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