ARTICLE IN PRESS. 2 Work in progress report - Cardiac general 3. 6 muscle activity 7 a, b b

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1 icvts Mp 1 Friday Apr :45 AM 5,18 ARTICLE IN PRESS doi: /icvts Interactive CardioVascular and Thoracic Surgery xxx (xxx) xxx xxx 2 Work in progress report - Cardiac general 4 Short-term transcutaneous electrical nerve stimulation after cardiac 5 surgery: effect on pain, pulmonary function and electrical 6 muscle activity 7 a, b b 8 Gerson Cipriano Jr. *, Antonio Carlos de Camargo Carvalho, Graziella França Bernardelli, 9 Paulo Alberto Tayar Peres b acardiovascular Surgery Division, Department of Surgery, Federal University of São Paulo, Napoleão de Barros, 715, rd floor, , São Paulo, SP, Brazil 12 bcardiology Division, Department of Medicine, Federal University of São Paulo, São Paulo, Brazil 14 Received 19 September 2007; received in revised form 22 March 2008; accepted 25 March Abstract This study aimed to evaluate the effectiveness of transcutaneous electrical nerve stimulation (TENS) for treatment of postoperative pain 29 in patients who underwent cardiac surgery. In addition, we sought to determine whether TENS would be related to improved pulmonary 0 function and muscle electrical activity in this patient population. Forty-five patients, 2 males and 1 females, aged years were 1 randomly allocated to receive TENS (ns2) or sham treatment (ns22) during 4 h on the third postoperative day. A 0 10 visual analogic 2 scale was used to assess pain; lung function was evaluated by spirometry and surface electromyography (ns10 in each group) was used to quantify electrically-induced muscle activity (trapezius and pectoralis major). TENS was associated with significant reductions on 4 spontaneous and cough-induced postoperative pain as compared to sham (P-0.05). There was also improvement in chest wall-pulmonary 5 mechanics after TENS with proportional increases in tidal volume and vital capacity (P-0.05). In addition, electrical activity of both 6 muscle groups was enhanced after TENS, but not post sham (P-0.05). TENS is a valuable strategy to alleviate postoperative pain following 7 cardiac surgery with positive effects on pulmonary ventilatory function and electrical activity of thoracic and girdle muscles Published by European Association for Cardio-Thoracic Surgery. All rights reserved Keywords: Transcutaneous electrical nerve stimulation; Cardiac surgery; Pain; Pulmonary function; Electromyography Introduction In addition, decline on pulmonary-ventilatory function was not always lessened after TENS w7x. Therefore, the actual Cardiac surgery is a life-saving procedure which is fre- role of TENS in controlling post-cabg pain and its undesir quently related to significant postoperative pain w1x. A able consequences is still controversial number of lung defense mechanisms may become impaired, The present study was undertaken to evaluate if short or overtly ineffective, due to intense chest pain: deep term TENS (4 h) would present with positive effects on breathing, body mobilization and, in particular, coughing postoperative pain, pulmonary function and local muscle w2x. Although narcotics and opiates may be effective for electrical activity after cardiac surgery as compared to pain control, they are associated with side effects, includ- 52 ing respiratory depression wx. Therefore, there is a longplacebo TENS standing interest in the development of non-chemical 54 strategies for effective pain control. 2. Material and methods 7 55 Transcutaneous electrical nerve stimulation (TENS) has Forty-five patients (aged years, 2 males and been used since the early 1970s as an adjunctive therapy females) from the teaching hospital of the Federal Univer for chronic and acute pain control in several medical and sity of São Paulo comprised the study group. All patients surgical conditions w4x. TENS has also been shown to be underwent cardiac surgery through median sternotomy by effective in the postoperative period of cardiac and nonthe same surgical team and intra-operative anesthesic cardiac thoracic surgery w5 9x. However, the positive protocol. The surgeries included coronary artery bypass effects of TENS have not been uniformly reported: some graft (CABG) (ns4), valve replacement (ns5), aortic researchers found that TENS was not effective in all surgery (ns5) and Mixom (ns1). From 4 patients who 81 6 patients, especially in those with more intense pain w7, 8x. were submitted to CABG, saphenous vein (ns) and internal thoracic arteries (ns0) were used for grafting *Corresponding author. Tel.: q(55) (11) ; fax: q(55) (11) They had no other abnormalities or conditions that required address: ciprianeft.dcir@epm.br, another surgery at the time of the cardiac surgery. Informed ciprianeft@uol.com.br (G. Cipriano Jr.). consent (as approved by the Institutional Medical Ethics Published by European Association for Cardio-Thoracic Surgery 1 15

