Chapter 4 Notes: Anesthestic Machine – Flashcards
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Open System
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"open cone", "open drop" of anesthetic; control of anesthetic was crude; anesthetist is unable to protect the airway
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Endotracheal Tube
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a flexible tube placed in the trachea of an anesthetized patient used to transfer anesthetic gases directly from the anesthetic machine to the patient's lungs, bypassing the oral and nasal cavities, pharynx, and larynx
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Murphy Tubes
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have a beveled head and a side hole called the "Murphy eye" and may or may not have a cuff
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Cole Tubes
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have no cuff or side hole, but are designed with an abrupt decrease in diameter near the patient end of the tube; used for species that have complete tracheal rings such as birds and some reptiles to prevent damage to the trachea that would be caused by a cuffed tube
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PVC Tubes
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polyvinyl chloride; transparent and are somewhat stiffer than other types; stiffness minimizes the risk of collapse, but increases the risk of trauma to tracheal mucosa during tube placement, when turning the patient, and during patient transfer
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Red Rubber Tubes
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more flexible and less traumatic; more prone to kinking or collapsing, especially if small; may absorb disinfectants, resulting in irritation from contact and tend to dry and crack after prolonged use
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Spiral or Anode Tubes
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contain a coil of metal or nylon embedded in the rubber designed to resist kinking or collapse from external pressure
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Silicone Tubes
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more expensive; combine strength with pliability and are resistant to collapse and are less irritating to tissues than either rubber or vinyl tubes
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Internal Diameter (ID)
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most commonly used to express tube size; written on the surface of each tube
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Asphyxiation
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the act of cutting off the supply of oxygen; suffocation; end hole of tube can become blocked with mucous
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Endotracheal Tube Parts
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-valve with syringe attached -pilot balloon -machine end -connection -tie -measurement of internal diameter -inflated cuff -patient end -Murphy eye
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Use For a Cuff
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-prevent leakage of air and gases around the tube and reduces waste gas pollution in the operating room -minimizes risk of aspiration of blood, saliva, vomitus, and other material into the lungs -prevent animal from breathing room air
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Points Noted With Endotracheal Tubes
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-should not bend during placement -tubes reduce dead space -caution when used with laser surgery
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Laryngoscope
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a device used to increase visibility of the larynx while placing an endotracheal tube; often used in small ruminants, camelids, and swine; helpful in dogs and cats, not generally used in adult cattle and horses
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Anesthetic Masks
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cone-shaped devices used to administer oxygen to non-intubated patients via the nose and mouth; used in patients difficult to intubate, for anesthetic induction and maintenance, or to administer pure oxygen; usually made of plastic or rubber; allows for rapid administration of oxygen; do not maintain an open airway, no protection against pulmonary aspiration, anesthetist is unable to ventilate the patient
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Anesthetic Chambers
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clean, aquarium-like boxes used to induce general anesthesia in small patients that are feral, vicious, or intractable, or cannot be handled without undue stress; made of acrylic or Perspex; have a removable top with 2 ports for a gas source and exit of waste gas; prevent close monitoring of the patient
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Basic Principles of the Anesthetic Machine
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liquid anesthetic is vaporized into a carrier gas which delivers the anesthetic to the patient via a breathing circuit
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Functions of Anesthetic Machine and Breathing Circuit
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-carrier gases must be delivered at a controlled flow rate -precise concentration of a liquid inhalant must be vaporized, mixed with the carrier gases, and delivered to the patient -exhaled gases containing CO2 must be moved away from the patient and either removed through a scavenging system or recirculated to the patient without CO2
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Compressed Gas Supply
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supplies carrier gases-oxygen and sometimes nitrous oxide
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Anesthetic Vaporizer
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vaporizes liquid inhalant anesthetic and mixes it with the carrier gases
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Vaporizer-Out-of-Circuit (VOC)
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a vaporizer in which carrier gas from the flow meter flows into the vaporizer before entering the breathing circuit; precision vaporizers are precisioned this way
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Vaporizer-in-Circuit (VIC)
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a vaporizer that is located in the breathing circuit; non-precision vaporizers are often positioned this way
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Breathing Circuit
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conveys the carrier gases and inhalant anesthetics to the patient and removes exhaled carbon dioxide; classified as rebreathing or non-rebreathing circuits
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Scavenging System
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disposes of excess and waste anesthetic gases
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In a healthy, conscious patient breathing room air with ___% oxygen, approximate concentration in alveolus is ___%, aterial blood is ___%, capillary blood at tissue level is ___%, and in tissues is ___%.
