Transcript Inhaled Anesthetic Delivery Systems

Inhaled Anesthetic
Delivery Systems
พญ.เพชรรัตน์ วิสุทธิเมธีกร
พ.บ., ป. ชั้นสูงสาขาวิสญ
ั ญีวิทยา, วว.(วิสญ
ั ญี)
ภาควิชาวิสญ
ั ญีวิทยา
วิทยาลัยแพทยศาสตร์กรุ งเทพมหานคร
และวชิรพยาบาล
Inhaled Anesthetic Delivery Systems
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Anesthesia machine
Vaporizers
Anesthetic breathing circuit
Ventilator
Scavenging system
Anesthesia Machine
เครื่ องดมยาสลบ
Vaporizers
ANESTHESIA MACHINES
Generic Anesthetic Machine
• The pressures within the anesthesia machine
can be divided into three circuits
– High-pressure
– Intermediate-pressure
– Low-pressure circuit
Gas supply
แหล่ งจ่ ายก๊ าซ
Pipeline
Cylinder
Pipeline supply
แหล่งจ่ายก๊าซหลัก
• primary gas source for the anesthesia
machine
• oxygen, nitrous oxide, and air
• "normal working pressure" 50 psi
• DISS (diameter index safety system)
Pipeline
Nuts
Nipples
Body Adaptors
Nut and Nipple
Combinations
Cylinder supply
แหล่งจ่ายก๊าซสารอง
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•
•
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reserve E cylinders
Color-coded
Pin Index Safety System (PISS)
high-pressure cylinder source
• pressure regulator
– oxygen 2200 psig to 45 psig
– nitrous oxide 745 psig to 45 psig
ขนาดและความจุของท่อออกซิ เจน ที่ความดัน 2200 Psig
ขนาด
เส้นผ่าศูนย์กลาง x สู ง
(นิ้ว)
D
E
F
G
H
4.5 X 17
4.5 X 26
5.5 X 36
8.5 X 51
9 X 51
ความจุ N2O เต็มที่ ความจุ O2 เต็มที่
745 Psig (L)
2200 Psig (L)
940
1590
13800
15800
360
622
1273
5259
6905
ค่าคงที่
0.28
3.14
Pin-Indexed Yoke Assemblies
Cylinder Valve Connections
Safety Devices for Oxygen Supply
Pressure Failure
• Oxygen Supply Failure Alarm
– oxygen supply pressure decreases to 30 psig
– activated within 5 seconds
• Second-Stage Pressure Regulator for
Oxygen
– set at between 12 and 19 psig
– supplies a constant pressure to the oxygen
flow control valve
Safety Devices for Oxygen Supply
Pressure Failure
• Fail-Safe Valves
– Pressure sensor's shut-off valve
– Oxygen failure protection device
(OFPD)
Pressure sensor's shut-off valve
A, The valve is open because the oxygen supply pressure is greater than
the threshold value of 20 psig.
B, The valve is closed because of inadequate oxygen pressure
The oxygen failure protection
device (OFPD)
OFPD responds proportionally to changes in oxygen supply pressure
Flow Meter Assemblies
Physical Principles of Conventional
Flow Meters
The clearance between the head of the float and the flow tube is known as the annular space.
It can be considered an equivalent to a circular channel of the same cross-sectional area.
Physical Principles of Conventional
Flow Meters
density (turbulent flow )
viscosity (laminar flow)
Flow Meter Assemblies
• Flow Control Valve
• Flow Meter Subassembly
– FLOW TUBES
• fine flow tube - 200 mL/min to 1 L/min
• coarse flow tube – 1 L/min to between 10 and 12
L/min
– INDICATOR FLOATS AND FLOAT STOPS
The flow meter sequence is a potential
cause of hypoxia
A and B, In the event of a flow meter leak, a potentially dangerous
arrangement exists when nitrous oxide is located in the downstream position.
