Spontaneous breathing
patient inhale and exhales on their own. a patient must start and end the breath.
CPAP/Continuous positive airway pressure
CPAP is a positive end expiratory pressure (PEEP) without air being pushed in by a machine. With CPAP, inspiration is accomplished entirely by the patient's own muscular effort.
The most frequent application of flow cycling is in...
the "Pressure Support" mode
Pressure Support ventilation
-the application of a set positive pressure to a SPONTANEOUS inspiratory effort. Flow delivery is decelerating, which is inherent to pressure ventilation.
-requires an intact respiratory drive
-patient determines resp rate, insp time, peak flow, and tidal
time cycling
-expiratory flow starts because a preset time interval has elapsed
-pressure, volume, and flow may vary according to other ventilator and patient characteristics
-insp time is constant breath to breath
-when the inspiratory time has elapsed
-a time has to
All adult volume-cycled ventilators incorporate a pressure limit (alarm or backup cycle function) In these devices, if the pressure necessary to deliver the volume rises to the alarm setting, what will happen?
the ventilator will alarm and will automatically cycle to end inspiration
a trigger variable
TO INITIATE THE INSP PHASE OF AN ASSISTED BREATH-what causes the breath to begin
-inspiration begins when some measured variable reaches a preset value
-can be controlled by the patient or the machine
-time (control ventilation)
-manual (operator control)
limit variable
-something that limits inspiration but does NOT terminate inspiration
-pressure
-volume
-flow
Patient trigger- flow
-machine sensitivity is based on a drop in flow from the circuit. A base flow is set or delivered, and when that flow drops by the preset value the ventilator responds
-there is always a small constant flow moving through the circuit
-as the patient pulls
trigger sensitivity
-this determines how easy it is for the patient to trigger the ventilator to deliver a breath
-the smaller the flow or the smaller the negative pressure the more sensitive the trigger
-typically set the sensitivity to -0.5 to -1.5 cmH2O
phase variables
-trigger mechanism
-limit variable
-cycle mechanism
pressure limited
-limits the peak inspiratory pressure (PIP) during inspiration
-a vent does one thing when a pressure limit is reached. stay at the same level until inspiration ends
-2 most common applications are pressure control vent and pressure support ventilation.
-
volume limited
-limits the amount of tidal volume (Vt) delivered during inspiration to a set amount
-vents that are time cycled and volume limited will deliver the preset tidal volume but insp will be maintained until a preset time elapses
cycle mechanism
-what causes a breath to end
-one of the following is ALWAYS the cycling parameter: pressure, volume, flow, or time
pressure cycling
-insp ends when a preset pressure is reached
-volumes vary according to other ventilator and patients characteristics
-most often used for IPPB or pressure alarms
-on the pressure (Paw) waveform monitor the triangles do not have to look the same as long a
time trigger
-ventilator gives the breath at a predetermined time interval
-the rate control divides each minute into equal time segments, flow and volume determine inspiratory time and expiratory time OR
-seperate control for insp time and exp time
patient trigger sensitivity
-sensitivity setting establishes the trigger variable
-the trigger variable determines when the ventilator recognizes a patient's insp effort
-when patient effort is recognizes, the ventilator is triggered to deliver a breath
-the trigger can be a change
patient trigger-pressure
-insp effort causes a drop in circuit pressure
-the sensitivity determines at what level the vent will sense the patient effort
-the sensitivity should be set between -0.5 to -1.5 cmH2O
control variable
-the primary variable the ventilator controls during insp
-pressure (PC), volume (VC),flow, or time (usually based on the other parameters)
-which parameter remains constant despite changes in pulmonary mechanics
-only 1 control the other 2 will be variab
control variable-pressure
-ventilator controls pressure so it will be constant
-volume will vary with changes in compliance and resistance
volume control
-ventilator controls volume so volume (and flow) will be constant.
-pressure will vary with changes in compliance and resistance (resp mechanics)
-during VC ventilation, the PIP varies with changes in the patient's conditions, while the volume and the flo
If compliance DECREASES the pressure will?
increase to maintain the same Vt
flow limit
-most modes of ventilation allows for a limit or adjustment of flow
volume cycling
-when a preset volume is delivered out of the system, insp ends
-pressures vary according to other ventilator or patients characteristics.
