Anesthesia Equipment & Technology(test 2) Flashcards
What 2 factors affect the resistance of flow in the patients anesthesia circuit?
- width of tubing
2. length of tubing
What effects does the resistance of the anesthesia circuit have on the patient?
increases the work of breathing such that a spontaneously breathing patient under anesthesia should always be assisted
What are the advantages of using a rebreathing circuit?
- cost reduction
- increased warmth and humidity of inspired gases
- decrease of OR contamination
What effects do higher FGF have on rebreathing?
Higher FGF is associated with less rebreathing and the higher the FGF the more gas concentration in circuit will resemble that at the common gas outlet
What are 3 effects of rebreathing?
- heat and moisture retention
- altered inspired O2/CO2
- altered agent concentrations
What factors affect rebreathing(4)?
- FGF
- apparatus dead space
- breathing system design
- empty space
How is hypercarbia avoided as related to dead space ventilation?
to avoid hypercarbia with increased dead space….minute ventilation must increase(alveolar ventilation = VE - VD)
What are 4 characteristics of a non-rebreathing circuits(4)?
- low resistance
- less dead space/empty space
- lack of unidirectional valves
- lack of CO2 absorption
What is the most popular non-rebreathing circuit?
Mapleson D;
Why is the Mapleson D the most popular non-rebreathing circuit?
as excess gas savaging is easy and most efficient during controlled ventilation
D group most common
What is the Bain modification to the Mapleson circuit?
involves placement of the FGF through the expired gases to heat inspired gases
FGF runs inside the corrugated tube
What are the advantages of using a NRB circuit(6).
- inexpensive, rugged, excellent method to deliver + pressure ventilation
- variations in minute volume affects ETC02 less (less dead space)
- in bain system: insp. limb heated by warm exhaled gases
- Resistance usu very low (supports spontan. ventilation)
- less drag on mask or ETT (lightweight)
- changes in fresh gas concentrations—> result in rapid changes
- no carbon monoxide or compound A (no C02 absorbent)
What are the disadvantages of the NRB circuit
- High FGF required (1.5x minute ventilation)— resulting in pollution and economic
waste - low inspired heat and humidity— bc higher FGF
- requires frequent adjustment in FGF
- Not suitable for pt with MH history—> bc inability to increase FGF enough to blow
off C02
What are 3 reasons for a decline in the use of NRB circuits?
- modern efficient ventilators
- conservation of heat with rebreathing circuits
- waste gas management
What are the advantages of the circle systems(rebreathing circuits?
* economical: ‣ expired oxygen reused ‣ anesthetic vapor reused ‣ FGF & anesthetic agent utilization are minimized * Humidifies inspired gas * Preserves heat and pt temp
What are the disadvantages of the circle systems?
- Complex
- less portable than non-rebreather
- opportunities for disconnect
- unidirectional valves may malfx
- incr. dead space
- incr. “empty space” (longer diffusion time)
Describe the basic configuration of the circle system in regard to location of the ventilator/bag, FGF and carbon dioxide absorbent
- FGF enters circuit from CGO of anesthesia machine
- FGF through the one-way valve on the inspiratory limb of the anesthesia circuit toward the patient Y
- is exhaled from patient and goes through the one-way valve on the expiratory limb of the anesthesia circuit
- enters and exits reservoir bag
- excess gas if vented out through the pop-off valve to scavenging system(APL)
- through the absorbent canister where CO2 is removed
- then back to the patient
Compare semi-closed circle systems to closed and semi-open systems
Semi-closed:
- delivers positive pressure
- delivers oxygen and anesthetic gas
- Removes waste and anesthetic gas
- Conveys excess gas to scavenging system
- Humidification
- Nominal dead space
- Low FGF
Semi-Open:
- Delivers positive pressure
- Delivers oxygen and anesthetic gas
- Removes waste and anesthetic gases
- Excess gas released into air
- No humidification
- Minimal dead space
- *High FGF(1.5xMV)
What are 2 functions of the APL valve?
- releases gas into scavenging system
* controls pressure in breathing circuit
What are the basic characteristics of carbon dioxide absorbents(5)?