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21%; 13%; 12%; 5%; 2%
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Tidal Volume (Vt)
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the volume of a normal breath (approximately 10-15 mL/kg body weight)
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Compressed Gas Cylinder
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contain a large supply of carrier gas in a highly pressurized state; enables large supply of gas to be stored in a space small enough to be of practical use; either small (E-tanks) or large (H-tanks)
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Line Pressure
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oxygen pressure remaining in the intermediate-pressure lines after the valve is closed
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Potential Risks From Compressed Gas Cylinders
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-oxygen and nitrous oxide support combustion -forceful release of gas from an unprotected outlet port may tear the skin or injure an eye -if a cylinder is dropped and the valve breaks off, the cylinder may cause serious personal injury -if inadvertently attached to a valve, yoke, or hose intended for a different type of gas, the wrong gas will be delivered to the patient
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Tank Pressure Gauge
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a device attached to the yoke of a machine, or the pressure regulator of an H tank, that indicates the pressure of gas remaining in a compressed gas cylinder measured in pounds per square inch (psi) in the U.S. or kilopascals in Europe and Canada
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Pressure in a full oxygen tank is about __________psi or _________kPa.
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2200 psi; 15,000 kPa
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Pressure Reducing Valve
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located near the tank pressure gauge; gas flows through here after exiting the tank then into an intermediate gas line; reduces pressure of a gas to 40-50 psi (275-345 kPa) regardless of pressure changes within the tank
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Line Pressure Gauge
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indicates the pressure in the intermediate-pressure gas line between the pressure-reducing valve and the flow valves; when oxygen is on, gauge should read 40-50 psi
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Oxygen Flush Valve
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a button or lever that, when activated, delivers a large volume of pure oxygen at a flow rate of 35-75 L/min. directly from the line exiting the pressure-reducing valve into the common gas outlet or into the breathing circuit of a rebreathing system, bypassing the anesthetic vaporizer and oxygen flow meters
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Flow Meter
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after leaving the pressure-reducing valve, carrier gas flows through an intermediate-pressure gas line, into the flow meter; a vertical glass cylinder of graduated diameter with a valve attached to the bottom; an indicator within the cylinder rises to indicate the gas flow expressed in liters of gas per minute; reduces pressure of gas in the intermediate-pressure line to 15 psi
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Pressure Manometer
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a gauge that indicates the pressure of the gases within the breathing circuit, and by extension, the pressure in the animal's airways and lungs; expressed in centimeters of water (cm H2O), millimeters of Mercury (mm Hg), or kilopascals (kPa)
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Non-Rebreathing System
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an anesthetic machine fitted with a non-rebreathing circuit; little or no exhaled gases are returned to the patient and removed from the circuit by use of appropriately high flow rates of carrier gas and evacuated by a scavenger connected to a pressure-limiting valve or other exit port; most commonly used for patients under 2.5-3 kg body weight
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Aensthetic Vaporizer
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converts a liquid anesthetic to a gaseous state and adds controlled amounts of the vaporized anesthetic to the gas anesthetic
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Fresh Gas
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oxygen and anesthetic mixture
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Precision Vaporizer
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allows precise control of the amount of anesthetic delivered to the patient; expressed as the percent of the total gases exiting the vaporizer
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Non-Precision Vaporizer
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used in the past to deliver low-pressure anesthetics; practice is uncommon now
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Factors Affecting Vaporizer Output
