Sevoflurane Tec 7 Vaporizer Output as a Function of Fresh Gas Flow and Room Temperature
Tarone Thirawatananond, BS; Nikolaus Gravenstein, MD; Christopher Edwards, MD
Department of Anesthesiology, University of Florida College of Medicine, Gainesville, FL
- Unheated variable-bypass vaporizers are manufactured to perform optimally at a certain fresh gas flow (FGF) rate1.
- As FGF increases beyond that rate it is more difficult for the gas exiting the vaporizing chamber to reach full saturation1,2.
- This has implications in pediatric anesthesiology as it affects the speed and efficiency of inhalational induction.
- Ambient temperature can affect the saturated vapor pressure within the vaporizer chambers and is posited to create an underperformance in rooms with cold temperatures1,2.
- The aim of this study is to elucidate the variability of GE Datex Ohmeda Tec 7 sevoflurane vaporizer output in relationship to FGF rate and room temperature.
- The experiment used an OR, thermostat, and anesthesia workstation.
- Three GE Datex Ohmeda Tec 7 Vaporizers were used to dispense sevoflurane with the vaporizer dial set at 8%.
- Inspired sevoflurane (Fi) was sampled at the elbow of a corrugated breathing circuit.
- Fi was recorded at 15 second intervals across different FGF rates and two room temperatures (20.8°C & 25.3/25.6°C)
- The external vaporizer temperature was monitored with a temperature probe adhered to the bottom of the vaporizer.
- The external vaporizer temperature remained within ±0.1°C across all experiment runs.
- As FGF increases >5 L/min, the maximum Fi progressively decreases.
- At FGF <5 L/min, more time is required to reach an Fi approaching 8%.
- No significant differences in Fi were seen between the two temperatures tested.
- FGF of 5 L/min allows for both a rapid rise in Fi and achievement of an Fi of 8%.
- FGF <5 L/min prolongs the initial rise in Fi.
- FGF >5 L/min, prevents achievement of the 8% Fi set on the vaporizer dial.
- FGF >5 L/min leads to additional waste with diminished anesthetic concentration delivered.
- No significant difference in Fi within a temperature range routinely seen in ORs, likely due to the internal temperature compensation of the vaporizer.
- Inhalational induction with a FGF of 5 L/min will be more rapid and efficient than using a higher or lower FGF.
- Datex Ohmeda Inc. Tec 7 Vaporizer-User’s Reference Manual. 1175 0013 000 06 02 A. 2002, Section 7.
- Boumphrey S, Marshall N. Understanding vaporizers. Continuing Education in Anaesthesia Critical Care & Pain 2011;11:199-203.