-the RT sets the volume you want to deliver; not necessarily does the volume get to the patient
-the waveforms will
flow cycling
-provides gas under pressure until flow drops to specified level
-usually in a % of the insp flow
-insp flow has to drop to some level for breath to end
basic design features of a ventilator
-input power (electrical energy or compressed gas)
-power transmission and conversion (drive and output control mechanism)
-control system (understand the pressure needed to drive gas into the airway and inflate the lungs)
-output (pressure, volume, and f
tidal volume
-the amount of gas that is delivered during inspiration expressed in ml or liters
-Vt can be a set parameter in volume control ventilation
what a ventilator actually does
-obtains power and converts this power into a force that can move gas into a patient's lung
-sends gas down a circuit to the patient interface and back to ventilator for analysis of data
breath rate (f)
-respiratory rate or frequency
-the number of times over a one minute period inspiration is initiated (bpm)
-breath rate per minute
-may be set (mechanical)
-may be spontanous (patient)
FiO2
-fractional concentration of inspired oxygen delivered expressed as a % (21-100)
-as a rule of thumb in an emergency situation use as much O2 as possible until resolved
Positive End Expiratory Pressure
-for baseline pressure to exceed atmospheric pressure
-at the end of exhalation (either mechanical or spontaneous), patient airway pressure is maintained above atmospheric pressure by exerting pressure that opposes complete passive emptying of the lung
-i
how does the mechanical ventilator control the various parameters of ventilation such as starting and stopping a breath?
control variables
electrical power ventilator
-uses voltage from electrical line outlet
-110-115 volts alternating current (A/C) (60Hz)
-A/C current may be reduced and converted to direct current (D/C)
-indirect application via an electric motor or compressor
Pneumatically powered ventilator
-uses compressed gas as its power source
-regulated 50 psi gas source applying a direct application of compressed gas
What changes the base line pressure?
-baseline
-PEEP or CPAP
What happens when the trigger is not sensitive enough?
-increased WOB
-asynchrony with the vent
-fighting the vent
What happens when the trigger is too sensitive?
-triggers too many breaths (chattering, auto-cycling)
-could lead to air trapping and baratrauma
What ventilator modes may use PEEP?
-A/C
-SIMV
-PCV
FRC
-functional residual capacity
PIP
Peak Insp Pressure, the highest pressure produced during the insp phase.
Peak Inspiratory Flow
-determines how quickly the volume of gas will be delivered
-approximately 60 L/min with a range of 40 to 80 L/m
inspiratory flow time
-time during which the inspiratory flow is delivered to the patient.
inspiratory hold time
-during which inspiratory flow has ceased but expiratory flow is not yet allowed
inspiratory time
-the time spent in the insp phase of the ventilatory cycle
-amount of time spent in inspiration/amount of time it will take for inspiration phase
-time it will take for a set value (pressure/volume) to change from low value to highest value.
-time= volume
patient cycling
-the patient must be able to change the inspiratory time by making an insp or exp effort
-for example, with pressure cycling, the patient can make insp time longer by making an insp effort. bc the patient is breathing in, it takes longer for the ventilato
machine cycle
if it is not possible for the patient to change the insp time, by making either a insp or exp effort...
-time cycled
cycling
-volume, time, pressure, flow
-what cycles, or changes the ventilator from one phase of respiratory cycle to the other
-insp ALWAYS ends or terminates because some variable has reached a preset value
limiting
-volume, pressure, time
-what limits the delivery of gas to the patient during the insp phase
what causes the breath to end?
cycle variable
what causes the breath to begin?
trigger
the VORTRAN Automatic Resuscitator
-is an example of a device that is purely patient cycled using pressure (either actively using muscle activity or passively via the time constant)
response time
-how fast the ventilator mechanism responds to a patient effort
flow trigger
-typically provides a continuous flow of gas through its circuit
-set the base continuous flow and a trigger flow level
-trigger flow level is set to 1 to 3 L/min (below baseline)
-using flow as a trigger decreases a pt's WOB
-when the patient makes an in
baseline variable
-the parameter controlled during expiration
-pressure control is the most practical
-expiratory pressure
-ALWAYS measured and set relative to atmospheric pressure
ZEEP
-zero end-expiratory pressure
-the default baseline value during positive pressure ventilation
-equals atmospheric pressure
-when exhalation begins, the ventilator's expiratory valve open to the atmosphere, exposing the pt's airway to a relative pressure
NEEP
-negative end exp pressure
-the baseline could be set below atm pressure
-application of subatmospheric pressure to the airway during exhalation
-a way to help pts overcome exp airway resistance
conditional variables
-is used by a ventilator's control circuit to make decisions
-IF the value of a conditional variable reaches some preset level, THEN some action occurs to change the vent pattern
modes of ventilation
-a ventilator mode must refer to a predetermined pattern of interaction between the patient and the vent
WHAT is a breath?
-a positive change in airway flow (inspiration) paired with a negative change in flow (expiration) measured from a baseline
what are 2 major types of breathing?
