Efficacy and safety of PCA-assisted continuous paravertebral block in subacute herpes zoster-associated pain: study protocol for a randomized, controlled, double-blind superiority trial.

Background: Pain management for herpes zoster-associated pain (ZAP) is essential to improve patients' daily lives and potentially intervene in the chronicity. Long-lasting, repetitive painful stimuli might lead to central sensitization and neuropathic pain generation. The subacute phase is the main period for ZAP patients to seek medical attention, and it is also a critical treatment time window for the transformation of ZAP to chronic pathological changes. Although there is still a lack of rigorous considerable sample evidence, the pain degree of ZAP and the incidence of postherpetic neuralgia (PHN) may decrease accordingly with increasing adequate analgesia. Compared to repeated paravertebral nerve block (PVB), patient-controlled analgesia (PCA)-assisted continuous PVB provides more prolonged and comprehensive pain relief according to patient needs. Given this, we intend to test the hypothesis that PCA-assisted continuous PVB delivers a safe and better analgesic effect and reduces PHN incidence in subacute ZAP patients.

Methods: A total of 82 eligible subacute herpes zoster (SHZ) patients will be recruited and randomly assigned to the PCA-assisted continuous PVB group (Group PCA) and the repeated PVB group (Group rPVB) at a 1:1 ratio. All enrolled patients will undergo thoracic paravertebral space (TPVS) catheterization and receive similar doses of medication for 7 days. The main intervention factor lies in the different drug administration manners. PCA-assisted continuous PVB treatment will be achieved by pumping, while repeated PVB treatment will be conducted by injecting other therapeutic solutions. The participants and investigators will be both blinded to group allocation. The primary outcome is the VAS scores 1 month after treatment. The secondary outcomes include the incidence of PHN and the adverse events during treatment and follow-up.

Discussion: The results from this study will provide clinical evidence on the efficacy and safety of PCA-assisted continuous PVB for subacute ZAP patients.

Trial registration: Chinese Clinical Trial Registry ChiCTR2300068158. Registered on 9 February 2023.