4. anesthetic equipment
TRANSCRIPT
1Copyright © 2011, 2003, 2000, 1994 by Mosby, Inc., an affiliate of Elsevier Inc.
Anesthetic Equipment
The purpose, function, use, and maintenance of machines and equipment used to administer
inhalation anesthetics
Chapter 4
2Copyright © 2011, 2003, 2000, 1994 by Mosby, Inc., an affiliate of Elsevier Inc.
Endotracheal Tubes (ET Tubes)
Flexible tube placed in the trachea Delivers anesthetic gases directly from the
anesthetic machine to the lungs Advantages
Open airway Less anatomical dead space Precision administration of anesthetic agent Prevents pulmonary aspiration Responds to respiratory emergencies Monitors respirations
3Copyright © 2011, 2003, 2000, 1994 by Mosby, Inc., an affiliate of Elsevier Inc.
Types of Endotracheal Tubes
Murphy tubes Beveled end and side holes Possible cuff
Cole tubes No side hole or cuff Abrupt decrease in diameter of the tube Used in birds and reptiles
4Copyright © 2011, 2003, 2000, 1994 by Mosby, Inc., an affiliate of Elsevier Inc.
Types of Endotracheal Tubes (Cont’d)
5Copyright © 2011, 2003, 2000, 1994 by Mosby, Inc., an affiliate of Elsevier Inc.
Properties of Endotracheal Tubes
Materials Polyvinyl chloride: clear and stiffer Red rubber: flexible and less traumatic, absorbent, and may
kink or collapse Silicone: pliable, strong, less irritating, resist collapse
Length Standard lengths Scale marks distance from patient end (centimeters)
Size Measured by internal diameter (ID) Range from 1 mm to 30 mm
6Copyright © 2011, 2003, 2000, 1994 by Mosby, Inc., an affiliate of Elsevier Inc.
Parts of the Endotracheal Tube
Patient end Machine end Connector Cuff Pilot balloon and valve
7Copyright © 2011, 2003, 2000, 1994 by Mosby, Inc., an affiliate of Elsevier Inc.
Parts of the Endotracheal Tube (Cont’d)
8Copyright © 2011, 2003, 2000, 1994 by Mosby, Inc., an affiliate of Elsevier Inc.
Laryngoscope
Used to increase the visibility of the larynx while placing an ET tube
Parts Handle containing batteries Blade to depress tongue and epiglottis Light source to illuminate the throat
Sizes Small animal 0 to 5; large animal up to 18-inch blade
Types Miller blades McIntosh blades
9Copyright © 2011, 2003, 2000, 1994 by Mosby, Inc., an affiliate of Elsevier Inc.
Laryngoscopes (Cont’d)
10Copyright © 2011, 2003, 2000, 1994 by Mosby, Inc., an affiliate of Elsevier Inc.
Masks
Cone-shaped devices used to administer oxygen and anesthetic gases to nonintubated patients
Used for induction and maintenance of anesthesia in very small animals
Plastic or rubber Variety of diameters and lengths Rubber gasket
11Copyright © 2011, 2003, 2000, 1994 by Mosby, Inc., an affiliate of Elsevier Inc.
Anesthetic Mask
12Copyright © 2011, 2003, 2000, 1994 by Mosby, Inc., an affiliate of Elsevier Inc.
Anesthetic Chambers
Clear, aquarium-like boxes used to induce general anesthesia
Used in feral, vicious, or intractable animals to reduce stress
Acrylic or Perspex Removable top with two ports Cannot monitor patient closely
13Copyright © 2011, 2003, 2000, 1994 by Mosby, Inc., an affiliate of Elsevier Inc.
Anesthetic Chamber (Cont’d)
14Copyright © 2011, 2003, 2000, 1994 by Mosby, Inc., an affiliate of Elsevier Inc.
Anesthetic Machines
Used to deliver precise amounts of oxygen and volatile anesthetic under controlled conditions
15Copyright © 2011, 2003, 2000, 1994 by Mosby, Inc., an affiliate of Elsevier Inc.
Principles of Operation of Anesthetic Machines
Carrier gas: oxygen or nitrous oxide Liquid inhalant anesthetic: to be vaporized Mixed gases delivered to patient Exhaled gases removed from patient:
scavenging system or recirculated
16Copyright © 2011, 2003, 2000, 1994 by Mosby, Inc., an affiliate of Elsevier Inc.
