The anesthesia machine is divided into what 4 component subsystems?
- High pressure system
- Low pressure system
- Breathing system
- Scavenging system
What is the typical operating pressure of the pipeline gas supply?
50-55 psig
E tanks contain how many liters of gaseous oxygen compared to H tanks?
660 L vs. 6900 L
To keep oxygen in its liquid phase, what temperature must it be kept at?
-297 degrees F
What are the advantages and disadvantages of oxygen generators?
- Advantage: cost saving
- Disadvantage: noisy, needs power supply, higher cost initially
What gas is no longer used for anesthesia machines due to concerns about substance abuse?
N2O
What is the role of the pressure regulator?
facilitates constant pressure and flow (prevents flowmeter fluctuations), reducing the pressure to approx. 45 psig, forcing the pipeline supply to be used
What part of the anesthetic machine provides a direct connection between the high pressure and breathing systems?
oxygen flush valve; considered a part of the high pressure system
When it’s depressed, the oxygen flush valve delivers O2 at what rate?
35-75 L/min
What is the role of the flow control valve?
- it separates the high and low pressure systems and adjusts the flow of gas
What is the part of the machine that measures the flow of gas emerging from the flow control valve called?
Flow meter
T or F: Flowmeters can be interchanged
False; floats and flow tubes are calibrated as a pair for a specific gas
A flow meter should be read how?
at the top of the bobbin, unless it is the ball type, which is read in the center
What is the function of the vaporizer?
facilitates the change of liquid anesthetic into its vapor and adds a controlled amount of this vapor to the fresh gas flow
Describe the characteristics of a precision vaporizer we use today?
- Concentration calibrated or variable bypass output
- Flow over vaporization method
- Thermocompensation
- Out of the circuit
- Agent specific
- Plenum (high) resistance
Describe an open breathing system
No reservoir for anesthetic mixture and no rebreathing of expired gas
- e.g open drop method on a cloth
Describe a semi-open breathing system
With or without reservoir for anesthetic mixture, no rebreathing of expired gas and without CO2 absorption
- non-rebreathing systems (Ayre’s T piece, Bain, Jackson-Rees, Mapleson)
Describe a semi-closed breathing system
With reservoir for anesthetic gas and partial rebreathing of expired gas with CO2 absorption
- e.g. Circle with oxygen flow higher than the metabolic requirement of the patient
What is the difference between low-flow and high-flow anesthesia?
- Low-flow: fresh gas flow b/t metabolic O2 requirement and below 22 ml/kg/min
- High -flow: fresh gas flow higher than 22 ml/kg/min
Describe a closed breathing system
With reservoir for anesthetic mixture, complete rebreathing of expired gas without the CO2 (CO2 removed by soda lime canister)
- O2 supply = metabolic requirement
- O2 flow b/t 4-7 ml/kg/min
e.g. circle with oxygen flow equal to metabolic requirement of patient
What are the advantages of a closed breathing system?
- Economical
- Conserve heat and humidity
- Reduced operating room/environmental pollution
- Can estimate O2 consumption of patient/dx hypermetabolic states
- Less danger of barotrauma b/c takes longer to develop high pressure with such low O2 flows
What are the disadvantages of a closed breathing system?
- Requires knowledge of uptake
- More attention required (fresh gas flow must balance uptake)
- Inability to change inspired concentrations quickly
- Danger of hypercapnia if CO2 not changed regularly
- Accumulation of undesirable gases in breathing circuit (e.g. Compound A)
What is Compound A?
a noxious compound produced by Sevoflurane reacting with soda lime which causes proximal tubular damage in the kidneys
What is the most commonly used breathing system in most veterinary clinics?
A semi-closed system using a circle breathing circuit and a high flow of fresh O2
