ORIGINAL ARTICLE
Effect of Modulated-Frequency and Modulated-Intensity Transcutaneous Electrical Nerve Stimulation After Abdominal Surgery A Randomized Controlled Trial Mitsunori Tokuda, MSc, Kazuyuki Tabira, PhD, Takashi Masuda, MSc, Takashi Nishiwada, MD, and Koji Shomoto, PhD
Purpose: This study aimed to evaluate the effectiveness of transcutaneous electrical nerve stimulation (TENS) for treatment of postoperative pain and pulmonary functions (vital capacity [VC]; cough peak flow, [CPF]) in patients who underwent abdominal surgery. Materials and Methods: Forty-eight patients were randomly allocated to receive TENS, placebo TENS, or no TENS (control) 1 hour a day for 3 days postoperatively. A 0-100 visual analog scale was used to assess pain at preintervention, mid-intervention, and postintervention on the third postoperative day. Pulmonary functions (VC, CPF) were evaluated by spirometer at preoperation (baseline) and at preintervention, mid-intervention, and postintervention on the third postoperative day. One-way analysis of variance was used to assess differences between groups at baseline. Mann-Whitney test was used to compare the control group with the placebo-TENS and TENS group, at each assessment timepoint. Two-way analysis of variance and Bonferroni post hoc test assessed the difference between the 2 (placebo-TENS TENS) groups. A value of P < 0.01 was considered statistically significant. Results: The baselines were not significantly different between any groups. The TENS group had significant reductions in postoperative pain compared with the placebo group (P < 0.01) and control group (P < 0.01). There was also improvement in pulmonary functions (VC, CPF) at mid-TENS and post-TENS, but not in the placebo-TENS (P < 0.01) or control groups (P < 0.01). Conclusions: TENS is a valuable treatment to alleviate postoperative pain and improve pulmonary functions (ie, VC, CPF) in patients following abdominal surgery. Key Words: electrical nerve stimulation, postoperative pain, cough peak flow, abdominal surgery
(Clin J Pain 2014;30:565–570)
P
ulmonary complications are common after abdominal surgery, with an incidence of 12% to 53%.1–5 The characteristic postoperative abnormality in respiration is a mechanically restrictive pattern of ventilation with a significant reduction in vital capacity (VC), tidal volume, forced expiratory volume in one second, functional residual Received for publication September 27, 2012; accepted April 26, 2013. From the Heisei Memorial Hospital, Kashihara City, Nara, Japan. The authors declare no conflict of interest. Reprints: Mitsunori Tokuda, MSc, Heisei Memorial Hospital, Kashihara City, 827 Shijyo-cho, Kashihara-city, Nara, 634-0813, Japan (e-mail: [email protected]). Supplemental Digital Content is available for this article. Direct URL citations appear in the printed text and are provided in the HTML and PDF versions of this article on the journal’s Website, www.clinicalpain.com. Copyright r 2014 by Lippincott Williams & Wilkins
Clin J Pain
Volume 30, Number 7, July 2014
capacity, and cough peak flow (CPF). Pain is the principle symptom of these abnormalities.6–8 CPF is defined as the ability to clear airway secretion (sputum). Systemic opiates and sedatives suppress the cough reflex, and inhibition of its expulsive force by pain renders it less effective. Gastric and oral aspiration are common side effects of these same drugs. Sputum retention with bacterial overgrowth of the airways is therefore induced, while at the same time the stress response to surgery impairs the immune system, suppressing natural killer cell activity.3 Therefore, effective airway clearance (improvement of CPF) and a reduction of analgesics are critical for preventing pulmonary complications in postoperative patients. Transcutaneous electrical nerve stimulation (TENS) is a nonpharmacologic strategy that is used to treat postoperative pain during cholecystectomy,9,10 laparoscopic sterilization,11 surgical abortion,12 hysterectomy, and myomectomy.13 Further, in systematic reviews, Bjordal et al14 showed decreases in analgesic consumption in patients using TENS postoperatively, and Sbruzzi et al15 showed that it provides more effective pain relief compared with pharmacological analgesia alone in cases of sternotomy. In previous studies, mixed low and high frequencies of stimulation during the same treatment have been shown to increase postoperative pain relief and reduce postoperative analgesic requirements and side effects more effectively than the separate application of low-frequency or high-frequency TENS.16,17 An animal study showed that onset of analgesic tolerance to repeated application of TENS is delayed by approximately 1 week by combining low-frequency and high-frequency (mixed frequency) TENS, further supporting the increased effectiveness of modulated-frequency TENS.18 Many fundamental studies have reported that different endogenous opioids are released depending on the frequency of TENS.19–24 As for intensity, high-intensity TENS has been reported to be a significantly more effective analgesia than low-intensity TENS.17 However, if the intensity of electrical stimulation is excessive, the analgesic effect may be decreased because of tolerance. Although it has not been investigated, the intermittent use of TENS for modulated intensity rather than a continual high-intensity mode might minimize accommodation (or habituation) to the electrical stimulation. Thus, when performing TENS in postoperative patients, we consider it important to modulate both the frequency and the intensity. In fact, we have demonstrated that modulating the frequency and intensity of TENS increases pain relief in patients after shoulder surgery.16 As for patients after abdominal surgery, some studies have shown the effects of TENS in reducing analgesic drug use,11,13,25 however, none has assessed CPF. Thus, the goal of www.clinicalpain.com |
565
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Tokuda et al
this study was to evaluate the effectiveness of postoperative analgesia and pulmonary function improvement by modulated-frequency and modulated-intensity TENS in patients recovering from abdominal surgery. We hypothesized that application of TENS in combination with pharmacological treatment will result in a greater reduction in pain intensity and swifter recovery of pulmonary function when compared with both placebo-TENS and no-TENS groups.
