Anesthesia machine Flashcards
oxygen percentages
room air = ~21% O2
alveolus = ~13% O2
arterial blood = ~12% O2
capillary blood at tissue level = ~5% O2
tissue = ~2% O2
gas supply (oxygen)
gas cylinder tanks stored on a cart or chained to the wall
types: H tank 6900 L and E tank 660 L
bulk tank: contains large quantity of O2 in liquid
oxygen concentrator: extracts O2 from the room air, concentrates it, and pressurizes it for use
flammable vs inflammable
flammable needs fire to blow up but inflammable can blow up without fire
what is the pressure of each type of O2 tank?
H tank 6900 L (1,300-2,200 psi/kPa), can fluctuate 690-1380 psi/kPa
E tank 660 L (1,900-2,200 psi/kPa), can fluctuate 100-200 psi/kPa
yoke
piece that directly connects to the oxygen tank to release its content
uses a pin-index safety system
rubber washers reccommended
pressure-reducing valve
aka pressure regulator
located near pressure gauge, attaches to tank
decreases pressure of gas exiting tank to a constant pressure of 40-50 psi
works passively
tank pressure gauge
device that attaches to the yoke or pressure regulator of a tank and indicates pressure of gas remaining in a compressed gas cylinder
tank valve must be opened (wrench)
600 psi at 1L/min = 1 hr of use
line pressure gauge
indicates the pressure in the intermediate pressure gas line between the pressure-reducing valve and the flowmeter
gauge should read 40-50 psi
works passively
flowmeter
graduated glass cylinder with a valve attached at the bottom
gas flows from the regulator through the intermediate line into flowmeter for precise O2 delivery
gas enters the cylinder at the bottom and exits the top
indicates in L/min
further reduces pressure to 15 psi
what is the relative atmospheric pressure?
14.7 psi
oxygen flush valve
rapidly delivers large amounts of pure O2 at a flow rate of 35-75 L/min directly from the intermediate line and pressure regulator into the common gas outlet or breathing circuit
sometimes excluded in non-breathing circuit
used to fill reservoir bag with pure O2, bleed the system of anesthetics, or for leak tests
how does the system work with the common gas outlet included?
O2 flush valve delivers O2 to rebreather and nonrebreather
how does the system work without the common gas outlet?
O2 flush valve delivers O2 to rebreather only
anesthetic vaporizers types and factors that affect output
precision (%) and nonprecision (on/off)
factors that affect vaporizer output: temperature, carrier gas flow rate, and back pressure/resistance (precision vaporizers compensate for these factors)
nonprecision anesthetic vaporizer
available for isoflurane and sevoflurane
not common
may be dangerous (may reach 30%)
how are most vaporizers classified?
as variable-bypass flow-over
(regulates the agent output by routing a portion of the carrier gas through the vaporizer chamber and the remainder is bypassed)
precision vaporizers
most common
color coded to a specific anesthetic
anesthetics come in liquid and are poured into vaporizer
vaporizer also controls the amount of anesthetic to be picked up by O2
how does O2 enter and exit the vaporizer?
after exiting the flowmeter O2 enters the vaporizer through the inlet port
fresh gas exits the vaporizer through the outlet port which then enter the breathing circuit through the fresh gas inlet
where can the vaporizer be located?
either in or out of circuit
vaporizer out of circuit (VOC)
O2 from flowmeter enters vaporizer before entering breathing circuit
uses precision vaporizer
vaporizer in circuit (VIC)
carrier gas enters breathing circuit directly from flowmeter without entering vaporizer
vaporizer located in breathing circuit between expiratory breathing tube and expiratory unidirectional valve
exhaled gas enters vaporizer each time patient breathes
uses nonprecision vaporizer
how do you decide if the vaporizer should be VOC or VIC?
