Anesthesia Machine Flashcards
SPDD
supply, processing, delivery, and disposal model.
Supply
Pipeline and Cylinders
Processing
How gasses are prepared before delivery to the patient. Fail-safe Flowmeters Oxygen flush Low pressure alarms vent-driving gas proportioning system oxygen second stage regulator Vaporizers Check valves distal to vaporizors Common Gas Outlet (CGO)
Delivery
Interaction with the patient is controlled and monitored; Breathing circuit
Gas delivery hose from CGO to circuit nonrebreathing or circle CO2 absorption vent monitors; O2 analysis; disconnect; spirometry Vent alarms PEEP Humidification
Disposal
How are gasses disposed of? : Scavenger
Closed: active v. passive or open
Scavenger flowmeter
High pressure components
Receives gasses from the high pressure E cylinders attached to the back of the anesthesia machine (2000 psi for O2, 745 psi for N2O)
Consists of:
Hanger Yoke (reserve gas cylinder holder)
Check valve (prevent reverse flow of gas, or gas leaks)
Cylinder Pressure Indicator (Gauge)
Pressure Reducing Device (Regulator)
Usually not used, unless pipeline gas supply is off
Intermediate Pressure components
Receives gasses from the regulator or the hospital pipeline at pressures of 40-55 psig (common is 50psi) Consists of: Pipeline inlet connections Pipeline pressure gauges Piping Ventilator power inlet Master switch Oxygen pressure-failure devices Oxygen flush valve Additional reducing devices Flow control valves
Low pressure components
Extends from the flow control valves to the common gas outlet Consists of: Flowmeter tubes Vaporizer mounting device Check valves Common gas outlet
Pressure fail-safe devices
This valve is controlled by the O2 supply pressure and shuts off or proportionately decreases the supply pressure of all other gasses as the O2 supply pressure decreases
Historically there are 2 kinds of fail-safe valves
Pressure sensor shut-off valve (Ohmeda) (O2 opens if psi>20)
Oxygen failure protection device (Drager) (The pressure of all gases controlled by the OFPD will decrease proportionately with the oxygen pressure)
Oxygen Flush Valve
Receives O2 from pipeline inlet or cylinder reducing device and directs high, unmetered flow directly to the common gas outlet (downstream of the vaporizer)
Machine standard requires that the flow be between 35 and 75 L/min
The ability to provide jet ventilation
Hazards
May cause barotrauma
Dilution of inhaled anesthetic
Proportioning systems
Maintains N2O:O2 ratio 3:1, with a minimum of 25% O2.
5 tasks of oxygen
1: proceeds to fresh gas flowmeter
2. powers the O2 flush
3. activates failsafe mechanism
4. activates O2 low-pressure alarms
5. Compresses bellows of mechanical vents
Managing oxygen pipeline supply Failure
Always have Ambubag and O2 tank
If pipeline pressure fails or PaO2 drops:
1: Don’t try to fix analyzer
2: Turn on tank, disconnect pipeline
If FiO2 doesn’t increase, use ambubag with RA
3: Low flow of O2. Keep going with volatile
4: Turn off vent, ventilate manually
5: Call for help, get more O2 tanks, calculate remaining time on current tanks
6: How long will failure last? make a plan
7: Don’t reconnect until pipeline is tested
8: If circle isn’t working, use BVM with O2 or RA, and TIVA.
E-cylinder O2
1900 psi, 660L
N2O
745 psi, 1590 L (Needs to be weighed, don’t go off psi)
Air
1900 psi, 625 L
Path of gases (Ox, N2O, air)
supply ->fail-safe valve-> flowmeter -> common manifold (O2 is added to all gases at this point) -> vaporizor -> CGO
Oxygen flush
35 - 75 L/min Fill circuit quickly jet ventilation AVOID DURING INHALATION proceeds directly from supply to the CGO
Inspired oxygen analysis
o Ensure that oxygen is present in the pipeline or cylinder
o required in EVERY GETA
o Function checked every time
Variable-bypass
allows a small portion of FGF to come into contact with liquid and pickup the vapor. Sevoflurane, Isoflurane Splits total fresh gas flow into 2 portions: First portion (20%) passes into vaporization chamber, becomes saturated with vapor Second portion passes into bypass chamber , they mix at patient outlet Delivers known concentration of gas Temperature sensitive strip expands and contracts to offset temperature changes due to evaporation Splitting Ratio = flow through vaporizing chamber/flow through bypass chamber
Vaporizer
Agent specific, outside breathing circuit.
Vaporization depends on temperature, VP of liquid, and partial pressure of vapor above the evaporating liquid
Tilting or tipping must be avoided; if this is done, vaporizer is not usable until serviced!
Air flow “carrier gas” carries vapor to patient
Variables include molecular make-up of vapor (vapor pressure) and temperature
Tec-6
Desflurane ONLY
o Flow not split; vapor “injected” into fresh gas
Amount of Des released depends on:
Concentration setting set on control dial
Fresh gas flow rate
Des is heated to 39OC, this maintains desired vapor pressure for delivery
Separate electrical supply
Dead Space
Anatomical dead space:
Areas of the tracheal/bronchial tree not involved in gas exchange
Includes equipment dead space: ETT and tubing distal to Y connector of circuit
Alveolar dead space:
Alveoli that do not participate in gas exchange due to lack of blood flow
Total dead space reflects the above sum; most pathologically significant changes in dead space represent changes in alveolar dead space
Circle system advantages
Most popular in USA
Advantages:
Cleanses CO2 but allows rebreathing of all other gases
Conservation of respiratory moisture and heat
Decreases ppm of vapors in the OR
Lower resistance
