Intubation and Anesthetic Machines

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Intubation and Anesthetic Machines

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Endotracheal Intubation

• Types of endotracheal tubes
• Plain
• Used in birds
• Occasionally used in cats
• A plain tube does not form an airtight seal
  within the trachea
• Will allow secretions, blood or gastro-intestinal
  fluid to enter the lungs

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Endotracheal Intubation

• Types of endotracheal tubes
• Cuffed
• Used in all species
• Cuff is inflated with air to produce a leak proof
  seal
• A pilot balloon is used to estimate degree of
  inflation
• Alternatively the cuff is filled until no leak of
  air can be heard when the lungs are inflated to
  25 cm H2O pressure

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Endotracheal Intubation

• Types of endotracheal tubes
• Cole
• Originally designed for babies
• The tube has excellent pressure-flow
  characteristics and provides less resistance to
  breathing
• Absence of cuff allows insertion of a larger tube
• A cole tube is commonly used for cats
• "Shoulders" of the tube form an airtight seal at
  the entrance to the larynx

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Endotracheal Intubation

• Size of endotracheal tube
• Choose an endotracheal tube as large as possible
  without forming a "push-fit
• Check the tube length alongside the animal
• The tip of the tube must be beyond the larynx but
  not extend past the thoracic inlet

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Endotracheal Intubation

• Size of endotracheal tube
• Tube sizes refer to the internal diameter of the
  part of the tube residing in the trachea
• A few manufacturers print both internal and
  external diameters on their endotracheal tubes
• Purchase tubes with thin walls especially when
  they are to be used on cats and small dogs
• A thin wall allows a tube with a larger lumen to
  be used

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Endotracheal Intubation

• Technique of intubation
• Orotracheal Intubation
• Dogs and Cats
• Open the dog or cat's mouth and view the larynx
• Use a bright overhead light or a laryngoscope
• There is no excuse for doubt when inserting an
  endotracheal tube
• You can see where it is -- in the trachea or in
  the esophagus

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Endotracheal Intubation

• Technique of intubation
• Orotracheal Intubation
• Dogs and Cats
• Pull the tongue forward gently in the dog and cat
  to move the larynx more rostral . Do not pull
  hard on the tongue or it will could lacerated or
  have nerve damage
• Do not put your fingers inside the mouth (jaw
  tone and the ability to reflexively close the
  jaws persists into light anesthesia)
• A plastic or metal stilette can be used inside an
  endotracheal tube to stiffen it
• This is to improve control of the direction of
  the tip of the tube, not so that you can force
  the tube into the larynx
• Make sure that the tip of the stilette is not
  sharp and does not extend beyond the end of the
  tube, where it might lacerate the trachea

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Endotracheal Intubation

• Technique of intubation
• Orotracheal Intubation
• Dogs and Cats
• If you use a laryngoscope
• Place the tip of the blade over the tongue and
  under the epiglottis
• Placing it on the epiglottis will distort the
  laryngeal opening and make it harder to intubate
• Tracheal intubation can be performed with the
  animal on its side, sternum, or back
• The position may be dictated by the animal's
  condition (e.g., with GI obstruction always
  intubate the animal in sternal position, with the
  head up) or by personal preference of the surgeon

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Endotracheal Intubation

• Technique of intubation
• Orotracheal Intubation
• Pigs and small ruminants
• Technique used is the same for dogs and cats
• The anatomy of the pharynx and larynx of these
  species differs
• Adult Cattle
• Intubation can be performed using a laryngoscope
  with an extra long blade
• Intubation most frequently accomplished without
  viewing the larynx
• You introduce your hand and arm into the mouth to
  palpate the laryngeal opening and to guide the
  tip of the endotracheal tube into the trachea
• Horses
• Intubation performed "blind", without viewing the
  larynx and without palpation.

