Analgesic Efficacy of Transcutaneous Electrical Nerve Stimulation - Essay Example

Evaluation of the Current Strength of Evidence for analgesic efficacy of Transcutaneous Electrical Nerve Stimulation for Post Operative Pain Management in Children Name: College: Date: Evaluation of the Current Strength of Evidence for analgesic efficacy of Transcutaneous Electrical Nerve Stimulation for Post Operative Pain Management in Children Pain following surgery is a common cause of serious sufferings in people belonging to all age groups, especially in children (Gedhoo, 2004). Therefore effective management of pain is fundamental for maintaining high quality of health care services. Since the use of conventional analgesic drugs (especially opioids) is limited by numerous side effects like nausea, vomiting, respiratory depression, hypotension, constipation, urinary retention, addiction etc, there has been an increasing trend towards the use of complimentary therapies for effective pain management. Also pain is a symptom which greatly varies from individual to individual and its severity is often related to the psychological, cognitive and emotional responses of an individual towards tissue damage. As a result, use of complementary, non-pharmacological therapies for management of pain appears to be an effective and safe option (Zollman & Vickers, 1999). Complimentary therapy has been defined by the Zollman and Vickers (1999, p.693) as “group of therapeutic and diagnostic disciplines which exist outside the institutions where conventional health care is taught and provided.” Some of practices of complimentary medicine like chiropractic medicine, transcutaneous electrical nerve stimulation (TENS), acupuncture etc are increasingly being accepted and used clinically by mainstream medical practitioners (Zollman & Vickers, 1999). Complimentary therapy is now increasingly becoming an important aspect of the health care system in the U.K. Transcutaneous electrical nerve stimulation Transcutaneous electrical nerve stimulation is a drug-free method of pain relief in which a small machine, called the TENS unit is used to transmit electrical currents through the skin to stimulate the underlying nerve endings at or near the area where pain occurs (Hicks, 2006). The electric impulses which are generated by the TENS device are delivered to the area of pain through the sticky pad electrodes, which are placed on the skin in the painful area. Electrical impulses which stimulate the nerve endings at or near the site of pain help in diminishing the pain. Mechanism through which TENS work is not known for sure. Depending on the intensity and frequency of electric current used by TENS machine, it can be sub-classified into two sub-types: low-intensity (1–2 mA) and high-frequency (50–100 Hz) TENS or high-intensity (15–20 mA) and low-frequency (1–5 Hz) TENS (White et al, 2001).The mechanism of action of TENS is thought to involve both spinal (gate-control theory) and supraspinal theories (release of endogenous opioid like substances). High-frequency and low-intensity TENS is thought to control pain through ‘Melzack and Wall’s theory of spinal gating’ (Erdogan et al, 2005). According to this theory activation of large myelinated afferent nerve fibres though TENS would inhibit transmission of pain impulses in small and unmyelinated primary afferent nociceptive fibres (A-delta fibres and C fibres), which are responsible for transmitting painful impulses to the brain. Blocking of nerve impulses in these fibres thus would provide relief from pain. On the other hand, low-frequency and high-intensity TENS work by stimulating the production of natural pain-relieving hormones called β endorphins in the body (Erdogan et al, 2005). TENS machine can be used for 15 to 20 minutes, several times a day (Hicks, 2006). Since the device can be controlled by the patient himself, he can manipulate its use depending on the amount of pain he is experiencing. Various parameters of the TENS machine like frequency, duration and intensity of electric current and the site of stimulation can influence the effectiveness of TENS machine (Chen et al, 1998). These .parameters of the TENS machine can be adjusted by the health care professional depending on the patient’s underlying medical condition. TENS is increasingly being used in treatment of acute pain (migraine, dysmenorrhoea, pain due to bursitis, musculoskeletal pain following sports injury, labour pain etc) as well as chronic pain (chronic back pain, chronic pain of arthritis etc) (White et al, 2005). Post operative pain immediately following surgery is acute in nature. Tissue damage as a result of surgery may set up pathophysiological processes in the peripheral and central nervous systems leading to production of chronic pain which may start several days after surgery (Gehdoo, 2004). Neuropathic pain due to nerve injury can also commonly develop post-surgery (Gehdoo, 2004). Thus in order to prove beneficial in post-operative patients, the TENS should be able to counteract all these types of pains. Use of TENS machine is not associated with any significant side effects side. Only minor side effects like skin irritation, minor allergic reactions or skin burns have been seen to be associated with the use of TENS