MATERIALS AND METHODS Study Design Our study was a prospective randomized, single-blind, placebo-controlled, 3-group parallel-design, unicenter study including a series of consecutive patients undergoing abdominal surgery or laparoscopic surgery. Patients who presented themselves to the surgeon and met inclusion criteria were recruited from Heisei Memorial Hospital. Written informed consent, approved by the University of Kio ethics committee, was obtained from all patients 1 day before their surgical procedures. After signing the informed consent, patients were randomly enrolled into 3 groups according to a computergenerated randomization sequence: (1) TENS; (2) placebo TENS; and (3) control (no TENS). The inclusion criteria were that the patient (1) was undergoing abdominal surgery or laparoscopic surgery; (2) was American Society of Anesthesiology (ASA) I or II physical status, according to ASA26; and (3) had no hearing, visual, or speaking impairments. Exclusion criteria included (1) cognitive disturbance; (2) previous history of chronic pain; (3) neurological or pulmonary diseases that would seriously affect the results of the tests; (4) presence of a pacemaker; (5) contraindications for TENS; (6) preoperative use of opioids; and (7) prior TENS use. The estimation of the desired sample size to draw conclusions about the dependent variable was determined by using the CPF of the first 25 patients enrolled in the study, because there was no previous study on the effectiveness of TENS for pulmonary function such as CPF. We found that an effect size of 0.40, a = 0.05, and power = 80% required a sample size of at least 11 patients/group.
Participants Between April 2011 and March 2012, 62 patients underwent abdominal surgery or laparoscopic surgery. Ultimately, 55 patients were enrolled in the study; 5 patients were excluded because the did not meet the inclusion criteria, and 2 refused to participate. Patients were randomly divided in 3 groups: the TENS group (19 patients), placebo-TENS group (18 patients), and control group (18 patients). After the operation, all patients received standard medication using continuous intravenous fentanyl analgesia (20 mg/h) for the first 2 days. Patient-control analgesia (intravenous fentanyl at a dose of 20 mg per times) was given when the patient experienced strong pain. After the third postoperative day, diclofenac (administered orally at a dose of 25 mg) was given every 8 hours. Rescue analgesia included pentazocine (intramuscular administration at a dose of 30 to 60 mg).
Apparatus and Interventions The TENS unit we used (Intellect Advanced Combo; Chattanooga Co., TN) provides a symmetric biphasic pulse waveform, pulse duration of 100 ms. The frequency was modulated from 1 to 250 Hz to encourage the release of various endogenous opioids. Two pairs of adhesive electrodes
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(PALS, Platinum, 5 9 cm; Axelgaard Manufacturing Co., CA) were positioned on either side of the incision, approximately 2 to 3 cm away from the suture line at adjacent dermatomic levels. TENS was performed for 60 min/d for the first 3 days after surgery. In the TENS group the intensity was modulated in the range from the maximum intensity, which was the maximal tolerance without muscle contraction, down to 40% of the maximum intensity as the lower limit. The placebo group received the same current as the TENS group for the first 1 minute, and thereafter received no current. However, in the placebo group, the TENS unit displayed an active indicator light, suggesting to the patient that the unit was active. The control group had no intervention with TENS.
Outcomes and Measurement Procedure Each assessment was measured at preintervention, mid-intervention (after 30 min from intervention start), and postintervention (20 min after the intervention ended) on the third postoperative day. The assessment of the control group was 1 time on the third postoperative day, because they underwent no intervention. The physical therapist who administered the TENS or placebo-TENS groups was the only person who knew what type of treatment each patient was receiving. He informed the TENS group patients that they could expect to feel the electrical stimulation and not pain, whereas he informed the placebo-TENS patients that they could expect to not feel anything from the treatment. The assessor was the physical therapist or nurse who was in charge of the patient.
Pain In the third postoperative day, the participants were asked to quantify their incision pain using a 100-mm visual analog scale (VAS) from 0 (no pain at all) to 10 (the worst imaginable pain). The scale was applied at rest (horizontal), after the patients had coughed, and after the patients sat up.
Pulmonary Functions Pulmonary function tests (VC, CPF) were performed using a Spirometer (Microspiro HI-201, Japan, Nihonkohden Co.). The best of 3 efforts, completed with the patient sitting on the edge of the bed, was used for the analysis. On the day before operation, the patients were asked to perform pulmonary function tests (VC, CPF) to provide preoperative baseline values.
