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Ann Thorac Surg 1997;63:608-610
© 1997 The Society of Thoracic Surgeons
Departments of Anesthesiology and Cardiothoracic Surgery, Stanford University School of Medicine, Stanford, California
The focus of the prospective study of 324 patients from the University of Torino Medical School in Italy [1] was on the ability of transcutaneous electrical nerve stimulation (TENS) to help reduce postoperative pain in the first 12 hours after five different thoracic surgical procedures.
Transcutaneous electrical nerve stimulation was introduced into clinical practice in 1972 as an adjunct to other pain therapies [2]. Since then it has been used often for postoperative pain relief, including after thoracic operations [3–5]. The mechanism of action of TENS is still not completely understood. Analgesia may be produced by the modulation of nociceptive input in the dorsal horn of the spinal cord by peripheral electrical stimulation of large sensory afferent nerves, the so-called gate control theory of pain [6]. Alternatively, electrical stimulation of certain receptor sites in the dorsal horn of the spinal cord may release endorphins, in turn producing analgesia that can be reversed by naloxone [7]. High-frequency and low-voltage stimulation, as used in this study to provide analgesia, is usually well tolerated by patients.
The potential advantage of TENS as an adjunct to other pain therapies is that TENS is noninvasive and safe. Few side effects or complications have been associated with its use [8]. But does TENS work? The efficacy of TENS in improving pulmonary function and reducing opioid requirements after thoracic operations remains controversial.
Benedetti and colleagues [1] found TENS to have little or no benefit after procedures associated with severe pain (posterolateral thoracotomy) and only moderate benefit as a supplement to reduce the amount of opioid analgesics after less invasive, less painful procedures (muscle-sparing thoracotomy, costotomy, and sternotomy). Because the opioid analgesic regimens differed between groups in this study and were not comparable (buprenorphine for some patients, metamizol or ketorolac for others) the intergroup comparisons are not valid and Benedetti and colleagues' conclusions are questionable. Results from previous studies after lateral thoracotomy or sternotomy are mixed, with many studies supporting the efficacy of TENS in patients undergoing these operations [3–5, 9, 10], and others finding TENS of little or no value after identical procedures [11].
Unfortunately, Benedetti and colleagues also give us no details on the intraoperative anesthetic management of their patients. It is doubtful that all the anesthetics were comparable because the management of a thoracotomy patient is very different from that of a patient undergoing a video-assisted thoracoscopic (VATS) procedure. Because general anesthetics and supplemental analgesic drugs differed between surgical groups, and perhaps within specific groups, it is again difficult to draw firm conclusions from their intergoup comparisons. Transcutaneous electrical nerve stimulation or sham TENS was begun "about 1 hour after recovery from anesthesia." Certainly, the amount and type of intraoperative opioids and other drugs given to each patient would have had a major impact on the length of the recovery period, and also on the time interval until the first analgesic was requested in the recovery room. In addition, the use of opiates preoperatively is known to affect the response to TENS postoperatively. Patients naive to opioids have better results with TENS compared with patients who have previously received opioid analgesia [12]. These missing data would have been important in putting the findings of Benedetti and colleagues in perspective. Unfortunately, because of these deficiencies this study still does not clarify the role for TENS, if any, after major thoracic procedures.
The important finding of this study was the beneficial effect of TENS in reducing opioid requirements after VATS procedures. The miniaturization of video equipment during the past decade has led to a virtual revolution in the number and types of operative procedures performed by endoscopy. This is true in thoracic surgery as it is in other fields. Today, pleurodesis, lung and pleural biopsies, wedge resections, lung volume reduction, and even anatomic pulmonary resections [13] are done by VATS, and new applications are continually being described.
The rationale for VATS replacing older, established procedures seems evident. Video-assisted thoracoscopy is less invasive than thoracotomy. Because there is less interruption of the chest wall, VATS patients should experience less pain and their recovery from the operation should be more rapid. Therefore, any procedure performed by VATS rather than by traditional thoracotomy should translate into cost savings to the patient and institution even when the increased cost of the equipment is included [14, 15].
Pain after VATS is often considered minor, at least when compared with the pain associated with open thoracotomy. In our experience, the degree of discomfort experienced by patients after VATS is highly variable and often unpredictable. Although Benedetti and colleagues described their VATS patients' pain as "mild to moderate," the visual analogue pain scores they report for this group were a mean of 3.2 ± 2.4 (standard deviation). This suggests great variability within the VATS group, with some patients probably experiencing what would be considered severe pain. The surgical procedure itself, the degree of pleural irritation, the presence and site of chest tubes, and the number and extent of port incisions differ for each patient, and every patient has a different pain threshold. Therefore, another weakness of this study is the failure to differentiate the types of procedures that made up the VATS group, and whether or not there were any subgroups of VATS patients in whom TENS was not successful.
