Ventilators Flashcards
What type of pressure do ventilators use?
positive pressure
What are the 4 phases of one cycle in ventilation?
- inspiration
- transition from insp to exp
- expiration
- transition from exp to insp
Which phase is most important? Why?
inspiration (is active)
expiration is passive
Does an anesthesia ventilator have rebreathing?
Yes. (ICU vents do not rebreathe)
How are vents classified mainly? (phase)
inspiratory phase and how they cycle
What are 3 different types of vent inspiratory features?
Describe them.
- constant flow
- non constant flow
- constant pressure generators
What is constant flow delivery?
How does a high pressure gas source affect insp flow?
How does a low pressure gas source affect insp flow?
- constant flow regardless of circuit a/w pressure
- high pressure gas (5-50 PSI) allows insp flow to be constant despite a/w resistance
- low pressure gas (venturi) - varies with a/w pressure
What is non constant flow delivery?
-flow varies with each insp cycle
What is constant pressure generators delivery?
delivers constant pressure throughout insp (regardless of gas flow); gas flow will stop when a/w pressure = set ins pressure
What is time cycled?
How does this affect TV?
-Time is set for duration of inspiration and expiration
(I:E ratio)
-TV is dependent on the set insp time and insp flow
What is volume cycled?
What does this prevent against?
Does the patient always receive all of the TV?
- TV is set (insp can be limited by this)
- Barotrauma
- TV is always lost due to compliance of system (4-5 cc)
What is pressure cycled?
pressure is set
tv and insp time may vary
What is flow cycled?
-Has pressure and flow sensors that allow vent to monitor insp flow at set insp pressure
What are the 3 power sources for vents?
- most commonly bellows (uses gas and electricity)
- compressed gas (gas only)
- piston (electricity only)
What are 2 options to drive a vent?
- double circuit - bellows compress by gas and pneumatic drive
- piston - bellows compress by electricity
What phase drives bellows?
Expiration
What do most of our vents have for
cycle
power
set limit
most of our vents are
time cycled
electronic control
with volume limit
What are the 4 parameters for ventilators in delivery gas?
- time
- volume
- pressure
- flow rate
Describe each parameter.
- time
- volume
- pressure
- flow rate
- I:E ratio, in SECONDS (always) = # of resp cycles in time (i.e. RR)
- TV of gas from vent to pt , in mls or liters (MV = L)
- impedance from breathing circuit or pts airway due to a/w resistance or lung-thorax compliance [obesity], in cmH2O, mmHg, or kPa
- volume of gas to pt over time , L/sec or L/min
* machine sets flow rate to meet settings?*
What separates driving gas from pt gas circuit?
bellows
What happens to the bellows and ventilator relief valve on inspiration?
driving gas enters chamber and increases pressure which causes:
1. ventilator relief valve to close - no gas escapes and all goes to pt
2. bellows are compressed, gas WITHIN bellows is delivered to patient
(gas IN bellows goes to pt, gas outside of bellows (in chamber) does NOT)
What happens to the bellows and ventilator relief valve on expiration?
- driving gas exits bellow chamber, pressure drops which causes ventilator relief valve to open
- exhaled gas fills bellows before any scavenging occurs bc ball (of ventilator relief valve) produces a 2-3 cm H2O back pressure
When does gas go to scavenging?
On expiration only AFTER bellows are full of exhaled gas
How do you determine a tidal volume setting?
6-8 ml/kg
What is a normal RR setting?
What is a normal I:E ratio?
8-12 bpm
1:2
How do you calculate flow rate?
4-6 x MV
MV = TV x RR
How do you calculate TI (time of inspiration)?
TI = TV/flow rate (x 60 sec if in minutes)
i.e. flow = 30L/min, RR = 12, TV = 500 ml
500/30000 = 0.0167 x 60 seconds = 1 seconds
How do you calculate TE (time of expiration)?
RR/60 seconds = total time - TI
if RR is 12 then 12/60 seconds = 1 breath per 5 seconds
5 seconds = total time of I + E
then 5 seconds -1 second (insp) = 4 seconds in exp
What does the inspiratory pause/sigh feature do?
What happens to gas flow?
What is the result?
- increases inhalation time by 25%
- gas flow stops but gas pressure in bellows is same
- result = total volume of gas is held in pts lung until exp
What is the calculation for O2 delivery?
CO x O2 content
What is the calculation for O2 content?
(hgb x O2sat x 1.39 mlO2) + (PaO2 x .0031 mlO2)
PO2 of 100 mmHg = 0.3 ml of O2/100 ml
(hgb bound O2 + dissolved O2)
How do you calculate PaO2 (arterial concentration of O2)
FiO2 - PaCO2/R
FiO2 = (Pb - PH2O) = 713 R = 0.8 F = neglible = 0
What happens to PaO2 when you increase FiO2 by 10%?
PaO2 increases by 50 mmHg
increase FiO2 = increase SaO2
i.e. PaO2 of 100 = FiO2 of 21%
inc by 10% = PaO2 of 150 = FiO2 of 30%
Describe the following alarms of the ventilator:
- low pressure alarm
- sub atm pressure alarm
- sustained/continuing pressure alarm
- high peak a/w pressure alarm
- low O2 supply alarm
- vent setting alarm
- detects drop in peak circuit pressure (disconnect)
- if pressure 10 secs
- detects excess pressure over 60 cm H2O unless set diff by clinician
- vent can’t deliver set MV
What are 3 important monitors on the ventilator?
ETCO2 - detects disconnect
O2 analyzer - most important, calibrate at 21% O2
Respirometer
VIGILANCE!!!!!!
What does the respirometer do?
Where is it located?
- has sensors to detect TV throughout ventilation
- alarms if flow reverses toward pt
- cartridge is always on exp limb
How do you determined EXHALED tv?
TV set on vent + FGF tv - TV lost in system
What is different in an ICU vent (vs anesthesia vent)?
- more powerful (pressure, volume, etc)
- no CO2 absorber (each breath is fresh)
- more vent modes
- gas from vent all goes to pt (vs anesthesia and bellows)
- no bellows in ICU
