The Pre-brief
Airway pressure release ventilation (APRV) is a pressure-controlled mode that has a longer inspiratory phase compared to the expiratory phase and allows the patient to breathe spontaneously while giving mandatory release phases for ventilation. It is often used as a rescue mode in patients with difficulty oxygenating in acute respiratory distress syndrome (ARDS). While this mode sounds great in theory, it does come with its limitations that should be considered prior to initiating it on any patient.
What is APRV?
APRV was introduced into clinical practice in the late 1980s. It was introduced as a salvage mode in patients with refractory hypoxemia and was thought to be useful because it allowed the combination of time cycled and patient effort breaths, alveolar recruitment by using inverse ratio breathing, and less ventilator-induced lung injury due to the avoidance of high pressures. The settings are different from other ventilator modes, which can make it a scary and difficult mode to use if you’re not familiar with it. Excluding the FiO2, there are four settings that are applied by the clinician, as noted in Table 1.
For more information on the background of this mode, you can refer to our previous post APRV 101.
However, before choosing this mode, consider the following limitations.
Limitations of APRV:
- There have been no randomized controlled trials assessing the efficacy of what the initial optimal settings specifically for APRV should be. Ideally, a clinician should set the P high above the upper inflection point of the pressure-volume curve, and the P low above the lower inflection point or at a level low enough to cause auto-PEEP. This is time-consuming, cumbersome, and some patients may not be paralyzed or sedated enough to allow for passive breathing to get the proper settings.
- Inevitably, by giving a short expiratory time (T low), there will be auto-PEEP, which is in part, the purpose of this mode. However, this can be variable with every breath and is determined by the lung elastance, compliance, and resistance, all of which dynamically change with mechanical ventilation.
- While spontaneous breathing may allow for less ventilator asynchrony, it is postulated that this may increase oxygen consumption and cause more stress on the patient, thus worsening hemodynamics, but studies have been conflicting regarding this.
- Patients with morbid obesity may need a higher P high, which can increase driving pressure and cause more lung injury.
- In specific patient populations, as in obstructive lung disease patients, a short expiratory time may cause more ventilator asynchrony and patient discomfort.
- Due to the air trapping, auto-PEEP, and short expiratory time, hypercapnia is a consequence of this mode. Oftentimes, in ARDS patients, this is already an issue, and it may be difficult to continue this mode if the patient becomes more acidotic.
- There have been no studies that suggest how to wean patients from APRV. Historically, the clinician gradually decreases the P high by increments of 2, while prolonging the T high by 0.5 seconds (drop and stretch method). Eventually, the patient will be on a continuous positive pressure mode (CPAP). During this time, a patient can suddenly have derecruitment and become more hypoxemic.
- There have been no large randomized control trials examining this mode and its benefits in ICU length of stay in medical intensive care units.
- While some studies have shown a trend towards decreasing mortality using APRV and one study showed an improvement in mortality (Zhou 2017), there have been no double-blind, large, randomized control trials examining APRV versus conventional volume or pressure-controlled ventilator modes in adults.
The Debrief
While APRV has its advantages, the disadvantages of this mode may outweigh the benefits of using it on your patient. Think about your patient’s clinical situation, acid-base, and volume status prior to initiating the mode, and always monitor your patient’s hemodynamics and get a blood gas 30 minutes to one hour after starting this mode to assess if any changes need to be made.
References
- Bein T, Wrigge H. Airway pressure release ventilation (APRV): do good things come to those who can wait?. J Thorac Dis. 2018;10(2):667-669.
- Daoud EG. Airway pressure release ventilation. Ann Thorac Med. 2007;2(4):176-179. doi:10.4103/1817-1737.36556
- Daoud, Ehab G, Farag, Hany L, Chatburn, Robert L. Airway Pressure Release Ventilation: What Do We Know? Respiratory Care. 2012;57(2):282-292.
- Sato, R., Hamahata, N. & Daoud, E.G. Are we really preventing lung collapse with APRV?. Crit Care 23, 178 (2019).
- Sun, Xuri MDa,∗; Liu, Yuqi MDa; Li, Neng MDb; You, Deyuan MDa; Zhao, Yanping MDc. The safety and efficacy of airway pressure release ventilation in acute respiratory distress syndrome patients, Medicine: 2020;99(1):p e18586.
- Zhou Y, Jin X, Lv Y, Wang P, Yang Y, Liang G, Wang B, Kang Y. Early application of airway pressure release ventilation may reduce the duration of mechanical ventilation in acute respiratory distress syndrome. Intensive Care Med. 2017 Nov;43(11):1648-1659.
APRV has worked in almost every patient I had to use as a rescue mode ( pre covid ) for oxygenation failure . 100% agree not a great literature to support its use. Cannot use if too acidotic, hypercarbic, bad obstructive airway disease and has high minute ventilation but if chosen wisely it absolutely works. I start the Phigh close to their plateau pressures on assist mode of the ventilator. One has to watch the tidal volumes on APRV as they might be in range that may be injurious but I will be a devil’s advocate here .We know 6ml/kg of IBW is better than 12 ml/kg IBW but I am not aware of any data to prove that 6 ml/kg is better than 8 (as long as Driving pressure is less than 14 i dont think it makes a difference ) I had literally patients watch tv, use tv remote, press call button , use their own suction to clean their mouth. on high vent settings with 80% FiO2 , with Phigh of any where from 26-30 with absolutely minimal sedation requirement. My experienced is a little skewed towards obese patients though where i think it works the best. I almost always provide some pressure support over Phigh to let them take whatever breath they want to take. Have people extubate straight from APRV. It works !