Vet 135 Chapter 4

Front 1

Anesthetic Chambers

Back 1

A clear box used to induce general anesthesia in small patients that are feral, vicious, or intractable or that cannot be handled without undue stress

Front 2

Anesthetic Mask

Back 2

a cone-shaped device, ideally made of transparent material, used to administer oxygen and anesthetic gases to nonintubated patients via the nose and mouth. Also used to administer pure oxygen to dyspneic, hypoxic, or toher critically ill patients requiring supplemental oxygen.

Front 3

Anesthetic vaporizer

Back 3

the anesthetic machine system that vaporizes liquid inhalant anesthetic and mixes it with the carrier gases. Classified as precision or nonprecision and out of circuit or in circuit.

Front 4

asphyxiation

Back 4

the act of cutting off the supply of oxygen

suffocation

Front 5

atelectasis

Back 5

collapse of a portion or all of one or both lungs

Front 6

ayre's t-piece

Back 6

a non-rebreathing circuit with a fresh gas inlet entering at the patient end of the breathing tube at a 90 degree angle and without a reservoir bag at the opposite end of the breathing tube - Mapleson E circuit

Front 7

Bain coaxial circuit

Back 7

a non-rebreathing circuit with a "tube within a tube" configuration that discharges fresh gas at the patient end of the breathing tube. Both the overflow valve and the reservoir bag are located away from the patient at the opposite end of the breathing tube - modified mapleson d circuit

Front 8

Breathing circuit

Back 8

the anesthetic machine system that conveys the carrier gases and inhalant anesthetic to the patient and removes exhaled carbon dioxide. Classified as rebreathing or non-rebreathing.

Front 9

breathing tubes

Back 9

corrugated tubes that complete a rebreathing circuit by carrying the anesthetic gases to and from the patient. Each tube is connected to a uni-directional valve at one end and to the y-piece at the other end

Front 10

carbon dioxide absorber canister

Back 10

the part of a rebreathing circuit that holds the carbon dioxide absorbent granules. The granules, primarily made of calcium hydroxide, remove expired CO2

Front 11

closed rebreathing system

Back 11

a rebreathing system in which the pop-off valve is kept nearly or completely closed and the flow of oxygen is relatively low, providing on ly the volume necessary to meet the patient's metabolic needs.

Front 12

common gas outlet

Back 12

the point where the oxygen, inhalant anesthetic, and N2O if used exit the anesthetic machine on the way to the breathing circuit.

Front 13

compressed gas cylinders

Back 13

a container that holds a large volume of highly pressurized gas. Stores Oxygen, nitrous oxide, medical air, and carbon dioxide. Small tanks = E, large tanks =H

Front 14

compressed gas supply

Back 14

the anesthetic machine system that supplies carrier gases

Front 15

endotracheal tube

Back 15

a flexible tube placed inside the trachea of an anesthetized patient and used to transfer anesthetic gases directly from the breathing circuit into the patient's trachea, bypassing the oral and nasal cavities, pharynx, and larynx

Front 16

flow meter

Back 16

a glass cylinder of graduated diameter that indicates carrier gas flow expressed in liters of gas per minute (L/min). Reduces the pressure of the gas in the intermediate-pressure line from about 50 psi to 15psi

Front 17

fresh gas inlet

Back 17

the point at which the carrier and anesthetic gases enter the breathing circuit

Front 18

Jackson-Rees circuit

Back 18

a non-rebreathing circuit with a fresh gas inlet at the patient end of the breathing tube and a reservoir bag at the opposite end. The fresh gas inlet enters the breathing tube at a 45 to 90 degree angle - Mapleson F circuit

Front 19

Lack Circuit

Back 19

a non-rebreathing circuit that has an expiratory tube that runs from the ET tube connector to an overflow valve near the bag. The fresh gas inlet, the overflow valve and the reservoir bag are located away from the patient at the opposite end of the breathing tube - modified mapleson a system

Front 20

laryngoscope

Back 20

a device consisting of a handle, a blade, and a light source that is used to increase visibility of the larynx during placement of an endotracheal tube

Front 21

line pressure gauge

Back 21

a gauge that indicates the pressure in the intermediate-pressure gas line between the pressure-reducing valve and the flow meters

Front 22

magill circuit

Back 22

a non-rebreathing circuit with an overflow valve at the patient end of the breathing tube. Both the fresh gas inlet and the reservoir bag are located away from the patient at the opposite end of the breathing tube - mapleson a circuit

