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APRV

Definition

  • Airway Pressure Release Ventilation (APRV) introduced by Stock and Downs in 1987.
  • Applies CPAP (P high) for a prolonged time (T high) to maintain adequate lung volume and alveolar recruitment with a time cycled release to a lower pressure (P low) for a shorter period of time (T low). This release phase is where most of the CO2 removal occurs. The patient can spontaneously breathe at P high due to an open exhalation valve during T high.
  • Time triggered, pressure limited, time cycled
  • In theory, should facilitate recruitment, increase mean airway pressure while limiting peak pressures, avoid repeated alveolar collapse/atelectotrauma, allow spontaneous respiration (and thereby reduce sedation and need for neuromuscular blockade)

APRV Quick Reference Sheet

APRV Review: Habashi CCM 2005


Primary Indications

  • ARDS with low lung compliance
  • Diffuse pneumonia
  • Potentially tracheo-esophageal fistula

Relative Contraindications

  • Elevated Intracranial Pressure
  • Large bronchopleural fistula
  • Possibly significant obstructive lung disease

Parameters



Initial Settings

1) P high at the P plateau (or desired . P mean + 3cm H2O). Try to keep P high below 30-35 cm H2O
2) T high at 4-6 seconds
3) P low at 0 (to optimize expiratory flow)
4) T low at 0.5 to 0.8 seconds: Adjust the T low to cut off the expiratory flow during a release at about 50% of peak expiratory flow (see figure below). Do not allow the termination of expiratory flow to go <25% of the peak expiratory flow rate. This intrinsic PEEP allows P low to be set at 0 without causing derecruitment. T low can be as low as 0.3 seconds (closer to 75% peak expiratory flow rate) in restrictive lung disease and as high as 1.5 seconds (closer to 25% peak expiratory flow rate) in obstructive diseases. 
5) ATC (automatic tube compensation) or PS for spontaneous breaths


Titration

Hypercarbia:

Delta P (P high- P low) determines flow out of the lungs and volume exchange. Hence:

1) Decrease T high in 0.5 second increments. Shorter T high means more releases/min. (should generally not decrease to <4seconds)
2) Increase P high to increase delta P and volume exchange by increments of 2-3 cm H2O. Monitor Vt and P high
3) Check T low. If possible, increase T low to allow more time for alveolar emptying while keeping expiratory flow greater than 25% of peak expiratory flow rate. 


Hypocarbia:

1) Increase T high (fewer releases) in increments of 0.5 seconds
2) Decrease P high to lower delta P (monitor oxygenation and avoid derecruitment)


Hypoxia:

1) Increase P high in increments of 2 cm H20 to improve mean airway pressure
2) Decrease T low to be closer to 75% peak expiratory flow rate

Weaning:

When FiO2 is below 50%, recruitment maximized, and patient is breathing spontaneously, continuous gradual wean can begin by:

1) Decrease P high by 1-2 cm H2O AND increasing T high by 0.5 seconds for every 1 cm H20 drop in p high (drop and stretch)
2) Drop and stretch every 2 hours as tolerated. P mean gradually lowered so will need to monitor SpO2.
3) When P high reaches 10 cm H20 and T high reaches 12-15 seconds, change the mode to CPAP with PEEP at 10 and PS at 5-10 (ATC off). 



Evidence

  • RCT of 52 pediatric patients with pediatric ARDS (stopped early due to harm in the APRV/intervention group) showed increased mortality (multivariable adjusted RR of 2.02 , p=0.05) in the APRV group compared to conventional ventilation. (Ganesan et al, AJRCCM 2018)
  • A trial of APRV in 138 adult patients with ARDS found (Zhou et al, ICM 2017)higher median number of ventilator free days (19 vs 2) as well as shorter ICU stay and a trend toward improved mortality rates.
From Ganesan et al (AJRCCM 2018):