Mechanical Ventilation: Airway Pressure Release Ventilation (Respiratory Therapy)

ALERT

Don appropriate personal protective equipment (PPE) based on the patient’s signs and symptoms and indications for isolation precautions.

Airway pressure release ventilation (APRV) is not recommended in patients who require deep or heavy sedation.

Neuromuscular blockade should not be used with APRV that requires a spontaneously breathing patient.

OVERVIEW

APRV is a time-triggered, pressure-limited, time-cycled mode of ventilation that uses extreme inverse inspiratory-to-expiratory (I:E) ratios that allows unrestricted spontaneous breathing with or without pressure support throughout the entire ventilatory cycle. By allowing patients to spontaneously breathe during APRV, dependent lung regions may be preferentially recruited without the need to raise applied airway pressure. There are several modes that are like APRV but use different manufacturer names, including but not limited to BiVent^™ and DuoPAP^™. Setting options, terminology, and abbreviations may be brand specific based on the mechanical ventilator specifications.^{undefined#ref3">3} APRV is a lung-protective strategy that helps to meet the goals of acute respiratory distress syndrome (ARDS) management and to diffuse pneumonia and atelectasis by maximizing alveolar recruitment while limiting the transalveolar pressure gradient and barotrauma.

Conceptually, APRV applies a high continuous positive airway pressure (CPAP) (P high) identical to CPAP for a prolonged time (T high) to maintain adequate lung volumes that promote alveolar recruitment and oxygenation. However, APRV adds a time-cycled release phase to a lower set CPAP (P low) for a short period of time (T low, or release time) where most of the ventilation and carbon dioxide removal occurs (Figure 1). The goal is to maintain adequate oxygenation and ventilation without alveolar overdistention at P high or intrinsic positive end-expiratory pressure (PEEP) at P low.

Very few randomized controlled trials have been conducted to study APRV, and consensus among practitioners regarding initial APRV settings is limited.⁶ A time-controlled adaptive ventilation (TCAV) protocol should be used to establish appropriate APRV settings for each patient.⁵

Given the current focus on the deleterious side effects of sedation medication and neuromuscular blockade, including delirium,^2,6 APRV may be a good option to improve patient-ventilator synchrony without the need for heavy sedation or neuromuscular blockade. APRV has been shown to improve oxygenation, achieve a better ventilation–perfusion match, and decrease dead space compared with conventional mechanical ventilation.⁴

In APRV, the extended inspiratory time increases the mean airway pressure (MAP). Increasing the T high and P high increases MAP and lengthens the time for gas mixing, thereby optimizing the gas exchange surface area that promotes oxygenation.

In APRV, ventilation may be optimized by the T high, P high, and T low settings. Arterial partial pressure of carbon dioxide (PaCO₂) levels may rise if T high is increased, P high is decreased, or T low is decreased. If the measured PaCO₂ becomes excessively high, incremental adjustments to decrease T high, increase P high, or increase T low should allow for more carbon dioxide release that should bring the PaCO₂ down to the desired level.

Patients who have obstructive lung disease with airflow obstruction and who require a prolonged expiratory time may not tolerate APRV because of patient-ventilator asynchrony caused by auto-PEEP and inverse I:E ratios.

EDUCATION

• Provide developmentally and culturally appropriate education based on the desire for knowledge, readiness to learn, and overall neurologic and psychosocial state.
• Explain the need for ventilator changes to the patient and family.
• Encourage questions and answer them as they arise.

ASSESSMENT AND PREPARATION

Assessment

1. Perform hand hygiene before patient contact. Don appropriate PPE based on the patient’s need for isolation precautions or the risk of exposure to bodily fluids.
2. Introduce yourself to the patient.
3. Verify the correct patient using two identifiers.
4. Assess the patient’s level of consciousness and ability to understand and participate in decisions. Include the patient as much as possible in all decisions.
5. Observe the patient for signs of ARDS.
   1. Decreasing partial pressure of arterial oxygen/fraction of inspired oxygen (PaO₂/FIO₂) ratio
   2. Increasing plateau pressure, peak inspiratory pressure (PIP), or MAP
   3. Bilateral infiltrates on a chest radiograph
6. Assess the patient’s hemodynamic and cardiorespiratory systems.

Preparation

1. Gather equipment, including a ventilator with APRV mode, circuit, humidification device, filters (if needed), and closed-suction device.
2. Before initiating the mechanical ventilator, check the system microprocessor or ventilation system. Perform a short self-test as appropriate.
   1. Verify compliance of the ventilator circuit with the humidification device and filters (if needed).
   2. Document the completed ventilation system test. Include pass or fail, date, and initials or signature and credentials of the respiratory therapist (RT).
3. Verify the authorized practitioner’s order for the initiation of mechanical ventilation.
4. Use a TCAV protocol to guide ventilator settings and strategy when using APRV.

