Inhaled Anesthetic Delivery Systems

1
Inhaled Anesthetic Delivery Systems

• ??.????????? ?????????????
• ?.?., ?. ???????????????????????, ??.(???????)
• ???????????????????
• ???????????????????????????????
• ?????????????

2
Inhaled Anesthetic Delivery Systems

• Anesthesia machine
• Vaporizers
• Anesthetic breathing circuit
• Ventilator
• Scavenging system

3
Anesthesia Machine??????????????
4
Vaporizers
5
ANESTHESIA MACHINES
6
Generic Anesthetic Machine

• The pressures within the anesthesia machine can
  be divided into three circuits
• High-pressure
• Intermediate-pressure
• Low-pressure circuit

7
(No Transcript)
8
Gas supply?????????????
Pipeline
Cylinder
9
Pipeline supply?????????????????

• primary gas source for the anesthesia machine
• oxygen, nitrous oxide, and air
• "normal working pressure" 50 psi
• DISS (diameter index safety system)

10
Pipeline
11
Nuts
Nipples
Body Adaptors
Nut and Nipple Combinations
12
Cylinder supply??????????????????

• 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

13
??????????????????????????? ?????????? 2200 Psig
???? ???????????????? x ??? (????) ?????? N2O ??????? 745 Psig (L) ?????? O2 ??????? 2200 Psig (L) ????????
D E F G H 4.5 X 17 4.5 X 26 5.5 X 36 8.5 X 51 9 X 51 940 1590 - 13800 15800 360 622 1273 5259 6905 0.28 3.14
14
Pin-Indexed Yoke Assemblies
Cylinder Valve Connections
15
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

16
Safety Devices for Oxygen Supply Pressure Failure

• Fail-Safe Valves
• Pressure sensor's shut-off valve
• Oxygen failure protection device (OFPD)

17
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
18
The oxygen failure protection device (OFPD)
OFPD responds proportionally to changes in oxygen
supply pressure
19
Flow Meter Assemblies
20
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.
21
Physical Principles of Conventional Flow Meters
density (turbulent flow )
viscosity (laminar flow)
22
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

23
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
24
An oxygen leak from the flow tube can produce a
hypoxic mixture, regardless of the arrangement of
the flow tubes
25
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

26
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
27
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.
28
Oxygen Flush Valve
29
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

30
Oxygen Flush Valve

• Several hazards
• Barotrauma
• Awareness
• dilutes the inhaled anesthetic

31
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 1C.
• Thermal Conductivity

32
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.
33
Variable-bypass vaporizer
34
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
35
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.
36
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 39C, 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
pressure-regulating 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
37
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.

38
Mapleson Systems
39
Mapleson Systems

• Factors influence carbon dioxide rebreathing
• the fresh gas inflow rate
• the minute ventilation
• the mode of ventilation (spontaneous or
  controlled),
• the tidal volume
• the respiratory rate
• the inspiratory to expiratory ratio
• the duration of the expiratory pause
• the peak inspiratory flow rate
• the volume of the reservoir tube
• the volume of the breathing bag
• ventilation by mask
• ventilation through an endotracheal tube
• the carbon dioxide sampling site.

40
Mapleson Systems

• Prevention of rebreathing, during spontaneous
  ventilation A gt DFE gt CB.
• During controlled ventilation, DFE gt BC gt A
• A, B, and C systems are rarely used today

41
The Bain circuit

• a modification of the Mapleson D system
• spontaneous and controlled ventilation.

42
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

43
Components of the Circle system
APL, adjustable pressure limiting B, reservoir
bag V, ventilator
44
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

45
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

46
Circle Breathing System

• Rules to prevent rebreathing of carbon dioxide
  in a traditional circle system
• 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.

47
Circle Breathing System

• Advantages
• stability of inspired gas concentrations,
• conservation of respiratory moisture and heat,
• prevention of operating room pollution
• Disadvantage
• complex design

48
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)

49
ABSORPTION

• Soda lime (most commonly used )
• 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)

50
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

51
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

52
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

53
ABSORPTION

• Sevoflurane interaction with carbon dioxide
  absorbents
• Compound A
• fluoromethyl-2,2-difluoro-1-(trifluoromethyl)vinyl
  ether
• Factors
• 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

54
ABSORPTION

• Desiccated soda lime and Baralyme
• carbon monoxide
• after disuse of an absorber for at least 2 days,
  especially over a weekend

55
ABSORPTION

• Several factors appear to increase the production
  of CO and carboxyhemoglobin
• Anesthetic agents (desflurane enflurane gt
  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)

56
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

57
ABSORPTION

• Interventions have been suggested to reduce the
  incidence of carbon monoxide exposure
• 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

58
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

59
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
driving-gas 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
60
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,
negative-pressure relief valve.
61
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

62
Components of a scavenging system. APL valve,
adjustable pressure limiting valve
63
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
64
Closed scavenging interfaces. Interface used
with a passive disposal system (left). Interface
used with an active system (right)
65
Anesthesia Apparatus Checkout Recommendations
66
EMERGENCY VENTILATION EQUIPMENT

• 1. Verify Backup Ventilation Equipment Is
  Available and Functioning

67
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

68
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

69
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.

70
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.

71
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 lt10 cm H2 O.

72
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

73
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.

74
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
  Y-piece.
• 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.

75
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.

76
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.

77
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)