Indian Journal of Pain

: 2020  |  Volume : 34  |  Issue : 1  |  Page : 22--26

Effect of preoperative transcutaneous electrical nerve stimulation on intraoperative anesthetic drug consumption and pain scores in patients undergoing lumbar discectomy under general anesthesia

Nayani Radhakrishna1, Vanitha Rajagopalan2, Rajendra Singh Chouhan2, Shalendra Singh3, Mihir Prakash Pandia2,  
1 Department of Anaesthesiology and Critical Care, Army Hospital R&R, Delhi Cantt, New Delhi, India
2 Department of Neuroanaesthesiology and Critical Care, AIIMS, New Delhi, India
3 Department of Anaesthesiology and Critical Care, Armed Forces Medical College, Pune, Maharashtra, India

Correspondence Address:
Dr. Shalendra Singh
Department of Anaesthesiology and Critical Care, Armed Forces Medical College, Pune - 411 040, Maharashtra


Objective: Transcutaneous electrical nerve stimulation (TENS) is a common modality used to treat acute and chronic painful conditions. The aim of this study is to find out the effect of immediate preoperative TENS on intraoperative anesthetic drug consumption in patients undergoing lumbar discectomy under general anesthesia. Methods: Sixty patients undergoing lumbar discectomy were randomly divided into two study groups. In TENS group (Group T), TENS was applied for 1 h in the immediate preoperative period with 20 mA current, at 100 Hz frequency, in pulses of 250 μs on either side of the planned incision site. In Sham TENS group (Group S), TENS was applied for 1 h preoperatively to the patients, although with the current intensity set at “zero” mA. The pain intensity during rest as well as movement was recorded before and after TENS, by using the Visual Analog Scale (VAS) scores in both the groups. Intraoperatively, titrated doses of propofol were used to maintain a bispectral index value of 50 ± 5, and IV fentanyl was administered to maintain the heart rate and blood pressure within 20% of baseline values. Postoperatively, fentanyl 0.5 μg/kg IV was administered to achieve VAS of <4. Results: Application of TENS was found to significantly reduce the preoperative VAS score (P < 0.001). Intraoperatively, no difference in propofol and fentanyl consumption was observed in either group (P < 0.6) (P < 0.27). Recovery time and postoperative VAS scores recorded at various time intervals were comparable in both the groups. No difference in fentanyl consumption or rescue analgesia was noted in the postoperative period in both groups. Conclusions: Application of preoperative TENS provided immediate relief from pain, although without any significant decrease in the intraoperative or postoperative analgesic requirement. Furthermore, no difference was noted in the intraoperative anesthetic consumption.

How to cite this article:
Radhakrishna N, Rajagopalan V, Chouhan RS, Singh S, Pandia MP. Effect of preoperative transcutaneous electrical nerve stimulation on intraoperative anesthetic drug consumption and pain scores in patients undergoing lumbar discectomy under general anesthesia.Indian J Pain 2020;34:22-26

How to cite this URL:
Radhakrishna N, Rajagopalan V, Chouhan RS, Singh S, Pandia MP. Effect of preoperative transcutaneous electrical nerve stimulation on intraoperative anesthetic drug consumption and pain scores in patients undergoing lumbar discectomy under general anesthesia. Indian J Pain [serial online] 2020 [cited 2020 May 31 ];34:22-26
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Pain is a potent trigger for the stress response, wherein activation of the autonomic nervous system causes adverse effects on multiple organ systems.[1] In addition to preoperative pain, the surgical incision as well as postoperative inflammatory processes may intensify acute pain by releasing peripheral/central neuromodulators. At present, various multimodal approaches to peri-operative analgesia are being used to lessen postoperative pain and curtail the injudicious use of analgesics.[2],[3] Opioids, which have conventionally been used for the past three decades during perioperative period, result in many troublesome side effects, including the potential for misuse, or opioid use disorder postoperatively.[4] Literature also revealed that patient's first exposure to opioids may be during the perioperative period. These potential side effects led to the emergence of multimodal approaches to deal with perioperative pain and reduce opioid use perioperatively.[4] Transcutaneous electrical nerve stimulation (TENS) is one such modality that may be used to treat painful conditions, including pain in the postoperative period, although with only weak evidence supporting its use.[5],[6],[7] However, while the usage of TENS as a modality for reducing pain has been studied, the effect of the same in postoperative opioid consumption apart from its use as a solitary modality for the management of acute nociceptive pain and the impact of its preoperative use on anesthetic requirement has not been previously reported. The theoretical potential of the modality to decrease peri-operative pain and anesthetic requirement apart from reducing postoperative opioid use were considered relevant while conceptualizing the research, since it has the potential to significantly improve peri-operative practices and protocols.

We hypothesized that administering preemptive analgesia in the form of TENS will reduce intra-operative analgesic requirements. The primary objective of this study was to find out the effect of immediate preoperative TENS on intraoperative fentanyl and propofol requirement in patients undergoing lumbar discectomy. In addition, studying its effects on postoperative analgesic requirement was the secondary objective.


