Anesthesia Delivery Systems - EXAM 2 Flashcards
CO2 can also be eliminated from the breathing circuit by the use of _____________ .
carbon dioxide absorbent media
CO2 is eliminated from the breathing circuit by washout of ______________?
fresh gas flow
Essential requirements of the breathing system are:
- deliver gases from the machine to the alveoli in the same concentration as set and in the shortest possible time
- effectively eliminate carbon dioxide
- have minimal apparatus dead space
- have low resistance
What will decrease resistance in the breathing system?
-short tubing, large diameter tubing, avoid sharp bends, caution with valves, minimize connections
2 ways rebreathing is beneficial:
- cost reduction
- adds humidification/heat to gases
(do NOT want to rebreathe CO2)
Higher fresh gas flows allows for __________?
less rebreathing (in any type of circuit)
What can increase the chance of rebreathing CO2?
-dead space
How can apparatus dead space be minimized?
- by separating the inspiratory and expiratory stream as close to the patient as possible
What are the four classification of anesthesia delivery systems?
- open
- semi open
- semi closed
- closed
Characteristics of an open system:
- NO gas reservoir bag
- NO valves
- NO breathing of exhaled gas
What are the 2 types of open systems?
- insufflation/blow-by
- open drop
The “Steal” induction is considered to be which kind of delivery system?
Open (insufflation)
What are some examples of insufflation (open system):
- blow-by, tent, bronchoscopy port, NC, steal induction
What are the advantages of insufflation?
- avoids direct patient contact
- no rebreathing of CO2
- no reservoir bags or valves
What are some disadvantages of insufflation?
- no ability to assist or control ventilation
- may have CO2/O2 accumulation under drapes
- no control of anesthetic depth/FiO2
- environmental pollution
What is an example of a “true” open circuit?
- Schimmelbusch mask (used either ether, chloroform, halothane)
What is an example of the open drop method?
- Ether mask (Schimmelbusch)
Disadvantages of the open drop method are:
- poor control of inspired concentration of anesthetics
- accumulation of CO2 under mask
- predisposes to hypoxia risk
- cannot control ventilation
- OR pollution/health care provider risk
Semi open system is characterized by what 5 characteristics?
- facemask or ETT
- pop-off valve
- reservoir tubing
- fresh gas inlet
- reservoir bag
CO2 rebreathing depends on:
- fresh gas inflow rate
- minute ventilation of patient
- type of ventilation (spontan or controlled)
What are the 3 function groups of semi open systems? And was is their corresponding Mapleson letter?
- Group 1: Mapleson A (pop-off valve near the facemask, FGF at opposite end)
- Group 2: Mapleson B & C (pop-off and FGF are near facemask)
- Group 3: Mapleson D, E, F (FGF near facemask, pop-off at opposite end- opposite of Mapleson A)
Which Mapleson is most efficient during controlled ventilation?
- Mapleson D (can be used for spontaneous and controlled ventilation)
During spontaneous respiration FGF (is determined by an equation):
- FGF= 2-3 x MV
During controlled ventilation FGF (is calculated by this equation):
- FGF= 1-2 x MV
What is unique about Mapleson E (T piece)?
- NO reservoir bag (expiratory limb is the reservoir)
- NO pop-off valve
What is unique about Mapleson F (Jackson- Rees)?
- pop-off valve is at the end of the reservoir bag (common in pediatrics)
The Bain Circuit is a coaxial modification of ________?
- Mapleson D
In the Bain Circuit, FGF within the large bore corrugated tubing allows for:
- allows exhaled gas to to warm the inspired gas
- preserves heat and humidity
Bain Circuit can be used for what types of breathing?
- controlled or spontaneous ventilation
Disadvantages of the Bain Circuit:
- potential for inner tube leaks, kinking or disconnection
The Ambu bag is most similarly related to which Mapleson?
- Mapleson A with non-rebreathing valve
Characteristics of the Ambu bag:
- contain non rebreathing valves
- capable of delivering high FiO2
- reservoir self filling
- requires high fresh gas flow
- depends on minute ventilation
Whats are the advantages of the Mapleson System?
- simple components
- lightweight
- can provide positive pressure ventilation
- portable
- low resistance
- more predictable anesthetic concentration and decreased room pollution
Disadvantage of the Mapleson System:
- requires calculation of FGF
- control of anesthetic depth is variable
- if FGF not maintain, possibility of CO2 buildup/rebreathing
- poor conservation of other gases
- FGF costly
- requires special assembly
The circle system can be used in which systems?
