Low flow anesthesia (LFA) is used less than desirable, partly because one has considered that there might be danger of underdosing of anesthesia gas and thus risk of awareness under anesthesia.LFA has several advantages such as reducing loss of moisture and heat in the inhaled air under anesthesia and to reduce the consumption of anesthetic gas. A few anesthesia machines include an automatic gas control system: the Aisys machine, by GE Healthcare (Madison, WI, USA), and the Flow-i machine, by Maquet (Sweden).

Since these machines were introduced, only a few studies have reported their functionality and effect on gas consumption. 20 to 55% reduction of gas consumption was found. The potential reduction may have been underestimated because in the majority of cases a FGF higher than 1 l/min was still used.

In this study the consumption of anesthetic gas (desflurane) delivered by two different anesthesia machines (Aisys and Flow-i) will be compared, with and without gas control delivery systems. Gas consumption and the time needed to reach the target level of anesthetic gas concentration will be assessed. Data needed will be collected directly from the anesthesia machine, PICIS ( Electronic anesthesia record) and EPJ (Electronic patient journal). The results of this study are of interest for intraoperative ventilation and of economic and ecological interest

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Inclusion Criteria:

• Patients undergoing robot assisted laparoscopic prostatectomy, robot assisted laparoscopic cystectomy or robot assisted laparoscopic gynecological surgery

Exclusion Criteria:

• Cognitive failure, which compromises the ability for an informed consent.
• Pregnancy
• American Society of Anesthesiologists physical status classification system (ASA) IV-VI

Patients who are included in the study can be excluded for the following reasons:

• surgical technical problems (for example surgically impossible to complete the operation with robot assisted surgery)
• technical problems with the anesthesia machine