Adequate pain control following thoracic surgery is important to enhance post-operative recovery. Paravertebral catheters have been reported to have a variety of clinical applications, including the blunting of surgical pain, lessening the need for opioids, and improvement in post-operative ventilation. The spread of local anesthesia to multiple paravertebral spaces is needed to establish an effective block. We have determined that the spread of contrast dye by a catheter in the thoracic paravertebral space is greater in a programmed intermittent bolus than in a continuous basal infusion.