High-frequency ventilation

Published on 07/02/2015 by admin

Filed under Anesthesiology

Last modified 07/02/2015

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High-frequency ventilation

Joshua Horowitz, DO and Keith A. Jones, MD

High-frequency ventilation (HFV) is the delivery of small tidal volumes (equal to or less than the anatomic dead space) at rates of 60 to 900 or more cycles per minute. The nomenclature for HFV includes high-frequency positive-pressure ventilation (HFPPV), high-frequency jet ventilation (HFJV), and high-frequency oscillation (HFO). High-frequency chest wall compression is occasionally discussed in the literature under the heading of HFV, but high-frequency chest wall compression is not used to ventilate patients; it is a chest physiotherapy technique used primarily on patients with cystic fibrosis to help them clear secretions.

Table 160-1 compares the major types of HFV. HFPPV can be delivered by a standard mechanical ventilator, though most are not designed to achieve rates greater than 60 to 100/min.

Physiology

Gas transport (i.e., O2 insufflation and CO2 elimination) at ventilation rates greater than 170 breaths/min depends on convection, diffusion, and other complex mechanisms that are very different from those that occur during conventional mechanical ventilation (CMV) and are not well understood. CO2 elimination can and does occur at tidal volumes that are much lower than the volume of air contained in the anatomic dead space. The decrease in airway resistance associated with HFV somehow facilitates penetration of gas to alveoli, alveolar minute ventilation, and CO2 elimination. However, CO2 elimination increases linearly as ventilation rate increases up to only a certain point (3-6 Hz; 180-360 breaths/min); at higher rates, dead-space to tidal volume ratio and alveolar minute ventilation are constant.

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