PROCEDURE

1. Perform hand hygiene and don gloves. Don additional PPE based on the patient’s need for isolation precautions or the risk of exposure to bodily fluids.
2. Verify the correct patient using two identifiers.
3. Explain the procedure and ensure that the patient agrees to treatment.
4. Transition the patient to APRV from conventional ventilation settings.
   1. Set P high by using the measured plateau pressure of the volume-controlled mode or the set peak airway pressure of the pressure-controlled mode that should result in an expired minute ventilation that is several liters per minute less than the conventional ventilation settings. Typically, the maximum goal for P high is 30 cm H₂O.⁷

      Rationale: Limiting P high to 30 cm H₂O may minimize ventilator-associated lung injury.⁷

   2. Set P low at 0 cm H₂O.⁷

      Rationale: P low of 0 produces minimal expiratory resistance and facilitates rapid pressure drops, thus accelerating unimpeded expiratory flow rates.³

   3. Set T high from 3 to 6 seconds and adjust according to the patient’s needs.⁷

      Rationale: T high of less than 3 seconds may result in lower MAP that may not achieve alveolar recruitment.⁷ T high of greater than 6 seconds may cause carbon dioxide retention.⁷

   4. Set T low from 0.5 to 0.8 seconds as determined by the TCAV protocol including expiratory gas flow curve analysis.⁷

      Rationale: The goal is to terminate expiratory gas flow at about 75% to 50% of the peak expiratory flow rate to prevent the peak expiratory flow from returning to a zero baseline.³ T low should be short enough to prevent alveolar derecruitment and long enough to obtain a suitable tidal volume (VT).⁴

5. Transition the patient who is newly intubated to APRV.
   1. Set P high to a maximum of 30 cm H₂O (this higher transalveolar pressure recruits the lungs).⁷
   2. Set P low at 0 cm H₂O.³
   3. Set T high from 3 to 6 seconds and adjust according to the patient’s needs.⁷
   4. Set T low from 0.5 to 0.8 seconds.⁷
   5. Set FIO₂ for the desired PaO₂ or peripheral oxygen saturation (SpO₂) level.
   6. Set pressure support as needed to augment spontaneous breathing efforts.
6. Transition the patient to APRV from high-frequency oscillatory ventilation (HFOV).
   1. Set P high using the set MAP on HFOV plus 2 to 4 cm H₂O.⁷
   2. Set P low at 0 cm H₂O.⁷
   3. Set T high from 3 to 6 seconds and adjust according to the patient’s needs.⁷
   4. Set T low from 0.5 to 0.8 seconds.⁷
   5. Set pressure support as needed to augment spontaneous breathing efforts.
7. Adjust settings based on the patient’s release and spontaneous VT, SpO₂, end-tidal carbon dioxide (ETCO₂), arterial blood gas (ABG) values, expiratory gas flow pattern, and clinical status.
   1. To decrease PaCO₂:
      1. Decrease T high to no shorter than 3 seconds.³

         Rationale: A shorter T high means more releases per minute.

      2. Increase P high in 2- to 3-cm H₂O increments to increase MAP and volume exchange.⁷

         Monitor VT and peak inspiratory pressure, which is best below 30 cm H₂O.³

      3. Increase T low to allow more time for exhalation and PaCO₂ removal.

         Monitor oxygenation because increasing T low may cause alveolar derecruitment.¹

   2. To increase PaCO₂:
      1. Increase T high (fewer releases per minute) slowly.
      2. Decrease P high to decrease MAP and volume exchange.

         Monitor oxygenation and avoid alveolar derecruitment.¹

   3. To increase PaO₂:
      1. Increase FIO₂.
      2. Increase MAP by increasing P high in 2-cm H₂O increments.⁷
      3. Increase T high slowly (in 0.5-second increments).⁷
      4. Use alveolar recruitment maneuvers.
      5. Consider decreasing T low in 0.1-second increments (this may reduce VT and affect PaCO₂).⁷
8. Evaluate the patient’s readiness for weaning.
   1. Wean FIO₂ to 40% first to rule out refractory hypoxemia.
   2. Simultaneously decrease P high and increase T high incrementally until transitioning to CPAP is possible.^1,7
      1. Decrease P high in 2- to 3-cm H₂O increments until it is less than or equal to 10 cm H₂O.¹
      2. Increase T high in 0.5- to 2-second increments until it is approximately 12 to 15 seconds.¹
      3. Changes should be incremental, and the time interval between each simultaneous P high and T high change is patient dependent.
   3. Transition to CPAP mode.
   4. Set pressure support as needed to augment spontaneous breathing efforts.

      Rationale: Pressure support augments spontaneous breathing efforts and volumes.

9. Remove PPE and perform hand hygiene.
10. Document the procedure in the patient’s record.

MONITORING AND CARE

1. Regularly perform a check of ventilator settings and measured parameters.
2. Ensure that all ventilator alarms are on and set appropriately for the patient’s individual ventilator settings.
3. Monitor the patient’s ventilator pressure-time and flow-time waveforms to evaluate spontaneous and delivered pressure and inspiratory and expiratory flow patterns.
4. Monitor the patient’s SpO₂, ETCO₂ level, and hemodynamic status.
5. Report any signs of increase in MAP.
6. Assess the patient’s exhaled minute volume, release VT, and spontaneous VT.
7. Monitor the patient’s ABG values as needed.
8. Assess the patient’s overall level of comfort.
9. To minimize alveolar derecruitment during the suction procedure, consider using a closed-suction device to minimize the number of times the patient is disconnected from the ventilator.
10. Observe the patient for signs or symptoms of pain. If pain is suspected, report it to the authorized practitioner.