decided by the resistance of the flow of gases through it
patient respiratory drive during normal breathing is the force that moves gases around the breathing circuit
when resistance to gas flow is high respiratory drive is insufficient to push gases through the vaporizer so precision vaporizers must be placed outside the circuit
nonprecision vaporizers offer little resistance to gas flow so they are placed in circuit
unidirectional valves
aka flutter valves (inspiratory and expiratory valves)
function passively as the patient breathes and prevents the patient from rebreathing CO2 or CO2 absorbent granules
located inside a housing unit with a clear plastic dome on top for visualization
when patient inhales respiratory flutter valve opens allowing gas to enter breathing circuit and patient’s lungs
when patient exhales exhalation flutter valve opens allowing gas to enter anesthesia machine
pop-off valve
aka pressure relief valve
in open position: allows excess gas to exit from breathing circuit to be scavenged
in closed position: contains gas to create pressure in order to administer an intermittent positive pressure ventilation
danger: excess pressure may cause over-distention and rupturing of alveoli, excess intrathoracic pressure and decrease return of blood to heart which leads to decreased CO
pressure manometer
measures pressure within the circle system and the patient’s lungs
measured in cmH2O
used when bagging an animal to determine pressure being exerted on an animal’s lungs or when leak testing
spontaneous ventilation pressure manometer reading
0 to -2 cmH2O
normal pulse pressure variation (PPV) manometer reading
8-12 cmH2O
air intake valve
aka negative pressure relief valve
safety mechanism that admits room air when negative pressure occurs in the anesthesia machine due to patient ventilation and the lack of a present gas
reservoir bag
aka breathing bag
rubber bag that is often black or green and is a flexible storage for gases
can observe breaths by looking at the bag movement
used to administer intermittent positive-pressure ventilation
size is important to adequately inflate patient’s lungs and decrease breathing resistance (keep bag ~3/4 full)
reservoir bag sizes
range from 0.25 - 30 L
common small animal sizes: 0.5L, 1L, 2L, 3L, 4L, 5L
how do you determine what size of reservoir bag to use?
tidal volume = kg x 10-20 mL
Vt x 3-6 = bag size in mL
60mL x kg = bag size in mL
CO2 absorber
absorbent granules absorb CO2 in order to recycle anesthetic gases and save money
exhaled gases are directed by the expiratory unidirectional valve to the CO2 absorber canister before being returned to patient
CO2 absorbent granules
primary ingredient: calcium hydroxide and 14-19% water
exhausted granules are white and brittle
exhausted granules mixed with certain anesthetics may result in CO2, excessive heat, and formaldehyde production
when mixed with CO2 heat and water is produced and granules may change to a purple or pink color
good for 8-12 hours of use or change after 2 weeks
scavenging
important to diminish anesthetic pollution in the workplace by collecting wasted gas and releasing it outside
consists of tubing attached to anesthetic machine at the pop-off valve to a scavenging system
active vs passive scavenging
active: vacuum generator, may require a reservoir bag to allow excess gases to be stored if vacuum is not strong enough to suction it out and prevent over vacuuming of gases within circle system
passive: F/air canister (saturated when gained 50g in weight)
rebreathing circuit
allow for exhaled gases to be recycled
CO2 granules absorb exhaled CO2 and make the exhaled anesthetic gas resuseable
may be closed or partial rebreathing (depending on if positive pressure relief valve is open or closed)
most common type used in practice is partial
non-rebreathing circuit
doesn’t recycle gases
gases exhaled by the patient are directly scavenged
allows for less breathing resistance by bypassing complex parts to the anesthesia machine
commonly used for patients < 2.5-3 kg
rebreathing tubes
inspiratory and expiratory breathing tubes complete breathing circuit by carrying anesthetic gases to and from patient
each tube connects to unidirectional valves and to a Y piece
standard/adult circuits used in patients > 7kg
pediatric circuits used in patients 2.5-7 kg
non-rebreathing systems
used in patients < 2.5-3 kg
less breathing resistance
alternative machine configuration, most of the anesthetic machine bypassed
little or no exhaled gases returned to the patient, instead gas is scavenged
non breathing circuit connected to the vaporizer outlet port or common gas outlet port and other end connects to scavenge hose
disadvantages of non-breathing systems
patients are more likely to accidentally rebreathe their own expired gas
how are re-breathing systems wasteful?
they require higher O2 rates and they don’t recycle anesthetic
how do you do a leak test?
- seal off end of breathing circuit (Y piece of end that goes to patient) with a cork or your finger
- close pop-off valve
- set O2 flow rate to 2L/min
once pressure manometer reaches 30cmH2O, decrease O2 flow rate to 20 mL/min
- pressure should be maintained for 30 seconds, may use O2 flush valve to fill the machine quicker, leaving O2 on at 2L/min may cause false negative - open pop-off valve before removing finger/cork from the Y piece
if leak is present but not obvious, use waterless shampoo or soapy water to identify
