This is part 2 of our series focusing on assessing high-frequency oscillatory ventilation. Check out part one here.

Due to difficulties in assessing the outputs (from the patient’s perspective) of HFOV ventilators, many analysts have resorted to monitoring pressure outputs. The theory is that so long as an adequate FIO2 (fraction of inspired oxygen) reaches the patient and the pressures remain safe, the ventilation is a success. Unfortunately, this method does little to help us understand HFOV on a deeper level, and without this understanding, it is difficult to know how the science and practice of modern ventilation will progress in the future.

Why is it important to understand volume and flow parameters?

Measuring ventilated volume is a common way of fact-checking a ventilator. For the display on a ventilator to show an accurate delivered volume the vast majority of the unit’s internal systems must be working properly. Flow, similarly, can offer insight into what might be going wrong with one of these ventilators, should it malfunction or require calibration. These parameters are sometimes overlooked in testing as the ventilator itself will display variations of them. Other variables make themselves in apparent when the problem of calibration is approached scientifically. Compressible volume in the airway and lungs can damage the accuracy of calculations performed by the ventilator, and without the ability to control airway resistance and lung compliance to a known value outputs are not always consistent.

The patient’s perspective.

Changes in flow and volume must be explored from the perspective of the patient as a way to understand, calibrate, and tweak ventilators. This sort of testing, however, requires a new type of test lung device capable of measuring flows, volumes, and pressures at different points throughout the respiratory system of a simulated patient.

We’ll get into test lung devices in part three. In the meantime, if you have any questions about the use of high-frequency oscillatory ventilation, don’t hesitate to contact Michigan Instruments anytime.