2 2 G. Cipriano Jr. et al. / Interactive CardioVascular and Thoracic Surgery xx (2008) xxx xxx 87 Committee) was obtained from all patients before the airflow being measured by a calibrated turbine. The sub- 88 surgical procedure. jects completed at least three acceptable maximal slow expiratory maneuvers: vital capacity (VC, l) was recorded Design and procedures Tidal volume (V T, ml) and respiratory rate (RR, bpm) were also obtained. 90 This was a prospective and randomized study. The patients 91 were randomly allocated to the treatment arm only after Electrical muscle activity by biofeedback 92 surgery as peri-incisional pain was an inclusion criterion. (surface electromyography) 9 Out of 49 patients, four did not report significant pain. The Muscle electrical activity of the trapezius and the pector- 94 other 45 subjects were then submitted to TENS (ns2, 16 TM alis major was obtained by using the Myomed 92 System 95 males, aged years, body mass indexs26.".5 (Enraf Noniuns, Rotterdam, The Netherlands): positioning 2 96 kgym ) or sham TENS (ns22, 16 males, aged years, of a reference and two exploratory electrodes were stan body mass indexs26.5". kgym ). In the first preopera- dardized as described elsewhere w12x. In the present study, 98 tive day, the patients were submitted to spirometry; in the patients were asked to perform a maximum voluntary 99 addition, electrical activity of selected girdle and upper contraction against a fixed resistance during 4 5 s at stan- 100 thoracic muscle (trapezius and pectoralis major, respec- dardized positions w12x. The maneuvers were performed in 101 tively) was recorded. Patients were then familiarized with triplicate: the highest and the average value of electrical 102 the TENS equipment and an analogue-visual scale. After potential (ma) were recorded. 10 returning on the third postoperative day, the above-ment- 104 ioned outcomes were obtained before and after TENS or 2... Pain 105 sham TENS. The treatment was applied after the patients The participants were asked to quantify their incision pain 106 had remained at least 8 h without pharmacological using a numbered 10-cm analogue-visual scale ranging from 107 analgesia. 0 ( no pain at all ) to 10 ( the worst imaginable pain ) w1x. The scale was applied at rest and after the patients had Transcutaneous electrical stimulation coughed. 109 TENS and sham stimulation were delivered by a portable 110 stimulator (TENS Device, KLD, Amparo, SP, Brazil). The 111 electrical current was delivered by two self-adhesive sur- 112 face electrodes (10=.5 cm), which were placed at the 11 subclavicular region on either side of the incision, approx- 114 imately 2 cm from the suture line. During the 4-h treat- 115 ment period, pulse duration was kept constant (150 ms) at 116 a wave frequency of 80 Hz and a duty cycle (on:off time) 117 of 0y ms w10, 11x. The sham stimulation equipment 118 had the internal programming modified in order to reduce 119 the rest time between the pulses from 50 ms to 0 s, 120 without significant changes in sensations produced by the 121 stimulator. Therefore, after 4 h TENS group received almost min of active treatment current while the sham group 12 received only 2.7 min of active current. 124 Treatment duration was selected considering the local 125 characteristics of the postoperative unit: we reasoned that 126 longer stimulation period would significantly affect the 127 routine of patient s care. Patients adjusted the stimulation 128 intensity to the point that they felt a strong, but comfort- 129 able tingling sensation: they were specifically instructed as 10 reduce the stimulation intensity in case of pain. The same 11 equipment and treatment duration were used to deliver 12 sham TENS: the patients received identical instructions as 1 those in the active treatment group, even if they were not 14 sure if they were feeling any electrical current. They were 15 instructed that after some time