Review Exam 1 Chapter 15 Flashcards
Nitrous Oxide E Cylinder Color
Blue (blue international)
Oxygen E Cylinder Color
Green (white international)
Air E Cylinder Color
Yellow (Black & White international)
Oxygen E Cylinder PSI
1900
Nitrous Oxide E Cylinder PSI
745
Air E Cylinder PSI
1900
Oxygen E Cylinder Volume
660 L
Nitrous Oxide E Cylinder Volume
1590 L
Air E Cylinder Volume
625 L
Oxygen, N2O, and Air PISS Positions
Oxygen - 2,5
N20 - 3,5
Air- 1,5
In the PISS how many pin positions are there and what side does 1 start on?
6 positions.
1 starts on the left side of the cylinder.
What are the three functions of the hanger yoke?
- Orients the cylinder
- provides a gas-tight seal
- ensures unidirectional flow into the machine
What is the formula for calculating amount of gas remaining in O2 and Air E Cylinder?
Full Capacity (L) / Full PSI = Current capacity (L) / Current PSI
*Will have current PSI and solve for current capacity
How do you determine how much time to empty of an oxygen E Cylinder?
current cylinder volume / flow rate
ex: 174 L / 2 L/min = 87 min
Why doesn’t the PSI of N2O estimate the volume in an E cylinder
N2O is stored as a liquid, therefore the cylinder pressure is the vapor pressure of the liquid at room temp.
When will the PSI of a N2O E cylinder drop?
When all of the liquid is gone. At this point the cylinder is more than 3/4 empty
What are the contents of compressed air?
Nitrogen (78%) Oxygen (21%) Argon (1%) Carbon Dioxide (0.03%) Other gases in trace amounts
What are the 5 tasks of oxygen in the anesthesia machine?
- proceeds to the fresh gas flowmeter
- powers the oxygen flush
- activates the fail-safe mechanisms
- activates oxygen low-pressure alarms
- compresses the bellows of mechanical ventilators
What is the delivery rate of the oxygen flush valve?
35 - 75 L/min
What is the fail-safe system?
A device that halts the delivery of all other gases if the patient has a potential to receive a hypoxic gas mixture (less than 21% oxygen)
Does the fail-safe system analyze oxygen pipeline content?
NO! It is only activated if oxygen pipeline pressure falls below 20 psi. It does not protect the patient from a pipeline crossover.
When does a low pressure alarm activate?
When oxygen pressure drops below 28 psi
What are the two types of oxygen analyzer sensors?
Which is more widely used?
- electrochemical (galvanic fuel cell) & paramagnetic
- paramagnetic is more widely used due to fast response, low cost, and low maintenance
What is latent heat of vaporization?
As evaporation proceeds, the evaporating molecules acquire heat from the remaining liquid causing the liquid to cool.
This cooling slows the rate of further vaporization
Why is copper used in vaporizers?
High Thermal conductivity and thermal capacity prevents cooling of liquid and maintains vaporization.
The rate of vaporization depends on what three things?
- temperature
- vapor pressure of the liquid
- partial pressure of the vapor above the evaporating liquid
What is the splitting ratio?
gas entering the vaporizing chamber divided by total gas flow
How does the variable-bypass vaporizer deliver volatile anesthetic to the patient?
A small portion of gas flow (carrier gas) enters the gas chamber and flows over the liquid anesthetic and picks up anesthetic vapor. This fully saturated carrier gas is then diluted with the remainder of gas flow (bypass flow) to produce a desired final concentration of gas.
How does a measured-flow vaporizer deliver anesthetic to the patient?
The gas never comes into contact with the liquid anesthetic, instead vapor is added to the fresh gas flow as it flows through the vaporizer.
Why can’t desflurane be placed in a variable-bypass vaporizer
Desflurane is near boiling at room temperature and it would constitute a 100% output and a hypoxic breathing mixture would result.
What is a time constant?
- 1 time constant is capacity divided by flow to bring a system 63% of the way to equilibrium
- 2 time constants 86%
- 3 time constants 95%
What is the purpose of all anesthesia breathing circuits?
delivery of oxygen/anesthetic and the elimination of carbon dioxide.
What is the effect of increased dead space?
Higher likelihood of rebreathing exhaled CO2
How does one avoid hypercarbia in the face of acute increased dead space?
Increase minute ventilation
How is alveolar ventilation calculated?
Minute ventilation minus dead space ventilation
VA = VE - VD
When the minute ventilation is fixed, what happens to alveolar ventilation when dead space is increased?
