Airway Pressure Release Ventilation (APRV)

Airway Pressure Release Airway Pressure Release Ventilation (APRV)Ventilation (APRV)

ObjectivesObjectives

Provide the definition and names for Provide the definition and names for APRVAPRV

Explain the four set parameters.Explain the four set parameters. Identify recruitment in APRV using Identify recruitment in APRV using

exhaled COexhaled CO22.. Recommend appropriate initial Recommend appropriate initial

settings for APRVsettings for APRV Make adjustments based on arterial Make adjustments based on arterial

blood gas resultsblood gas results Discontinue ventilation with APRVDiscontinue ventilation with APRV

IntroductionIntroduction

Airway pressure release ventilation (APRV) is Airway pressure release ventilation (APRV) is a relatively new mode of ventilatory support a relatively new mode of ventilatory support that, although outlined in 1987, did not that, although outlined in 1987, did not become available in the United States until become available in the United States until the mid-1990s. the mid-1990s.

APRV augments alveolar ventilation. Airway APRV augments alveolar ventilation. Airway pressure is released from an elevated pressure is released from an elevated baseline pressure to produce an expiration. baseline pressure to produce an expiration. The elevated pressure facilitates The elevated pressure facilitates oxygenation, while the pressure release oxygenation, while the pressure release increases minute ventilation.increases minute ventilation.


APRV has been successfully used in neonatal, APRV has been successfully used in neonatal, pediatric, and adult forms of respiratory failure. pediatric, and adult forms of respiratory failure. Experimental and clinical use of APRV has been Experimental and clinical use of APRV has been shown to facilitate spontaneous breathing and shown to facilitate spontaneous breathing and is associated with decreased peak airway is associated with decreased peak airway pressures and improved oxygenation/ventilation pressures and improved oxygenation/ventilation when compared with conventional ventilation. when compared with conventional ventilation. Additionally, improvements in hemodynamic Additionally, improvements in hemodynamic parameters, splanchnic perfusion, and reduced parameters, splanchnic perfusion, and reduced sedation/neuromuscular blocker requirements sedation/neuromuscular blocker requirements have been reported.have been reported.


APRV may offer potential clinical advantages APRV may offer potential clinical advantages for ventilator management of acute lung for ventilator management of acute lung injury/acute respiratory distress syndrome injury/acute respiratory distress syndrome and may be considered as an alternative and may be considered as an alternative “open lung approach” to mechanical “open lung approach” to mechanical ventilation. Whether APRV reduces mortality ventilation. Whether APRV reduces mortality or increases ventilator-free days compared or increases ventilator-free days compared with a conventional volume-cycled “lung with a conventional volume-cycled “lung protective” strategy will require future protective” strategy will require future randomized, controlled trialsrandomized, controlled trials

http://www.youtube.com/watch?v=BIT2Gy9nxp4

APRV DescriptionAPRV Description

A mode of ventilation along with A mode of ventilation along with spontaneous ventilation to promote spontaneous ventilation to promote lung recruitment of collapsed and lung recruitment of collapsed and poorly ventilated alveoli.poorly ventilated alveoli.

The CPAP is released periodically for a The CPAP is released periodically for a brief period.brief period.

The short release along with The short release along with spontaneous breathing promote COspontaneous breathing promote CO22 elimination.elimination.

Release time is short to prevent the Release time is short to prevent the peak expiratory flow from returning to peak expiratory flow from returning to a zero baseline.a zero baseline.

APRVAPRV

APRV (Airway Pressure APRV (Airway Pressure Release Ventilation)Release Ventilation)

Provides two levels of CPAP and allows spontaneous Provides two levels of CPAP and allows spontaneous breathing at both levels when spontaneous effort is breathing at both levels when spontaneous effort is presentpresent

Both pressure levels are time triggered and time cycledBoth pressure levels are time triggered and time cycled

AKAAKA

BiVent – ServoBiVent – Servo APRV – DragerAPRV – Drager BiLevel – Puritan BennettBiLevel – Puritan Bennett APRV – HamiltonAPRV – Hamilton Etc.Etc.

Lung Protective Lung Protective StrategiesStrategies

Acute lung injury (ALI) and acute Acute lung injury (ALI) and acute respiratory distress syndrome respiratory distress syndrome (ARDS)(ARDS)

Keep plateau pressures < 30 cm HKeep plateau pressures < 30 cm H22OO Use low tidal volume ventilation (4-6 Use low tidal volume ventilation (4-6

mL/kg IBW)mL/kg IBW) Use PEEP to restore the functional Use PEEP to restore the functional

residual capacity (FRC)residual capacity (FRC)


As recently as 1993, the American College of As recently as 1993, the American College of Chest Physicians (ACCP) consensus Chest Physicians (ACCP) consensus conference failed to agree on an optimal conference failed to agree on an optimal mode of ventilation for any disease state or an mode of ventilation for any disease state or an optimal method of weaning patients from optimal method of weaning patients from mechanical ventilation. The ACCP agreed that mechanical ventilation. The ACCP agreed that well-controlled clinical trials that defined the well-controlled clinical trials that defined the indications and uses of specific modes of indications and uses of specific modes of ventilation were lacking. Now, quite a few ventilation were lacking. Now, quite a few years later, the hard science out there is still a years later, the hard science out there is still a bit scarce, but, we have learned a few things. bit scarce, but, we have learned a few things.


