Question Answer
3 ways to power a vent are electricity, pneumonic (gas) or combined (most common)
*Drive mechanism on a vent is converts input power to useful power, 1 direct-compressed gas via reducing valve or 2 indirect-elec motor or compressor
Output control valve on a vent regulates flow of gas to pt (on/off), can shape output waveform
2 most common waveforms are constant (square), descending (most common)
Waveforms when press, volume and flow are plotted as a function of time, waveforms of either volume-controlled(rectangle) or press-controlled (square)
Sinosodal waveform normal spontaneous breathing waveform
Constant waveform fixed size breath-low resistance
Decelerating waveform aka descending, most common because of >RAW
Mechanism of breathing changeable variables of pressure, volume and flow, that are measured relative to their baseline or end expiratory values
Time constant in any mode of ventilation, the E time should be at least three time constants long to avoid gas trapping
TC Time constant, (Raw x CS)e, where e represents volume exhaled as a percent, 1 is 63%, 2 is 86%, 3 is 95% and 5 is 100% exhaled. TC <3 leads to air trapping.
Control circuit/system electric, electronic, fluidic, mechanical or pneumatic, that manipulates press, volume or flow. Measures and directs output to replace or assist pt breathing
Fluidic control circuit uses coanda effect, no moving parts, no metal, used for MRI
Most vents today us what kind of control circuit electronic
When do we want the lowest flow end expiration
Lower flow creates what more laminar flow, less RAW
Where is RAW lowest in the trach, it’s the largest airway
Control variables primary variable vent manipulates to cause inspiration. press (pt initiated), flow (pt initiated) and time (mach initiated)
Press control variable if the ventilator controls press, the press wave form will remain constant, but the volume and flow will vary with changes in resp system mechanics (>Raw=<vol and <flow)
Volume control variable if the ventilator controls volume, the volume and flow waveforms will remain constant, but the pressure will vary with changes in resp mechanics, can be controlled indirectly by controlling flow.
Volume and flow are inverse functions of what time, volume is the integral of flow and flow is the derivative of volume (F x T eq V)
Can flow or time effect press no (think SVN, we adjust flow but pressure stays the same or we wouldn’t have aerosol)
Ventilator cycle 4 phases, initiation of inspiration, the inspiration itself, end of inspiration and expiration
Phase variables initiates a phase of the ventilator cycle, trigger variable, limit variable, cycle variable and baseline variable
Trigger variable phase causes breath to begin, time (mach), press (pt) or flow (pt)
Trigger variable if machine initiates then the trigger is time, if pt initiates then trigger is press, flow or volume
Patient triggering mach senses pt inspiratory effort, can be measured in press, flow or volume
Time triggering mach initiated breath according to predetermined time interval, no regard for pt effort
Trigger Sensitivity setting (pressure) the pressure drop need to trigger a breath, norm is .5-1.5 cmH20 below baseline. To > and pt works to hard to get breath, to low and mach is to sensitive.
Response time how fast the vent mechanism respond to pt effort, short is better to maintain synchrony w/pt effort
What can affect response time large pressure drop (low sensitivity setting), delay in flow delivery
Flow-triggering system has continuous flow of gas through the circuit, think instant hot water
What is the advantage of flow triggering over pressure triggering decreases pt WOB
What is the disadvantage of flow triggering over pressure triggering flow triggering machines are highly susceptible to circuit leaks or movement caused by turbulence of gas flow through condensed water in circuit
Limit variable phase press or volume, limits the magnitude of the parameter during inspiration, BUT DOES NOT TERMINATE INSPIRATION, preset by machine
*Cycle variable phase variable that is measured and used to end the inspiration, can be press, volume, flow or time ENDS THE BREATH!
Pressure cycling when preset inspiratory press is reached, inspiration stops and expiration begins, most common in alarm settings (time cycled press limited), and IPPB (press limited press cycled)
Volume cycling delivers flow until preset volume is met, and then expiration begins. (volume cycled volume limited)
Flow cycling (push support) delivers flow (at a preset pressure) until level is met, most often used in pressure control mode EPAP, IPAP BIPAP.
