Background

Laparoscopic cholecystectomy is indicated for various diseases of the gallbladder and is one of the most commonly performed procedures all over the world [Javid and Brooks 2004]. It is a widely preferred procedure over open cholecystectomy by both surgeons and patients due to its various advantages such as lesser postoperative pain, faster recovery time, and shorter hospital stay. But like any other surgical procedure, it comes with its own challenges which are dealt by the anesthesiologist. One such challenge happens to be postoperative pain whose origins and nature are yet to be fully understood. Nausea and vomiting are the most commonly reported postoperative complaint after pain (Lee et al. 2001). Interestingly, post-laparoscopic cholecystectomy pain does not resemble the postoperative pain that is reported after other laparoscopic procedures (Bisgaard et al. 2001a, b, c; Bisgaard et al. 2001a, b, c; Wills and Hunt 2000). Acute pain after laparoscopic cholecystectomy has three components: incisional (somatic), deep abdominal (visceral), and shoulder pain (presumably referred visceral pain) (Bisgaard et al. 2001a, b, c). The causative factors range from the stretching of the diaphragm and peritoneum due to gas insufflation, to irritants like blood, bile, and pus (O’Hanlon et al. 2002). Treating postoperative pain with drugs like opioids is the common practice which in turn causes adverse effects like sedation, respiratory depression, urinary retention, nausea, and vomiting (White 1995; Za´rate 2001). This problem gets confounded as pain itself plays a role in increasing postoperative nausea and vomiting (PONV) in these patients and is the main reason for prolonged hospital stay (Bisgaard et al. 2001a, b, c; Lau and Brooks 2001) and convalescence (Bisgaard et al. 2001a, b, c; Bisgaard et al. 2001a, b, c). Intense acute pain after the procedure has also been associated with the development of chronic pain and post-laparoscopic cholecystectomy syndrome (Bisgaard et al. 2001a, b, c). Non-steroidal anti-inflammatory drugs (NSAIDs) and cyclooxygenase -2 (COX-2) inhibitor treatment resulted in higher opioid sparing (approximately 30%) compared to other classes of drugs and significantly reduced PONV and sedation by approximately 30%, though the effects on urinary retention and respiratory problems were inconclusive. The benefits of opioid-sparing in certain cases were outweighed by the adverse effects such as bleeding with NSAIDs and cardiovascular complications in certain high-risk patients with COX-2 inhibitors. Non-pharmacological methods have been successfully used in both chronic and acute pain, including postoperative pain. The mechanism involves modulation of neural conduction as described in Melzak and Wall’s gate control theory as well as the release of endogenous opioids at the level of the central nervous system, the spinal cord specifically (Melzak and Wall 1965; Rushdon 2002). This study evaluated not only the effectiveness of TENS for pain relief and hemodynamic stability but also its potential to decrease the use of pharmacologic analgesic methods along with its effect on nausea and vomiting in patients. Transcutaneous electrical nerve stimulation (TENS) has been shown to have definite benefits as a complementary therapy in managing acute postoperative pain and has no side effects, unless and until contraindicated in particular patients(Javid and Brooks 2004; Lee et al. 2001 ) Effective TENS analgesia can facilitate early post-operative recovery and reduce hospital stay.

Methods

After due clearance from the hospital ethical committee, the prospective interventional comparative study was conducted in our institution as per the study protocol submitted to the board. Informed and written consent was obtained from all patients for inclusion in the study. A total of 64 American Association of Anesthesiologists (ASA) Grade 1 and 2 patients in the age group 18 years to 60 years of either gender posted for elective laparoscopic cholecystectomy were randomly allocated to one of the two groups using a computer-generated sequence of random numbers as follows: Group P (n= 32): Patients receiving sham TENS or placebo TENS and Group A (n= 32): Patients receiving active TENS for 45 min at predetermined amplitude and at 100 Hz. Patients with intra-surgical complications, history of seizures, motion sickness, neurological disease, neuropathy, and pacemakers were excluded from the study. Patients were informed about the study procedure and that the postoperative pain would be measured using a visual analog scale (VAS). The VAS consisted of a 10-cm horizontal line with the words “no pain” written on the left end of the scale and the words “worst pain possible” written on the right end of the scale. The patient was asked to mark a line at a place corresponding to his or her pain level. Subjects were informed that two types of TENS therapy will be tested, one in which little or no sensation will be felt and one in which a strong sensation will be felt. Standard general anesthetic technique was used with injection fentanyl (2mcg/kg), injection propofol (2mg/kg), and injection vecuronium (0.08mg/kg) followed by intubation with appropriate-sized endotracheal tube. Following intubation, HR, ECG, SpO2, and BP were monitored throughout the surgery. Maintenance of anesthesia was achieved with N2O (66%), O2 (33%), and sevoflurane (1–2%). Residual neuromuscular blockade was reversed with neostigmine 0.05mg/kg and glycopyrrolate 0.01mg/kg at the end of surgery. Just prior to extubation all patients participating in the study were given injection paracetamol 1000mg intravenously. In TENS Group A, electrodes were placed at the site of pain in the recovery room and the TENS equipment was applied for 45 min. The generator was connected by lead wires to two sterile electrodes with a pre-gelled contact surface. These electrodes were placed parallel to and on either side of the incisions through which trocars were inserted by the surgical team, approximately 2 to 3 in. away. This distance was recommended by Mannheimer and Lampe, as most pain from the surgical incision is from trauma to tissue and muscle (as a result of surgical retraction) and not at the incision site itself (Mannheimer and Lampe 1984). The intensity of TENS was increased if the patient informed us about any accommodation. In the placebo TENS Group P, electrodes were placed in a similar manner as described for Group A but no electrical current was applied. In all patients, blood pressure, heart rate, and VAS scores were measured at 0 min (T1) and after 45 min (T2) of TENS. Subsequent data was collected at 2, 4, 6, and 8 h, i.e., T3, T4, T5, and T6, respectively. Pain assessment VAS scores, hemodynamic parameters, and rescue analgesia dose at T1, T2, T3, T4, T5, and T6 were noted. Rescue analgesia with injection of diclofenac 75 mg IM was given after TENS if any patient gave a score of more than 3 on VAS at any point of time during the next 8 h (Fig. 1).