Recently, discovery of the potential for mechanical Recently, discovery of the potential for mechanical ventilation to produce ventilator-associated lung injury ventilation to produce ventilator-associated lung injury has resulted in the development of new lung has resulted in the development of new lung protective strategies. Lung protective strategies protective strategies. Lung protective strategies include those described in the open lung approach include those described in the open lung approach promoted by Amato et al. promoted by Amato et al. The open lung approach The open lung approach uses reduced tidal volumes (6 mL/kg or less) to uses reduced tidal volumes (6 mL/kg or less) to prevent high-volume lung injury and over-prevent high-volume lung injury and over-distension of alveoli.distension of alveoli.

In addition, Amato et al. used elevated end In addition, Amato et al. used elevated end expiratory pressure (average positive end-expiratory pressure (average positive end-expiratory pressure [PEEP] 16 cmH2O), to expiratory pressure [PEEP] 16 cmH2O), to prevent low volume lung injury from cyclic prevent low volume lung injury from cyclic airway closure and re-opening.airway closure and re-opening.

Open the Lung and Open the Lung and Keep it OpenKeep it Open

ARDSNet study compared conventional tidal volume ARDSNet study compared conventional tidal volume (mL/kg) to reduced tidal volume (6 mL/kg). (mL/kg) to reduced tidal volume (6 mL/kg).

The results of the ARDSNet trial and a study The results of the ARDSNet trial and a study conducted by Amato et al. suggest an association conducted by Amato et al. suggest an association between reduced tidal volume and improved outcome. between reduced tidal volume and improved outcome.

Improved outcomes seen in the ARDSNet study were a Improved outcomes seen in the ARDSNet study were a result of not only reduced tidal volumes, but also result of not only reduced tidal volumes, but also increased PEEPincreased PEEP

As a result, ARDSNet As a result, ARDSNet AAssessment of ssessment of LLow tidal ow tidal VVolume olume and and EElevated end-expiratory volume to levated end-expiratory volume to OObviate bviate LLung ung Injury (ALVEOLI) study was conducted to evaluate the Injury (ALVEOLI) study was conducted to evaluate the role of higher levels of PEEP on survival, results were role of higher levels of PEEP on survival, results were inconclusive inconclusive

Lung RecruitmentLung Recruitment

Complete recruitment exceeds the lower Complete recruitment exceeds the lower inflection point used by Amato et al. to inflection point used by Amato et al. to determine optimal PEEP levels. Recruitment determine optimal PEEP levels. Recruitment begins at the lower inflection point and begins at the lower inflection point and continues to the upper inflection point. continues to the upper inflection point.

Therefore, elevated baseline airway pressure Therefore, elevated baseline airway pressure during APRV may produce near complete during APRV may produce near complete recruitment, thus minimizing low volume lung recruitment, thus minimizing low volume lung injury from cyclic recruitment. injury from cyclic recruitment.

APRV is less likely to produce over-inflation or high-APRV is less likely to produce over-inflation or high-volume lung injury, as airway pressures are lowered volume lung injury, as airway pressures are lowered (released) in order to accomplish ventilation. (released) in order to accomplish ventilation.


Maintaining a constant airway pressure may Maintaining a constant airway pressure may be advantageous for several reasons. be advantageous for several reasons. Constant airway pressure facilitates alveolar Constant airway pressure facilitates alveolar recruitment; enhances diffusion of gases; recruitment; enhances diffusion of gases; allows alveolar units with slow time constants allows alveolar units with slow time constants to fill, preventing over-distension of alveoli; to fill, preventing over-distension of alveoli; and augments collateral ventilation. Van Allen and augments collateral ventilation. Van Allen et al. noted that complete obstruction of an et al. noted that complete obstruction of an airway unit did not always result in collapse of airway unit did not always result in collapse of the alveoli and, therefore, hypothesized that the alveoli and, therefore, hypothesized that alternative pathways must exist. alternative pathways must exist.


