Gürkan 2018.

Study characteristics
Methods	Prospective, randomised, controlled, single‐blinded study Ethics approval obtained Randomisation was achieved using the sequentially numbered, opaque, sealed envelope technique. A pain nurse blinded to the study groups was responsible for postoperative follow‐up.
Participants	Setting: School of Medicine, Kocaeli University, Kocaeli, Turkey Sample size: 50 female patients Participant (baseline) characteristics: Age 20 to 65 years ASA I‐II Inclusion criteria: adult female patients scheduled for elective surgery for breast cancer. Only unilateral surgical procedures were included. Exclusion criteria: obesity (BMI > 35 kg/m2), infection of the skin at the site of the needle puncture, known allergies to any of the study drugs, coagulopathy and recent use of opioid drugs
Interventions	Intervention group: ESPB Comparator group: no block
Outcomes	Primaryoutcome: mean morphine consumption Secondary outcomes: numeric rating scale (NRS) pain scores recorded at 1, 6, 12 and 24 hours postoperatively
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