Complementary Therapies in Clinical Practice 20 (2014) 5e10
Contents lists available at ScienceDirect
Complementary Therapies in Clinical Practice journal homepage: www.elsevier.com/locate/ctcp
High frequency TENS as a complement for pain relief in postoperative transition from epidural to general analgesia after pancreatic resection Kristofer Bjerså a, b, *, Thomas Andersson c a
Division of Nursing, Department of Neurobiology, Care Sciences and Society, Karolinska Institutet, Stockholm, Sweden Division of Nursing Science, Department of Medical and Health Sciences, University of Linköping, Linköping, Sweden c Department of Surgery, Sahlgrenska University Hospital, Gothenburg, Sweden b
a b s t r a c t Keywords: Transcutaneous electrical nerve stimulation Complementary therapies Epidural analgesia Postoperative pain Pancreaticoduodenectomy
Aim: This study investigated the effect of high frequency transcutaneous electric nerve stimulation (TENS) as a pain relieving complementary therapy at the transition from epidural (EDA) to general analgesia after pancreatic surgery by horizontal, abdominal incision. Method: Fifty-five consecutive patients undergoing pancreatic resection were enrolled in the study and randomly assigned to active or sham TENS treatment. Twenty subjects were included in the analysis. Pain, quality of recovery and additional analgesia consumption were measured during the 24 h of transition from EDA to general analgesia. Results: Additional analgesic consumption and pain estimations at 24 h after EDA termination differed between the two groups, but was not statistically significant. Conclusion: This study did not find support to reject use of high frequency TENS as complement during transition from EDA to general analgesia after major abdominal surgery with horizontal incision. Ó 2013 Elsevier Ltd. All rights reserved.
1. Introduction Effective postoperative pain relief is a crucial factor for a successful recovery process after surgery. A good postoperative analgesic administration regime after abdominal surgery is epidural analgesia (EDA) [1,2], where analgesic infusion is given via a catheter in the epidural cavity and controlled by a pump. EDA is a feasible analgesia technique as concerns compliance and side effects if the catheter is correctly located corresponding to the origin of pain. However, EDA is not a predictor of faster and easier recovery [3]. During the postoperative phase, the analgesic regime will be changed from EDA to general, often per oral, analgesia combined with morphine injections when needed. Breivik [4] suggests that the transition from EDA to general analgesia is performed during the fourth to the fifth postoperative day after upper abdominal surgery. To our knowledge, there are no studies that have explored patients’ experience of this transition, even though the change in
* Corresponding author. Division of Nursing, Department of Neurobiology, Care Sciences and Society, Karolinska Institutet 23 300, 141 83 Huddinge, Sweden. Tel.: þ46 (0) 727 436156. E-mail addresses:
[email protected],
[email protected] (K. Bjerså). 1744-3881/$ e see front matter Ó 2013 Elsevier Ltd. All rights reserved. http://dx.doi.org/10.1016/j.ctcp.2013.11.004
analgesic regime often clinically results in increased pain for the patient during the 24 h after EDA termination. A non-invasive, complementary therapy against postoperative pain is transcutaneous electrical nerve stimulation (TENS). By placing electrodes on the skin in the area or the representative area (e.g. dermatome) of the pain, and applying a light electric voltage between the pads with a high frequency (80e100 Hz), it has been demonstrated that TENS, via stimulating A-beta fibres, activates the so called gate control in the dorsal horn at the same segmental level as the pain [5]. The clinical effect of TENS is disputed, due to a lack of high quality studies [6e12]. However, if TENS is applied with strong intensity against postoperative pain, it seems to result in better pain relief [13]. The effects of TENS after abdominal surgery are also contradictory, but some studies report TENS to be a feasible complement to pharmacological analgesia in the postoperative phase [14e16]. Use of TENS has reported very few side effects [17,18], which makes it useable even in fragile patients. A study by Chandra et al. [19] advises the use of TENS as a complement to EDA after thoracotomy to decrease patients’ pain intensity. Hence, to our knowledge, no previous study has investigated the benefit of TENS in postoperative termination of EDA. The aim of this study was therefore to investigate the effectiveness of TENS as a pain relieving complement at the transition from EDA to general analgesia after surgery by horizontal, abdominal incision.
