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Ann Thorac Surg 1997;63:773-776
© 1997 The Society of Thoracic Surgeons

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Original Article: General Thoracic

Control of Postoperative Pain by Transcutaneous Electrical Nerve Stimulation After Thoracic Operations

Department of Neuroscience, CIND Center for the Neurophysiology of Pain, and Department of Thoracic Surgery, University of Torino Medical School, Torino, Italy

Accepted for publication September 5, 1996.

	Abstract

Top Footnotes Abstract Introduction Material and Methods Results Comment References

 
Background. Transcutaneous electrical nerve stimulation (TENS) has been used extensively to control postoperative pain, but its effects are controversial. This is probably due to the different types of operations performed and, therefore, to the varying intensity of postoperative pain. Here we present an extensive study with TENS in 324 patients who underwent different types of thoracic surgical procedures: posterolateral thoracotomy, muscle-sparing thoracotomy, costotomy, sternotomy, and video-assisted thoracoscopy.

Methods. Each patient cohort was randomly subdivided into three treatment groups: TENS, placebo TENS and control. The effectiveness of TENS was assessed by two factors: the time from the beginning of treatment to the request for further analgesia and the total medication intake during the first 12 hours after operation.

Results. Whereas posterolateral thoracotomy produced severe pain, muscle-sparing thoracotomy, costotomy, and sternotomy caused moderate pain, and video-assisted thoracoscopy caused only mild pain. The TENS treatment was not effective in the posterolateral thoracotomy group, but it was useful as an adjunct to other medications in the muscle-sparing thoracotomy, costotomy, and sternotomy groups. In contrast, representing the only pain control treatment with no adjunct drugs, it was very effective in patients having video-assisted thoracoscopy.

Conclusions. These findings show that TENS is useful after thoracic surgical procedures only when postoperative pain is mild to moderate; it is uneffective for severe pain.

	Introduction

Top Footnotes Abstract Introduction Material and Methods Results Comment References

 
For editorial comment, see page 608.

Narcotics have been associated with undesirable side effects, such as respiratory depression, sedation, nausea, and vomiting [1, 2]. Therefore, adjunctive methods of postoperative pain control that may limit narcotic side effects are of considerable interest. Transcutaneous electrical nerve stimulation (TENS) has been used to control postoperative pain after various procedures, for example, cardiac operations [3–6], cholecystectomy [7, 8], cesarean delivery [9], and thoracotomy [10–13]. In addition, some studies [14, 15] showed a lower incidence of postoperative complications, such as paralytic ileum, atelectasis, and reduction in pulmonary function, after TENS treatment. However, many authors do not agree on the effectiveness of TENS for acute postoperative pain. In fact, some studies show that TENS may not be of major benefit compared with regular opiate analgesics after cardiac operations [6], cholecystectomy [7], and thoracotomy [11]. This discrepancy could be due to the different types of surgical procedures performed and thus to the different levels of postoperative pain. Certainly, some surgical procedures appear to be too painful for TENS to have a significant effect on the pain [6].

Here we present an extensive study on the use of TENS with different types of thoracic surgical procedures over a 2-year period. We were interested mainly to see whether TENS is effective in reducing acute pain during the first 12 hours after operation.

	Material and Methods

Top Footnotes Abstract Introduction Material and Methods Results Comment References

 
Patient Cohorts
Three hundred twenty-four patients participated in the study after informed consent had been obtained. The patients underwent five types of surgical procedures producing mild, moderate, and severe postoperative pain. Eighty-three patients underwent standard posterolateral thoracotomy (PL) for pneumonectomy (23 patients) and lobectomy (60 patients); 41 underwent muscle-sparing thoracotomy (MS) for lobectomy (19 patients) and segmentectomy (22 patients); 48 underwent costotomy (CT) for empyema drainage; 57 underwent sternotomy (ST) for thymectomy in myasthenia gravis; and 95 underwent video-assisted thoracoscopy (VAT) (Table 1). There were no differences in mean age and sex between the five cohorts or between the three treatment groups.

The TENS unit (Pabisch TX-3) provided an asymmetric square biphasic waveform at a frequency of 100 pulses/s and a pulse width of 200 µs. The placebo TENS unit was identical to the treatment unit but did not provide current. Two sterile electrodes (first unit channel) were placed on one side of the incision and two other electrodes (second unit channel), on the other side. The electrodes (5 x 5 cm) were positioned 1 cm away from the suture line. The TENS group adjusted the stimulus intensity until a strong but comfortable tingling sensation was felt, whereas the placebo TENS group was told that the electrical stimulation was silent, producing no sensation.

About 1 hour after recovery from anesthesia, electrical stimulation or sham stimulation was instituted for 1 hour only in patients who had no analgesics in the recovery room. A 1-hour rest interval followed to avoid accommodation of nerve fibers. Then 1-hour stimulation or sham stimulation was performed again. At any time, patients could request further analgesia if necessary according to a patient-controlled analgesia procedure. The analgesic medications were different in the five patient cohorts: PL, MS, and CT patients were treated on request with a 0.1-mg intravenous bolus of buprenorphine hydrochloride, the ST patients received a 500-mg intramuscular injection of metamizol, and the VAT patients were treated with a 10-mg intravenous bolus of ketorolac. Patients could request further analgesia during the first 12 hours after operation, and the same doses were administered at each request (buprenorphine, 0.1 mg intravenously; metamizol, 500 mg intramuscularly; ketorolac, 10 mg intravenously). The time from the beginning of treatment to the request for analgesics was recorded and was assumed to represent the effectiveness of the TENS treatment. In addition, the total medication intake was recorded during the first 12 postoperative hours. Initial pain intensity (before treatment) was assessed by means of a numeric rating scale from 0 (no pain) to 10 (unbearable pain).

