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Airway pressure release ventilation _APRV_ clinical guide

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					                Airway pressure release ventilation (APRV) clinical guide

Terminology:
Phigh: PEEP high, elevated baseline pressure
Plow: PEEP low, low pressure (not actually reached due to Tlow setting)
Thigh: Time at which Phigh is maintained (minimum 4 sec)
Tlow: Time at which Phigh is terminated; set to achieved a T-PEFR of 50%-25%
T-PEFR: Peak Expired Flow Rate Termination Point
TOP: Threshold Opening Pressure

Goals
       Increase (recruit) and maintain lung volume (Phigh and Thigh)
       Decrease elastic WOB
       Limit derecruitment; set Tlow to ensure T-PEFR is 50-25%
       Keep in mind that patients don’t have to be breathing. APRV promotes spontaneous
        breathing, but at high Phigh levels this can be uncomfortable. The goal is to allow
        spontaneous breathing within 24 – 48 hrs of APRV application

Set-up—adults
Newly intubated
Phigh—set at desired plateau pressure (typically 20–35 cm H2O)
Plow—0 cm H2O
Thigh—4–6 secs
Tlow—0.2–0.8 adjust for T-PEFR 50-25%

Transition from conventional ventilation
Phigh—plateau pressure in volume-cycled mode or peak airway pressure in pressure-cycled mode
Plow—0 cm H2O
Thigh—4.5 secs
Tlow—0.2–0.8 adjust for T-PEFR 50-25%

Transition from HFOV
Phigh—Paw on HFOV plus 2–4 cm H2O
Plow—0 cm H2O
Thigh—4.5 secs
Tlow—0.2–0.8 adjust for T-PEFR 50-25%

Note: Phigh ≥35 cm H2O may be necessary in patients with decreased
thoracic/abdominal compliance or morbid obesity in order to reach their TOP
(Threshold Opening Pressure)
                Airway pressure release ventilation (APRV) clinical guide

Oxygenation
PaO2 Low
    Reassess release volume and ensure T-PEFR is approx. 50%-25%
    Increase Phigh to recruit by reaching TOP
    Increase Phigh and Thigh simultaneously
          o Lengthening Thigh (decreasing the rate) increases gas mixing and recruits lung
             units with high resistance time constants
          o This will also increase your mean airway pressure
    Assess hemodynamics
PaO2 High
    Decrease FiO2
    Only decrease Phigh (2 – 4 cm H2O increments) if your pH is within desired range

Ventilation
PCO2 High
    Reassess release volume and ensure T-PEFR is approx. 50%-25%
    Increase minute ventilation: shorten Thigh (increase rate) and increase Phigh
       simultaneously (see precautions below)
    Increase alveolar ventilation: increase Phigh or Phigh and Thigh simultaneously
           o This seems opposite to what is appropriate, but increasing time for gas exchange
               (alveolar ventilation) may help rather than increasing a minute volume that is
               inefficient at CO2 clearance
    If your patient has been spontaneously breathing, assess for over sedation
PCO2 Low
    Decrease minute ventilation: lengthen Thigh (decrease rate)
    Only decrease Phigh (2cm H2O increments) if your Oxygenation is within desired range

Weaning
      Wean the Phigh if PaO2 is within desired range
      “Drop and Stretch”
          o Simultaneously reduce Phigh (2 – 4 cm H2O increments) and lengthen Thigh
              (decrease rate) as the patient’s spontaneous breathing begins to contribute to
              the total minute ventilation. Wean Phigh to 15-20 and try switching to PS with
              PEEP of 10 cm H2O (to maintain Paw)

Precautions
    Adjustment of Tlow differs with lung disease, lung volume and artificial airway size. Tlow
      values provided are typical but not absolute.
    If you decrease Thigh (increase the rate) to increase minute ventilation (for CO2
      clearance) you must keep in mind that the Paw and gas exchanging surface area will be
      reduced; This may actually cause an increase in CO2 if you don’t simultaneously increase
      Phigh
    Phigh and Thigh reduction (increase in rate) may produce less mean alveolar volume
      (lung volume) and will result in shorter emptying time, so keep in mind you may need to
      adjust the Tlow
    Tlow should not be extended solely to lower CO2 as this may lead to airway closure
      (derecruitment)

				
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