C and D, The safest configuration exists when oxygen is located in the
downstream position
An oxygen leak from the flow tube can
produce a hypoxic mixture, regardless
of the arrangement of the flow tubes
Proportioning Systems
• Prevent delivery of a hypoxic mixture
• N2O and O2 are interfaced
mechanically or pneumatically
• Minimum O2 concentration at the
common gas outlet is between 23%
and 25%
N2O and O2 flow control valves are identical. A 14-tooth sprocket is attached to
the N2O flow control valve, and a 28-tooth sprocket is attached to the O2 flow
control valve. A chain links the sprockets. The combination of the mechanical
and pneumatic aspects of the system yields the final oxygen concentration. The
Datex-Ohmeda Link-25 proportioning system can be thought of as a system that
increases oxygen flow when necessary to prevent delivery of a fresh gas mixture
with an oxygen concentration of less than 25%
North American Dräger
Oxygen Ratio Monitor
Controller (ORMC)
The ORMC is composed of an O2
chamber, a N2O chamber, and a
N2Oslave control valve, all of which are
interconnected by a mobile horizontal
shaft. The pneumatic input into the
device is from the O2 and the N2O flow
meters. These flow meters have
resistors located downstream from the
flow control valves that create
backpressures directed to the O2 and
N2O chambers. The value of the O2 flow
tube's resistor is three to four times that
of the N2O flow tube's resistor, and the
relative value of these resistors
determines the value of the controlled
fresh gas concentration of O2. The
backpressure in the O2 and the N2O
chambers pushes against rubber
diaphragms attached to the mobile
horizontal shaft. Movement of the shaft
regulates the N2O slave control valve,
which feeds the N2Oflow control valve.
Oxygen Flush Valve
Oxygen Flush Valve
• Direct communication between the
oxygen high-pressure circuit and the
low-pressure circuit
• Delivers 100% oxygen at a rate of 35
to 75 L/min to the breathing circuit
• High pressure of 50 psig
Oxygen Flush Valve
• Several hazards
–Barotrauma
–Awareness
• dilutes the inhaled anesthetic
VAPORIZERS
• Vapor Pressure
• Latent Heat of Vaporization
– calories required to change 1 g of liquid into vapor
without a temperature change
• Specific Heat
– calories required to increase the temperature of 1 g
of a substance by 1°C.
• Thermal Conductivity
Vapor pressure versus temperature curves
for desflurane, isoflurane, halothane,
enflurane, and sevoflurane
The vapor pressure curve for desflurane is steeper and shifted to higher
vapor pressures compared with the curves for other contemporary inhaled
anesthetics.
Variable-bypass vaporizer
Ohmeda Tec-type vaporizer. At high temperatures, the vapor pressure inside the
vaporizing chamber is high. To compensate for the increased vapor pressure, the
bimetallic strip of the temperature-compensating valve leans to the right, allowing more
flow through the bypass chamber and less flow through the vaporizing chamber. The net
effect is a constant vaporizer output. In a cold operating room environment, the vapor
pressure inside the vaporizing chamber decreases. To compensate for the decreased
vapor pressure, the bimetallic strip swings to the left, causing more flow through the
vaporizing chamber and less through the bypass chamber. The net effect is a constant
vaporizer output
North American Dräger Vapor 19.1 vaporizer. Automatic
temperature-compensating mechanisms in bypass chambers
maintain a constant vaporizer output with varying temperatures.
An expansion element directs a greater proportion of gas flow
through the bypass chamber as temperature increases.
Tec 6 desflurane vaporizer. The vaporizer has two independent gas circuits arranged in parallel.
The fresh gas circuit is shown in red, and the vapor circuit is shown in white. The fresh gas
from the flow meters enters at the fresh gas inlet, passes through a fixed restrictor (R1), and
exits at the vaporizer gas outlet. The vapor circuit originates at the desflurane sump, which is
electrically heated and thermostatically controlled to 39°C, a temperature well above
desflurane's boiling point. The heated sump assembly serves as a reservoir of desflurane vapor.
Downstream from the sump is the shut-off valve. After the vaporizer warms up, the shut-off
valve fully opens when the concentration control valve is turned to the on position. A pressureregulating valve located downstream from the shut-off valve downregulates the pressure. The
operator controls desflurane output by adjusting the concentration control valve (R2), which is
a variable restrictor
ANESTHETIC CIRCUITS
• Deliver oxygen and anesthetic gases to the
patient
• Eliminate carbon dioxide
– adequate inflow of fresh gas
– carbon dioxide absorbent
• Semiclosed rebreathing circuits and the circle
system.
