Exam 4: Lecture 4.1 - Ventilators Flashcards
lung function?
ventilation, oxygenation
-filtration, drug administration
what is minute ventialtion?
alveolar ventilation + total dead space ventilation
what is anatomic dead space?
volume of air that fills conducting zones
do not participate in gas exchange
what are conducting zones?
nose, trachea, bronchi
how much of normal tidal volume is considered dead space?
30%
physiologic dead space?
anatomic dead space + alveolar dead space
what is alveolar dead space?
at the lung apices where alveolar pressure is high and perfusion is low
considered negligible in healthy adults
arterial partial pressures that measure ventilation and oxygenation?
PAO2 and PACO2
what is the oxygen consumption rate of a 70 kg adult?
250 mL/minute
may be lower under anesthesia
apneic oxygenation?
passive flow without ventilation
nc in the nose on a patient you’re about to intubate
what is denitrogenation?
pre-oxygenation
increasing the oxygen ratio over nitrogen ratio in the lungs
when the patient is breathing oxygen the pulmonary reservoir represents how many minutes of metabolic consumption?
12 minutes
what is the respiratory quotient?
Respiratory quotient is the ratio of the volume of carbon dioxide produced to the volume of oxygen consumed in respiration over a period of time
what is the respiratory quotient equal to?
VQ ratio
produce 200 mL CO2 and consume 250 mL O2 per minute
200/250=0.8
what do you need in order to denitrogenate?
a good mask seal, will reset if they breath room air
apparatus dead space?
ETT, HME, circuit, anything added like connectors
what is the work of breathing?
overcoming resistance aspects of circuit, ETT, and the large (upper) and small (lower) airways
does compliance mean expansion or contraction of the lungs?
expansion
does elasticity contract or expand the lungs?
contract
what is flow a function of?
resistance
what is a change in pressure proportional to?
a change in volume
is pressure a measure of force?
yes
is exhalation active or passive during mechanical ventilation?
passive
is exhalation active or passive during spontaneous ventilation?
active
is inhalation active or passive during spontaneous ventilation?
passive
is inhalation active or passive during mechanical ventilation?
active
what is cycle time?
how long it takes for a breath to complete
RR 10 breath/min=6 sec cycle time
peak inspiratory pressure
under 35 cm H2O
plateau pressure
below 30 cm H20
protective under 16 cm H2O
tidal volume
6-8 mL/kg ideal body weight
minute volume/ventilation
tidal volume x RR
OR [tidal volume - dead space (20 or 30%)] x RR
peak airway pressure
frequency
respiratory rate
I:E ratio
inspiratory: expiratory ratio of cycle length
normal I:E
1:2
what does it mean to expand I:E ratio?
increase expiratory phase, without adding time to cycle time
1:2 to 1:3 or 1:4
who needs an expanded I:E ratio?
copd, asthma
what will have to increase to expand the I:E ratio?
pressure
and shorten inspiratory phase to get the same volume in
what is dead space?
ventilation without oxygenation/perfusion
what is shunt?
perfusion without ventilation
how does anesthesia affect lung function?
adversely
how does anesthesia adversely effect lung function?
-physical insult by ETT
-retention of secretions
-suppression/damage to mucociliary expectoration system
-dehumidification
-cooling
how does anesthesia increase WOB?
ETT is smaller than normal trachea
-breathing through a straw
how does airway suctioning effect lung function?
-negative pressure
-atelectasis
-airway irritation
-coughing can place cardiovascular strain on the patient and the surgical wound
post nasal surgery coughing? good or bad?
bad
-increase in intrathoracic pressure
-pressure feeds back to jugular
-increased pressure in nose/brain
-increased bleeding
where can you get the most accurate EtCO2 reading?
sample line from ETT/LMA
why do you inflate the cuff in an ETT?
protect airway from gastric secretions
is an LMA a protected airway?
No
why is a face mask a less accurate measure of EtCO2?
dilutional from room air and flow
how can you reduce WOB?
mechanical ventilation
what does MAC stand for?
monitored anesthesia care
what is lung protective strategy?
to avoid baro and volutrauma with lower Vt
-atelectrauma, shear trauma of the parenchyma, distruptions of alveolar-capillary membrane
how does PEEP lessen lung injury?
how does PEEP increase physiologic dead space?
the positive pressure holding the alveoli open can lead to capillary occlusion - increases intrathoracic pressure - reduce RV capacity to pump to pulm circuit - decreased CO
-overall less perfusion
what is recommened Vt for lung protective strategy ventilation?
6-8 mL/kg ideal body weight
what alveolar pressures may be associated with lung injury?
greater than 30-40 cm H2O
alveolar pressure may be lower than Paw
how does peep improve oxygenation?
more positive pressure pushed through thickened membrane (pna, secretions, fibrosis) to better perfuse
-holds alveoli open longer to increase oxygenation
-maximized FRC
what are conservative recommendations for plateau pressure?
