Four-site distal paravertebral blocks improve physiologic indicators of analgesia in the immediate postoperative period as opposed to a three-site distal paravertebral block

Objective: To determine differences in surgical and post-operative analgesia between 3-site distal paravertebral (DPV) blocks and modified 4-site DPV blocks. Animals: 12 healthy dairy or dairy cross steers. Methods: Steers were randomized into one of two treatments, 3-site DPV (3DPV) or 4-site DPV (4DPV). 2 mg/kg of 2% lidocaine was administered at each site, lumbar vertebrae 1, 2, and 4 in 3DPV (6mg/kg), and at lumbar vertebrae 3 for 4DPV (8mg/kg). Heart and respiratory rates, temperature, reaction scores, and surgical condition scores were collected. Post-operative pain scores and physiologic data were collected for 24 hours following surgery. An ordinal logistic mixed effects model was used to compare surgical conditions, reaction scores, and pain scores. A linear mixed effects model was used for normally distributed data. Results: The success rate of 3DPV blockade was 5/6 (83%) and 4DPV 6/6 (100%). Only 11 steers were included in the data analysis due to the failed block. The 4DPV group had lower respiratory rates following the return to stall (32 breaths per minute +/- 3 vs. 44 +/- 4, p<0.019). Additionally, the 4DPV group had significantly lower heart rates immediately following the return to the stall (62 beats per minute +/- 8 vs. 88 +/- 9, p<0.036). No differences in pain scores or intraoperative conditions were identified. Conclusions: Adding an injection site at L3 in a DPV reduced post-operative HR and RR in steers following laparotomy. Clinical Relevance: Adding a fourth injection site at L3 decreases physiologic indicators of postoperative discomfort.