Sympathetic nerve blocks for persistent pain in adults with inoperable abdominopelvic cancer.

BACKGROUND

Persistent visceral pain is an unpleasant sensation coming from one or more organs within the body. Visceral pain is a common symptom in those with advanced cancer. Interventional procedures, such as neurolytic sympathetic nerve blocks, have been suggested as additional treatments that may play a part in optimising pain management for individuals with this condition.

OBJECTIVES

To evaluate the benefits and harms of neurolytic sympathetic nerve blocks for persistent visceral pain in adults with inoperable abdominopelvic cancer compared to standard care or placebo and comparing single blocks to combination blocks.

SEARCH METHODS

We searched the following databases without language restrictions on 19 October 2022 and ran a top-up search on 31 October 2023: CENTRAL; MEDLINE via Ovid; Embase via Ovid; LILACS. We searched trial registers without language restrictions on 2 November 2022: ClinicalTrials.gov; WHO International Clinical Trials Registry Platform (ICTRP). We searched grey literature, checked reference lists of reviews and retrieved articles for additional studies, and performed citation searches on key articles. We also contacted experts in the field for unpublished and ongoing trials. Our trial protocol was preregistered in the Cochrane Database of Systematic Reviews on 21 October 2022.

SELECTION CRITERIA

We searched for randomised controlled trials (RCTs) comparing any sympathetic nerve block targeting sites commonly used to treat abdominal pelvic pain from inoperable malignancies in adults to standard care or placebo.

DATA COLLECTION AND ANALYSIS

We independently selected trials based on predefined inclusion criteria, resolving any differences via adjudication with a third review author. We used a random-effects model as some heterogeneity was expected between the studies due to differences in the interventions being assessed and malignancy types included in the study population. We chose three primary outcomes and four secondary outcomes of interest. We sought consumer input to refine our review outcomes and assessed extracted data using Cochrane's risk of bias 2 tool (RoB 2). We assessed the certainty of evidence using the GRADE system.

MAIN RESULTS

We included 17 studies with 1025 participants in this review. Fifteen studies with a total of 951 participants contributed to the quantitative analysis. Single block versus standard care Primary outcomes No included studies reported our primary outcome, 'Proportion of participants reporting no worse than mild pain after treatment at 14 days'. The evidence is very uncertain about the effect of sympathetic nerve blocks on reducing pain to no worse than mild pain at 14 days when compared to standard care due to insufficient data (very low-certainty evidence). Sympathetic nerve blocks may provide small to 'little to no' improvement in quality of life (QOL) scores at 14 days after treatment when compared to standard care, but the evidence is very uncertain (standardised mean difference (SMD) -0.73, 95% confidence interval (CI) -1.70 to 0.25; I² = 87%; 4 studies, 150 participants; very low-certainty evidence). The evidence is very uncertain about the risk of serious adverse events as defined in our review as only one study contributed data to this outcome. Sympathetic nerve blocks may have an 'increased risk' to 'no additional risk' of harm compared with standard care (very low-certainty evidence). Secondary outcomes Sympathetic nerve blocks showed a small to 'little to no' effect on participant-reported pain scores at 14 days using a 0 to 10 visual analogue scale (VAS) for pain compared with standard care, but the evidence is very uncertain (mean difference (MD) -0.44, 95% CI -0.98 to 0.11; I² = 56%; 5 studies, 214 participants; very low-certainty evidence). There may be a 'moderate to large' to 'little to no' reduction in daily consumption of opioids postprocedure at 14 days with sympathetic nerve blocks compared with standard care, but the evidence is very uncertain (change in daily consumption of opioids at 14 days as oral milligrams morphine equivalent (MME): MD -41.63 mg, 95% CI -78.54 mg to -4.72 mg; I² = 90%; 4 studies, 130 participants; very low-certainty evidence). The evidence is very uncertain about the effect of sympathetic nerve blocks on participant satisfaction with procedure at 0 to 7 days and time to need for retreatment or treatment effect failure (or both) due to insufficient data. Combination block versus single block Primary outcomes There is no evidence about the effect of combination sympathetic nerve blocks compared with single sympathetic nerve blocks on the proportion of participants reporting no worse than mild pain after treatment at 14 days because no studies reported this outcome. There may be a small to 'little to no' effect on QOL score at 14 days after treatment, but the evidence is very uncertain (very low-certainty evidence). The evidence is very uncertain about the risk of serious adverse events with combination sympathetic nerve blocks compared with single sympathetic nerve blocks due to limited reporting in the included studies (very low-certainty evidence). Secondary outcomes The evidence is very uncertain about the effect of combination sympathetic nerve blocks compared with single sympathetic nerve blocks on participant-reported pain score and change in daily consumption of opioids postprocedure, at 14 days. There may be a small to 'little to no' effect, but the evidence is very uncertain (very low-certainty evidence). There is no evidence about the effect on participant satisfaction with procedure at 0 to 7 days and time to need for retreatment or treatment effect failure (or both) due to these outcomes not being measured by the studies. Risk of bias The risk of bias was predominately high for most outcomes in most studies due to significant concerns regarding adequate blinding. Very few studies were deemed as low risk across all domains for any outcome.

AUTHORS' CONCLUSIONS: There is limited evidence to support or refute the use of sympathetic nerve blocks for persistent abdominopelvic pain due to inoperable malignancy. We are very uncertain about the effect of combination sympathetic nerve blocks compared with single sympathetic nerve blocks. The certainty of the evidence is very low and these findings should be interpreted with caution.