of pain related to physical therapy after abdominal surgery*
Estimulación eléctrica nerviosa transcutánea no alivio del dolor postoperatorio relacionado con los procedimientos fisioterapéuticos en pacientes sometidos a intervenciones quirúrgicas abdominales
Rodrigo Marques TonellaI; Sebastião AraújoII; Áurea Maria Oliveira da SilvaIII
do Departamento de Cirurgia da FCM-UNICAMP; Fisioterapeuta do Centro de Terapia
Intensiva da Unidade de Emergência do HC da FMRP-USP
IIProfessor Assistente Doutor do Departamento de Cirurgia da FCM-UNICAMP
IIIDoutoranda em Clínica Médica pela FCM-UNICAMP; Fisioterapeuta da Enfermaria de Gastrocirurgia do HC-UNICAMP
METHODS: A clinical, randomized, prospective study was undertaken with 48 patients on the first postoperative day, who presented a pain score > 3 on the visual analogic scale (VAS). Patients were divided in three groups: Control Group: treated with the usual analgesic routine, without TENS, and with physical therapy; Study Group: treated with the usual analgesic routine associated with TENS and physical therapy; Contrast-Placebo Group: treated with the usual analgesic routine associated with physical therapy but TENS was off. A visual analogic scale of pain was presented to the patients before (M1), after TENS (M2), and after physical therapy (M3) cough, incentive spirometry, changing lateral decubitus and sitting to quantify the efficacy of the analgesia. Electrical stimulation was done during 30 minutes.
RESULTS: The Study Group presented a significant relief of the pain when compared to the other two groups only for coughing at M3 (p= 0.015). In this group, there was a significant reduction in pain associated with coughing (p= 0.003) [M1 versus M3]; with lateral decubitus (p= 0.025), sitting (p= 0.001), and with incentive spirometry (p= 0.017) [M1 versus M2]; and when changing to the lateral decubitus (p= 0.03) and sitting (p= 0.001) [M1xM3]. There were no significant differences in the Contrast-Placebo Group.
CONCLUSIONS: The Study Group presented a reduction in pain in a few moments and parameters. Further studies are needed since TENS is indicated only as an adjuvant in controlling postoperative pain.
MÉTODO: Se realizó un estudio clínico, prospectivo, con distribución aleatoria, incluyendo 48 pacientes en el 1º día de postoperatorio, que presentaban un puntaje de dolor > 3 puntos en la escala visual analógica (VAS), divididos en tres grupos: Grupo Control: con rutina analgésica habitual, sin TENS y con fisioterapia; Grupo Estudio, recibiendo rutina analgésica habitual más TENS, y fisioterapia; Grupo Contraste-Placebo, recibiendo rutina analgésica habitual, fisioterapia y TENS desvinculada. Se presentó a los pacientes una escala visual analógica de dolor antes (M1), después de la TENS (M2) y después de la fisioterapia (M3) tos, incentivador respiratorio, cambio de decúbito lateral y sentado cuantificando la efectividad de la analgesia. El tiempo de electroestimulación fue de 30 minutos.
RESULTADOS: Hubo un alivio significativo del dolor en el Grupo Estudio, comparándolo con los tres grupos, apenas para el procedimiento tos, en el M3 (p = 0,015). Dentro de ese grupo hubo una disminución significativa del dolor para tos (p = 0,003) [M1 versus M3]; para decúbito lateral (p = 0,025), sentarse (p = 0,001) y utilizar el incentivador inspiratorio (p = 0,017) [M1 versus M2]; y al cambiar para decúbito lateral (p = 0,03) y sentarse (p = 0,001) [M1xM3]. No hobo diferencia significativa en el Grupo Contraste Placebo.
CONCLUSIONES: Hubo disminución del dolor en el Grupo Estudio, en algunos momentos y parámetros. Estudios adicionales se hacen necesarios, ya que la utilización de la TENS está indicada apenas como coadyuvante en el control del dolor postoperatorio.
Surgical procedures cause, inevitably, tissue damage, may it be by direct visceral manipulation, through the incision itself, and by the use of surgical retractors that help expose the surgical field. Pain after surgery causes discomfort to the patient, preventing the patient from relaxing, leading to shallow breathing, and hindering the patient's movements in bed 1. Thus, postoperative complications secondary to a difficult balance between thoracic and abdominal muscular activities, which decrease diaphragmatic breathing and cough efficacy that might lead to atelectasis, especially in the lower lung fields, are expected to worsen the inflammatory process and pain related to the surgical procedure even more 1.