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Nasotracheal Intubation

• Dogs, cats, pigs and ruminants
• Not performed
• Horses
• Easy to insert a tube from the nares through the
  ventral nasal meatus, into the trachea
• Used in some foals to administer halothane or
  isoflurane to induce anesthesia
• Used in adult horses during recovery from
  anesthesia to relieve nasal obstruction from
  mucosal swelling

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Pharyngostomy Intubation

• Tracheal intubation through a pharyngostomy
• Dogs and cats
• May be used in dogs and cats requiring oral
  surgery, e.g., repair of fractured jaw, cleft
  palate repair, lacerations of hard palate
• Allows the surgeon greater access to the surgical
  field

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Exotics

• Reptiles Most reptiles can be intubated if
  large enough.
• Avian Endotracheal intubation sometimes used.
  High incidence of mucous blockage in tubes due to
  very small tracheal openings and high mucous
  production. Most avian veterinarians prefer air
  sac cannulization. This is a surgical procedure
  when a tracheal tube is inserted directly into an
  air sac near the leg.

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Endotracheal Intubation

• Complications of endotracheal intubation
• If the internal diameter of the endotracheal tube
  is too small in relation to the animal
• There will be increased resistance to breathing
• Hypoventilation will result
• If the cuff is over inflated, or if it is
  inflated for too long
• The tracheal mucosa, and sometimes the cartilage,
  will die and slough
• Later the animal will show signs of tracheitis
• Only inflate the tube cuff with enough air to
  prevent a leak when the animal's lungs are
  artificially inflated
• If you have a device to measure intra-cuff
  pressure, inflate the cuff to 25 cm H2O pressure
• If the duration of surgery is long, provided that
  regurgitation has not occurred, the cuff should
  be deflated and the tube repositioned every 2
  hours

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Endotracheal Intubation

• Complications of endotracheal intubation
• If the tube is too long
• A primary bronchus may be intubated
• One lung will collapse
• Cyanosis may develop
• Delivery of inhalation anesthetic is impaired
• The animal may wake up
• Endotracheal tubes can cause airway obstruction
• They become twisted or kinked
• The bevel of the tube lies against the tracheal
  wall
• The cuff is over inflated and squashes the tube
  lumen
• The cuff bulges over the end of the tube
• K-Y lubricant is allowed to dry inside the tube
• Mucus and secretions accumulate during anesthesia
  (especially cats and small dogs) or are allowed
  to dry inside the tube (improper cleaning after
  anesthesia).

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Endotracheal Intubation

• Complications of endotracheal intubation
• Trauma of the larynx and trachea
• Can produce laryngitis/tracheitis which will last
  for several days
• Laryngeal trauma may also predispose the animal
  to laryngospasm or to granuloma formation at a
  later date
• Mucosal swelling in the recovery period may cause
  partial or complete airway obstruction
• Preferably do not cause trauma, but if swelling
  occurs, inject dexamethasone IV and provide
  supportive treatment (oxygen, reintubate) until
  the swelling is reduced
• Irregular heart rhythm
• Laryngoscopy causes bradycardia
• Tracheal intubation causes tachycardia and,
  sometimes, ventricular premature depolarizations
• Atropine premedication should prevent bradycardia
• Lidocaine, 2 mg/kg, applied directly to the
  larynx or injected intravenously before
  intubation should modify or prevent tachycardia
• Lidocaine is used when tachycardia is anticipated
  to cause deterioration of the patient.

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Endotracheal Intubation

• Complications of endotracheal intubation
• Leak in the cuff preventing an airtight seal and
  controlled ventilation
• Always check the cuff for leaks before inducing
  anesthesia
• Transfer of infection
• Clean tubes thoroughly, inside and outside,
  between patients
• Use a bristle brush and betadine (or similar)
  solution
• If ethylene oxide (ETO) sterilization is used,
  adequate aeration is needed to eliminate irritant
  residues

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Endotracheal intubation

• Complications of endotracheal intubation
• Bracycephalic syndrome (short nose breeds)
• Stenotic nares
• Everted layrngeal saccules
• Elongated soft palate
• Hypoplastic trachea
• Airways can collapse easily after extubation
• Wait until the dog has a good gag reflex before
  extubating
• Preoxygenate for 5 minutes before induction in
  case of a difficult intubation

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Endotracheal Intubation

• Complications of endotracheal intubation
• Cats
• Can be very difficult to intubate due to
  laryngeal spasms
• Small amount of lidocaine swabbed on larynx can
  numb it long enough to intubate
• Many need to use a stylet in endotracheal tube to
  help pass it

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Endotracheal Intubation

• Complications of endotracheal intubation
• Collapsing trachea
• Genetically weak trachea
• Preoxygenate severe cases
• Intubate as gently as possible as not to irritate
  the trachea