Components of the Anesthetic Machine
Compressed gas supply Anesthetic vaporizer (precision or
nonprecision; VOC or VIC) Breathing circuit (rebreathing or
nonrebreathing) Scavenging system
17Copyright © 2011, 2003, 2000, 1994 by Mosby, Inc., an affiliate of Elsevier Inc.
Components of the Anesthetic Machine (Cont’d)
18Copyright © 2011, 2003, 2000, 1994 by Mosby, Inc., an affiliate of Elsevier Inc.
Components of the Anesthetic Machine (Cont’d)
19Copyright © 2011, 2003, 2000, 1994 by Mosby, Inc., an affiliate of Elsevier Inc.
Compressed Gas Supply
Oxygen Used to increase inspired air to at least 30% oxygen Level necessary to maintain cellular metabolism under
anesthesia Used to carry vaporized anesthetic to patient
Cylinders (tanks) Contain large volume of gas under high pressure E tanks (small), attached directly to anesthetic machine H tanks (large), attached remotely to anesthetic machine
20Copyright © 2011, 2003, 2000, 1994 by Mosby, Inc., an affiliate of Elsevier Inc.
Compressed Gas Supply (Cont’d)
Control valve (outlet port) Located on top of the tank Left loose (open), right tight (closed)
Pressure-reducing valve Reduces outgoing pressure to a usable level
21Copyright © 2011, 2003, 2000, 1994 by Mosby, Inc., an affiliate of Elsevier Inc.
Compressed Gas Cylinders
22Copyright © 2011, 2003, 2000, 1994 by Mosby, Inc., an affiliate of Elsevier Inc.
Size H Compressed Gas Cylinder
23Copyright © 2011, 2003, 2000, 1994 by Mosby, Inc., an affiliate of Elsevier Inc.
Safety Issues with Compressed Gas
Combustibility Yoke attachment High-pressure release Storage Color coding
Oxygen: green (United States) or white (Canada and Europe)
Nitrous oxide: blue Medical air: yellow (United States) or white and
black (Canada and Europe) Carbon dioxide: gray
24Copyright © 2011, 2003, 2000, 1994 by Mosby, Inc., an affiliate of Elsevier Inc.
Carbon Dioxide and Oxygen Tanks
25Copyright © 2011, 2003, 2000, 1994 by Mosby, Inc., an affiliate of Elsevier Inc.
Tank Pressure Gauge
Indicates the pressure of gas remaining in a compressed gas cylinder Measured in pounds per square inch (psi) (United
States) or kilopascals (kPa) (Canada and Europe) Determine the number of liters remaining in a
tank Label tanks: full, in service, or empty Keep backup full tank on the machine
26Copyright © 2011, 2003, 2000, 1994 by Mosby, Inc., an affiliate of Elsevier Inc.
Labeling Cylinders
27Copyright © 2011, 2003, 2000, 1994 by Mosby, Inc., an affiliate of Elsevier Inc.
Pressure-Reducing Valve (Pressure Regulator)
Reduces gas pressure to a constant 40-50 psi (275-345 kPa)
Color coded
28Copyright © 2011, 2003, 2000, 1994 by Mosby, Inc., an affiliate of Elsevier Inc.
Line Pressure Gauge
Indicates pressure in the gas line between the pressure-reducing valve and flowmeter
Should read 40-50 psi after the oxygen tank is opened
After turning the tank off, use the oxygen flush valve to evacuate line pressure until the gauge reads 0 psi.
29Copyright © 2011, 2003, 2000, 1994 by Mosby, Inc., an affiliate of Elsevier Inc.
Flowmeter
Indicates gas flow expressed in liters per minute (L/min)
Reduces pressure of gas to 15 psi (~100 kPa)
Specific for each type of gas Flow rate is controlled by anesthetist
30Copyright © 2011, 2003, 2000, 1994 by Mosby, Inc., an affiliate of Elsevier Inc.
Flowmeters (Cont’d)
31Copyright © 2011, 2003, 2000, 1994 by Mosby, Inc., an affiliate of Elsevier Inc.
