Experiences Using Airway Pressure Release Ventilation for Pneumonia with Severe Hypercapnia or Postoperative Pulmonary Edema

Abstract

Airway pressure release ventilation (APRV) was introduced as a new method to manage a supportive level of continuous positive airway pressure (CPAP) while simultaneously assisting CO2 elimination [1,2]. APRV maintains CPAP while permitting spontaneous breathing without airway pressure fluctuation [2] and producing alveolar ventilation [3]. It is an established mode of ventilation based on the openlung approach with the following settings: (1) pressure during the inspiration/ CPAP phase (Phigh); (2) time during the inspiration/CPAP phase (Thigh); (3) pressure during the expiration/release phase (Plow); (4) time during the expiration/ release phase (Tlow); and (5) percent CPAP (%CPAP) to reflect the time spent at Phigh relative to the entire breath duration [2] during which positive pressure (Phigh) was applied for a prolonged time (Thigh) with a release phase (Plow) that is short (Tlow) [1,4,5]. Without self-breathing, the APRV mode is like pressure-controlled inverse ratio ventilation [3]. For patients with acute respiratory distress syndrome (ARDS), the APRV mode has been used as an inverse ratio ventilation with a prolonged inspiratory time and a short expiratory time [3]. Potential benefits of APRV mode include recruitment of lung by rising functional residual capacity and reduction in atelectrauma by decreasing cyclic recruitment and derecruitment to improve ventilation/perfusion (V/Q) matching, while not restricting spontaneous breathing and reducing the sedatives and neuromuscular blockades requirements [4,5]. Because of these advantages, APRV mode is the most used and most studied mode for use in patients with ARDS. However, there have been few clinical trials showing that APRV can improve gas exchange, and it is uncertain whether APRV will improve clinical outcomes.