with the equipment, it 16 could produce a continuous or intermittent current, being 17 both aimed to produce analgesia Measurements Spirometry 140 Spirometric tests were performed by using the Spirobank 141 TM G (Medical International Research, Rome, Italy) with 2.4. Statistical analysis Mean and standard deviations (S.D.) were obtained for spirometric and electromyographic data in subjects of both groups. Pain scores are reported as median and interquartile range. Repeated measures analysis of variance was used to assess the effects of TENS and sham stimulation. The probability of a Type I error was established at 0.05 (P-0.05).. Results.1. Effects of TENS on pain As expected, cardiac surgery was associated with significant pain, either spontaneously or after cough (Table 1). Electrical stimulation was well-tolerated by all patients and no relevant side effect was observed. There was a systematic decrease in pain after TENS treatment, especially cough-related pain: as shown in Fig. 1, all patients had lower pain scores (at least 1 U less) after active stimulation. Accordingly, TENS, but not sham, was related to significant decrease in median pain scores (Table 1). Improvement in pain was negatively associated with baseline pain: from nine patients with severe pain ()7U), seven of them decreased at least U after TENS (Fig. 2)..2. Effects of TENS on pulmonary function There were significant differences between pre- and postoperative values of all lung function variables: cardiac surgery was associated with lower tidal volume (V T) which reduction was less than that found for vital capacity (VC), i.e. VTyVC increased after surgery in both groups. As overall pulmonary-ventilation did not change, the patients adopted

3 G. Cipriano Jr. et al. / Interactive CardioVascular and Thoracic Surgery xx (2008) xxx xxx Table 1 4 Effects of transcutaneous electrical nerve stimulation (TENS) and sham TENS on pain (visual analogue scale, VAS), pulmonary mechanics and electrically-induced 5 muscle activity in patients who underwent cardiac surgery TENS (ns2) Sham stimulation (ns22) 9 10 Preoperative Postoperative Preoperative Postoperative 11 Pretreatment Posttreatment Pretreatment Posttreatment 20 Pain score (VAS) 21 Spontaneous (2) 2 (1) (1,5) (2,25) 22 Cough-induced 7 (2) 4 (2) 6 (1,5) 5 (2) 2 Lung function V E (lymin) 8.2" " " " " " V T (l) 0.47" "0.07* 0.46"0.08** 0.51" "0.07* 0.4" RR (bpm) 17" 20"4* 18"** 15"2 18"* 18" 28 VC (l) 2.2" "0.44* 1.8"0.41** 2.84" "0.57* 1.88" VTyVC 0.21" "0.05* 0.26" " "0.09* 0.25" RRyV T 6.4" "10.7* 40.9"10.0** 1.7" "9.5* 4.7"9.4 1 Electromyography 2 Trapezius Mean potential, ma 67"5 447"9* 525"44** 62"71 452"71* 4"10 4 Peak potential, ma 796"8 551"67* 651"80** 808"61 578"68* 59"6 5 Pectoralis Major 6 Mean potential, ma 171"28 105"10* 147"20** 171"25 105"9* 111"11 7 Peak potential, ma 200"28 114"10* 175"19** 205"2 120"1* 127"12 8 V E, minute ventilation; V T, tidal volume; RR, respiratory rate; VC, vital capacity. Data are reported as mean"s.d., with exception of pain scores (median and 9 interquartile range) P-0.05: *Preoperative vs. pretreatment postoperative; **post- vs. pretreatment in the postoperative period. ns10 in each group Fig. 1. Individual and mean effects of TENS (ns2) and sham (ns22) stim- 46 ulation in cough-induced incisional pain after cardiac surgery (data are over layed). *P a more tachypneic breathing pattern to attain the ventilatory demands (Table 1). After TENS treatment, there were significant and proportional increases in both VT and VC at similar ventilatory levels (Fig. ). In addition, respiratory rate (RR) and the RRyVT ratio decreased only in the active treatment group (P-0.05)... Surface electromyography In similarity with the above-mentioned data, mean and peak electrical potentials recorded in the trapezius and pectoralis major were found to be reduced in either group after surgery (ns10 in each group). After TENS, but not Fig. 2. Association between pre- and post-tens pain with cough: note that 5 substantial reductions in pain with TENS (-2U) were more frequent in 54 patients with higher pre-tens scores (above 6). Fig.. TENS stimulation (solid lines), but not sham (dotted lines), was associated with a significant increase in vital capacity in the postoperative period. *P-0.05 (within-treatment effect)