Time cycling expiratory flow starts because a preset time interval has elapsed
Baseline variable phase set and measured relative to atmospheric pressure, it describes what happens during expiration, we must know what baseline variable is in effect. PEEP, ZEEP, NEEP
PEEP breathing at a baseline above 0, norm 5-15
Hazard of pos press to cardiac pt is what <venous return, >ICP, <CO, <BP
What are we trying to accomplish using mech vent CONTROL pt ventilation and oxygenation because they can’t, or SUPPORT pt as they wean from vent
Control modes (variables) aka assist control modes, are PC, VC, PRVC, CMV and IMV, they deliver a set breath, (size and duration determined by Doctor)
PC press controlled, press limited-time cycled, IMV where breath is controlled by press, waveform is square, does not control volume
PC advantages >flow more comfortable w/pt stiff lungs, <flow to avoid barotraumas, descending waveform is better distribution and >oxygenation, press limited so <risk of barotraumas, at PIP it recruits to improve ventilation
Disadvantage of PC cannot regulate VE so cannot regulate C02, >mean airway press, caution w/COPD, to much press on cardio decreases CO
*VC volume control, volume limited time cycled, set VT & set flow (IT) pt gets full mach breath, so V is FxT, can be pt or mach trigger DOES NOT CONTROL PIP
VC uses very weak resp effort, allows for synchrony with pt but max support. NEVER FOR WEANING,
VC advantages regulate CO2 and regulate VE
Disadvantage of VC higher pressure (PIP), barotraumas, uses constant flow so poor distribution of volume
Dual control modes PRVC or VC+, control both press and volume, allows for both press limit and target VT, mach adjusts press until target VT is met, wave is square, with mandatory breath mach controls volume, sacrifices volume for press
Mandatory dual control modes VC+PRVC-CVM, press limited time cycled volume target
Spontaneous dual control modes press limited flow cycled, PS, spont only (no fixed breath), VAPS and VS (volume assured, press limited, flow cycled, volume targeted)
PS press support, press limited flow cycled, gives mach press to spontaneous breaths, can be set to PSV w/alarm-pt stops breathing alarm but no machine breaths. No fixed volume
VS or VAPS spontaneous control modes, volume assured PS (press limited flow cycled volume targeted
*Control mode with the highest MAP PC-CMV
*Control mode with the lowest MAP VC-SIMV
How much does PEEP increase/decrease MAP increases MAP 1:1, has the biggest impact of MAP
Support modes VS, PS, CPAP, BiPAP, and SIMV. Determines when pt gets a breath and what kind they receive. *karyl says cpap is an application not a mode
What is the variable in Volume Control press
What is the variable in Press Control volume and time
What is the effect of changing flow on I time decreasing flow >IT, increasing flow <IT
Flow control minimum always set enough flow to meet or exceed the pts demand
Trigger variable phase starts the breath, time (mach), press (pt) or flow (pt)
Limit variable phase actual breath mach delivers, press (mach), volume (mach), limits breath to a set volume or press set by machine
Cycle variable phase end variable, time (time cycled press limited), volume (volume cycled volume limited), flow (IPAP press support), pressure ((IPPB press limited press cycled)
Baseline variable phase PEEP, ZEEP, NEEP
Types of breaths mandatory (mach) or spontaneous (pt)
*CMV continuous mandatory ventilation, <WOB, best way to control CO2, best on apneic and exhausted pt, locks pt out-use w/caution
Assist control modes VC, PC and PRVC, vent guarantees pt will receive the set minimum number of breaths and pt is able to trigger more
Mandatory breath machine determined, based on phase variables trigger, limit, cycle and baseline
Spontaneous breath pt initiated, but depending on limit variables, mach may or may not control volume and press
Advantage of AC allows pt to rest
Disadvantage of AC >risk of hyperventilation because of pain, met acidosis, anxiety or fever
CMV continuous mandatory ventilation, not used, does not allow pt to initiate breath
SIMV synchronized intermittent mandatory ventilation, mach sets a rate but pt can also initiate breaths during the cycle, during cycle pt initiated breaths are supported, but other pt breaths are not.
