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