Front 23

Mapleson classification system

Back 23

a system developed by W.W. Mapleson that is used to classify non-rebreathing circuits based on the position of the fresh gas inlet, the reservoir bag and the pressure-limiting valve

Front 24

non-rebreathing system

Back 24

an anesthetic machine fitted with a non-rebreathing circuit in which little or no exhaled gases are returned to the patient but are instead 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. Used most commonly for patients under 2.5 to 3kg in body weight

Front 25

norman mask elbow

Back 25

a non-rebreathing circuit with a fresh gas inlet at the patient end of the breathing tube and a reservoir bag at the opposite end. The fresh gas inlet enters the breathing tube at a 45 - 90 degree angle, and the endotracheal tube connector is at right angles to the breathing tube - Mapleson F circuit

Front 26

oxygen flush valve

Back 26

a button or lever that rapidly delivers a large volume of pure oxygen at a flow rate of 3 to 75 L/min directly to the common gas outlet or breathing circuit of a rebreathing system, bypassing the anesthetic vaporizer and oxygen flow meters

Front 27

pop-off valve

Back 27

point of exit of anesthetic gases from the breathing circuit (pressure relief valve, exhaust valve, adjustable pressure limiting valve, overflow valve)

Front 28

pressure manometer

Back 28

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. Express in millimeters of mercury (mmHg) or kilopascals (kPa)

Front 29

pressure reducing valve

Back 29

a valve that reduces the pressure of a compressed gas to a constant safe operating pressure of 40 to 50 psi regardless of pressure changes within the tank

Front 30

rebreathing system

Back 30

an anesthetic machine fitted with a rebreathing circuit, exhaled gases minus carbon dioxide are recirculated and rebreathed by the patient, along with variable amounts of fresh oxygen and anesthetic. appropriate for patients over 2.5 to 3kg

Front 31

reservoir bag

Back 31

a rubber or plastic bag that serves as a flexible storage reservoir for expired and inspired gases. Allows the anesthetist o observe respirations, confirm proper endotracheal tube placement, and ventilate for the patient

Front 32

respiratory minute volume

Back 32

the amount of air that moves into and out of the lungs in a minute. The tidal volume multiplied by the respiratory rate

Front 33

scavenging system

Back 33

the anesthetic machine system that disposes of excess and waste anesthetic gases outside of the building, so that inhalation by techs is minimized

Front 34

semi-closed rebreathing system

Back 34

a rebreathing system in which the pop-off valve is positioned partially open, and the flow of oxygen is relatively high, providing more vole than is necessary to meet the patient's metabolic needs

Front 35

tank pressure gauge

Back 35

a device attached to the yoke of an anesthetic machine or the pressure regulator of an H tank. Indicates the pressure of gas remaining in a compressed gas cylinder measured in pounds per square inch (psi) or kilopascals (kPa)

Front 36

Tidal Volume (Vt)

Back 36

the volume of a normal breath- approximately 10 to 15 mL/kg

Front 37

unidirectional valves

Back 37

the inspiratory valve or expiratory valve of a rebreathing circuit. controls the direction of gas flow through a rebreathing circuit as the patient breathes

Front 38

vaporizer in circuit (VIC)

Back 38

vaporizer located in the breathing circuit. Nonprecision vaporizers usually located this way

Front 39

Vaporizer out of circuit (VOC)

Back 39

vaporizer in which carrier gas from the flow meter flows into the vaporizer before entering the breathing circuit. Precision vaporizers typically positioned this way

Front 40

Chapter 4 notes

Back 40

-ET tubes maintain open airway, decrease anatomic dead space, prevent aspiration, allow for rapid response during emergencies, and allow the technician to accurately monitor and control respirations

-Murphey ET tubes have a beveled end and a side hole (murphy eye) and may or may not have a cuff.

-Cole tubes have no cuff or hole, but are designed with an abrupt decrease in diameter near the patient end of the tube. Used in patients with complete tracheal rings (birds and some reptiles). The neck of the tube is seated at the tracheal opening creating a seal.

-ET tubes can be made of polyvinyl chloride (PVC) which is transparent and stiffer than others minimizing risk of tube collapse, but increasing trauma during placement, red rubber are more flexible and less traumatizing but are prone to kinking or collapsing, may absorb cleaning solutions which if reused will irritate tracheal mucosa and tend to dry and crack with extended use, anode or spiral tubes contain a coil of metal or nylon embedded in the rubber to resist kinking or collapse, or silicone which are more expensive but are strong and pliable, resistant to collapse and less irritating to tissues.