The pores of Kohn, located in the septa of The pores of Kohn, located in the septa of the alveoli and open only during inspiration, the alveoli and open only during inspiration, first were believed to be responsible. first were believed to be responsible. However, two additional pathways were However, two additional pathways were later credited with playing a role: (1) later credited with playing a role: (1) Lambert's canals connect terminal and Lambert's canals connect terminal and respiratory bronchioles with adjacent respiratory bronchioles with adjacent peribronchial alveoli, and (2) channels of peribronchial alveoli, and (2) channels of Martin interconnect respiratory bronchioles Martin interconnect respiratory bronchioles and serve to bypass the main pathwayand serve to bypass the main pathway

Keeping Plateau Pressure < 30 cm Keeping Plateau Pressure < 30 cm HH2200

What do you do if COWhat do you do if CO22 is rising is rising and the plateau pressure is at 30 and the plateau pressure is at 30 cm Hcm H22O?O?– Change to pressure control/increase Change to pressure control/increase

rate/sedationrate/sedation– Permissive hypercapnia?Permissive hypercapnia?– Low VT/high rates?Low VT/high rates?– HFVO?HFVO?– APRV…APRV…

Goals with APRV Goals with APRV include the following:include the following:

Avoiding extension of lung injury Avoiding extension of lung injury Minimal oxygen toxicity with high Minimal oxygen toxicity with high

mean airway pressuremean airway pressure Recruiting alveoli & preventing de-Recruiting alveoli & preventing de-

recruitmentrecruitment Minimizing peak airway pressure Minimizing peak airway pressure Preventing atelectasis Preventing atelectasis Using sedation and paralysis Using sedation and paralysis

conservatively conservatively

Why APRVWhy APRV

Clinicians have learned that cyclical opening and Clinicians have learned that cyclical opening and closing of injured lung units damages them closing of injured lung units damages them (particularly if tidal volumes are large). We would (particularly if tidal volumes are large). We would prefer if the patient could be ventilated at the top of prefer if the patient could be ventilated at the top of the volume pressure curve, at high lung volumes, the volume pressure curve, at high lung volumes, without phasic changes. This can be achieved using without phasic changes. This can be achieved using high frequency oscillation, but adult oscillators are not high frequency oscillation, but adult oscillators are not widely available. For the majority of patients, widely available. For the majority of patients, increasing mean airway pressure without increasing increasing mean airway pressure without increasing peak pressure means prolonging the inspiratory time peak pressure means prolonging the inspiratory time in a pressure control mode. The longer the inspiratory in a pressure control mode. The longer the inspiratory time (Ti), the better the oxygenation benefittime (Ti), the better the oxygenation benefit

IndicationsIndications Primarily used as an alternative Primarily used as an alternative

ventilation technique in patients ventilation technique in patients with ARDS.with ARDS.

Used to help protect against Used to help protect against ventilator induced lung injury.ventilator induced lung injury.

IndicationsIndications The main causes of hypoxemia associated with ALI are shunting The main causes of hypoxemia associated with ALI are shunting

due to alveolar collapse and reduction in functional residual due to alveolar collapse and reduction in functional residual capacity. Therefore, a primary goal of the treatment of ALI is capacity. Therefore, a primary goal of the treatment of ALI is recruitment of alveoli and prevention of de-recruitment. recruitment of alveoli and prevention of de-recruitment. Sustained plateau pressure is used to promote alveolar Sustained plateau pressure is used to promote alveolar recruitment, while being maintained at an acceptable level [no recruitment, while being maintained at an acceptable level [no more than 30 cmH2O, if possible]. more than 30 cmH2O, if possible].

In addition, the number of respiratory cycles is minimized to In addition, the number of respiratory cycles is minimized to prevent both the repetitive opening of alveoli and alveolar prevent both the repetitive opening of alveoli and alveolar stretch that may result in lung injury. Patients in early-phase ALI stretch that may result in lung injury. Patients in early-phase ALI often do not have impaired respiratory muscle strength or often do not have impaired respiratory muscle strength or inadequate respiratory drive. Frequently, CPAP alone is sufficient inadequate respiratory drive. Frequently, CPAP alone is sufficient to restore lung volume and increase lung compliance. However, to restore lung volume and increase lung compliance. However, when assistance with ventilation is required, APRV can be used. when assistance with ventilation is required, APRV can be used. Intermittent airway pressure release allows alveolar gas to be Intermittent airway pressure release allows alveolar gas to be expelled via natural lung recoil. expelled via natural lung recoil.

GoalGoalTo provide the lung protective To provide the lung protective

ventilation supported by the ventilation supported by the ARDSnet research. ARDSnet research.

Use an “Open lung” approach.Use an “Open lung” approach.

Minimize alveolar overdistension.Minimize alveolar overdistension.

Avoid repeated alveolar collapse and Avoid repeated alveolar collapse and reexpansion.reexpansion.

