CRNA 560- Machine

the anesthesia machine is made up of

3 pressure systems
-high
-intermediate
-low

where does the high pressure system begin and end

begins- cylinder
end- cylinder regulators

what components does the high pressure system contain

hanger yoke
yoke block with check valves
cylinder pressure gage
cylinder pressure regulators

where does the intermediate pressure system begin and end

begins- pipeline
ends- flowmeter valve

what is the gas pressure from the pipeline to the intermediate pressure system

50 psi

what is the gas pressure from the tank in the intermediate pressure system

45 psi

what components does the intermediate pressure system contain

pipeline inlets
pressure gauges
ventilator power inlet
oxygen pressure failure system
oxygen second stage regulator
oxygen flush valve
flowmeter valve

what does the machine do when activating the O2 flush valve

pathway for O2 to travel from the intermediate system to the common gas outlet (breathing circuit)
-bypass the low pressure system

when O2 flush valve is pressed what is your pressure, flow, and percent of oxygen delivered

100% O2 flowing at 35-75L/min
O2 pressure of 50 psi (coming from pipline)

what are risks associated with pressing the O2 flush valve

barotrauma- due to high pressure during inspiration (50psi, 35-75L/min)
possible awareness- bypasses vaporizers (volatile gas) causing diluated partial pressure of the volatile agent

where does the low pressure system begin and end

begins- flowmeter tubes
ends- common gas outlet

what components does the low pressure system contain

flowmeter tubes
vaporizers (anesthetic gases)
check valves (if present)
common gas outlet

what is the SPDD model

Supply
-gas entering anesthesia machine (pipeline or cylinder)

Processing
-how anesthesia machine prepare gas before delivered to pt (inside machine to common gas outlet)

Delivery
-prepared gas brought to patient (breathing circuit)

Disposal
-gas removed from breathing circuit (Scavenging system)

what is the carbon dioxide absorbent

absorbs exhaled CO2 from patient and is absorbed via soda lime

what is the Scavenging system

disposal of gas
-to minimize environmental expose to waste anesthetic gas

tasks of oxygen in the anesthesia machine

1- O2 pressure failure alarm
2- O2 pressure failure device (failsafe)
3- O2 flow meter
4- O2 flush valve
5- ventilator drive gas (if vent has bellows)

what is the PISS

Pin index safety system
-prevents misconnection of cylinder to wrong hanger yoke
-each gas cylinder has its own PISS configuration

what can more than one washer between hanger yoke and cylinder cause

bypass PISS and allow wrong cylinder to be connected

what color is oxygen's cylinder

green

what color is nitrous oxide's cylinder

blue

what color is air's cylinder

yellow

what color is carbon dioxide's cylinder

gray

what color is helium's cylinder

brown

what color is nitrogen's cylinder

black

what is air's PISS configuration

1 & 5

what is oxygen's PISS configuration

2 & 5

what is nitrous oxide's PISS configuration

3 & 5

what is DISS

Diameter Index Safety System
-prevents misconnection of gas hoses to anesthesia machine
-each gas hose connector has different diameters

what is oxygen's max volume and pressure in its cylinder

Max Volume- 660L
Max Pressure- 1900 psi

what is air's max volume and pressure in its cylinder

Max Volume- 625L
Max Pressure- 1900 psi

what is nitrous oxide's max volume and pressure in its cylinder

Max Volume- 1590L
Max Pressure- 745 psi

How do you calculate FiO2 set at the flowmeter

FiO2 = (Air flow rate x 21)+ (Oxygen flow rate x 100) / total flow rate

what is fresh gas coupling

when fresh gas flow (FGF) is not calculated into the set tidal volume on the vent

instead it is FGF + tidal volume on vent = delivered tidal volume to patient

how to calculate delivered tidal volume to patient when fresh gas coupling is present

(FGF in ml/min x I:E ration)/RR=x
x plus preset tidal volume on vent

I:E ratio of 1:1= 1/2
I:E ratio of 1:2= 1/3
I:E ratio of 1:3= 1/4
I:E ratio of 1:4= 1/5

soda lime can absorb up to...