Fig. 1
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Consolidated standards of reporting trials (CONSORT) flow diagram

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Statistical analysis

The sample size was determined based on a previous study, assuming a difference of 1 in postoperative VAS between the two groups as clinically significant. A sample size of minimum of 28 patients per group was calculated with an effect size of 0.67, at an alpha error of 0.05 and power of 90% (Silva et al. 2012 ). Statistical analysis was performed by the SPSS program for Windows, version 17.0 (SPSS, Chicago, Illinois). Continuous variables were presented as mean ± SD, and categorical variables were presented as absolute numbers and percentage. Data was also checked for normality before applying tests for statistical analysis. Normally distributed continuous variables were compared using the unpaired t test. Variables not normally distributed were tested with the Mann-Whitney U test. Chi-square test or Fisher’s exact test was used to analyze categorical variables. A P value <0.05 was considered statistically significant.

Results

The two groups were statistically similar in terms of age, gender (female predominance), and weight (Table 1).

Table 1 Demographic data
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The mean systolic blood pressure was significantly reduced at 45 min and 2 h post-TENS application in Group A as compared to Group P (p<0.001) (Table 2 and Fig. 2).

Table 2 Comparison of the two groups in terms of change in systolic BP (mmHg) over time
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Fig. 2
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Change in mean systolic BP with time

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The mean diastolic blood pressure also followed a similar trend with Group P demonstrating significantly reduced mean diastolic pressure at 45min, 2 h, and 4h (Table 3 and Fig. 3).

Table 3 Comparison of the two groups in terms of change in diastolic BP (mmHg) over time
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Fig. 3
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Change in mean diastolic BP with time

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Compared to Group P, the heart rate was lower after applying TENS at T2, T3, and T4 in Group A with p values of 0.012, 0.017, and <0.001, respectively (Table 4 and Fig. 4).

Table 4 Comparison of the two groups in terms of change in heart rate (BPM) over time
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Fig. 4
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Change in heart rate (BPM) over time in the two groups

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The VAS scores were significantly lower in patients in the active TENS group for up to 2 h after surgery, and the total weighted dose of diclofenac consumed over 8 h in the active TENS group was significantly lower as compared to the placebo TENS group. Total episodes of nausea and emesis though less in the active TENS group were statistically insignificant (Table 5, Fig. 5, Table 6 and Fig. 6).

Table 5 Comparison of the two groups in terms of change in VAS over time
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Fig. 5
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Change in mean VAS score over time

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Table 6 Comparison of the two groups in terms of change in diclofenac dose (mg) over time
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Fig. 6
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Change in diclofenac dose (mg) over time in the two groups

