Preoperative Computed Tomography Volumetry of the Thoracic Paravertebral Space and Analgesic Outcomes After Thoracic Paravertebral Block: A Retrospective Cohort Study

Background and Objectives: Whether anatomical variation in the thoracic paravertebral space influences analgesia after thoracic paravertebral block (TPVB) is unknown. We examined the association between CT-measured paravertebral space volume and analgesic outcomes. Materials and Methods: In this retrospective cohort, 134 adults undergoing video-assisted thoracoscopic surgery (VATS) or thoracotomy received unilateral T5 TPVB with 20 mL bupivacaine 0.25%. T3–T7 volumes were segmented on CT by two blinded radiologists. The primary outcome was cumulative 24 h intravenous PCA morphine consumption; an exploratory analysis included total 24 h opioid consumption in morphine equivalents. Spearman correlation and multivariable regression were used. Results: Median ipsilateral T5 volume was 1.34 (1.09–1.69) cm3 and 24 h morphine consumption was 15.5 (8–30) mg. T5 volume was not correlated with morphine consumption (ρ = −0.03, 95% CI −0.20 to 0.14; p = 0.695), total opioid consumption (ρ = −0.04; p = 0.618), or NRS scores, and did not discriminate rescue analgesia. Volume increased with age; the sex difference observed in univariable analysis did not persist after adjustment. Conclusions: CT-measured paravertebral space volume was not associated with analgesic outcomes after 20 mL TPVB. These exploratory findings do not exclude an effect of compartment size under other block conditions.