Variable-bypass vaporizers

Deliver fixed partial pressures of volatile anesthetics based on dialed settings
Works for isoflurane, sevoflurane
Desflurane req heated vaporizer (high vapor pressure and boiling point near room T → use with VBV unpredictable)
Dial settings don’t change at high altitudes (pp unchanged, although volume % concentration increases)
OTOH desflurane injector has constant 2 atms pressure, injects constant concentration (but variable pp) → must manually increase conc for anesthesia