Labor pain relief using transcutaneous electrical nerve stimulation, maternal and fetal impacts

a randomized-controlled study

Abstract

Objective 

To assess the effectiveness of transcutaneous electric nerve stimulation (TENS) in controlling labor pain.

Study design 

This was a randomized-controlled study that was carried out in the Obstetric Department, Cairo University Teaching Hospital, Egypt.

Patients and methods 

A total of 100 parturients in active labor and who were seeking labor analgesia were assigned randomly to two groups: group A used a TENS plus dual channel machine and group B (control group) used pethidine, intramuscular (50–100 mg). Pain was assessed by visual analogue scale. Forty-eight hours postpartum questionnaire was administered to assess women’s satisfaction.

Our primary outcome was the degree of labor pain relief by TENS; the secondary outcomes included duration of first stage, labor augmentation, mode of delivery, fetal outcome, and adverse events.

Results 

Both groups were comparable in maternal age, gestational age, and parity. There was a decrease in pain score readings in both groups, but the difference did not reach statistical significance (P=0.06). Forty-eight hours postpartum questionnaire indicated greater satisfaction in the TENS group (83 vs. 10% in the control group).

There was no statistical difference between both groups in the mode of delivery (P=0.7) and length of the first stage, but there was a statistical difference between both groups in the need for labor augmentation (P=0.046); fewer number of parturients in the TENS group needed labor augmentation.

There was no difference in the Apgar score reading at 1 min (P=0.43), but at 5 min, there was statistically significant difference (P=0.002).

Conclusion 

TENS is effective for labor pain relief, but with greater satisfaction reported by women and no side effects.

Introduction

Labor is a very painful physiological process. Labor pain relief remains of interest to both obstetricians and anesthesiologists. The perception of pain is a subjective issue that depends on many different psychological factors including previous experience, present expectation, stress, cultural factors, and in addition, the intensity, frequency of uterine contractions, and speed of cervical dilatation.

Pain in the first stage of labor originates from uterine contractions and cervical dilatation, which is a visceral pain carried through Aδ and C fibers to end in T10–L1. During the late first stage and second stage, pain is of the somatic type because of stretching of the lower genital tract, pelvic floor, and perineum, which are carried through the pudendal nerve (S2–S4) by Aδ fibers ¹.

Unrelieved maternal pain leads to many maternal and fetal adverse effects including increased circulating catecholamines, which cause tachycardia and hypertension, and increased oxygen demands, which have a negative effect on oxygenation of the placenta, fetus, and on the progress of labor; pain also delays the time of gastric emptying, increasing the risk of inhalation in case of emergency anesthesia, and is also assumed to precipitate postpartum depression ².

Many modalities are used to alleviate labor pains, including pharmacological and nonpharmacological methods. Pharmacological methods include inhalational agents, parenteral opiods, and epidural analgesia. The latter is considered the gold standard for pain relief; parenteral opiods carry the risk of neonatal respiratory depression. Pharmacological methods include hypnosis, psychoanalgesia, biofeedback, acupuncture, aromatherapy, water birthing, and transcutaneous electric nerve stimulation (TENS); these are easy to use, with minimal side effects ³.

TENS is a noninvasive method for pain relief that was used a very long time ago, and has been used in the management of labor pain since 1970. Its exact mechanism of action is not known; many theories had been proposed, the first of which is the gate control theory. TENS stimulates Aβ fibers (large diameter, low threshold mechanoreceptive) that inhibit the transmission of signals from nociceptive small-diameter high threshold fibers (Aδ and C fibers) to reach higher centers in the brain through presynaptic and postsynaptic inhibition at the dorsal horn of the spinal cord ⁴.

Although the use of TENS in control of labor pains is still a topic of debate, it is used in the UK in 16% of low-risk primiparas and between 15 and 25% of all births ⁵. In Egypt, there is no previous experience with the use of TENS in teaching or public hospital obstetric units.