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Discussion

Laparoscopic cholecystectomy is one of the most commonly performed surgical procedures all over the world and still remains a major cause of postoperative pain. Our objective was to assess if something as simple and non-invasive like TENS can benefit patients undergoing laparoscopic cholecystectomy. Kara et al. observed significantly lower pain scores in patients who received both TENS and patient-controlled analgesia (PCA) as compared to PCA alone (p<0.05) (Kara et al. 2011). Eidy et al. in 2016 evaluated the effects of preoperative TENS on post-inguinal hernia repair pain and showed that the mean estimated postoperative pain intensity was significantly reduced at 2 and 4 h after the surgery (3.54± 1.48 and 5.12±1.41 (p < 0.001), respectively) (Eidy et al. 2016). In our study, we observed significantly lower VAS scores in patients who received TENS at 45 min and 2 h after surgery. We found that the differences were statistically significant with p values of 0.002 at both 45 min and at 2 h. Subsequent VAS scores were also lower till 8 h, but they were not statistically significant. Hamza et al. observed that morphine requirements were reduced down to 53 % using mixed frequency TENS when compared to the placebo group. They also noted a decrease in morphine-related side effects (Hamza et al. 1991). Bjordal et al. conducted a meta-analysis to analyze if acupuncture like TENS (ALTENS) could reduce analgesic consumption in surgery. They found the mean reduction in analgesic consumption after TENS/ALTENS to be 26.5% (range −6 to +51%) better than the placebo groups in all trials. In nine of the trials, mean weighted analgesic consumption was 4.1% (range −10 to +29%) which was in favor of ALTENS while eleven trials reported a mean weighted reduction in analgesic consumption of 35.5% (range 14–51%) (Bjordal et al. 2003). We also noticed a lower requirement of rescue analgesia doses of diclofenac at 45 min and 2 h. The total dose of diclofenac for the active TENS group was much lower over 8 h (11.72 ± 27.67) when compared to the placebo group (39.84 ± 42.53). This difference was significant with a p value of 0.003. TENS has anti-nociceptive effects similar to acupuncture which can last for much later as was found by Sjolund et al. in 1976 (Sjolund et al. 1976). Oncel et al. concluded that for mild pain after minor rib fractures, TENS can be more effective than NSAIDs (Oncel et al. 2002). TENS is not only a viable adjuvant therapy with pharmacological analgesia but can be the only or main therapy for mild surgical or post-surgical pain, with NSAIDS and opioids reserved for rescue analgesia. Benedetti too underlined the lack of side effects of TENS when compared with conventional opioid and non-opioid analgesics which have side effects like nausea and vomiting. These adverse effects add to the general discomfort of postoperative patients who are already dealing with postoperative pain (Benedetti 1997). TENS itself has the effect of reducing nausea and vomiting as Silva et al. found in their study (Silva et al. 2012). We also found that complaints of nausea and emesis were fewer among patients receiving active TENS (14.3%) as compared with the placebo TENS group (emesis, 23.8%; nausea, 38.1%). Also, the relative risk of nausea and emesis was 2.17 times greater in the placebo TENS group. Although in our active TENS group, the mean of total incidences of nausea or emesis was lower (0.25 ± 0.76) than that in the placebo group (0.56 ± 1.27), but this difference was statistically not significant with a p value of 0.4253. Chandra et al. found that patients who underwent posterolateral thoracotomy for decortication of the lung, reported significantly lesser VAS scores in group II (TENS group) at 2, 4, 6, and 8 h (p < 0.01, p < 0.05, p < 0.05, p < 0.05, respectively). Similarly, the systolic blood pressure was found to be significantly lesser in group II at 2, 4, and 6 h after surgery, with a p < 0.02, p < 0.01, and p < 0.01, respectively (Chandra et al. 2010).

In our study, the mean of systolic blood pressure changes was significant at 45 min and 2 h with p values of <0.001 and <0.001, respectively, but not on subsequent measurements at 4, 6, and 8 h. Mean diastolic pressure in the study group also remained significantly lower than the placebo group at 45 min, 2 h, and 4 h measurements, with p values of <0.001, .004, and <0.001, respectively. The heart rate is another indicator of hemodynamic stability and can also be a cue for pain. We found that heart rate in the active TENS group remained significantly lower than the placebo TENS group till 4 h after application of TENS with p values of 0.012, 0.017, and less than 0.001 at 45 min, 2 h, and 4 h, respectively. Patients who received TENS had heart rates closer to their baseline values, and there was no statistically significant difference at 6 and 8 h in the active TENS group. The average heart rates of patients in the placebo group became comparable with their baseline heart rate after 8 h had passed. The change in heart rate in the active TENS group over time was not statistically significant with a p value of 0.478, but the heart rate varied significantly from baseline in the placebo group with a p value less than 0.001 which demonstrates the benefit of TENS when it comes to hemodynamic stability. The limitation of our study was that we tested TENS on only ASA grade I and II patients and further studies need to be done on a wider range of patients. Also, larger studies need to be conducted to ascertain its role in the general wellbeing of the patients in the postoperative period.

Conclusions

We conclude that TENS is an effective adjuvant non-pharmacologic modality for postoperative pain relief after laparoscopic cholecystectomy with significant pain relief in the early postoperative period and reduced pharmacological analgesia requirement. We recommend the use of TENS in post-surgical recovery zone for patients undergoing laparoscopic cholecystectomy.