Oxygen Flush Valve
Delivers a short, large burst of pure oxygen directly into the rebreathing circuit or common gas outlet
Bypasses vaporizer and flowmeter Used to refill breathing bag, to deliver pure
oxygen to a patient, or to dilute the anesthetic gas remaining in the circuit at the end of anesthesia
32Copyright © 2011, 2003, 2000, 1994 by Mosby, Inc., an affiliate of Elsevier Inc.
Vaporizer Inlet Port
Where carrier gas (usually oxygen) enters a vaporizer from the flowmeter
33Copyright © 2011, 2003, 2000, 1994 by Mosby, Inc., an affiliate of Elsevier Inc.
Anesthetic Vaporizer
Converts liquid anesthetic agent to a gaseous state
Adds a controlled amount of vaporized agent to the carrier gas
Gas mixture leaves vaporizer through the outlet port
Mixture is known as fresh gas and enters the breathing circuit
Variable-bypass, flow-over vaporizers
34Copyright © 2011, 2003, 2000, 1994 by Mosby, Inc., an affiliate of Elsevier Inc.
Types of Anesthetic Vaporizers
Nonprecision vaporizer Used to deliver low vapor pressure anesthetics Rarely used
Precision vaporizers Used to deliver a precise amount of anesthetic to
the patient Expressed as a percent of total gases leaving the
vaporizer Used to deliver high-vapor pressure anesthetics Anesthetist controlled
35Copyright © 2011, 2003, 2000, 1994 by Mosby, Inc., an affiliate of Elsevier Inc.
VOC vs. VIC Vaporizers
VOC = Vaporizer-out-of-circuit Not localized within
the breathing circuit Oxygen from the
flowmeter enters the vaporizer prior to entering the breathing circuit
Precision vaporizers High resistance gas
flow
VIC = Vaporizer-in-circuit Oxygen enters the
breathing circuit from the flowmeter
Exhaled gases pass through the vaporizer
Nonprecision vaporizers
Low-resistance gas flow
36Copyright © 2011, 2003, 2000, 1994 by Mosby, Inc., an affiliate of Elsevier Inc.
Factors That Affect Vaporizer Output
Vaporizer setting The primary determinant of output in both
compensated and noncompensated vaporizers Controlled by anesthetist
Carrier gas flow influences the concentration of anesthetic in breathing circuit in both compensated and noncompensated vaporizers
37Copyright © 2011, 2003, 2000, 1994 by Mosby, Inc., an affiliate of Elsevier Inc.
Factors That Affect Vaporizer Output (Cont’d)
Factors that affect output of noncompensated vaporizers Temperature
• Ambient room temperature • Temperature of carrier gas
Carrier gas flow rate Respiratory rate and depth (nonprecision only) Back pressure
• Due to manual ventilation or activation of oxygen flush valve
38Copyright © 2011, 2003, 2000, 1994 by Mosby, Inc., an affiliate of Elsevier Inc.
Use of Vaporizers
Specific-use vaporizers are color coded Isoflurane = purple Sevoflurane = yellow Halothane = red Desflurane = blue
Induction and maintenance rates Isoflurane = 3-5% induction; 1.5-2.5% maintenance Sevoflurane = 4-6% induction; 2-4.5% maintenance Desflurane = 10-15% induction; 8-12% maintenance
39Copyright © 2011, 2003, 2000, 1994 by Mosby, Inc., an affiliate of Elsevier Inc.
Precision Vaporizer
40Copyright © 2011, 2003, 2000, 1994 by Mosby, Inc., an affiliate of Elsevier Inc.
Safety with Vaporizers
Leakage Human exposure After using a non-rebreathing circuit, always
be sure to reattach the connector of the rebreathing circuit to the outlet port or common gas outlet
41Copyright © 2011, 2003, 2000, 1994 by Mosby, Inc., an affiliate of Elsevier Inc.
Vaporizer Outlet Port and Common Gas Outlet
Vaporizer outlet port Oxygen/anesthetic exits the vaporizer Connected to the common gas outlet or directly
into the breathing circuit Common gas outlet
Fresh gas outlet Connected to the vaporizer outlet port and
breathing circuit
42Copyright © 2011, 2003, 2000, 1994 by Mosby, Inc., an affiliate of Elsevier Inc.