-spontaneous
-mandatory breath
inspiratory flow rate
-how fast a volume of gas will be delivered during inspiration
* flow = volume (Vt) / time
-peak inspiratory flow
*minute ventilation = Vt x f
dual control
-a ventilator can automatically switch from between pressure control and volume control in an attempt to guarantee minute ventilation while maximizing patient synchrony
spontaneous breath
-are initiated AND ended by the patient
-patient triggered AND patient cycled
-may occur during a mandatory breath
Mandatory breath
-are initiated OR ended by the ventilator
-all mandatory breaths are by definition assisted breaths
Assisted breath
-a breath for which all OR part of the insp OR exp flow is generated by the vent
-a mandatory breath is by definition an assisted breath
-ALL breaths are patient triggered
-can be volume control OR pressure control
no required cycle for assisted
continuous mandatory ventilation (CMV)
-A/C
-ALL breaths are mandatory and delivered at a set minimum frequency BUT any insp effort by pt during exp phase can trigger the next mandatory breath
-can have spontaneous breaths between mandatory breaths
Assisted Control Ventilation
-a certain amount of mandatory breaths and the patient make an insp effort an identical breath is given to the patient at the SAME flow, volume, FiO2
I:E ratio
- the inspiratory time compared to
the expiratory time; I + E = total cycle time
flow pattern
the shape of the curve
representing the breath delivery; it can be
square wave of decelerating
mean airway pressure
The average pressure that is exists at the airway over
the ventilatory cycle.
Mathematically equivalent to the area under the
pressure time curve from the beginning of one cycle the
the beginning of the next breath. Divided by the
ventilatory period.
This mode has a fixed minimum rate and volume are delivered by the machine, but each of the patient's spontaneous breaths triggers the ventilator to deliver a selected volume. Every breath is a mandatory breath even though the patient can trigger the brea
Volume Control/Assisted Control
The peak inspiratory pressure is a product of which of the following.
1. total airflow resistance of the ventilator
2. total airflow resistance of the airway
3. compliance of the lung
4. compliance of the chest wall
all 1,2,3,4
For which of the following uses might you consider the use of a purely pneumatically powered ventilator?
I. as a backup to electrically powered ventilators
II. when electrical device cannot be used (e.g., magnetic resonance imaging)
III. during certain ty
I,II,III
A volume-cycled ventilator has a rate knob for setting the controlled frequency of breathing. If this control is set to 15/min, which of the following other settings will determine the inspiratory and expiratory times?
I. FIO2
II. flow
III. volume
II & III
Mr. Smith is a 67-year-old man with a history of COPD that has developed an upper respiratory tract infection. His weight is approximately 150 lbs. Upon admission his is cyanotic, obtunded, with shallow gasping breathing, breath sounds diminished with som
225
The volume waveform generated by a ventilator remains the same against changing lung mechanics. Which of the following parameters might this device be controlling?
I. volume
II. flow
III. pressure
I & II
Decelerating Inspiratory flow pattern with automatic adjustment of the Inspiratory pressure for changes in compliance and resistance resulting in a guaranteed tidal volume. Ventilator monitors each breath and compares the delivered tidal volume with the s
Volume Control +
What is the primary physiological effect of positive end-expiratory pressure (PEEP)?
increase FRC
The I:E Ratio is 1:4
What is the inspiratory time [1]?
0.8
What is the inspiratory time in seconds assuming an I:E Ratio of 1:2
Vt= 800
rate = 10
2
TCT = 6 60sec/min / 10 breathis per min
TCT/ I+E 6 sec/ 1+2
TI = 2
what is the exp time with ratio 1:2
vt = 800
rate 10
4
What is the required flow rate in (milliliters/second). Assuming an I:E of 1:2
vt 800
rate 10
400
(
convert 400 ml/sec to liters/min
24
(400 ml = 0.4 L x 60)
1:4
rate 15; vt 600; what is the insp time in seconds?
0.8
what control of a vent controls the TCT?
frequency
what determines your i time?
inspiration
what determines you E time?
i time and frequency settings
tidal volume
-during each cycle(inspiration and expiration), a volume of gas moving in and out of the resp tract
-the volume measured during either inspiration or expiration
-typically about 500 mL.
-the amount of gas that is delivered during inspiration, expressed in
Breath rate
-frequency
-the number of times over a one minute period of inspiration is initiated (bpm)
What factors control inspiratory time?
flow & volume (unless you have an I time
How is inspiratory time set?
...
how is I:E ratio determined?
Ti & Te
what physiologic parameters does FiO2 affect?
PaO2 (oxygenation)
An FiO2 change would be most appropriate to change?
oxygenation
This mode has a fixed minimum rate and volume are delivered by the machine, but each of the patient's spontaneous breathes triggers the ventilator to deliver a selected volume. Every breath is mandatory breath even though the patient can trigger the breat
VC-CMV/AC
A 68 Kg man has a resp rate of 10 per min and a tidal volume of 600 mls. A change in his resp rate to 15 per min would do what to the following?
