Wednesday, April 24, 2013

Limits of Pressure-Control Ventilation: a Introduction to the Mid-Frequency Simulator

In respiratory therapy school I was never taught about the various mathematical models of pressure-control ventilation (PC-CMV) and we probably only had a hour lecture on respiratory time constants. In clinical rotations PC-CMV was seldom used and had a bad reputation only being used on the sickest patients. This was due to the practice of utilizing  inverse-ratio ventilation in treating patients with ARDS and  serve hypoxia, which led to the administration of neuro-muscular blocking agents and poor outcomes.

Even today many practitioners are unfamiliar with the most versatile mode of ventilation (PC-CMV) and do not know how to optimize the settings. If one wants to have a understanding of the advance modes of ventilation, PC-CMV is were to start.

The above video introduces the "Mid-Frequency Simulator" [1], which was created from mathematical models of pressure-control ventilation [2]. This simulator is a good tool to help understand limitations of pressure control ventilation in regards to:

-Tidal volume delivery
-Minute ventilation
- Mean airway pressure
- Auto-PEEP

This simulator can also demonstrate the ideal way to set T-Low for lung protective goals 
when utilizing APRV (aka. BiLevel, BiVent).

These same models also can be applied to Adaptive Pressure Control ventilation to determine latency time and time for tidal volume equilibrium after changes in lung mechanics. 

I will be using this simulator as a teaching  tool, for my upcoming courses:

-Pressure Control Ventilation
-Adaptive Pressure Ventilation
- Mid-Frequency Ventilation



1. Chatburn, R. (2008). Mid-Frequency Ventilation Simulator. Cleveland Clinic. Cleveland, OH.
2. Marini, J. et. al. (1989). Determinants and limits of pressure-preset ventilation: a mathematical model of pressure control. Journal of Applied Physiology. 67 (3): 1081-1092. 
3. Chatburn, R. and Mireles-Cabodevila, E. (2011). Handbook of Respiratory Care. Third Edition. Jones & Barlett. Sudbury, MA.