APRV mode Ventilation

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Understanding Basics about APRV
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What you will do if Plateau Pressure going above
30
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APRV

• Introduced first 1987 by Stock and Down as CPAP
  with Intermittent release phase.

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Proper measurement of ingredients vs. improper
ingredient
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Airway Pressure Release Ventilation APRV

• APRV is a pressure control mode of mechanical
  ventilation that utilizes an inverse ratio
  ventilation strategy.
• APRV is an applied CPAP that at a set timed
  interval releases the applied pressure.
• APRV applies CPAP with an intermittent release
  phase.
• The application of CPAP (P high) for a prolonged
  time (T high) maintains adequate lung volume and
  alveolar recruitment.
• There is a time-cycled release phase to a lower
  set of pressure (P low) for a short period of
  time (T low or release time) where most of
  ventilation and CO2 removal occurs.
• This mode allows for spontaneous breathing
• Breaths can be unsupported, pressure supported,
  or
• supported by automatic tube compensation.

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What Lung Protective Method we do

• In ALI and ARDS
• Keep plateau pressures lt 30 cm H2O
• Use low tidal volume ventilation (4-6 mL/kg IBW)
• Use PEEP to restore the functional residual
  capacity (FRC)

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Main Goals in APRV

• Minimize alveolar over distension.
• Avoid repeated alveolar collapse and expansion.
• Restore FRC through recruitment
• Maintain FRC by creating intrinsic PEEP.

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APRV
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How we name APRV in the other Ventilators

• BiVent Servo
• APRV Drager
• BiLevel Puritan Bennett
• APRV Hamilton

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Indications for APRV

• (ALI/ARDS)
• Diffuse pneumonia
• Pulmonary edema
• Atelectasis requiring greater than 50 FiO2
• Tracheo-esophageal fistuala

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Who are APRV Candidates

• Bilateral Infiltrates
• PaO2/FIO2 ratio lt 300 and falling
• Plateau pressures greater than 30 cm H2O
• No evidence of left heart disease
• In other words, persistent ARDS

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4 main Parameters in APRV

• P High the upper CPAP level
• P low is -- the lower pressure setting.
• T High- is IT(s) phase for the high CPAP level (P
  High).
• T PEEP or T low- is the release time allowing CO2
  elimination

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Initial Settings P High/P Low

• P High plateau pressure (adult) mean airway
  pressure (pediatric)
• From CMV use plateu,from PRVC or PC use PEAK
  pressure, from HFOV MAP2-4
• Typically about 20-25 cm H2O.
• In patients with Pplateau at or above 30 cm H2O,
  set at 30 cm H2O
• PLow at 0 cmH2O to optimize expiratory flow. The
  large pressure ramp allows for tidal ventilation
  in very short expiratory times.

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Initial Setting T High

• The inspiratory time (Thigh) is set at a minimum
  of about 4.0 -6 seconds,3 for pedia,1.5-2 for
  neonat.
• Thigh is progressively increased (10 to 15
  seconds (Habashi, et al)
• Target is oxygenation.
• TLow at 0.5-0.8 seconds. The expiratory time
  should be short enough to prevent derecruitment
  and long enough to obtain a suitable tidal
  volume.
• Ideal CPAP duration should be gt90 in adult and
  neonats 80-85 .

Dr nadir Habashi Univerity of Maryland
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P High P low and T high T low determination

• Difference between P high and P low is driving
  pressure, Larger driving pressure means greater
  inflation deflation and smaller driving pressure
  means smaller inflation deflation.
• T high and T low determine the frequency of
  Inflation deflation. For example if some patient
  T high is 12 and T low is 3 it means the total
  cycle of inflation deflation is 15. It allows 4
  inflation and deflation occur in a minute.
• Spontaneous breathing occurs at P high and Plow
  level but mostly it occurs at P high.

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APRV
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Pressure and Flow during Spontaneous Breathing
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Monitoring a patient on APRV

• APRV should help rest the inspiratory muscles and
  utilize the diaphragm.
• Once the initial settings are applied, look for
  anterior chest muscles to be used much less and
  the diaphragm to be doing the majority of the
  work.
• The earlier APRV is used, the more effective it
  is in recruiting the lung and the more likely it
  is to be tolerated.
• if initiating APRV late in the course of ARDS,
  patients sometimes will not look comfortable
  despite optimal APRV settings, and they may need
  an alternative mode.

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Making Adjustments to the APRV Settings

• Oxygenation Options
• When possible wean FiO2 to lt50 for a SpO2 gt90
  or a PaO2 gt60 torr.
• To improve oxygenation via higher PMean
• Increase PHigh in increments of 2 cmH2O.
• Decrease TLow to be closer to 75 PEFR.