Statistical Analysis Means and SDs were obtained for VAS score and pulmonary function data in all groups. The preoperative baseline (pulmonary functions) and the preintervention baseline (pain, pulmonary functions) were analyzed using 1-way analysis of variance (ANOVA) with repeated measurements. The Mann-Whitney test was used to compare the control group with the placebo-TENS group and the TENS group, for each assessment timepoint. Two-way ANOVA with repeated measurements was used to evaluate the effect of the intervention (placebo TENS, TENS) and the assessment timepoint (preintervention, mid-intervention, and postintervention). Bonferroni corrections were applied to any data undergoing multiple comparisons. Four subgroups analyses were also performed for the location of incision groups (upper, lower) and type of operation groups (open, laparoscopic). A value of P < 0.05 was considered significant. Data analysis was undertaken using SPSS version 16 (Chicago, IL). In addition, the effect sizes for the studies were calculated. r
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RESULTS
Modulated-Frequency and Modulated-Intensity TENS
TABLE 1. Patient Characteristics
Patient Characteristics and Trial Profile Of the 55 patients enrolled, 7 were lost to follow-up. Four patients refused to continue the study for the following reasons: 1 patient in the control group could not perform pulmonary function tests because of strong pain; another in the placebo-TENS group refused intervention because they considered it ineffective; and to others TENS-group patients stopped participating because of discomfort associated with TENS. Three other patients who were given rescue analgesia within 3 hours were not evaluated because we considered that the rescue analgesia (pentazocine) administration influenced the results (ie, there were missing data). Figure 1 is a study flow diagram according to CONSORT guidelines. The characteristics of the 3 study groups are summarized in Table 1. The sex ratio, mean age, location of incision, and type of operation were similar in all the groups. Table 2 summarizes the VAS scores for the resting pain, coughing pain, and sitting-up pain, as well as VC and CPF for the 3 groups. No significant difference was revealed in the preoperative baseline (pulmonary functions) and the preintervention baseline (pain, pulmonary functions) at enrollment among the 3 groups (P > 0.05) (Table 2). Similarly, there was no significant difference in the preoperative baseline values and the preintervention baseline values at enrollment among the 3 groups and among the subgroups (upper, lower, open, and laparoscopic) (P > 0.05). Table 3 summarizes the results of 2-way ANOVA and effect size.27,28
Parameters
Control Group
Sex (n) 16 Male 10 Female 6 Age (y) Mean ± SD 69.3 ± 13.7 Range 37-86 Location of incision (n) Upper 11 abdominal Lower 5 abdominal Type of operation (n) Open 8 Laparoscopic 8
Placebo-TENS Group
TENS Group
16 9 7
16 10 6
71.0 ± 9.6 46-85
71.3 ± 12.0 42-88
10
10
6
6
8 8
9 7
TENS indicates transcutaneous electrical nerve stimulation.
compared with postintervention (P < 0.01) (Table 2). Similarly, in all subgroup analyses, the TENS group values at mid-intervention and postintervention were significantly lower than those of the control group and the placebo-TENS group at all assessment timepoints (P < 0.05), and 2-way ANOVA showed a significant effect for the interaction (P < 0.05). Post hoc analyses also revealed significantly lower VAS scores for mid-intervention and postintervention compared with preintervention (P < 0.05).
Resting Pain
Coughing Pain, Sitting-Up Pain
The TENS group’s resting pain values at mid-intervention and postintervention were significantly lower than those of the control and the placebo-TENS groups at all assessment timepoints (P < 0.01) (Table 2), and the 2-way ANOVA showed a significant main effect of intervention, assessment timepoint, and their interaction (P < 0.01) (Table 3). Post hoc analyses revealed significantly lower VAS scores for mid-intervention and postintervention compared with preintervention (P < 0.01), and for mid-intervention
The TENS group values for coughing pain and sittingup pain at mid-intervention and postintervention were significantly lower than those of the control and the placeboTENS groups at all assessment timepoints (P < 0.01) (Table 2). In addition, the 2-way ANOVA showed a significant main effect of assessment timepoint, but not of intervention (P > 0.05) or of their interaction (P < 0.01) (Table 3). Post hoc analyses revealed significantly lower VAS scores for mid-intervention and postintervention compared
FIGURE 1. Study flow diagram according to CONSORT guidelines. TENS indicates transcutaneous electrical nerve stimulation. r
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Values are mean ± SD. P < 0.01: *preintervention versus mid-intervention; **preintervention versus postintervention; ***postintervention versus both preintervention and mid-intervention in TENS group. wP < 0.01, significantly different versus control group with Bonferroni correction. zP < 0.01, significantly different versus placebo-TENS group at preintervention, mid-intervention, and postintervention. CPF indicates cough peak flow; TENS, transcutaneous electrical nerve stimulation; VAS, visual analog scale; VC, vital capacity.
1.66 ± 0.42 208.8 ± 50.0 1.57 ± 0.42 186.5 ± 78.3
1.63 ± 0.41 186.0 ± 75.4
2.80 ± 0.66 360.1 ± 85.1 1.64 ± 0.41 189.0 ± 77.7
2.02 ± 0.49*wz 1.90 ± 0.52***wz 239.0 ± 52.2*wz 230.3 ± 51.8***wz
8.4 ± 7.4***wz 70.1 ± 15.2**wz 61.3 ± 9.48**wz 5.9 ± 6.5*wz 67.3 ± 12.2*wz 58.0 ± 12.7*wz 16.9 ± 9.6 79.8 ± 8.3 70.8 ± 6.6 24.0 ± 6.4 78.6 ± 4.9 66.5 ± 6.7 23.8 ± 5.9 80.1 ± 6.3 68.1 ± 6.9 24.5 ± 6.2 80.7 ± 5.5 70.1 ± 7.0
Preoperation Postoperation Preoperation Preintervention Mid-Intervention Postintervention Preoperation Preintervention Mid-Intervention Postintervention
Pain (VAS) (mm) Resting pain 24.8 ± 14.6 Coughing pain 82.3 ± 7.9 Sitting-up pain 70.0 ± 9.4 Pulmonary function VC (L) 3.02 ± 0.82 1.78 ± 0.60 2.82 ± 0.78 CPF (L/min) 301.2 ± 113.6 170.0 ± 56.6 333.6 ± 135.3
Postoperation Postoperation
Placebo-TENS Group TABLE 2. VAS Scores, VC and CPF Results
Control Group
TENS Group
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Volume 30, Number 7, July 2014
with preintervention (P < 0.05) (Table 2). Similarly, in all subgroup analyses, the TENS group values at mid-intervention and postintervention were significantly lower than those of the control and the placebo-TENS groups at all assessment timepoints (P < 0.05), and the 2-way ANOVA showed a significant effect for the interaction (P < 0.05). Post hoc analyses also revealed significantly lower VAS scores for mid-intervention and postintervention compared with preintervention (P < 0.05).