Fresh Gas Inlet
Where carrier and anesthetic gases enter the breathing circuit
Connected to the vaporizer outlet port or common gas outlet
43Copyright © 2011, 2003, 2000, 1994 by Mosby, Inc., an affiliate of Elsevier Inc.
Breathing Circuit
Carries anesthetic and oxygen from the fresh gas inlet to the patient
Conveys expired gases away from the patient Rebreathing or non-rebreathing
44Copyright © 2011, 2003, 2000, 1994 by Mosby, Inc., an affiliate of Elsevier Inc.
Rebreathing System
Circle systems Used on all but very small animals Carbon dioxide removed from exhaled air Exhaled air is inhaled again with added
oxygen and anesthetic
45Copyright © 2011, 2003, 2000, 1994 by Mosby, Inc., an affiliate of Elsevier Inc.
Rebreathing System (Cont’d)
Air flow: Inhalation unidirectional valve → Inhalation tube → Animal → Exhalation tube → Exhalation unidirectional valve → Carbon dioxide absorber canister → past reservoir bag → Pop-off valve → Pressure manometer → Inhalation unidirectional valve
46Copyright © 2011, 2003, 2000, 1994 by Mosby, Inc., an affiliate of Elsevier Inc.
Rebreathing System (Cont’d)
Closed rebreathing system Total system Pop-off valve is nearly or completely closed and
oxygen flow is low Used mostly in large animal anesthesia
Semiclosed rebreathing system Partial system Pop-off valve is open and oxygen flow is high Excess air is released into scavenging system Most common configuration
47Copyright © 2011, 2003, 2000, 1994 by Mosby, Inc., an affiliate of Elsevier Inc.
Breathing Systems
48Copyright © 2011, 2003, 2000, 1994 by Mosby, Inc., an affiliate of Elsevier Inc.
Parts of a Rebreathing System
Unidirectional valves Reservoir bag Pop-off (pressure relief) valve Carbon dioxide absorber canister Air intake valve Pressure manometer Corrugated breathing tubes Y-piece
49Copyright © 2011, 2003, 2000, 1994 by Mosby, Inc., an affiliate of Elsevier Inc.
Parts of a Rebreathing System (Cont’d)
50Copyright © 2011, 2003, 2000, 1994 by Mosby, Inc., an affiliate of Elsevier Inc.
Unidirectional Valves
Control the direction of gas flow Inspiratory (inhalation) Expiratory (exhalation) Open and close as patient breathes Monitor respiratory rate and depth
51Copyright © 2011, 2003, 2000, 1994 by Mosby, Inc., an affiliate of Elsevier Inc.
Pop-off Valve
Also known as the exhaust valve, adjustable pressure limiting valve, or overflow valve Allows excess carrier and anesthetic gases to exit
the breathing circuit and enter the scavenging system
Prevents excessive pressure or volume of gases in the circuit
Closed when manually ventilating a patient Controlled by anesthetist
52Copyright © 2011, 2003, 2000, 1994 by Mosby, Inc., an affiliate of Elsevier Inc.
Pop-off Valve (Cont’d)
53Copyright © 2011, 2003, 2000, 1994 by Mosby, Inc., an affiliate of Elsevier Inc.
Reservoir Bag (Rebreathing Bag)
Flexible air storage reservoir Indicator of respiratory rate and depth Confirms proper endotracheal tube
placement Allows delivery of anesthetic gases or pure
oxygen to patient Manual ventilation or “bagging”
Various sizes: 500 mL to 30 L Controlled by anesthetist
54Copyright © 2011, 2003, 2000, 1994 by Mosby, Inc., an affiliate of Elsevier Inc.
Reservoir Bags
55Copyright © 2011, 2003, 2000, 1994 by Mosby, Inc., an affiliate of Elsevier Inc.
Manual Ventilation (Bagging)
Minimize atelectasis Ventilate every 5-10 minutes
Force fresh gas into alveoli to normalize gas exchange
Normalize respiratory rate
56Copyright © 2011, 2003, 2000, 1994 by Mosby, Inc., an affiliate of Elsevier Inc.