machine (Chen et al, 1998). However these can be easily avoided if proper precautions are taken. These include: use of gel before applying the electrodes, proper cleaning of patient’s skin before application of electrodes, etc (Chen et al, 1998). Since the use of complimentary therapy like TENS for relief from pain is devoid of any significant adverse effects and risk of addiction, it presents as a lucrative option for providing relief from post-operative pain, especially in children (Gehdoo, 2004). In immediate post-operative period, children might find it difficult to take analgesics orally. Also children have an inherent fear towards parental and intramuscular injections. Non-pharmacological therapy like TENS is easily accepted by the children (Gehdoo, 2004). Thus use of TENS is increasingly being considered in children especially to provide relief against post-operative pain (Gehdoo, 2004). This essay will focus on review of existing evidence regarding the efficacy of TENS in control of pain following surgery in children and on the rigorousness of that evidence. Gehdoo (2004), in a systematic review of literature, evaluating the effectiveness of various strategies in controlling post-operative pain has suggested the use of non-pharmacological modalities like TENS in children in order to provide effective relief against post-operative pain. However no large randomized case-controlled study evaluating the effectiveness of TENS in controlling post-operative pain in children could be identified in the available published literature. Therefore I have presented the evidence regarding the efficacy of TENS in controlling post-operative pain in adults. Current Evidence Regarding the Efficacy of TENS in Controlling Post-Operative Pain Various studies conducted till now have presented conflicting results regarding the effectiveness of TENS in providing relief from postoperative pain. The Royal College of Anaesthetists (U.K) do not regard TENS as an effective modality for proving relief against moderate to severe postoperative pain (Hicks, 2006). In the U.K, TENS is mainly being used for providing relief from labour pains in women. However at present there is there is no good evidence regarding its effectiveness in providing relief from labour pains. TENS has been used extensively to control postoperative pain, but its effects in controlling post operative pain in different studies have been found to be controversial. While Carroll et al, who conducted a systematic review of literature in 1996 did not find any beneficial action of TENS in providing relief from post-operative pain, some of the recently conducted randomized trials have highlighted beneficial effect of TENS when used post-operatively, especially after surgical procedures like thoracotomy (Erdogan et al, 2005) hysterectomy and myomectomy (Chen al, 1998), haemorrhoidectomy and dental surgeries (White et al, 2001). Postthoracotomy pain has been considered to be one of the most severe forms of pain. This pain is also responsible for reducing the lung compliance causing inability to exhale or cough out forcefully. This can result in retention of pulmonary secretions, atelectasis, and lung infection (Erdogan et al, 2005). Use of conventional analgesic agents like opioid medicines in such patients can cause further respiratory depression. Thus, use of TENS, which is free from the side effect of respiratory depression, has increasingly been considered in patients who have undergone thoracotomy in order to provide relief from post-thoracotomy pain. Erdogan et al (2005) conducted a prospective, randomized, double-blind, placebo-controlled study in order to investigate the efficacy of TENS for controlling post-operative pain in patients undergoing thoracotomy. In this study, the use of TENS during the post-operative period for first five days after the surgery caused a statistically significant (P = 0.013) reduction in requirement of opioid analgesics and improvement in pulmonary function tests during postoperative period in the study group in comparison to the control group. Also the use of TENS in this study was not associated with any side effects or intolerance. Thus use of TENS can help in significantly reducing the side effects related to opioid analgesics. The study by Chen et al (1998) has shown that use of Transcutaneous electrical stimulation in women following uterine surgeries (myomectomy, hysterectomy etc) can significantly decrease the requirement for opioid analgesics in the post-operative period. Use of TENS in this study was also associated with reduced incidence of opioid-related side effects like nausea, dizziness, respiratory depression etc. This study has also shown that the site of electrical stimulation is an important determinant of effectiveness of TENS in providing relief against post-operative pain. This fact was demonstrated by this study because, decreased requirement for post operative opioids was observed in the study only when electrical stimulation was applied at the dermatomal levels corresponding to the area of skin incision or at Zusanli acupoints, which are traditional Chinese points use in acupuncture (corresponding to the dermatome ST 36).The requirement for post-operative opioids was reduced by 35% in the patients