VC, CPF The VC/CPF values of the TENS group at mid-intervention and postintervention were significantly higher than those of the control and the placebo-TENS groups at all assessment timepoints (P < 0.01) (Table 2). The 2-way ANOVA showed a significant main effect of assessment timepoint, but not of intervention (P > 0.05) or of their interaction (P < 0.01) (Table 3). Post hoc analyses revealed a significant increase in VC/CPF for mid-intervention and postintervention compared with preintervention (P < 0.01), and for mid-intervention compared with postintervention (P < 0.05) (Table 2). Similarly, in all subgroup analyses, the TENS group values at mid-intervention and postintervention were significantly higher than those of the control and the placebo-TENS groups at all assessment timepoints (P < 0.01), and the 2-way ANOVA showed a significant effect for the interaction (P < 0.01). Post hoc analyses also revealed a significant increase in VC/CPF for mid-intervention and postintervention compared with preintervention (P < 0.05). TABLE 3. Results of 2-Way ANOVA and Effect Size, “Interventions” (Placebo-TENS, TENS) and “Assessment Timepoints” (Preintervention, Mid-Intervention, Postintervention)
Resting pain Interaction Main effect of Main effect of timepoint Coughing pain Interaction Main effect of Main effect of timepoint Sitting-up pain Interaction Main effect of Main effect of timepoint VC Interaction Main effect of Main effect of timepoint CPF Interaction Main effect of Main effect of timepoint
F (df)
P
Effect Size
intervention assessment
46.1 (2, 60) 31.6 (1, 30) 59.8 (2, 60)
0.0001* 0.0001* 0.0001*
0.08 0.77w 0.10
intervention assessment
11.5 (2, 60) 37.8 (1, 30) 9.72 (2, 60)
0.0001* 0.0257 0.0002*
0.16w 0.35w 0.22w
intervention assessment
17.0 (2, 60) 3.0 (1, 30) 37.7 (2, 60)
0.0001* 0.093 0.0001*
0.16w 0.36w 0.20w
intervention assessment
24.2 (2, 60) 2.46 (1, 30) 50.3 (2, 60)
0.0001* 0.1276 0.0001*
0.12 0.48w 0.25w
intervention assessment
41.0 (2, 60) 2.83 (1, 30) 42.1 (2, 60)
0.0001* 0.1027 0.0001*
0.08 0.77w 0.09
*P < 0.01. wEffect size is large (Z2 Z0.14). ANOVA indicates analysis of variance; CPF, cough peak flow; TENS, transcutaneous electrical nerve stimulation; VC, vital capacity.
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DISCUSSION This prospective, randomized investigation evaluated the effect of TENS in the postoperative management of pain and pulmonary function in patients who underwent different abdominal surgeries. The present results show that the TENS group at mid-intervention and postintervention had significantly lower VAS scores for pain at rest, at coughing, and sitting up compared with those of the control or placebo-TENS groups at all timepoints. In previous studies, after abdominal surgery, lower abdominal incisions were found to result in less postoperative suppression of pulmonary function compared with upper abdominal incisions,29,30 and laparoscopic surgery was found to result in less postoperative suppression of pulmonary function and decreased pain compared with open surgery.31,32 Although we performed a subgroup analysis in consideration of these previous findings, of note was the similar pattern of changes among the subgroups and the comparable effect size achieved regardless of the subgroup (upper, lower, open, and laparoscopic), as shown in Table 3 (see the Appendices, Supplementary Digital Content 1–4, http://links.lww.com/CJP/ A111; http://links.lww.com/CJP/A112; http://links.lww.com/ CJP/A113; http://links.lww.com/CJP/A114, for the details of all of the subgroup analyses). Therefore, we found that TENS provided beneficial effects not only in postoperative pain, but also in VC and CPF in patients who underwent abdominal surgery. This study represents the first investigation of the CPF, defined as the ability to clear airway secretion, in relation to a complementary nonpharmacologic therapy as an adjunct for postoperative pain relief after abdominal surgery. The findings of this study suggest that TENS at modulated frequency and at modulated intensity significantly increased CPF and decreased postoperative pain intensity after abdominal surgery. Importantly, TENS increased CPF and reduced cough pain both during and immediately after the TENS therapy. CPF correlates directly to the ability to clear secretions from the airway,33 and values 160 L/min, however, do not guarantee adequate airway clearance, because respiratory muscle function can deteriorate during respiratory infections.35 For this reason, a CPF of 270 L/min has been recommended as a goal for patients by the American Thoracic Society.36 Masuda et al37 reported that CPF did not reach 270 L/min until the eighth day after abdominal surgery. However, the CPF results of the present study in the TENS group at mid-intervention and postintervention were 239.0 and 230.3 L/ min, respectively. Although our data were
Effect of Modulated-Frequency and Modulated-Intensity Transcutaneous Electrical Nerve Stimulation After Abdominal Surgery A Randomized Controlled Trial Mitsunori Tokuda, MSc, Kazuyuki Tabira, PhD, Takashi Masuda, MSc, Takashi Nishiwada, MD, and Koji Shomoto, PhD
