Anesthesia Machine Flashcards
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
Describe the principle of operation for a circle breathing circuit
animal inspires from and expires to the circuit through a Y-piece, gases are directed around the circuit by unidirectional valves, CO2 is absorbed by soda lime, and the O2 consumed by the patient is replaced by the fresh gas flow
Describe the Unviersal F circuit
it is a coaxial rebreathing system (tube within a tube) that can be used in small animals up to 90 kg where the expired gas warms the inspired gas inside the smaller tube
What are the advantages of F circuits?
- Small size and light weight
- allows heat and moisture retention to maintain body temp
What are the disadvantages of F circuits?
- smaller inner tube provides resistance to breathing in big dogs
- elongation of outer corrugated tubing results in more dead space
- more difficult to clean
What are the advantages of a vaporizer out of a circuit?
- Output not affected by changes in ventilation, temp, or O2 flow rate
- Assisted or controlled ventilation will not greatly increase inhaled anesthetic concentration
- known anesthetic concentration delivered
What are the disadvantages of a vaporizer out of a circuit?
- Expensive
- Slow changes in anesthetic concentration especially with low flow of O2
What oxygen flow rate should dogs be started on immediately after induction with a VOC? What is the maintenance flow rate?
2-3 L/min (to reduce the dilution effect of the expired gas to the inspired anesthetic concentration); 1 L/min
What are the advantages of a vaporizer in the circuit?
- Cheap
- Economical; less anesthetic used
- Less environmental pollution
- More humidified
What are the diadvantages of having a vaporizer in the circuit?
- Inspired anesthetic concentration varies with changes in carrier gas flow rate, variations in temp, use of positive pressure ventilation, and patient’s ventilation
- anesthetic concentration in circuit is unknown
What are the general principles of using a VIC system?
- The higher the O2 flow rate, the lower the inspired anesthetic concentration (dilution)
- Inspired anesthetic concentration increases with:
- controlled or spontaneous ventilation and warm room temp
If you wish to use a circle breathing system with a VOC for closed circuit anesthesia, what are the necessary steps for this?
- Use semi closed system to achieve stable plane of anesthesia
- lower O2 flow and increase vape setting 2-3X over maintenance
- if patient wakes up or when vape is turned off for recovery, switch back to semi closed
What type of non-rebreathing system do we use at UF?
modified Bain (Mapleson D)
What is the usual oxygen flow rate for a non-rebreathing system?
200-300 ml/kg/min (ie. 2-3x minute ventilation)
Non-rebreathing systems are indicated for small patients (<7-10 kg). The two main reasons for this are what?
- Provide less dead space than circle breathing systems
- Provide less or no resistance to breathing compared to circles
What are the advantages of non-rebreathing systems?
- no valves, so low resistance
- good control of anesthetic concentration (inspired AC should = vape setting)
- does not require CO2 absorber
- less dead space
What are the disadvantages of non-rebreathing systems?
- Very high gas and anesthetic consumption esp in bigger animals
- Inspired gas not humidified
- Breathing of cool/dry gas results in more fluid loss
- Wasteful of anesthetic
What non-rebreathing system is used in VCOP?
Modified Jackson-Rees (Mapleson F)
Circle breathing systems can be used in small patients provided what two things?
- A breathing hose with a smaller Y-piece is used (decrease dead space)
- Ventilation is supported to prevent the fatigue of respiratory muscles resulting from breathing against the resistance of the unidirectional valves
What is the role of the scavenging system?
Collect waste gases from the breathing system and eliminate them from the workplace
