New Modes of Mechanical Ventilation Key Ideas for Understanding Mechanical Ventilation 1. 2. 3. 4. 5. Mathematical models Equation of motion Time constant Mean airway pressure Control variables Pressure, volume, dual Phase variables Trigger, limit and cycle Breath types/patterns
pressure = (to deliver tidal volume) resistive pressure (to make air flow through the airways) + elastic pressure (to inflate lungs and chest wall) P = Presistive + Pelastance P= RxV + ExV
Phase Variables Trigger (start) Begins inspiratory flow Cycling (end) Ends inspiratory flow Limiting (continue) Places a maximum value on a control variable pressure volume flow time
Trigger Variable Start of a Breath Time Control ventilation Pressure Patient assisted Flow Patient assisted Volume Patient assisted Manual Operator control Inspiratory Delivery Limits Maximum value that can be reached but will not end the breath Volume Flow Pressure
End of InspCycle Mechanisms The phase variable used to terminate inspiration Volume Pressure Flow Time Breath Type Only Two (For now)! Mandatory Ventilator does the work Ventilator controls start and stop
Spontaneous Patient takes on work Patient controls start and stop The Control Variable Inspiratory Breath Delivery Flow (volume)-controlled Pressure may vary Pressure-controlled Flow and volume may vary Time-controlled (HFOV) Pressure, flow, volume may vary Volume/Flow Control Control Inspiration
3 Time (s) 0 -3 Time (s) Volume Control Breath Types 60 Paw SEC cmH20 -20 120
Flow L/min 1 2 3 4 5 6 INSP SEC 1
2 3 4 5 120 6 EXH If compliance decreases, the pressure increases to maintain the same Vt New Modes of Ventilation Dual-Controlled Modes Type
Manufacturer; ventilator Name Dual control within a breath VIASYS Healthcare; Bird 8400Sti and Tbird VIASYS Healthcare; Bear 1000 Volume-assured pressure support Pressure augmentation Dual control breath-tobreath: Pressure-limited flowcycled ventilation
Siemens; servo 300 Cardiopulmonary corporation; Venturi Volume support Variable pressure support Dual control breath-tobreath: Pressure-limited timecycled ventilation Siemens; servo 300 Hamilton; Galileo Drager; Evita 4 Cardiopulmonary corporation; Venturi Pressure-regulated volume control
Adaptive pressure ventilation Autoflow Variable pressure control Dual control breath-to- Hamilton; Galileo Adaptive support Dual Control Within a Breath Volume-Assured Pressure Support This mode allows a feedback loop based on the volume Switches even within a single breath from pressure control to volume control if minimum tidal volume has not been achieved Bear 1000
Bird 8400Sti Tbir d Dual Control Within a Breath Volume-Assured Pressure Support The Respiratory Therapist sets Pressure limit = plateau seen during VC Respiratory rate Peak flow rate (the flow if TV < target)
PEEP FiO2 Trigger sensitivity Minimum tidal volume 40 aw P cmH0 Pressure limit overridden Set pressure limit 2 -20 0.6 Volume
L 0 60 Flow L/min Set tidal volume cycle threshold Tidal volume Tidal volume not met met Inspiratory flow greater than set flow Flow cycle Set flow limit Inspiratory flow equals set flow
L/min 60 Switch from Pressure control to Volume/flow control trigger Pressure at Pressure support no flow= 25% peak yes yes
delivered VT set VT no Cycle off inspiration Insp flow > Set flow yes no no yes delivered VT = set VT
Switch to flow control at peak flow setting no PAW
If peak flow is set too low, the switch from pressure to volume is late in the breath; inspiratory time is too long Dual Control Within a Breath Volume-Assured Pressure Support Amato et al Chest 1992; 102: 1225-1234 Compared VAPS to simple AC volume Lower WOB Lower Raw Less PEEPi Dual Control Breath-to-Breath Pressure-Limited Flow-Cycled Ventilation Volume Support Tidal volume is used as feedback control to adjust the
pressure support level All breaths are patient-triggered, pressure-limited, and flow-cycled Automatic weaning of pressure support as long as tidal volume matches minimum required VT (VT set in a feedback loop to adjust pressure) Dual Control Breath-to-Breath Pressure-Limited Flow-Cycled Ventilation Volume Support Servo 300 Maquet Servo-i VS vs. VAPS How does volume support differ from VAPS ? In volume support, we are trying to adjust pressure so that within a few breaths, desired VT is reached In VAPS, we are aiming for desired VT tacked on to
