Obese patients may need higher doses of acetaminophen (APAP) for adequate analgesia, due to increased total clearance and distribution volume. APAP-induced hepatotoxicity is mainly caused through CYP2E1 pathway. Its activity is induced by obesity, potentially endangering the safety profile of APAP. Metabolic-dysfunction associated liver disease (MASLD) is an important associated risk factor for APAP induced-hepatotoxicity. The primary endpoint of this study is to validate Van Rongen's prediction model on plasma concentration of paracetamol and its metabolites and extend it to the steady state phase over a period of 30 hours by measuring plasma concentrations of paracetamol and its metabolites and comparing them with the plasma concentrations predicted by the model by Van Rongen et al. In addition, results obtained from venous blood will be compared with results obtained via VAMS after finger stick. If VAMS correlates well with plasma concentrations of paracetamol and its NAPQI adducts, future interventional studies may utilize the patient-friendly VAMS technology in an effort to further investigate the safety and efficacy of higher doses of paracetamol in obese patients and possibly other patient groups. The secondary endpoints of this study are liver function tests before and after 30hrs of paracetamol administration, the VAS pain scores, the surgical pleth index (SPI) and the consumption of piritramide as recorded by a PCIA pump.