Carbon Dioxide Absorber Canister
Contains absorbent granules Primary absorbent ingredient: calcium hydroxide Also: water, sodium hydroxide, potassium
hydroxide, calcium chloride, calcium sulfate Granules react with carbon dioxide to form
calcium carbonate Heat and water produced Becomes more acidic with more use Granules must be replaced when depleted
57Copyright © 2011, 2003, 2000, 1994 by Mosby, Inc., an affiliate of Elsevier Inc.
Carbon Dioxide Absorber Canister (Cont’d)
58Copyright © 2011, 2003, 2000, 1994 by Mosby, Inc., an affiliate of Elsevier Inc.
Pressure Manometer
Indicates the pressure of gases within the breathing circuit Expressed as centimeters of water (cm H2O),
millimeters of mercury (mm Hg), or kPa Used when manually ventilating (bagging) the
patient to prevent excessive pressure in the lungs
Monitored by the anesthetist
59Copyright © 2011, 2003, 2000, 1994 by Mosby, Inc., an affiliate of Elsevier Inc.
Pressure Manometer (Cont’d)
60Copyright © 2011, 2003, 2000, 1994 by Mosby, Inc., an affiliate of Elsevier Inc.
Air Intake Valve
Negative pressure relief valve Admits room air into the circuit if negative
pressure is detected in the breathing circuit May be separate or incorporated into inspiratory
unidirectional valve or pop-off valve Negative pressure is indicated by a collapsed
reservoir bag Patient will develop hypoxemia
61Copyright © 2011, 2003, 2000, 1994 by Mosby, Inc., an affiliate of Elsevier Inc.
Breathing Tubes and Y-Piece
Breathing tubes Corrugated breathing tubes or inspiratory and
expiratory breathing tubes Carry anesthetic gases to and from the patient Connected to unidirectional valve and Y-piece Three sizes: 50 mm, 22 mm, and 15 mm in
diameter Y-piece
Connects breathing tubes Connects to mask or endotracheal tube
62Copyright © 2011, 2003, 2000, 1994 by Mosby, Inc., an affiliate of Elsevier Inc.
Breathing Tubes
63Copyright © 2011, 2003, 2000, 1994 by Mosby, Inc., an affiliate of Elsevier Inc.
Non-rebreathing Systems
Semiopen system Used in very small patients (<2.5 kg) Little exhaled gas is returned to the patient Exhaled gas is evacuated by the scavenging system Fresh gas is routed to the patient directly from the vaporizer No carbon dioxide absorber canister, pressure manometer,
or unidirectional valves Several configurations are available
Components: Endotracheal tube connector, fresh gas inlet, reservoir bag, overflow valve, scavenger tube, and scavenger system
64Copyright © 2011, 2003, 2000, 1994 by Mosby, Inc., an affiliate of Elsevier Inc.
Configurations of Nonrebreathing Circuits
Bain coaxial circuit (modified Mapleson D system)
Ayres T-Piece (Mapleson E system) Magill circuit (Mapleson A system) Lack circuit (modified Mapleson A system) Jackson-Rees circuit (Mapleson F system) Norman mask elbow (Mapleson F system)
65Copyright © 2011, 2003, 2000, 1994 by Mosby, Inc., an affiliate of Elsevier Inc.
Operation of an Anesthetic Machine
Daily inspection Oxygen and liquid anesthetic levels Leaks Pop-off valve or overflow valve
Machine choice is based on patient body weight Small animal machine <150 kg Large animal machine 150 kg
Choose rebreathing system
66Copyright © 2011, 2003, 2000, 1994 by Mosby, Inc., an affiliate of Elsevier Inc.
Choice of Breathing System
Primarily based on patient size Also based on
Cost Control of anesthetic depth Conservation of heat and moisture Production of waste gas
Choice of breathing system will determine Type of equipment required Position of pop-off valve Carrier gas flow rates
67Copyright © 2011, 2003, 2000, 1994 by Mosby, Inc., an affiliate of Elsevier Inc.
Carrier Gas Flow Rates
Calculating gas flow rate Patient body weight Tidal volume (VT) 10 mL/kg/min Respiratory minute volume (RMV) = VT ×
respiratory rate (~20 bpm) Type of breathing system Expected period of anesthesia
68Copyright © 2011, 2003, 2000, 1994 by Mosby, Inc., an affiliate of Elsevier Inc.