-Tube size is expressed as the internal diameter in mm.

-Cuffed tubes prevent animals from breathing room air making anesthesia depth difficult to maintain and leakage of gases reducing gas pollution in the operating room, and minimize risk of aspiration

-Use cuffed tubes with caution in small patients as the cuff if overinflated may cause tissue necrosis

-ET tubes should be no longer than than the distance between the most rostral aspect of the mouth and the thoracic inlet. If longer there is increased risk of the patient end entering one main stem bronchus meaning only one lung will be infused with the gases leading to hypoventilation, hypoxemia, and possible difficulty keeping patient anesthetized. If the tube extends beyond the most rostral aspect then mechanical dead space is increased resulting in hypoventilation especially small patients. If tube is 2.5cm longer than the correct distance it should be shortened.

-Masks allow for rapid administration of oxygen, but they don't maintain an open airway making airway obstruction possible, they don't protect against aspiration, and the anesthetist is unable to ventilate the patient.

-Room air is about 21% oxygen

-In a healthy, conscious patient breathing room air the approximate concentration in the alveolus is 13%, in arterial blood 12%, in capillary blood at tissue level 5%, and in the issues 2%.

-anesthetized patients have lower tissue oxygen concentrations because most anesthetics decrease respiratory rate and tidal volume.

-oxygen flow rates affect concentration of anesthetic in the breathing circuit through dilution and absorption.

-Induction rate for isoflurane is 3% to 5% and maintenance is 1.5% to 2.5%

-Induction rate for sevoflurane is 4% to 6% and maintenance is 2.5% to 4%.

-Induction rate for desflurane is 10% to 15% and maintenance is 8% to 12%.

-Carbon dioxide absorbents exhaust after absorption of 26L of CO2 per 100g of absorbent. Using depleted granules results in rebreathing of CO2 leading to hypercapnia.

-If there is a carbon dioxide level higher than 0 mmHg at peak inspiration then the CO2 absorbent is possibly exhausted.

-CO2 absorbent granules should be changed after 6-8 hours of use regardless of whether the color change has appeared

-pressure manometer determines the pressure exherted on the patient's lungs during ventilation and should not exceed 20cm of water in small animals and 40cm of water in large animals. It should read 0 to 2 cm of water when the patient is spontaneously breathing.

-Excessive pressure in the circuit can result in dyspnea, lung damage, or pneumothorax

-rebreathing systems are recommended for patients weighing 7kg or more

-changes in anesthetic depth are quicker using non-rebreathing systems

-non-rebreathing systems are often associated with significant heat and water loss from the patient because the patient is breathing dry, cool, fresh gas.

-Carrier gas flow rates: Very high flow rates are required for chamber or mask induction. These flood the circuit with anesthetic and dilutes expired gases. Mask induction should equal 30 times the Vt (about 300ml/kg/min) for cats and small dogs and somewhat less for larger dogs, so 1 to 3 L/min for patients less than 10kg and 3 to 5 L/min for patients over 10kg. Chamber induction flow rate is recommended to be 5 L/min regardless of weight.

-Flow rates for semiclosed rebreathing systems: after induction, during depth changes and recovery 50 to 100ml/kg/min with a maximum of 5L/min

semiclosed during maintenance: 20 to 40ml/kg/min with a minimum of 250ml/min regardless of size (low flow)

semiclosed during maintenance with minimal rebreathing: 200 to 300ml/kg/min up to a max of 5L/min (machine functions similar to non-rebreathing system)

closed system maintenance: 5 to 10ml/kg/min

-non rebreathing flow rates for mapleson a, modified mapleson a, and modified mapleson d 150 to 200ml/kg/min

-non rebreathing flow rates for modified mapleson d, mapleson e, and mapleson f systems 400 to 600ml/kg/min

-large animal oxygen flow rates: semiclosed system after induction, during change or recovery 8 to 10L/min, semiclosed system during maintenance 3 to 5 L/min, closed system during maintenance 1 to 2.5L/min

-once vaporizer is turned off patient still exhales anesthetic gas which remains in the circuit until replaced by fresh oxygen, if allowed to remain in the circuit recovery is delayed. Once vaporizer is turned off increase the flow to the same rate used during induction (50 - 100ml/kg/min) with the pop off valve open, use gentle pressure to evacuate the reservoir bag and refill it with short bursts from the oxygen flush valve. Maintain higher flow for 5 minutes or until patient must be extubated.