Statistical Analysis
The differences between and within treatment groups were analyzed by means of analysis of variance followed by the Newman-Keuls multiple range test for multiple comparisons. Data are presented as the mean ± standard deviation. Differences were considered to be significant at a p value of less than 0.05.

	Results

Top Footnotes Abstract Introduction Material and Methods Results Comment References

 
The five types of surgical procedures produced different intensities of postoperative pain. The PL cohort always experienced severe pain, with a mean numeric rating score of 8.8 ± 1.1, and the MS, CT, and ST cohorts had moderate to severe pain, with mean scores of 5.7 ± 2.1, 5.1 ± 1.8, and 5.5 ± 1.9, respectively. In contrast, the VAT cohort experienced only mild to moderate pain (mean score, 3.2 ± 2.4). No differences in pain intensity scores were found between the three treatment groups (TENS, placebo TENS, control) in each patient cohort.

When TENS treatment was started in the PL group, the first request for further analgesia was made after 18 ± 7 minutes (Fig 1A). No difference was found between the TENS and placebo TENS groups (p = 0.344); in fact, the placebo group requested further analgesia after 16 ± 8 minutes (see Fig 1A). During the first 12 hours, the TENS and placebo TENS groups received on request 0.31 ± 0.11 mg and 0.28 ± 0.09 mg, respectively, of buprenorphine (Fig 1B). There was no difference between these two groups (p = 0.285) and the control group (p = 0.435), which received no TENS treatment (0.33 ± 0.08 mg of buprenorphine).

View larger version (16K): [in this window] [in a new window]   Fig 1. . Patient cohort: standard posterolateral thoracotomy. Effect of transcutaneous electrical nerve stimulation ( TENS), placebo TENS, and no treatment (control) on (A) time to analgesia request and (B) buprenorphine intake during the first 12 hours after operation.

View larger version (30K): [in this window] [in a new window]   Fig 2. . Patient cohorts: (A) muscle-sparing thoracotomy, (B) costotomy, and (C) sternotomy. Effect of transcutaneous electrical nerve stimulation ( TENS), placebo TENS, and no treatment (control) on (left) time to analgesia request and (right) medication intake during the first 12 hours after operation.

View larger version (15K): [in this window] [in a new window]   Fig 3. . Patient cohort: video-assisted thoracoscopy. Effect of transcutaneous electrical nerve stimulation ( TENS), placebo TENS, and no treatment (control) on (A) time to analgesia request and (B) ketorolac intake during the first 12 hours after operation.

	Comment

Top Footnotes Abstract Introduction Material and Methods Results Comment References

Our findings show that TENS is effective in the control of postoperative pain only when the pain is not severe. In fact, we found that the effectiveness of TENS follows a gradient of pain intensity: from mild pain in VAT patients to moderate pain in MS, CT, and ST patients to no effectiveness for severe pain in PL patients. We conclude that the severe postoperative pain experienced after PL cannot be controlled by electrical stimulation. Transcutaneous electrical nerve stimulation does represent a useful therapeutic tool in the control of moderate pain after a procedure such as MS, CT, and ST. In these patients, however, it cannot be used as the first or only pain control system but as an adjunct to postoperative medications. Therefore, TENS helps to reduce total drug intake during the first 12 postoperative hours. In contrast, we found that TENS was highly effective in reducing mild postoperative pain after VAT. In this case, TENS may represent the analgesic treatment of choice, with no need of medications.

It is important to point out that our placebo TENS patients did not experience any sensation, as no stimulation was delivered. Although it is difficult to plan a true placebo stimulation in TENS studies, a sham treatment (that is, with the TENS unit turned off) seems to be the most reliable method [6]. In addition, our placebo TENS patients were told that stimulation produced no sensations and thus they did not expect stimulus perception. Also, we used only one frequency of stimulation. Therefore, we do not know whether other frequencies could be beneficial in PL patients. However, this is unlikely, as it has been widely demonstrated that a frequency of around 100 Hz is the most effective for a variety of painful conditions [16–19].

Besides the importance they have in thoracic surgery, these results can be applied to all types of surgical procedures producing mild, moderate, or severe postoperative pain. In this sense, the findings of the present study are in agreement with previous studies showing that TENS is not effective when the operation is too painful [6, 7, 11], and thus, TENS is not of major benefit compared with the usual opioid and nonopioid analgesics when pain intensity is high. In contrast, TENS can be used as an adjunct to other medications when pain is moderate and can be the only pain therapy when pain is mild. We emphasize that the absence of complications and side effects of TENS compared with conventional opioid and nonopioid analgesics makes electrical stimulation a safe and reliable therapeutic procedure.

	Footnotes

Top Footnotes Abstract Introduction Material and Methods Results Comment References

 
Address reprint requests to Dr Benedetti, Dipartimento di Neuroscienze, Università di Torino, Corso Raffaello 30, 10125 Torino, Italy.

	References

Top Footnotes Abstract Introduction Material and Methods Results Comment References

 

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This Article Abstract Alert me when this article is cited Alert me if a correction is posted Citation Map Services Email this article to a friend Similar articles in this journal Similar articles in PubMed Alert me to new issues of the journal Add to Personal Folders Download to citation manager Author home page(s): Giuliano Maggi Permission Requests Citing Articles Citing Articles via HighWire Citing Articles via Google Scholar Google Scholar Articles by Benedetti, F. Articles by Maggi, G. Search for Related Content PubMed PubMed Citation Articles by Benedetti, F. Articles by Maggi, G.