Mechanical Ventilation: Bilevel Ventilation (Respiratory Therapy)

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ALERT

Bilevel ventilation is not recommended in patients who have deep or heavy sedation or obstructive lung conditions that require longer expiratory time.

Neuromuscular blockade should not be used with bilevel ventilation that requires spontaneous breathing to meet the patient’s ventilatory needs.

OVERVIEW

Bilevel uses pressure-controlled, time-triggered, and time-cycled settings that allows unrestricted, spontaneous breathing with or without pressure support (PS).^{undefined#ref3">3} Similar modes, like BiVent^™ and DuoPAP^™, have brand-specific terminology and settings.³ Bilevel recruits dependent lung regions without increasing airway pressure, making it a lung-protective strategy for managing acute respiratory distress syndrome (ARDS), pneumonia, and atelectasis by maximizing alveolar recruitment while minimizing pressure-related lung injury. Bilevel incorporates the principles of airway pressure release ventilation (APRV) when inverse ratio ventilation (IRV) is used.⁴ There is limited consensus on initial settings, so a time-controlled adaptive ventilation (TCAV) protocol should be considered when using APRV.¹

Bilevel uses two set pressures, called P high, to keep lungs open and improve oxygenation, and P low, where ventilation and carbon dioxide removal occurs (Figure 1). The difference between P high and P low determines the tidal volume (VT) delivered.⁶ The difference between P high and P low should be adjusted to deliver a VT of 6 to 8 mL/kg in accordance with ARDS Network protocol.⁵ Depending on the brand of ventilator used, the PS is generally applied at P low. PS should be set correctly for P high according to the manufacturer’s instructions, as this can vary between ventilators.

Bilevel uses a set frequency in conjunction with three time-variable options to determine the time at P high and P low. The set frequency may be referred to as the release rate or release breath, which means the number of times the ventilator releases the pressure from P high to P low in a 60-second time frame. Although there are three possible time-variable options available, only one of them is a set value that is locked constant. The other two time-variables are determined by the set frequency and the set time-variable that is locked constant. Three time-variable options include:

• Time high (T high), which is the length of time at P high
• Time low (T low), which is the length of time at P low
• Time high-to-time low ratio (T high:T low), which is the ratio of time at P high to P low

The T high:T low ratio is known as the inspiratory-to-expiratory (I:E) ratio in relationship to the total ventilatory cycle during conventional ventilation modes. The T high:T low value is often set for inverse ratio ventilation (IRV), where inspiratory time is longer than expiratory time, increasing mean airway pressure (MAP) and optimizing gas exchange. Patients with obstructive lung disease may not tolerate bilevel due to auto-positive end-expiratory pressure (PEEP) and IRV causing patient-ventilator asynchrony.^4,6

SUPPLIES

See Supplies tab at the top of the page.

EDUCATION

• Give developmentally and culturally appropriate education based on the desire for knowledge, readiness to learn, preferred learning style, 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. Assess the patient for indications for bilevel use and signs of ARDS.³
   1. Decreasing partial pressure of arterial oxygen/fraction of inspired oxygen (PaO₂/FIO₂) ratio
   2. Increasing plateau pressure, peak inspiratory pressure (PIP), or mean airway pressure (MAP)
   3. Bilateral lung infiltrates on a chest radiograph
2. Assess the patient’s hemodynamic and cardiorespiratory systems.
3. Determine if the patient or family has health literacy needs or requires tools or assistance to effectively communicate. Be sure these needs can be met without compromising safety.
4. Review the patient’s and family’s previous experience and knowledge of mechanical ventilation and understanding of the care to be provided.

Preparation

1. Gather equipment, including the ventilator with bilevel or equivalent mode, circuit, humidification device, filters (if needed), manual resuscitation bag, 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, initials or signature, and credentials of the respiratory therapist (RT).
3. Verify the authorized practitioner’s order for the initiation of mechanical ventilation.
4. Consider a TCAV protocol to guide ventilator settings and strategy when using APRV, whether the patient is newly intubated or being transitioned from conventional ventilation.

PROCEDURE

1. Clean hands and put on appropriate personal protective equipment (PPE) based on the risk of exposure to body fluids or infection precautions.
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 bilevel from conventional ventilation.

   Setting options, terminology, and abbreviations may be brand specific based on the trademarked mechanical ventilator specifications.⁶

5. Set P high.
   1. Use the measured plateau pressure if transitioning from a volume-controlled mode as a starting point.^1,3
   2. Use the set inspiratory pressure if transitioning from a pressure-controlled mode as a starting point.^1,3

      P high should not exceed 30 cm H₂O to minimize the risk of ventilator-induced lung injury.^3,6

6. Set P low at 0 cm H₂O, although 2 to 5 cm H₂O may be preferred.^1,3
7. Set the frequency.
8. Determine which of the time-variable settings will be constant and locked if this option is available. Time-variable options include:
   1. T high is the length of time at P high.
   2. T low is the length of time at P low.
   3. T high:T low ratio is the length of time at P high in relationship to P low.