Restore FRC through recruitment and,Restore FRC through recruitment and,

Maintain FRC by creating intrinsic Maintain FRC by creating intrinsic PEEP.PEEP.

Consider APRV when Consider APRV when the Patient Has --the Patient Has -- Bilateral InfiltratesBilateral Infiltrates PaOPaO22/F/FIIOO22 ratio < 300 and falling ratio < 300 and falling Plateau pressures greater than 30 Plateau pressures greater than 30

cm Hcm H22OO No evidence of left heart failure No evidence of left heart failure

(e.g. PAOP of 18 mm Hg or greater)(e.g. PAOP of 18 mm Hg or greater) In other words, persistent ARDSIn other words, persistent ARDS

Possible Possible ContraindicationsContraindications

Unmanaged increases in Unmanaged increases in intracraneal pressure.intracraneal pressure.

Large bronchopleural fistulas.Large bronchopleural fistulas. Possibly obstructive lung disease.Possibly obstructive lung disease. Technically, it may be possible to Technically, it may be possible to

ventilate nearly any disorder.ventilate nearly any disorder.

TerminologyTerminology

Four commonly used terms include: pressure Four commonly used terms include: pressure high (P High), pressure low (P Low), time high high (P High), pressure low (P Low), time high (T High), and time low (T Low).(T High), and time low (T Low).

P HighP High – the upper CPAP level. Analogous to MAP – the upper CPAP level. Analogous to MAP (mean airway pressure) and thus affects (mean airway pressure) and thus affects oxygenation. oxygenation. P High is the baseline airway P High is the baseline airway pressure level and is the higher of the two pressure level and is the higher of the two airway pressure levels. Other authors have airway pressure levels. Other authors have described P High as the CPAP level, the described P High as the CPAP level, the inflating pressure, or the P1 pressure (P1), inflating pressure, or the P1 pressure (P1), also called High Peep.also called High Peep.

P-HighP-High

p-High is the upper CPAP or pressure setting when utilizing APRV.p-High regulates end-inspiratory lung volume & is analogous with mean airway pressure

TerminologyTerminology PEEPPEEP (Also called Plow or Low Peep) is the lower (Also called Plow or Low Peep) is the lower

pressure setting.pressure setting. P Low is the airway pressure level resulting from P Low is the airway pressure level resulting from

the pressure release. Other authors may refer to the pressure release. Other authors may refer to P Low as the PEEP level, the release pressure, or P Low as the PEEP level, the release pressure, or the P2 pressure (P2). the P2 pressure (P2).

P-LowP-Low

The p-Low setting, sets the lower level of CPAP during the release phase.The term "p-Low" is used in Draeger & Hamilton medical ventilators.

Servo I: Bi-Vent Draeger Evita

PB 840 BiLEVEL

T-HighT-High

T High- is the inspiratory time IT(s) phase for the high CPAP level (P High).

T High corresponds with the T High corresponds with the length of time for which P High is length of time for which P High is maintainedmaintained

T-HighT-High

Allows for sustained recruitment allowing for improved gas exchange by increasing alveolar surface area.

T-LowT-Low

T Low is the length of time for which T Low is the length of time for which the P Low is held (i.e. for which the the P Low is held (i.e. for which the airway pressure is released) airway pressure is released)

T High plus T PEEP (T low) is the T High plus T PEEP (T low) is the total time of one cycle.total time of one cycle.

I:E ratio becomes irrelevant because I:E ratio becomes irrelevant because APRV is really best thought of as APRV is really best thought of as CPAP With occasional releasesCPAP With occasional releases

T-LowT-Low

The t-Low sets the time interval for the low pressure/CPAP phase (p-Low).Allows for intermittent release in airway pressure, providing paCO2 removal.Partially unloads the patients work of breathing associated with pure CPAP breathing.The name "t-Low" is used in both Draeger and Hamilton ventilators. note- t-Low should not be considered "expiratory time" as the patient may exhale throughout the entire inspiratory phase. When using Bi-Level on the PB 840 there is no setting to set the low pressure interval. The operator must change frequency & "TH" to set a t-Low. This can become problematic when trying to precisely set a t-Low interval.

APRV: Setting P-High based on the APRV: Setting P-High based on the Static Pressure Volume Curve Static Pressure Volume Curve

Some newer mechanical ventilators provide the operator with automated tools to obtain a static Pressure Volume (P/V) Curve in the ventilated patient. These tools provide the clinician a simple, safe, and reproducible method to assess the P/V curve for various pulmonary conditions.