23L of CO2 per 100g of absorbent

what happens to patient if carbon dioxide absorbent is full

patient retains CO2
rebreathing

when do you change carbon dioxide absorbent

when the soda lime is 50-70% purple
(soda lime turns purple when absorbs CO2)

carbon dioxide absorbent is exhausted and you are unable to change it during the procedure what can you do instead

increase fresh gas flow- converts circle system into a semi-open configuration

do NOT increase minute ventilation it can lead to hypercarbia (pt still rebreathing)

what is an open breathing circuit

no breathing
no reservoir
ex.) simple mask, NC

what is a semi-open breathing circuit

no rebreathing

circle system: FGF > minute ventilation

what is a semi-closed breathing circuit

partial rebreathing

circle system: FGF < minute ventilation

what is a closed breathing system

complete rebreathing

circle system with very low FGF and APL closed

what are unidirectional valves

directs respiratory gas flow
allows gas to move in ONE direction

examples
-inspiratory valve open during inspiration but closed during expiration
-expiratory valve open during expiration but closed during inspiration

essential characteristics of unidirectional valves

low resistance and high competence

what is the APL valve

Adjustable Pressure Limiting valve
-determines how much pressure can be inside the breathing circuit
-when pressure in circuit exceed value on APL gas is diverted to scavenger system

what is the reservoir bag

reservoir of anesthetic gas
method of generating positive pressure ventilation

what is the fresh gas inlet

where gases (anesthetics with oxygen/air) from anesthesia machine enter the breathing circuit

how do Mapleson circuits work

no unidirectional valves or CO2 absorbent

rebreathing is prevent by adequate fresh gas flow into the circuit and venting exhaled gas through the APL valve before inspiration

best and worst Mapleson circuits for spontaneous breathing

Best: A is best
A> DFE> CB

Worst: B

best and worst Mapleson circuits for controlled breathing

Best: D is best
DFE> BC> A

Worst: A

Mapleson A circuit

Best for spontaneous breathing
Worst for controlled breathing
APL on patient side
Fresh as inlet near reservoir bag

Mapleson B circuit

Worst for spontaneous breathing

fresh gas inlet and APL on patient side

Mapleson C circuit

no corrugated tube

Mapleson D circuit

Best for controlled breathing

Distant APL (away from patient)

Also called Bain

Mapleson E circuit

No reservoir bag and no APL

Also called T-piece

Maplesone F circuit

No APL

Also called Jackson Rees

how to know if breathing circuit is disconnected

Capnography
resp volume monitors
Low expired volume alarm
Low peak pressure alarm
Ascending bellows do not fill
bag deflation with piston ventilators

what is absolute humidity

weight of water vapor in 1L of gas (mg/L)

what is relative humidity

ratio between the amount of water in given volume of gas to the maximum amount of water possible at a particular temperature

what are HMEs

heat and moisture exchangers
used to humidify the gas brought to the patient

between Y piece and right angle connector of breathing circuit

what position should the APL be in for spontaneous ventilation

fully open APL
-minimizing the pressure

what occurs if APL is partially closed during spontaneous ventilation

high pressures (like PEEP) make it difficult for patient to breath
-causes inc PaCO2 and dec PaO2

what position should the APL be in for manual or assisted bag ventilation

partially closed APL

APL not sufficiently closed can cause what with manual ventilation

prevent manual ventilation because of loss of circuit volume due to leak

APL that are closed to much or fully closed can cause

pulmonary barotrauma
hemodynamic compromise

fresh gas flow decoupling

tidal volume set on vent is what the patients actually receives (adds in FGF)

when do bellows fill with gas

during expiration
-bellows has "e" in it think expiration

what occurs to ascending (standing) bellows, descending (hanging) bellows, and piston driven when a circuit disconnect occurs

Ascending bellows: bellows do NOT fill
Descending bellows: bellows can continue to rise and fall
Piston: reservoir bag collapsed

what happens with bellow vs piston ventilators with pipeline failure

Bellows- can exhaust cylinder O2 bc needed to drive the bellows

Piston- electricity is driving force, mechanical ventilation will still continue without exhausting cylinder

what does the positive pressure relief valve due in piston ventilators

valve opens at 75 + or - 5 cm H2O
-prevents pressure build up in circuit
-reduces risk for barotrauma

what does the negative pressure relief valve due in piston ventilators

valve opens at -8cm H2O
-RA enters breathing circuit which dilutes O2 and anesthetic gases

