Breathing systems Flashcards
What are the 2 breathing systems?
Re-breathing: Circle/Y-piece, universal “F” Non-rebreathing: Mapleson(s), Bain
What are the 2 types of re-breathing systems? What are the components?
- Circle/Y-piece or universal F Components:
- Fresh gas and O2 flush
- unidiretional valves (1 inspiratory, one expiratory)
- breathing hoses (circle or universal F)
- CO2 absorber (i.e. soda lime)
- APL valve (aka pop-off), reservoir bag
T/F: The re-breathing system has a 2-way gas flow.
FALSE–it is a one-way (circular) gas flow
What does the CO2 absorber do in the re-breathing system?
Prevents rebreathing of excessive CO2
What are the advantages of the re-breathing system?
Lower fresh gas flow rate: saves $$$, decreases pollution, patient breaths warm, humidified gases
What are the disadvantages of the re-breathing system?
More components–>more potential for leaks Increased resistance for smaller patients (
Oxygen flush valve
Bypasses vaporizer: dilutes gases in breathing system and reservoir bag Delivers O2 directly to the breathing system: 35-75 L/min of 100% oxygen
When should you avoid using the oxygen flush valve?
Avoid activation with patient attached to system; NEVER NEVER NEVER use with non-rebreathing system
What must you check when changing breathing systems?
Connection of the fresh gas inlet
What is the adjustable pressure-limiting (APL) valve?
Aka pop-off valve Limits pressure buildup in breathing system
When is the APL valve closed?
OPEN ALWAYS unless: pre-use machine check (must OPEN when done); Must close to administer positive pressure ventilation (manual or controlled)
What happens when the APL valve is closed?
Closed APL valve–>increased pressure in breathing system–>cardiopulmonary injury–>DEATH
What is the breathing system pressure gauge?
Measures pressure in the breathing system; SHOULD BE ZERO
When will the breathing system pressure gauge NOT measure zero?
Performing leak checks (pre-use check) Providing positive pressure ventilation (IPPV)
Carbon dioxide absorber
Soda lime most commonly used Absorber assembly has canister to hold soda lime, 2 ports for connecting breathing tubes, fresh gas inlet, +/- unidirectional valve mount and bag mount
What is soda lime?
Calcium hydroxide with small amount of sodium hydroxide and color indicator
Indicator = ethyl violet (fresh = white; exhausted = purple)
What happens to soda lime when active?
Heat reaction and color change
When filling soda lime…
Do not pack tightly, avoid dust of broken particles Check gaskets and seals as a source of leaks (esp. if dust particles present)
What are the signs of soda lime exhaustion
- Increase end tidal CO2
- If at a light enough plane of general anesthesia: increased ventilation, increase in HR and BP initially (then decrease)
- Rebreathing (seen on ETCO2)
- Respiratory acidosis
- Red mucous membranes (carbon monoxide production and inhalation)
What are the functions of a reservoir bag?
Observe ventilation, inspiratory reserve, administer manual positive pressure ventilation
How do you calculate the reservoir bag size?
Tidal volume (10-20 mL/kg) x 6 Round up if between sizes
What is the typical oxygen flow rate (re-breathing) for induction and recovery in small animals?
HIGH: 50-100 mL/kg/min O2
What is the typical maintenance oxygen flow rate (re-breathing) in small animals?
SEMI-CLOSED: 20-50 mL/kg/min O2
What is the typical induction and recovery oxygen flow rate (re-breathing) in large animals?
20-50 mL/kg/min O2
What is the typical maintenance oxygen flow rate (re-breathing) in large animals?
LOW: 10-20 mL/kg/min O2
What are the components of the non-rebreathing system?
Fresh gas non-rebreathing tubes
APL (Mapleson D) OR open/close (Mapleson F) valve
Reservoir bag
What are the missing components in the non-rebreathing system (compared to the re-breathing system)?
Soda lime canister Unidirectional valves O2 flush button (NEVER USE WITH NON-REBREATHING SYSTEM)
What are the advantages of the non-rebreathing system?
Very light, with minimal dead space or resistance to ventilation (good for patients = 3-10 kg) Fewer components = fewer potential for leaks [Anesthetic gas] changes rapidly (high gas flow)
What are the disadvantages of the non-rebreathing system?
High gas flow rates: $$$ to run in larger patients, increased pollution, no rebreathing = gases not as warm or humidified
What are the oxygen flow rates in non-rebreathing systems (compared to re-breathing systems)?
HIGH: O2 flow is mechanism for eliminating CO2 Must be at least 2-3 x tidal volume in most cases (200-300 mL/kg/min O2)
What are the indications of endotracheal tubes and intubation?
- Maintain patent airway
- Protect airway from foreign material (blood, regurgitation)
- Provide intermittent positive pressure ventilation (IPPV)
- Apply tracheal or bronchial suction
- Administer oxygen
- Deliver inhalant anesthesia
What are the benefits of intubation?
Reduced anatomical dead space (IF correct size/position of tube; dead space = air without gas exchange)
Maintain inhalant anesthesia with minimal environmental contamination (properly inflated cuff)
What are the 4 routes of intubation?
