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Keywords:

  • Labour pain;
  • low back pain;
  • sterile water injection;
  • systematic review

Abstract

  1. Top of page
  2. Abstract
  3. Introduction
  4. Methods
  5. Results
  6. Discussion
  7. Conflicts of interest
  8. Contribution to authorship
  9. Details of ethics approval
  10. Funding
  11. Acknowledgements
  12. References

Background  Up to one-third of labouring women will experience painful ‘back labour’. Sterile water injected lateral to the lumbosacral spine is a simple and well-researched approach to this pain.

Objective  To determine if sterile water injection for low back pain compared to placebo or alternative therapy increased or decreased the rate of Caesarean section.

Search strategy  We performed a literature search with no language restriction in four databases: the Cochrane library, EMBASE (1980–2009), Ovid Medline (1950–2009) and CINAHL (1982–2009).

Selection criteria  We included all randomised controlled trials (RCTs) of sterile water injection for labour pain that included outcomes of interest and original data.

Data collection and analysis  We compared Caesarean section rates among women who received sterile water injection in labour with those who received either placebo treatment or another non-pharmacological treatment modality. Other outcomes included pain scores, use of regional analgesia and women’s assessment of treatment. We used Revman 5 for the meta-analysis. Data were entered by one reviewer and independently cross-checked. Pooled outcomes were reported as Relative Risk (RR) or Weighted Mean Difference using Mantel–Haenszel fixed-effects model except when the I2 value >50% indicated significant heterogeneity in which case random-effects model was used.

Main results  We included eight RCTs. The Caesarean section rate was 4.6% in the sterile water injection group and 9.9% in the comparison group (= 828) (RR 0.51, 95% CI: 0.30, 0.87).

Conclusion  We believe that a large RCT should be mounted to validate our findings regarding the impact of sterile water injections on mode of delivery.


Introduction

  1. Top of page
  2. Abstract
  3. Introduction
  4. Methods
  5. Results
  6. Discussion
  7. Conflicts of interest
  8. Contribution to authorship
  9. Details of ethics approval
  10. Funding
  11. Acknowledgements
  12. References

The most significant pain likely to be experienced by women is that associated with childbirth. Uterine muscle hypoxia, lactic acidosis, distension of the lower uterine segment, stretching of ligaments and pressure on the bony pelvis may all contribute to the pain experienced in the first stage of labour.1 This pain arises as a result of stimulation of the C afferent nerves originating from the uterine corpus and cervix. These fibres terminate in the dorsal horns of the spinal segments T10 to L1 and cause visceral pain, which is often referred to the lower back.2 Up to one-third of women will also experience ‘back labour’, which is thought to arise specifically from pressure of the fetal occipital bone against the maternal spine and pelvis when the fetus is in the suboptimal, occipital posterior position.1 Back labour poses a specific challenge to women and care providers because of the extreme discomfort it adds to the labour and because the associated pain is often reported to be constant, even between contractions.

Epidural anaesthesia/analgesia has become the most common and effective intervention used to help women cope with labour pain. In Canada, epidural anaesthesia/analgesia was used in 46% of all vaginal deliveries in 2002.3 In the Province of Ontario in 2006, 59% of women giving birth used an ‘epidural’ during childbirth; the percentage was highest in Level 3 hospitals (78%) reflecting accessibility to anaesthetic services.4 The use of regional anaesthesia in labour, typically epidural, spinal or spinal–epidural combination is not without consequence and is associated with increased frequency of instrumental delivery (forceps or vacuum)5 and some degree of motor weakness in the parturient. Supplementation of local anaesthetics with opiates lessens motor blockade, but may be associated with opiate side effects, such as nausea, pruritus, urinary retention and respiratory depression.6,7 The most frequent complications of epidural block in obstetrics include dural puncture, vascular placement, hypotension and insufficient block.8 For these reasons among others, some women prefer to avoid the use of regional anaesthesia. For other women who desire regional anaesthesia, this approach may not be available because of the nature of anaesthetic service availability in some hospitals including restricted access to any service, or time constraints on the specialists who are available.