6
K. Bjerså, T. Andersson / Complementary Therapies in Clinical Practice 20 (2014) 5e10
2. Method 2.1. Design This study was conducted as a prospective, randomized, singleblinded study. All patients scheduled for pancreas resection Ad Modum Whipple (pancreaticoduodenectomy) from October 2008 to June 2011, consecutively except for the summer months, were recruited to the study. Surgery and postoperative care were given at a university hospital in the west of Sweden. Inclusion criteria were pancreas resection with Peustow incision due to pancreatic cancer, postoperative analgesia as EDA, and that the patient should be TENS naïve. Exclusion criteria were pacemaker, not having Swedish as the native language, cognitive or psychiatric diagnosis, active abuse of alcohol or drugs, and additional or unexpected surgery after the primary operation. Patients were consecutively recruited and randomized into one of two groups, active TENS with high frequency, strong intensity, and sham TENS with high frequency,
barely noticeable intensity, before termination of the EDA infusion. Randomization was done by a person from an independent institution, not involved in the study. The assistant randomly put information about allocation to the two groups in opaque sealed envelopes. Each subject was randomized by taking the prepared envelops consecutively. The patients were blinded to the group to which they were randomized. A total of 55 subjects were included, and 20 of these completed the full study protocol (see Fig. 1). 2.2. Treatment All patients were treated according to a standard care protocol and postoperatively given thoracal epidural analgesia with an infusion of Bupivacain 1 mg/ml, Fentanyl 2 mg/ml and Adrenaline 2 mg/ml [4,20]. When EDA infusion was terminated, analgesia were given per os as 400 mg/day tramadol hydrochloride (Tradolan retardÒ 200 mg morning and evening) and 4 g/day paracetamol (PamolÒ 500 mg two tablets morning, lunch, supper and evening).
Patients planned for pancreatic resection Ad Modum Whipple October 2008 to June 2011 n= 102 Age (mean/median/min-max):62.5/64/35-81 Gender (men/women): 51/51
Surgery during summers n= 16 Age (mean/median/min-max):58.8/60.5/39-78 Gender (men/women): 5/10
Patients approached for study participation n= 86 Age (mean/median/min-max):63.2/64.5/36-81 Gender (men/women): 40/46
Exclusion n= 31 Age (mean/median/min-max):57.6/57/36-75 Gender (men/women): 17/14 Reasons: Declined participation (n=14) Non Swedish speaking (n=10) Previous use of TENS (n=7)
Patients randomized for study participation n= 55 Age (mean/median/min-max): 66.4/67/50-81 Gender (men/women): 26/29
Allocated to active TENS treatment
Allocated to sham TENS treatment (control)
n=25 Age (mean/median/min-max): 67.7/68/58-81 Gender (men/women): 13/12
n=30 Age (mean/median/min-max): 65.3/65.5/50-81 Gender (men/women): 13/17
Dropout
Dropout
n=16 Age (mean/median/min-max): 66.9/68/58-81 Gender (men/women): 8/8 Reasons: Radical surgery not possible (n=9) Change to other analgesia then EDA (n=4) Decline participation postoperatively (n=3)
n=19 Age (mean/median/min-max): 65.2/65/50-81 Gender (men/women): 5/14 Reasons: Radical surgery not possible (n=9) Change to other analgesia then EDA (n=5) Decline participation postoperatively (n=2) Postoperative EDA complications (n=2) Postoperative cognitive function failure (n=1)
Analyzed subjects
Analyzed subjects
n=9 Age (mean/median/min-max): 69.1/68/61-81 Gender (men/women): 5/4
n=11 Age (mean/median/min-max): 65.5/66/78-75 Gender (men/women): 8/3
Fig. 1. Flow chart of study subject, exclusion and dropouts.