- Gas tends to travel along periphery (outside) of canister and inlet
- Carbon dioxide absorbers do not support bacterial growth
- Each canister should last 20-30 hours (25 liters of carbon dioxide per 100 grams of absorbent)
- Each canister is approximately 55% granules, 45% air space
- Smaller granules absorb more but create more dust and “cake” or harden, so usually a mixture of large and small are packaged
Identify moisture content and granule size of common carbon dioxide absorbents
- Soda lime: 14-19% water; 4-8 mesh granules
- Baralyme: ?
- Medisorb: 16-20% water; 4-8 mesh granules
- Dangersorb: 14% water; 4-8 mesh granules
- Ansorb: 14.5% water; 4-8 mesh granules
Describe the chemical reaction involving CO2 and soda lime
- Reaction occurs as water (H2O) reacts with carbon dioxide (CO2) to produce carbonic acid (H2CO3) and heat (canister may become warm)
- H2CO3 (acid) then reacts with the base in the soda lime (sodium hydroxide, or NaOH) to form sodium carbonate, water and heat
- CO2 + H2O = H2CO3
- H2CO3 + 2 NaOH=Na2CO3 + CO + 2 H2O + Heat
- Na2CO3 + Ca(OH)2=CaCO3+ 2 NaOH
- Water is necessary to react with CO2, dissipate heat and humidify gases
List common clinical signs(7) of CO2 canister exhaustion
- rise in heart rate(later will fall)
- increased respiratory rate
- respiratory acidosis
- dysrhythmia
- signs of SNS activation(flushed, sweating)
- increased bleeding
- increased ETCO2
Describe the function of the expiratory valve on the circuit
The expiratory valve closes to prevent rebreathing of exhaled gas that still contains CO2. Valve incompetence is usually due to warped disks or seat irregularities. The exp. valve is especially vulnerable since it is exposed to the humidity of expired gas.
Identify measurement units for airway pressure
kPa or cm H20
What are the 4 uses of the pressure gauge?
- used to measure circuit pressure between inspiratory and expiatory valves
- higher pressures reflect change in compliance or resistance
- lower pressures reflect circuit leak
- pressure higher than 20 cmH20 opens esophageal sphincter(mask induction or anesthetic)
What are 4 uses for the reservoir bag?
- provides a means for delivering positive pressure
- can serve as a monitor for spontaneous ventilation
- allows the use of lower FGF
- protects the patient from excessive pressure in the breathing circuit
What are 3 characteristics of a closed system?
- oxygen supply equals metabolic consumption of the patient(no “waste” of oxygen, hence term “closed circuit”)
- extremely economical as far as fresh gas and agent
- retains more heat and humidity
- less environmental pollution
What are 3 breathing circuit hazards?
- circuit disconnection is a leading cause of critical incidents and the most common place this occurs is at the Y
- inability to ventilate secondary to a leak in the circuit.
To detect leaks and disconnects—> circuit must be check by a positive pressure test
What is the component of the machine check that verifies an intact circuit?
To detect leaks and disconnects circuit must be checked by inflating and testing ability to hold positive pressure.
List 5 criteria activating a ventilator alarm.
- High pressure
- Pressure less than volume or pressure threshold for greater than 15 seconds
- Continuing high pressure
- Subatmospheric pressure
- Low tidal volume or minute ventilation
- High respiratory rate
- Reverse flow (incompetent expiratory limb valve)
- Apnea/disconnect alarm
List 5 causes of increased peak inspiratory pressure.
- Increased tidal volume
- Decreased pulmonary compliance
- CHF
- Trendelenburg
- Pleural effusion
- Abdominal packing/insufflation
- Obesity
- Tension pneumothorax
- Endobronchial intubation
- Increased airway resistance
- Kinked ET tube, airway compression
- Bronchospasm
- Secretions/foreign body
List 2 disadvantages to using descending ventilator bellows.
- Inability to visually detect leak
- Leak causes room air to enter the bellow
- Tidal volume lost but unknown to CRNA
List 2 advantages and disadvantages associated with an electronic(piston) ventilator.