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-temperature: volatile anesthetics vaporize more readily at higher temperatures than lower; temperature of anesthetic can be affected by carrier gas flow -carrier gas flow rate: amount of carrier gas flowing through the vaporization chamber determines anesthetic output; also influences the concentration of the anesthetic in the breathing circuit -respiratory rate and depth: in VIC non-precision vaporizers, this will affect anesthetic delivery by affecting the flow of carrier gas through the vaporization chamber -back pressure: refers to an increase in pressure at the vaporizer outlet port caused by manual ventilation or activation of the oxygen flush valve -barometric pressure
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Isoflurane
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induction rate: 3-5% maintenance rate: 1.5-2.5%
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Sevoflurane
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induction rate: 4-6% maintenance rate: 2.5-4%
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Desflurane
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induction rate: 10-15% maintenance rate: 8-12%
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Vaporizer Inlet Port
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the point where oxygen and any other carrier gases enter the vaporizer from the flow meters
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Vaporizer Outlet Port
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the point where the oxygen, inhalant anesthetic, and N2O exit the vaporizer on the way to the breathing circuit
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Common Gas Outlet
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the point where the oxygen, inhalant anesthetic, and N2O exit the anesthetic machine on the way to the breathing circuit
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Breathing Circuit
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consists of a group of components that carry anesthetic and oxygen from the fresh gas inlet to the patient and convey expired gases away from the patient
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Rebreathing System
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an anesthetic machine fitted with a rebreathing circuit; also called "circle systems" because exhales gases minus carbon dioxide are recirculated and rebreathed by the patient along with variable amounts of fresh oxygen and anesthesia
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Closed Rebreathing System
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a rebreathing system in which the pop-off valve is kept nearly or completely closed and the flow of oxygen is relatively low, providing only the volume necessary to meet the patient's metabolic needs
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Semi-Closed Rebreathing System
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a rebreathing system in which the pop-off valve is positioned partially open, and the flow of oxygen is relatively high, providing more volume than is necessary to meet the patient's metabolic needs
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Rebreathing circuit consists of:
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-fresh gas inlet -unidirectional or one-way valves -pop-off or pressure relief valve -reservoir bag -carbon dioxide absorber canister -pressure manometer -air intake valve -breathing tubes -y-piece
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Carbon Dioxide Absorber Canister
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the part of a rebreathing circuit that holds the carbon dioxide absorbent granules; these granules; primarily made of calcium hydroxide, remove expired CO2
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Exhaled gases include:
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O2, anesthetic vapor, CO2, nitrogen, water vapor, and nitrous oxide (if used)
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Flow of gas:
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inspiratory unidirectional valve-->inspiratory tube-->animal-->expiratory tube-->expiratory unidirectional valve-->carbon dioxide canister-->past the reservoir bag, pop-off valve, and pressure manometer-->back to the inspiratory unidirectional valve
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Fresh Gas Inlet
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the point at which the carrier and anesthetic gases enter the breathing circuit; permanently attached to the breathing circuit
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Unidirectional Valves
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control the direction of gas flow through the rebreathing circuit as the patient breathes
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Pop-Off Valve
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also called the pressure relief valve, adjustable pressure limiting (APL) valve, or overflow valve; the point of exit of anesthetic gases from the breathing circuit; main function is to allow excess gases to exit from the breathing circuit and enter the scavenging system
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Functions of a reservoir bag:
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1. serve as a flexible storage reservoir 2. allows the anesthetist to observe the animal's respirations 3. may be used to confirm proper ET tube placement 4. allows delivery of anesthetic gases to the patient
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Why bagging is beneficial:
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1. atelectasis occurs to some degree in many anesthetized patients and to compromise gas exchange 2. most anesthetics depress respiratory drive and decrease Vt to as little as 50% of the volume seen in a normal, awake patient 3. anesthetized patients frequently experience a decreased respiratory rate or apnea
