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Mech vent chap 39
WillWallace Mech Vent Chap 39
| 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) |
| *SEPARATE REGULATION OF INHALATION AND EXHALATION | BIPAP OR BILEVEL |
| COPD lungs | <RAW and >CL floppy |
| ARDS lungs | <CL stiff |
Created by:
williamwallace
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