ObjectivesPost-operative pain after a modified radical mastectomy ranges from moderate to severe. Pectoralis (PECS) block has been found to be more effective than erector spinae block in reducing pain and the consumption of rescue analgesia in the post-operative period. This study aimed to compare the effect of erector spinae block and PECS block on the quality of recovery after modified radical mastectomy using the quality of recovery (QoR-40) score.MethodsThis randomised controlled study was conducted at King George’s Medical University, Lucknow, India, from 9thOctober 2020 to 9thOctober 2021. After general anaesthesia, patients were given blocks according to computer-generated randomisation: Group I: PEC I and PEC II (PECS) blocks; Group II: erector spinae plane (ESP) block; and Group III: control group (no intervention). The QoR-40 score was observed on the morning of the surgery and after 24 hours. Time to rescue analgesia and the total consumption of rescue analgesia in the first 24 hours were also observed.ResultsA total of 90 patients were included (30 in each group). In the post-operative period after 24 hours, global QoR-40 scores were 183.64 ± 6.36, 179.68 ± 6.38 and 171.37 ± 6.88 in the PECS, ESP and control groups (P<0.0001). But there was no statistically significant difference between the QoR scores of PECS and ESP group patients (P= 0.0551). The total requirement of rescue analgesic was significantly lower in the PECS group (137.28 ± 31.46 mg) than in the ESP (189.46 ± 42.98 mg) and control (229.57 ± 46.80 mg) groups (P<0.0001). Time to first rescue analgesia was significantly higher in the PECS group (6.53 ± 2.78 hours) than in the ESP (4.05 ± 2.91 hours) and control (2.15 ± 1.51 hours) groups (P<0.0001).ConclusionBoth ESP and PECS blocks were effective in improving the QoR score and in reducing the consumption of rescue analgesia after modified radical mastectomy.