Correlation Between Temperature Rise After Sympathetic Block and Pain Relief in Patients with Complex Regional Pain Syndrome.

Objective: Determine the correlation between post-sympathetic block temperature change and immediate- and intermediate-term pain relief.

Design: Retrospective analysis.

Setting: Academic setting.

Subjects: Seventy-nine patients with complex regional pain syndrome who underwent sympathetic block.

Methods: Pre- and post-block temperatures in the affected extremity and pain scores immediately (based on 6-hour pain diary) after the block and at the intermediate-term 4- to 8-week follow-up were recorded. Post-block pain reductions of 30-49% and ≥50% were designated as partially sympathetically maintained pain and sympathetically maintained pain, respectively. A decrease in pain score ≥2 points lasting ≥4 weeks was considered a positive intermediate-term outcome for sympathetic block.

Results: A weak correlation was found between immediate-term pain relief and the extent of temperature rise for the cohort (R = 0.192, P = 0.043). Greater immediate-term pain reduction was reported among patients who experienced a temperature increase ≥7.5°C (mean 4.1; 95% confidence interval [CI]: 3.33 to 4.76) than among those who experienced a temperature increase <2°C (2.3; 95% CI: 1.36 to 3.31) or ≥2°C to <7.5°C (2.9; 95% CI: 1.8 to 3.9; P = 0.036). The correlations between temperature increase and intermediate-term pain score reduction at 4-8 weeks (R = 0.052, P = 0.329) and between immediate- and intermediate-term pain relief (R = 0.139, P = 0.119) were not statistically significant.

Conclusions: A weak correlation was found for those who experienced greater temperature increases after the block to also experience greater immediate pain relief. Higher temperature increase cutoffs than are typically used might be necessary to determine whether a patient with complex regional pain syndrome has sympathetically maintained pain.