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Endotracheal Intubation

• Procedure for tracheal extubation in dogs and
  cats
• Leave tube in place until swallowing reflex
  returns
• Remove blood clots from nasopharynx
• Deflate the cuff before extubation
• Exceptions
• When bleeding into the nose and mouth has
  occurred
• Excessive salivation has occurred
• Regurgitation has occurred
• Prevent the animal biting the tube while it is
  being removed
• Cost prohibitive
• Animal (dog or cat) can easily inhale or swallow
  pieces of tube

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Parts of an Anesthetic Machine

• Gas cylinders
• Oxygen and nitrous oxide are contained in
  compressed gas cylinders
• Found as E cylinders that are usually attached to
  the machine via yokes that are equipped with a
  specific pin system
• Tanks also come in large G and H cylinders

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Parts of an Anesthetic Machine

• Gas cylinders
• Pressure gauge attached to the cylinder indicates
  the pressure of the gas in the tank
• Pressure in a full O2 cylinder is 2200 psi
• Oxygen tanks should be changed when pressure
  drops below 500 to 600 psi
• The volume of O2 in an E cylinder can be
  calculated by multiplying the psi by 0.3
• A full tank of 2200 psi will contain 660 L of O2

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Parts of an Anesthetic Machine

• Gas cylinders
• Nitrous tanks are stored at lower pressures
• A full tank is 770 psi
• Nitrous tanks should be changed when pressure
  gauge drops below 500 psi
• Both liquid and gas states are present but the
  gauge reads only the gas state
• Liquid evaporates to gas as soon as the gas
  leaves the tank so the pressure in the tank will
  not change until all the liquid state has
  evaporated

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O2 cylinder, pressure releasing valve, pressure
gauge
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Parts of an Anesthetic Machine

• Pressure releasing valve (regulator)
• Reduces the high pressure of the O2 or nitrous
  leaving the tank to a low pressure of 50 psi

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Parts of an Anesthetic Machine

• Flow meter
• Measure O2 or nitrous in L/min
• Allows the anesthetist to set the O2 or nitrous
  oxide flow rates that will be delivered to the
  animal
• As the gas passes through the flow meter gas
  pressure is reduced further to 15 psi

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Flow meter
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Parts of an Anesthetic Machine

• Vaporizer
• Converts the liquid anesthetic into a gas state
• Controls the amount of vaporized amount of
  vaporized anesthetic mixed with the carrier gas

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Sevoflurane vaporizer
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Parts of an Anesthetic Machine

• Check valves
• Inhalation/Exhalation flutter valves
• Insures a uni-directional flow of gas to and from
  the patient when delivering a circle system
• Y connector
• Connects the endotracheal tube to the inspiratory
  and expiratory tubes of a circle system

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Parts of an Anesthetic Machine

• Rebreathing bag (reservoir bag)
• Allows the animal to breath easier from a
  reservoir of gas
• Can be used to deliver O2 (with or without
  anesthetic gas) and manually assist respirations,
  bagging
• Bags should have a minimum volume of 60 ml/kg of
  patient weight

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Parts of an Anesthetic Machine

• Carbon dioxide absorber
• Soda lime canister
• Used in rebreathing systems to remove CO2 from
  the expired gases
• Exhaust gases enter a canister containing soda
  lime or barium hydroxide
• Na, K, Ca2 and Ba2 hydroxide reacts with the
  exhaled CO2 and water to form carbonate
• Heat is liberated and the pH decreases

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Parts of an Anesthetic Machine

• Carbon dioxide absorber
• Soda lime canister
• A pH color indicator turns blue on consumption
• When the soda lime or barium hydroxide granules
  turn color or the granules become hard instead of
  crumbly, they are saturated with CO2 and should
  be replaced
• When in use, the granules will produce heat and
  condensation within the canister
• The color reaction is time limited
• Exhausted crystals should be removed immediately
  and replaced with new granules

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Parts of an Anesthetic Machine

• Carbon dioxide absorber
• Soda lime canister
• Should be changed after 6 to 8 hours of use
  depending on the size of the animal and the gas
  flow rate
• If machines are left standing for longer than 30
  days, granules should be replaced before using
  machine

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Parts of an Anesthetic Machine