Alveolar ventilation is decreased, thus increasing arterial CO2
Where does dead space end in a circle breathing system?
At the Y-piece (where inspiratory and expiratory gas streams diverge
Is dead space increased with longer inspiratory and expiratory hoses?
No
In open breathing circuits is there a reservoir (breathing bag)? Rebreathing? Name an example.
Reservoir: NO
Rebreathing: NO
Example: Nasal cannula or simple face mask
In semi-open breathing circuits is there a reservoir? Rebreathing? Name an example.
Reservoir: Yes
Rebreathing: No
Example: Circle at high fresh gas flow (more than minute ventilation)
In semi-closed breathing circuits is there a reservoir? Rebreathing? Name an example.
Reservoir: Yes
Rebreathing: Yes (partial)
Example: circle at low fresh gas flow (less than minute ventilation)
In closed breathing circuits is there a reservoir? Rebreathing? Name an example.
Reservoir: yes
Rebreathing: Yes (complete)
Example: Circle at extremely low fresh gas flow with APL valve closed
What are some common features of nonreabreathing systems?
- All lack unidirectional valves
- All lack soda lime carbon dioxide absorption
- fresh gas flow determines amount of rebreathing
- resistance and work of breathing are low.
How do you calculate fresh gas flow required to prevent rebreathing?
two to three times minute ventilation.
-as a general rule minimum of 5L/min is used
What are advantages of a nonreabreathing system?
- lightweight
- convenient
- easily sterilized and scavenged
- exhaled gases in corrugated limb may give heat and humidity to inhaled gas
What are disadvantages to nonrebreathing systems?
- unrecognized disconnection or kinking of fresh gas hose in the bain circuit
- pollution increased costs of agents and gases due to need for higher flows
- loss of heat from patient
- may require disconnection of circle fresh gas supply hose and scavenger connections for assembly -> can be reassembled improperly
Why is the circle system most commonly used?
It prevents rebreathing of CO2 while allowing rebreathing of all other gases
If the APL valve is completely open where does gas go when the bag is squeezed?
To the scavenger
If the APL valve is completely closed where does gas go when the bag is squeezed?
Ventilates the lungs
What are two reasons for increased inspired CO2 in a circle system?
Absorbent granules have been exhausted or the unidirectional valves are faulty.
If inspired CO2 is more than ____ fresh gas flows should be increased to ___ converting the circle system to a ____ system
- 1 to 3 mmHg
- 5 to 8 L/min
- semi-open
If inspired CO2 decreases after increasing fresh gas flow what is the cause? If it does not decrease?
- exhausted absorbent canister
- incompetent unidirectional valves
What are advantages of the circle system?
- constant inspired concentrations
- conservation of respiratory tract heat and humidity
- minimal OR & environmental pollution
- useful for closed, low flow and semi open configurations
- low resistance (not as low as nonrebreathing circuits)
What are disadvantages of circle systems?
- relatively complex
- opportunities for misconnection or disconnection
- malfunctioning of unidirectional valves
- less portable
- increased dead space.
Circle systems with smaller volume will have shorter ___
Time conastants
What is a time constant?
- Capacity divided by flow
- measures how quickly a breathing system reaches equilibrium with a change in the inflow
When is a circle system with higher flows desired? Why?
- When rapid changes are desired, such as induction and emergence
- each breath reflects the dialed concentration because there is no rebreathing of exhaled gases
What are absolute contraindications to low fresh gas flow (<1L/min)?
- smoke inhalation injury or malignant hyperthermia (because washout of dangerous gases or a high O2 uptake is expected)
- failure of inspired O2 or anesthetic agent monitors
- failure of soda lime granules.
What are relative contraindications to low fresh gas flow?
- using older equipment that is less leak-proof
- face mask anesthesia
- during rigid bronchoscopy
- when using an uncuffed ETT
How do heat and moisture exchanging filters work?
They precipitate exhaled water vapor in their filter media. The next inhalation returns the water to the patient. Heat loss is reduced because they decrease the rate of evaporation of water from the tracheal mucosa.
What are the activators of soda lime to speed the reaction of CO2 and soda lime?
NaOH and KOH
*KOH used less frequently because of implications with production OF CO and compound A
What is produced when CO2 interacts with the activators?
water and energy
The absorption of 1 mol of CO2 produces how much energy?
13,000 kcal of heat energy
What is ethyl violet
an indicator of absorbent pH in soda lime
What is the critical pH that changes ethyl violet from colorless to purple?