- By eliminating the need for a drive gas circuit, a more stable flow can be provided
- Tidal volume more precise
- Reservoir bag is NOT isolated from breathing system and acts to modulate pressure increases in the system
- During inspiration, the bag is isolated from the breathing system and collects FGF from breathing system (bag expands and contracts)
- Disadvantages include lack of conventional bellows (up and down), no audible excursion of bellows and limited ability to adapt to nonrebreathing circuit
Identify a risk involved with switching ventilator modes during an anesthetic
• Must be careful when switching between modes to assess compliance changes (PIP and/or VT may be inappropriate)
Identify the most commonly used mode of ventilation and why it is used.
- Volume control
- Preset tidal volume is administered, independent of patient effort
- Flow rate is fixed at a constant value during inspiration
- Changes in compliance or resistance are reflected in changes in PIP
- Delivers a set volume at a set flow rate with pressure dependent on compliance and resistance
- Flow is constant throughout the inspiratory cycle (square waveform)
- Pressure increases throughout the inspiratory cycle
- Pressure waveform resembles a shark fin
- Rate of volume increase is linear
Define volume control ventilation(flow pattern, effect of compliance and resistance).
- Preset tidal volume is administered, independent of patient effort
- Flow rate is fixed at a constant value during inspiration
- Changes in compliance or resistance are reflected in changes in PIP
- Delivers a set volume at a set flow rate with pressure dependent on compliance and resistance
- Flow is constant throughout the inspiratory cycle (square waveform)
- Pressure increases throughout the inspiratory cycle
- Pressure waveform resembles a shark fin
- Rate of volume increase is linear
Define pressure control ventilation(flow pattern, effect of compliance and resistance).
- Ventilator generates pressure to set level and maintains flow
- Decelerating inspiratory flow allows alveolar recruitment (flow rates are NOT fixed)
- Tidal volume may fluctuate with changes in resistance and compliance
- Reaches a preset pressure but achieves a target volume
- Volume achieved depends on compliance and resistance
- Pressure is constant throughout the inspiratory cycle
- Flow decreases as pressure in lung decreases (plateaus) but peak flow remains the same
- Increased mean airway pressures
- Improved alveolar recruitment from decelerating inspiratory phase
- Recruits slow alveoli
Identify advantages and disadvantages to the use of pressure controlled ventilation(PCV).
- Advantages
- Decelerating inspiratory phase allows recruitment of slow alveoli
- PCV improves oxygenation with lung injury, OLV and obese as gas is delivered to less complaint alveoli
- Disadvantages
- Tidal volume fluctuates with changes in resistance and may be very low or high
- Increasing respiratory rate decreases inspiratory time and lowers tidal volume
- PEEP decreases tidal volume
Identify 2 patient populations that may benefit from PCV.
• Lung injury, OLV, obese
Describe the potential effects of I:E manipulation on patients with lung disease.
- Reverse I:E ratio
- Alveolar recruitment may be improved by prolonging the inspiratory period
- Slow alveoli are recruited similar to pressure control
- May be problematic in obstructive lung disease with “stacking”
- Longer I:E ratio
- Prolonged expiratory phase (1:3 or 1:4) allows compensation for flow related collapse
- Medium sized airways (generations 11-14) stay open longer
- FRC potentially improved through recruitment via “pseudo-PEEP”
List 2 settings which require manual adjustment during the use of SIMV and why they are necessary.
- Minimum minute ventilation must be selected
* pressure support ventilation
Compare SIMV and PSV(differences between the two modes, which mode is best used for an LMA).
- Designed to augment patient’s spontaneous breaths by supplying positive pressure in response to patient-initiated breaths
- Support may be pressure or flow initiated and is usually used with LMA
- Support usually pressure-based (tidal volume determined by pressure, lung compliance etc.)
- Back-up or “apneic” SIMV rate is usually part of this mode
- Psv best for LMA
List 3 advantages of PEEP
- Increases lung compliance and recruits alveoli
- Increases functional residual capacity
- Decreases ventilation-perfusion mismatch*
- Increases tidal volume above closing volume
- Redistribution of extravascular water
