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Cryotherapy for reducing the pain of sterile water injections: A three-arm multicentre randomised controlled trial
Nigel Lee1, Emma Ballard2, Lauren Kearney3
1Level 3 Chamberlain Building, School of Nursing Midwifery and Social Work, University of Queensland, 4072, St Lucia, Queensland, Australia.
Background:
Sterile water injections have been shown to be safe and efficacious in the management of childbirth pain, particularly labour back pain. The only commonly experienced side effect of the technique is the significant injection pain. Cryotherapy, in the form of vapocoolant sprays or cold packs has been shown in previous studies to reduce injection pain generally. However, it is not known if cryotherapy would mitigate the pain of sterile water injections.
Objective:
To assess the efficacy of vapocoolant spray or chemical cold pack in reducing sterile water injection pain for labour back pain.
Design:
Three-arm multicentre open label superiority randomised controlled trial.
Setting:
Three maternity hospitals in Brisbane, Australia.
Methods:
Consenting participants were allocated 1:1:1 using an independently produced randomisation schedule to either the application of a vapocoolant spray, chemical cold pack or standard care (no cryotherapy). The primary outcome was the difference between groups in self-reported visual analogue pain scale at time of injection. Secondary outcomes included skin temperature at the time of injection and visual analogue pain scores for back pain up to 120 min following injection.
Results:
Between February 2024 and June 2025 a total of 133 women randomised to either vapocoolant spray (n = 45), chemical cold pack (n = 45) or control group (n = 44). Consent forms were not completed for four participants, and four withdrew. There was no difference in visual analogue pain scores at injection between groups (control: mean 84.73 mm (SD 22.75); vapocoolant: mean 81.23 mm (SD = 24.94); chemical ice pack: mean 86.89 mm (SD = 18.21)) (p = 0.51). Skin temperature in both the vapocoolant (median 29.05 IQR 25.9, 31.8) and chemical cold pack (median 27.23, IQR 23.8, 30.5) was lower than the control group (median 32.75, IQR 31.8, 34.2) (p = <0.001). All three arms showed lower post injection pain scores across all time points.
Conclusion:
Neither the application of a vapocoolant spray or chemical cold pack prior to sterile water injections resulted in a statistically significant reduction in associated pain. The use of cryotherapy to the mitigate pain of sterile water injections cannot be recommended.
Trial Registration:
The trial is registered at the Australian and New Zealand Clinical Trials Registry (Trial ID: ACTRN12623000585628). Registration date: 29/05/2023. First recruitment 21st February 2024.