the end of a breath if a pressure-limited breath is going to fail to achieve VT VS (Volume Support) Entirely a spontaneous mode Delivers a patient-triggered (pressure or flow), pressure- targeted, flow-cycled breath Can also be timed cycled (if TI is extended for some reason) or pressure cycled (if pressure rises too high) Similar to pressure support except VS also targets set VT. It adjusts pressure (up or down) to achieve the set volume (the maximum pressure change is < 3 cmH2O and ranges from 0 cmH2O to 5 cmH2O below the high-pressure alarm setting Used for patients ready to be weaned from the ventilator and for patients who cannot do all the WOB but who are breathing spontaneously VS (Volume Support)
(1) VS test breath (5 cmH2O); (2) pressure is increased slowly until target volume is achieved; (3) maximum available pressure is 5 cmH2O below upper pressure limit; (4) VT higher than set VT delivered results in lower pressure; (5) patient can trigger breath; (6) if apnea alarm is detected, ventilator switches to PRVC yes Calculate new Pressure limit trigger n o Pressure limit based on VT/C Volume from
ventilator= Set tidal volume Flow= 5% of Peak flow calculate compliance yes cycle off no Control logic for volume support mode of the servo 300 Dual Control Breath-to-Breath Pressure-Limited Flow-Cycled Ventilation Volume Support
Little data to show it actually works If pressure support level increases to maintain TV in pt with increased airways resistance, PEEPi may increase If minimum TV set too high, weaning may be delayed VS (Volume Support) Indications Spontaneous breathing patient who requires minimum E Patients who have inspiratory effort who need adaptive support
Patients who are asynchronous with the ventilator Used for patients who are ready to wean VS (Volume Support) Advantages Guaranteed VT and E Pressure-supported breaths using the lowest required pressure Decreases the patients spontaneous
respiratory rate Decreases patient WOB Allows patient control of I:E time Breath-by-breath analysis Variable I to meet the patients demand VS (Volume Support) Disadvantages Spontaneous ventilation required VT selected may be too large or small for patient Varying mean airway pressure Auto-PEEP may affect proper functioning
A sudden increase in respiratory rate and demand may result in a decrease in ventilator support Dual Control Breath-to-Breath Pressure-Limited Time-Cycled Ventilation Pressure-Regulated Volume Control Servo 300 Maquet Servo-i Dual Control Breath-to-Breath Pressure-Limited Time-Cycled Ventilation Pressure-Regulated Volume Control Delivers patient- or timed-triggered, pressure- targeted (controlled), and time-cycled breaths Ventilator measures VT delivered with VT set on the controls. If delivered VT is less or
more, ventilator increases or decreases pressure delivered until set VT and delivered VT are equal Dual Control Breath-to-Breath Pressure-Limited Time-Cycled Ventilation Pressure-Regulated Volume Control The ventilator will not allow delivered pressure to rise higher than 5 cmH2O below set upper pressure limit Example If upper pressure limit is set to 35 cmH2O and the ventilator requires more than 30 cmH2O to deliver a targeted VT of 500 mL, an alarm will sound alerting the clinician that too much pressure is being required to deliver set volume (may be due to bronchospasm, secretions, changes in CL, etc.) PRVC (Pressure-Regulated Volume
Control) PRVC. (1) Test breath (5 cmH2O); (2) pressure is increased to deliver set volume; (3) maximum available pressure; (4) breath delivered at preset E, at preset f, and during preset TI; (5) when VT corresponds to set value, pressure remains constant; (6) if preset volume increases, pressure decreases; the ventilator continually monitors and adapts to the patients needs yes Calculate new Pressure limit trigger n o Pressure limit based on VT/C
Volume from ventilator= Set tidal volume calculate compliance time= set yes Inspiratory time cycle off no Control logic for pressure-regulated volume control and autoflow PRVC (Pressure-Regulated Volume Control) Disadvantages and Risks
Varying mean airway pressure May cause or worsen auto-PEEP When patient demand is increased, pressure level may diminish when support is needed May be tolerated poorly in awake, nonsedated patients A sudden increase in respiratory rate and demand may result in a decrease in ventilator support PRVC (Pressure-Regulated Volume Control) Indications
