Airway Pressure Release Ventilation (APRV)

Pressure Release Ventilation (PRV), also known as Airway Pressure Release Ventilation (APRV), sometimes referred to as BiVent, is a mode of mechanical ventilation that provides two levels of continuous positive airway pressure (CPAP) and allows spontaneous breathing throughout the respiratory cycle. It is particularly useful for patients with acute respiratory distress syndrome (ARDS) and other forms of severe respiratory failure.

Concept:

  • APRV works based on the principle of keeping the lungs open (open lung approach) to improve oxygenation.
  • It achieves this using two pressure levels:
    • High Pressure (P-high): This is a continuous positive airway pressure (CPAP) like setting that keeps the alveoli (air sacs) open for gas exchange.
    • Low Pressure (P-low): This is a brief, time-cycled release phase that allows for exhalation and removal of carbon dioxide (CO2).
    • Spontaneous Breathing: Patients can breathe spontaneously at any time during the respiratory cycle, which helps improve ventilation-perfusion matching and oxygenation.

Key Points:

  • P-high: The high pressure phase that helps keep the alveoli open and improves oxygenation.
  • P-low: The low pressure phase that allows for exhalation and helps eliminate CO2.
  • T-high: The duration of time the ventilator stays at P-high.
  • T-low: The duration of time the ventilator stays at P-low.

How It Works:

  1. High Pressure Phase (P-high): The ventilator maintains a high airway pressure for a set duration (T-high), which helps recruit and stabilise alveoli, improving oxygenation.
  2. Release Phase: After the T-high period, the ventilator drops to a lower pressure (P-low) for a short duration (T-low), allowing for passive exhalation.
  3. Cycle Repeat: The cycle of P-high and P-low continues, with the patient able to breathe spontaneously at both pressure levels.

Indications:

  • Acute Respiratory Distress Syndrome (ARDS): PRV is effective in improving oxygenation and lung recruitment in ARDS patients.
  • Severe Hypoxaemia: Patients with refractory hypoxaemia benefit from the improved alveolar recruitment and oxygenation provided by PRV.
  • Acute Lung Injury (ALI): Similar to ARDS, patients with ALI can benefit from the lung-protective strategies of PRV.

Advantages:

  • Improved Oxygenation: The sustained high pressure helps keep alveoli open, enhancing oxygenation.
  • Spontaneous Breathing: Allows for more natural breathing patterns and better patient comfort.
  • Reduced Ventilator-Induced Lung Injury: By maintaining alveolar recruitment and reducing cyclic opening and closing of alveoli, PRV can reduce the risk of ventilator-induced lung injury.
  • Reduced Strain on the Heart: The constant pressure support of APRV may help to decrease the workload on the heart, which can be beneficial for patients with compromised cardiovascular function.

Disadvantages:

  • Complexity: PRV requires careful setting adjustments and close monitoring, which can be complex and time-consuming.
  • Potential for Hypercapnia: The short release phase (T-low) might not be sufficient for adequate CO2 elimination in some patients.
  • Requires Patient Effort: PRV is more suitable for patients who have some degree of spontaneous breathing effort.

Clinical Monitoring and Management:

  • Adjusting Settings: Clinicians must carefully set and adjust P-high, P-low, T-high, and T-low to optimise oxygenation and ventilation while minimising risks.
  • Monitoring: Continuous monitoring of arterial blood gases, tidal volumes, and patient comfort is crucial.
  • Weaning: Gradually reducing P-high and increasing T-low can help transition patients to conventional ventilation modes or spontaneous breathing.

Summary:

Pressure Release Ventilation (PRV) is a dynamic mode of mechanical ventilation designed to improve oxygenation and alveolar recruitment while allowing spontaneous breathing. Its application in ARDS and severe respiratory failure makes it a valuable tool in critical care, though it requires careful management and monitoring.

References:

  1. Intensive Care Society – ARDS Guideline.
    • Provides comprehensive guidelines on the management of ARDS, including ventilation strategies like PRV.
  2. British Thoracic Society – Guidelines and Standards.
    • Offers guidelines on respiratory care practices, including invasive ventilation methods such as PRV.
  3. MacIntyre, N. R., & Branson, R. D. (2009). Mechanical Ventilation. Elsevier Health Sciences.
    • Covers various aspects of mechanical ventilation, including detailed explanations and clinical guidelines for PRV.
  4. Kacmarek, R. M., Stoller, J. K., & Heuer, A. J. (2016). Egan’s Fundamentals of Respiratory Care. Elsevier.
    • A comprehensive resource on respiratory care, offering in-depth discussions on different ventilation modes, including Pressure Release Ventilation (PRV).