Transcript Slide 1
Inhaled anesthetic Delivery Systems
Sahmeddini MD Department of Anesthesia Shiraz medical university
Inhaled anesthetic Delivery Systems
Safety Standards
ANSI - (American National Standards
Institute) 1979 -- Standards set for all machines sold in
the U.S.
ASTM -- (American Society for Testing and
Materials 1988 1994: ASTM F1161-94 2000: ASTM F1850-00
To comply with the 2000 ASTM F1850-00 standard Continuous breathing system pressure
Exhaled tidal volume Ventilatory carbon dioxide concentration Anesthetic vapor concentration Inspired oxygen concentration Oxygen supply pressure
Arterial oxygen saturation of hemoglobin Arterial blood pressure Continuous electrocardiogram.
Functions of anesthesia machine Convert supply gases from high pressure to
low pressure Convert liquid agent to gas Deliver in a controlled manner Provide positive pressure for ventilation Alert the provider to malfunction
Prevent delivery of a hypoxic mixture
Testing Specific Components of the Anesthesia Delivery System 1)Calibration of the oxygen analyzer 2) The low-pressure circuit leak test 3) The circle system tests.
High Pressure System
Receives gasses from the high pressure E cylinders attached to the back of the anesthesia machine. ( 2200 psig for O2, 745psig for N2O
)
High Pressure System Receives gasses from the high
pressure E cylinders attached to the back of the anesthesia machine 2200 psig for O2 745 psig for N2O Usually not used, unless
pipeline gas supply is off
High Pressure System
Hanger Yoke
Hanger Yoke: orients
and supports the cylinder Providing a gas-tight
seal Ensuring a
unidirectional gas flow into the machine
Pin Index Safety System(PISS )
Prevents tank swaps
Pin positions
Air 1-5 Oxygen
2-5
Nitrous oxide
3-5
Pin Index Safety System(PISS)
Two sources of gas: Pipeline 50 psig Tanks
»Oxygen: 2200 psig »Nitrous oxide: 745 psig »Both reduced to 45 psig upon entering the
machine
• • • • •
Tank
H Tank E Tank
E Size Compressed Gas Cylinders
Cylinder Characteristics
Colour
Oxygen
White
Nitrous Oxide
Blue
Air
Black State Contents (L) Empty Weight (kg) Gas 625 5.90
Liquid and gas 1590 5.90
Gas 625 5.90
Full Weight (kg) Pressure Full (psig) 6.76
2000 8.80
750 6.50
1800
Approximate remaining time# Oxygen cylinder pressure(psig)
200 .oxygen flow rate(L/min)
Intermediate Pressure System
Intermediate Pressure System
Receives gasses
from the regulator or the hospital pipeline at pressures of 40-55 psig
Pipeline Inlet Connections
Mandatory N2O and O2,usually have air and suction too Inlets are non interchangeable due to
• •
specific threading as per the Diameter Index
Safety System (DISS)
Diameter Index Safety System (DISS)
Oxygen Pressure Failure Devices
Machine standard requires that an anesthesia machine be designed so that whenever the oxygen supply pressure is reduced below normal, the oxygen concentration at the common gas outlet does not fall below 19%
Oxygen Pressure Failure Devices
A Fail-Safe valve is present in the gas line supplying each of the flow meters except O2.
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
Oxygen Pressure Failure Devices
Historically there are 2 kinds of fail-safe valves Pressure sensor shut-off valve (Ohmeda)
Oxygen failure protection device (Drager)
Pressure Sensor Shut-Off Valve
Oxygen supply pressure opens the valve as long as
it is above a pre-set minimum value (e.g.20 psig).
If the oxygen supply pressure falls below
the threshold value the valve closes and the gas in that limb (e.g..N2O), does not advance to its flow control
Pressure sensor shut-off valve
Oxygen Failure Protection Device
(OFPD)
Based on a proportioning principle rather than a shut-off principle.
•
The pressure of all gases controlled by the OFPD will decrease proportionately with the
•
Oxygen failure protection device
Oxygen Supply Failure Alarm
The machine standard specifies that whenever
the oxygen supply pressure falls below a manufacturer specified threshold (usually 30 psig)
alarm shall blow within 5 seconds.
Limitations of Fail-Safe Devices/Alarms
Fail-safe valves do not prevent administration
of a hypoxic mixture because they depend on pressure and not flow.
Do not prevent hypoxia from accidents such as
pipeline crossovers or a cylinder containing the wrong gas.