Patient who requires the lowest possible pressure and a guaranteed consistent VT ALI/ARDS Patients requiring high and/or variable I Patient with the possibility of CL or Raw changes PRVC (Pressure-Regulated Volume Control) Advantages
Maintains a minimum PIP Guaranteed VT and E Patient has very little WOB requirement Allows patient control of respiratory rate and E Variable E to meet patient demand Decelerating flow waveform for improved gas distribution Breath-by-breath analysis A New Twist
6 EXH Many Dual Modes start out looking like PCV Volume-Targeted (Pressure-Controlled) 60 Paw SEC cmH20 -20 120 Flow L/min
1 2 3 4 5 6 INSP SEC 1 2
3 4 5 6 120 As compliance changes, flow and volumes change EXH New Volume Targeted Breath Pressure Variability is Controlled 60 Paw
SEC cmH20 -20 120 Flow L/min 1 2 3 4 5 6
INSP SEC 1 2 3 4 5 6 120 EXH
Pressure then raises to assure that the set tidal volume is delivered Dual Control Breath-to-Breath Adaptive Support Ventilation ASV (Adaptive Support Ventilation) A dual-control mode that uses pressure ventilation (both PC and PSV) to maintain a set minimum E (volume target) using the least-required settings for minimal WOB depending on the patients condition and effort It automatically adapts to patient demand by increasing or decreasing support, depending on the patients elastic and resistive loads ASV (Adaptive Support Ventilation)
The clinician enters the patients IBW, which allows the ventilators algorithm to choose a required E. The ventilator then delivers 100 mL/min/kg A series of test breaths measures the system C, resistance, and auto-PEEP If no spontaneous effort occurs, the ventilator determines the appropriate respiratory rate, VT, and pressure limit delivered for the mandatory breaths I:E ratio and TI of the mandatory breaths are continually being optimized by the ventilator to prevent auto-PEEP If the patient begins having spontaneous breaths, the number of mandatory breaths decreases and the ventilator switches
to PS at the same pressure level Pressure limits for both mandatory and spontaneous breaths are always being automatically adjusted to meet the E target ASV (Adaptive Support Ventilation) Indications Full or partial ventilatory support Patients requiring a lowest possible PIP and a guaranteed VT
ALI/ARDS Patients requiring high and/or variable Patients not breathing spontaneously and not triggering the ventilator Patients with the possibility of work land changes (C L and Raw) Facilitates weaning ASV (Adaptive Support Ventilation) Advantages Guaranteed VT and E
Minimal patient WOB Ventilator adapts to the patient Weaning is done automatically and continuously Variable to meet patient demand Decelerating flow waveform for improved gas distribution Breath-by-breath analysis ASV (Adaptive Support Ventilation) Disadvantages and risks Inability to recognize and adjust to changes in alveolar VD
Possible respiratory muscle atrophy Varying mean airway pressure In patients with COPD, a longer TE may be required A sudden increase in respiratory rate and demand may result in a decrease in ventilator support Automode The ventilator switches between mandatory and spontaneous breathing modes. Combines Volume Support (VS) and PressureRegulated Volume Control (PRVC). If patient is paralyzed, the ventilator will provide PRVC. All breaths are mandatory that are ventilator-triggered, pressure-controlled and time-cycled; the pressure is
adjusted to maintain the set tidal volume. If the patient breathes spontaneously for two consecutive breaths, the ventilator switches to VS. All breaths are patient-triggered, pressure-limited, and flow-cycled. If the patient becomes apneic for 12 seconds; the ventilator switches back to PRVC. MMV (Mandatory Minute Ventilation) AKA Minimum Minute Ventilation or Augmented minute ventilation Operator sets a minimum E which usually is 70% - 90% of patients current E. The ventilator provides whatever part of the E that the patient is unable to accomplish. This is accomplished by increasing the breath rate or the preset pressure. It is a form of PSV where the PS level is not set, but rather variable according to the patients need.
