Ventilator Settings Flashcards
fraction of inspired oxygen (FiO2)
concentration of oxygen in the inspired gas; can be set from 0.21 (room air) to 1.0 (100%)
tidal volume (Vt)
volume of gas, either inhaled or exhaled, during a breath and commonly expressed in mL; Vt generally set between 8-12 mL/kg (better practice for LPV is 6-8 mL/kg to prevent lung overdistention and injury)
respiratory rate (RR) or frequency
number of breaths per minute that the ventilator delivers; commonly set between 10-20 breaths per minute; if patient is making spontaneous respiratory efforts, RR will be higher
minute ventilation (VE)
average volume of gas entering, or leaving, the lungs per minute; commonly expressed in L/min; Vt x RR = VE; normal VE is between 5-10 L/min
peak flow rate OR peak inspiratory flow
the highest flow or speed that is set to deliver the Vt during inspiration; usually measured in L/min; when flow rate is high, the speed of gas delivery is faster and inspiratory time is shorter
inspiratory time
time spent in the phase of inspiration
expiratory time
time spent in the phase of expiration
I/E ratio
the speed at which the Vt is delivered; setting a shorter i time results in a faster inspiratory flow rate; average adult inspiratory time is 0.7 to 1.0 s; I/E is usually 1:2 or 1:3
peak airway pressure (Paw)
represents the total pressure that is required to deliver the Vt and depends upon various airway resistance, lung compliance, and chest wall factors; expressed in cm H2O
plateau pressure (Pplat)
the pressure needed to distend the lung, which can be measured by applying an end-inspiratory pause setting on the ventilator; it is expressed in cmH2O
sensitivity or trigger sensitivity
effort or negative pressure required by the patient to trigger a machine breath, commonly set so that minimal effort (-1 to -2 cmH2O) is required to trigger the breath; some vents may have flow triggering which is more sensitive than pressure triggering if flow setting is set correctly; a decrease in flow is sensed when patient makes a spontaneous effort and triggers the machine to deliver the breath
Positive end expiratory pressure (PEEP)
amount of positive pressure that is maintained at end-expiration; expressed in cmH2O; purpose is to increase end-expiratory lung volume and reduce air-space closure at end-expiration
continuous positive airway pressure (CPAP)
continuous pressurization of the breathing circuit when a patient breaths spontaneously; may be used as a last step in the weaning process or as a noninvasive method of providing a pneumatic splint to the upper airway in OSA
mandatory breath
a breath in which the timing and/or size of the breath is controlled by the ventilator; the machine triggers and/or cycles the breath
spontaneous breath
a breath in which both the timing and size are controlled by the patient; the patient both triggers and cycles the breath
A/C
assist control
CMV
controlled mechanical ventilation OR continuous mandatory ventilation
PSV
pressure support ventilation
PCV
pressure control ventilation
SIMV
synchronized intermittent mandatory ventilation
VCV
volume controlled ventilation
volume targeted mode of ventilation volumes
volume constant –> guarantees volume at expense of variable airway pressure
volume targeted mode of ventilation inspiration
inspiration terminates when present Vt is delivered
volume targeted mode of ventilation preset Vt delivered
unless a specified pressure limit is exceeded (upper airway pressure alarm is set) or patient’s cuff or ventilator tubing has air leaks that cause a decrease in Vt delivered
volume targeted mode of ventilation peak airway pressure
variable; determined by changes in airway resistance, lung compliance, or extrapulmonary factors; the peak airway pressure increases as needed to deliver prescribed Vt
volume targeted mode of ventilation inspiratory flow rate
fixed; if patient inspires faster or more vigorously, work of breathing increases; clinician needs to promptly correct airway resistance and/or lung compliance problems, readjust flow-rate setting higher to match inspiratory demands
examples of volume targeted vent modes
CMV, VCV, A/C, SIMV
pressure targeted modes volume
volume variable; guarantees pressure at expense of letting Vt vary
pressure targeted modes inspiration
inspiration terminates when preset pressure reached; preset pressure delivered and volume is variable and determined by the set pressure level, airway resistance, and lung compliance factors, specified time or flow cycling criteria
pressure targeted modes peak airway pressure
fixed; determined by set pressure level; volume delivered is variable and decreases with increased airway resistance, decreased lung compliance, or extrapulmonary factors
pressure targeted modes inspiratory flow rate
variable; if patient inspires faster or more vigorously, variable flow rate may match change in inspiratory demand or may be insufficient; clinician needs to promptly correct airway resistance and/or lung compliance problems, may need to readjust pressure support or I/E settings
goals of mechanical ventilation in OR
- maintain homeostasis
- ensure adequate oxygenation
- ensure adequate CO2 removal
- safe and effective surgery
PiP
- peak inspiratory pressure
- total pressure required to distend lungs and airways
- pressure used to calculated dynamic compliance
Pplat
- plateau pressure
- distending pressure to expand only the LUNGS
- measure’s redistribution of air flow through lungs
- Pplat is used to calculate static compliance
- performed with an inspiratory hold in VCV only
- tells us about the intrinsic pressure in the lungs
4 parts of a breath
- start of inspiration
- inspiration itself