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Atelectasis
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collapse of a portion or all of one or both lungs
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Magill Circuit
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Mapleson A system; has an overflow valve at the patient end of the breathing tube; fresh gas inlet and reservoir bag are located away from the patient at the opposite end of the breathing tube; relatively low fresh gas flow required during spontaneous ventilation
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Lack Circuit
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Modified Mapleson A system; has an expiratory tube that runs from the ET tube connector to an overflow valve near the bag; fresh gas inlet, overflow valve, and reservoir bag are located away from the patient at the opposite end of the breathing tube
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Bain Coaxial Circuit
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Modified Mapleson D system; fresh gas outlet at the patient end of the breathing tube; overflow valve and reservoir bag are located away from the patient at the opposite end of the breathing tube; overflow valve may be built into or near the bag; the tube supplying fresh gas is surrounded by the larger, corrugated tubing--allows incoming gases to be warmed by exhaled gases surrounding them before reaching the patient
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Ayre's T-Piece
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Mapleson E system; T-shaped tube with a fresh gas inlet entering the patient end of the breathing tube at a 90-degree angle; does not have a reservoir bag at the opposite end of the breathing tube
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Jackson-Rees Circuit and Norman Mask Elbow
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Mapleson F systems; fresh gas outlet at the patient end of the breathing tube and a reservoir bag at the opposite end; Jackson-Rees Circuit-fresh gas inlet enters the breathing circuit then enters the breathing circuit at a 45- to 90-degree angle; Norman Mask Elbow-ET tube connector is at right angles to the breathing tube
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Respiratory Drive
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the force generated by the respiratory muscles during breathing
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Choice of system is important in terms of use and setup because it determines:
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-the type of equipment required -position of the pop-off valve -carrier gas flow rates
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Factors in making a system decision:
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-cost -control of anesthetic depth -conservation of heat and moisture -production of waste gas
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Flow rates for anesthetic procedures are calculated by:
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-using the patient's body weight and the Vt or RMV -Vt is considered to be approximately 10mL/kg/min. in most anesthetized animals -RMV is Vt x respiratory rate in breaths per minute (average of 20 breaths/min. in most patients) -RMV is considered to be about 200 mL/kg/min.
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Flow rates with a semi-closed rebreathing system-------after induction with an injectable agent
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flow rate should be relatively high (50-100 mL/kg/min.)--results in a flow rate of about 500 mL-5L/min. for smaller animals or large animals connected to a small animal anesthetic machine depending on patient weight; initial flow rate for large animals on a large animal machine range from 8-10 L/min.
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Flow rates with a semi-closed rebreathing system--------when making changes in anesthetic depth
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higher oxygen flow rate (50-100 mL/kg/min.) when patient's level of anesthesia is too deep or too light and a change in anesthetic depth is needed; higher end of range will result in more rapid change in the desired anesthetic concentration within the breathing circuit
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Flow rates with a semi-closed rebreathing system------during maintenance
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rate may be reduced; rebreathing systems require low flow rates compared with non-rebreathing systems during this period because carbon dioxide is removed from the expired gases, whic h are then returned to the patient; rates of 20-40 mL/kg/min. are recommended for small animals and 3-5 L/min. for adult large animals
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Flow rates with a semi-closed rebreathing system-------during anesthetic recovery
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-remove waste gas by: -turning vaporizer off -increase flow rate to 50-100 mL/kg/min. -with pop-off valve open, use gentle pressure to evacuate reservoir bag and refill it using short bursts from oxygen flush valve -maintain higher flow rate for 5 minutes or until patient must be extubated -large animals on large animal anesthetic machine-same procedure but use rate of up to 10 L/min.
