A high SVP will require a smaller proportion of the total gas flowing through the vaporiser to pass through the vaporising chamber to produce a given concentration than a low SVP.
There are two ways the amount of Desflurane is controlled and injected into the FGF:
1. The dial on the top controlled by the anaesthetist - setting the desired conc %
2. The differential pressure transducer inside that detects FGF.
If FGF increases, the pressure also increases and is relayed through the transducer.
A microprocessor then opens the valve of the heating chamber to increase desflurane output (and vice-versa)
There is no fresh gas flow into the heating chamber itself - this is unlike a pass-over model.
- Needs electricity and time to warm up before it can be used.
- Unaffected by ambient temperature because the desflurane is heated.
- Automatically compensates for variation in FGF.
- Has visual and audible alarms to alert if almost empty or no output.
Dr. David Lyness
If the desflurane temperature were to decrease, the vaporizer would fail to deliver accurate concentrations. Solenoid operated locks in the vaporizer dial and at the vaporizing chamber outflow are only released once the operating temperature is reached.
www.wotol.com - Draeger Image
www.clinicalgate.com - Vaporiser Imagehttp://ceaccp.oxfordjournals.org/content/11/6/199.full.pdf+html
- Desflurane is presented as a liquid anaesthetic in a blue-bottle with a valve-like cap for filling.
- As an agent, it has a low blood gas partition co-efficient which means it has rapid onset and offset.
- It is an irritable gas, poorly tolerated as an induction agent when contrasted to sevoflurane.
- Desflurane has a high SVP - which means it will require a smaller proportion of the total gas for a given conc.
- Because it is a liquid with a boiling point so close to room temperature, using a pass-over vaporiser would yield erratic results.
- Therefore, it is heated in a chamber, to 42°c and pressurised to ~2atm.
- This precise heating and pressurising allows one to know the actual concentration of the vapour leaving the chamber.
- One does not need temperature compensation in a Tec6 vaporiser (as it is already heated to a specific temp)