Many types of TENS machines are available in the market: conventional TENS, acupuncture-like TENS, and intense TENS. Conventional TENS produces waves with low intensity and high frequency that activate large diameter Aβ fibers without activating Aδ and C fibers (pain related), causing segmental analgesia with rapid onset and offset. Acupuncture-like TENS, so called because it causes extrasegmental analgesia in the same manner as acupuncture, induces activation of G1 efferent fibers, causing muscle contractions resulting in activation of afferent fibers that cause extrasegmental analgesia and at the same time activate Aβ fibers, causing segmental analgesia with delayed onset and offset.

Intense TENS causes activation of Aδ afferent fibers by high-frequency, high-amplitude waves that induce blockade of nociceptive afferent activity with segmental and extrasegmental analgesia with rapid onset and delayed offset ^6,7.

Patient and methods

Our study was carried out in the Obstetric Department, Cairo University Teaching Hospital, Egypt, from January 2011 to January 2012 (1 year duration) on 100 parturient women who were in active labor (cervix dilated≥4 cm), fulfilled the inclusion criteria, and were seeking labor analgesia.

Inclusion criteria were as follows: term pregnancy, singleton, vertex presentation, planned vaginal delivery, active labor, maternal age from 20 to 40 years, and noncomplicated pregnancy.

Exclusion criteria were as follows: cephalopelvic disproportion, multiple gestations, presence of a cardiac pace maker, known congenital anomalies, complicated pregnancy such as preeclampsia, antepartum hemorrhage, and fetal asphyxia.

A total of 100 parturients were recruited and were subjected to a systematic random sampling technique. Group A (TENS group) included 50 parturients and group B (control group) included 50 parturients.

All patients were subjected to full assessment of history, general examination, and local examination (cervical dilatation, effacements, station, position, and state of membrane); informed consent to participate in our study was obtained.

In group A, labor analgesia was induced by TENS plus dual channel TENS (AMG Medical Inc., Montreal, Quebec, Canada), which can be used in a conventional, modulation, or burst mode by simply adjusting the selector button. It operates on a 9-V rechargeable battery and weighs 130 gm (including the battery).

Pulse amplitude ranged from 0 to 80 mA, each channel, and was adjustable; pulse frequency ranged from 2 to 150 Hz and was adjustable. Pulse width ranged from 60 to 250 μs and was adjustable.

Two electrodes were placed in the paravertebral area: one at the level of T10–L1 and the other at the level of S2–S4 (the spinal level that receives nociceptive signals from the uterus and cervix). Parturients can control the intensity and frequency of pulses and can also shift from a pulsed to a conventional mode.

TENS was applied when the parturient experienced painful regular uterine contractions. The amplitude was increased gradually until the parturient felt the pulse as a pleasant tingling sensation. Conventional TENS was used during contractions and shift to burst in between contractions. TENS was stopped on full cervical dilatation or if the parturient was not satisfied with its use.

In the placebo group, 50–100 mg pethidine (meperidine hydrochloride) was administered as an intramuscular injection into the upper outer quadrant of the gluteal region every 4 h or more as needed.

Pain relief was assessed using the visual analogue scale (VAS), which is the most simple and reliable method of pain measurement. Briefly, it is a 10 cm horizontal line, wherein one end indicates 0, which means no pain, the other side indicates 10, which means severe pain, and in between different degrees of pain can be indicated. Pain was assessed before the use of TENS, after 30 min, and every hour until full cervical dilatation.

A 48-h postpartum questionnaire was administered to assess their satisfaction (easy adjustment, easy handling, no nausea or vomiting, no effect on maternal awareness or mobility, and willingness to use it again in subsequent deliveries).

Our primary outcome was degree of labor pain relief by TENS; secondary outcomes included duration of first stage, need for labor augmentation, mode of delivery, fetal outcome (Apgar scores at 1 and 5 min), and adverse events.

