Vent and Airway Flashcards
What is compliance a ratio of? What does it measure?
ratio of change of V to change of P. It measures distensibility
What is a good way to determine baseline compliance of your patient’s lungs?
you can feel it when you use the reservoir bag to ventilate the patient
what is measured as the ratio of change in driving pressure to change to change in flow rate?
resistance; think Ohm’s Law: flow= (change in pressure/resistance) t/f: resistance= (change in pressure/flow rate)
What is expiratory flow time?
time b/w beginning and end of expiratory flow; how long it takes to exhale
What is expiratory pause time?
time from end of expiratory flow to start of inspiratory flow
What is inspiratory flow time?
time b/w beginning and end of inspiratory flow
where are you more likely to have underinflated alveoli? What do you use?
zone 3/ dependent areas; use PEEP
What is inspiratory pause time? What is another name for this?
portion of inspiratory phase time during which the lung is held inflated in a fixed pressure or volume. aka “sigh”
What is the I:E expressed in? What is normal?
seconds; 1:2
What does the volume parameter of the vent measure?
measure of the TV delivered by ventilator to patient
What is volume measured in?
liters for MV
What is the equation for TV in a normal person?
5ml per kg of ideal body weight
What is the equation for TV in a ventilated patient?
6-8ml/kg; or 10-15ml/kg depending on who you ask.
why do you see bigger volumes when the patient is ventilated?
going from physiologic to nonphysiologic way of breathing; with PP ventilation, cant expand the lung as well so you need bigger volumes
What is the definition of pressure in relation to vents?
impedance to flow
What causes impedance?
breathing circuit; patient’s airway and lungs
What is backpressure generated as a result of?
airway resistance (asthma attack), lung-thorax compliance; breathing circuit
What is pressure measured in?
cmH2O, mmHg, kPa
what is back pressure?
the pressure coming back to you
What is flow rate?
rate at which gas volume is delivered to patient
Where does flow rate span?
from patient connection of breathing system to the patient
What is flow rate expressed in?
L/sec or L/min
What will constant flow deliver?
a constant inspiratory gas flow regardless of a/w circuit pressure
How are vents characterized? Why
by inspiratory flow; because expiration is always passive
What does a vent w/ non constant flow deliver?
consistently varying flow w/ each inspiratory cycle
What does a constant pressure generator flow deliver?
maintains constant pressure irrespective of flow during inspiratoin
With constant pressure generator, when does flow stop?
when airway pressure equals set inspiratory pressure
How does anesthesia vent provide ventilation? What are the phases?
PP ventilation inspiration transition btw I & E expiration transition btw E & I
What are different types of vents?
time cycle, volume cycle, pressure cycle
Is gas involved in a piston driven ventilator? What is required?
no, electricity
What type of machines require O2 and power to work?
compressible
What is the difference btw the air that drives an ICU vent and the air that drives an anesthesia vent?
ICU vent: air that goes in is what goes to the patient; no bellows
anesthesia vent: air that goes in is to drive bellows and is separate from the O2 that goes to the patient (which is mixed w/ NO & anesthetic gases)
Are cycling mechanism vents new or old technology?
older
How does a time cycled vent work?
vent goes to expiratory phase of breath after a specific, predetermined time interval has passed from time of inspiration
TV is a product of the set inspiratory time and inspiratory flow rate
How does a volume cycle vent work?
terminates inspiration after a predetermined TV is delivered
What type of vents are most adult vents? What do they have to avoid barotrauma?
volume cycled; second limiit on inspiratory pressure
A % of TV is lost in v-cycled ventilation d/t what? How much?
compliance of the system; usually about 4-5ml cmH2O
How does a pressure cycled vent work? What may vary?
cycle into expiratory phase when a/w pressure reaches predetermined level
TV and inspiratory time may vary
How does a flow cycled vent work?
pressure and flow sensors allow the vent to monitor inspiratory flow at a preselected fixed inspiratory pressure
when flow hits this predetermined level the vent cycles from I to E
What determines movement of the bellows?
expiration
Ascending bellows expand in what direction and when?
up; on exhalation
Why aren’t descending bellows used anymore?
if there was a problem ventilating you couldn’t tell because bellows would still fall
What is the air inside the bellows? What is the air outside the bellows
inside: gas that patient will receive; mixed w/ NO and anesthetics
outside: O2 being used to drive the movement of the bellows
During __________the driving gas of the bellows enters the chamber and increases pressure.