Purpose: This study aimed to evaluate the effectiveness of transcutaneous electrical nerve stimulation (TENS) for treatment of postoperative pain and pulmonary functions (vital capacity [VC]; cough peak flow, [CPF]) in patients who underwent abdominal surgery. Materials and Methods: Forty-eight patients were randomly allocated to receive TENS, placebo TENS, or no TENS (control) 1 hour a day for 3 days postoperatively. A 0-100 visual analog scale was used to assess pain at preintervention, mid-intervention, and postintervention on the third postoperative day. Pulmonary functions (VC, CPF) were evaluated by spirometer at preoperation (baseline) and at preintervention, mid-intervention, and postintervention on the third postoperative day. One-way analysis of variance was used to assess differences between groups at baseline. Mann-Whitney test was used to compare the control group with the placebo-TENS and TENS group, at each assessment timepoint. Two-way analysis of variance and Bonferroni post hoc test assessed the difference between the 2 (placebo-TENS TENS) groups. A value of P < 0.01 was considered statistically significant. Results: The baselines were not significantly different between any groups. The TENS group had significant reductions in postoperative pain compared with the placebo group (P < 0.01) and control group (P < 0.01). There was also improvement in pulmonary functions (VC, CPF) at mid-TENS and post-TENS, but not in the placebo-TENS (P < 0.01) or control groups (P < 0.01). Conclusions: TENS is a valuable treatment to alleviate postoperative pain and improve pulmonary functions (ie, VC, CPF) in patients following abdominal surgery. Key Words: electrical nerve stimulation, postoperative pain, cough peak flow, abdominal surgery
(Clin J Pain 2014;30:565–570)
P
ulmonary complications are common after abdominal surgery, with an incidence of 12% to 53%.1–5 The characteristic postoperative abnormality in respiration is a mechanically restrictive pattern of ventilation with a significant reduction in vital capacity (VC), tidal volume, forced expiratory volume in one second, functional residual Received for publication September 27, 2012; accepted April 26, 2013. From the Heisei Memorial Hospital, Kashihara City, Nara, Japan. The authors declare no conflict of interest. Reprints: Mitsunori Tokuda, MSc, Heisei Memorial Hospital, Kashihara City, 827 Shijyo-cho, Kashihara-city, Nara, 634-0813, Japan (e-mail: [email protected]). Supplemental Digital Content is available for this article. Direct URL citations appear in the printed text and are provided in the HTML and PDF versions of this article on the journal’s Website, www.clinicalpain.com. Copyright r 2014 by Lippincott Williams & Wilkins
Clin J Pain
Volume 30, Number 7, July 2014
capacity, and cough peak flow (CPF). Pain is the principle symptom of these abnormalities.6–8 CPF is defined as the ability to clear airway secretion (sputum). Systemic opiates and sedatives suppress the cough reflex, and inhibition of its expulsive force by pain renders it less effective. Gastric and oral aspiration are common side effects of these same drugs. Sputum retention with bacterial overgrowth of the airways is therefore induced, while at the same time the stress response to surgery impairs the immune system, suppressing natural killer cell activity.3 Therefore, effective airway clearance (improvement of CPF) and a reduction of analgesics are critical for preventing pulmonary complications in postoperative patients. Transcutaneous electrical nerve stimulation (TENS) is a nonpharmacologic strategy that is used to treat postoperative pain during cholecystectomy,9,10 laparoscopic sterilization,11 surgical abortion,12 hysterectomy, and myomectomy.13 Further, in systematic reviews, Bjordal et al14 showed decreases in analgesic consumption in patients using TENS postoperatively, and Sbruzzi et al15 showed that it provides more effective pain relief compared with pharmacological analgesia alone in cases of sternotomy. In previous studies, mixed low and high frequencies of stimulation during the same treatment have been shown to increase postoperative pain relief and reduce postoperative analgesic requirements and side effects more effectively than the separate application of low-frequency or high-frequency TENS.16,17 An animal study showed that onset of analgesic tolerance to repeated application of TENS is delayed by approximately 1 week by combining low-frequency and high-frequency (mixed frequency) TENS, further supporting the increased effectiveness of modulated-frequency TENS.18 Many fundamental studies have reported that different endogenous opioids are released depending on the frequency of TENS.19–24 As for intensity, high-intensity TENS has been reported to be a significantly more effective analgesia than low-intensity TENS.17 However, if the intensity of electrical stimulation is excessive, the analgesic effect may be decreased because of tolerance. Although it has not been investigated, the intermittent use of TENS for modulated intensity rather than a continual high-intensity mode might minimize accommodation (or habituation) to the electrical stimulation. Thus, when performing TENS in postoperative patients, we consider it important to modulate both the frequency and the intensity. In fact, we have demonstrated that modulating the frequency and intensity of TENS increases pain relief in patients after shoulder surgery.16 As for patients after abdominal surgery, some studies have shown the effects of TENS in reducing analgesic drug use,11,13,25 however, none has assessed CPF. Thus, the goal of www.clinicalpain.com |
565
Clin J Pain
Tokuda et al
this study was to evaluate the effectiveness of postoperative analgesia and pulmonary function improvement by modulated-frequency and modulated-intensity TENS in patients recovering from abdominal surgery. We hypothesized that application of TENS in combination with pharmacological treatment will result in a greater reduction in pain intensity and swifter recovery of pulmonary function when compared with both placebo-TENS and no-TENS groups.