Data were coded and entered on a data sheet prepared on Excel program and then transposed to the statistical package for social sciences (SPSS, version 16; SPSS Inc., Chicago, Illinois, USA) for analysis. Data checking was carried out by simple frequencies. Quantitative data are shown as mean and SD, whereas qualitative data are shown as percentages. Comparison between the two groups was carried out using the χ²-test. (Whenever the count within the distribution was <5, a corrected P-value of significance was considered.) Comparison between the two groups was carried out using Student’s t-test for gestational age and the pain scores. All statistical tests were considered significant at a P-value less than or equal to 0.05.

Informed consent was obtained from all the parturients who agreed to participate in our study after they were clearly informed about the mechanisms of action, their use, and the advantages and disadvantages of TENS.

All parturients were free to withdraw at any time without giving any reason. Strict confidentiality was maintained throughout the process of data collection, entry, and analysis.

Our study was approved by the Ethical Committee of Obstetrics and Gynecology, Cairo University.

Results

Both groups were comparable in maternal age, gestational age, and parity, which are shown in Table 1.

Table 1: Demographic data of the transcutaneous electric nerve stimulation group and the control group

Pain relief was assessed by VAS; pain relief was indicated by a reduction in the level of pain by 4 points or more on VAS readings. The difference between both groups was not statistically significant (P=0.065), but in terms of women’s satisfaction, parturients in group A were more satisfied by TENS in pain relief (83 vs. 10% in control group) and showed their willingness to use it again in subsequent deliveries; the women in group B were not satisfied by pethidine analgesia, causing drowsiness and nausea and vomiting, as shown in Fig. 1.

Figure 1: Differences between both groups in pain during labor using visual analogue scale (VAS).

In terms of the need for labor augmentation in both groups, there was a statistical difference between both groups in the number of parturients who needed labor augmentation, which is shown in Table 2; the numbers of parturients who needed oxytocin augmentation in the TENS group were less than those in the control group.

Table 2: The need of oxytocin augmentation in both groups

There was no statistically significant difference between both groups in the mode of delivery; in the TENS group, there were 10 cesarean section and 40 vaginal deliveries. In the control group, there were 12 cesarean section and 38 vaginal deliveries, as shown in Table 3.

Table 3: Mode of delivery among both groups

The difference in the length of the first stage of labor in both groups was not statistically significant (primiparas or multiparas) in both groups (P=0.58 and 0.7, respectively) which is shown in Table 4.

Table 4: Difference in the duration of first stage of labor

The neonatal outcome was assessed using the Apgar score 1 and 5 min after delivery in both groups; there was no statistical significance in the Apgar score at 1 min (P=0.433), but there was a statistical difference between both groups in the 5 min Apgar (all neonates in the TENS group had an Apgar score above 7 at 5 min, whereas only 15 neonates of 50 in the pethidine group had an Apgar score above 7 at 5 min) (P=0.002). Clinically, all infants in both groups were healthy.

Discussion

Pain is annoying but at the same time a protective sensation; labor pain is an alert to seek help. Although perception of pain is subjective, it is aggravated by anxiety, stress, expectations, and previous experience.

Unrelieved labor pain leads to major metabolic changes that may adversely affect the fetus and progress of labor. Many methods are used for labor pain management, including pharmacological and nonpharmacological; however, there is no single method that meets all needs of women and is suitable under all circumstances ³.

Nonpharmacological methods are noninvasive, easy to use, and lead to no maternal or fetal side effects. TENS is one of the nonpharmacological methods based on the gate control theory and was used in the UK several years ago ⁴.

Many types of TENS are available in the market; in our study, we used TENS plus dual channel TENS, in which we can shift from a conventional to a burst mode simply by switching the selector button. Our experience with the use of labor TENS is very limited in Egypt; thus, in this study, we attempted to assess the effectiveness of TENS in control of labor pain among our population.