- Oral
- Nasal
- External pharyngotomy
- Tracheostomy
What is the advantage of cuffed endotracheal tubes?
Protect airway and environment better, but need to inflate carefully to avoid trauma
What are the 2 cuff types?
High volume-low pressure (preferred) High pressure-low volume (protect trachea)
What connects the endotracheal tube to the breathing system?
15 mm OD connector
What are the different types of endotracheal tubes? Which is most commonly used in veterinary anesthesia?
Murphy (most commonly used in vet med)
McGill
Wire-reinforced (avoid use in MRI)
Cole (some avian pts) tracheostomy
How do you decide which size endotracheal tube to use?
Poiseuille’s law: R = 8nl/pi*r^4 Tubes with larger radius and shorter length will have LESS resistance to air flow
What size tubes do you use for the following (general guidelines, adult):
Cat
Beagle
Labrodor
Great dane
Sheep
(~40kg) Horse
- Cat = 3.5-4.5
- Beagle = 8.0-10
- Labrodor = 10, 11, 12
- Great dane = 14, 16
- Sheep = 10.0, 11, 12
- Horse = 26, 30
What steps are taken when preparing to intubate?
- ETT: check size (diameter–ID, palpate; length–tip of nose to thoracic inlet; set up 3 sizes: 1 you think, 1 smaller, 1 larger), inflate cuff to check for leaks, ensure it’s clean and dry
- Cuff syringe
- Tube tie (1st tube, then around ears or muzzle) +/- special supplies (stylet, mouth gags, etc.)
Laryngoscope–what does it do, how do you use it?
- Makes intubation safer and easier
- Allows visualization of airway
- Light source
- How to use it:
- Apply light pressure to base of tongue, just rostral to epiglottis
- Apply gentle pressure ventrally, this tilts larynx, opens glottis, and frees soft palate from epiglottis (if it was entrapped)
- DO NOT apply significant pressure directly on epiglottis! (risk = fracture of hyoid apparatus)
Safe ETT cuff inflation
- After intubation, connect patient to breathing system with O2 flowmeter ON
- GOAL: NO audible release of gas from around the endotracheal tube when the APL valve is closed and the reservoir bag is squeezed to 20 cmH20
- However, at 30 cmH20 air should be audibly escaping around tube (If not, remove air from pilot balloon until heard–prevents over-inflation)
- Do NOT inflate cuff without first checking to see if you need any air in it
- Caution when moving patient with inflated ETT cuff
Potential complications of ETT
- Laryngeal damage (mostly small animals);
- laryngospasm (esp. cat, sheep, pig, rabbit),
- hematoma, edema
- Tracheal damage (over-inflated cuff, moving/twisting inflated cuff)
- poss. consequences = mucosa sloughing, stenosis, persistent tracheal membrane (avian), tracheal rupture, pneumothorax, pneumomediastinum
- Tube obstruction (patient position, secretions, cuff over-inflation)
- Endobronchial intubation
- ETT advanced too far in airway
- Hypoxemia, tachypnea, cynosis?
- ETT inhalation, ingestion
- Always extubate rostrally to avoid shearing teeth!
What is the purpose of scavenging waste gases? What types are there?
- Essential to SAFE anesthesia practices!
- To collect and transport waste gases from anesthesia machine to safe disposal area
- 2 types: active and passive
What are the 4 elements of scavenging waste gases?
- Collecting system (APL valve)
- Transfer system/interface
- Receiving system
- Disposal system
What is the ppm for scavenging waste gases? What should exposure to halogenated anesthetic agents such as isoflurane and sevoflurane be?
100% gas = 1,000,000 ppm
1% gas = 10,000 ppm
Olfactory >/= 125 ppm
Exposure should be < 2 ppm
What are the 7 steps in scavenging waste gases?
- Scavenge everything (even in recovery)
- No leak technique (< 300 mL/min acceptable)
- Use properly inflatted cuffed ETT
- Check for tight fittings
- Maintain on closed or low flow system
- Good room ventilation = minimum 15 air changes per hour
- Leak test before every machine use
What are the passive systems in scavenging waste gases?
- Non-recirculating room ventilation systems
- Charcoal absorption (F air canisters)*
- does NOT scavenge nitrous oxide
- Piping direct to atmosphere (i.e. via window)
What is the active system when scavenging waste gases?
Piped vacuum (white drop and tubing)*–central vacuum system capable of handling high volume (30 L/min flow)
What are the advantages of using charcoal absorption when scavenging waste gases?
- Absorbs hydrocarbons
- Does not release to ozone
- Portable
What are the disadvantages to using charcoal absorption when scavenging waste gases?
- Does not absorb N2O (only absorbs hydrocarbons)
- Flow-limited
- Added resistance
- Weigh before use (record # of grams)
- Discard when 50 g + or 8-12 hours of use
- FINITE use
What are some other sources of pollution to consider?
- Gas sampling monitors
- Capnograph
- Spirometry
- Induction
- Chamber/box
- Face masks
- Recovery rooms
- Patient exhales inhalent to recover
- 20 air exchanges per hour needed
- Leave patient on machine with O2 and scavenge