Mapleson Systems
Mapleson Systems
Factors influence carbon dioxide rebreathing
(1) the fresh gas inflow rate
(2) the minute ventilation
(3) the mode of ventilation (spontaneous or controlled),
(4) the tidal volume
(5) the respiratory rate
(6) the inspiratory to expiratory ratio
(7) the duration of the expiratory pause
(8) the peak inspiratory flow rate
(9) the volume of the reservoir tube
(10)the volume of the breathing bag
(11)ventilation by mask
(12)ventilation through an endotracheal tube
(13)the carbon dioxide sampling site.
Mapleson Systems
• Prevention of rebreathing, during spontaneous
ventilation: A > DFE > CB.
• During controlled ventilation, DFE > BC > A
• A, B, and C systems are rarely used today
The Bain circuit
• a modification of the Mapleson D system
• spontaneous and controlled ventilation.
The Bain circuit
• Exhaled gases in the outer reservoir tubing add
warmth to inspired fresh gases
• unrecognized disconnection or kinking of the
inner fresh gas hose
• The fresh gas inflow rate necessary to prevent
rebreathing is 2.5 times the minute ventilation
Components of the Circle system
APL, adjustable pressure limiting; B, reservoir bag; V, ventilator
Circle Breathing System
• A circle system can be semiopen, semiclosed,
or closed, depending on the amount of fresh
gas inflow
– Semiopen system has no rebreathing and requires a
very high flow of fresh gas
– Semiclosed system is associated with rebreathing
of gases
– Closed system is one in which the inflow gas
exactly matches that being consumed by the
patient
Circle Breathing System
Components of The circle system
(1) a fresh gas inflow source
(2) inspiratory and expiratory unidirectional valves
(3) inspiratory and expiratory corrugated tubes (4) a
Y-piece connector
(5) an overflow or pop-off valve, referred to as the
APL valve
(6) a reservoir bag
(7) a canister containing a carbon dioxide absorbent
Circle Breathing System
•
Rules to prevent rebreathing of carbon
dioxide in a traditional circle system
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Unidirectional valves must be located between
the patient and the reservoir bag on the
inspiratory and expiratory limbs of the circuit.
The fresh gas inflow cannot enter the circuit
between the expiratory valve and the patient.
The overflow (pop-off) valve cannot be located
between the patient and the inspiratory valve.
Circle Breathing System
• Advantages
– stability of inspired gas concentrations,
– conservation of respiratory moisture and
heat,
– prevention of operating room pollution
• Disadvantage
– complex design
ABSORPTION
• Lack of toxicity with common anesthetics, low
resistance to airflow, low cost, ease of
handling, and efficiency
• 3 formulations
– soda lime
– Baralyme
– calcium hydroxide lime (Amsorb)
ABSORPTION
•
Soda lime (most commonly used )
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–
•
80% calcium hydroxide, 15% water, 4% sodium
hydroxide, and 1% potassium hydroxide (an
activator)
silica
The equations
1) CO2 + H2 O ⇔ H2 CO3
2) H2 CO3 + 2NaOH (KOH) ⇔ Na2 CO3 (K2
CO3 ) + 2H2 O + Heat
3) Na2 CO3 (K2 CO3 ) + Ca(OH)2 ⇔ CaCO3 +
2NaOH (KOH)
ABSORPTION
• Baralyme
– 20% barium hydroxide and 80% calcium
hydroxide
• Calcium hydroxide lime
– lack of sodium and potassium hydroxides
– carbon monoxide and the nephrotoxic substance
known as compound A
ABSORPTION
• Absorptive Capacity
– soda lime is 26 L of carbon dioxide per 100 g of
absorbent
– calcium hydroxide lime has been reported at 10.2
L per 100 g of absorbent
• size of the absorptive granules
– surface area
– air flow resistance
ABSORPTION
• Indicators
– Ethyl violet :pH indicator added to soda lime and
Baralyme
– from colorless to violet when the pH of the
absorbent decreases as a result of carbon dioxide
absorption
– Fluorescent lights can deactivate the dye
ABSORPTION
• Sevoflurane interaction with carbon dioxide absorbents
– Compound A
• fluoromethyl-2,2-difluoro-1-(trifluoromethyl)vinyl ether
• Factors
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–
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low-flow or closed-circuit
concentrations of sevoflurane
higher absorbent temperatures
fresh absorbent
Baralyme dehydration increases the concentration of
compound A, and soda lime dehydration decreases the
concentration of compound A
ABSORPTION
• Desiccated soda lime and Baralyme
– carbon monoxide
– after disuse of an absorber for at least 2 days,
especially over a weekend