K. Bjerså, T. Andersson / Complementary Therapies in Clinical Practice 20 (2014) 5e10
When needed, and/or if pain ratings on the visual analogue scale (VAS) were >40 mm, a 5 mg intra venues injection of morphine hydrochloride (morphine 10 mg/ml á 0.5 ml per occasion) was administered, with a minimum of ten minutes between injections. TENS was given to all participants as a biphasic, alternating current with a stimulation frequency of 80 Hz [17]. The TENS device used was Cefar rehab x4 (CefarCompex Scandinavia AB). Electrodes (oval self-adhesive, size 5 10 cm) were applied in three pairs: first pair bilaterally, cranial of the incision, second pair bilaterally, sacral of the incision, and third pair bilaterally of columna innervating the dermatome for Th5 to Th9, see Fig. 2. Cables and all sides of the electrodes were fixed by self-adhesive tape (MepixÒ). TENS treatment was regulated by the patient and given with no time limitations, except that every treatment period started, if not continuous, should be at least 30 min. It was also possible for the participants to continue TENS treatment as long as they desired during the hospital stay. For the active TENS group, participants were instructed to use the TENS with “as high intensity as possible, but without pain or discomfort”. Subjects in the sham TENS group were given the instructions to “increase stimulation until first sensitivity occurs and keep the stimulation as low as possible”. Such gentle TENS treatment is considered ineffective against postoperative pain [17]. TENS electrodes were applied two to four hours prior to EDA termination (approximately at 12 AM), followed by patient education and testing (see Fig. 3). Initially, due to the loss of sensitivity in the abdomen by the EDA, TENS treatment was given in the third electrode pair, i.e. bilateral columna (dermatome stimulation). Participants were instructed to use the TENS as much as possible, but, if necessary, request additional analgesia. Applying the electrodes and instructing the subject in successful use of the TENS took approximately one hour. 2.3. Measurements In addition to the demographics parameters, the measured variables were:
7
Quality of recovery measured with a Swedish version of Quality of Recovery 40 (QoR-40) [22], measured preoperatively, before EDA termination and after 24 h after termination. The total score was used for analysis, which varies between worst recovery (40 points) and best recovery (200 points). The total amount of additional analgesia consumption (Morphine) during the 24 h after EDA termination. EDA infusion rate (ml/h) at termination. Total time of TENS usage in minutes during the day of EDA termination and the day after. 2.4. Statistical analysis A power calculation on the primary variable VAS was initially performed, based on the Erdogan et al. [23] trial, with a clinical difference of 15 mm in VAS and an equal standard deviation, based on the large individual differences, with Alfa 0.05 and power 80%. The calculation estimated 20 subjects in each group, but 30 subjects in each group was desired due to the risk of dropout in the postoperative phase. Because of the unexpected high dropout rate and the time of inclusion (two and a half years), inclusion was terminated after 55 subjects. Demographic data were compiled using Microsoft Excel. Data are presented in numbers (n), mean, standard deviation (SD), median and range. The Area Under the Curve (AUC) was calculated using the trapezoidal rule, i.e. splitting the time span between measuring occasions in half, and was used as a summarizing variable of the pain scored with POM lying prone between prior to EDA termination and 24 afterwards. Analyses were performed using IBM SPSS version 19.0, SAS 9.2 and a local statistical software at Statistiska Konsultgruppen (http://www.stat-grp.se; Gothenburg, Sweden). Fisher’s non-parametric permutation test was used [24,25] for comparison of continuous variable between two groups. All the tests were two-tailed and conducted at the 5% significance level. 2.5. Ethical considerations
Pain by Pain-O-Meter (POM) [21], measuring perspectives, location and amount of current pain. Only pain estimations on a 100 mm scale are reported in this paper and in the following positions: Lying prone in bed (Primary variable), measured preoperatively, before EDA termination, and one, four and 24 h after EDA termination. After a short walk (at least ten steps), measured preoperatively, and four and 24 h after EDA termination. After five deep breaths sitting, measured preoperatively, and four and 24 h after EDA termination.
The Regional Ethics Review Board in Gothenburg, Sweden, approved the study (Dnr. 392-08). All participants received written and verbal information about the study before giving their written consent to participate. 3. Results Of the 55 subjects included in the study, 20 followed the study protocol. Patient demographics are presented in Table 1. Relevant differences between the groups are the EDA infusion rate, which
Fig. 2. TENS pad pair locations.
K. Bjerså, T. Andersson / Complementary Therapies in Clinical Practice 20 (2014) 5e10
Time
Surgery
Treatment
Measure
POM lying POM walking POM sitting QoR-40 Demography
1 hour after EDA termination
2 to 4 hours before EDA termination
Preoperatively
Apply electrodes, testing, teaching and starting dermatome TENS stimulation
POM lying QoR-40
EDA termination
8
4 hours after EDA termination
Start full TENS stimulation
POM lying
POM lying POM walking POM sitting
24 hours after EDA termination End TENS stimulation (if not request for continued treatment) POM lying POM walking POM sitting QoR-40 Total morphine consumption
Fig. 3. Timeline for intervention and measurements.
