Inclusion Criteria:  undergoing unilateral percutaneous nephrolithotomy analgesic plan includes a single-injection erector spinae plane block age 18 years or older  Exclusion Criteria:  morbid obesity as defined by a body mass index > 40 (BMI=weight in kg / [height in meters]2) renal insufficiency (abnormal preoperative creatinine or estimated glomerular filtration rate) chronic opioid use (daily use within the 2 weeks prior to surgery and duration of use > 4 weeks) history of opioid abuse any comorbidity which results in moderate or severe functional limitation inability to communicate with the investigators or hospital staff pregnancy bilateral or multi-stage surgical procedures incarceration known allergy to any study medication any contraindication to perineural catheter insertion (e.g., infection at the catheter insertion site)