Lecture Notes on APRV Settings and Physiologic Rationale

Introduction

• Workshop format: informal discussion
• Goal: Discuss settings for APRV (Airway Pressure Release Ventilation)
• Focus on the settings, rationale, and encourage questions
• Emphasis on prevention of acute lung injury, ARDS, and ICU disease

Background on APRV

• Conceptualized as a CPAP-type breath where patients can superimpose their breathing pattern
• CPAP is intermittently released to aid in metabolic loading, create favorable inspiration points, and decrease work of breathing
• Main goal: Decrease elastic and metabolic work of breathing, and maintain compliance

Main Settings for APRV

• APRV settings can be adjusted based on lung mechanics and disease spectrum
• Key elements: P High, P Low, T High, T Low
• Focus: Maintain alveolar volume and prevent lung collapse

Detailed Explanation of Settings

P Low

• Set to zero, controlled by time instead of pressure
• Purpose: Maintain alveolar stability and prevent de-recruitment
• Importance of time constants over pressure for end expiratory lung volume
• Adjust based on peak expiratory flow

P High

• Purpose: Create enough pressure for stable part of the pressure-volume curve
• Adjust according to patient condition, e.g., higher for patients with high intra-abdominal pressure
• Maintain lung volume against forces causing collapse
• Continuous recruitment maneuver concept

T High

• Long T High periods encourage diffusive ventilation and alveolar stability
• Adjust to increase patient contribution to minute ventilation
• Use prolonged T High in initial phases to maintain diffusion

T Low

• Maintain alveolar stability and prevent de-recruitment
• Do not alter for hypercarbia; focus on P High and T High instead

Spontaneous Breathing in APRV

• Encouraged to start within 24 hours of admission
• Switches the patient’s focus to expiratory muscle use
• Better distribution of ventilation and maintenance of lung volume

Clinical Application and Patient Management

• Use early in critically ill patients and adjust based on patient feedback
• Maintain lung volume to prevent complications
• Transition to CPAP when patient shows capability

Troubleshooting and Weaning

• Ensure adequate P High and adjust T High for optimal alveolar volume
• Reduce T High only when other methods are exhausted
• Monitor patient’s work of breathing and adjust settings accordingly

Conclusion

• APRV aims to maintain alveolar stability, improve ventilation efficiency, and reduce complications
• Adjust settings based on lung mechanics, disease state, and patient feedback
• Use as a continuous supportive strategy to manage critically ill patients effectively.