was lower in the active TENS, but not significant (p ¼ 0.057). There were no significant differences in TENS usage time (p ¼ 0.878). The primary variable was prone VAS measured on a 100 mm scale. There were no differences in pain ratings during the EDA termination interval (before EDA termination to 24 h after EDA termination) or at any rating occasion, as shown in Table 2. The change over time of prone pain estimation is also shown in Fig. 4. Pain ratings after walking and after deep breathing were also made preoperatively and four and 24 h after EDA termination but did not show any significant differences between the groups at any occasion (see Table 2). However, a non-significant mean difference of approximately 20 mm was observed between the groups at 24 h. Subjective recovery, measured by total score of QoR-40 with a best value of 200 and a worst value of 40, did not differ between the two groups at any time point or in change before EDA termination and 24 h after (see Table 2). Intra venous morphine consumption, given as extra analgesia, was measured from the termination of the EDA and until the following day. The active TENS group consumed a mean of 22.1 mg/ patient during these days and the control group 37.3 mg/patient (see Table 2). Other than the measured variables, in seven protocols comments from the patients and the nurses about the TENS treatment were documented. These stated that the TENS treatment restricted out-of-bed activities due to the additional cables and contributed to time spent on sorting snared cables and tubes and maintenance of the TENS pads. 4. Discussion The aim of this study was to investigate benefits of high frequency TENS as a pain relieving complement at the transition from EDA to general analgesia after surgery by horizontal, abdominal incision. However, it was not possible to detect any significant benefits in the time after EDA termination. The small sample size with scattered values present in this study may contribute to a statistical type II error, where a possible treatment effect is rejected. Based on the noticeable but non-significant difference in pain after walking and after deep breathing between the groups at 24 h as shown in Table 2, this is a reasonable possibility. Table 1 Demography of the study groups (n ¼ 20). Median and Range are presented in brackets after each mean value. Variable
Active TENS (n ¼ 9)
Sham TENS (n ¼ 11)
Body mass index (BMI) (kg/m2) Intraoperative time (min) Postoperative day of EDA termination EDA infusion rate at termination (ml/h) Usage of TENS the first day after EDA termination (min)
25 (24; 22e32) 341 (331; 226e499) 7 (7; 5e10)
25 (25; 18e33) 343 (343; 225e487) 7 (7; 6e9)
7.7 (8; 6e12)
9.5 (10; 4e12)
403 (390; 120e720)
400 (420; 90e800)
Also the non-significance may be due to the extensive surgical procedure, which demands extensive pain relief management. TENS may not be able to affect such strong pain. A previous study of patients operated with different thoracotomy procedures suggests that TENS is more suitable after minor surgery than major [26]. Further, Björdal et al. [17] report in a meta-analysis that there are few studies that find significant differences in postoperative pain measured by VAS in a TENS treatment group compared to sham or placebo treatment. Even if a difference in pain estimation occurs, it is vital to reflect on the clinical importance of such a change. As Gallagher et al. [27] state, a minimum of 13 mm in significant difference should be considered a clinically important change in pain measured by VAS. Analgesia consumption was lower in the active TENS group compared to the sham group but did not differ significantly. Björdal et al. [17] summarize that the majority of studies included in the analysis showed significant differences between TENS group and placebo group in postoperative analgise consumption. However, other studies report contradictory results [15,28]. Location, duration, frequency and intensity are central in the use of TENS [29,30]. Pad position is important [30,31] and in this study they were placed locally, “close to the incision”, as well as dermatome referred on the subject’s back. The intention was that, by using both these stimulation areas, it would be more likely to gain an analgesic effect from the TENS. However, no differences have been found in using dermatome located positioning in comparison to acupuncture point positioning in gynaecological, abdominal surgery [31]. The duration of TENS treatment in this study was without a time limitation but with a minimum of 30 min per started occasion and, according to the patient registrations, often used for hours in a row. In previous trials reporting a positive TENS effect, treatment duration varies from 30 min to constant TENS treatment for days, or during a whole procedure such as coloscopy [15,19,32e35]. Perhaps a better analgesic effect could have been obtained in this study if TENS had been administered constantly during the 24 h after EDA termination. Further research should determine the clinical possibility and whether this would be accepted by the patient. Regarding