APRV-TCAV Basics
APRV (Airway Pressure Release Ventilation) was first described in 1987. Even after 30+ years, many still struggle with how and when to use it. This may be due to its infrequent use in many facilities. I believe this is because much of the data from APRV studies lack a consistent protocol, making them a poor representation of its efficacy.
Enter TCAV (Time-Controlled Adaptive Ventilation). TCAV is one of the most popular protocols to set APRV and was developed by Dr. Nader Habashi and his team. Here’s a simple breakdown of the recommended starting settings when transitioning from conventional ventilation:
- P High (Pressure High): Set using the plateau pressure from the previous mode.
- P Low (Pressure Low): Always set to 0 cmH₂O.
- T High (Time High): Duration of the CPAP phase, set to approximate the previous respiratory rate. This parameter can be shortened to increase respiratory rate and thus, increase bulk ventilation or lengthened to increase the time spent under the curve. Also note the equation for determining respiratory rate:
60 / (T High + T Low) = RR
- T Low (Time Low): Duration of the release phase, set to terminate at 75% of peak expiratory flow. This personalizes the mechanical breath profile based on lung and chest wall elastance. For example, ARDS patients typically need shorter T Low times due to their shorter time constants, while patients with higher compliance require longer T Low times.
I’ll cover T Low in detail tomorrow as it requires some waveform analysis to set accurately. Hope this helps!