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Questions and Answers
What are the four main functions of an anesthesia machine?
What are the four main functions of an anesthesia machine?
Delivery of oxygen to the patient, Delivery of anesthetic gas, Assistance with ventilation, Removal of exhaled carbon dioxide from the patient
What is the primary purpose of a regulator in an anesthesia machine?
What is the primary purpose of a regulator in an anesthesia machine?
To convert variable high pressure from a gas source to a constant working pressure, typically around 50-60 psi.
What is the main function of a flowmeter in an anesthesia machine?
What is the main function of a flowmeter in an anesthesia machine?
Control the rate of gas delivery to the low-pressure area of the breathing system.
What is the purpose of a vaporizer in an anesthesia machine?
What is the purpose of a vaporizer in an anesthesia machine?
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What is the main difference between non-rebreathing and rebreathing anesthetic systems?
What is the main difference between non-rebreathing and rebreathing anesthetic systems?
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The size of the reservoir bag in an anesthetic breathing system should be 6-10 times the tidal volume of the patient.
The size of the reservoir bag in an anesthetic breathing system should be 6-10 times the tidal volume of the patient.
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Breathing tubes in a circle system should be highly flexible and offer low resistance.
Breathing tubes in a circle system should be highly flexible and offer low resistance.
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What are the two primary types of safety systems used in anesthesia machines to ensure the correct gas is connected to the machine?
What are the two primary types of safety systems used in anesthesia machines to ensure the correct gas is connected to the machine?
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The pop-off valve should always be left open during spontaneous breathing.
The pop-off valve should always be left open during spontaneous breathing.
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The O2 flush on an anesthesia machine can be used with both circle and non-rebreathing systems.
The O2 flush on an anesthesia machine can be used with both circle and non-rebreathing systems.
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What are the two main types of anesthetic breathing systems?
What are the two main types of anesthetic breathing systems?
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What is the main advantage of a rebreathing system over a non-rebreathing system?
What is the main advantage of a rebreathing system over a non-rebreathing system?
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What is the primary role of a scavenging system in an anesthesia machine?
What is the primary role of a scavenging system in an anesthesia machine?
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A dedicated person is always required to operate an anesthesia ventilator.
A dedicated person is always required to operate an anesthesia ventilator.
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What are some common indications for using an anesthesia ventilator?
What are some common indications for using an anesthesia ventilator?
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The pressure-limiting adjustment on an anesthesia ventilator should be set to a maximum working pressure of 30 cmH2O or less.
The pressure-limiting adjustment on an anesthesia ventilator should be set to a maximum working pressure of 30 cmH2O or less.
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Study Notes
Anesthesia Equipment
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Learning Objectives:
- Describe the functions of an anesthesia machine and its components.
- Describe safety features.
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Anesthesia Machine:
- Delivers oxygen to the patient (most veterinary machines use 100% oxygen).
- Delivers anesthetic gas.
- Assists with ventilation.
- Removes exhaled carbon dioxide from the patient.
Anesthesia Machine: Basic Components
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Medical gas source (O2, air):
- E-cylinder: 2200 psi, 700L (half full = 1100 psi, 350L)
- H-cylinder: 7,000L
- Liquid O2: Pipeline pressure 50-60 psi
- Medical air is compressed ambient air, filtered for impurities (water, oil).
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Regulator: Converts high pressure to a constant working pressure (50-60 psi).
- E-tanks have one-stage regulators.
- Pipeline systems use regulators at the O2 source set to 50-55 psi.
- 2-stage regulators allow for variable output pressure.
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Flowmeter: Controls the rate of gas delivery to the low-pressure area.
- Specific for gas (density, viscosity)
- Colour-coded.
- Liters/minute.
- Operated by a needle valve.
- A precision instrument.
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Vaporizer: Vaporizes anesthetic agent at a set concentration.
- Agent specific
- Temperature compensated
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Fresh (common) gas outlet: Part of the breathing system.
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Breathing system: Divided into high and low pressure parts.
Identification and Safety System (gas specific)
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Color coding:
- Oxygen (O2): white or green labels.
- Pin-index safety system (PISS): Used with E-cylinders.
- Diameter Index Safety System (DISS): Used with H-cylinders (body, nut, and stem connectors).
Vaporizer Safety
- Color coding: Helpful for identification.
- Key-indexed filler systems: Important for safety.
- Lock on dial: Prevent accidental changes.
- Do not overfill: Risk prevention.
- Do not tip vaporizer: Prevent spills and damage.