who received electrical stimulation at peri-incisional dermatomes whereas it was reduced by 38% who received stimulation at traditional acupoints. Since the patients in this study in whom sham TENS (disabled TENS) was used also appeared to gain some degree of comfort from post-operative pain, it can be concluded that non-pharmacological therapy like TENS is also associated with some placebo effect (Chen et al, 1998). From the studies by Chen et al (1998) and Erdogan et al (2005), it can be observed that though the use of TENS, solely on its own may not lead to guaranteed pain relief , use of TENS in conjunction with other conventional modalities for pain treatments (parental and oral analgesics) is significantly effective. In the study by Erdoganet al (2005) use of TENS as the primary and sole method of pain control was effective against mild to moderate type of post-thoracotomy pain but it was not effective against severe postthoracotomy pain. Thus TENS should be used along with other conventional methods of pain control especially in cases where pain is very severe in nature. Carroll et al (1996) conducted a systemic review of literature to show the effectiveness of TENS after various post-operative procedures like cardiothoracic, orthopaedic and gastro-intestinal surgeries, caesarean section etc. In this review they considered 46 studies, out of which 17 were randomized controlled trials and 29 were non- randomized trials. 10 studies were excluded from the analysis due to methodological problems, small size of studies etc. After considering the outcome of these 17 randomized controlled trials and 29 non-randomized controlled trials, Carroll et al (1996) reached a conclusion that adequate randomization of studies which estimated the pain outcome after use of TENS was of utmost importance in order to act as a source of good evidence. From the analysis of the results of seventeen well designed randomized controlled trials in their systematic review, Carroll et al (1996) reached a conclusion that TENS was not an effective intervention for controlling pain in post-operative patients. Carroll et al (1996) observed that TENS did not prove to be an effective method of pain control either with use of primary or secondary outcome measures or by measurement of pain using various pain scores. Primary outcome measures which measured the effectiveness of TENS based on its capability to reduce the consumption for other analgesics were more commonly used by most of the studies considered in this review. Secondary outcome measure was based on assessment of patient’s preference for TENS over other methods of pain control for purpose of pain control in future. Carroll et al (1996) also observed that beneficial effect of TENS machines as indicated by Agency for Health Care Policy and Research (AHCPR) for pain management of acute post-operative pain was probably due to the consideration of non-randomized trials in their analysis. Rigorousness of the current evidence Good quality and safe medical practice relies on good scientific evidence. Rigorous scientific evidence is based on well designed good quality studies. The study design and method of study plays a key role in determining the accuracy of the results of the study (Carroll et al, 1996). Some of features of the study which determine its rigorousness and can affect the accuracy of its results are described below. Randomization of clinical trials Randomization of a clinical trial is of utmost importance for it to be labelled as a good source of evidence (Carroll et al, 1996). This is so, since the accuracy of non-randomized trials may be affected by presence of confounding (contradictory) factors in the various study groups. Randomization of clinical trials involves random selection of the subjects (both cases and controls) to ensure that no bias is introduced due to the presence of confounding factors and all the groups in the study are statistically equivalent (Pildal et al, 2005). Non–randomization of clinical trials can result in overestimation of the analgesic effect of TENS in controlling acute-post-operative pain in children (Carroll et al, 1996). Systematic review of literature by Carroll et al (1996) has shown that out of various studies which aimed at estimating the efficacy of TENS, the studies which were non-randomized or which were not properly randomized resulted in over-exaggeration of positive results of TENS. In this systemic review Carroll et al (1996) observed that only two studies out seventeen adequately randomized studies showed positive effects of TENS in controlling post-operative pain, where as seventeen studies out of nineteen studies, which were not properly randomized showed positive effect of TENS in controlling post-operative pain. According to Schulz et al (1995, cited in Carroll et al, 1996) improper or inadequate randomization of clinical trials can lead to exaggeration of analgesic effectiveness of TENS machine in treatment of post-operative pain by as much as 40%. The studies by both Chen et al (1998) and Erdogan et al (2005) were randomized controlled trials thus they can be regarded as good source of evidence. Quality of randomized controlled trials The method of randomization is also equally important as it is vital to ensure