Effect of angle of needle advancement during intermittent ultrasound-guided thoracic paravertebral block

During ultrasound scanning for intermittent ultrasound guided paravertebral block, delta angle refers to the change in needle angle that is predicted to be necessary to advance the needle off the transverse process and into the paravertebral space.

• If the delta angle is set too small (orange dashed line), the needle will hit the same TP or the rib below it.
• If the delta angle is set too large, the needle will hit the TP or rib caudad to TPVS.
• A delta angle anywhere between the orange and yellow dashed lines may be adequate.