New Modes of Mechanical Ventilation Mazen Kherallah, MD, FCCP Consultant Intensivist King Faisal Specialist Hospital.
Download ReportTranscript New Modes of Mechanical Ventilation Mazen Kherallah, MD, FCCP Consultant Intensivist King Faisal Specialist Hospital.
New Modes of Mechanical Ventilation Mazen Kherallah, MD, FCCP Consultant Intensivist King Faisal Specialist Hospital Key Ideas for Understanding Mechanical Ventilation 1. Mathematical Models – – – Equation of motion Time constant Mean airway pressure 2. Control Variables – Pressure, volume, dual 3. Phase Variables – Trigger, Limit and Cycle 4. Breath Types/Patterns 5. Optimum Mode Selection Lung Mechanics resistance = Dpressure / Dflow flow transairway pressure transrespiratory pressure volume transthoracic pressure elastance = Dpressure / Dvolume Equation of Motion ventilation 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 VariableStart 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 Insp…cycle 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 VariableInspiratory 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 Inspiration Pressure Control Expiration 20 Inspiration Expiration 20 Paw Pressure Paw 0 1 0 2 20 0 1 2 0 1 2 20 Volume 0 0 1 0 2 3 Flow 0 -3 3 Time (s) 0 -3 Time (s) Volume Control Breath Types 60 Paw SEC cmH20 -20 120 1 2 3 4 5 6 INSP SEC Flow L/min 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 to breath: Pressure-limited flow-cycled ventilation Siemens; servo 300 Cardiopulmonary corporation; Venturi Volume support Variable pressure support Dual control breath to breath: Pressure-limited time-cycled ventilation Siemens; servo 300 Pressure-regulated volume control Adaptive pressure ventilation Autoflow Variable pressure control Dual control breath to breath: SIMV Hamilton; Galileo Hamilton; Galileo Drager; Evita 4 Cardiopulmonary corporation; Venturi Adaptive support ventilation 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 Tbird 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 Pressure limit overridden 40 Set pressure limit Paw cmH20 -20 0.6 Volume L Set tidal volume cycle threshold Tidal volume Tidal volume not met met 0 60 Inspiratory flow greater than set flow Flow cycle Set flow limit Inspiratory flow equals set flow 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 Switch to flow control at peak flow setting no yes delivered VT = set VT no PAW <PSV setting yes Control logic for volume-assured pressure-support mode Dual Control within a Breath volume-assured pressure support • If pressure too high, all breaths are pressure-limited. • If the peak flow setting is too high , all breaths will be volume-controlled • If the pressure is set too high or the minimum tidal volume is set too low; the volume guarantee is negated • If peak flow 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 cm H2O and ranges from 0 cm H2O to 5 cm H2O 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 cm H2O); (2), pressure is increased slowly until target volume is achieved; (3), maximum available pressure is 5 cm H2O 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 no Pressure limit Based on VT/C Volume from Ventilator= Set tidal volume calculate compliance Flow= 5% of Peak flow 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 require minimum E • Patients who have inspiratory effort who need adaptive support • Patients who are asynchronous with the ventilator • Used for patient who are ready to wean VS (Volume Support) • Advantages • Guaranteed VT and E • Pressure supported breaths using the lowest required pressure • Decreases the patient’s spontaneous respiratory rate • Decreases patient WOB • Allows patient control of I:E time • Breath by breath analysis • Variable I to meet the patient’s 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 cm H2O below set upper pressure limit • Example: If upper pressure limit is set to 35 cm H2O and the ventilator requires more than 30 cm H2O 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 cm H2O); (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 patient’s needs yes Calculate new Pressure limit trigger no Pressure limit Based on VT/C Volume from Ventilator= Set tidal volume calculate compliance time= set Inspiratory time yes 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 non-sedated 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 require 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 Variable E to meet patient demand Decelerating flow waveform for improved gas distribution • Breath by breath analysis E A New Twist… Volume Targeted 60 Paw SEC cmH20 -20 120 1 2 3 4 5 6 INSP SEC Flow L/min 1 2 3 4 5 6 120 EXH Many Dual Modes start out looking like PCV Volume Targeted (Pressure Controlled) 60 Paw SEC cmH20 -20 120 1 2 3 4 5 6 INSP SEC Flow L/min 120 1 2 3 4 5 6 EXH As compliance changes - flow and volumes change New Volume Targeted Breath Pressure Variability is Controlled 60 Paw SEC cmH20 -20 120 1 2 3 4 5 6 INSP SEC Flow L/min 120 1 2 3 4 5 6 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 patient’s condition and effort – It automatically adapts to patient demand by increasing or decreasing support, depending on the patient’s elastic and resistive loads ASV (Adaptive Support Ventilation) • • • • • • The clinician enters the patient’s IBW, which allows the ventilator’s 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 decrease 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 Patient requiring high and/or variable Patients not breathing spontaneously and not triggering the ventilator Patient with the possibility of work land changes (CL 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 switch between mandatory and spontaneous breathing modes • Combines volume support (VS) and pressure-regulated 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 patient’s current E. The ventilator provides whatever part of the E that the patient is unable to accomplish. This 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 patient’s 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 Patient’s 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 patient’s spontaneous effort, the greater the patient’s effort, the higher the flow, volume, and pressure • The operator sets the ventilator’s volume and flow assist at approximately 80% of patient’s elastance and resistance. The ventilator then generates proportional flow and volume assist to augment the patient’s 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 patientventilator 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 • Enabled 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? • 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 time cycled 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 breath 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 (i.e., COPD or asthma) • Auto-PEEP is usually present • Caution should be used with hemodynamically unstable patients • Asynchrony can occur is spontaneous breaths are out of sync with release time • Requires the presence of an “active exhalation valve” Airway Pressure Release Ventilation Spontaneous Breaths 60 Paw Releases cmH20 -20 1 2 3 4 5 6 7 8 Modes of Ventilation • Questions?