Ch 4 Flashcards
endotracheal tube?
a flexible tube, placed inside the trachea of an anesthetized patient, that is used to transfer anesthetic gases directly from the anesthetic machine into the patient’s lungs, bypassing the oral and nasal cavities, pharynx, and larynx
ET tubes are commonly used for patients undergoing general anesthesia because?
- they maintain an open airway
- decrease anatomic dead space
- allow precise administration of inhalant anesthetics and oxygen
- prevent pulmonary aspiration of stomach contents, blood and other material
- enable rapid response to respiratory emergencies
allow the anesthetist to accurately monitor and control patient respirations
What are the two basic types of ET tubes?
Murphy tubes and Cole tubes
Murphy tubes have?
beveled end, side opening (Murphy’s eye), and are cuffed or noncuffed
Cole tubes have?
no cuff or side hole but have an abrupt decrease in diameter near the patient end of the tube
Cole tubes are used specifically for?
species that have complete tracheal rings such as birds and some reptiles - this is to prevent damage to the trachea that would be caused by a cuffed tube
What are ET tubes made of?
- PVC (polyvinyl chloride)
- red rubber
- silicone
PVC tubes are?
transparent and somewhat stiffer than other types
Red rubber tubes are?
flexible and less traumatic but can kink or collapse, absorb disinfectant solutions, and tend to dry and crack after prolonged use
What are specialized rubber tubes?
spiral or anode tubes which contain a coil of metal or nylon embedded in the rubber designed to resist kinking or collapse from external pressure
Silicone tubes are?
expensive but combine strength with pliability r- resistant to collapse and less irritating to tissues
ET tubes come in ____ lengths.
standard
What is the scale on the side of the ET tube used for?
marks the distance from the patient end in centimeters
- used to estimate the appropriate distance to advance the tube
Tube size is most commonly expressed as the?
internal diameter (ID) in millimeters
ET tubes range in size from ___ to ___.
1 mm for exotic animals to 30 mm for mature large domestic animals
What are the endotracheal Tube parts?
patient end of tube, Murphy’s eye, the machine end, cuff or no cuff, pilot balloon, a valve and a tube tie
What does the Murphy’s eye do?
minimizes the risk of patient asphyxiation in the event that the end hole is blocked with mucous
What is asphyxiation?
act of cutting off the supply of oxygen supply; suffocation
The machine end of the ET tube does what?
protrudes from the mouth or nose and is connected to the breathing circuit of the anesthetic machine via the connector
What does the cuff do?
creates a seal between the tube and trachea
The cuff is connected via a small tube to a pilot balloon and a valve
What is the valve used for on the ET Tube?
used to inflate the cuff. The valve opens to permit air to enter or exit the cuff when a syringe is seated firmly into the valve opening and automatically closes when the syringe is removed.
What is the pilot balloon used for?
allows the anesthetist to monitor cuff inflation visually or manually
A cuffed tube is recommended for what reasons?
- the inflated cuff helps prevent leakage of air and gases around the tube
- minimizes the risk of aspiration of blood, saliva, vomitus, and other material into the lungs
- prevents the animal from breathing room air which could dilute anesthetic gases
ET tubes should be no longer than?
the distance between the most rostral aspect of the mouth and the thoracic inlet
What are the risks if the ET tube is too long?
- if the tube extends an excessive distance inside the trachea, the patient end may enter one main stem bronchus - only one lung will be infused with oxygen and anesthetic gas leading to hypoventilation, hypoxemia and difficulty keeping the patient anesthetized.
- if the tube extends beyond the rostral aspect of the mouth, it will increase mechanical dead space, resulting in hypoventilation (esp in small patients)
What is the guideline for ET Tubes?
if the tube is more than 2.5 cm longer than the distance between the most rostral aspect of the mouth and the thoracic inlet, it is too long and should be cut shorter or replaced with a shorter tube.
What is a laryngoscope?
a device used to increase visibility of the larynx while placing an ET tube
What is the blade of the laryngoscope used for?
to depress the tongue and epiglottis
What are the types of laryngoscopes?