- semi open
- semi closed
- closed
2 advantages of the circle system:
- prevents rebreathing of CO2 by chemical neutralization
- allows re-breathing of other exhaled gases
Name the 7 components that characterize the circle system
- FGF source
- inspiratory and expiratory unidirectional valves
- inspiratory and expiratory limbs/corrugated tubing
- Y piece connector
- adjustable pressure-limiting valve (APL)
- reservoir bag
- CO2 absorber
What are the 4 functions of reservoir bag?
- accumulation of gas during exhalation
- assist/control ventilation
- visual/tactile monitor to observe spontaneous respirations
- protects against excessive pressure reservoir of gas
Desirable requirements of a breathing system:
- economy of fresh gas
- conservation of heat
- adequate humidification of inspired gas
- light weight
- convenience during use
- efficiency during spontaneous and controlled ventilation
- adaptability for adults, children and mechanical ventilators
- provision to reduce environmental pollution
What kind of system does the anesthesia machine use?
- circle system
Excess gas can vented out via the ________ to the ________.
- APL valve
- scavenging system
Characteristics of breathing tubes:
- large bore, non rigid corrugated tubing
- rubber or clear plastic
- 22 mm female fitting w/ machine
- Patient end: T piece 22 mm male, 15 mm female coaxial fitting
List the function of breathing tubes:
- flexible, low resistance, lightweight connection
- reservoir
Purpose of the APL valve: (“pop-off valve”, pressure relief, safety-relief valve)
- release gases to the scavenge or atmosphere exhaust port
- provides control of pressure in the system- pressure gauge absorber
During spontaneous respiration, what is the function of the APL valve?
- valve is fully open
- closed partially only if reservoir bag collapses
During assisted ventilation, what is the function of the APL valve?
- valve partially opened
- bag squeezed on inspiration
During mechanical ventilation, what is the function of the APL valve?
- valve closed
- ventilator switch turned on
Where is majority of the dead space in the circle system located?
- if the unidirectional valves are working properly, the only dead space in the system is the Y piece and the patient
Where must the unidirectional valves be located in the anesthesia circuit?
- between the patient and the reservoir bag on the inspiratory and expiratory limb of the circuit
Where can FGF NOT enter the circuit?
FGF cannot enter the system btw the expiratory valve and the patient
Where can the APL valve NOT be located in the system?
- The APL cannot be located btw the patient and inspiratory valve
Semi-open system is mostly used for:
- sedation (mask placed over face to increase FiO2)
List the characteristics of a semi-open system:
- no re-breathing occurs
- requires a very high flow of fresh gas flows (10-15L/min) to eliminate rebreathing of gases
- no conservation of wastes gases and heat
- APL valve is open all the way
What is the most commonly used breathing system is U.S. practice?
- semi-closed circle system
What are 4 characteristics of the semi-closed circle system?
- requires relatively low flow rates (1-3L/min)
- conserves some heat and gases
- some re-breathing of agents and exhaled gases (minus CO2)
- APL valve is closed and partially adjusted as needed
Closed circle system are often used in:
- third world countries
List 4 characteristics of the closed circle system:
- inflow gas exactly matches metabolic needs/ O2 consumption of the patient using very low flow rates (O2 flow= @ 200ml/min)
- total re-breathing of all gases after absorption of CO2
- total conservation of all exhaled gases
- APL valve is CLOSED
Formula for O2 consumption is:
- VO2 = 10 x kg^3/4
Name the advantages of the Circle System:
- relative stability of inspired gases
- conservation of moisture and heat
- prevention of OR pollution
- can be used for closed-system anesthesia
- can be used with fairly with low flows with no rebreathing of CO2
- economy of anesthetics and gases
- can scavenge waste gases
List the disadvantages of the Circle System:
- complex design
- has at least 10 connections (potential leaks, disconnections or obstruction)
- a third of malpractice claims resulted from disconnects or misconnects of the system
- potential of malfunctioning of valves
- increased resistance to breathing
- less portable and convenient than the Mapleson systems
Discuss how to perform a leak test for the circle system check:
- set all gas flows to zero, occlude the Y-piece, close the APL valve
- pressurize the circuit to 30 cm of water pressure using the O2 flush valve
- ensure pressure hold for 10 seconds
- listen for sustained pressure alarm
- open APL valve and ensure pressure decreases
(this test does not assess integrity of unidirectional valves)
Discuss how to perform the flow test of the circle system check:
- attach breathing bag to the Y- piece
- turn on the ventilator
- and assess the integrity of the unidirectional valves
