ABSTRACT
Mechanical ventilation at high rates places special constraints on equipment design and operation. Ventilation at these higher rates is accompanied by increased flow and pressure transients. Monitoring the effectiveness of gas exchange with high frequency ventilation (HFV) is also different — and perhaps more difficult — than with conventional rates and volumes. This chapter discusses HFV system designs and addresses some of these special concerns. Many different methodologies have been devised for deliverying HFV. The number of design variations approximates the number of investigators in the field. Ultrasonic flowmeters, specially designed pneumotachs, and hot-wire anemometers may be used. Volume monitoring is inaccurate in open systems because there is no way to confirm that all of the escaping gas has actually participated in exchange with the lung. Size of the ventilation catheter may be an important factor in determining ventilatory efficacy.