Our study was carried out in the Obstetric Department, Cairo University Teaching Hospital, on 100 parturients who were in active labor and were seeking labor analgesia. Parturients were assigned randomly to two groups: group A used the TENS machine (study group) and group B used pethidine (control group). Both groups were comparable in maternal age, gestational age at the time of delivery, and parity.

The primary outcome (pain relief) was assessed by VAS readings; both groups showed no statistically significant difference (P=0.065), but clinically, the TENS group was more satisfied and willing to use it again in subsequent deliveries, which is in agreement with Bundsen et al.⁸, Harrison et al.⁹, Hughes et al.¹⁰, Thomas et al.¹¹, Labrecque et al.¹², Neumark et al.¹³, and Nesheim et al.¹⁴, who compared TENS (to the back) versus placebo or routine care; the difference did not reach statistical significance, but the TENS group was less likely to report severe pain.

Van der Spank et al. ¹⁵ reported that pain scores in the TENS group were lower than those of the control group but did not reach significant difference (P=0.06).

Peng et al.¹⁶ and Chao et al.¹⁷ investigated the use of TENS at the acupuncture site for relief of labor pain and reported a statistically significant reduction in VAS scores; in addition, TENS was an effective, safe, and noninvasive method for labor pain analgesia.

Thakur et al.¹⁸ compared TENS versus tramadol hydrochloride in control of labor pain and showed a highly significant difference in the onset and duration of analgesia.

Carroll et al.¹⁹ reviewed the effectiveness of TENS for labor pain relief in a systematic review and reported that the evidence for reduced labor pain with the use of TENS was weak.

There was statistically significant difference between both groups in the need for labor augmentation (P=0.046); fewer number of parturients in the TENS group needed oxytocin augmentation, which was in not in agreement with Van der Ploeg et al.²⁰ and Chao et al.¹⁷.

In terms of the length of the first stage, there was no statistical difference between both groups among primiparas and multiparas (P=0.58 and 0.7, respectively), which is similar to the results of Thomas et al.¹¹, Van der Spank et al.¹⁵, Peng et al.¹⁶, Thaur and Patidar ¹⁸, Steptoe and Bo ²¹, Lee et al.²², and Miller Jones ²³. However, Kaplan et al.²⁴ showed that the use of TENS significantly reduced the duration of the first stage of labor.

There was no statistically significant difference between both groups in the mode of delivery (P=0.7), which was in agreement with many previous studies ^{8,9,11,12,14,18,20,25}.

Fetal outcome was assessed by the Apgar score at 1 and 5 min after delivery; our study found no statistical difference between both groups in the Apgar score at 1 min (P=0.4). However, there was a statistically significant difference in the Apgar score at 5 min (P=0.002), which was not in agreement with Harrison et al.⁹, Thomas et al.¹¹, Peng et al.¹⁶, Chao et al.¹⁷, Thaur and Patidar ¹⁸, Steptoe and Bo ²¹, Miller Jones ²³, and Erkkola et al.²⁶, who found no difference.

No adverse effects were encountered in the TENS group, whereas the control group (using pethidine) experienced nausea, vomiting, and drowsiness; on administration of the 48-h questionnaire, TENS groups indicated their willingness to use it again in subsequent deliveries.

Conclusion

TENS is as effective as conventional methods for labor pain relief, but with greater satisfaction reported by women and no side effects.

Limitation of the study

Our study was carried out at the Cairo University Teaching Hospital, which is a tertiary referral center receiving patients from areas of low educational and socioeconomic levels; in addition, not all of them had received antenatal care follow-up in our hospital. Thus, we encountered difficulty in describing our machine to the women, which is reflected in our sample size.

Acknowledgements

The author thanks all parturients who agreed to participate in our study, the medical staff at the Obstetrics and Gynecology Department, Cairo University Teaching Hospital for their help and cooperation.

Conflicts of interest

There are no conflicts of interest.