The duration of the surgical procedure is another aggravating and important risk factor for postoperative pulmonary complications. It increases significantly postoperative complications due to the greater exposure to risk factors inherent to the procedure, such as mechanical ventilation, analgesics, and the accumulation of pulmonary secretions 2.
Moreover, it is known that early movement and ambulation are fundamental for an effective and fast postoperative recovery 3. Besides preventing pulmonary complications, ambulation also prevents the ileus that is frequent in the postoperative period of abdominal surgeries 4.
Pain is an important negative influence in the postoperative evolution of abdominal surgeries, especially those in the upper abdomen, even using analgesic drugs.
Transcutaneous electrical stimulation is a physical therapy tool widely used to relieve pain. It stimulates nerve fibers that send signals to the brain, which the thalamus interprets as pain. The impulses transmitted transcutaneously stimulate myelinated A fibers, which transmit proprioceptive ascendant information. These fibers are sensitive to interrupted biphasic and monophasic waves, such as those delivered by TENS. The effects of TENS follow the "Gate Theory" postulated by Melzack et al. 5 in 1965, in which the superstimulation of type A fibers block the entrance of stimuli conducted by type C fibers in the gates of the gelatinous substance, the posterior horn of the spinal cord, and the transmission cells 6.
Transcutaneous electrical stimulation can be used in the postoperative hospital routine as adjuvant to conventional analgesia 4,7,8. Besides being a non-invasive and non-pharmacologic technique, it is comfortable for the patient in 95% of the cases 4, can be effective in controlling pain after abdominal surgeries 9, and has no side effects 3,8,9.
It can prevent pulmonary complications, such as atelectasis, pneumonias, and others, secondary to the accumulation of pulmonary secretions, besides decreasing the use of analgesics 10, increasing mobility in bed, and allowing for early ambulation. Pain hinders the use of more vigorous physical therapy for bronchial hygiene and early exercises in bed 9. Early movement in bed associated with ambulation is fundamental for the patient's speedy recovery 3,11.
The aim of this study was to determine the efficacy of transcutaneous electrical stimulation (TENS) as an adjunct in decreasing patient's pain and discomfort, allowing for more effective physical therapy maneuvers in the postoperative period.
This study was approved by the Ethics Committee on Research of the Institution, protocol number 141/2001. Forty-eight patients, older than 18, who underwent abdominal surgeries and presented a pain score > 3, measured by the visual analogic scale (VAS) on the first postoperative day, were included in this study. Data were gathered during a 12-month period. After informing patients about the procedures to which they would be submitted, an informed consent was signed.
This was a randomized, prospective study, taking into consideration the presence of pain in the same severity reported in the first postoperative day. Patients were randomly divided in three groups: Control Group: followed the usual hospital analgesic routine and physical therapy; Study Group: followed the usual hospital routine regarding analgesics associated with TENS and physical therapy; and Contrast-Placebo Group: followed the analgesic routine, TENS was applied, but it was not turned on.
Exclusion criteria included patients younger than 18 years, with cognitive deficiencies that hinder understanding and signing of the informed consent, and the need for mechanical ventilation or vasoactive drugs for postoperative hemodynamic instability.
An electrical stimulation unit containing TENS, connected to the electrical network, and with rectangular (10 x 3 cm) silicone-rubber, carbon-treated electrodes. An aqueous gel was used and electrodes were fixed to the skin with hypoallergenic tape.
A form designed especially for this study was used to record the data, which included personal data, type of surgery, anesthesia, type of surgical incision, type of postoperative analgesia, pulmonary auscultation, and pain scores for cough, voluntary change of decubitus, and use of incentive spirometry in three different moments: before TENS (M1), immediately after TENS (M2), and after routine physical therapy (M3).
The visual analogic scale, graded from zero to 10, in which zero means no pain, and 10 very severe pain, was used for the objective evaluation of pain. It was used as a parameter to quantify pain, and was shown to the patient before and after each procedure proposed for the three groups allowing, therefore, for an evaluation of the change in pain score.