Sterile water injected lateral to the lumbosacral spine is a simple and well-researched approach to ameliorating the visceral pain of labour including that of back labour. This intervention was first used to alleviate pain associated with kidney stones,9 and was introduced to obstetrics in the 1970s.10 The approach is easy to administer, inexpensive, has minor side-effects and can be administered without specialist care. The procedure involves injecting small amounts of sterile water either subcutaneously or, more typically, intracutaneously at four points lateral to the lumbar spine. The injections are associated with acute somatic pain that lasts for 30 seconds, but as the pain of the injections subsides, so does the visceral referred pain of the low back. The effect begins quickly and has been shown to be effective for 2 to 3 hours;11,12 long after the acute pain of the injection has subsided. Physiologically the hypotonic, sterile water does not act as a local anaesthetic and does not directly inhibit the visceral pain fibres; in fact, sterile water will cause the firing of C fibres as well as A-delta fibres normally associated with somatic pain. The leading hypothesis explaining the efficacy of sterile water is that the firing of A-delta fibres overwhelms the visceral pain input from C fibres such that the visceral pain is not noticeable. This hypothesis relies somewhat on gate control theory of pain13 although it may also be that intracutaneous sterile water leads to endorphin release similar to that found in acupuncture.

Sterile water for pain management is most often administered using four intracutaneous injections: two sites lateral to the lumbosacral spine and two sites 2–3 cm below and 1–2 cm medial to the original two injection sites. 0.1 ml of sterile water is injected between the dermal layers to raise a small bleb on the skin surface at each of the four sites. In labour, the injections are administered sequentially during a uterine contraction, with the series of four injections being completed within 20–30 seconds.

Sterile water injections are associated with significant reduction in pain when compared to placebo or a variety of controls,11,12 and maternal relaxation is enhanced following sterile water injection compared to acupuncture.14 We wondered if sterile water injection may have a therapeutic effect that goes beyond pain relief in labour, and undertook this systematic review and meta-analysis to determine if sterile water injection for low back pain compared to alternative therapy or to placebo increased or decreased the rate of Caesarean section.

Methods

  1. Top of page
  2. Abstract
  3. Introduction
  4. Methods
  5. Results
  6. Discussion
  7. Conflicts of interest
  8. Contribution to authorship
  9. Details of ethics approval
  10. Funding
  11. Acknowledgements
  12. References

We compared the outcomes in groups of women who received sterile water by injection for low back pain in labour with groups of women who received either placebo treatment (injection of isotonic saline solution) or another treatment modality, such as acupuncture or transcutaneous electric nerve stimulation (TENS). The primary outcome, decided a priori, was Caesarean section; other outcomes included ratings of pain scores at 10–30 minutes, 45–60 minutes and 90–120 minutes following the intervention; subsequent use of regional analgesia/anaesthesia for labour pain; and women’s assessment of the intervention.

Inclusion and exclusion criteria

The review included randomised controlled trials that compared intracutaneous or subcutaneous injections of sterile water with a placebo, or with other non-pharmacological methods of pain relief such as TENS, or acupuncture in a population of pregnant women who had lower back pain during the active stage of labour and requested pain medication. We included all studies that were randomised and that included original data on at least one of our outcomes of interest.

Search strategy

To identify all relevant studies, we performed a literature search with no language restriction in four databases: the Cochrane library, EMBASE (1980–2009), Ovid Medline (1950–2009), CINAHL (1982–2009). We searched using MESH headings and key words as follows: (analgesia, obstetric analgesia, pain, back pain, back ache, labour pain, birth or parturition) and (injections intracutaneous, injections intradermal or intradermal drug administration) and (water, sterile water or sterile water injection).

Data extraction and quality assessment

Three reviewers independently assessed the eligibility of identified studies and extracted data from included trials, using a previously prepared data extraction form. Any difference in extracted data between completed forms was resolved by re-reviewing the corresponding articles and reaching a consensus agreement. The methodological quality of each trial was also independently assessed using the modified Jadad scale.15 Trials rated 10 or more are considered high quality. A sensitivity analysis was planned comparing those studies of high quality and those of low quality together with those of high quality alone.

Analysis

We used Revman version 5 for the meta-analysis. Data were entered by one reviewer and independently cross-checked by the other two reviewers. Dichotomous outcomes were entered as rates and expressed as a relative risk (RR) of harm or untoward outcome and 95% confidence intervals (CIs). For continuous variables, we used the mean outcome and the standard deviation (SD) reported in the original trial when this was available. The pooled results for continuous variables were reported as a weighted mean difference (WMD) and 95% CI. When trials reported only the mean and range,16 the SD was estimated using a factor of 0.25 of the range. For trials that reported only the median and interquartile range (IQR),17 the median was used and the SD was estimated using a factor of 1.35 of the IQR.18 For studies that reported pain outcomes as change from baseline,19 findings were included as part of a subgroup analysis and pooled along with those studies reporting findings as final values.20 Two studies were of a three group design.17,21 For the study including two sterile water intervention groups, we included only data from the intracutaneous group.21 The study with transcutaneous electric nerve stimulation (TENS) and a usual care control group contributed only to the primary outcome.17 As Caesarean section is a discrete variable, we were able to combine the data from both the control groups. To minimise the impact of heterogeneity among trials, when the I2 value of >50% indicated significant heterogeneity, pooled outcomes were calculated by means of random-effects models. For all other analysis, the Mantel–Haenszel fixed-effects model was used.

