INTRODUCTION TO BI-VENT (APRV) INTRODUCTION TO BI-VENT (APRV) PROGRAM OBJECTIVES PROVIDE THE DEFINITION FOR BI-VENT EXPLAIN THE BENEFITS OF BI-VENT EXPLAIN SET PARAMETERS IDENTIFY RECRUITMENT IN APRV USING EXHALED CO2 RECOMMEND APPROPRIATE INITIAL SETTINGS FOR APRV MAKE ADJUSTMENTS BASED ON ARTERIAL BLOOD GAS RESULTS DISCONTINUE VENTILATION WITH APRV 1
INTRODUCTION TO BI-VENT (APRV) INDICATIONS FOR BI-VENT (APRV) Primarily used as an alternative ventilation technique in patients with ALI/ARDS Lung protective strategy to help protect against Ventilator Induced Lung Injury (VILI) Potential use for patients with airway disease Infrequently used by clinicians for patients with Chronic Obstructive Pulmonary Disease Habashi CCM, 2005 INTRODUCTION TO BI-VENT (APRV) ARDS DEFINED In 1994 the AECC (AMERICAN EUROPEAN CONSENSUS CONFERENCE) refined the definition of ARDS to include 4 Components Acute clinical presentation Hypoxemia with a P/F ratio less than 200 Bilateral chest infiltrates must be present The clinical findings can t be due to cardiac failure In addition they introduced the idea of ACUTE LUNG INJURY to include all of the above with the exception of the fact that the P/F ratio should be less than 300 2
INTRODUCTION TO BI-VENT (APRV) ARDS DEFINED In 2011 the AECC convened as a result of an initiative by the ESICM ( European Society of Intensive Care Medicine and endorsed by the ATS and the SCCM, to redefine ARDS in order to improve the feasibility, reliability, and objective evaluation of ARDS related data The so called Berlin Definition of ARDS emerged, It separates ARDS into three separate and distinct categories based on the extent to which hypoxia presents as defined by P/F ratio Mild: Moderate: Severe: 201-300 mmhg with PEEP or CPAP 5 cmh2o 101-200 mmhg with PEEP 5 cmh2o 100 mmhg with PEEP 5 cmh2o BI-VENT (APRV) DEFINITION Bi-Vent (APRV) is classified as a time-triggered, pressure-limited, time-cycled (partial) mode of ventilation, which allows for unrestricted, spontaneous breathing throughout the entire ventilatory cycle CPAP at two levels, for different, alternating time limits, with most time at the upper pressure level Bi-Vent, unlike CPAP, allows for increased CO 2 removal through brief releases in airway pressure Rasansen. J., Principles of Mechanical Ventilation. 1994:341-348 T High No spontaneous breathing Spontaneous breathing T Low 3
BI-VENT (APRV) DESCRIPTION Bi-Vent (APRV) provides two levels of CPAP/PEEP The upper CPAP provides a moderately high level of pressure (15-30 cmh 2 O), which increases mean airway pressure and augments oxygenation Bi-Vent (APRV) allows a briefrelease of pressure to a lower PEEP/CPAP which allows exhalation/elimination of CO 2 Release time is short to prevent the peak expiratory flow from returning to baseline, which limits derecruitment Rasansen. J., Principles of Mechanical Ventilation. 1994:341-348 BI-VENT (APRV) BENEFITS Similar to CPAP, with additional ventilatory effects Specific Advantages include: Facilitation of spontaneous breathing Increased patient comfort vs. conventional ventilation Decreased sedation Elimination of NMB Rx s Increased hemodynamic performance Decreased ppeak(pip) for any given MAP Increased recruitment, and limited de-recruitment 4