- 3
* as CO2 is absorbed the CO2 absorbent becomes less alkaline, reaching the critical pH to which it is exhausted.
What is the water content of soda lime?
15-20%
What is the size of absorbent granules?
4-8 mesh
What is the trade off with larger & smaller sized granules?
- Larger granules have a decreased resistance to flow but lower absorbent capacity
- smaller granules have an increased resistance to flow but greater absorbent capacity.
What anesthetics are degraded the least and most in soda lime?
least: desflurane
most: sevoflurane
What may be produced when sevoflurane contacts dessicated soda lime?
Compound A
What is the recommendation to prevent production of compound A with sevoflurane use.
Do not use fresh gas flows less than 1-2 L/min for more than 2 MAC-hours
Which methyl ethyl ether has the highest incidence of carbon monoxide production?
Desuflurane, followed by isoflurane.
What is channeling and the wall-effect?
Exhaled gas follows a path of low resistance (along the canister wall or other channels) that may be exhausted before the capacity of the bulk container is exhausted.
What are early clinical signs of CO2 absorbent exhaustion?
- Increased ETCO2
- Respiratory Acidosis
- Hyperventilation
- signs of SNS activation
- increased bleeding at surgical site
- color indicator
What is the average maximum production of CO2 by the anesthetized adult?
12-18 L/hr
What is the purpose of the ventilator relief valve?
It maintains circuit volume and pressure in a gas-driven bellow system by releasing gas into the scavenger at a rate equal to fresh gas flows during the expiratory phase.
how much PEEP do standing bellows deliver to the patient?
2-3 cm H2O
What is volume controlled ventilation?
Inspiration is terminated when the desired tidal volume is delivered or if an excessive pressure is reached (60-100 cm H2O). Peak inspiratory pressure is uncontrolled.
What is Pressure-controlled ventilation?
Target pressure is adjusted for the desired tidal volume.
Tidal volume is uncontrolled.
Which patients would benefit from pressure controlled ventilation?
patients with high inspiratory pressure, low compliance, or airway leaks.
What are some examples of patients with high inspiratory pressure?
- emphysema
- neonates
- LMAs
What are some examples of patients with low compliance?
- pregnancy
- laparoscopic surgery
- morbid obesity
- ARDS
What are some examples of airway leaks?
- uncuffed ETTs
- LMAs
What is pressure-controlled ventilation with volume guarntee?
Begins by delivering a volume breath at the set tidal volume. The patient’s compliance is determined and then the inspiratory pressure is adjusted for the next breath.
What is synchronized intermittent mandatory ventilation?
Intermittent mandatory breaths are delivered in synchrony with and triggered by the patient’s spontaneous efforts.
-Volume, pressure, rate, trigger window, and sensitivity are set
What is the trigger window?
Controls the amount of time during each expiratory cycle the ventilator is sensitive to spontaneous breaths.
When switching from adult to pediatric circuits what machine checks must be repeated?
leak and compliance tests
How is the total tidal volume delivered to the patient determined?
volume delivered from the ventilator + fresh gas flow during the inspiratory phase.
What does an I:E ratio of 1:2 mean?
The ventilator spends 20 seconds (1/3 of time) in the inspiratory phase and 40 seconds (2/3 of time) in the expiratory phase
How is fresh gas flow during the inspiratory phase calculated?
Determine the inspiratory fraction of the I:E ratio, multiply it by the total fresh gas flow in mL, then divide the answer by respiratory rate.
Ex: IE ratio of 1:2, RR of 10, and fresh gas flow of 4L/min. 1/3 of 4,000 = 1320 mL; 1320/10 = 132 mL
What are the components of the scavenger system?
- Gas collection assembly
- Transfer tubing (19 or 30mm)
- Scavenging interface (most important part)
- Gas disposal tubing
- Gas disposal assembly (active or passive)
What are the OSHA recommendations for occupational exposure to halogenated agents and N2O?
Halogenated agents : <2 ppm
N2O: <25 ppm
What is a closed interface?
- Communicates with the atmosphere through valves
- must have positive pressure relief valve if used with passive or active disposal system
- negative pressure relief valve if used with active disposal system.
What is the purpose of a positive pressure relief valve in the scavenging system?
It vents excess system pressure if obstruction occurs downstream from the interface.
What is the purpose of a negative pressure relief valve?
protects the circuit from subatmospheric pressure if active disposal is used.
What is the open interface on a scavenger system
- No valves, is open to atmosphere
- Must only be used with an active system
- A reservoir is required
- Safer for the patient (less risk of barotrauma)