A double-blind randomized placebo-controlled study was designed and conducted at a tertiary care neurosurgery center. Ethical approval for this study was provided by the Institutional Ethical Committee of the All India Institute of Medical Sciences, New Delhi on October 29, 2015. We screened 64 patients undergoing elective lumbar discectomy surgeries (March 2015–September 2016), of which 4 were not included in the study (two patients did not meet inclusion criteria and two patients expressed their unwillingness to participate in the study). Patients of the American Society of Anesthesiologists' physical status Grade I or II, aged between 18 and 65 years were included in the study. The presence of pregnancy implanted electronic devices or history of chronic opioid treatment, drug abuse and epilepsy were the exclusion criteria. A simple 10-point Visual Analog Scale (VAS) to assess the severity of pain was explained to all the consenting patients. The study population was randomized with the help of a computer generated chart into two study groups, i.e., TENS group (Group T) and Sham TENS group (Group S).

On the day of the surgery, patients were asked to lie supine in the bed and preoperative VAS scores at rest and movement were recorded by the attending nurse. Patients were then made to lie in prone position and 02 self-adhesive electrode pads were applied on each side about 4–5 cm lateral to the midline in the region of the planned incision (four-channel device-LG-8™Elite [LG Med Supply, USA]). TENS frequency was set at 100 Hz, with a pulse width of 250 μs and electrical current intensity of either 20 mA or “zero” mA as per the study group. The “in-use” LED light on the TENS device was flashing in both the groups, thus blinding the patient and the anesthesiologist responsible for intraoperative/postoperative management and recording. In addition, all patients were told that they may or may not be able to appreciate the electrical stimulation when the TENS device was started as the current used was low. After 60 min, TENS pads were removed and VAS scores on rest and movement were recorded again before shifting the patient to the operation theatre.

In the operating room, standard noninvasive monitoring was commenced, and baseline heart rate (HR), mean blood pressure (MBP), oxygen saturation (SpO2), and bispectral index (BIS) were recorded. Anesthesia was induced with injection propofol (2–2.5 mg/kg) proceeded by fentanyl (2 μg/kg). Rocuronium (0.1 mg/kg) was administered to facilitate tracheal intubation. Patients were ventilated with oxygen and air in equal proportions to maintain end-tidal carbon dioxide (EtCO2) of 35–40 mmHg. For the maintenance of anesthesia, propofol infusion was started at 100 μg/kg/min and titrated to a BIS value of 50 ± 5. Rocuronium 0.2 mg/kg/h was administered as a continuous infusion. A bolus of propofol (0.5 mg/kg) was administered and the infusion rate was increased by 5 ml/h on encountering an increase in HR or MBP of >20% from baseline with a BIS value >55. This procedure was repeated until BIS decreased to <55. The propofol infusion rate was decreased by 5 ml/h if BIS was <45. If HR or MBP were >20% from baseline and BIS value was <55, fentanyl bolus of 0.5 μg/kg was administered and repeated every 5 min till HR and MBP returned to within 20% of baseline values. Hypotension (MBP <20% of baseline) was treated with rapid infusion of fluids and/or vasopressors (Injection mephentermine 3 mg in repeated doses if needed). Normothermia (36°C–37°C) was maintained throughout the surgery rocuronium infusion was stopped at the start of surgical closure; while propofol infusion was stopped after skin suturing was complete. After giving neostigmine 70 μgm/kg and glycopyrrolate 10 μgm/kg to reverse neuromuscular blockade tracheal tube was removed once the patient was fully awake. Recovery time was calculated from the time of stopping propofol to the time of tracheal extubation.

Postoperatively, fentanyl 0.5 μg/kg was administered to achieve VAS of <4. Patient-controlled analgesia (PCA) pump was programmed with a bolus of 0.25 μg/kg, lockout interval of 10 min and a maximum 1 h dose of 2 μg/kg. HR, MBP, SpO2, and VAS were recorded every 60 min for the first 4 h and then every 4 h till 24 h after the surgery. Intravenous ketorolac 30 mg was used for rescue analgesia.

Statistical analysis was performed with STATA 12.1 (College Stations, Texas, USA). Values of intraoperative haemodynamic parameters, BIS, temperature, and VAS were analyzed to detect intra- and inter-group differences at various time points. The sample size calculated for this study was based on published data indicating fentanyl consumed through PCA (mean ± standard deviation [SD]; 360 ± 117 μg) within 24 h postoperatively in the placebo group and also by a published study, in which VAS score (mean ± SD; 7.47 ± 1.7) was estimated preoperatively in cases of lumbar canal stenosis.[8],[9] A sample size of 27 patients per group would be sufficient to detect a difference of 35% between VAS score preoperatively and postoperatively for a two-tailed α = 0.05 with a study power of 0.8. To account for an anticipated 20% drop out rate, we have managed to recruit 64 patients in this study. Student's t-test was used for inter-group comparison of mean values of continuous parameters. For categorical variables, Chi-square test and Fisher's exact test were performed. A value of P < 0.05 was considered statistically significant.


