Desflurane is increasingly used in general anesthesia. Its pharmacokinetic properties are known and its distribution is easily modeled. Yet these models fail in practice. In order to increase accuracy, any model should include cardiac output, alveolar ventilation and alveolar dead space, all of which are either hard to measure or impractical, at least.

A previous study performed by the same investigator showed that time to target endtidal concentration of sevoflurane is prolonged with increased cardiac output, but only if the patient has increased muscle mass. Although desflurane has lower muscle and fat solubility, our observations suggest a similar prolongation in case of increased muscle mass.

The investigators aim to investigate if patient characteristics such as gender, age, height, weight, body type prolongs time to reach target endtidal desflurane concentration in low flow anesthesia.

Low flow anesthesia is a frequently used application in anesthesiology practice. With the widespread use of modern anesthesia devices, the implementation of this application has become easier and its complications have been greatly reduced. It is routinely applied in our clinic, accompanied by both the protocols in the literature and the protocols the investigators have created.

Desflurane is the most recently developed inhaler anesthetic agent, and it has advantages such as faster recovery from anesthesia and less metabolism compared to sevoflurane. Although the physicochemical properties of desflurane are known, computer models for its use with low-flow anesthesia are based on desflurane's physicochemical properties, and not on the pharmacokinetic properties of patients. The inhaled induction times obtained with these models do not agree with our observations in practice.

In a study conducted in 2021, it was shown that parameters such as cardiac output and alveolar ventilation can increase the accuracy of these models. Among these models, the most frequently used one in the literature is included in the Gas Man simulator, which is also used in anesthesia specialty training. It allows one to perform studies that compare simulation-based and in vivo values are carried out.

A similar study was conducted by us with sevoflurane in 2018; A significant difference was found in the rate of increase in alveolar sevoflurane concentration according to cardiac output and muscle mass. Based on this study, the investigators aimed to investigate the effect of the patient's muscle mass evaluated by pragmatic measures such as height, body weight and body type on the rate of increase in the alveolar concentration of desflurane.

For this purpose, the investigators aimed to investigate the relationship between the time to reach the targeted alveolar desflurane gas concentration and patient characteristics. The investigators believe that the results of the study will be useful in explaining the factors affecting the induction of general anesthesia with desflurane.

Inclusion Criteria:

• age > 18 years
• planned elective surgery
• planned inhalational anesthesia
• planned use of desflurane

Exclusion Criteria:

• emergency surgery
• use of other inhalational anesthetic agent (sevoflurane, isoflurane, nitrous oxide)
• disclosed or recognized pregnancy

Adult patients, who are scheduled for elective general anesthesia. Maintenance of anesthesia with desflurane should be included in the routine anesthesia plan.