BI-VENT (APRV) ORIGINATION FIRST THINGS FIRST What: Designed initially to improve oxygenation, and augment ventilation in patients with recruit-able ALI or ARDS Why: To reverse intrapulmonary shunting, re-establish FRC, and support ventilation in a Protective Open Lung Strategy How: Uses MAP through extreme I:E ratios and patient effort to recruit FRC, and maintain FRC above CC BI-VENT (APRV) MECHANISMS OF FUNCTION The following are supposed mechanisms of function of Bi-Vent used as APRV: Lung recruitment over time Collateral channels of ventilation Mean Airway Pressure (MAP) Facilitation of spontaneous efforts V/Q match Time constants (T high and T PEEP) Maintain FRC above closing Capacity on expiration 5
BI-VENT (APRV) SET PARAMETERS APPLICATION Since its infancy circa 1987, differing techniques have emerged (one example): APRV: Shock Trauma, UMMS, Habashi, 1995 Set: P High at previous Pplatif <35, or 30 cmh 2 O w/o prior settings Set: PEEPto Zero cmh 2 O Set: T high and T PEEP at nontraditional IRPCVI:E ratios (7:1 or 8:1) BI-VENT (APRV) SET PARAMETERS P high High Pressure during Bi-Vent (P1) PEEP Low Pressure during Bi-Vent (P2, P low) T high Time at Higher Pressure (T1) T PEEP Time at Lower Pressure (T2,T low) O 2 conc. -% of oxygen delivered T insp. rise -Inspiratory Rise Time % Trigger Set sensitivity to patient comfort Insp. cycle off Inspiratory Cycle-off % PS above P high Pressure Support above P high PS above PEEP Pressure Support above PEEP All parameters are set independently of one another 6
BI-VENT (APRV) SET PARAMETERS P high, PEEP, T high, T PEEP BI-VENT (APRV) SET PARAMETERS P high T high 5.5s 30cmH 2 O 0cmH 2 O T PEEP 0.8s 7
BI-VENT (APRV) SET PARAMETERS P HIGH The upper pressure level This establishes the upper pressure level and should be at or above the patient s FRC (Functional Residual Capacity) Patients can breathe spontaneously at this level at any time Too high a P high will over distend the lung due to the increase in volume P high is relative to MAP and affects oxygenation Watch inhaled/exhaled tidal volumes. As recruitment takes place, the tidal volumes moved by spontaneous breaths will increase BI-VENT (APRV) SET PARAMETERS P high 30cmH 2 O 8
BI-VENT (APRV) SET PARAMETERS T HIGH T high- Is the inspiratory time phase for the ventilator controlled breaths Is a large part of a set rate control, if viewed as traditional ventilation The shorter the T high the more releases, which increases respiratory rate It s during the release phase that most C02 is eliminated The more releases, the more you decrease PC02, and vice versa The patient is able to breathe spontaneously between the releases BI-VENT (APRV) SET PARAMETERS T high 5.5s 9
BI-VENT (APRV) SET PARAMETERS PEEP The level of mechanical PEEP at the baseline Set by open lung methods to ensure accuracy Can utilize the Open Lung Tool or similar to find an optimal PEEP It will be necessary to balance such protection against CO 2 evacuation BI-VENT (APRV) SET PARAMETERS 0cmH 2 O 10
BI-VENT (APRV) SET PARAMETERS T PEEP Is the expiratory time phase for the ventilator control breaths Normally set from 0.5 to 1.0 sec. (Tcon displayed values is good starting point) Changes in T PEEP will affect intrinsic PEEP When increased, it decreases intrinsic PEEP and vice versa Total Peep should be measured. This is the average pressure in the lung at end expiration. You want enough Total Peep to ensure there is no derecruitment, but too much can cause overdistention and hemodynamic compromise BI-VENT (APRV) SET PARAMETERS T PEEP 0.8s 11