• Exhaust valve
• Also called the pop-off valve, or pressure relief
  valve
• Exhaust gases leave the system via the exhaust
  valve entering the scavenger system
• Valve can be fully or partially open when a
  patient is using the machine
• Valve is closed for leak tests or when filling
  the reservoir for assisted respirations

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Parts of an Anesthetic Machine

• Manometer
• Measures the pressure in the system in mm Hg or
  cm H20
• Generally calibrated form -30 to 50 cm H20
• Gauge thus reflects the pressure of gas in the
  animals airways and lungs
• The pressure should be at 0 and never more than
  15 cm H20 (11 mm Hg)
• When providing positive assisted ventilation, the
  pressure should not exceed 15 to 20 cm H20 (11 to
  15 mm Hg)

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Parts of an Anesthetic Machine

• Oxygen flush valve
• O2 bypasses vaporizer, delivering 100 O2 to
  breathing system
• Enables the anesthetist to flush the system with
  pure O2
• Fills the reservoir and system for leak test
• Also flushes the anesthetic gases out of the
  circuit and replaces with pure oxygen
• Never use O2 flush valve with a Bain circuit in a
  small animal because it produces too much pressure

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Parts of an Anesthetic Machine

• Scavenger system
• Attached to the exhaust valve
• Consists of tubing that collects gases and
  directs them outside the building or to a
  charcoal canister
• Can be active or passive

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Parts of an Anesthetic Machine

• Negative pressure relief valve
• Some newer machines have this safety feature
• Valve opens in response to a negative pressure
  situation in the system
• Allows room air into the circuit
• Negative pressure could be due to an active
  scavenger system or a low oxygen supply

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Maintenance

• Oxygen tanks must be turned off to prevent excess
  pressure on the regulator
• Flush the remaining O2 to minimize damage to the
  pressure gauge and reducing valves
• Turn flowmeter off to prevent sudden rush of O2
  into the flowmeter when O2 is turned back on
• Dont over tighten because the knobs can be
  easily twisted off

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Maintenance

• After each anesthesia induction, removable
  machine parts and anesthetic equipment that come
  in contact should be washed in a mild, soapy
  solution, soaked in a cold disinfectant,
  thoroughly rinsed and dried
• The dome valves and absorbent canister should be
  disassembled and wiped dry.
• Flutter valves need periodic removal and cleaning
  with a disinfectant to prevent adherence to the
  machine housing

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Maintenance

• Vaporizers should be turned off when not in use
  and periodically emptied to prevent buildup of
  the preservative and other residue
• Best to clean and recalibrate by authorized
  personnel every 6 to 12 months
• Isoflurane does not contain a preservative

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Maintenance

• Barium hydroxide or soda lime granules found in
  the CO2 absorbers need replacing when the
  granules have changed color or cannot be easily
  crumbled
• Do not tightly pack and leave about 1 cm (1/2
  inch) of air space
• Avoid having dust enter tubing or hoses of the
  machine
• Rubber items will likely need to be replaced
  after prolonged use

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Environmental concerns

• Environmental pollution can be minimized through
  proper equipment use and scavenging of the gases
• Safe exposure limit for inhalant anesthetic
  agents has been set at 2 p.p.m. in room air
• Everyone, especially pregnant women, should avoid
  high levels of waste anesthetic gases
• Much of the anesthetic levels are because of
  leaks in anesthetic machines

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Environmental concerns

• Vaporizers and CO2 absorbers should be filled
  with minimal personnel in a well ventilated area
  while wearing gloves and masks
• Do not turn the vaporizer on and off until or
  while, the patient is connected to the machine
• During recovery, keep patient in a well
  ventilated area and on the machine until expired
  gases are scavenged

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Environmental concerns

• Use active scavenging systems whenever possible
  to ensure waste gases are drawn out of the area
• If passive scavenging is used, keep the hose as
  short as possible and have it travel downward
  toward the exhaust
• If it is not possible to install scavengers in
  all rooms where machines are used, either use an
  activated charcoal cartridge that must be
  replaced after 12 hours or substitute injectable
  anesthesia

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Environmental concerns

• Before anesthesia, the machine should be checked
  for both high and low pressure leaks
• Leakage of nitrous is the major environmental
  concern
• A high pressure system test monitors NO2 and O2
  leakage
• A low pressure system leak is in the anesthetic
  machine itself

