Comparison of a single vs. a four intradermal sterile water injection for relief of lower back pain for women in labour: A randomised controlled trial

Abstract

Objective

sterile water injections are a simple, safe, effective, non-pharmacological technique for relieving back pain in labour, however the number of injections required to achieve optimal analgesia is unknown. The objective of this trial was to evaluate the degree and duration of analgesia provided by a single injection of sterile water, compared to four injections.

Design

randomised controlled non-inferiority trial.

Participants and setting

three hundred and five women in labour at term, requesting analgesia for back pain were recruited from two metropolitan hospitals in Brisbane, Australia.

Intervention

participants were randomly assigned to receive either one (n=147) or four (n=158) sterile water injections.

Outcome measures

difference in self-reported pain measured using a visual analogue scale (VAS) between baseline and 30 mins post-intervention. The clinically acceptable margin of difference was defined as ≤1 cm on the VAS between the single injection compared to four injection technique. Secondary outcomes include VAS score on injection and 10, 60, 90 and 120 mins post-intervention, analgesia use, mode of birth and maternal satisfaction.

Findings

the mean difference in the pre and post (30 mins) injection scores between two groups was −1.48 cm (95% CI −2.10, −0.86) in favour of the FI technique, however the injection pain associated with the FI was significantly greater than that of the SI technique (p<0.001). There were no significant differences between the two groups in terms of other analgesic use, mode of birth or maternal satisfaction.

Conclusion

the four injection technique was associated with increased level of analgesia at 30 mins post-intervention compared to the single injection, but also a greater degree of injection pain.

Introduction

Almost one in three women in labour suffer from severe lower back pain (Melzack and Schaffeberg, 1987, Tzeng and Su, 2008). Clinicians often associate back pain with varying degrees of fetal malposition, particularly an occipito-posterior (OP) position (Simkin, 2010), as this is thought to cause pressure on pain-sensitive structures within the pelvis. Back pain in labour may also be referred pain (Ader et al., 1991). Characteristically, the pain persists throughout the normally painless resting intervals between contractions (Tzeng and Su, 2008). It may be associated with greater use of pharmacological analgesia, including epidural anaesthesia (Hutton et al., 2009) which is associated with a cascade of interventions and iatrogenic sequelae such as increased augmentation of labour, instrumental birth and urinary retention (Lieberman and O'Donoghue, 2002, Weiniger, 2006). Sterile water injections (SWI) administered into the lower back have been demonstrated to provide a suitable analgesic alternative with none of the aforementioned negative outcomes, hence their suitability for women wishing to avoid regional anaesthesia, or in localities where this service is not available (Hutton et al., 2009). The procedure is inexpensive, low technology, safe, and suitable for most maternity care settings (Hutton et al., 2009). The injection of sterile water causes somatic and mechanical irritation resulting in a brief (15–30 s), but significant, stinging sensation. Pain relief follows almost immediately and may last for up to 2 hrs; the procedure can be repeated a number of times (Martensson and Wallin, 2008). The physiology of the effect is thought to be related to the stimulation of ascending (gate control theory) (Melzack and Wall, 1965) and descending (diffuse noxious inhibitory controls; DNIC) (Le Bars et al., 1979) pain modulation systems. The most frequently used SWI technique consists of four intradermal injections into the skin surrounding the Michaelis rhomboid over the sacral area (Reynolds, 2000). Two clinicians, working in tandem, administer the injections concurrently.

All the blinded RCTs that have previously compared the four injection (FI) technique using sterile water against normal saline placebo controls demonstrated a statistically significant reduction in pain in favour of SWI (Ader and Hansson, 1990, Trolle and Moller, 1991, Martensson and Wallin, 1999, Wiruchpongsanon, 2006, Saxena and Nischal, 2009). However Derry et al. (2012) highlighted the need for SWI trials to report findings in a clinically relevant format. The intensity of the injection pain associated with the FI technique, may impact on the acceptability of the procedure to women (Fogarty, 2008, Martensson and Wallin, 2008). Hypothesising that one injection would result in less pain, two studies tested a single injection (SI) technique compared to a placebo and also reported a significant reduction in pain (Bahasadri and Ahmadi-Abhari, 2006, Kushtagi and Bhanu, 2009). Prior to our study no SI trial had been designed to compare the analgesic outcomes with the FI technique and hence it was not known if the two techniques provided similar levels of analgesia (Fogarty, 2008, Martensson and Wallin, 2008). The aim of this study was therefore to compare a single intradermal SWI with the four injection technique in both the degree and duration of analgesic effect. The results have significant implications for midwifery practice, and for women seeking alternatives to pharmacological interventions for the relief of back pain in labour.