Modes of Ventilation Flashcards
Goals of Mechanical Ventilation
Maintain homeostasis
OR Goal of MV
ensure adequate oxygenation and CO2 removal for safe and effective surgery
ICU goal of MV
treatment for severe respiratory distress
provide lungs with a “break” to rest and heal
decrease O2 consumption by providing rest for respiratory muscles
Flow
the amount of air moving through a system
Pressure
amount of force you build to distend lung
Driving Pressure:
peak plateau pressure- PEEP
restrictive pressure
overall pressure required to overcome pressure in airways
distending pressure
required to open up lungs to open up lunges to provide gas exchange
Peak Inspiratory Pressure
PiP
total pressure required to distend lungs and airways
pressure used to calculate dynamic compliance
signals pressure required to overcome both intrinsic factors and chest wall (extrinsic factors) to distend both pressure
Plateau Pressure
distending pressure to extend only the lungs
measure redistribution of air flow through the lungs
used to calculate static compliance
Measures intrinsic factors of lung compliance
How do you measure plateau pressure?
during an inspiratory hold
Control Variables
respiratory Rate
tidal volume
pressure (Pip/PAW/Pplateau)
I:E ratio
4 Parts of Respiratory Cycle
start of inspiration
inspiration itself
end of inspiration
expiration
Components of a breath
Ti
Te
TCT (total cycle time)
Total respiratory Cycle variables
impact how each mechanical breath is initiated sustain and terminated trigger variable (start of inspiration) limit variable (maintenance of inspiration) cycling variable (transition to expiration) Baseline variable (end expiration)
Trigger Variable
represents the start of inspiration
can be affected with or w/o pt inspiratory effort by either Pressure, Volume, flow or time
trigger variable (pressure)
pressure decrease in circuit stimulates ventilator to deliver breath
Trigger Variable as Volume
volume change in circuit can stimulate ventilator to deliver breath
Trigger Variable as flow
change in flow in circuit stimulates ventilator to deliver breath
Trigger Variable as time
set time interval triggers ventilator to deliver breath (occurs independent of pt effort)
Limit Variable
controls how an inspiratory breath is maintained once threshold is reached variable will not exceed set limit
Limit variable does not
cause termination of inspiration
Pressure as the limit variable
sets upper pressure limit that cannot be exceeded
stops airway pressure, but maintains breath
Volume as the limit variable
set upper volume limit that cannot be exceeded
decrease flow in gas, but Vt maintained
Flow as the limit variable
sets maximum airflow that cannot be exceeded
used in ICU
Cycling Variable
transition from inspiration to expiration
Volume as Cycling variable
ventilator delivers flow until set volume is achieved
if inspiratory pause set (typically 10-20%) this variable changes to time based cycling variable
Pressure as cycling variable
once pressure achieved flow will transition to expiration
Flow as cycling variable
once inspiratory flow achieved flow drops below set threshold (default at 25%) ventilator will transition to expiration
noted in pressure support ventilation mode
Time as cycling variable
ventilator terminated inspiratory breath after pre-determined inspiratory time has been delivered
What is the most common cycling variable
time (d/t NMB)
Baseline variable
pressure maintained in the circuit at end expiration (PEEP)
must be individualized to patient
used to prevent atelectasis
PEEP
alveolar pressure above atmospheric
Goal of PEEP
to improve oxygenation
Intrinsic PEEP
secondary to incomplete expiration
auto peep
incomplete breath prior to initiation of next breath
causes progressive air trapping
extrinisc PEEP
provided by mechanical ventilator
applied PEEP
Causes of AUTO PEEP
high Minute ventilation
expiratory flow limitation
expiratory resistance
Volume Control Ventilation (VCV)
delivers set tidal volume as set respiratory rate time is trigger variable volume is limit variable time is cycling variable airflow will remain constant
What changes in VCV?
airway pressure (PIP/Pplateau) will change on a breath. by breath basis during this mode of ventilation based on changing respiratory compliance
Why choose VCV?
maintenance of set minute ventilation through direct manipulation of Vt and RR
must set individualized alarms for airway pressure to protect patient
increasing airway or lung resistance will stimulate generation of higher pressure to deliver set Vt
Pressure Control Ventilation
Delivers set inspiratory pressure as set RR
time is trigger variable
pressure is limit variable
time is cycle variable
in PCV, what is controlled by user?
airway pressures volumes change breath by breath basis depending on total respiratory system compliance
Why choose PCV?
set pressure limit to avoid barotrauma from delivery of excessive pressure
decelerating flow pattern allows for homogenous distribution of inspired gas throughout lung
must set patient appropriate high and low VT alarms as change in respiratory compliance can affect Vt delivery
Pressure control-volume guarantee (PCV-VG)
respiratory cycle variables are same as PCV, but ventilator adjust pressure delivered if current volume is not set volume
adjustments take 3-5 breaths to complete
can allow for atelectasis development if compliance decreases and ventilator is delayed in providing adequate pressure to distend lungs
Most common mode of ventilation
PCVVG
Variables for PCV-VG
trigger: time
limit: pressure
cycling: time
SIMV
synchronized intermittent mandatory ventilation
delivers a set Vt at a set RR in conjunction with patients initiated breathes
time/patient : trigger variable
flow or volume (if in VCV) are limit variables
volume is cycle variable
patient initiated breaths are not supported (unless in SIMV-PSV)
Why chose SIMV
useful when weaning from controlled mechanical ventilation to spontaneous respiration (less desynchrony) with pt initiated breaths
When does Hypoventilation occur in SIMV
if set Vt and RR are too low adn patient’s spontaneous respiration effort adequate
When does hyperventilation occur in SIMV
if using SIMV- PSV and pressure support level too high
Pressure support ventilation
supported mode of ventilation for spontaneously breathing patient
pressure support level set by user
patient is trigger varaible
pressure is limit variable
flow is cycle variable
patient controls most aspects of ventilation, but the anesthetist can adjust certain variables to augment or limit support given to prepare patient for extubation
Why choose PSV?
great for end of case in preparation for extubation
patient must be breathing spontaneously or ventilator will switch to backup mode
just like PCV pressure controlled, changes in respiratory system compliance will alter Vt delivered
High PIP pressures with normal peak plateau pressures indicate
resistance problem
What are resistance problems
small ET tube kinking bitiing obstructed ET tube high flow rate or Vt ventilator asynchrony mucous plug, blood clot bronchospasm
High PIP and HIgh peak plateau pressures indicate
compliance problem
What are compliance problems
ARDS, edema, ateletasis pneumothorax, effusion air trapping (auto peep) R mainstem intubation fibrosis, ILDs obesity abd compartment syndrome