that a particular therapeutic intervention is randomly allotted to the participants in a sequential and irreversible manner and also remains well concealed to the medical personnel who are in charge of enrolling the subjects and allocating treatment to them (Pildal et al, 2005). Selection bias can occur in randomized controlled trials if the researchers come to know about the subjects who would be subjected to a particular therapeutic modality (Pildal et al, 2005). The researchers might inadvertently allocate a particular treatment modality to a selected group of patients (e.g. those with a better prognosis or those with more severe disease). This may result in the introduction of selection bias. Unclear or inadequate concealment of random allocation is associated with approximately 20-30% exaggeration of the treatment effect of a therapeutic modality (Pildal et al, 2005). The method of randomization was not described by most of the studies reviewed by Carroll et al (1996) or in the studies by Chen et al (1998) and Erdogan et al (2005). Thus it is difficult to estimate the accuracy and quality of randomization of these studies. Proper blinding of trials Proper blinding of clinical trials is also important to eliminate selection bias and act as a source of good evidence. Double blinding of clinical trials implies that neither the patients nor the doctors, nurses and other staff involved in the research have any knowledge regarding the allocation of particular modality of pain control; neither of the parties knows whether the particular subject is getting active drug or placebo drug (Carroll et al, 1996). Blinding of a non-pharmacological procedure is more difficult as compared to blinding of drugs used for pain control. Not only is the machine visible to the patients, the patients would also be able to feel the electrical impulses produced by the machine. Most of the studies achieve blinding using ‘sham TENS machines’ or disabled TENS machines (in which batteries have been removed) or using machines which would produce electrical impulses below the required therapeutic threshold intensity. Schultz et al (1995, cited Carroll et al, 1996) have observed that lack of proper blinding of clinical trials aimed at estimating the clinical effectiveness of TENS in management of post-operative pain can exaggerate the effects of treatment by about 17%. The study by Chen et al (1998) was only singly blinded. This implies that patients were not aware of the particular pain control modality allotted to them but the doctors, nurses and other staff involved in the research knew whether a particular patient was give an active form of treatment or not. Thus positive results of this study could be an exaggeration related to presence of bias introduced in the absence of double blinding in the study. The study by Erdogan et al (2005) was double blinded. Thus this study acts as a good source of evidence. Nature of analgesic scoring method Since pain is a subjective sensation, measurement of pain and analgesic effect produced by the TENS machine can present as a difficult task. This is especially important in children as they might be too small (less than 4 years of age) to be able to speak out their feelings or convey their exact symptoms (Gedhoo, 2004). Furthermore, there is no reliable method available for assessment of child pain. Thus, it can become very difficult to evaluate the effectiveness of TENS in providing relief from post-operative pain, especially in children (Gehdoo, 2004). Carroll et al (1996) in their analysis observed that almost all studies included in their analysis, lacked the use of rigorous methods of pain scoring which would allow a proper statistical analysis. In most of the studies included in their analysis, pain scoring was based on the use of methods which did not allow data extraction for further detailed statistical analysis. Also the information was not presented in a format which could allow the meta-analysis of the results (Carroll et al, 1996). Therefore studies employing more rigorous methods of pain scoring, which allow adequate statistical analysis of the results are required in future (Carroll et al, 1996). Size of the studies Number of subjects included in the study is also an important determinant of the accuracy of the study results. Carroll et al (1996) reached their final conclusion about non-effectiveness of analgesic effect of TENS only after excluding studies which contained less than 10 subjects. The study by Chen et al (1998) consisted of 100 subjects with 25 subjects in each of the four groups: [Group I (sham TENS) Group II (electrical stimulation at the shoulders or nonacupoint), Group III (electrical stimulation at the peri-incisional dermatomal region) and Group IV (electrical stimulation at the Zusanli acupoints)]. Study by Erdogan et al (2005) also included more than 100 subjects. Type of controls used The type of control used can also affect the results of the study due to the inherent placebo effect related to non-pharmacological therapeutic interventions (Chen et al, 1998). Out of the 17 randomized controlled trials considered in the systematic review conducted by Carroll et al (1996), 14 studies compared the analgesic effect of TENS with sham TENS, whereas 3 studies