ABSORPTION
•
Several factors appear to increase the
production of CO and carboxyhemoglobin:
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–
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Anesthetic agents (desflurane ≥ enflurane >
isoflurane ≥ halothane = sevoflurane)
The absorbent dryness (completely dry absorbent
produces more carbon monoxide than hydrated
absorbent)
The type of absorbent (at a given water content,
Baralyme produces more carbon monoxide than
does soda lime)
ABSORPTION
• Several factors appear to increase the
production of CO and carboxyhemoglobin:
– The temperature (a higher temperature increases
carbon monoxide production)
– The anesthetic concentration (more carbon
monoxide is produced from higher anesthetic
concentrations)
– Low fresh gas flow rates
– Reduced animal size per 100 g of absorbent
ABSORPTION
•
Interventions have been suggested to reduce
the incidence of carbon monoxide exposure
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Educating anesthesia personnel regarding the cause
of carbon monoxide production
Turning off the anesthesia machine at the
conclusion of the last case of the day to eliminate
fresh gas flow, which dries the absorbent
Changing carbon dioxide absorbent if fresh gas
was found flowing during the morning machine
check
ABSORPTION
• Interventions have been suggested to reduce
the incidence of carbon monoxide exposure
– Rehydrating desiccated absorbent by adding water
to the absorbent
– Changing the chemical composition of soda lime
(e.g., Dragersorb 800 plus, Sofnolime, Spherasorb)
to reduce or eliminate potassium hydroxide
– Using absorbent materials such as calcium
hydroxide lime that are free of sodium and
potassium hydroxides
Inspiratory (A) and expiratory (B) phases of gas
flow in a traditional circle system with an
ascending bellows anesthesia ventilator. The
bellows physically separates the driving-gas
circuit from the patient's gas circuit. The drivinggas circuit is located outside the bellows, and the
patient's gas circuit is inside the bellows. During
the inspiratory phase (A), the driving gas enters
the bellows chamber, causing the pressure within
it to increase. This causes the ventilator's relief
valve to close, preventing anesthetic gas from
escaping into the scavenging system, and the
bellows to compress, delivering the anesthetic
gas within the bellows to the patient's lungs.
During the expiratory phase (B), the driving gas
exits the bellows chamber. The pressure within
the bellows chamber and the pilot line declines
to zero, causing the mushroom portion of the
ventilator's relief valve to open. Gas exhaled by
the patient fills the bellows before any
scavenging occurs because a weighted ball is
incorporated into the base of the ventilator's
relief valve. Scavenging happens only during the
expiratory phase, because the ventilator's relief
valve is open only during expiration
Inspiratory (A)
and expiratory (B)
phases of gas flow
in a Dräger-type
circle system with
a piston ventilator
and fresh gas
decoupling. NPR
valve, negativepressure relief
valve.
SCAVENGING SYSTEMS
• The collection and the subsequent removal of
vented gases from the operating room
• Components
(1) the gas-collecting assembly
(2) the transfer means
(3) the scavenging interface
(4) the gas-disposal assembly tubing
(5) an active or passive gas-disposal assembly
Components of a scavenging system. APL valve, adjustable
pressure limiting valve
Each of the two open scavenging interfaces requires an active disposal system. An
open canister provides reservoir capacity. Gas enters the system at the top of the
canister and travels through a narrow inner tube to the canister base. Gases are stored
in the reservoir between breaths. Relief of positive and negative pressure is provided
by holes in the top of the canister. A and B, The open interface shown in A differs
somewhat from the one shown in B. The operator can regulate the vacuum by
adjusting the vacuum control valve shown in B. APL, adjustable pressure limiting
valve
Closed scavenging interfaces.
Interface used with a passive disposal system (left).
Interface used with an active system (right)
Anesthesia Apparatus Checkout
Recommendations
EMERGENCY VENTILATION
EQUIPMENT
1. Verify Backup Ventilation Equipment Is
Available and Functioning
HIGH-PRESSURE SYSTEM
2. Check Oxygen Cylinder Supply
– Open O2 cylinder and verify that it is at least half
full (about 1000 psi).