Miller (blades are straight) and Mcintosh (blades are curved)
What are anesthetic masks?
cone-shaped devices used to administer oxygen and anesthetic gases to nonintubated patients via the nose and mouth
What are the anesthetic masks made of?
plastic or rubber
What are anesthetic chambers?
clear, aquarium-like boxes used to induce general anesthesia in small patients that are feral, vicious, or intractable (not easily controlled) or cannot be handled without undue stress
What is the primary function of any anesthetic machine?
to deliver precise amounts of oxygen and volatile anesthetic under controlled conditions to patients undergoing general anesthesia
What is the liquid that is typically used in anesthesia machines?
isoflurane and sevoflurane
What are the components of the anesthetic machine?
compressed gas supply, anesthetic vaporizer,
breathing circuit, scavenging system
What components are included in the compressed air supply?
compressed gas cylinders, tank pressure gauge, pressure reducing valve, line-pressure gauge, flow meter(s), oxygen flush valve
What components are included in the anesthetic vaporizer?
vaporizer inlet port, vaporizer outlet port and common gas outlet
What components are included in the breathing circuit - rebreathing (R) or non-rebreathing (N-R)?
Fresh gas inlet (R and N-R), unidirectional valves (R only), pop-off valve (R and N-R), reservoir bag, R and N-R), carbon dioxide absorber canister (R only), pressure manometer (R only), air intake valve (R only), breathing tubes (R only), Y-piece (R only)
What components are included in the scavenging system?
discharge hose (passive or active system) pressure regulator (active system outflow pipe (passive or active system) pump (active system)
What does the compressed gas supply do?
supplies carrier gases (oxygen, and sometimes nitrous oxide)
What does the anesthetic vaporizer do?
vaporizes liquid inhalant anesthetic and mixes it with the carrier gases
What does the breathing circuit do?
conveys the carrier gases and inhalant anesthetic to the patient and removes exhaled carbon dioxide
Breathing circuits are classified as?
rebreathing circuits or non-rebreathing circuits
What does the scavenging system do?
disposes of excessand waste anesthetic gases
What is tidal volume (Vt)?
the volume of a normal breath (approx 10 - 15 mL/kg body weight)
What is the carrier gas flow rate?
the amount of carrier gas that flows through the vaporization chamber (primarily controlled by the vaporizer dial setting) determines anesthetic output.
How do you determine the appropriate carrier gas flow?
calculated using the patient body weight and the tidal volume Vt or RMV (respiratory minute volume)
What is the Vt (tidal volume) considered to be approx?
10 mL/kg/min in most anesthetized animals
What is the RMV?
Vt (tidal volume) multiplied by the respiratory rate in breaths per minute (average 20 breaths/min in most patients)
- therefore RMV is considered to be about 200 mL/kg/min
Carrier gas flow rates depend on?
types of breathing sytstems (closed rebreathing, semiclosed rebreathing, or nonrebreathing)
Carrier gas flow rates depend on what periods of anesthesia?
induction, maintenance, or recovery or when changing the anesthetic depth
Relatively high carrier gas flow rates are used for what breathing system at all times regardless of the period of anesthesia?
non-rebreathing system
What breathing system are flow rates low (only enough to meet the metabolic needs of the patient?
closed rebreathing system
What does the semiclosed rebreathing system do in regards to flow rate?
flow rates vary from relatively low rates when maintaining a patient at a desired anesthetic depth to a relatively high rates during induction and recovery and when changing anesthetic depth
What are the high flow rates when using a mask or chamber induction?
1 to 3 L/min < 10 kg (mask)
3 to 5 L/min>10 kg (mask)
5 L/min induction chambers
What are the flow rates for a semi-closed rebreathing system?
- post induction (injectable agent)- high 50 to 100 mL/kg/min
- making changes in anesthetic depth - because of patient to light or too deep - higher flow rate 50 to 100 mL/kg/min
- maintenance - low flow - 20 to 40 mL/kg/min - small animals
3 to 5 L/min - large animal - anesthetic recovery - 50 to 100 mL/kg/min - maintain for 5 min or until patient must be extubated
Flow rates for non-breathing system?
high flow rates per unit body weight during all periods of general anesthesia (induction, maintenance, and recovery
What is the psi of the gas that the pressure-reducing valve decreases before the gas enters the flow meters?
40 to 50 psi
Flows are expressed in?
liters per min
What is fresh gas?
the combination of anesthetic vapor,oxygen and nitrous oxide (if present)
Where is the waste gas exit from the anesthesia machine?
at the pop-off valve and is removed by the scavenging system
Carbon dioxide is removed form a rebreathing circuit by?
absorbent granules -
How often does the absorbent granules need to be replaced?
when saturated or at least every 6 to 8 hours
What does the manometer measure?
the pressure of gases within the breathing circuit and the patient’s lungs
What are the guidelines for selecting a bag?
500 mL for up to 3 kg 1 L for 4 to 7 kg 2 L for 8 to 15 kg 3 L for 16 to 50 kg 5 L for 51 to 150 kg 30 L for large animals over 150 kg
