Introduction to Mechanical Ventilation (IMV Lesson 9)

Introduction to Mechanical Ventilation RES 281 PRVC, VSV, APRV PRESSURE REGULATED VOLUME CONTROL (PRVC)  What is PRVC? Pressure control breaths that targets a set tidal volume Pressure limited, time cycled mode Names of PRVC on different ventilators: Hamilton: AP...

Introduction to Mechanical Ventilation RES 281 PRVC, VSV, APRV PRESSURE REGULATED VOLUME CONTROL (PRVC)  What is PRVC? Pressure control breaths that targets a set tidal volume Pressure limited, time cycled mode Names of PRVC on different ventilators: Hamilton: APV/CMV CareFusion: PRVC Drager: Autoflow Servo: PRVC Medtronics: VC+  Settings Target tidal volume Respiratory rate Inspiratory time PEEP FiO2 Alarms High inspiratory alarm = pressure limit Pressure is not able to exceed 5 below the PIP limit  PRVC Taxonomy Pressure = the control CMV or SIMV = breath sequence Adaptive = targeting scheme ◦Ventilator automatically sets target(s) between breaths in response to varying patient conditions  PRVC Pressure controlled ◦Calculated based off of previous breath Volume targeted Patient or machine triggered Time cycled  Breath Delivery 1st breath delivered: Volume controlled with plateau pressure Every breath after this is a pressure controlled breath ◦2nd breath is set to the plateau pressure of the first breath and measures what the volume is ◦ Does it meet the targeted tidal volume? ◦3rd breath will adjust the pressure to meet the targeted tidal volume ◦And so on…  PRVC Take Away The ventilator will adjust flow every breath to meet the target (set tidal volume) If you increase flow, you will increase pressure and volume If you decrease flow, you will decrease pressure and volume The ventilator analyzes each and every breath to make adjustments needed to meet the set tidal volume without exceeding pressure limit If the lungs have low compliance and the pressure limit is reached, the vent will not give the full tidal volume Protects lungs from barotrauma  PRVC Indications ◦ Patient who require the lowest possible pressure and a guaranteed consistent VT ◦ ALI/ARDS ◦ Patients who might exhibit variable VT, PIP or TI ◦ Patient with the possibility of CL or RAW changes  PRVC Advantages ◦ Maintains a minimum PIP ◦ Guaranteed VT and VE ◦ Patient has very little WOB requirement ◦ Decelerating flow waveform for improved gas distribution ◦ Breath by breath analysis  PRVC Disadvantages ◦ 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 ↑RR and demand may result in a decrease in ventilator support With worsening compliance, what will PRVC do? Improving compliance? 14  Pressure Regulated Volume Control 60 PAW cmH2O SEC -20 1 2 3 4 5 6 120 INSP Flow SEC L/min 1 2 3 4 5 6 120 EXH If compliance decreases the pressure increases to maintain the same VT , until pressure limit is reached Volume Support Ventilation (VSV)  Volume Support Ventilation (VSV) Similar to PRVC and Pressure Support Spontaneous mode of ventilation Pressure support with a volume target Patient triggered Volume targeted Flow cycled  VSV Volume Support Ventilation is only available on: ◦Servo-I ◦ Name: VS ◦PB 840 ◦ Name: VS ◦Drager V500 ◦ Name: SPN-CPAP/VS  VSV Settings Input: Patient determines: ◦Target Vt ◦Respiratory Rate ◦This is a minimum ◦Inspiratory time value, patient can breathe higher Vt ◦Pressure limit ◦FiO2 ◦PEEP ◦Sensitivity  VSV Ventilator adjusts pressure over several breaths to achieve target tidal volume As patient condition improves, less pressure is needed ◦“Self weaning mode” ◦Patient does more of the WOB = lower PS ◦Patient has lower WOB = more PS All breaths are spontaneous ◦Set backup mode appropriately P V V Airway Pressure Release Ventilation (APRV) Uses 2 CPAP