The study is a single-centre, placebo-controlled, crossover study on healthy volunteers aiming to explore non-inferiority of methoxyflurane and fentanyl compared to placebo on the tolerance to hypovolemia.

The study will explore the effects of fentanyl and methoxyflurane versus placebo (NaCl; saline) on the hemodynamic response to hypovolemia in healty volunteers. Hypovolemia will be induced in the "lower body negative pressure" model. XX healthy volunteers will be exposed to inhaled methoxyflurane, 3 ml or intravenous fentanyl, XX mg or placebo in a randomized order (cross-over) at least 3 days apart.

Inclusion Criteria:

• Must be at least 18 years of age.
• Must be below 65 years of age.
• Signed informed consent and expected cooperation for the study and follow up must be obtained and documented according to ICH GCP, and national/local regulations.

Exclusion Criteria:

• Any medical condition limiting physical excertional capacity or requiring regular medication (allergy and oral contraceptives excepted)
• Pregnancy
• History of syncope (syncope of presumed vasovagal nature with known precipitating factor excepted)
• Any known cardiac arrhythmia
• History of renal disease
• History of liver disease
• Previous substance abuse
• Allery or known serious side-effects to opioids or methoxyflurane

Both drug interventions (intravenous fentanyl and inhaled methoxyflurane) will have NaCl placebo comparators. As the methoxyflurane has a characteristic smell, some drops of methoxyflurane will be placed on the exterior of the placebo methoxyflurane inhalation devices. Further, the subjects will rinse the mouth with a mouthwash shortly before inhalation to cover the taste of methoxyflurane.