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Environmental concerns

• Low pressure system test
• A low pressure system leak occurs between the
  flowmeter and the patient
• Turn the tank on, close the pop-off valve, and
  occlude the end of the hose so the gas should
  have nowhere to escape
• Adjust the flowmeter to at least 2 L/min of O2
  allowing the bag to fill gradually and then turn
  off the flowmeter
• If there is no escape of air when the bag is
  gently squeezed, then there is no low pressure
  system leakage

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Environmental concerns

• Low pressure system test
• System can also be checked by occluding as above
  and using the flowmeter to allow the system to
  pressure at 30 cm H2O
• Turn off the flowmeter
• The pressure should be maintained for at least 10
  seconds
• One can also listen for the hiss of escaping air
  or use a detergent solution as described earlier

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Breathing Systems

• Rebreathing systems
• Circle systems
• Rebreathing refers to breathing a mixture of
  expired gases and fresh gases
• The amount of CO2 in inhaled gases depends on
• Whether the rebreathing system has a CO2 absorber
• The flow rate of fresh gases (the higher the
  fresh gas flow rate, the more expired gas is
  pushed out the scavenger and not rebreathed
• Depending on the flow rate of fresh gas, the
  system is classified as a closed system (total
  rebreathing of expired gases) or semi-closed
  system (partial rebreathing of expired gases)

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Breathing Systems

• Closed rebreathing systems
• With closed systems the fresh gas flow rate is
  does not exceed the patients metabolic O2
  consumption of 5 to 10 mL/kg/min
• The system may be used with a closed pop-off
  valve and a fresh gas flow rate of 5 to 10
  mL/kg/min
• Expired gases are recirculated (after CO2
  removal) with incoming fresh gases

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Breathing Systems

• Closed rebreathing systems
• Danger of increased CO2 accumulation if CO2
  absorber not working efficiently
• It is economical and there is minimal pollution
• It takes longer to change planes of anesthesia
• O2 depletion and N2O buildup are common, so do
  not use N2O with this system
• Requires constant monitoring to ensure pressures
  do not build up in the system if the O2 flow
  delivered exceeds the metabolic requirement

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Breathing Systems

• Closed rebreathing systems
• It can be dangerous to run a rebreathing system
  with the pop-off valve closed, if the pop-off
  valve does not have a safety release at high
  pressures
• It is recommended that the pop-off valve be left
  partially open to prevent increases in pressure
  in the system and to adjust the O2 flow rate
  accordingly to prevent the rebreathing bag from
  collapsing
• If the bag does not collapse you can be confident
  that sufficient O2 is being delivered to meet the
  patients metabolic requirements

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Breathing Systems

• Semi-closed or partial rebreathing systems
• With semi-closed systems, the fresh gas is
  delivered in excess of metabolic consumption at
  25 to 50 mL/kg/min (suggested economical flow
  rate)
• The gas escapes through the pop-off valve to the
  scavenger or after having the CO2 removed by the
  soda lime and then recirculated with the fresh
  gases
• Higher flow rates can be used
• Less rebreathing will occur
• N2O buildup is less of a concern with higher flow
  rates
• Important to flush the system to prevent nitrogen
  buildup from the expired gases

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Breathing Systems

• Non-rebreathing systems
• There is no mixing of inhaled and exhaled gases
  and no rebreathing of expired gases all expired
  gas goes to the scavenger
• CO2 absorber not required
• Fresh gas flow rates required at 200 to 300
  mL/kg/min
• Fresh gas flow rates required at 130 to 200
  mL/kg/min with the Bain system
• May be some rebreathing of exhaled gases if a
  reservoir bag and low flow rate

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Breathing Circuits

• Many kinds of breathing circuits available
• Circle system
• Universal F-circuit
• Bain system (Coaxial)

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Breathing Circuits

• Circle system
• CO2 absorber
• Inspiratory and expiratory unidirectional valves
  (check valves or flutter valves)
• Two breathing hoses connected with a Y-piece to
  the patient
• Rebreathing bag
• Pop-off valve (exhaust valve)
• scavenger

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Breathing Circuits

• Circle system
• Can be used as a non-rebreathing system (200
  mL/kg/min)
• Can be used as a partial rebreathing system (25
  to 50 mL/kg/min)
• Can be used as a total rebreathing system (5 to
  10 mL/kg/min)

