Background: Cytoreductive surgery is associated with extensive fluid resuscitation, inadvertent periop. hypothermia and high dose usage of vasopressors which may alter intraop. tissue oxygenation (StO2), microperfusion and subsequently reduce postop. outcome. We hypothesize that preop. forced-air warming (PW) may help to prevent intraop. hypothermia as a prerequisite to improve StO2 and microperfusion.Material and Methods: After ethics approval 47 women scheduled to have cytoreductive surgery were prospectively enrolled. All women received a thoracic PDA, an arterial line, a central venous catheter during induction of GA and intraop. forced-air warming. According to their randomization women were treated with either 30 min. of 43u00b0C PW (Gr. 1, Fig 1A), PW + subcutaneous microdialysis (MD, Gr. 2, Fig 1B), MD without PW (st/MD, Gr. 3) or no intervention (st., Gr. 4). StO2, central venous-arterial carbon dioxide difference (dCO2) and ethanol ratio via MD for microperfusion and core temp. (hourly) were defined as primary outcome. Additionally, hemodynamic parameters (MAP, CVP, HF, norepinephrine) and glucose, lactate and glycerol in MD were obtained. Statistical analysis was performed using the Mann-Whitney-U-Test and non-parametric-longitudinal analysis. Results: No significant differences in StO2 of 86.0% (84.0-88.0) in Gr. 1+2 (n= 24) compared to 84.0% (80.0 - 87.5) in Gr. 3+4 (n=23) were detectable at 60 min and over the entire intraop. Period (Fig. 2). The dCO2 at 60 min (Gr. 1+2: 6.3mmHg (5.4 - 7.8) vs. Gr. 3+4: 5.7mmHg (4.7 - 6.9)) and over the entire intraop. period remains without significant differences. In MD the ethanol ratio in Gr. 2 (n= 7) is fairly constant at 0.4 compared to a slight decrease from 0.45 to 0.25 in Gr. 3 (n=7). Lactate, glucose and glycerol in Gr. 2 tend to be more constant over the entire period without significant differences to Gr. 3 (Fig.3).The median core temp. of 36.7u00b0C (36.6-36.9) in Gr. 1+2 at 60min was significantly (p