Electrodes were placed in a crossover periscar distribution, about 2 cm from the surgical wound (Figure 1). To apply TENS, the type of incision was not taken into consideration, but the presence of a pain score > 3 in the VAS for at least one physical therapy procedure and the first postoperative day were considered. Treatment with TENS lasted 30 minutes, and after each procedure the pain score was evaluated once more using the visual analogic scale. Respiratory physical therapy consisted of manual maneuvers of bronchial toilette, manual maneuvers of pulmonary reexpansion, vibro-compression using an electric vibrator, increase in the expiratory flow, and assisted coughing to aid expectoration of pulmonary secretions. Besides respiratory physical therapy, motor physical therapy, including leaving the bed and assisted ambulation, when possible, was also done.
The frequency used for TENS was 150 Hz with a pulse width between 150 and 250 ms, using two channels. The intensity of the electrical stimulation was changed according to the feeling reported by the patient in order to promote intense stimulation without discomfort. The physician's analgesic prescription was not changed.
After the patient arrived in the ward and was placed in bed, the informed consent was read to him/her. After all questions were answered, he/she signed the form or was asked to place his/her fingerprint. The visual analogic pain scale was shown to the patient at rest, explaining the proper way of using it. He was then stimulated to cough, while in the sitting position, with the bed at an inclination of about 45°. It was then followed by a voluntary change in decubitus, sitting, and finally the incentive spirometry. Pain scores were recorded after each procedure. Transcutaneous electrical stimulation was applied after these procedures after which pain scores were recorded once again. Respiratory and routine motor physical therapy were then performed and pain scores were recorded again.
The Kruskal-Wallis test was used to evaluate the differences in pain scores according to the physical therapy procedure among the three groups. The Friedman test was used to determine the presence of score differences according to the physical therapy procedures within each group at different moments (M1, M2, and M3). When this test demonstrated any difference, the Wilcoxon test was used to identify those moments (two by two). The Mann-Whitney and Wilcoxon tests were used to determine whether the use of analgesics contributed for the significant differences. A 5% level was considered significant.
Forty-eight patients, 20 (42%) women and 28 (58%) men, mean age of 49.6 years in the Control Group, 54.1 years in the Study Group, and 54 years in the Contrast-Placebo Group, were evaluated in this study. Table I shows the types of surgical procedures patients underwent. Incisions were infra umbilical (2%), right subcostal (17%), bilateral subcostal (25%), supra- and infra-umbilical (17%), and supra umbilical (39%). Table II shows the postoperative pharmacological analgesia used before TENS.
Comparing study groups in order to detect any intergroup differences for each parameter in each moment, i.e., before TENS (M1), after TENS (M2), and after physical therapy (M3), the only statistically significant difference occurred for the parameter cough in M3, that is, after TENS and physical therapy (p= 0.015) (Figure 2).
Initially, the differences within the Study Group, followed by the results of the Control Group are shown. The comparisons within the Contrast-Placebo Group did not show statistically significant differences at any moment for any of the parameters.
In the Study Group there were also differences for the parameters sitting and decubitus change in different moments, as shown in Table III. Pain scores were significantly reduced for the parameter sitting (M1 versus M2 and M1 versus M3), and also during changes in decubitus (M1 versus M2 and M2 versus M3).
Postoperative pain involves and worries the multidisciplinary team as far as choosing the best way of decreasing it, especially because its presence can mask postoperative surgical complications 12 and hinder physical therapy. Incisional pain at rest and during movements is one way that cellular lesion and inflammation secondary to the surgery manifest themselves. It is very often difficult to control with conventional analgesia with opioiods 13. In 2001, Nguyen et al. 14 concluded that pain at rest and with patient mobilization caused by laparoscopic gastroplasty was much less severe than that caused by the traditional surgery, with reduced use of postoperative morphine (p < 0.001), which was probably due to a reduced degree of surgical damage. In the current study, most patients complained of pain in the surgical incision in the immediate postoperative period.
The routine postoperative drug therapy for pain was maintained in every patient in this study. However, some of them were assisted by the physical therapist and evaluated by the protocol before the administration of the analgesics for that time. Statistical analysis showed that in all three groups the analgesic medication did not influence most of the procedures and moments.