compared the analgesic affect of TENS with the analgesic effect of opioid medicines. No difference was found in the analgesic effect in patients in which TENS was used in comparison to those in which sham TENS was used. Also, seven out of these seventeen randomized controlled studies compared the combined analgesic effect obtained by combination of TENS and opioid medicines with the analgesic effect produced by the use of opioid medicines as a sole source of analgesia. Of these seven studies, five studies failed to show any beneficial affect due to combined use of TENS and opioid medicines. Both the studies by Chen et al (1998) and Erdogan et al (2005) compared the analgesic affect of TENS against controls in which sham TENS were used. Other factors which can affect the accuracy of results Studies (Chen et al, 1998; Erdogan et al, 2005) have also shown that TENS may not be able to provide adequate post-operative pain relief on its own. However TENS may be effective when used in combination with other pain treatments. Thus studies in future need to focus on use of TENS as a sole method for producing analgesia as well use of TENS in combination with other conventional methods of pain control. The specific details regarding the stimulation parameters (intensity, frequency and duration of stimulation) employed by the TENS machine need to be adequately defined. Most of these parameters were lacking in the studies reviewed by Carroll et al (1996) and also in the studies by Chen et al (1998) and Erdogan et al (2005). Type of Research needed in future Order to Provide Rigorous Evidence for analgesic efficacy of TENS in Post-Operative Pain Management in Children. From the above discussion it becomes clear that in order to present as a good source of evidence, the clinical trials in future should be adequately randomized. The method of randomization is also equally important. Since larger sized studies tend to give more accurate results, multicentric studies including a large number of subjects across diverse geographical locations would give better results compared to trials involving the cases from a localized geographical location. Studies employing more rigorous methods of pain control, which allow adequate statistical analysis, should be conducted in future. Since the type of control used in the study may act as a source of bias due consideration must be given in order to select appropriate bias free controls for the study. Studies also need to be conducted to in order to determine the long term effectiveness and side-effects of this treatment modality, especially in children. Most of the studies documenting the safety of TENS have been conducted in adult subjects. The children may be more susceptible towards development of certain side effects in comparison to adults. Conclusion There is a need for an effective and risk free method for providing relief from post- operative pain, especially in children. Nowadays, a new complementary approach for pain relief, in form of TENS machine is increasingly being considered as a safe and effective method for providing relief from post operative pain in children. However current clinical evidence regarding the effectiveness of TENS is not adequate enough to advocate its use in children as a sole source of analgesia for post-operative pain management. The reliability of various studies aimed at estimating the analgesic effect of TENS remains controversial due of the potential sources of bias introduced due to improper randomization and blinding, defects in study design, improper methods of pain scoring and difficulty in quantifying the inherent placebo effect of the therapy. Also these studies have been conducted in adult subjects. Thus, there is a need for large well designed randomized double blinded controlled multicentric trials having rigorous and standardized methods of pain scoring conducted on children in future in order to determine the effectiveness of TENS in treatment of post-operative pain in children. Till the time results of such trials become available, the use of TENS should be limited to adjunctive therapy to be used along with conventional opioid and non-opioid analgesic agents for controlling post-operative pain. References Carroll, D., Tramer, M., Mcquay, H., Nye, B., & Moore, A. (1996) Randomization is important in studies with pain outcomes: Systematic review of transcutaneous electrical nerve stimulation in acute postoperative pain. British Journal of Anaesthesia, 77 (6), 798-803. Chen, L., Tang, J., White, P.F., Sloninsky, A., Wender, R.H., Naruse, R., & Kariger, R. (1998) The effect of location of transcutaneous electrical nerve stimulation on postoperative opioid analgesic requirement: acupoint versus nonacupoint stimulation. Anaesthesia Analgesia, 87, 1129-1134. Erdogan, M., Erdogan, A., Erbil, N., Karakaya, H., & Demircan, A. (2005) Prospective, randomized, placebo-controlled study of the effect of tens on postthoracotomy pain and pulmonary function. . World Journal of Surgery, 29 (12), 1563-1570. Gehdoo, R.P. (2004). Post operative pain management in paediatric patients. Indian Journal of Anaesthesia, 48 (5), 406-414. Hicks, R. (2006). Transcutaneous electrical nerve stimulation (TENS). 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