Medical Gas Systems Vaporizers Flashcards
What are the sources of gases?
Your machine is equipped with two sources of gas: pipeline, and cylinder. Piped gas comes from hospital main course, and is what is used primarily everyday. Machines are also equipped with cylinders – usually used as a back up when pipeline fails or is not working. “E”-cylinder is just referring to the size, which we will get into a little later.
Explain the Diameter Index Safety System (DISS)
Provides non-interchangeable connections for the medical gas lines
Connection consists of a *body, *nipple, and *nut combination
Only properly mated parts will fit together and allow the threads to engage
Required for every anesthesia machine
Explain the body the DISS
As the diameter of the body increases/decreases, the matching “nipple” will do so in tandem. This combination is unique for each gas inlet and ensures only properly matched parts fit together
Pin index safety system
*Required for every anesthesia machine
Uses a series of *pins to connect associated gas cylinders valves with its matching yoke clamp
Position of *holes on the cylinder valves *corresponds with the *pins on the yoke attached to the equipment
*Each gas has a unique pin configuration
Prevents connection of the wrong cylinder to a yoke
Pin indexes
oxygen
nitrous
air
oxygen: 2, 5
nitrous: 3, 5
air: 1,5
Explain the Link proportioning system
One of the Fail-safe mechanisms of the anesthesia machine: does not allow you to deliver a hypoxic mixture. If you were to try to only turn on nitrous, your oxygen will automatically be turned on to a concentration that is at least room air
Explain the Electronic Flow Meter – ADU/Ohmeda
New machines with electronic flowmeters still contain this fail safe mechanism. Proportioning link system is internalized – wont let you turn N2O on without Oxygen on. You will see this when we go to the lab and get to play with the machines.
Color coding Oxygen Nitrous Oxide Air Nitrogen Helium
Oxygen = Green Nitrous Oxide = Blue Air = Yellow Nitrogen = Black Helium = Brown
Cylinder capacity air
Full air cylinders considered full at 1900-2000 psi, w/ ~625 liters. Just like oxygen, pressure falls in proportion to the volume remaining in tank
Cylinder capacity for O2
Full E-sized O2 cylinder considered full at 2000-2200 psi w/ ~625-700 liters. As O2 is used from cylinder, pressure falls in proportion to the amount left in the tank
Cylinder capacity for N2O
*Full N2O cylinder would read pressure of 745 psi and have ~1590 liters and stored as a liquid. Pressure does not indicate amount left in tank
Regulatory agencies
Purity of medical gases is specified in the US Pharmacopoeia and enforced by the Food and Drug Administration (FDA)
The Department of Transportation (DOT) establishes the requirements for manufacturing, filling, qualification, transportation, storage, handling, maintenance, re-qualification, and disposition of medical gas cylinders and containers.
Explain Cylinder markings
Markings designed to indicate ownership, specification, pressure ratings, and other important data such as, serial number, date of manufacture
How are Cylinders labeled? Explain!
Labeling: Each cylinder must have a label or decal on the side or on the shoulder, but may not cover any permanent markings
Cylinder tags
Tags: Full, In Use, Empty connected by perforations. Denotes the amount of cylinder contents and is not used for identification purposes
What are theSafe Handling Procedures for Cylinders
- Never stand a cylinder upright without support
- Never leave empty cylinders on the machine
- Never leave the plastic tape on the port while installing the cylinder
- Never rely only on the cylinder’s color for identification of its contents
- Never oil valves
- Before any fitting is applied to the cylinder valve, particles of dust, metal shavings, and other foreign matter should be cleared from the outlet by slowly and briefly “cracking” the valve away from you and/or other personnel. WHY??
- The valve should always be fully open when a cylinder is in use. Marginal opening may result in failure to deliver adequate gas.
Explain Vaporization. Why is it Important?
What is vaporization dependent on?
Vaporization is the conversion of liquid to a gas
Why is this important?
The inhalation agents we use today are liquids that must be converted to a vapor to be inhaled
Anesthetic gases are also referred to as “Volatile Agents” because they are liquids that have a high propensity to vaporize into gas form.
Dependent on:
Vapor pressures
Temperature
Amount of carrier gas used
Explain activity of molecules during vaporization?