treatment frequency, a previous study indicates that high frequencies (80 Hz) are superior to low frequencies (2 Hz) in pain relieving effect [36]. There are however contradictory results [37]. Modelled frequency TENS, i.e. continuous alternating frequencies, has also been found, as a complement to conventional analgesia, to reduce pain intensity in walking and deep breathing after abdominal surgery [16]. Similar results after major gynaecological surgery showed favourable usage of modelled frequency (2e 100 Hz) in comparison to only high (100 Hz) or low frequency (2 Hz) [38]. It is possible that the results of this pilot study could have shown greater success if a modelled frequency had been used. Concerning intensity, Moran et al. [39] show that higher amplitude gives the best analgesic effect. As the amplitude was not measured in this study, it is unclear whether it could have been possible to elevate the amplitude further. However, based on the
K. Bjerså, T. Andersson / Complementary Therapies in Clinical Practice 20 (2014) 5e10
9
Table 2 Compilation of measure variables. Data are presented as: Mean (SD)/Median (Range). For comparison between groups, Fisher’s non-parametric permutation test was used for comparison between the groups. Variable VAS (mm) measured lying prone in bed Mean of area under the curve (AUC) for measurement occasions; before, 1, 4 and 24 h after termination (AUC0e24) VAS (mm) measured sitting on the bed after at least 10 steps walking Preoperatively 4 h after EDA termination 24 h after EDA termination VAS (mm) measured sitting on the bed after five deep breaths Preoperatively 4 h after EDA termination 24 h after EDA termination Postoperative recovery measured with a 40 questions questionnaire (QoR-40) Preoperatively Before EDA termination 24 h after EDA termination Change in quality of recovery 24 h after EDA termination and before EDA termination Morphine consumption Total consumed intra venous morphine during the 24 h after EDA termination (ml)
instructions given, the limit of coping with TENS should have been reached. Some patients may perceive self-administered TENS as difficult. The age and postoperative cognitive function among the subjects in this study may be a bias in using the TENS device. Support and assistance in using TENS was given, but some of the participants experienced having difficulties managing technical devices. Perhaps a non-patient-controlled TENS treatment would be more suitable for these people. However, this would impair the effect of patient control and participation. A more user-friendly TENS device is consequently recommended in further studies. The economic perspective is also important. TENS requires costly disposable electric pads and substantial time for the health
Active TENS (n ¼ 9)
Sham TENS (n ¼ 11)
p-Value
23.2 (19.3) 29.8 (0.0e56.1)
24.8 (18.1) 25.7 (0.5e61.3)
0.848
5.9 0.0 37.2 28.0 19.4 8.0
(15.9) (0.0e48.0) (40.1) (0.0e100.0) (32.5) (0.0e100.0)
2.6 0.0 44.4 42.0 39.6 28.0
(7.2) (0.0e24.0) (33.1) (0.0e100.0) (32.0) (8.0e100.0)
0.594
5.3 0.0 36.6 25.0 23.2 9.0
(16.0) (0.0e48.0) (41.4) (0.0e100.0) (32.7) (0.0e100.0)
4.0 0.0 35.3 39.0 37.0 30.0
(9.1) (0.0e30.0) (29.5) (0.0e100.0) (28.1) (9.0e100.0)
0.830
(14.6) (140.0e193.0) (15.4) (152.0e196.0) (19.3) (135.0e190.0) (11.2) (29.0e3.0)
0.597
182.3 190.0 165.7 172.0 164.6 167.0 1.1 4.0
(13.0) (157.0e194.0) (32.2) (110.0e196.0) (24.0) (126.0e200.0) (25.1) (48.0e41.0)
22.1 (23.7) 17.5 (0.0e70.0)
178.7 178.0 173.1 175.0 162.6 159.0 10.5 10.0
37.3 (23.1) 35.0 (10.0e80.0)
0.671 0.180
0.936 0.330
0.513 0.850 0.290
0.163
care staff to apply and adjust the TENS and to give patient education, at the same time with a minimum of side effects for the patient. This in contrast to the injection of analgesia such as morphine, with a low pharmacological cost and shorter administration time for the health care staff, but with known side effects that can influence the postoperative period. From these two perspectives and from the results of this study, it does not seem that TENS is beneficial in this setting. However, a multicenter collaboration to gain a correct number of subjects would be preferable in future trials. 4.1. Conclusion This study did not find support to reject use of high frequency TENS as a complement during transition from EDA to general analgesia after major abdominal surgery with horizontal incision. Conflict of interest statement The authors declare that they have no competing interests, and were free to interpret the data according to strict scientific rationale. Acknowledgement This study was supported by grants from the R&D council for Gothenburg and the south Bohuslän, Sweden. We also wish to thank Monika Fagevik Olsén, Elisabet Stener-Victorin, Anders Hyltander and Filip Rådberg for contributing to the study design, TENS treatment strategy and manuscript revision. References
Fig. 4. Pain estimation by VAS lying prone in bed at each measuring occasion and total during EDA termination by AUC mean (0 ¼ Before EDA; 24 ¼ 24 h after EDA). “Before EDA” represents the measurement made before the termination of EDA. Mean is marked by X.