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When minimal rebreathing of anesthetic gases is desired:
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when oxygen flow rate matches or exceeds patient's RMV (at least 200-300 mL/kg/min.), rebreathing system can function like a non-rebreathing system; rates help flush exhaled gases from the breathing circuit through the pop-off valve and may be necessary until the problem is rectified
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Flow Rates When Using a Closed Rebreathing System:
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-oxygen flow must equal only the oxygen requirements of the animal -minimum metabolic oxygen requirement for the anesthetized animal is 5-10 mL/kg/min. -when flow rates of less than 250 mL/min. are used, some precision vaporizers and flow meters might not accurately deliver the dialed vaporizer concentration and oxygen flow -large animals, esp. adult horses and cattle, have lower metabolic oxygen requirements and oxygen rates and can be as low as 3-5 mL/kg/min. during maintenance with a closed rebreathing system
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Safety Concerns With a Closed Rebreathing System
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1. carbon dioxide circulation-can build up within the circuit; less likely to happen in a semi-closed rebreathing system 2. increased pressure in the anesthetic circuit; risk is lessened with a semi-closed rebreathing system because the pop-off valve is partially to fully open and excessive gas is vented
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Flow Rates--Non-Rebreathing System
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-relatively high flow rates per unit of body weight during all periods of general anesthesia--removal of carbon dioxide from the circuit is dependent on fresh gas flow -rates based on body weight--typically used on patients 7kg or under, so max rates are based on that
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Mapleson A, Modified Mapleson A, Modified Mapleson D flow rates
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carrier flow gas should be close to RMV (200 mL/kg/min.--should equal 0.5-1.5 L/min.
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Modified Mapleson D with no rebreathing, Mapleson E, Mapleson F flow rates
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-require oxygen flow rate of 2-3 x's the RMV (400-600 mL/kg/min.) with a max flow of 3 L/min. for patients under 7 kg. -equals 1-3 L/min. depending on patient size
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To remove an E-tank from the machine:
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-be sure tank valve is closed and oxygen is purged from the system -place you shoe under the tank to support it -loosen the wing nut and back the valve port off of the yoke -carefully remove your shoe and lower the tank until the valve clears the yoke -tank should be stored in an upright position until it is picked up by the company for refilling
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When replacing an E-tank on a machine:
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-inspect the valve port for cleanliness then place a single washer between the valve port and the nipple -gently raise the tank into place-line the valve port and the pin holes with the corresponding structures on the yoke -tighten the wing nut as securely as you are able to by hand -open the tank slowly and listen for leaks IF LEAKS-->recheck holes for proper alignment, tighten wing nut further, or use a new washer
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Pressure-Reducing Valve Maintenance
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may need to be adjusted if line pressure is not correct; may have an external adjusting screw that is turned left or right to increase or decrease the pressure
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Flow Meter Maintenance
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do not overtighten valve when turning off
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Testing Flow Meter Accuracy
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1. empty reservoir bag completely 2. close pop-off or overflow valve 3. occlude the y-piece or ET tube connector 4. choose a flow setting that corresponds to the size of the reservoir bag in liters 5. accurate if the bag is filled completely in 1 minute
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Unidirectional Valve Maintenance
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periodically disassemble, clean, and inspect to prevent a buildup of water vapor, mucus, and dust from carbon dioxide absorbent, and other material
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Cleaning the Unidirectional Valve
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1. unscrew valve collar and remove valve parts 2. clean dome, collar, valve, valve seal, and gaskets with alcohol or mild disinfectant 3. dry off 4. inspect valve and valve seal to be sure they are not damaged or warped 5. reassemble the valve
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Testing Integrity of Unidirectional Valves
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1. put on a surgery mask 2. detach the expiratory breathing tube from the y-piece 3. place the end of the tube up to your mouth with surgery mask in between so that the air will pass through the mask 4. attempt to inhale through the tube 5. detach the inspiratory breathing tube from the y-piece and place the end up to your mouth 6. attempt to exhale through the tube -any air movement through either tube indicated an incompetent valve
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Reservoir bag, breathing tubes, and y-piece
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removed and cleaned to prevent interpatient transfer of infections agents that collect inside; hang in vertical position until completely dried
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Changing Absorbent in the Carbon Dioxide Absorber Canister
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1. remove the absorber canister and dispose of absorbent granules 2. disassemble canister 3. clean each part with mild soapy disinfectant, rinse thoroughly 4. dry each part 5. check all gaskets for integrity 6. reassemble canister 7. loosely fill with fresh granules, but leave 1cm.-1/2 in. air space at the top to allow unimpended air flow --Handle granueles with gloves
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Disinfecting Anesthetic Equipment
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1. disassemble any parts that can be removed 2. wash any parts thoroughly with disinfectant, rinse, dry, and reassemble