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Which level is easy and safe to inflate
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How The More time for a limited pressure gives
benefit
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Expiratory Flow
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To Decrease PaCO2

• Decrease T High.
• Shorter T High means more release/min.
• No shorter than 3 seconds
• Example T High 5 sec. 12 releases/min
• T High 4 sec 15 releases/min
• Increase P High to increase DP and volume
  exchange. (2-3 cm H2O/change)
• Monitor Vt
• PIP (best below 30 cm H2O)
• Check T low. If possible increase T low to allow
  more time for exhalation.

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How to Increase PaCO2

• Increase T high. (fewer releases/min)
• Slowly! In increments of 0.5 to 2.0 sec.
• Decrease P High to lower DP.
• Monitor oxygenation and
• Avoid derecruitment.
• It may be better to accept hypercapnia than to
  reduce P high so much that oxygenation decreases.
• Turn ATC off if no spontaneous respirations.

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For PaO2

• To Increase PaO2
• Increase FIO2
• Increase MAP by increasing P High in 2 cm H2O
  increments.
• Increase T high slowly (0.5 sec/change)
• Recruitment Maneuvers
• Maybe shorten (T low) to increase PEEPi in 0.1
  sec

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Increased Respiratory Efforts

• Increase PHigh. This will elevate the PMean and
  encourage recruitment.
• Decrease TLow only if you can maintain the flow
  during the release phase lt75 of PEFR and the
  PaCO2 and pH are acceptable.

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Forceful expirations

• Decrease the PHigh in 1-2 cmH2O increments and
  increase THigh (to maintain the same PMean).
• Increase the TLow. Allowing more time to exhale
  only if you can maintain the flow during the
  release phase gt25 of PEFR.
• CXR should be monitored for lung over-inflation.

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Weaning From APRV

• FiO2 SHOULD BE WEANED FIRST. (Target lt 50 with
  SpO2 If PO2 gt55 and sat 88
• Reducing P High, by 2 cmH20 increments until the
  P High is below 20 cmH2O.
• Increasing T High to change vent set rate by 5
  releases/minute
• If switching to PCV or VC mode keep PEEP 14-16 or
  if Phigh reachs 10 then better direct extubation.

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During Weaning

• Add Pressure Support to P High in order to
  decrease WOB while avoiding over-distention,
• P High PS lt 30 cmH2O.

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Possible Contraindications

• Unmanaged intracraneal pressure.
• Large bronchopleural fistulas.
• Possibly obstructive lung disease.

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Advantages of APRV

• Using low Airway pressure to maintain oxygenation
  and ventilation without compromising the
  patients hemodynamics (Syndow AJRCCM 1994,
  Kaplan, CC, 2001)
• VQ Mismatch Improving(Putensen, AJRCCM, 159,
  1999)

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Another Advantage

• During PPV atelectasis formation can occur near
  the diaphragm, when activity of this muscle is
  absent. (paralysis)
• However, if spontaneous breathing is preserved,
  the formation of atelectasis is offset by the
  activity of the diaphragm. (Hedenstierna, Anesth,
  1994)
• Spontaneous breathing during ventilatory support
  improves ventilation-perfusion distributions in
  patients with acute respiratory distress
  syndrome.Putensen C, Mutz NJ, Putensen-Himmer G,
  Zinserling J
• Am J Respir Crit Care Med. 1999 Apr 159(4 Pt
  1)1241-8.

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Disadvantage

• APRV is a pressure-targeted mode of ventilation.
• Volume delivery depends on lung compliance,
  airway resistance and the patients spontaneous
  effort.
• APRV does not completely support CO2 elimination,
  but relies on spontaneous breathing

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Disadvantages of APRV

• COPD
• the ability to eliminate CO2 may be more
  difficult
• Due to limited emptying of the lung and short
  release periods.
• If spontaneous efforts are not matched during the
  transition from Phigh to Plow and Plow to Phigh,
  may lead to increased work load and discomfort
  for the patient.
• Limited staff experience with this mode may make
  implementation of its use difficult.

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References

• (Hedenstierna, Anesth, 1994
• Varpula, Acta Anaesthesiol Scand 2001)
• (Putensen, AJRCCM, 159, 1999)
• (Syndow AJRCCM 1994, Kaplan, CC, 2001)
• CritCareMed. 200533S228 Other Approaches to
  Open-Lung VentilationAirway Pressure Release
  Ventilation.
• CleveClinJMed 201178101 Airway Pressure Release
  VentilationAlternative Mode of Mechanical
  Ventilation in Acute Respiratory Distress
  Syndrome.
• AnnThoracMed 20072178 Airway pressure release
  ventilation.
• AACNClinicalIssues 200112234 Airway Pressure
  Release VentilationTheory and Practice.

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• SHAMS ALI SHAH RT
• PSCCQ