EXPECTED OUTCOMES

• Improved oxygenation
• Improved ventilation
• Improved patient-ventilator synchrony and comfort
• Alveolar recruitment
• Minimal ventilator-induced lung injury
• Reduced sedation requirements

UNEXPECTED OUTCOMES

• Alveolar overdistention
• Alveolar derecruitment
• Increased work of breathing
• Worsening oxygenation
• Worsening ventilation

DOCUMENTATION

• P high
• P low
• T high
• T low
• FIO₂
• T high:T low ratio (set)
• I:E ratio (actual)
• Pressure support
• Minute volume (total)
• Minute volume (spontaneous)
• Exhaled VT release breath
• Exhaled VT spontaneous breath
• Respiratory rate (total)
• MAP
• SpO₂
• ETCO₂ (optional)
• Patient’s tolerance of procedure
• Education
• Unexpected outcomes and related interventions

REFERENCES

1. Cairo, J.M. (Ed.). (2020). Chapter 5: Selecting the ventilator and the mode. In Pilbeam’s mechanical ventilation: Physiological and clinical applications (7th ed., pp. 58-79). St. Louis: Elsevier.
2. Devlin, J. and others. (2018). Clinical practice guidelines for the prevention and management of pain, agitation/sedation, delirium, immobility, and sleep disruption in adult patients in the ICU. Critical Care Medicine, 46(9), e825-e873. doi:10.1097/CCM.0000000000003299 (Level I)
3. Hess, D.R., Kacmarek, R.M. (Eds.). (2019). Chapter 8: Advanced modes of mechanical ventilation. In Essentials of mechanical ventilation (4th ed., pp. 73-86). New York: McGraw-Hill Education.
4. Holt, G.A., Habib, S.A., Shelledy, D.C. (2020). Chapter 3: Principles of mechanical ventilation. In D.C. Shelledy, J.I. Peters (Eds.), Mechanical ventilation (3rd ed., pp. 95-154). Burlington, MA: Jones & Bartlett Learning.
5. Kollisch-Singule, M. and others. (2019). The time-controlled adaptive ventilation protocol: Mechanistic approach to reducing ventilator-induced lung injury. European Respiratory Review, 28(152), 180126. doi:10.1183/16000617.0126-2018 (Level VII)
6. Mallory, P., Cheifetz, I. (2020). A comprehensive review of the use and understanding of airway pressure release ventilation. Expert Review of Respiratory Medicine, 14(3), 307-315. doi:10.1080/17476348.2020.1708719 (Level VII)
7. Shelledy, D.C., Peters, J.I. (2020). Chapter 6: Ventilator initiation. In D.C. Shelledy, J.I. Peters (Eds.), Mechanical ventilation (3rd ed., pp. 311-366). Burlington, MA: Jones & Bartlett Learning.

ADDITIONAL READINGS

Carsetti, A. and others. (2019). Airway pressure release ventilation during acute hypoxemic respiratory failure: A systematic review and meta-analysis of randomized controlled trials. Annals of Intensive Care, 9(44), 1-9. doi:10.1186/s13613-019-0518-7

Fredericks, A.S. and others. (2020). Airway pressure release ventilation: A review of the evidence, theoretical benefits, and alternative titration strategies. Clinical Medicine Insights: Circulatory, Respiratory and Pulmonary Medicine, 14, 1-9. doi:10.1177/1179548420903297

Nieman, G.F. and others. (2020). Prevention and treatment of acute lung injury with time-controlled adaptive ventilation: Physiologically informed modification of airway pressure release ventilation. Annals of Intensive Care, 10(3), 1-16. doi:10.1186/s13613-019-0619-3

Othman, F. and others. (2021). The efficacy of airway pressure release ventilation in acute respiratory distress syndrome adult patients: A meta-analysis of clinical trials. Annals of Thoracic Medicine, 16(3), 245-252. doi:10.4103/atm.ATM_475_20

Shelledy, D.C., Peters, J.I. (2020). Chapter 7: Patient stabilization: Adjusting ventilatory support. In D.C. Shelledy, J.I. Peters (Eds.), Mechanical ventilation (3rd ed., pp. 367-400). Burlington, MA: Jones & Bartlett Learning.

Elsevier Skills Levels of Evidence

• Level I - Systematic review of all relevant randomized controlled trials
• Level II - At least one well-designed randomized controlled trial
• Level III - Well-designed controlled trials without randomization
• Level IV - Well-designed case-controlled or cohort studies
• Level V - Descriptive or qualitative studies
• Level VI - Single descriptive or qualitative study
• Level VII - Authority opinion or expert committee reports