APRV: Setting P-High based on the APRV: Setting P-High based on the Static Pressure Volume Curve Static Pressure Volume Curve

For example many Respiratory care practitioners utilize the P/V to identify the lower and upper inflection points. “The lower section of the P/V curve, where the compliance is less favorable, corresponds to a condition in which a given number of alveolar units are collapsed”

It is common for the practitioner to set Positive End-Expiratory Pressure (PEEP) 1-to-2 cmH2O above the lower inflection point to prevent de-recruitment and minimize injury related to shear stress from the repetitive opening and closing of the alveoli.

The upper inflection point indicates a decrease in lung compliance and may specify over-distention of the lung units. The assessment of the static P/V curve can provide insight on how well a patient will respond to the application of Airway Pressure Release Ventilation. Evaluation of the “hysteresis” (difference between the inflation and the deflation limb) can indicate the extent of potential lung units that may be recruited. If the patient has very little probability for alveolar recruitment then APRV is less likely to be beneficial and unjustified.

APRV: Setting P-High based on the APRV: Setting P-High based on the Static Pressure Volume CurveStatic Pressure Volume Curve

If the patient meets indications for utilizing APRV, the operator can use points on the P/V to safely set P-High.

P-High should be set always below the pressure which generated the “Upper Inflection Point”.

P-High can be set 1-to-2 cmH2o above the “Lower Inflection Point”.The practitioner can calculate “Best Compliance” and set P-High according to the pressure that generated the best compliance (some P/V tools automatically calculate this).

The static P/V curve provides a more diagnostic and patient tailored approach to setting P-High.

P/V Tool for more intelligent patient assessmentThe automated P/V Tool uses an empirical and repeatable method to find best PEEP, based on respiratory mechanics.It also enables sophisticated lung recruitment maneuvers and therapy assessment. This maneuver records the static pressure/volume curve quickly and easily at the bedside. It employs an adjustable pressure ramp, in which airway pressure is slowly increased to an upper limit as resultant volume and pressure are recorded.

After the maneuver, the cursor function lets you inspect inflection points so that you can easily visualize the linear portion of the compliance curve.

Advantages of APRVAdvantages of APRV Uses lower PIP to maintain Uses lower PIP to maintain

oxygenation and ventilation without oxygenation and ventilation without compromising the patient’s compromising the patient’s hemodynamicshemodynamics (Syndow AJRCCM 1994, Kaplan, CC, (Syndow AJRCCM 1994, Kaplan, CC, 2001)2001)

Shown to improved V/Q matchingShown to improved V/Q matching (Putensen, AJRCCM, 159, 1999)(Putensen, AJRCCM, 159, 1999)

Required a lower VRequired a lower VEE suggesting suggesting reduced Vreduced VDD/V/VTT (Varpula, (Varpula, Acta Anaesthesiol ScandActa Anaesthesiol Scand 2001) 2001)

APRV vs. PCIRVAPRV vs. PCIRV

Although both modes increase Although both modes increase PAW, PCIRV usually requires PAW, PCIRV usually requires higher PIP and heavy higher PIP and heavy sedation/paralytic, whereas APRV sedation/paralytic, whereas APRV allows for spontaneous breathingallows for spontaneous breathing

Increases cardiac index Increases cardiac index Decreases central venous Decreases central venous

pressurepressure

Additional Advantages Additional Advantages - Compared to PCIRV- Compared to PCIRV APRV increases oxygen delivery APRV increases oxygen delivery

and and Reduces the need for sedation and Reduces the need for sedation and

paralysisparalysis APRV also improves renal perfusion APRV also improves renal perfusion

and urine output when and urine output when spontaneous breathing is spontaneous breathing is maintained. maintained. (Kaplan, Crit Care, 2001; Hering, Crit (Kaplan, Crit Care, 2001; Hering, Crit Care Med 2002)Care Med 2002)

APRV vs. SIMVAPRV vs. SIMV

Conventional vs APRVConventional vs APRV

Advantages of Spontaneous Advantages of Spontaneous BreathingBreathing The benefits of APRV may be related to The benefits of APRV may be related to

the preservation of spontaneous the preservation of spontaneous breathing.breathing.

Maintaining the normal cyclic decrease Maintaining the normal cyclic decrease in pleural pressure, augmenting in pleural pressure, augmenting venous return and improving cardiac venous return and improving cardiac output. output. (Putensen, AJRCCM, 1999)(Putensen, AJRCCM, 1999)

The need for sedation is decreased.The need for sedation is decreased.

Preserve Spontaneous Preserve Spontaneous BreathingBreathing

The dashed line in each figure represents The dashed line in each figure represents the normal position of the diaphragm. the normal position of the diaphragm.