OXYGEN FLUSH VALVE
By passes vaporizer
Delivers large volumes
of oxygen to breathing circuit Is under high(er)
pressure caution!!!
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 barotraumas Dilution of inhaled anesthetic
Second-Stage Reducing Device Located just upstream of the flow control valves Receives gas from the pipeline inlet or the cylinder reducing device and reduces it further to
26 psig for N2O and 14 psig for O2
Purpose is to eliminate fluctuations in pressure supplied to the flow indicators caused by fluctuations in pipeline pressure
Low Pressure System
Extends from the flow control valves to the common gas outlet Consists of:
Flow meters Vaporizer mounting device Check valve
Common gas outlet
Flow Meter Assembly
Flow Meter
When the flow control valve is opened the gas enters at the bottom and flows up the tube elevating the indicator • The indicator floats freely at a point where the downward force on it (gravity) equals the upward force caused by gas molecules hitting •
Flow Meter Standards
Oxygen flow control knob Physically different
Larger and projects further Different shape All knobs are colour coded Knobs are protected
Electronic flow sensors Some newer anaesthesia workstations have now replaced the conventional glass flow tubes with electronic flow sensors that measure the flow of the individual gases. • These flow rate data are then presented to the anaesthesia care provider in either numerical format, graphic format, or a combination of the two. •
Cracked tubes
In the presence of a flow meter leak (either at the “O” ring or the glass of the flow tube) a hypoxic mixture is less likely to occur if the O2 flow meter is downstream of all other flow meters
Proportioning Systems
Mechanical integration of the • N2O and O2 flow control valves • Maintain a minimum 25% concentration of oxygen with a maximum N2O:O2 ratio of 3:1 •
Proportioning Systems
Proportioning Systems
Proportioning Systems
Vaporizers
A vaporizer is an instrument designed to change a liquid anesthetic agent into its vapor and add a controlled amount of this vapor to the fresh gas flow •
Vaporizers
Classification of Vaporizers
Methods of regulating output concentration Concentration calibrated Method of vaporization Flow-over Bubble through Injection Temperature compensation: Thermocompensation Supplied heat
Applied Physics
Vapor pressure
Based on characteristics of agent Varies with temperature Boiling point: Vapor pressure equals atmospheric pressure Latent heat of vaporization: Heat required to change liquid into a vapor Comes from liquid environment • • • • • • •
Ohmeda and Drager Characteristics
Variable bypass Flow over Temperature compensated Agent specific Out of circuit
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Basic Design
Gas enters vaporizer Flow is split Majority is by passed Some enters vaporizing chamber Saturated gas leaves chamber Diluted by bypass gas Delivered to patient • • • • • • •
Generic Bypass Vaporizer
Flow from the flow meters enters the inlet of the vaporizer The function of the concentration control valve is to regulate the amount of flow through the bypass and vaporizing chambers • Splitting Ratio = flow though vaporizing chamber/flow through bypass chamber • •
Factors that Effect Output
Flow rate
Accurate at most flows Lower than dial setting at both extremes of
flow Temperature Vapor pressure varies with temp
Accurate at 20 - 35 C
Factors that Effect Output
Intermittent back pressure
Retrograde flow Higher than dial setting especially at low flows and high ventilator pressures
Carrier gas composition
N2O causes transient drop • • • • • • •
Carbon Dioxide Absorbents
Two formulations of carbon dioxide absorbents are commonly available today: soda lime calcium hydroxide lime Baralyme, or barium hydroxide lime
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CO2 Absorption (con’t)
Soda lime –94% calcium hydroxide –5% sodium hydroxide –1% potassium hydroxide –silica to harden granules –ethyl violet as an indicator
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CO2 Absorption (con’t)
Ethyl violet is the pH indicator added to both soda lime Ethyl violet changes from colorless to violet when the pH of the absorbent decreases as a result of carbon
dioxide absorption. • •
Unfortunately, in some circumstances ethyl violet may not always be a reliable indicator of the functional status of absorbent
•
Anesthesia Ventilators
The ventilator on the modern anesthesia workstation serves as a mechanized substitute for the hand of the anesthesia care provider in manipulating the reservoir bag of the circle system, or another breathing system.
