The investigators hypothesize that cefazolin perfusion to subcutaneous adipose tissue is reduced in morbidly obese patients. The primary objective of this exploratory pilot study is therefore to investigate target site (subcutaneous adipose tissue) penetration of cefazolin in morbidly obese patients and non-obese patients. The investigators aim to examine whether and how cefazolin plasma concentrations are predictive of subcutaneous (target) cefazolin concentrations. Possible factors of influence on the distribution of cefazolin (tissue perfusion, body weight, distribution of adipose tissue, other) will be identified.

Inclusion Criteria:

• Body Mass Index > 40 kg/m2
• BMI between 20-25
• undergoing laparoscopic gastric banding, or bypass surgery or sleeve gastrectomy (See population description for surgery type of the non-obese group)
• 21-60 years old
• American Society of Anaesthesiologists (ASA) physical status II to III

Exclusion Criteria:

• pregnancy
• breastfeeding
• known allergy for cefazolin/nadroparin
• known ejection fraction of < 35%
• renal insufficiency

8 morbidly obese patients undergoing weight reducing surgery And 8 non-obese patients undergoing surgery which will require an arterial line, nadroparin and cefazolin administration perioperatively and postoperative stay at the Post-Anesthesia Care Unit.