Results

  1. Top of page
  2. Abstract
  3. Introduction
  4. Methods
  5. Results
  6. Discussion
  7. Conflicts of interest
  8. Contribution to authorship
  9. Details of ethics approval
  10. Funding
  11. Acknowledgements
  12. References

The search identified 54 possibly relevant papers. On review, 14 were clinical studies. (Figure 1) Six clinical studies were excluded; one randomised controlled trial (RCT) because the population consists of non-pregnant women only;22 two clinical trials used no randomisation;23,24 two cohort studies had no comparison group;25,26 and one appeared to report duplicate data.27 We included eight RCTs of which five used intracutaneous sterile water injections with the more common four injection method;16,17,19,21,28 two used a single subcutaneous injection,29,30 one used four subcutaneous injections.14 The control group in one paper, used acupuncture,14 in one TENS and ‘usual care’,21 and the remainder of the trials compared sterile water to isotonic saline injections. Characteristics of the studies are reported in Table 1. There was no disagreement with regard to categorisation of the studies as high or low quality and all, but one19 was classified as high, thus no sensitivity analysis was performed.

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Figure 1.  Results of literature review.

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Table 1.   Randomised controlled trials on the use of sterile water injections for labour pain
Author and countryProtocolOutcomeConclusion
ExperimentalControl
Ader et al.19  Sweden Inclusion: term pregnancy; first-stage labour; severe low back pain; no analgesics within 3 h prior to participation. Intervention: intracutaneous sterile water versus subcutaneous isotonic saline injections given as 4 injections of 0.1 ml Outcome: VAS reported as reduction in mean score from baseline Sample size: N = 45 Quality score: 8Intracutaneous sterile water (n = 24) Mean pain reduction:  10 min: 4.25  45 min: 3.6  90 min: 2.9  Caesarean section: 2/24Subcutaneous isotonic saline (n = 21)  Mean pain reduction:   10 min: 1.85   45 min: 1.5   90 min: 0.7  Caesarean section: 1/21Mean reduction in pain significantly greater for sterile water group at 10, 45, 90 min.
Bahasadri et al.29  Iran Inclusion: term pregnancy; first-stage labour; low back pain; no analgesics prior to participation. Intervention: sterile water versus isotonic saline given as a single 0.5 ml subcutaneous injection at the point of most pain Outcome: Likert type 5 point Faces Scale. Sample size: N = 100 Quality score: 12Subcutaneous sterile water (n = 50) Median pain score:  Baseline: 4  10 min: 2  45 min: 2  Caesarean section: 2/50Subcutaneous isotonic saline (n = 50) Median pain score:  Baseline: 4  10 min: 4  45 min: 4 Caesarean section: 3/50Median pain score was significantly lower in sterile water group.
Kushtagi and Bhanu30  India Inclusion: early part of active labour, low back pain; no analgesics prior to participation. Intervention: sterile water versus isotonic saline given as a single 0.5 ml subcutaneous injection at centre of Michaeli’s rhomboid. Outcome: 10 point scale reported as median at 10 and 45 min. Sample size: N = 100 Quality score: 10Subcutaneous sterile water (n = 50) Median pain score:  Baseline: 8  10 min: 5  45 min: 4  Caesarean section: 4/50Subcutaneous isotonic saline (n = 50) Median pain score:  Baseline: 8  10 min: 7  45 min: 7 Caesarean section: 6/50Median pain score was significantly lower in the sterile water group.
Labrecque et al.21  Canada Inclusion: first-stage labour, back pain, low obstetrical risk Intervention: intracutaneous sterile water given as 4 injections of 0.1 ml versus TENS versus Standard care Outcome: VAS, with pain intensity and pain unpleasantness score in mm collected at 15, 60, 90, 120 and 180 min post administration, but reported as a mean score during intervention. No baseline reported. Sample size: N = 34 Quality score: 10Intracutaneous sterile water (n = 10) Mean pain intensity score during intervention: 32 Caesarean section: 0Standard care (n = 12) Mean pain intensity score during intervention: 79 Caesarean section: 1 TENS (n = 12) Mean pain intensity score during intervention: 66 Caesarean section: 4Mean pain intensity was significantly lower in the sterile water group compared to other 2 groups. Fewer women in intracutaneous sterile watergroup would use intervention again.