SIMV uses commonly used in many settings, can be a weaning mode
SIMV advantages allows work with the pt, somewhat friendlier
SIMV disadvantages any other breaths during the cycle are not supported
SIMV+PS SIMV with pressure support, extra breaths in the cycle are supplemented with pressure support
PRVC pressure regulated volume control, volume control assist control mode that adjust the flow rate of the delivered air to deliver the set VT at or below the set max press
PRVC uses pt with high airway press, but can be used with any pt
PRVC advantages gives guaranteed VT but minimizes barotraumas
PRVC disadvantages new, none
How can RT get the affects of control mode without using it? paralytics, allows pt to rest but keeps pt from fighting machine
VC volume control, volume cycled volume limited
PC press control, press limited time cycled
Relationship between PS and RAW PS is dependent on RAW, RAW of 12 then PS must be set to 12, adding PS will overcome >RAW of machine
Pressure limited time cycled with spontaneous breaths above baseline, press limited flow cycled PC-SIMV+PEEP+PS
Press limited time cycled PC-CMV
Press limited time cycled with spontaneous breaths above 0 PC-SIMV+PEEP
Volume cycled w/spontaneous breathing VC-SIMV
Spont breathing at a level above baseline CPAP
PS+PEEP BiPAP-separate regulation of inhalation and exparation
What effect does an >VT have on IT >IT
What effect does an >flow have on IT <IT
What effect does RR have on IT none, can only be effected by > or < in flow
When using IT% what is the best setting closest to percentage to get closest to 1 second IT
Can RAW be to low no just to high, norm 5-12 cmH20/L/sec
VE or MV Minute ventilation, calc is VT x RRset, flow of expired gas in one minute, norm is 5-8L/min
RAW Airway Resistance norm is 5-12cmH2O/L/Sec for intubated pt, (PIP-Pplat)/(flow in min/60 sec). Increase in RAW reflects an issue with airways, bronchospasm, secretions, edema etc.
Cs static lung compliance, aka Cstat or CLstat, norm for vent pt is .035-.055L/cmH20, calc is Vt(L)/(Pplat-PEEP), represents the combination of lung elasticity and chest wall recoil while on vent. Up with stiff lungs
SpontVE VEtot-(VTset x RRset)
SpontRR RRtot-RRset
SpontVT VEtot-(VTset x RRset)/(RRtot-RRmach) norm is .2L or 200cc. Measured when machine in SIMV mode represents what the patient is actually breathing on his/her own.
PIP Peak pressure, norm is <50cmH2O, the press required to overcome both compliance and resistance
TCT total cycle time, 60 sec/RRset, amount of time for a single breath cycle both I and E. If I:E is 1:2 then TCT is 3
I-time represents relationship for volume (Liters), flow (L/sec) and time (seconds). V eq F x T or F eq V/T
How much flow do you need for a 1 second I-time and a VT of 750cc? .750 equals L/sec x 1 or .750L/sec flow. To convert to L/min .750 x 60 equals 45L/m, this is the vent flow setting to deliver a VT in 1 second I-time.
High press on vent obstruction (90% of time is secretions)
Low press on vent leak in system
Non-invasive PEEP CPAP
Best treatment for flail chest PEEP
Resp failure type I is caused by Hypoxemic respiratory failure, PaO2 <60 on R/A, caused by VQ mismatch, shunt, diffusion impairment, perfusion/diffusion impairment, altitude, pneumonia, atelectasis
Resp failure type II is caused by hypercarbia, PaCO2 >50 on R/A, caused by decreased vent drive, resp muscle fatigue or increased WOB
Control types open loop and closed loop
Which setting is pure control CMV
Trigger criteria for flow 1-3L below baseline flow of 6-8L
*PRE-SET PRESS FOR INSPIRATION PSV (press limited flow cycled spont breathing)
COPD lungs <RAW and >CL floppy
ARDS lungs <CL stiff