Postoperative physical therapy is necessary for patient's recovery, having a preventive and curative action in some possible complications, such as atelectasis and penumonia 1. Routine physical therapy procedures can increase the patient's pain 15 because it uses manual resources and specific exercises associated with intense mobilization, improving respiratory function (maintenance of pulmonary permeability and expansion), and stimulating early ambulation (motor rehabilitation).
Postoperative respiratory physical therapy includes manual and mechanical (using an electrical vibrator) maneuvers of pulmonary reexpansion, mobilization of secretions through manual thoracic vibro-compression, stimulation of cough by verbal commands, assisted coughing, stimulation of the sternal notch, and stimulation of pulmonary reexpansion through respiratory exercises and incentive spirometry 16. Forced coughing, especially after surgeries in the upper abdomen, is one of the most painful procedures because it demands vigorous contraction of the diaphragm and abdominal musculature in the presence of a surgical wound with obvious inflammatory and painful processes. Although coughing is one of the procedures that increases pain the most, it is fundamental to mobilize and eliminate accumulated pulmonary secretions, guaranteeing the protection, hygiene, and equilibrium of the respiratory tract decreasing, therefore, the risk of atelectasis and infections.
Transcutaneous electrical nerve stimulation, a non-invasive procedure virtually devoid of side effects, can be used as an adjunct to conventional analgesia 4,7,8,13. In the present study, TENS was chosen to promote postoperative pain relief, especially that secondary to physical therapy maneuvers, in patients who underwent abdominal surgeries because the greater the patient's cooperation and participation in the exercises, the better the efficacy of the technique and the faster his/her recovery and rehabilitation.
Recently, Bjordal et al 10 published a metanalysis of the studies that used TENS for postoperative analgesia between 1966 and 2001. Results showed that TENS reduced the use of analgesics in the first three postoperative days, decreasing the side effects of opioids, besides promoting a statistically significant reduction in pain scores in the Study Group when compared to the Contrast-Placebo Group, which was also demonstrated in the present study. They also showed that it is necessary to use high intensity electrical currents (the maximum tolerated by the patient without causing discomfort) for better efficacy, which is also demonstrated in the present study.
Postoperative pain is caused, basically, by tissue damage and the resulting inflammatory process. There is also the primary postoperative hyperalgesia, which is an extension of the local painful process to areas adjacent to the lesion due to the increased release of painful mediators. This process reduces pain threshold and increases the sensitivity of adjacent nerve endings, causing hyperalgesia to stimuli that were not previously painful, such as touch 17. Performing any procedure during this process can cause even more pain, especially while mobilizing and moving the patient, which reflects in the area of the surgical wound 13.
In this study, TENS was effective in relieving pain caused by physical therapy maneuvers only for the parameter cough in M3, i.e., after physical therapy (p = 0.015). It is important to decrease cough related pain due to the possible pulmonary complications that can happen after abdominal surgeries. Besides, decreasing pain when the patient coughs may guarantee an effective bronchial toilette, early pulmonary rehabilitation, and prevention of atelectasis and pneumonia secondary to accumulation of secretion. This data is similar to that obtained by Ali et al. 9, who also demonstrated the efficacy of TENS in relieving postoperative pain when taking into consideration the increased forced vital capacity (FVC) and residual volume (RV), therefore decreasing the tendency for respiratory complications by decreasing pain in the surgical wound.
In the TENS Group there was also a reduction in pain scores when performing some procedures before and after electrical stimulation and after physical therapy, indicating the therapeutic importance of TENS as an adjuvant in respiratory and motor physical therapy.
Pain scores associated with coughing were reduced in the Study Group comparing scores between M1 and M3 (p = 0.009) and between M2 and M3 (p = 0.003). This reduction in scores demonstrated the efficacy of TENS as an adjuvant in controlling pain for physical therapy. It is important to mention that the scores in M3 (after physical therapy) were even smaller than in M1 and M2. The efficacy of the analgesia with TENS was important, allowing patients to perform the necessary physical therapy procedures, and the reduction in the score at the last moment demonstrates the continuation of the analgesic effect of TENS during coughing. This effect obtained after physical therapy can be explained by the modulation of pain caused by TENS in the A delta fibers that conduct nociceptive stimuli. During mobilization, pain is transmitted through the A delta fibers. However, opioids inhibit the C fibers, making it less effective in controlling pain triggered by moving or coughing12,13. Transcutaneous electrical stimulation generates a tactile stimulus that is transmitted by C fibers, closing the gate to the painful stimulus generated by the A delta fibers13.