Mårtensson and Wallin17  Sweden Inclusion: term pregnancy; first-stage labour; severe low back pain Intervention: intracutaneous sterile water (4 injections, 0.1 ml) versus subcutaneous injections of sterile water (4 injections 0.5 ml) versus subcutaneous injections of isotonic saline (4 injections, 0.5 ml) Outcome: VAS, with median pain score reported in cm at baseline, 10, 45 and 90 min after administration. Sample size: N = 99 Quality score: 12Intracutaneous sterile water (n = 33) Median pain score at: Baseline: 7.6 10 min: 2.3 45 min: 2.5 90 min: 6.1 Median pain score of intervention: 7.7 Caesarean section: 1/33 Subcutaneous sterile water (n = 33) Median pain score at: Baseline: 7.4 10 min: 2.3 45 min: 2.0 90 min: 4.1 Median pain score of intervention: 7.0 Caesarean section: 1/33Subcutaneous isotonic saline (n = 33) Median pain score at: Baseline: 7.4 10 min: 5.2 45 min: 6.2 90 min: 7.5 Median pain score of intervention: 2.5 Caesarean section: 1/33Median pain scores were significantly lower in the two sterile water treatment groups compared with placebo. The pain of administration of subcutaneous injections of sterile water was slightly less than intracutaneous sterile water. Subcutaneous injection of isotonic saline was the least painful
Mårtensson et al.14  Sweden Inclusion: term pregnancy; first-stage labour; require pain relief; no analgesic, sterile water, TENS within 10 h of study; no epidural, spinal, paracervical block; no augmentation Intervention: subcutaneous injections of sterile water (4–8 injections of 0.5 ml) versus acupuncture Outcome: VAS, with mean pain score reported in mm at baseline, 30, 60, 90, 120, 150 and 180 min post administration. Sample size: N = 128 Quality score: 13Subcutaneous sterile water (n = 66) Mean pain score at: Baseline: 72.9 30 min: 52.3 60 min: 53.2 90 min: 52.3 120 min: 58.8 150 min: 58.6 180 min: 62.7 Caesarean section: 4/66Acupuncture (n = 62) Mean pain score at: Baseline: 72.9 30 min: 69.7 60 min: 72.7 90 min: 73.8 120 min: 76.8 150 min: 72.0 180 min: 79.5 Caesarean section: 5/62Mean pain was significantly lower in the sterile water group at all time points following intervention.
Trolle et al.16  Denmark Inclusion: severe low back pain Intervention: intracutaneous sterile water versus intracutaneous injections of isotonic saline, 4 injections, 0.1 ml Outcome: VAS, with mean pain score in mm recorded at baseline, 60 and 120 min post administration. Sample size: N = 272 Quality score: 10Intracutaneous sterile water (n = 141) Mean pain score at:  Baseline: 83  60 min: 29.5  120 min: 53.5 Caesarean section: 6/141Intracutaneous isotonic saline (n = 131) Mean pain score at:  Baseline: 81  60 min: 76  120 min: 82 Caesarean section: 15/131Mean pain score was significantly lower at 60 and 120 min and there were fewer Caesarean section in the intracutaneous sterile water group
Wiruchpongsanon28  Thailand Inclusion: term pregnancy; first-stage labour; severe low back pain (VAS>7); no analgesics within 3 h. Intervention: intracutaneous sterile water versus intracutaneous injections of isotonic saline, 4 injections, 0.1 ml Outcome: VAS with pain score in mm recorded at baseline, 30, 60 and 120 min post administration. Sample size: N = 50 Quality score: 10Intracutaneous sterile water (n = 25) Mean pain score at:  Baseline: 86.5  30 min: 31.4  60 min: 14.9  120 min: 17.0 Caesarean section: 0/25Intracutaneous isotonic saline (n = 25) Mean pain score at:  Baseline: 89.2  30 min: 70.6  60 min: 73.2  120 min: 72.2 Caesarean section: 3/25Mean pain scores were significantly lower in the intracutaneous sterile water group at 30, 60 and 120 min

All eight included studies reported on rates of the primary outcome, Caesarean section. All studies, with the exception of two29,30 measured pain using a visual analogue scale (VAS). One study reported findings in only a summary score21 thus provided no useable pain scores. Of the remaining five studies, one reported change scores19, which provided data (presented in figures as a subgroup, for clarity) for outcomes following the intervention, but no data for the baseline pain measure. The remaining four studies14,16,17,28 are included in the baseline measure of pain prior to the intervention, as well as at various time frames for which they measured pain following the intervention.