MMV (Mandatory Minute Ventilation) Indications Any patient who is spontaneously and is deemed ready to wean Patients with unstable ventilatory drive Advantages Full to partial ventilatory support Allows spontaneous ventilation with safety net
Patients E remains stable Prevents hypoventilation MMV (Mandatory Minute Ventilation) Disadvantages An adequate E may not equal sufficient A (e.g. rapid, shallow breathing) The high-rate alarm must be set low enough to alert clinician of rapid, shallow breathing Variable mean airway pressure An inadequate set E (>spontaneous E) can
lead to inadequate support and patient fatigue An excessive set E (>spontaneous E) with no spontaneous breathing can lead to total support PAV (Proportional Assist Ventilation) Provides pressure, flow assist, and volume assist in proportion to the patients spontaneous effort The greater the patients effort, the higher the flow, volume, and pressure The operator sets the ventilators volume and flow assist at approximately 80% of patients elastance and resistance. The ventilator then generates proportional flow and volume assist to augment the patients own effort. Drager Evita
4 PAV (Proportional Assist Ventilation) Indications Patients who have WOB problems associated with worsening lung characteristics Asynchronous patients who are stable and have an inspiratory effort Ventilator-dependent patients with COPD Drager Evita 4
PAV (Proportional Assist Ventilation) Advantages The patient controls the ventilatory variables ( I, PIP, TI, TE, VT) Trends the changes of ventilatory effort over time When used with CPAP, inspiratory muscle work is near that of a normal subject and may decrease or prevent muscle atrophy Lowers airway pressure Drager Evita 4 PAV (Proportional Assist Ventilation)
Disadvantages Patient must have an adequate spontaneous respiratory drive Variable VT and/or PIP Correct determination of CL and Raw is essential (difficult). Both under - and over-estimates of CL and Raw during ventilator setup may significantly impair proper patient-ventilator interaction, which may cause excessive assist (Runaway) The pressure output from the ventilator can exceed the pressure needed to overcome the system impedance (CL and Raw) Air leak could cause excessive assist or automatic cycling Trigger effort may increase with auto-PEEP BiLevels What is BiLevel Ventilation? Is a spontaneous breathing mode in which two levels of
pressure and hi/low are set Enables utilizing an active exhalation valve Substantial improvements for spontaneous breathing Better synchronization, more options for supporting spontaneous breathing, and potential for improved monitoring BiLevel Ventilation Spontaneous Breaths Synchronized Transitions 60 Spontaneous Breaths Paw cmH20
-20 1 2 3 4 5 6 7 What is BiLevel Ventilation? At either pressure level the patient can breathe
spontaneously Spontaneous breaths may be supported by PS If PS is set higher than PEEPH, PS supports spontaneous breath at upper pressure BiLevel Ventilation 60 PEEPH Paw PEEPL cmH20
-20 Pressure Support PEEPHigh + PS 1 2 3 4 5 6 7
Then What is APRV? It is a Bi-level form of ventilation with sudden short releases in pressure to rapidly reduce FRC and allow for ventilation Can work in spontaneous or apneic patients APRV is similar but utilizes a very short expiratory time for pressure release This short time at low pressure allows for ventilation APRV always implies an inverse I:E ratio All spontaneous breathing is done at upper pressure level APRV (Airway Pressure Release Ventilation) Provides two levels of CPAP and allows spontaneous breathing at both levels when spontaneous effort is present
Both pressure levels are time-triggered and timecycled APRV (Airway Pressure Release Ventilation) Allows spontaneously breathing patients to breathe at a high CPAP level, but drops briefly (approximately 1 second) and periodically to allow CPAP level for extra CO2 elimination (airway pressure release) Mandatory breaths occur when the pressure limit rises from the lower CPAP to the higher CPAP level APRV (Airway Pressure Release Ventilation) Indications
Partial to full ventilatory support Patients with ALI/ARDS Patients with refractory hypoxemia due to collapsed alveoli Patients with massive atelectasis May use with mild or no lung disease APRV (Airway Pressure Release Ventilation) Advantages
Allows Inverse Ratio Ventilation (IRV) with or without spontaneous breathing (less need for sedation or paralysis) Improves patient-ventilator synchrony if spontaneous breathing is present Improves mean airway pressure Improves oxygenation by stabilizing collapsed alveoli Allows patients to breathe spontaneously while continuing lung recruitment Lowers PIP May decrease physiologic deadspace APRV (Airway Pressure Release Ventilation) Disadvantages and Risks
Variable VT Could be harmful to patients with high expiratory resistance (e.g. COPD or asthma) Auto-PEEP is usually present Caution should be used with hemodynamically unstable patients Asynchrony can occur; this is when spontaneous breaths are out of sync with release time Requires the presence of an active exhalation valve
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