Besides respiratory physical therapy, patients were also submitted to active exercises of the upper and lower limbs, sitting on a chair with assistance and, even after all these procedures, the final score when coughing maneuvers were performed did not increase.
Incentive spirometry in the postoperative period of abdominal surgeries is recommended as an adjuvant in lung reexpansion, since it provides the patients feedback on their efforts through the number of spheres elevated with each inspiration and is widely used in hospitals to prevent pulmonary complications 18. The proper use of this instrument depends on the understanding of the technique. A diaphragmatic reeducation is necessary to perform this exercise in order to promote pulmonary reexpansion, preferentially in the bases, with a predominantly diaphragmatic respiratory pattern and sustained maximal inspiration 19. Diaphragmatic excursion is weakened by the painful process and local edema caused by the abdominal surgery, incentive spirometry is a potential source of added pain.
There was a significant reduction in pain scores with incentive spirometry in the Study Group when M1 was compared to M2. Transcutaneous electrical neuro stimulation reduced pain effectively for this parameter only in M2, i.e., shortly after electrical stimulation. Pain scores were not reduced in M3, after physical therapy, and the analgesic efficacy of TENS in controlling pain associated with this parameter in M3 was not demonstrated. Since the knowledge about the technique can influence directly the performance of incentive spirometry, it is possible that the patients already knew the device and/or had a better respiratory pattern after physical therapy, while sitting outside the bed, which enabled them to use the device more effectively, resulting in a higher pain score than recorded shortly after TENS.
In the Study Group, the reduction in pain scores in the three moments also happened for decubitus change and sitting. There were statistical differences between M1 and M2 (p = 0.025) and between M1 and M3 (p = 0.03) for decubitus change, and between M1 and M2 (p = 0.001) and M1 and M3 (p = 0.001) for sitting. Note that the effectiveness of TENS in these procedures was already evident in M2, i.e., immediately after it was done. Its effects lasted until after physical therapy (respiratory and motor), with a lower score than the initial one (before TENS). The reduced score is important for decubitus change and sitting, since these procedures demand intense recruitment of the abdominal musculature (rectus abdominis and abdominal oblique), and this must be done in the presence of a surgical wound in the abdomen that is painful when mobilized 13. Early mobilization is important because it prevents ileus 4, the respiratory complications described previously, and even vascular complications, such as deep venous thrombosis 20.
Ambulation was initially chosen as a parameter to evaluate pain scores, but its implementation was jeopardized because it had to be done in three moments, before any other intervention. Ambulation is usually done after all respiratory and motor physical therapy procedures in bed are done, precluding the inclusion of ambulation in the study, although it had been done during the routine motor physical therapy, in M3.
Another point that is worth mentioning is that there are very few studies in the literature evaluating TENS as a means of decreasing pain during physical therapy. Most works compare analgesia with TENS and conventional analgesia, or the decreased need for analgesics with TENS without taking into consideration that patients need postoperative physical therapy. In 2003, Rakel and Frantz 13 showed that TENS reduced the severity of pain during deep inspiration and ambulation in the first postoperative day.
Transcutaneous electrical neuro stimulation decreased pain scores for some procedures and moments. However, these results must be analyzed cautiously because the study population was small and the differences were not so noticeable. Thus, the use of TENS as a non-pharmacologic analgesic alternative should be further studied, since it is only indicated as an adjuvant in the control of postoperative pain and pain caused by physical therapy maneuvers.
The authors would like to thank the physical therapist Lucian Ysayama, master in Experimental Research by the Surgery Service of the Faculdade de Ciências Médicas da Universidade Estadual de Campinas (FCM-UNICAMP), and Professor José Milton Sanches for the statistical analysis of the data.
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Dr. Rodrigo Marques Tonella
Rua Izabel Pantaleão Silveira, 304 Parque São Quirino
13088-650 Campinas, SP
Submitted for publication
26 de janeiro de 2006
Accepted for publication 30 de agosto de 2006
* Received from Enfermaria de Gastrocirurgia do Hospital das Clínicas da Universidade Estadual de Campinas (HC-Unicamp), Campinas, SP