TCT
Insp Time
Exp Time
Minute Ventilation
Alveolar Vent
PaCO2
TCT: decreases
Insp Time: stays the same
Exp Time: decrease
Ve: increase
Alveolar ventilation: increases
PaCO2: decreases
A patient is struggling to initiate inspiration on an ventilator set in the A/C mode. Which settings would you first check to determine the cause of the problem?
sensitivity
A volume control vent has an individual rate setting that determines the controlled frequency of breathing in breaths per minute. Assuming this control remains set at 12/min which parameters will determine the length of: a. inspiration b. expiration
flow and volume (unless you have an I time)
A patient is receiving volume-controlled ventilation. The low pressure alarm suddenly begins to sound. The respiratory therapist should?
bag the patient then look for a leak
PEEP is indicated in a patient with a decreased PaO2 and decreased tissue oxygenation caused by?
-decreased FRC
-shunt
-derecrutment
Describe when and how inspiratory static pressure is taken?
-insp pause
-delivered flow reach
-no gas movement
-exhalation valve remains closed
-plateau pressure
what does it mean when you set the sensitivity level?
whenever it reaches that level the ventilator DELIVERS a breath
What levels should your sensitivity be set between?
the trigger level is set 0.5 to 1.5 cmH2O below the baseline expiratory pressure
3 ways to decrease a patient's PaCO2 in the APRV mode?
decrease pressure low
-increase pressure high
-increase the rate/frequency (changes the Ti & Te)
-increase the change from baseline to high pressure (true in ANY PC ventilation)
In APRV mode the greater difference in pressure the _____ in volume?
greater
A patient is being mechanically ventilated via VC ventilation, the set Vt of 700ml. Her blood gases are acceptable but there is a desire she be switched to pressure control ventilation for lung protection. PC is set at 40 cmH2O. Measurements show an exhal
decrease the pressure
with an increase in compliance?
in VC= decrease pressure
in PC= increase volume (bc pressure stays the same)
In volume-control ventilation the peak inspiratory pressure is a product of what?
-Vt
-flow
-lung compliance
-resistance
In VC changes in the compliance and resistance is best monitored by which parameter?
Pressure
A patient receiving VC ventilation develops a marked increased in plateau pressure. What is most likely explanation for this event?
decrease in lung compliance
what is set for trigger FLOW level
1 to 3 L/min (below baseline)
Describe when and how static pressure is taken in VC ventilation
at the point which gas has been delivered and no more flow and the exhalation valve is closed.
during an insp pause
A patient who is being mechanically ventilated has insufficient time to exhale completely. Without changing his minute volume which 2 vent changes could correct this problem?
-increase insp flow (Vmax)
-change from ramp to square pattern
-flow rate
the patient is receiving VC ventilation. The patient's PaCO2 would be DECREASED by and INCREASE in the?
rate & tidal volume
Why do we not have an oppurtunity to set an inspiratory flow (in VC+)
becaused based on the patient's compliance and resistance the machine will set it
In VC+ what can you NOT control?
-DO NOT have a flow rate control
-you can NOT change the flow pattern
In VC you will always have?
a decelerated ramp b/c you want to deliver the same volume at lesser pressure
PIP is defined either by?
-flow rate
-volume you are pushing in
-speed type
during an inspiratory hold the plateau pressure represents?
the compliance
the difference between the PIP & Pplat represents?
the resistance
and increase in VT will _____ Ti & ______ Te?
-increase Ti
-decrease Te
an increase in Flow (V max, V peak) will _____ Ti & ___ Te?
increase Te
decrease Ti
what is consistent with an obstruction in the endotracheal tube of a patient who is receiving ____ controlled ventilation?
increase in pressure
when selecting an endotracheal tube size which of the following factors should be the considered to minimize airflow resistance?
endotracheal tube size
true about an end inspiratory hold
-insp hold prevents the exp valve from opening for a short period of time
-increases the insp time
-may shorten the exp time
compared to using pressure as a trigger variable, what is the major advantage of flow triggering?
decrease the WOB
a volume-cycled ventilator provides gas under a positive pressure during insp until what point?
a preselected volume of gas is expelled from the device
a physician request suggest the you switch from pressure trigger to flow trigger. which of the following new setting would be appropriate?
a. 0 L/min base flow trigger at 2 L/min
b. base flow 10 L.min trigger at -2 cmH2O
c. baseflow 10 L/min trigger @ 2 l
c. base flow 10 l/min and trigger at 2 l/m
when a ventilator reaches a preset pressure early in the inspiration phase but holds it for a time which inspiration ends. what mode of ventilatory support is in force?
pressure limited
time cycled