-helps protect pt against negative end-expiratory pressure

what is volume controlled ventilation

-delivers preset tidal volumes over preset time
-inspiratory pressure vary as pt compliance changes
-constant inspiratory flow during inspiration

what is pressure controlled ventilation

-delivers preset inspiratory pressure over preset time (pressure and time are fixed)
-Tidal volume and inspiratory flow will vary and are dependent on patients lung mechanics
-if rise airway resistance or decrease lung compliance occurs
*tidal volume will decrease
*higher inspiratory flow will be required to achieve present airway pressure

Tidal volume with decrease with PCV when

Decrease lung compliance
-pneumoperitoneum
-trendelenburg position

Increase airway resistance
-bronchospasm
-kinked ETT

Tidal volume will increase with PCV when

Increase lung compliance
-release of pneuomperitoneum
-going from trendelenburg to supine

Decrease airway resistance
-bronchodilator therapy
-removing airway secretions

what are the two most common sites for leak that cause low pressure

Y piece
CO2 absorbent canister (poor seal after granules have been changed or defective canister)

what is the ventilator spill valve

on bellow ventilators
-closed during inspiration, the driving gas closes the spill valve (ensures tidal voluming goes to patient and not to the scavenger)
-open during expiration, gas fills the bellows, when circuit pressure ~3cm H2O will open spill valve to direct gas to scavenger

what does the oxygen pressure failure device (failsafe device) do

Monitors for low oxygen pressure within anesthesia machine

When will the failsafe device alarm

O2 cylinder depletion

O2 hose disconnect

Decrease in O2 pipeline pressure

The failsafe device will not alarm when

O2 pipeline cross over (remember is it measuring pipeline pressure NOT concentration)

Flowmeter leak

Where does the failsafe device reside
What do the two components do

Intermediate

Components
-alarm when O2 pipeline psi below 28-30
-reduces or turns off nitrous oxygen when O2 pipeline falls below 20 psi

What does the hypoxia prevention safety device (proportion device) do

Limits N2O flow to 3 times the O2 flow
-ensures FiO2 does not drop below 25%

Prevents you from setting a hypoxic flow on the flow control valves

When can the hypoxia prevention safety device (proportioning device) NOT prevent a hypoxic mixture

Oxygen pipeline cross over
Leaks distal to flowmeter valve
Administration of a third gas
Defective mechanism

How to calculate FiO2 when using a NC

Add 4% until make 6L/min = 44%

RA-21%
1l- 24%
2L- 28%
3L- 32%
4L- 36%
5L- 40%
6L- 44%

What can change the tidal volume delivered to the patient when fresh gas coupling is present

RR
I:E ratio
FGF
Height of bellows

What is the oxygen analyzer
where it is located

Located- inspiratory limb of breathing circuit

Detects oxygen concentration
-alarms when FiO2 falls bellow 21%

Last defense to prevent delivery of hypoxic mixture

The oxygen analyzer will detect

Oxygen pipeline crossover
Leak in O2 flowmeter that causes hypoxic mixture

If oxygen analyzer alarms what two steps should be take

Turn ON O2 cylinder
Discount O2 pipeline

Oxygen concentration in the breathing circuit should increase- if it does NOT ventilate with an ambu bag and oxygen tank, start TIVA

Minimum test of ventilators for emergency

-suction
-means of another way to ventilate (Ambu bag and check O2 cylinder)
-High pressure leak test
-breathing bag fluctuation

Low pressure leak test checks

Aka negative pressure test

Assess integrity of lower pressure system from flowmeter valves to common gas outlet

Bulb add to create negative pressure
-if bulb inflates then there is a leak

High pressure leak test checks

Low pressure system and breathing circuit

Occluding common gas outlet, close APL and pressurize circuit to 30 and airway pressure gauge should staying constant

Trouble shooting Low Pressure

1.) check ETT place, Y connect, circuit tubing connects and conencts to vent
2.) check for cracks or leaks in the bellows
3.) Check CO2 absorbant for leaks
4.) check vaporaizers for tight seal
5.) check flow sensor
6.) check oxygen pipline/cylinder pressure
7.) check for faulty ventilator relief valve (ventilator spill valve)