– Close cylinder.
3. Check Central Pipeline Supplies
– Check that hoses are connected and that pipeline
gauges read about 50 psi
LOW-PRESSURE SYSTEM
4. Check Initial Status of the Low-Pressure
System
–
Close flow control valves, and turn vaporizers
off.
–
Check the fill level, and tighten the vaporizers'
filler caps
LOW-PRESSURE SYSTEM
5. Perform a Leak Check of the Machine's 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 fully collapsed.
–
–
Verify bulb stays fully collapsed for at least 10 seconds.
Open one vaporizer at a time, and repeat steps c and d
above.
–
Remove the suction bulb, and reconnect the frésh gas
hose.
LOW-PRESSURE SYSTEM
6. Turn on the Machine's Master Switch and
All Other Necessary Electrical Equipment.
7. Test Flow Meters
– Adjust flow of all gases through their full
range, checking for smooth operation of
floats and undamaged flow tubes.
– Attempt to create a hypoxic O2 /N2 O
mixture, and verify correct changes in the
flow and/or alarms.
SCAVENGING SYSTEM
8. Adjust and Check the Scavenging System
– Ensure proper connections between the scavenging system
and both the adjustable pressure limiting (APL) (pop-off) valve
and the ventilator's relief valve.
– Adjust the waste gas vacuum (if possible).
– Fully open the APL valve and occlude the Y-piece.
– With minimum O2 flow, allow the scavenger reservoir bag to
collapse completely, and verify that the absorber pressure
gauge reads about zero.
– With the O2 flush activated, allow the scavenger reservoir bag
to distend fully, and then verify that absorber pressure gauge
reads <10 cm H2 O.
BREATHING SYSTEM
9. Calibrate the O2 Monitor
– Ensure the monitor reads 21% in room air.
– Verify that the low O2 alarm is enabled and
functioning.
– Reinstall the sensor in the circuit, and flush the
breathing system with O2 .
– Verify that monitor now reads greater than 90%
BREATHING SYSTEM
10. Check Initial Status of Breathing System
– Set the selector switch to Bag mode.
– Check that the breathing circuit is complete,
undamaged, and unobstructed.
– Verify that the carbon dioxide absorbent is
adequate.
– Install the breathing circuit accessory equipment
(e.g., humidifier, PEEP valve) to be used during
the case.
BREATHING SYSTEM
11. Perform a Leak Check of the Breathing
System
– Set all gas flows to zero (or minimum).
– Close the APL (pop-off) valve, and occlude the Ypiece.
– Pressurize the breathing system to about 30 cm H2
O with an O2 flush.
– Ensure that pressure remains fixed for at least 10
seconds.
– Open the APL (pop-off) valve, and ensure that the
pressure decreases.
MANUAL AND AUTOMATIC
VENTILATION SYSTEMS
12. Test the Ventilation Systems and Unidirectional Valves
– Place a second breathing bag on the Y-piece.
– Set appropriate ventilator parameters for the next patient.
– Switch to automatic ventilation mode (i.e., Ventilator).
– Turn the ventilator ON, and fill the bellows and breathing bag
with an O2 flush.
– Set the O2 flow to minimum and other gas flows to zero.
– Verify that the bellows deliver an appropriate tidal volume
during inspiration and that the bellows fill completely during
expiration.
MANUAL AND AUTOMATIC
VENTILATION SYSTEMS
12. Test the Ventilation Systems and Unidirectional
Valves
– Set the fresh gas flow to about 5 L/min.
– Verify that the ventilator's bellows and simulated lungs fill
and empty appropriately without sustained pressure at end
expiration.
– Check for proper action of unidirectional valves.
– Exercise breathing circuit accessories to ensure proper
function.
– Turn the ventilator off, and switch to manual ventilation
mode (i.e., Bag/APL).
– Ventilate manually, and ensure inflation and deflation of
artificial lungs and appropriate feel of system resistance and
compliance.
– Remove second breathing bag from the Y-piece.
MONITORS
13. Check, Calibrate, and/or Set Alarm Limits of
all Monitors
– Capnometer
– Oxygen analyzer
– Pressure monitor with alarms for high and low
airway pressure
– Pulse oximeter
– Respiratory volume monitor (i.e., spirometer)