Meta analysis outcomes

There was no difference in baseline pain levels between groups (4 studies = 516; WMD 0.77; 95% CI: −1.94, 3.47), (Figure 2), but there was significant reduction in the pain score of the sterile water group compared with the placebo or other intervention group at all time points following administration of the intervention (Figures 3–5). At 10–30 minutes, we found a WMD on VAS scores of −26.04 mm, 95% CI:−34.14, −17.94 (4 studies, = 289); at 45–60 minutes, we found a WMD on VAS scores of −36.27 mm, 95% CI: −50.80, −21.74 (5 studies, = 542); at 90–120 minutes, we found a WMD on VAS scores of −27.74 mm, 95% CI: −39.03, −16.45 (5 studies, = 488).

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Figure 2.  Meta-analysis results: baseline VAS pain scores before randomisation.

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Figure 3.  Meta-analysis results: VAS pain score at 10–30 minutes following intervention.

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Figure 4.  Meta- analysis results: VAS pain score at 45–60 minutes following intervention.

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Figure 5.  Meta-analysis results: VAS at 90–120 minutes following intervention.

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We found no differences in groups in terms of their willingness to have the intervention again with 69% in the sterile water and 56% in the comparison group indicating willingness RR 1.18 95% CI: 0.90, 1.53, (4 studies = 521). We found no difference in the use of regional analgesia or anaesthesia subsequent to the intervention RR 0.89 95% CI: 0.60, 1.32 (2 studies, = 173).

All eight studies (= 828) comparing any sterile water injection with placebo (normal saline injection) or with other non-pharmacological intervention (such as TENS, acupuncture) reported on the primary outcome. The point estimate Caesarean section rate was 4.6% in the sterile water injection group and 9.9% in the comparison group (RR 0.51, 95% CI: 0.30, 0.87) (Figure 6).

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Figure 6.  Meta-analysis results: rate of caesarean section.

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Discussion

  1. Top of page
  2. Abstract
  3. Introduction
  4. Methods
  5. Results
  6. Discussion
  7. Conflicts of interest
  8. Contribution to authorship
  9. Details of ethics approval
  10. Funding
  11. Acknowledgements
  12. References

We found a significant decrease in the rate of Caesarean section when sterile water injections were used to manage low back pain of labour compared with the use of injection of isotonic saline or an alternate therapy (acupuncture or TENS). The physiological pathway leading to this difference is unclear. It is possible that pain reduction in the active phase of labour is associated with increased parasympathetic tone, which improves labour, resulting in descent of the fetus improving the likelihood of vaginal delivery. An alternate mechanism may be that enhanced relaxation accompanying the pain relief experienced with the sterile water injection promotes rotation of the fetal occiput to a position favourable to vaginal delivery.14 It may also be that the decrease in pain experienced by the parturient decreased the urgency for a Caesarean section and allowed for a long enough time for labour to progress normally. The studies included in this meta-analysis included a variety of control groups are small and some are unblinded. We think that the finding with regard to the mode of delivery is nevertheless interesting. We believe that a large RCT should be mounted to validate our findings regarding the impact of sterile water injections on mode of delivery. Such a study would ideally be double-blinded placebo control design and report on the use of regional analgesia following the intervention, rates of caesarean section, spontaneous and assisted vaginal delivery in addition to the effectiveness of pain relief.

Contribution to authorship

  1. Top of page
  2. Abstract
  3. Introduction
  4. Methods
  5. Results
  6. Discussion
  7. Conflicts of interest
  8. Contribution to authorship
  9. Details of ethics approval
  10. Funding
  11. Acknowledgements
  12. References

Eileen Hutton conceived the systematic review and worked with Marlies Kasperink and Marinde Rutten to develop the study protocol and the data extraction sheets. These three authors undertook the systematic review and data extraction and initial data entry. Angela Reitsma reviewed the papers and developed the detailed table, as well as cross checking the data entry. Dr Wainman contributed the physiological background. All authors contributed to the discussion and to the final review of the paper.

Details of ethics approval

  1. Top of page
  2. Abstract
  3. Introduction
  4. Methods
  5. Results
  6. Discussion
  7. Conflicts of interest
  8. Contribution to authorship
  9. Details of ethics approval
  10. Funding
  11. Acknowledgements
  12. References

No ethics was required to undertake this systematic review and meta-analysis; however, all papers included in the review reported having received ethics approval.

References

  1. Top of page
  2. Abstract
  3. Introduction
  4. Methods
  5. Results
  6. Discussion
  7. Conflicts of interest
  8. Contribution to authorship
  9. Details of ethics approval
  10. Funding
  11. Acknowledgements
  12. References