Although Emerson conceived of high-frequency oscillation in 1952 and Butler et al clinically validated his concept in 1980, the development of HFPV by the VDR is a relatively new and underexplored topic. In the limited published experience with HFPV in neonates, it is suggested that this method may improve oxygenation and CO2 elimination in premature infants with hyaline membrane disease. Gallagher et al was the first to report the use of HFPV in adults. They studied six patients with ARDS and increased ventilatory requirements on CV, and demonstrated a dramatic improvement in Pa02 levels, a slight fall in PaC02 levels, and no change in cardiac output. Hurst et al evaluated patients who developed ARDS after trauma. Hypoxemic patients showed significant improvement in Pa02 and pulmonary shunt after treatment with HFPV. this
Similarly, hypercarbic patients had improved CO2 elimination with a lower level of CPAP. There was no improvement in, or detriment to, cardiac output. An additional advantage of HFPV was shown by the same group in head-injured patients. The decrease in PIP and CPAP caused by HFPV reflected lower intracranial pressure values. In the only large-scale study that exists in the literature, 100 patients who entered a SICU and were thought to be at risk of developing respiratory failure were randomized to receive either HFPV or CV. Patients were treated to the same therapeutic endpoints (pH, > 7.35; Paco2, 35 to 45 mm Hg; Pao2/Fio2, > 225). Although patients on HFPV reached the therapeutic endpoints at a lower level of pulmonary pressures, there was no significant difference in mortality, ICU days, hospital days, and incidence of barotrauma.
The favorable gas exchange profile offered by HFPV results in immediate improvement in oxygenation, as shown in our study. This improvement is consistent over different types of CV (volume-con-trol or pressure-control) or patient diseases (medical or surgical). Pressure-control ventilation is usually reserved for the most sick patients. In these patients, conversion to HFPV improved dramatically their oxygenation. Patients who were initially maintained at volume-control CV had generally higher Pa02/ Fio2 ratios than pressure-control patients; this may be the reason that the mean ratio, although elevated after HFPV, was not improved significantly. This absence of statistical significance could also be a result of the limited number of patients available for analysis.
Tags: ARDS, high-frequency percussive ventilation, mean airway pressure, oxygen consumption, oxygen delivery, Pao2/fraction of inspired oxygen, peak inspiratory pressure