4 4 G. Cipriano Jr. et al. / Interactive CardioVascular and Thoracic Surgery xx (2008) xxx xxx 205 sham treatment, there were significant improvements in assess the effects of TENS on a more heterogeneous sample 206 the electromyographic variables recorded at both muscle presenting with more severe pain. For instance, Erdogan 207 groups (Table 1). et al. have recently found that TENS was highly effective in lessening pulmonary gas exchange after posterolateral Discussion thoracotomy w9x. Another important caveat was the lack of standardization of the use of analgesics during the inter- 209 This prospective and randomized investigation evaluated vention and control periods: previous studies have found 210 the effects of transcutaneous electrical nerve stimulation that TENS may be useful in reducing the need of opiates 211 (TENS) in the postoperative management of pain in patients for pain control w5, 6, 9x. However, most of our patients 212 who were submitted to different cardiac surgeries. We were not using opiates at the time of the study and due to 21 found that TENS presented with beneficial effects not only the short-term nature of the intervention it was not possi- 214 in postoperative pain, but also in selected pulmonary- ble to assess any change on daily need of analgesics. In 215 mechanical properties and electrical activity of thoracic fact, we were unable to evaluate whether longer periods 216 and girdle muscles. These data point out for a relevant of TENS would be also beneficial for cardiac surgery 217 role of TENS in the postoperative care of cardiac surgery patients although this was the case in those studies in 218 patients. which TENS was continuously applied for up to five days 219 A number of strategies have been used to control pain w5, 6, 9x. Another potential limitation was related to the 220 and its deleterious consequences after cardiac surgery, fact that patients underwent a number of different cardiac 221 including TENS w5 9x. Although the precise mechanism(s) surgery procedures. However, the same surgical access 222 for TENS-related hypoalgesia is currently unknown, they (median sternotomy) was used in all patients and the 22 could include peripheral blocking of nociceptive input, patients were free from additional cause of chest pain, 224 activation of descending inhibitory feedback circuits, gat- such as chest tubes or mediastinitis. Finally, electrical 225 ing of noxious stimuli at spinal segmental level, andyor muscle activity evaluation could be performed in only activation of either opioid and non-opioid systems at a participants due to financial constraints, nevertheless, the 227 cortical level w14x. In the present study, we were able to sample size was large enough to unravel a positive effect 228 confirm previous reports that TENS is effective and well- of TENS. 229 tolerated for the control of mild to moderate post-thora- In conclusion, this prospective and randomized study 20 cotomy pain (Fig. 1) w5, 6, 9x. However, even in patients demonstrated that TENS is a valuable strategy to alleviate 21 with more severe pain TENS showed to be useful (Fig. 2): postoperative incisional pain following cardiac surgery with 22 these data suggest that, at least when applied for a short positive effects on pulmonary ventilatory function and local 2 period of time (4 h), TENS may also be effective in these muscle electrical activity. 24 patients. 25 Although median sternotomy is known to be associated References 26 with less respiratory morbidity than postero-lateral inci- w1x Mack MJ. Advances in the treatment of coronary artery disease. Ann 27 sions, the former also is related to pulmonary-mechanical Thorac Surg 200;76:S2240 S2245. w2x Matthay M, Wiener-Kronish JP. Respiratory management after cardiac 28 abnormalities (Table 1) and more frequently performed surgery. Chest 1989;95: than the later. Postoperative reduction in VC (i.e. the wx Watt-Watson J, Stevens B. Managing pain after coronary artery bypass 240 difference between total lung capacity and residual vol- surgery. J Cardiovasc Nurs 1998;12: ume) after cardiac surgery is a consequence of pain and w4x Cheing GL, Hui-Chan CW. Transcutaneous electrical nerve stimulation: 242 decrease in rib cage compliance w15x. However, the closing nonparallel antinociceptive effects on chronic clinical pain and acute experimental pain. Arch Phys Med Rehabil 1999;80: volume of the dependent, small airways may also contrib- w5x Rooney SM, Jain S, McCormack P, Bains MS, Martini N, Goldiner PL. 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