Fifty-eight patients with lumbar spinal fusion surgery were randomized to receive either ultrasound-guided erector spinae plane block (ESPB; n=29) or freehand ESPB (n=29). The primary outcome of interest was the total amount of morphine consumed during the first 24 hours following surgery. Secondary outcomes included numerical rating scale (NRS) pain scores at various time points within the first 24 hours and the amount of fentanyl used during surgery. Outcomes were assessed at 2, 6, 12, and 24 hours postoperatively. Overall, the results revealed that the ultrasound-guided ESPB group had significantly lower total morphine consumption and longer first analgesic demand times compared to the freehand ESPB group. These findings suggest that ultrasound-guided ESPB is more effective in managing postoperative pain and reducing opioid use in lumbar spinal fusion surgeries.