Mask or Chamber Induction Flow Rates
High flow rates required Mask: ~30 times VT for dogs, cats, neonate
large animals, pigs (1-5 L/min) Chamber: 5 L/min for small animals
69Copyright © 2011, 2003, 2000, 1994 by Mosby, Inc., an affiliate of Elsevier Inc.
Flow Rates in a Semiclosed Rebreathing System
After induction with injectable agent: 50-100 mL/kg/min (SA machine) and 8-10 L/min (LA machine)
When making changes in anesthetic depth: 50-100 mL/kg/min (SA machine) and 8-10 L/min (LA machine)
During maintenance: 20-40 mL/kg/min (SA machine) and 3-5 L/min (LA machine)
During recovery: 50-100 mL/kg/min (SA machine) and 8-10 L/min (LA machine)
70Copyright © 2011, 2003, 2000, 1994 by Mosby, Inc., an affiliate of Elsevier Inc.
Flow Rates in a Closed Rebreathing System
Normally used during maintenance only Oxygen flow must equal oxygen requirements
of the patient Minimum requirement = 5-10 mL/kg/min
71Copyright © 2011, 2003, 2000, 1994 by Mosby, Inc., an affiliate of Elsevier Inc.
Safety Concerns with a Closed Rebreathing System
Carbon dioxide accumulation Increased pressure in anesthetic circuit
72Copyright © 2011, 2003, 2000, 1994 by Mosby, Inc., an affiliate of Elsevier Inc.
Flow Rates in a Non-rebreathing System
Require high flow rates per unit body weight during all periods
Rates are based on patient body weight and Mapleson classification of circuit
Usually used on patients weighing <7 kg
73Copyright © 2011, 2003, 2000, 1994 by Mosby, Inc., an affiliate of Elsevier Inc.
Care and Maintenance of Anesthetic Equipment
Compressed gas cylinders Inspected and maintained by company that owns
them Silicone or Teflon-based lubricants safe for difficult
tank valves Tank and line pressure gauges, pressure
manometer, and oxygen flush valve Require no regular maintenance
Pressure-reducing valve adjusted to 40-50 psi Flowmeters require no regular maintenance
Check accuracy occasionally
74Copyright © 2011, 2003, 2000, 1994 by Mosby, Inc., an affiliate of Elsevier Inc.
Care and Maintenance of Anesthetic Equipment (Cont’d)
Vaporizer Serviced and maintained by manufacturer or
service professional Vaporizer inlet port, outlet port, common gas
outlet, and fresh gas inlet Check and replace hoses as necessary Routine low-pressure leak tests
75Copyright © 2011, 2003, 2000, 1994 by Mosby, Inc., an affiliate of Elsevier Inc.
Care and Maintenance of Anesthetic Equipment (Cont’d)
Unidirectional valves Disassemble, clean, inspect Prevent water vapor, mucus, and dust buildup Check integrity of the valves
Pop-off valve Check for proper operation and adjust as
necessary Daily and during an anesthetic procedure
76Copyright © 2011, 2003, 2000, 1994 by Mosby, Inc., an affiliate of Elsevier Inc.
Care and Maintenance of Anesthetic Equipment (Cont’d)
Reservoir bag, breathing tubes, and Y-piece Remove and clean after each procedure Prevents patient-to-patient transfer Hang to dry Check integrity of each part before use
Carbon dioxide absorber canister Change granules and clean canister as per
guidelines Wear gloves and a mask when handling granules Check integrity of each part before use
77Copyright © 2011, 2003, 2000, 1994 by Mosby, Inc., an affiliate of Elsevier Inc.
Disinfecting Anesthetic Equipment
Endotracheal tubes, laryngoscope blades, face masks
To prevent spread of disease from patient to patient
Wash with disinfectant, rinse, dry, reassemble Check integrity of each part before use
78Copyright © 2011, 2003, 2000, 1994 by Mosby, Inc., an affiliate of Elsevier Inc.
Disinfecting Anesthetic Equipment (Cont’d)
Disinfectants Chlorhexidine gluconate: not 100% effective Glutaraldehyde solutions (2%): short shelf life,
toxic, absorbed Ethylene oxide gas: special equipment needed,
toxic, absorbed Steam under pressure (autoclave): damages
rubber surfaces Discard damaged equipment