The shaded area represents the The shaded area represents the movement of the diaphragm. movement of the diaphragm. (Froese, 1974)(Froese, 1974)

Spontaneous v.s. ParalyzedSpontaneous v.s. Paralyzed

Spontaneous breathing provides ventilation Spontaneous breathing provides ventilation to dependent lung regions which get the to dependent lung regions which get the best blood flow, as opposed to PPV with best blood flow, as opposed to PPV with paralyzed patients. paralyzed patients. ((Frawley, AACN Clinical 2001. Froese, ((Frawley, AACN Clinical 2001. Froese,

Anesth, 1974).Anesth, 1974).

Spontaneous v.s. Spontaneous v.s. ParalyzedParalyzed

During PPV (paralyzed patient), the During PPV (paralyzed patient), the anterior diaphragm is displaced anterior diaphragm is displaced towards the abdomen with the towards the abdomen with the non-dependentnon-dependent regions of the lung regions of the lung receiving the most ventilation receiving the most ventilation where perfusion is the least.where perfusion is the least.

Other Advantages of Other Advantages of Spontaneous BreathingSpontaneous Breathing

Reduces atrophy of the muscles of Reduces atrophy of the muscles of ventilation ventilation associated with the use of associated with the use of PPV and paralytic agents. PPV and paralytic agents. (Neuman, (Neuman, ICM,2002)ICM,2002)

Another AdvantageAnother Advantage

During PPV atelectasis formation During PPV atelectasis formation can occur near the diaphragm, can occur near the diaphragm, when activity of this muscle is when activity of this muscle is absent. (paralysis)absent. (paralysis)

However, if spontaneous breathing However, if spontaneous breathing is preserved, the formation of is preserved, the formation of atelectasis is offset by the activity atelectasis is offset by the activity of the diaphragm. of the diaphragm. (Hedenstierna, Anesth, 1994)(Hedenstierna, Anesth, 1994)

Initial Settings – P Initial Settings – P HighHigh P High – Set a plateau pressure P High – Set a plateau pressure

(adult) or mean airway pressure (adult) or mean airway pressure (pediatric)(pediatric)

Typically about 20-35 cm HTypically about 20-35 cm H22O. O. In patients with Pplateau at or In patients with Pplateau at or

above 30 cm Habove 30 cm H22O, set at 30 cm HO, set at 30 cm H22OO http://www.youtube.com/watch?v=

yW-S2ZGLRqs&feature=related

Setting PSetting Phighhigh

Over-distention of the lung must Over-distention of the lung must be avoided. Maximum Pbe avoided. Maximum Phighhigh of 35 of 35

cm Hcm H22O. (controversial)O. (controversial) Exceptions for higher settings – Exceptions for higher settings –

morbid obesity, decreased thoracic morbid obesity, decreased thoracic or abdominal compliance (ascites).or abdominal compliance (ascites).

Setting TSetting Thighhigh

The inspiratory time (TThe inspiratory time (Thighhigh) is set at ) is set at a minimum of about 4.0 seconds a minimum of about 4.0 seconds

In children, others use lower In children, others use lower settings (Children’s Med Ctr. Uses 2 settings (Children’s Med Ctr. Uses 2 sec.)sec.)

TThighhigh is progressively increased (10 is progressively increased (10 to 15 seconds (Habashi, et al)to 15 seconds (Habashi, et al)

Target is oxygenation.Target is oxygenation.

Setting TSetting Thighhigh

Progress slowly. For example, 5 Progress slowly. For example, 5 sec Tsec Thighhigh to 0.5 sec T to 0.5 sec Tlowlow, a 10:1 , a 10:1 ratio. ratio.

Increasing to 5.5 sec to 0.5 sec is Increasing to 5.5 sec to 0.5 sec is an 11:1 ratio; not a big change. an 11:1 ratio; not a big change.

Old patients may be fragile.Old patients may be fragile.

APRVAPRV

Release Time - TRelease Time - TPEEPPEEP Currently, with ARDS thinking is Currently, with ARDS thinking is

not to let exhalation go to not to let exhalation go to complete emptying, i.e. do not let complete emptying, i.e. do not let expiratory flow returning to zero. expiratory flow returning to zero. ((McCunn, Crit Care 2002)McCunn, Crit Care 2002)

Thus, regional auto-PEEP a Thus, regional auto-PEEP a desirable outcome with APRVdesirable outcome with APRV

FLOW

Setting PEEP or PSetting PEEP or Plowlow in in APRVAPRV

Set PEEP at zero cm HSet PEEP at zero cm H22O.O. This provides a rapid drop in pressure, This provides a rapid drop in pressure,

and a maximum and a maximum P for unimpeded P for unimpeded expiratory gas flow. expiratory gas flow. (Frawley, AACN Clin Issues (Frawley, AACN Clin Issues 2001)2001)

Avoid lung collapse during TAvoid lung collapse during Tlowlow. .