< 16 cm H2O and PEEP 5
how does permissive hypercapnia reduce ventilatory complications?
allows patients to keep their respiratory drive
what examples of humans tolerating respiratory acidosis well?
pH 7.15 and PaCO2 80 mm Hg
what patients should you avoid high PaCO2?
-high ICP
-recent MI
-pulm htn
how would you have to actually measure alveolar pressure?
with a sensor in the actual alveoli, we just estimate
what is the spill valve?
-pressure relief valve similar to APL valve on the manual circuit
-spill valve only on ventilation mode
what does the spill valve do during inspiration?
closed during inspiration so the ventilator can generate positive pressure
what does the spill valve do during exhalation?
valve is open to allow the driving gas to be released from the plastic housing of the bellows
what happens if the spill valve gets stuck in the closed position?
results in high airway pressures
(similar to a patient breathing against a closed/tightened APL valve)
what is peak inspiratory pressure?
highest circuit pressure measured during inspiration
what is an indication of dynamic compliance?
peak inspiratory pressure
what peak air way pressure puts patient at risk of barotrauma?
> 30 mmH2O
what is a conservative, lung protective peak airway pressure?
< 16 mm H2O and a PEEP 5
when is plateau pressure measured?
during the inspiratory pause
-between inspiration and expiration when no ventilatory movement is occuring
what is plateau pressure a measure of?
static compliance
what does the pressure do during the inspiratory pause?
drops slightly before dropping with exhalation
when is the low peak pressure alarm activated?
when the ventilator is turned on
what do low Vte and low EtCO2 alarms detect?
circuit disconnect
two types of bellows ventilators?
ascending and descending
which bellow ventilator is preferred?
ascending
how do bellow ventilators work?
pressurized oxygen from the anesthetic machine is fed into the plastic housing at 50 psi to compress the bellows with inspiration
the bellows expand when the patient exhales
if a leak exists in the bellows, the ventilator could transmit the high gas pressure to where?
the patients airway and you would see higher than expected FiO2
how do some bellow ventilators use a venturi device?
to draw air into the plastic housing
-oxygen sparing and FiO2 would not increase in the evnet of a leak
how do piston ventilators work?
substitute an electrically driven piston for the bellows and do not require pneumatic (oxygen, gas) power for ventilation
advantages to piston ventilators?
accuracy, ability to deliver accurate tidal volumes in patients with poor lung compliance or very small patients
what is a turbine ventilator?
electric motor powers a spinning turbine fan to produce drive gas pressure
what is the fixed input and variable output in volume control ventilation?
volume is fixed
output is variable
how do airway pressures rise with time as gas volume is pushed into the lung?
linearly
pressure control
pressure is fixed input
volume is a variable output
pressure control volume guarantee
the vent will dynamically titrate pressure (up to a specified limit) until a particular tidal volume is achieved
what is assist control ventilation?
patient will trigger a breath by pulling negative pressure (flow trigger)
when will a breath not be delivered in ACV?
as long as the patient triggers the ventilator more than the defined interval set by the control rate a control breath will not be delivered
what happens if the patient has a long pause or goes apneic in ACV?
the backup rate will kick in
what is pressure support ventilation?
clinician sets the peak airway pressure to be delivered and the flow trigger
what it the flow trigger?
how much work patient has to do to get a supported breath from the vent
what is a low flow trigger?
0.6
means the patient has to do less work before the vent gives a supported breath
less work - smaller breath or lower trigger that the vent will notice and finish with a supportive breath
what is a normal flow trigger that would show you’re closer to extubation?
1-3 L/min
if PSV fails and a backup mode will turn PSV off and completely take over, do you have to turn PSV back on?
yes
what is SIMV?
update of IMV
synchronizes patient breaths with automatic breaths
SIMV reduces risk of what?
breath stacking
when does SIMV place a time observation window of each respiratory interval?
at the beginning
in SIMV what does the ventilator monitor for?
pressure or flow changes
in SIMV if parameters are not exceeded , the mandatory breath is delivered when of the respiratory interval?
at the beginning
what does CPAP represent?
the airway pressure between exhalation and inhalation
how is CPAP dialed on the ventilator?
APL valve, lets pressure build up to this limit
what recruitment does CPAP serve?
alveolar
Does CPAP increase intrathoracic pressure?
yes
high frequency jet ventilation
high frequencies and small volumes
where are jet ventilators used?
NICU and thoracic surgery
ventilator concerns
-over pressurization of the airway
-hypothermia
-dry secretions
-hypercarbia, hypocarbia
-hypotension in the airway
-excess PEEP
-trauma
-tracheal tube cuff herniation
-bronchospasm
-cross-infection
what can cause over pressurization of the airway?
dis-synchrony
coughing against vent
O2 flush valve pushed when patient is in the inspiratory phase
bad input parameters