Anesthetic Breathing Systems
- Deliver oxygen and anesthetic gases to the patient.
- Allow elimination of CO2.
- Allow ventilation of lungs.
- Different types based on CO2 removal.
Non-Rebreathing Systems
-CO2 removal depends on fresh gas flow during expiratory pause.
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Use high gas flows (150-300 mL/kg/min).
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Advantages: Less resistance to breathing, less mechanical dead space, rapid manipulation of anesthetic depth.
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Disadvantages: Significantly higher waste of both carrier gas and high flow of dry cool gas (heat and humidity loss).
Rebreathing Systems
- Allow rebreathing and conservation of exhaled gases.
- Used for animals >10 kg (5-10kg pediatric).
- CO2 removal depends on the passage through the CO2 absorber (chemical reaction).
- Advantages: Decreased use of volatile anaesthetics, improved temperature/humidity control, reduced environmental pollution.
- Disadvantages: Difficult to rapidly adjust anaesthetic depth.
Rebreathing System Components
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Inspiratory one-way valve
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Inspiratory breathing tube
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Y-piece
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Expiratory breathing tube
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Expiratory one-way valve
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Reservoir bag
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CO2 absorber
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Breathing tubes/hoses: Flexible, low resistance conduits between Y-piece and one-way valves; reduce obstruction risk if bent. Add length for more volume to the system.
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F-circuit: Co-axial system (inspiratory inside expiratory)
Components of Circle System
- Y-piece: Unites ET-tube connector to inspiratory and expiratory breathing tubes.
- Septum: May be present to decrease dead space.
Universal F Breathing System
- Co-axial hose inside a hose.
- Inner hose carries fresh gas flow.
- Less bulk, dead space.
- Includes fresh gas inlet, inspiratory valve, inner tube, outer tube, expiratory adaptor, patient, expiratory valve, reservoir bag, CO2 absorber.
Rebreathing System: Denitrogenization
- Required for all rebreathing systems.
- Air is 21% O2 and 79% N2.
- Body and anesthetic machine are equilibrated with air; then once connected, N2 moves from body to the system.
- Takes ~20 minutes, High FGF (30 mL/kg/min) is used to flush out N2 and reduce risk of inhaling hypoxic mixtures.
One-Way Valves
- Prevent rebreathing of exhaled gas.
- Gases enter from below and raise a disc.
- Allow gas flow in one direction only; add resistance to breathing.
CO2 Absorber
- Contains chemical absorbent for CO2 removal from exhaled gases.
- Exothermic reaction; produces water.
- pH increases (pH sensitive indicator leads to color change).
- Granules change from white to purple as exhausted.
Circuit Pressure Gage (Manometer)
- Corresponds with pressure in the patient breathing circuit.
- Guide for positive pressure ventilation of lungs, and system leak test.
- Not greater than 10-25 cmH2O.
- Highest number corresponds to peak inspiratory pressure (PIP).
- Also watch chest expansion.
Scavenging System
- Conducts waste anesthetic gases away from the workspace.
- Passive (e.g., Charcoal canisters).
- Active (negative pressure system).
- Pink coloured hoses for safety.
Adjustable Pressure Limiting (APL) Valve / Pop-off valve/Exhaust valve/Scavenging valve
- Allows excess gas within the breathing system to be vented into a waste-gas scavenging system.
- Always leave open during spontaneous breathing.
- Only closed during lung ventilation and leak test or manual ventilation.
O2 Flush
- Allows oxygen to bypass flow meters and vaporizers.
- Oxygen delivered at high flow and pressure (40-70 L/min).
- Only be used with circle system.
- Used to flush anesthetic from circle system in emergency or leak test.
- Never use if a non-rebreathing circuit is connected to patient.
Anesthesia Ventilators
- Used to provide intermittent positive pressure ventilation (IPPV).
Ventilators
- Used to provide intermittent positive pressure ventilation (IPPV).
- Dedicated person can also provide IPPV.
- Ventilators allow other jobs.
- May require driving gas (O2, air) and electricity.
- Ventilator bellows replaces the rebreathing bag.
Ventilator Settings
- Tidal volume (TV): 10-15 mL/kg
- Respiratory rate (RR): 6-20 bpm
- Inspiratory time: 1-1.5 seconds
- I-E ratio: 1:2 - 1:4
- Peak inspiratory pressure (PIP): 10-20 cmH2O, max work pressure 30 cmH2O.
- Watch chest wall rise and fall normally.
- Guide ventilation settings with a capnograph
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