MATERIALS AND METHODS Study Design Our study was a prospective randomized, single-blind, placebo-controlled, 3-group parallel-design, unicenter study including a series of consecutive patients undergoing abdominal surgery or laparoscopic surgery. Patients who presented themselves to the surgeon and met inclusion criteria were recruited from Heisei Memorial Hospital. Written informed consent, approved by the University of Kio ethics committee, was obtained from all patients 1 day before their surgical procedures. After signing the informed consent, patients were randomly enrolled into 3 groups according to a computergenerated randomization sequence: (1) TENS; (2) placebo TENS; and (3) control (no TENS). The inclusion criteria were that the patient (1) was undergoing abdominal surgery or laparoscopic surgery; (2) was American Society of Anesthesiology (ASA) I or II physical status, according to ASA26; and (3) had no hearing, visual, or speaking impairments. Exclusion criteria included (1) cognitive disturbance; (2) previous history of chronic pain; (3) neurological or pulmonary diseases that would seriously affect the results of the tests; (4) presence of a pacemaker; (5) contraindications for TENS; (6) preoperative use of opioids; and (7) prior TENS use. The estimation of the desired sample size to draw conclusions about the dependent variable was determined by using the CPF of the first 25 patients enrolled in the study, because there was no previous study on the effectiveness of TENS for pulmonary function such as CPF. We found that an effect size of 0.40, a = 0.05, and power = 80% required a sample size of at least 11 patients/group.
Participants Between April 2011 and March 2012, 62 patients underwent abdominal surgery or laparoscopic surgery. Ultimately, 55 patients were enrolled in the study; 5 patients were excluded because the did not meet the inclusion criteria, and 2 refused to participate. Patients were randomly divided in 3 groups: the TENS group (19 patients), placebo-TENS group (18 patients), and control group (18 patients). After the operation, all patients received standard medication using continuous intravenous fentanyl analgesia (20 mg/h) for the first 2 days. Patient-control analgesia (intravenous fentanyl at a dose of 20 mg per times) was given when the patient experienced strong pain. After the third postoperative day, diclofenac (administered orally at a dose of 25 mg) was given every 8 hours. Rescue analgesia included pentazocine (intramuscular administration at a dose of 30 to 60 mg).
Apparatus and Interventions The TENS unit we used (Intellect Advanced Combo; Chattanooga Co., TN) provides a symmetric biphasic pulse waveform, pulse duration of 100 ms. The frequency was modulated from 1 to 250 Hz to encourage the release of various endogenous opioids. Two pairs of adhesive electrodes
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(PALS, Platinum, 5 9 cm; Axelgaard Manufacturing Co., CA) were positioned on either side of the incision, approximately 2 to 3 cm away from the suture line at adjacent dermatomic levels. TENS was performed for 60 min/d for the first 3 days after surgery. In the TENS group the intensity was modulated in the range from the maximum intensity, which was the maximal tolerance without muscle contraction, down to 40% of the maximum intensity as the lower limit. The placebo group received the same current as the TENS group for the first 1 minute, and thereafter received no current. However, in the placebo group, the TENS unit displayed an active indicator light, suggesting to the patient that the unit was active. The control group had no intervention with TENS.
Outcomes and Measurement Procedure Each assessment was measured at preintervention, mid-intervention (after 30 min from intervention start), and postintervention (20 min after the intervention ended) on the third postoperative day. The assessment of the control group was 1 time on the third postoperative day, because they underwent no intervention. The physical therapist who administered the TENS or placebo-TENS groups was the only person who knew what type of treatment each patient was receiving. He informed the TENS group patients that they could expect to feel the electrical stimulation and not pain, whereas he informed the placebo-TENS patients that they could expect to not feel anything from the treatment. The assessor was the physical therapist or nurse who was in charge of the patient.
Pain In the third postoperative day, the participants were asked to quantify their incision pain using a 100-mm visual analog scale (VAS) from 0 (no pain at all) to 10 (the worst imaginable pain). The scale was applied at rest (horizontal), after the patients had coughed, and after the patients sat up.
Pulmonary Functions Pulmonary function tests (VC, CPF) were performed using a Spirometer (Microspiro HI-201, Japan, Nihonkohden Co.). The best of 3 efforts, completed with the patient sitting on the edge of the bed, was used for the analysis. On the day before operation, the patients were asked to perform pulmonary function tests (VC, CPF) to provide preoperative baseline values.