pressures to recruit alveoli, prevent alveolar collapse, improve V/Q mismatch, and improve oxygenation P T  Airway Pressure Release Ventilation (APRV) Form of PC-IMV Uses inverse ratio ventilation ◦ I:E ratio where I > E Increases MAP ◦ Increases FRC ◦ Increases alveolar recruitment ◦ Increases oxygenation Allows spontaneous breathing  APRV Pressure Controlled Pressure limited ◦ Volume variable Patient and/or time triggered ◦ Patient allowed to trigger in between mandatory (time) triggered breaths  APRV Uses 2 set pressures: ◦P-high on inspiration ◦P-low on expiration Uses 2 set inspiratory times: ◦T-high on inspiration ◦T-low on expiration  Time T-high : time spent at Phigh ◦Inspiratory time ◦Usually 3 – 5 seconds T-low : time spent at Tlow ◦Expiratory time ◦Usually < 1 second ◦Short enough to prevent derecruitment ◦Long enough to obtain appropriate Vt (4-6 ml/kg)  P-high Inspiratory pressure When diffusion happens Set approximately at Pplat ◦Usually mid 20s If set too high, overdistention and increased WOB If set too low, derecruitment  P-low Expiratory pressure Baseline pressure Usually 0 – 5 cm H20 ◦Use the lowest possible pressure in order to get maximum ventilation in the short time frame ◦Pressure gradient between P-high and P-low creates expiratory tidal volume ◦Where removal of CO2 occurs  Correcting Respiratory imbalances Respiratory Acidosis: ◦Increase P-high ◦Increase T-low Respiratory Alkalosis: ◦Decrease P-high ◦Decrease T-low  Drop and Stretch Weaning APRV: ◦Gradually drop P-high ◦Gradually increase (stretch) Thigh This slowly decreases the amount of pressure required to prevent alveolar collapse Begins to closely replicate CPAP  APRV Not proven as a rescue strategy May be used as an alternative mode of ventilation in ARDS patients ◦Not formally recommended due to limited amount of studies and results ◦Small case study done during H1N1 showed patient improvement Not proven to decrease mortality rate Risks: high tidal volumes, increased transpulmonary pressures, higher chance of VILI APRV  APRV VS BiPAP APRV BIPAP Inspiration is longer Inspiration is shorter than expiration than or equal to expiration Sets limit on expiration time No limit on expiration No set RR time Set RR Prevents alveolar Prevents alveolar collapse by creating intrinsic PEEP collapse by directly setting the extrinsic PEEP (EPAP) Adaptive Support Ventilation (ASV) CURRENTLY ONLY AVAIL ABLE ON THE HAMILTON VENTIL ATORS  Settings 3 main settings: %MinVol Usually start at 100% PEEP FiO2 * Must also input correct IBW Additional Settings: P ASV Limit The maximum pressure delivered will be 10 cmH2O below this number Trigger/Sensitivity Ramp ETS  How ASV Works Based on lung compliance, resistance, and patient effort, the vent determines: RR Vt Ti This is done on a breath-by-breath basis, using Time Constants Time constant: how long it takes for one lung unit to fill or empty Time constant = compliance x resistance ASV “works on the assumption that the optimal breath pattern is identical to the one a totally unsupported patient will choose naturally (least work of breathing).” – ASV Quick Guide  How to Make Changes All of the rules regarding changing PaO2 and PaCO2 still apply Changing PEEP and FiO2 will change PaO2 Changing minute ventilation (%MinVol) will change PaCO2 Can we still use the C1V1 = C2V2 formula? Yes, we can! Just substitute the RR or Vt variable for %MinVol  Example A post-op patient with no history of lung disease is on ASV 100% PEEP +5 and 50%. The RT draws an ABG and sees the following results: ◦ pH 7.29 ◦ PaCO2 56 ◦ PaO2 93 ◦ HCO3- 23 What do you recommend? C1V1 = C2V2 (Where C = CO2 and V = %MinVol) 56 x 100 = 45 x %MinVol 5,600 = 45 x %MinVol New %MinVol = 124%