Establishing T PEEP Establishing T PEEP (Time at low pressure)(Time at low pressure) Set T PEEP (T low) so that Set T PEEP (T low) so that

expiratory flow from patient ends expiratory flow from patient ends at about 50 to 75% of peak at about 50 to 75% of peak expiratory flow.expiratory flow.

This can be determine saving a This can be determine saving a screen and calculating peak screen and calculating peak expiratory flow.expiratory flow.

Or, it can be estimatedOr, it can be estimated

Expiratory FlowExpiratory Flow

T PEEP – Setting The T PEEP – Setting The TimeTime

Adults 0.5 to 0.8 secondsAdults 0.5 to 0.8 seconds Pediatric/neonatal settings 0.2 to Pediatric/neonatal settings 0.2 to

0.6 seconds.0.6 seconds. Or one time constant. (TC = C x Or one time constant. (TC = C x

R)R)

T PEEP – Using the TcT PEEP – Using the Tc

Release Time in ARDSRelease Time in ARDS

Atelectasis can Atelectasis can develop in seconds develop in seconds when Paw drops when Paw drops below a critical value below a critical value in the injured lung.in the injured lung. (Neumann P, JAP 1998, Newmann P, AJRCCM (Neumann P, JAP 1998, Newmann P, AJRCCM 1998, Frawley, 2001; McCunn, Internat’l Anesth 1998, Frawley, 2001; McCunn, Internat’l Anesth

Clinics 2002).Clinics 2002).

Too long a release Too long a release time would interfere time would interfere with oxygenation and with oxygenation and allow lung units to allow lung units to collapse.collapse.

Initial SettingsInitial SettingsP high 20-30 cm H2O,

according to the following chart.

T High/T low- 12-16 releases

T low = 0.5 sec and P low = 0

P/F MAP<250 15-20<200 20-25<150 25-28

T High (s) T low (s) Freq.

3.0 0.5 17

4.0 0.5 13

5.0 0.5 11

6.0 0.5 9

T high range 4-6 sec. PS- as indicated with special attention given to PIP.

Review of SettingsReview of Settings

http://www.youtube.com/watch?v=yW-S2ZGLRqs&feature=related

Waveform ReviewWaveform Review

Airway Pressure Release Ventilation (APRV) showing the characteristic long inspiratory time (TIMEH) (A) and short "release" time (TIMEL) (B). Note that all spontaneous breathing occurs at PEEPH. [Note: Our module on APRV applies generally to all variations popularly used].

Bi-Vent SettingsBi-Vent Settings

Set Releases and I:E

Create releases and I:E

Bi-Vent VentilationBi-Vent Ventilation

P High

T HighT PEEP

Spontaneous BreathingSpontaneous Breathing

Spontaneous Breaths

Patient Trigger(On P High)

(On P High)

Spontaneous Breathing Spontaneous Breathing w/PSw/PS

Spontaneous Breaths w/PS

Identifying Lung Identifying Lung Recruitment – CORecruitment – CO22 MonitoringMonitoring

Making Changes in Making Changes in APRV Settings Based APRV Settings Based on ABGson ABGs

Control Settings for COControl Settings for CO22

P (PP (Phighhigh – P – Plowlow) determines flow out ) determines flow out of the lungs and volume exchange of the lungs and volume exchange (V(VTT and PaCO and PaCO22).).

Some clinicians suggest a target Some clinicians suggest a target minute ventilation of 2 to 3 L/min. minute ventilation of 2 to 3 L/min. (Frawley, 2001). (Frawley, 2001).

Optimize spontaneous ventilation.Optimize spontaneous ventilation.

COCO22 Elimination EliminationTo Decrease PaCOTo Decrease PaCO22::

Decrease T High.Decrease T High.– Shorter T High means more release/min.Shorter T High means more release/min.– No shorter than 3 seconds No shorter than 3 seconds – Example: T High 5 sec. = 12 releases/minExample: T High 5 sec. = 12 releases/min– T High 4 sec = 15 releases/minT High 4 sec = 15 releases/min

Increase P High to increase Increase P High to increase P and volume P and volume exchange. (2-3 cm Hexchange. (2-3 cm H22O/change)O/change)– Monitor VtMonitor Vt– PIP (best below 30 cm HPIP (best below 30 cm H22O)O)

Check T low. If possible increase T low to Check T low. If possible increase T low to allow more time for “exhalation.”allow more time for “exhalation.”

To Increase PaCOTo Increase PaCO22

Increase T high. (fewer releases/min)Increase T high. (fewer releases/min) Slowly! In increments of 0.5 to 2.0 Slowly! In increments of 0.5 to 2.0

sec.sec. Decrease P High to lower Decrease P High to lower P. P.

– Monitor oxygenation andMonitor oxygenation and– Avoid derecruitment.Avoid derecruitment.