BI-VENT (APRV) SET PARAMETERS T HIGH + T PEEP T high + T PEEP is the total cycle time for control breaths and thus gives you I:E ratios The clinician should note that through manipulation of the T high/t PEEP combination, extreme ranges in total respiratory rate are possible Neumann, P. e.t. Al. (2002). Influence of Different Release Times on Spontaneous Breathing Pattern During Airway Pressure Release Ventilation. Intensive Care Medicine. 28: 1742-1749 BI-VENT (APRV) SET PARAMETERS 12
BI-VENT (APRV) SET PARAMETERS PRESSURE SUPPORT - (P HIGH AND PEEP) Levels of PS may be added to augment the patient s spontaneous tidal volume at either P high or Peep Caution must be used when adding Pressure Support above the set P high, as patients may be at or near their inspiratory capacity and extra pressure may cause overdistention of the lungs Consider a drop in the P high by half the PS level, or to a level that maintains MAP Example: P high 30, MAP 26, PS 0 P high to 27, PS 6, MAP 26 BI-VENT (APRV) SET PARAMETERS SPONTANEOUS: PRESSURE SUPPORT (PS) 13
BI-VENT (APRV) SET PARAMETERS SPONTANEOUS: PRESSURE SUPPORT (PS) BI-VENT (APRV) GUIDELINES: INITIAL SETUP P High: Set to previous Pplat, if less than 35 cmh20 (If no previous mode, or higher than 35, set at 30 cmh20) T High: Set to 4.5 to 5.5 seconds PEEP Set to 0 cmh20 T PEEP: Set to 1 TC, or to keep expiratory flow to 25%-75% of PEFR 14
PREVIOUS MODE: T PEEP @ 1 TC 29 x 27 = 0.783sec BI-VENT (APRV) PARAMETERS: P 30/0, T 5.5/0.8 P high 30 cmh 2 O T high 5.5s Peep 0cmH 2 O T PEEP 0.8s 15
BI-VENT (APRV) PARAMETERS: CHECK T PEEP BY END EXPIRATORY FLOW 0.8sec 50% 35% = 1 Tc 100% BI-VENT (APRV) PARAMETERS: VALIDATION OF EXP. FLOW: PEAK EXP. FLOW 16
BI-VENT (APRV) PARAMETERS: VALIDATION OF FLOW: PEAK FLOW AT END OF T PEEP BI-VENT (APRV) PARAMETERS: OPEN LUNG TOOL-CLOSING PRESSURE 12 12 17
BI-VENT (APRV) PARAMETERS: PT TEST LUNG: T PEEP 0.8 S = PEEP TOT 9 Auto PEEP BI-VENT (APRV) PARAMETERS: PT TEST LUNG: T PEEP 0.6 S = PEEP TOT 12 18
BI-VENT (APRV) PARAMETERS: MANAGEMENT OF SETTINGS To increase PaO2 Increase P high in 2 cm increments (This increases MAP) Shorten T PEEP to increase intrinsic PEEP (Shortens the exhalation time to create an increase in intrinsic PEEP which will increase MAP. You may encounter a slight increase in CO2) Increase T High (you may encounter a slight increase in CO2) To decrease PaCO2: Decrease T high: Increases total minute ventilation (creates more releases per minute) Increase P High: Increases your tidal volume (This increases your minute ventilation) BI-VENT (APRV) PARAMETERS: MANAGEMENT OF SETTINGS The overall weaning strategy shall be to reduce the most invasive parameter first As usual FIO 2 should be the first to wean Generally, weaning consists of: Reducing P High, (by 2-3 cmh 2 0 at a time for if patients exhibit improved oxygenation) Increase T High, (by 0.5-1.0 sec for if patients exhibits improved ventilation) 19
BI-VENT (APRV) PARAMETERS: WEANING GRAPHICS Spontaneous Breaths BI-VENT (APRV) SUMMARY When ventilation improves, T high can be increased When oxygenation improves, P high can be decreased When increasing T high (decreasing effective rate) Patients should be increasing their spontaneous rate to compensate. Add Pressure Support judiciously When adding Pressure Support consider a decrease in P high to avoid over-distention yet try to maintain a consistent MAP Increasing T PEEP may result in de-recruitment and atelectasis Using a system like the Open Lung Tool will assist in obtaining ideal PEEP levels ( Time PEEP) DO NOT over sedate patients on this partial mode of ventilation 20
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