- end of inspiration
- expiration
components of a breath
- Ti = inspiratory time
- Te = expiratory time
- TCT = total cycle time
total respiratory cycle variables
- trigger variable (start of inspiration)
- limit [or target] variable (maintenance of inspiration)
- cycling variable (transition of expiration)
- baseline variable (end expiration)
trigger variable
- represents start of inspiration
- can be affected with or without patient inspiratory effort by either pressure, volume, flow, or time
pressure as trigger variable
pressure decrease in circuit stimulates ventilator to deliver breath
volume as trigger variable
volume change in circuit can stimulate ventilator to deliver breath
flow as trigger variable
change of flow in circuit stimulates ventilator to deliver breath
time as trigger variable
set time interval triggers ventilator to deliver breath; this occurs independent of patient effort; this is what we see most common because we are using NMBDs
limit [or target] variable
controls how an inspiratory breath is maintained, once threshold is reached variable will not exceed set limit; this does NOT cause termination of inspiration
pressure as limit variable
sets upper pressure limit that cannot be exceeded
volume as limit variable
sets upper volume limit that cannot be exceeded
flow as limit variable
sets maximum airflow that cannot be exceeded; most common in assist control mode in ICU
cycling variable
transition from inspiration to expiration; based on volume, pressure, flow or time
volume as cycling variable
ventilator delivers flow until set volume achieved; if inspiratory pause set (typically 10-20%), this variable changes to a time-based cycling variable
pressure as cycling variable
once pressure is achieved, flow will transition to expiration
flow as cycling variable
once inspiratory flow drops below set threshold (default at 25%) ventilator will transition to expiration; noted in pressure support ventilation mode
time as cycling variable
ventilator terminates inspiratory breath after predetermined inspiratory time has been delivered; most common because we use NMBD
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 = improved oxygenation and ventilatory mechanics
intrinsic PEEP
- secondary to incomplete expiration; referred to as auto-PEEP; incomplete expiration prior to initiation of next breath; causes progressive air trapping
- causes –> high minute ventilation; expiratory flow limitation; expiratory resistance
extrinsic PEEP
provided by a mechanical ventilator; referred to as applied PEEP
volume control ventilation (VCV)
- delivers set tidal volume at respiratory rate
- time is trigger variable
- volume is the limit variable
- time is the cycling variable
- airway pressure (PIP/Pplat) will change on a breath-by-breath basis during this mode of ventilation based on changing respiratory compliance
- airflow will remain constant
- *NOTE airway pressure on VCV will be upside down V
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 (PCV)
- delivers set inspiratory pressure at set RR
- time is trigger variable
- pressure is the limit variable
- time is the cycle variable
- airway pressures are controlled by the user, Vt can change on a 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 lungs; theoretically improves ventilation pattern and decreases WOB
- must set patient appropriate high and low Vt alarms as change in respiratory compliance can affect Vt delivered
pressure control-volume guarantee (PCV-VG)
- respiratory cycle variables mirror PCV, however ventilator adjusts pressure delivered if current volume is not set volume
- adjustments take 3-5 breaths to complete; vent will switch in to a volume mode to determine the pressure it needs to deliver
- can allow for atelectasis development if compliance decreases and ventilator is delayed in providing adequate pressure to distend lungs
synchronized intermittent mandatory ventilation (SIMV)
- delivers set Vt at set RR in conjunction with patient initiated breaths
- time or patient stimulate the trigger variable
- flow is the limit variable
- time or volume is cycle variable; most likely time in the OR
- patient initiated breaths are not supported (unless in SIMV-PSV)
why choose SIMV?
- useful when weaning from controlled mechanical ventilation to spontaneous respiration; less dyssynchrony with patient initiated breaths
- hypoventilation can occur if set Vt and RR are too low and patient’s spontaneous respiration effort inadequate
- hyperventilation can also occur if using SIMV-PSV and pressure support level too high
pressure support ventilation (PSV)
- supported mode of ventilation for spontaneously breathing patient
- pressure support level set by user
- patient is the trigger variable
- pressure is the limit variable
- flow is the cycle variable
- patient controls most aspects of ventilation, but 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 is controlled, changes in respiratory system compliance will alter Vt delivered
flow trigger
L/min required for the ventilator to sense that a patient is triggering a breath; the lower the flow trigger is set at, the more sensitive the ventilator is to any adjustment in flow through the circuit; if flow of any kind is sensed a breath will be triggered
trigger window
backup mode of SIMV-PSV; the percentage of time that the patient’s breath will be supported; if the patient initiates a breath within that % window, then the breath will be supported; if it is outside the % the breath will not be supported
backup time
when you change patient from PCV to PSV, how long the patient is allowed to be apniec before the backup mode on the ventilator is triggered