Thirty-one patients were evaluated in Group T and 29 were evaluated in Group S [Figure 1]. Demographic parameters and clinical characteristics were comparable between the groups [Table 1]. The median duration of pain before the presentation was 2.0 years in both the groups, with a range from 0.5 to 5.0 years. There was no statistical difference in the number and level of laminectomies in both groups [Table 1].{Figure 1}{Table 1}

Preoperatively, before the application of TENS, the mean VAS score at rest and movement were 4.7 and 5.9, respectively, in Group T which reduced to 3 and 3.4 (P < 0.01, P < 0.01) after application of TENS. However, in Group S the mean VAS score did not change significantly after TENS, although they reduced from 4.5 and 5.6 at rest and movement to 4.4 and 5.3, respectively (P < 0.46, P < 0.25).

During the intraoperative period, hemodynamic parameters (HR and MBP) were comparable between the two groups [Table 2]. There was a transient rise in HR and MBP in both the groups with laryngoscopy and intubation which settled down over 2–3 min. Three patients in each group experienced hypotension and were treated with boluses of mephentermine and rapid fluid boluses. Intraoperative variables such as anesthetic duration, fluid administration, and blood loss were comparable between the two groups. However, urine output was found to be slightly increased in Group S [Table 2]. Anesthetic requirement, as indicated by the total consumption of fentanyl, propofol, and rocuronium was comparable in both groups (P < 0.83, P < 0.71, P < 0.14) [Table 3]. Mean recovery times were also comparable between the two groups (P < 0.70) [Table 3].{Table 2}{Table 3}

Postoperative VAS scores recorded at various time intervals during the first 24 h were comparable between the two groups and were found to be ≤ 3 for the majority of the time during which the patients were assessed [Table 4]. The mean fentanyl utilized in the first 24 h during the postoperative period was comparable in between the groups (P < 0.62). In addition, rescue analgesia was required in 3 patients in Group T and 2 patients in Group S.{Table 4}


While TENS is a common modality used to treat pain, the literature on the effectiveness of the same in a variety of medical conditions reports a wide range of outcomes, from very positive to negative. Furthermore, the same TENS protocol may have different degrees of anti-nociception in acute pain compared with chronic pain in patients with chronic backache leading to the conflicting professional opinion on the use of TENS in acute pain, including perioperative pain.[10] The conflicting outcome in the utility of TENS for pain control is presumably due to different types of TENS electrode used, and duration and site of application.

As of now, there has been no study on the use of TENS in the intra-operative period when the patient is under general anesthesia. This is because of difficulty in applying TENS electrodes during the surgical procedure in addition to maintaining sterility apart from the concerns of fire, shock, and interference with electrocautery. In a study designed similar to ours, Unterrainer et al. administered TENS before skin incision as well as in postoperative period for patients undergoing major spinal surgery.[11] However, contrary to this study, they found that the postoperative demand of analgesia was significantly less in the preoperative and postoperative period. No such difference in intra-operative anesthetic or perioperative analgesic requirement was appreciated in this study.

Our study revealed that intraoperative fentanyl consumption was comparable in both groups. This may be attributed to either the absence of any beneficial effect of TENS or to a strong placebo effect obtained with sham-TENS. There is evidence to suggest that placebo analgesia may involve the release of endogenous opioids, which could thereby explain the comparability of both groups with respect to analgesic requirements.[12],[13],[14],[15],[16] The other reason could be due to the diminishing effect of a single dose of TENS therapy. Almost all clinical trials delineate that maximum alleviation of pain occurs when the TENS device is applied continuously, and the analgesic effect usually vanishes quickly once the device is switched off. However, Johnson et al. described that the duration of poststimulation analgesia varies widely, lasting anywhere between 2 and 18 h.[17] To obviate this problem in assessing the need for analgesia, we used the BIS monitor in an indirect way, and these parameters were considered while calculating the algorithm.[18] The BIS index was strictly maintained within the range of 45–55 and any increase in HR and BP in this range of BIS was considered to be due to inadequate analgesia and additional fentanyl was administered. Even though the recently introduced “qCON/qNOX” monitors claims to separately analyze the hypnotic and analgesic components of anesthesia,[19] they are presently not widely available and consequently have not been studied extensively.

There are some limitations to the study. The primary limitation is that it is difficult to design a true “control with blinding” in the studies involving TENS as subjects in the control group may deduce that they belong in the control group by virtue of not feeling any electrical stimulation on the application of sham-TENS. To obviate this problem, during the preoperative visit as well as at the time of TENS application, the patients were informed that they may or may not feel sensation produced by the TENS device as the electric current used is low. Another limitation is that we did not record the exact time of administration of additional fentanyl in the intra-operative period, which could have given us some idea of the duration of the analgesia provided by preoperative TENS in the perioperative period.


Although the application of TENS in the immediate preoperative period provided relief from pain, contrary to our hypothesis, there was no significant decrease in intraoperative fentanyl consumption between patients who received TENS as compared to those who did not. Furthermore, there was no significant decrease in intraoperative anesthetic and postoperative analgesic requirement in the two groups of patients. However, this is a small study and larger, randomized, placebo-controlled, blinded studies with possibly better analgesic monitoring are required to provide more clarity on this issue.

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Conflicts of interest

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