Vaporizers Flashcards
Definition of volatile anesthetics
Liquid at room temperature
Schematic of concentration-calibrated variable bypass vaporizer
Fresh gas enters the vaporizer, flow is split between larger bypass flow and smaller flow to the vaporizing chamber (sump) where the agent is at its SVP concentration - the saturated vapor mixes with the bypass flow which dilutes it to the concentration dial setting
Saturated vapor pressure defined
The gas phase above the liquid is said to be saturated when it contains all the anesthetic vapor it can hold at a given temp, the pressure that is exerted by the vapor is the SVP
How to obtain the partial pressure of an anesthetic?
Mac * 760 (Iso= .0115 x 760 = 8.7 mmHg)
How gas is arranged from patient and then away
Oxygen, air, nitrous
Splitting ratio of vaporizer
vaporizing chamber flow rate: bypass pathway flow rate
Simple variable bypass issues
High flows result in inadequate vaporization (wiking), temperature problem, accuracy of concentration with mechanical control knobs
Why do we compensate for temperature in vaporizers?
Heat (energy) is required to promote vaporization, heat is drawn from the liquid and the container, the anesthetic will cool as vaporization proceeds, if no heat is added vaporizer output would decline
Aladin cassette
Similar to variable bypass vaporizer but a computer controls the flows, will only allow delivery of one anesthetic at a time
What color is the aladin cassette for iso, sevo & des
iso - purple, des - blue, sevo - yellow
Why does des require a special vaporizer?
A conventional vaporizer would require really high flows to dilute it down & it would intermittently boil causing fluctuations in deliver (boiling increases, losing it’s heat decreases agent delivered)
What is des’ vaporizer?
Ohmeda Tec 6 - uses electrical filament that heats the des to 39 degrees centigrade & raises it’s SVP to almost 2 ATM - removes the need for a pressurized carrier gas
How does the Tec 6 work?
A certain amount of des is injected into fresh gas flow instead of utilizing variable bypass, the control dial determines how much desflurane is delivered
