However, due to the heterogeneity of the breast surgeries performed, no meaningful conclusion about length of hospital stay associated with ESPB should be drawn.35–37,61 Only 1 case report measured patient sleep quality and mentioned no postoperative insomnia.50 Prolactin and cortisol levels were measured in only 1 RCT which found no difference in either levels between patients who underwent ESPB and those who underwent a PECS block. This evidence concerns the gene PRL and insomnia.