Statistical Analysis Means and SDs were obtained for VAS score and pulmonary function data in all groups. The preoperative baseline (pulmonary functions) and the preintervention baseline (pain, pulmonary functions) were analyzed using 1-way analysis of variance (ANOVA) with repeated measurements. The Mann-Whitney test was used to compare the control group with the placebo-TENS group and the TENS group, for each assessment timepoint. Two-way ANOVA with repeated measurements was used to evaluate the effect of the intervention (placebo TENS, TENS) and the assessment timepoint (preintervention, mid-intervention, and postintervention). Bonferroni corrections were applied to any data undergoing multiple comparisons. Four subgroups analyses were also performed for the location of incision groups (upper, lower) and type of operation groups (open, laparoscopic). A value of P < 0.05 was considered significant. Data analysis was undertaken using SPSS version 16 (Chicago, IL). In addition, the effect sizes for the studies were calculated. r
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RESULTS
Modulated-Frequency and Modulated-Intensity TENS
TABLE 1. Patient Characteristics
Patient Characteristics and Trial Profile Of the 55 patients enrolled, 7 were lost to follow-up. Four patients refused to continue the study for the following reasons: 1 patient in the control group could not perform pulmonary function tests because of strong pain; another in the placebo-TENS group refused intervention because they considered it ineffective; and to others TENS-group patients stopped participating because of discomfort associated with TENS. Three other patients who were given rescue analgesia within 3 hours were not evaluated because we considered that the rescue analgesia (pentazocine) administration influenced the results (ie, there were missing data). Figure 1 is a study flow diagram according to CONSORT guidelines. The characteristics of the 3 study groups are summarized in Table 1. The sex ratio, mean age, location of incision, and type of operation were similar in all the groups. Table 2 summarizes the VAS scores for the resting pain, coughing pain, and sitting-up pain, as well as VC and CPF for the 3 groups. No significant difference was revealed in the preoperative baseline (pulmonary functions) and the preintervention baseline (pain, pulmonary functions) at enrollment among the 3 groups (P > 0.05) (Table 2). Similarly, there was no significant difference in the preoperative baseline values and the preintervention baseline values at enrollment among the 3 groups and among the subgroups (upper, lower, open, and laparoscopic) (P > 0.05). Table 3 summarizes the results of 2-way ANOVA and effect size.27,28
Parameters
Control Group
Sex (n) 16 Male 10 Female 6 Age (y) Mean ± SD 69.3 ± 13.7 Range 37-86 Location of incision (n) Upper 11 abdominal Lower 5 abdominal Type of operation (n) Open 8 Laparoscopic 8
Placebo-TENS Group
TENS Group
16 9 7
16 10 6
71.0 ± 9.6 46-85
71.3 ± 12.0 42-88
10
10
6
6
8 8
9 7
TENS indicates transcutaneous electrical nerve stimulation.
compared with postintervention (P < 0.01) (Table 2). Similarly, in all subgroup analyses, the TENS group values at mid-intervention and postintervention were significantly lower than those of the control group and the placebo-TENS group at all assessment timepoints (P < 0.05), and 2-way ANOVA showed a significant effect for the interaction (P < 0.05). Post hoc analyses also revealed significantly lower VAS scores for mid-intervention and postintervention compared with preintervention (P < 0.05).
Resting Pain
Coughing Pain, Sitting-Up Pain
The TENS group’s resting pain values at mid-intervention and postintervention were significantly lower than those of the control and the placebo-TENS groups at all assessment timepoints (P < 0.01) (Table 2), and the 2-way ANOVA showed a significant main effect of intervention, assessment timepoint, and their interaction (P < 0.01) (Table 3). Post hoc analyses revealed significantly lower VAS scores for mid-intervention and postintervention compared with preintervention (P < 0.01), and for mid-intervention
The TENS group values for coughing pain and sittingup pain at mid-intervention and postintervention were significantly lower than those of the control and the placeboTENS groups at all assessment timepoints (P < 0.01) (Table 2). In addition, the 2-way ANOVA showed a significant main effect of assessment timepoint, but not of intervention (P > 0.05) or of their interaction (P < 0.01) (Table 3). Post hoc analyses revealed significantly lower VAS scores for mid-intervention and postintervention compared
FIGURE 1. Study flow diagram according to CONSORT guidelines. TENS indicates transcutaneous electrical nerve stimulation. r
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Values are mean ± SD. P < 0.01: *preintervention versus mid-intervention; **preintervention versus postintervention; ***postintervention versus both preintervention and mid-intervention in TENS group. wP < 0.01, significantly different versus control group with Bonferroni correction. zP < 0.01, significantly different versus placebo-TENS group at preintervention, mid-intervention, and postintervention. CPF indicates cough peak flow; TENS, transcutaneous electrical nerve stimulation; VAS, visual analog scale; VC, vital capacity.
1.66 ± 0.42 208.8 ± 50.0 1.57 ± 0.42 186.5 ± 78.3
1.63 ± 0.41 186.0 ± 75.4
2.80 ± 0.66 360.1 ± 85.1 1.64 ± 0.41 189.0 ± 77.7
2.02 ± 0.49*wz 1.90 ± 0.52***wz 239.0 ± 52.2*wz 230.3 ± 51.8***wz
8.4 ± 7.4***wz 70.1 ± 15.2**wz 61.3 ± 9.48**wz 5.9 ± 6.5*wz 67.3 ± 12.2*wz 58.0 ± 12.7*wz 16.9 ± 9.6 79.8 ± 8.3 70.8 ± 6.6 24.0 ± 6.4 78.6 ± 4.9 66.5 ± 6.7 23.8 ± 5.9 80.1 ± 6.3 68.1 ± 6.9 24.5 ± 6.2 80.7 ± 5.5 70.1 ± 7.0
Preoperation Postoperation Preoperation Preintervention Mid-Intervention Postintervention Preoperation Preintervention Mid-Intervention Postintervention
Pain (VAS) (mm) Resting pain 24.8 ± 14.6 Coughing pain 82.3 ± 7.9 Sitting-up pain 70.0 ± 9.4 Pulmonary function VC (L) 3.02 ± 0.82 1.78 ± 0.60 2.82 ± 0.78 CPF (L/min) 301.2 ± 113.6 170.0 ± 56.6 333.6 ± 135.3
Postoperation Postoperation
Placebo-TENS Group TABLE 2. VAS Scores, VC and CPF Results
Control Group
TENS Group
Tokuda et al
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with preintervention (P < 0.05) (Table 2). Similarly, in all subgroup analyses, the TENS group values at mid-intervention and postintervention were significantly lower than those of the control and the placebo-TENS groups at all assessment timepoints (P < 0.05), and the 2-way ANOVA showed a significant effect for the interaction (P < 0.05). Post hoc analyses also revealed significantly lower VAS scores for mid-intervention and postintervention compared with preintervention (P < 0.05).