It may be better to accept It may be better to accept hypercapnia than to reduce P high hypercapnia than to reduce P high so much that oxygenation so much that oxygenation decreases.decreases.

Management of PaOManagement of PaO22

To Increase PaOTo Increase PaO22

1.1. Increase FIncrease FIIOO22

2.2. Increase MAP by increasing P High in 2 Increase MAP by increasing P High in 2 cm Hcm H22O increments.O increments.

3.3. Increase T high slowly (0.5 sec/change)Increase T high slowly (0.5 sec/change)4.4. Recruitment ManeuversRecruitment Maneuvers5.5. Maybe Maybe shorten T PEEP (T low) to shorten T PEEP (T low) to

increase PEEPi in 0.1 sec. increments increase PEEPi in 0.1 sec. increments (This may reduce V(This may reduce VTT and affect PaCO and affect PaCO22))

Weaning From APRVWeaning From APRV

1.1. FiOFiO22 SHOULD BE WEANED FIRST. (Target SHOULD BE WEANED FIRST. (Target < 50% with SpO< 50% with SpO22 appropriate.) appropriate.)

2.2. Reducing P High, by 2 cmHReducing P High, by 2 cmH220 increments 0 increments until the P High is below 20 cmHuntil the P High is below 20 cmH22O.O.

3.3. Increasing T High to change vent set rate Increasing T High to change vent set rate by 5 releases/minuteby 5 releases/minute

Weaning From APRVWeaning From APRV

3.3. The patient essentially The patient essentially transitions to CPAP with very few transitions to CPAP with very few releases. releases.

4.4. Patients should be increasing Patients should be increasing their spontaneous rate to their spontaneous rate to compensate. compensate.

During WeaningDuring Weaning

Add Pressure Support judiciously. Add Pressure Support judiciously.

Add Pressure Support to P High in Add Pressure Support to P High in order to decrease WOB while order to decrease WOB while avoiding over-distention, avoiding over-distention,

P High + PS P High + PS << 30 cmH 30 cmH22O.O.

Pressure Support with Pressure Support with APRVAPRV

Pressure Support with Pressure Support with APRVAPRV

PEEPPEEPHH

PEEPPEEPLL

Pressure SupportPressure SupportPEEPPEEPHigh High + PS + PS

PPawaw

cmHcmH2200

6060

-20-201 2 3 4 5 6 7

Weaning Bi-VentWeaning Bi-Vent

Lower Rate

Longer T High

Lower P HighAdd PS

Weaning Bi-VentWeaning Bi-Vent

Lower Rate

Longer T High

Lower P HighAdd PS

Weaning- Habashi method: Drop-and-Stretch

Perceived Perceived Disadvantages of Disadvantages of APRVAPRVAPRV is a pressure-targeted mode of APRV is a pressure-targeted mode of

ventilation.ventilation.Volume delivery depends on lung Volume delivery depends on lung

compliance, airway resistance and compliance, airway resistance and the patient’s spontaneous effort. the patient’s spontaneous effort.

APRV does not completely support APRV does not completely support COCO22 elimination, but relies on elimination, but relies on spontaneous breathing spontaneous breathing

Disadvantages of Disadvantages of APRVAPRV

With increased Raw (e.g.COPD) With increased Raw (e.g.COPD) – the ability to eliminate COthe ability to eliminate CO2 2 may be more difficultmay be more difficult

– Due to limited emptying of the lung and short Due to limited emptying of the lung and short release periods.release periods.

If spontaneous efforts are not matched If spontaneous efforts are not matched during the transition from Pduring the transition from Phighhigh to P to Plowlow and and

PPlowlow to P to Phighhigh, may lead to increased work load , may lead to increased work load

and discomfort for the patient. and discomfort for the patient. Limited staff experience with this mode Limited staff experience with this mode

may make implementation of its use may make implementation of its use difficult.difficult.

The End The End Lesson 1 LabLesson 1 Lab: Setup and manipulation of : Setup and manipulation of

APRV on the Galileo ventilator and BiLevel APRV on the Galileo ventilator and BiLevel on the PB 840. Use of clinical scenarios will on the PB 840. Use of clinical scenarios will be used to guide decision making. be used to guide decision making.

Lesson 1 assignmentLesson 1 assignment: Analyze current : Analyze current evidence based research on the use of APRV evidence based research on the use of APRV as a measure to decrease mortality in the as a measure to decrease mortality in the ARDS patient. Write a minimum of 3 pages ARDS patient. Write a minimum of 3 pages utilizing peer reviewed articles and APA utilizing peer reviewed articles and APA referencing to support or refute APRV use as referencing to support or refute APRV use as primary means to decrease mortality. primary means to decrease mortality.