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Breathing Circuits

• Circle system
• An advantage is the mixture of expired gases with
  incoming gases
• Humidifies and warms the incoming gases
• Main disadvantages of the circle system occur
  with smaller patients
• Excess weight and bulk of the hoses
• Excess dead space
• Resistance to breathing caused by the
  unidirectional valves

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Breathing Circuits

• Universal F-circuit
• Basically a modified circle system where the
  inspiratory hose is placed within the expiratory
  hose
• Still requires a CO2 absorber, rebreathing bag,
  unidirectional valves, pop-off valve and scavenger

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Breathing Circuits

• Universal F-circuit
• Incoming fresh gas is warmed also by expired
  gases
• The advantage is lighter weight and less bulk
• Disadvantage is that if the system is stretched,
  the end of the inspiratory hose pulls away from
  the end of the expiratory hose
• Considered a safety feature so that the hoses
  dont break
• Increases the dead space within the circuit
• Even when not stretched, the dead space is
  equivalent to the circle system

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Breathing Circuits

• Bain system
• Consists of one tube inside the other
• Fresh gases flow through the inner tube
• Unused and exhaled gases flow through the outer
  tube
• There also is a rebreathing bag with a clip on
  the tubing between the reservoir bag and
  scavenger connection but no CO2 absorber
• Between breaths, the fresh gases flow through the
  inner tube toward the patient and then back
  through the outer tube toward the scavenger

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Breathing Circuits

• Bain system
• When the patient inspires, the gases are drawn
  from the inner tube, which will be 100 fresh
  gases or a mixture of fresh gases and expired
  gases, depending on the fresh gas flow rate
• This system can be used as a non-rebreathing
  system with a fresh gas flow rate of 200 to 300
  mL/kg/min
• The high flow rate pushes exhaled gases away down
  the outer tube so there is no rebreathing of
  exhaled gases
• By changing the flow rate to 130 to 200 mL/kg/min
  the system acts as a partial rebreathing system
• Most of the gases get pushed away but there is
  partial rebreathing of some exhaled gases

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Breathing Circuits

• Bain system
• Ideal for small patients (lt7kg)
• Lightweight
• Minimal dead space
• Little resistance to breathing
• Good for all small animals in general but is not
  economical when the patient weighs in excess of
  10kg
• Limiting factor is the size of the patient
• The O2 flowmeter must provide flow rates required
  for a partial or non-rebreathing system (130 to
  300 mL/kg/min)
• Total volume of the Bain hose must be greater
  than the tidal volume of respiration of the
  patient to effectively prevent rebreathing

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Breathing Circuits

• Bain system
• Good for procedures involving the head (less
  tubing in the way)
• Good for procedures with much manipulation (i. e.
  radiography, because there is less weight pulling
  on the head)
• Warming and humidification are minimal with
  partial rebreathing
• Requires a precision vaporizer

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Vaporizers

• Vapor pressure is characterized by the amount of
  vapor related to its liquid in a closed container
• The pressure exerted by the gas is called the
  vapor pressure and will increase with increases
  in temperature
• Most anesthetics vaporize at a concentration
  higher than necessary for clinical anesthesia
• So a vaporizer is used to deliver diluted
  anesthetics to patients

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Vaporizers

• Precision vaporizer
• Enables delivery of controlled concentrations of
  anesthetic vapor independent of time, temperature
  and fresh gas flow rate
• Temperature and flow rate are compensated for by
  the vaporizer or manually by the anesthetic
  technician

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Vaporizers

• VOC (vaporizer out of circle)
• Vaporizer is added to the system between the O2
  flowmeter and the circle
• The circle consists of the inspiratory and
  expiratory valves, breathing hoses,CO2 absorber,
  pop-off valve, scavenger and rebreathing bag

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Vaporizers

• VIC ( vaporizer in circle)
• Vaporizer is placed inside the breathing system,
  usually between the inspiratory valve and the
  patient
• VICs are always non-precision
• The carrier gas passes over the surface of the
  anesthetic liquid or past a wick
• Incoming gases mix with warm exhaled gases in the
  system
• Better vaporization of liquid is obtained when
  low fresh gas flows are used
• High flows cool liquid and reduce vaporization
• Are also safest when used with agents with low
  vapor pressure (e. g. methoxyflurane)