VC, CPF The VC/CPF values of the TENS group at mid-intervention and postintervention were significantly higher than those of the control and the placebo-TENS groups at all assessment timepoints (P < 0.01) (Table 2). The 2-way ANOVA showed a significant main effect of assessment timepoint, but not of intervention (P > 0.05) or of their interaction (P < 0.01) (Table 3). Post hoc analyses revealed a significant increase in VC/CPF for mid-intervention and postintervention compared with preintervention (P < 0.01), and for mid-intervention compared with postintervention (P < 0.05) (Table 2). Similarly, in all subgroup analyses, the TENS group values at mid-intervention and postintervention were significantly higher than those of the control and the placebo-TENS groups at all assessment timepoints (P < 0.01), and the 2-way ANOVA showed a significant effect for the interaction (P < 0.01). Post hoc analyses also revealed a significant increase in VC/CPF for mid-intervention and postintervention compared with preintervention (P < 0.05). TABLE 3. Results of 2-Way ANOVA and Effect Size, “Interventions” (Placebo-TENS, TENS) and “Assessment Timepoints” (Preintervention, Mid-Intervention, Postintervention)
Resting pain Interaction Main effect of Main effect of timepoint Coughing pain Interaction Main effect of Main effect of timepoint Sitting-up pain Interaction Main effect of Main effect of timepoint VC Interaction Main effect of Main effect of timepoint CPF Interaction Main effect of Main effect of timepoint
F (df)
P
Effect Size
intervention assessment
46.1 (2, 60) 31.6 (1, 30) 59.8 (2, 60)
0.0001* 0.0001* 0.0001*
0.08 0.77w 0.10
intervention assessment
11.5 (2, 60) 37.8 (1, 30) 9.72 (2, 60)
0.0001* 0.0257 0.0002*
0.16w 0.35w 0.22w
intervention assessment
17.0 (2, 60) 3.0 (1, 30) 37.7 (2, 60)
0.0001* 0.093 0.0001*
0.16w 0.36w 0.20w
intervention assessment
24.2 (2, 60) 2.46 (1, 30) 50.3 (2, 60)
0.0001* 0.1276 0.0001*
0.12 0.48w 0.25w
intervention assessment
41.0 (2, 60) 2.83 (1, 30) 42.1 (2, 60)
0.0001* 0.1027 0.0001*
0.08 0.77w 0.09
*P < 0.01. wEffect size is large (Z2 Z0.14). ANOVA indicates analysis of variance; CPF, cough peak flow; TENS, transcutaneous electrical nerve stimulation; VC, vital capacity.
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DISCUSSION This prospective, randomized investigation evaluated the effect of TENS in the postoperative management of pain and pulmonary function in patients who underwent different abdominal surgeries. The present results show that the TENS group at mid-intervention and postintervention had significantly lower VAS scores for pain at rest, at coughing, and sitting up compared with those of the control or placebo-TENS groups at all timepoints. In previous studies, after abdominal surgery, lower abdominal incisions were found to result in less postoperative suppression of pulmonary function compared with upper abdominal incisions,29,30 and laparoscopic surgery was found to result in less postoperative suppression of pulmonary function and decreased pain compared with open surgery.31,32 Although we performed a subgroup analysis in consideration of these previous findings, of note was the similar pattern of changes among the subgroups and the comparable effect size achieved regardless of the subgroup (upper, lower, open, and laparoscopic), as shown in Table 3 (see the Appendices, Supplementary Digital Content 1–4, http://links.lww.com/CJP/ A111; http://links.lww.com/CJP/A112; http://links.lww.com/ CJP/A113; http://links.lww.com/CJP/A114, for the details of all of the subgroup analyses). Therefore, we found that TENS provided beneficial effects not only in postoperative pain, but also in VC and CPF in patients who underwent abdominal surgery. This study represents the first investigation of the CPF, defined as the ability to clear airway secretion, in relation to a complementary nonpharmacologic therapy as an adjunct for postoperative pain relief after abdominal surgery. The findings of this study suggest that TENS at modulated frequency and at modulated intensity significantly increased CPF and decreased postoperative pain intensity after abdominal surgery. Importantly, TENS increased CPF and reduced cough pain both during and immediately after the TENS therapy. CPF correlates directly to the ability to clear secretions from the airway,33 and values 160 L/min, however, do not guarantee adequate airway clearance, because respiratory muscle function can deteriorate during respiratory infections.35 For this reason, a CPF of 270 L/min has been recommended as a goal for patients by the American Thoracic Society.36 Masuda et al37 reported that CPF did not reach 270 L/min until the eighth day after abdominal surgery. However, the CPF results of the present study in the TENS group at mid-intervention and postintervention were 239.0 and 230.3 L/ min, respectively. Although our data were