      There are three possible time-variable options available, but only one at a time can be set constant or locked in the bilevel mode.

9. Set the constant time and the lock icon to the closed position on the time-variable that is desired to remain constant, if this option is available.

   Locking one of the time-variable settings ensures that the time-variable remains constant even when changes occur in the set frequency.

10. Set the T high, T low, or T high:T low ratio and adjust according to the patient’s needs.
    1. Set T high from 3 to 6 seconds.⁶
    2. Set T low from 0.5 to 0.8 seconds.⁶
    3. T high:T low ratio may be set as a conventional ratio or as an inverse ratio.
11. Set the inspiratory rise time (%) for patient comfort.
12. Set the patient sensitivity for flow-triggered or pressure-triggered spontaneous breaths.
13. Set the PS as needed to increase spontaneous VT at P low and P high.
    1. Verify spontaneous supported breaths at P low with the pressure-time waveform.

       PS is generally applied to P low and designed to support spontaneous breaths at P low.

    2. Verify spontaneous supported breaths at P high with the pressure-time waveform.

       Consider the difference between P high and P low when setting PS for P high. Refer to the brand-specific mechanical ventilator manual for specific recommendations.

14. Set the FIO₂ for the desired PaO₂ or peripheral oxygen saturation (SpO₂) level as prescribed.
15. Adjust settings based on the patient’s release and spontaneous VT, SpO₂, end-tidal carbon dioxide (ETCO₂), arterial blood gas (ABG) values, expiratory flow pattern, and clinical status.
    1. To decrease partial pressure of carbon dioxide (PaCO₂):
       1. Decrease T high (less time at T high allows more PaCO₂ removal at T low).
       2. Increase P high in 2- to 3-cm H₂O increments to increase MAP and tidal volume.⁶

          Monitor VT and PIP, which should be below 30 cm H₂O.⁶

       3. Increase set frequency.

          Rationale: More release breaths to P low means more time to remove PaCO₂.

    2. To increase PaCO₂:
       1. Decrease set frequency.
       2. Increase T high.
       3. Decrease P high.

          Monitor oxygenation and avoid alveolar derecruitment.²

    3. To increase PaO₂:
       1. Increase FIO₂.
       2. Increase T high.
       3. Increase P high.

          Rationale: Longer time at P high increases MAP, alveolar recruitment, and oxygenation.

       4. Decrease set frequency.

          Rationale: Less time at T low means less alveolar derecruitment time.

16. Ensure that all ventilator alarms are on and set appropriately for the patient’s individual ventilator settings.
17. Remove PPE and clean hands.
18. Document the procedure in the patient’s record.

MONITORING AND CARE

1. Regularly perform a check of ventilator settings, alarms, and measured parameters.
2. Monitor the patient’s ventilator pressure-time and flow-time waveforms to evaluate spontaneous and delivered pressure and inspiratory and expiratory flow patterns.
3. Maintain the humidification device and circuit temperature, if applicable, to avoid excessive condensation in the ventilator circuit.
4. Assess the patient’s overall level of comfort and patient-ventilator synchrony.
5. To minimize alveolar derecruitment, consider using a closed suction device to minimize the number of times the patient is disconnected from the ventilator.

EXPECTED OUTCOMES

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

UNEXPECTED OUTCOMES

• Alveolar overdistention
• Alveolar derecruitment
• Patient-ventilator asynchrony
• Pneumothorax
• Worsening oxygenation
• Worsening ventilation
• Ventilator-associated event (VAE)
• Hemodynamic compromise

DOCUMENTATION

• P high
• P low
• T high
• T low
• MAP
• FIO₂
• T high:T low ratio (set)
• I:E ratio (actual)
• PS
• Inspiratory rise time (%)
• Minute volume (total)
• Minute volume (spontaneous)
• Exhaled VT release breath
• Exhaled VT spontaneous breath
• Frequency (set)
• Respiratory rate (total)
• Patient’s tolerance of procedure
• Education
• Unexpected outcomes and related interventions

REFERENCES

1. APRV-TCAV Network. (2020). APRV-TCAV standard guidelines 2020. Retrieved April 25, 2025, from https://www.tcavnetwork.org/download/aprv-tcav-standard-guidelines-2020/
2. Cairo, J.M. (2024). Chapter 5: Selecting the ventilator and the mode. In Pilbeam’s mechanical ventilation: Physiological and clinical applications (8th ed., pp. 62-84). St. Louis: Elsevier.
3. Cairo, J.M. (2024). Chapter 23: Special techniques used in ventilatory support. In Pilbeam’s mechanical ventilation: Physiological and clinical applications (8th ed., pp. 492-521). St. Louis: Elsevier.
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. NIH NHLBI ARDS Clinical Network. (n.d.). Mechanical ventilation protocol summary. Retrieved April 25, 2025, from http://www.ardsnet.org/files/ventilator_protocol_2008-07.pdf
6. 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

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.

Clinical Review: Jennifer Elenbaas, MA, BS, RRT, AE-C

Published: June 2025