What does this increase in pressure cause?
inspiratory phase; ventilator relief valve closes (no gas can escape through scavenger); bellow are compressed and gas inside is delivered to patient
What valve on the vent is analagous to the APL valve?
pressure relief valve
During expiration, the driving gas ______________the chamber and the pressure in the bellows and the pilot drop to ____________
exits; 0
On expiration, does the vent pressure valve open or close? What kind of valve is it?
open; ball type
What happens to exhaled gas before it is sucked up by scavenger? Why?
exhaled gas fills bellows; pressure valve creates 2-3cmH2O of back pressure only
When does scavenging occur?
only when bellows is filled completely
The relief valve is only open during ______________ and any _____________ occurs at this point.
expiration; scavenging
What determines how much gas is driven in to compress bellows?
set TV (bellows size doesn’t change w/ different patient populations)
What kind of bellows does a piston vent have?
no bellows!
After turning the vent on, what is the first selection you must make?
mode: IMV, pressure control, etc
What are some advantages to piston vents?
quiet; no PEEP, greater precision in delivering TVs, less bulky, lack of O2 requirements means less concern if pipeline source is disrupted
Why is some PEEP required on bellows vents?
2-3cm H2O required d/t bellows spill vavlve
What is big disadvantage to piston vents? What monitor is important in detecting this?
can entrain air and continue to deliver TVs w/ hypoxic mixture; O2 analyzer
What are some disadvantages to piston vents that may not apply to new practitioners?
quiet; loss of familiar visual clues from seeing bellows
How does the inspiratory pause or sigh work?
flow of drive gas stops but pressure in bellows chamber stays the same
What happens to the volume of gas going to the patient during the sigh?
it is held in patient’s lungs until exhalation occurs
For the sigh, where is the time for this pause taken from?
time of expiration
What does it mean if you have T1 of 25%?
you will spend 25% more time at end of inspiration than you normally would
If your I:E is 1:2 and your pause time is 25% how much time are you spending in inspiration, expiration and pause? (inspiration is 2 sec, expiration is 4sec)
I=2sec; E=3.5; pause=.5sec
If you are using an inspiratory pause but want to keep I:E ratio at what it was before, what must you do?
turn the ratio back up after setting pause time
What can an inspiratory pause be beneficial for?
keep alveoli open a bit longer; kind of like PEEP
Do all vents have an I:E knob?
no, must enter in TV, rate and inspiratory flow and machine will figure ratio out
What is the cardinal way of telling if you are ventilating a patient adequately?
end tidal CO2
What is a normal end tidal CO2? Is it usually higher or lower than PaCO2?
35-45mmHg; usually lower
if your end tidal is 45, you need to make some adjustments because your PaCO2 is probably higher
If you dont think you are ventilating the patient appropriately do you usually want to adjust the RR or the volume? Why?
change the RR; you want to prevent atelectasis so you want to keep alveoli open; t/f avoid decreasing volumes
When would you choice to change volume instead of RR?
if peak pressure alarms are going off
If patient’s RR is >15, what is probably the issue?
pain, give narcs
For the vent settings, what is the TV set at? What is the formula for MV?
TV= 10-15ml/kg
MV=TV x RR
How much is flow rate?
4-6x MV
Do asthmatics usually require different I:E ratios?
yes, longer expiratory times
How do you determine inspiratory time?
TV/flow rate (in seconds)
How do you determine expiratory time?
1st: figure out how long each ventilation total time is (60/RR)
2nd: then subtract TI from total breath time
What is going to affect the patient’s O2 content more: PO2 or Hb?
Hb
What formula do you use to determine O2 content in blood?
CaO2= (Hb x SaO2 x 1.34) + (PaO2 x 0.003)
What is the rule of thumb regarding FiO2 and SaO2?
If FiO2 goes up, so will SaO2
Hypoventilation will reduce PaO2 unless what?
patient is breathing an enriched O2 mixture
If you increase FiO2 by 10%, how much do you increase PaO2?
50mmHg; another way of figuring this out is: 5xFiO2=PaO2
What does a low pressure alarm usually mean?
disconnection; a drop in peak circuit pressure is detected
What is a subatmospheric alarm? What do you do for this?
not enough flows in bag; pressure is less than or equal to 10cmH2O; bag is sucked in
turn up your flows
what is a sustained/continuing pressure alarm? What can cause it?
