The Ultrasound-guided Multiple-injection Costotransverse Block for Mastectomy and Primary Reconstructive Surgery.

The investigators have developed a novel ultrasound-guided nerve block indicated primarily for breast cancer surgery that mimic a thoracic paravertebral block (TPVB) - hitherto the internationally accepted regional anesthesia golden standard for anesthesia of the hemithorax - but hypothetically without the risks of adverse events associated with the TPVB (i.e. pneumothorax, risk of bleeding in the thoracic paravertebral space, random and unmanageable epidural spread etc.). The investigators have already tested the anatomical- and block execution hypothesis in a randomized cadaveric study, and the investigators now have anatomical proof of concept for the functionality of the block technique. The investigators have also conducted a small clinical pilot study with very promising results. The investigators wish to conduct a randomized, placebo controlled and double-blind study, comparing the effect of the ultrasound-guided multiple-injection costotransverse block (MICB) vs. placebo. The aim with this study is to investigate the efficacy of the MICB vs. placebo in patients undergoing unilateral mastectomy and primary reconstructive surgery due to breast cancer or ductal carcinoma in situ. The hypothesis is, that the unilateral MICB will significantly reduce the opioid consumption during the first 24 postoperative hours and significantly reduce the Numerical Rating Scale pain score (0-10) and opioid related side effects.