Molecules of a volatile agent in a closed container are distributed between the liquid and gas phases
The gas molecules bombard the surface of the liquid and the walls of the container creating vapor pressure
Vapor Pressure of Sevoflurane
160 mmhg
Vapor Pressure of Enflurane
172 mmhg
Vapor Pressure of Isflurane
240 mmhg
Vapor Pressure of Halothane
244 mmhg
Vapor Pressure of Desflurane
669 mmhg
What is Latent Heat of Vaporization
Number of calories required to change 1 gram of liquid into vapor without a temperature change
*note 1g=1mL
The energy for vaporization comes from the liquid itself (or from an outside source)
In the absence of outside source of energy, the temp of liquid itself will decrease during vaporization… rate of vaporization will further decrease. We need some sort of system where temp of liquid remains constant
What is specific heat
The number of calories required to increase the temperature of one gram of a substance by one degree centigrade
The substance can be liquid, solid or gas
Why is specific heat important in the design, operation and construction of vaporizers?
The concept of specific heat is important to the design, operation, and construction of vaporizers because it is applicable in two ways. First, the specific heat for an inhaled anesthetic agent is important because it indicates how much heat must be supplied to the liquid to maintain a constant temperature when heat is being lost during vaporization. Second, manufacturers select vaporizer component materials that have high specific heat because these materials better resist temperature changes associated with vaporization.
What is thermal Conductivity?
A measure of speed with which heat flow through a substance.
The higher the thermal conductivity, the better the substance conducts heat.
Vaporizers are constructed of metals that have relatively high thermal conductivity, why?
helps them maintain a uniform internal temperature during evaporation by allowing them to absorb environmental heat more effectively.
what are the characteristics of Vaporizers
- Agent Specific
- iso and halo has close vapor pressure - Temperature Compensated
- Compensating valve - Variable Bypass
Explain flow of gas through Variable bypass vaporizer
A portion of the gas flow will pass into the vaporizing chamber where it will become saturated with vapor.
This vapor-laden portion then rejoins the gas flow for dilution to deliverable concentrations.
Tec 6 Vaporizer
Specifically for Desflurane due to its high volatility
using an electrical filament that heats the desflurane to 39°C, ~2 atm. this high pressure removes the need for a pressurized carrier gas—instead, the fresh or diluent gas is entirely separate from the vaporizing chamber
Is theTec 6desflurane vaporizer isa variable bypass vaporizer?
No, it is a gas-vapor blender.
Electrically heated, constant temperature/pressure
Copper kettles
Measured flow, Bubble Through
1. Dedicated flowmeter for the kettle (MEASURED FLOW)
2. Gas comes up through central tube inside of the vaporizer to the LOVING CUP
3. Flow of gas is then directed down toward the liquid (BUBBLE THROUGH)
4. Highly concentrated vapor then exits the vaporizer and is
Diluted into the fresh gas flow
Is the copper kettle in circuit or out of circuit?
This is an out of circuit, non-(agent)specific, measured flow, bubble-through vaporizer. It is not something that you are likely to see in use in the United States.
Copper kettle calculations
Vapor Output =
CG x VP/ BP - VP
Where CG is the flow rate of the carrier gas in lpm, VP is the vapor pressure of the anesthetic agent and BP is the Barometric pressure.
Anesthetic Concentration =
Vapor output in mL/min / Total gas flow in ml/min
Altitude: Effect on Vaporization
Increased altitude – ↓ barometric pressure
Decreased altitude – ↑ barometric pressure
The % delivered is relative to the agent’s vapor pressure in comparison to the barometric pressure
Vaporizer must be re-calibrated to assure accurate % delivered anesthetic gas
Altitude effect on vaporizers
Variable Bypass
x’=x(p/p’)
Effect is that you are delivering a higher concentration of volatile agent at higher altitudes/lower barometric pressure but maintaining same partial pressure.
Tec 6
Required dial setting =
Normal dial setting (%) x 760mmHg/ Ambient pressure(mmHg)
Effect is that you would have to deliver higher dialed concentration of Des at higher altitude/lower barometric pressure. Conversely, you would alter your concentration dial to decrease output in lower altitude to avoid delivering overdose of anesthetic
Potential vaporizer hazards
Wrong Agent in the vaporizer High – Low – High Low – High - Low Contamination Tipping Overfilling Simultaneous Administration of More than One Vapor Leaks Pumping Effect
The % delivered is relative to the agent’s vapor pressure in comparison to the barometric pressure. T or F
T