The VATS group was composed of a total of 95 patients who were divided into control, placebo TENS, and TENS-treated subgroups. We are not told how many patients made up each subgroup; presumably there were approximately 30 patients in each group. Patients treated with TENS for a total of 2 hours in the recovery period required significantly less intravenous ketorolac, a nonsteroidal, antiinflammatory analgesic, than sham TENS and control patients during the 12-hour postoperative study period. The sham TENS group requested 32 ± 9 mg (standard deviation) of ketorolac and the control group 29 ± 12 mg compared with only 6 ± 4 mg for the TENS-treated group. Because no additional visual analogue pain scale measurements were made during the study period, it must be assumed that the actual degree of patient comfort after ketorolac medication was comparable between groups.
Although the reduction in ketorolac requirements seems impressive, the actual cost reduction is negligible. In our institution the charge to the patient for 30 mg of ketorolac is $46.59, whereas the cost for using a TENS unit is $293.00. Because TENS is usually used for long-term pain therapy, this initial charge also includes an evaluation and a teaching session with a physical therapist. Presumably, if the TENS unit was used for a short period, as in this study, the set-up and rental charge would be reduced but would still be high compared with the modest cost of 30 mg of ketorolac.
We usually treat our VATS patients with intravenous opioids and with local anesthetics (0.25% bupivicaine with 1:200,000 epinephrine, 0.5 mL/kg) administered through the chest tube and in the incisions at the completion of the procedure after the lung has been reexpanded. The Stanford University Medical Center pharmacy charge for a 30-mL ampule of 0.25% bupivicaine is $32.31, and the institution charges $29.28 for 10 mg of morphine sulfate and $28.86 for 50 mg of meperidine. Therefore, the total charge for our analgesic combination of local anesthetics and systemic opioids to treat postthoracoscopy pain would be approximately $60.00, far less than the cost of renting a TENS unit.
How does one measure the utility and effectiveness of a pain therapy? Benedetti and colleagues fail to tell us whether the application of TENS shortened recovery room stay. Did it reduce the length of hospitalization? Was pulmonary function improved in patients treated with TENS compared with sham TENS and control patients [14]? Were there fewer postoperative complications in the TENS-treated patients compared with controls? Most importantly, is the extra cost of using a TENS unit justified if a similar degree of analgesia and safety can be obtained by 30 mg of ketorolac at one-fifth of the cost to the patient?
Benedetti and colleagues' final conclusions are also unsubstantiated. Based on their data they recommend TENS as an adjunct to other medications for any and all types of surgical procedures when postoperative pain is "moderate," and suggest that TENS can even be the only pain therapy necessary when postoperative pain is "mild." Although it seems clear from this study that TENS did reduce the amount of ketorolac requested in the immediate postoperative period in patients undergoing VATS, too many questions are left unanswered to support this extremely broad interpretation of data from this study. In fact, several other well-controlled clinical studies have failed to demonstrate that TENS therapy is effective in reducing opioid requirements after procedures producing "mild" postoperative pain [8, 16, 17].
This study does draw our attention to the problem of pain after VATS. Because this pain is often considered "mild," there has been little focus on postthoracoscopy analgesia in the medical literature. In spite of its good features there are several shortcomings to this article, the major one being its failure to address the important question concerning the apparent effectiveness of TENS versus its expense.
Footnotes
Address reprint requests to Dr Brodsky, Department of Anesthesiology, H3580, Stanford University Medical Center, Stanford, CA 94305.
References
Related Article
This article has been cited by other articles:
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  S. Amini, A. Gabrielli, L. J. Caruso, and A. J. Layon The Thoracic Surgical Patient: Initial Postoperative Care Seminars in Cardiothoracic and Vascular Anesthesia, September 1, 2002; 6(3): 169 - 188. [Abstract] [PDF]
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 S. Toyota, T. Satake, and Y. Amaki Transcutaneous Electrical Nerve Stimulation as an Alternative Therapy for Microlaryngeal Endoscopic Surgery Anesth. Analg., November 1, 1999; 89(5): 1236 - 1236. [Full Text] [PDF]
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 F. Benedetti, M. Amanzio, C. Casadio, A. Cavallo, R. Cianci, R. Giobbe, M. Mancuso, E. Ruffini, G. Maggi, J. B. Brodsky, et al. Postthoracoscopy Pain: Is TENS the Answer? Ann. Thorac. Surg., September 1, 1997; 64(3): 890 - 891. [Full Text]
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