•
Ventilators Classified by:
Power source pneumatic – electric – both – Drive mechanism double circuit – driven by oxygen – • •
Ventilator Problems (con’t)
Leak in bellows assembly • Mechanical problems • Electrical problems •
Setting the Ventilator
Based on the principle that PaCO 2 is directly proportional to alveolar ventilation
AV X CO
2
= AV X CO
2 (what you have) (what you want) AV = alveolar ventilation CO 2 = carbon dioxide If you know 3, you can solve for the 4th
The Circuit: Circle System
Arrangement is variable, but to prevent re-breathing of CO2, the following rules must be followed: Unidirectional valves between the patient and the reservoir bag
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Fresh-gas-flow cannot enter the circuit between the expiratory valve and the patient
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Adjustable pressure-limiting valve (APL) cannot be located between the patient and the inspiratory valve
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Circle System
Relative stability Advantages: of inspired concentration – Conservation of respiratory moisture and heat – Prevention of operating room pollution – PaCO2 depends only on ventilation, not fresh gas flow – Low fresh gas flows can be used – High Complex resistance Disadvantages: design = potential for malfunction – (multiple one-way valves) = higher work of breathing – • •
The Adjustable Pressure Limiting (APL) Valve
User adjustable valve that releases gases to the scavenging system and is intended to provide control of the pressure in the breathing system Bag-mask Ventilation : Valve is usually left partially open. During inspiration the bag is squeezed pushing gas into the inspiratory limb until the pressure relief is reached, opening the APL valve. Mechanical Ventilation : The APL
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The Adjustable Pressure Limiting (APL) Valve
Scavenging Systems
Scavenging is the collection and removal of vented anesthetic gases from the OR Since the amount of anesthetic gas supplied usually far exceeds the amount necessary for the patient, OR pollution is decreased by scavenging • •
Scavenging Systems
Workers should not be exposed to an eight hour time-weighted average of > 2 ppm halogenated agents (not > 0.5 ppm if nitrous
oxide is in use) or > 25 ppm nitrous oxide.
Evidence of harm to anesthesia personnel from waste gases is suggestive but unproved (strongest relationship is N2O and reproductive difficulties).
Type of Scavenging Systems
Scavenging may be active (suction applied) • passive (waste gases proceed passively down corrugated tubing through the room ventilation exhaust grill of the OR). •
Hazards of scavenging
Obstruction distal to interface
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Occupational exposure
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Barotrauma or inability to ventilate
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System Checkout
High-Pressure System Checkout Check Oxygen Cylinder Supply.
Open the O 2 cylinder and verify that it is at
least half full (≈1000 psi) Close the cylinder.
Check Central Pipeline Supplies.
Check that hoses are connected and pipeline
gauges read about 50 psi.
Low-Pressure System
Check Initial Status of Low-Pressure System .
a. Close the flow control valves and turn the
vaporizers off. b. Check the fill level and tighten the
vaporizers’ filler caps.
Perform Leak Check of Machine Low Pressure System.
Verify that the machine master switch and flow control valves are OFF Attach a “suction bulb” to the common (fresh) gas outlet Squeeze the bulb repeatedly until it is fully collapsed.
Verify that the bulb stays fully collapsed for at least 10 seconds. Open one vaporizer at a time and repeat steps c and d as above. Remove the suction bulb and reconnect the fresh gas hose.
Turn on Machine Master Switch and All Other
a.
Necessary Electrical Equipment.
Test Flow Meters.
Adjust the flow of all gases through their
full range while checking for smooth operation of the floats and undamaged flow tubes. b.
Attempt to create a hypoxic O 2 /N 2 O mixture and verify correct changes in flow
and/or alarm.
Calibrate O
2
Monitor
c.
d.
a.
Ensure that the monitor reads 21% in
b.
room air. Verify that the low-O 2 alarm is enabled and functioning.
Reinstall the sensor in the circuit and flush
the breathing system with O 2 . Verify that the monitor now reads greater
than 90%.
Check Initial Status of Breathing System .
a.
Set the selector switch to “Bag” mode. b.
Check that the breathing circuit is
complete, undamaged, and unobstructed. c.
d.
Verify that CO 2 absorbent is adequate. Install the breathing circuit accessory
equipment (e.g., humidifier, positive end expiratory pressure [PEEP] valve) to be used during the procedure.
Perform Leak Check of Breathing System .
Set all gas flows to zero (or minimum).
Close the APL (pop-off) valve and occlude the
Y-piece. Pressurize the breathing system to about
30 cm H 2 O with an O 2 flush. Ensure that the pressure remains fixed for at
least 10 seconds. Open the APL (pop-off) valve and ensure that
the pressure decreases