[1] Flisberg P, Rudin A, Linner R, Lundberg CJ. Pain relief and safety after major surgery. A prospective study of epidural and intravenous analgesia in 2696 patients. Acta Anaesthesiol Scand 2003;47:457e65.
10
K. Bjerså, T. Andersson / Complementary Therapies in Clinical Practice 20 (2014) 5e10
[2] Mackintosh C. Assessment and management of patients with post-operative pain. Nurs Stand 2007;22:49e55 [quiz 8]. [3] Marret E, Remy C, Bonnet F. Meta-analysis of epidural analgesia versus parenteral opioid analgesia after colorectal surgery. Br J Surg 2007;94:665e 73. [4] Breivik H. How to implement an acute pain service. Best Pract Res Clin Anaesthesiol 2002;16:527e47. [5] Melzack R, Wall P. Pain mechanisms: a new theory. Science 1965;150:971e8. [6] Johnson MI. Does transcutaneous electrical nerve stimulation (TENS) work? Clin Eff Nurs 1998;2:111e20. [7] Meissner W. The role of acupuncture and transcutaneous-electrical nerve stimulation for postoperative pain control. Curr Opin Anesthesiol 2009;22: 623e6. [8] Osiri M, Welch V, Brosseau L, Shea B, McGowan J, Tugwell P, et al. Transcutaneous electrical nerve stimulation for knee osteoarthritis (Review). Cochrane Database Syst Rev 2009:1e22. [9] Khadilkar A, Milne S, Brosseau L, Robinson V, Saginur M, Shea B, et al. Transcutaneous electrical nerve stimulation (TENS) for chronic low-back pain (Review). Cochrane Database Syst Rev 2008. 3. [10] Mulvey MR, Bagnall AM, Johnson MI, Marchant PR. Transcutaneous electrical nerve stimulation (TENS) for phantom pain and stump pain following amputation in adults. Cochrane Database Syst Rev 2010;(5). [11] Robb K, Oxberry SG, Bennett MI, Johnson MI, Simpson KH, Searle RD. A cochrane systematic review of transcutaneous electrical nerve stimulation for cancer pain. J Pain Symptom Manage 2009;37:746e53. [12] Carroll D, Tramer M, McQuay H, Nye B, Moore A. Randomization is important in studies with pain outcomes: systematic review of transcutaneous electrical nerve stimulation in acute postoperative pain. Br J Anaesth 1996;77:798e803. [13] Bjordahl JM, Johnson M, Ljunggreen E. Transcutaneous electrical nerve stimulation (TENS) can reduce postoperative analgesic consumption. A metaanalysis with assessments of optimal treatment parameters for postoperative pain. Eur J Pain 2003;7:181e8. [14] VanderArk GD, McGrath KA. Transcutaneous electrical stimulation in treatment of postoperative pain. Am J Surg 1975;130:338e40. [15] Schomburg FL, Carter-Baker SA. Transcutaneous electrical nerve stimulation for postlaparotomy pain. Phys Ther 1983;63:188e93. [16] Rakel B, Frantz R. Effectiveness of transcutaneous electrical nerve stimulation on postoperative pain with movement. J Pain 2003;4:455e64. [17] Bjordal JM, Johnson MI, Ljunggreen AE. Transcutaneous electrical nerve stimulation (TENS) can reduce postoperative analgesic consumption. A metaanalysis with assessment of optimal treatment parameters for postoperative pain. Eur J Pain 2003;7:181e8. [18] Rushton DN. Electrical stimulation in the treatment of pain. Disabil Rehabil 2002;24:407e15. [19] Chandra A, Banavaliker JN, Das PK, Hasti S. Use of transcutaneous electrical nerve stimulation as an adjunctive to epidural analgesia in the management of acute thoracotomy pain. Indian J Anaesth 2010;54:116e20. [20] Niemi G, Breivik H. Epidural fentanyl markedly improves thoracic epidural analgesia in a low-dose infusion of bupivacaine, adrenaline and fentanyl. A randomized, double-blind crossover study with and without fentanyl. Acta Anaesthesiol Scand 2001;45:221e32. [21] Gaston-Johansson F. Measurement of pain: the psychometric properties of the Pain-O-Meter, a simple, inexpensive pain assessment tool that could change health care practices. J Pain Symptom Manage 1996;12:172e81.
