Flow-controlled expiration ventilation using a piston ventilator: effects of expiration time and speed on respiratory and pulmonary mechanics with focus on hysteresis and compliance in healthy horses.

Overview

• This study examined how different settings of flow-controlled expiration (FLEX) ventilation affect lung function in anesthetized healthy horses.
• The research compared traditional volume-controlled ventilation (VCV) to FLEX modes that control the speed and timing of lung emptying during expiration.

Introduction

• Mechanical ventilation supports breathing during anesthesia but traditional methods may not optimize lung mechanics.
• Flow-controlled expiration (FLEX) is a newer ventilation strategy aiming to control the rate and duration of air leaving the lungs during exhalation.
• This study focused on two FLEX modes: FLEX50 (emptying the lungs in 50% of expiration time) and FLEX100 (emptying over 100% of expiration time).
• The goal was to assess how these modes affect respiratory parameters such as lung compliance, hysteresis, and alveolar dead space.

Methods

• Subjects: Six healthy adult research horses, each anesthetized three times under controlled conditions.
• Study design: Randomized crossover, where each horse received all ventilation modes in random order, avoiding bias.
• Ventilation protocols:
  • VCV – Conventional volume-controlled ventilation.
  • FLEX50 – Flow-controlled expiration with linear lung emptying in first 50% of expiration time.
  • FLEX100 – Flow-controlled expiration with linear lung emptying throughout entire expiration.
• Duration: Each ventilation method applied for 60 minutes per anesthesia session.
• Primary outcomes measured:
  • Dynamic compliance (Cdyn): A measure of lung “stretchability” during breathing.
  • Hysteresis: The difference in lung inflation and deflation curves indicating energy loss or lung tissue changes.
  • Alveolar dead space: Portion of air in lungs not involved in gas exchange, indicating efficiency.
• Data analysis: Two-factor ANOVA with significance at P < .05.

Results

• Dynamic Compliance:
  • Horses ventilated with FLEX50 and FLEX100 demonstrated significantly higher dynamic compliance compared to VCV.
  • Improved compliance suggests lungs were more easily expanded during ventilation with FLEX modes.
• Hysteresis:
  • Both FLEX50 and FLEX100 showed significantly reduced hysteresis relative to VCV.
  • Lower hysteresis indicates better lung tissue mechanics and less energy loss during breathing cycles.
• Alveolar Dead Space:
  • FLEX50 ventilation led to the lowest alveolar dead space, significantly better than both FLEX100 and VCV.
  • FLEX100 also reduced alveolar dead space compared to VCV but not as much as FLEX50.
  • Reduced dead space means more effective gas exchange and improved respiratory efficiency.

Conclusions and Implications

• Both FLEX ventilation modes improved lung mechanics compared to traditional VCV in anesthetized healthy horses.
• The faster expiration setting FLEX50 provided additional benefits, notably the lowest alveolar dead space, suggesting enhanced respiratory efficiency.
• This research supports the potential use of flow-controlled expiration strategies to optimize mechanical ventilation in horses during anesthesia.
• Improved compliance and reduced hysteresis indicate more gentle and efficient lung inflation/deflation, which may benefit patient outcomes by reducing lung injury.
• Further studies could explore FLEX ventilation in diseased or compromised equine lungs and during different anesthesia settings.