15cmH2O for >10seconds; kink in tubing or issue w/ patient
What does a high peak pressure alarm detect?
excess pressure at 60cmH2O or what is set by practitioner
When will the ventilator setting alarm go off?
vent is unable to deliver set desired MV; need to turn up inspiratory flow
What monitor is the best for determining a disconnect?
end tidal CO2
What is the most important monitor on the anesthesia machine? What should it be calibrated at?
O2 analyzer; 21%
What is flow rate?
the rate at which the gas volume is being delivered to the patient
What does a respirometer measure?
rate of respiration based on rate of exchange of O2/CO2
Where on the vent should the respirometer be? Why?
expiratory limb; some of TV is always lost in the system: you want to measure after this happens
What do you expect the exhaled Vt to be?
Vt set on vent + Vt fresh gas flow - Vt lost in system
What part of the respirometer is always active while mechanically ventilating?
exhaled volume monitor; activated automatically once breaths are sensed
What other things can the respirometer sense?
reverse flow; apnea (insufficient breath based on TV setting not achieved w/ in 30 sec); low minute volume
What are more powerful and adaptive: ICU or anesthesia vents?
ICU
What is the most common mode of ventilation in the OR?
volume controlled
In volume controlled vents; what parameters are set by the provider? To what extent does patient effort play a role?
TV and RR; independent of patient effort
With volume control ventilation, what is controlled on inspiration? If this parameter is to high or too low, what happens?
flow rate
too low: wont work
too high: will add a pause or cause high peak pressures
What does the provider set w/ pressure controlled vent mode?
inspiratory pressure
How does gas flow w/ pressure mode ventilation?
flow decreases as airway pressure rises and ceases when airway pressure = set peak inflation pressure
T or F: TV is set a specific # in pressure control ventilation
false; it depends on rise time and set pressure
When is pressure control ventilation used?
when pressures are expected to be high; good for neonates and premature babies or patient w/ LMA in and you don’t want air to go into stomach
What is intermittent mandatory ventilation?
vent delivers mandatory breaths at preset rate
Does IMV allow for spontaneous breaths?
yep
With IMV, what does the vent have a secondary source of?
gas flow for spontaneous breaths
Where does the secondary source of gas flow for IMV come from?
either continuous gas flow w/in circuit or demand valve that opens to allow gas to flow from a reservoir
Is IMV an acceptable mode to wean patients off of vent?
yes; turn down the rate
How is SIMV different from IMV?
it is synchronized w/ patient’s effort; prevents breath stacking
What does SIMV time the mechanical breath with?
beginning of spontaneous effort
When is SIMV good to use?
when waking up patient in OR
What is the assist control mode of ventilation? What triggers the vent to deliver a predetermined TV in this mode?
intermittent mode of PP ventilation; patient’s inadequate inspiratory effort creates a sub-baseline pressure in the inspiratory limb
If you are using AC ventilation and the pts effort is inadequate what happens?
the vent will augment breaths; it will increase RR to set rate if patient isnt breathing fast enough
T/F: With AC ventilation only some of the patient’s breaths are augmented by the ventilator.
false; every breath is assisted
With AC ventilation is it pressure or volume controlled?
can be either
Describe pressure support ventilation
aid in normal breathing w/ predetermined level of positive airway pressure
How is pressure support different from IMV?
pressure support keeps airway pressure constant throughout entire inspiratory period
What is the goal of pressure support ventilation?
to increase pt’s spontaneous TV by delivering airway pressure to achieve volumes equal to 10-12ml/kg
What can pressure support ventilation prevent or delay?
work of breathing; muscle fatigue
What are some characteristics of high frequency ventilation?
low TVs: less than dead space; high RR (60-300bpm)
What are the typical settings for high frequency ventilation?
rate: 100-200 bpm
IT: 33%
drive pressure: 15-30psi
What is the goal of high frequency ventilation?
maintain pulmonary gas exchange at lower mean airway pressures
In the OR, what is a prime example of why you would use high frequency ventilation?
lithroscopy; patient has stone that needs to be zapped and regular ventilation will move the stone
What can you not do when doing high frequency ventilation (ie jet ventilation)?
use anesthetic gases; must use IV meds (propofol at high doses)
What is another formula for determining PaO2?
PaO2=PiO2-PaCO2/R + F (F is usually negligible); R=0.8