[22] Myles PS, Weitkamp B, Jones K, Melick J, Hensen S. Validity and reliability of a postoperative quality of recovery score: the QoR-40. Br J Anaesth 2000;84: 11e5. [23] Erdogan M, Erdogan A, Erbil N, Karakaya HK, Demircan A. Prospective, randomized, placebo-controlled study of the effect of TENS on postthoracotomy pain and pulmonary function. World J Surg 2005;29:1563e70. [24] Good P. Permutation tests. A practical guide to resampling methods for testing hypotheses. New York: Springer, Inc.; 2000. [25] Bradley JV. Distribution-free statistical test. London: Prentice-Hall, Inc.; 1968. [26] Freynet A, Falcoz PE. Is transcutaneous electrical nerve stimulation effective in relieving postoperative pain after thoracotomy? Interact Cardiovasc Thorac Surg 2010;10:283e8. [27] Gallagher EJ, Liebman M, Bijur PE. Prospective validation of clinically important changes in pain severity measured on a visual analog scale. Ann Emerg Med 2001;38:633e8. [28] Hargreaves A, Lander J. Use of transcutaneous electrical nerve stimulation for postoperative pain. Nurs Res 1989;38:159. [29] Bennett MI, Hughes N, Johnson MI. Methodological quality in randomised controlled trials of transcutaneous electric nerve stimulation for pain: low fidelity may explain negative findings. Pain 2011;152:1226e32. [30] White PF. The role of non-opioid analgesic techniques in the management of pain after ambulatory surgery. Anesth Analg 2002;94:577e85. [31] Chen L, Tang J, White P, Sloninsky A, Wender R, Naruse R, et al. The effect of location of transcutaneous electrical nerve stimulation on postoperative opioid analgesic requirement: acupoint versus nonacupoint stimulation. Anesth Analg 1998;87:1129e34. [32] Binder P, Gustafsson A, Uvnäs-Moberg K, Nissen E. Hi-TENS combined with PCA-morphine as post caesarean pain relief. Midwifery 2011;27:547e52. [33] Amer-Cuenca J, Goicoechea C, Girona-López A, Andreu-Plaza J, PalaoRomán R, Martínez-Santa G, et al. Pain relief by applying transcutaneous electrical nerve stimulation (TENS) during unsedated colonoscopy: a randomized double-blind placebo-controlled trial. Eur J Pain 2011;15:29e35. [34] DeSantana JM, Santana-Filho VJ, Guerra DR, Sluka KA, Gurgel RQ, da Silva WM. Hypoalgesic effect of the transcutaneous electrical nerve stimulation following inguinal herniorrhaphy: a randomized, controlled trial. J Pain 2008;9:623e9. [35] Cipriano Jr G, Carvalho ACC, Bernardelli GF, Peres PAT. Short-term transcutaneous electrical nerve stimulation after cardiac surgery: effect on pain, pulmonary function and electrical muscle activity. Interact Cardiovasc Thorac Surg 2008;7:539e43. [36] Chen CC, Johnson MI. An investigation into the hypoalgesic effects of high-and low-frequency transcutaneous electrical nerve stimulation (TENS) on experimentally-induced blunt pressure pain in healthy human participants. J Pain 2010;11:53e61. [37] Chen CC, Tabasam G, Johnson MI. Does the pulse frequency of transcutaneous electrical nerve stimulation (TENS) influence hypoalgesia?: a systematic review of studies using experimental pain and healthy human participants. Physiotherapy 2008;94:11e20. [38] Hamza MA, White PF, Ahmed HE, Ghoname EA. Effect of the frequency of transcutaneous electrical nerve stimulation on the postoperative opioid analgesic requirement and recovery profile. Anesthesiology 1999;91:1232e8. [39] Moran F, Leonard T, Hawthorne S, Hughes CM, McCrum-Gardner E, Johnson MI, et al. Hypoalgesia in response to transcutaneous electrical nerve stimulation (TENS) depends on stimulation intensity. J Pain 2011;12:929e35.
