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Three hundred nine patients were randomly allocated to two ventilatory protocols; 157 patients were supported with a volume-cycled ventilator (VCV) (Bear Medical BEAR 1) and 152 with a high-frequency jet ventilatory (HFJV) developed at our institution. The two ventilators were compared for safety, reliability, ease of use, and efficacy in maintaining gas exchange. On VCV, end points of therapy were: fractional concentration of oxygen in the inspired gas (FIo 2 ) ≤ 0.40; arterial oxygen pressure (PaO 2 ) ≥ 70 mm Hg; cardiac index (CI) ≥ 3.5 L/min/sq m; and spontaneous respiratory rate ≤ eight breaths per minute. On HFJV, end points were: FIo 2 ≤ 0.45; arterial oxygen saturation ≥ 0.90; and CI ≥ 3.5 L/min/sq m. Spontaneous ventilation and pulmonary venous admixture reduction were the goals on VCV, with oxygen transport the goal on HFJV, Total duration of use of the ventilators was approximately 800 days with both types of devices; there were no technical failures, and the incidence of barotrauma was less than 5 percent. The end point of mechanical ventilation was reached by a significantly higher percentage of the patients randomized to HFJV. Patients who failed to reach the therapeutic goal within 24 hours were crossed over to the other form of support. Those crossed from VCV to HFJV improved more rapidly and in greater number than those crossed from HFJV to VCV. When survival and total duration of stay in the intensive care unit were considered, there was no difference between VCV and HFJV. Considering data on gas exchange, VCV provided a higher PaO 2 at equivalent positive end-respiratory pressure than HFJV. Alveolar ventilation was slightly better on HFJV. Differences were statistically but not clinically significant. On HFJV, oxygenation and ventilation were maintained with lower peak inspiratory pressures and smaller tidal volumes than those required for VCV. This investigation proves that HFJV is a safe and reliable method to provide mechanical support which does not, at this time, offer obvious benefits over VCV.

High frequency jet ventilation (HFJV) is an incompletely studied technique of mechanical respiratory support. The authors have built a ventilator based on a solenoid valve, that allows independent selection of respiratory rate and inspiratory/expiratory ratio. The ventilator can be synchronized to the heart rate. Hum-idification is provided by warm saline dripped in front of the injector nozzle, so that the jet stream itself acts as a nebulizer. Tube diameter, length, and deformability are fundamental determinants of inspiratory flow rate and wave form. Cannula kinking and inadequate humidifi-cation were the most significant sources of complications.

A variety of technical decisions are required for the proper selection and safe and efficacious application of high-frequency jet ventilation (HFJV). Criteria for analyzing the performance of an HFJV system are presented, along with discussions of some of the more common respiratory measurements and their applicability to HFJV.

A pneumatic-to-electrical circuit analog is used to describe 2 separate mechanisms by which high-frequency jet ventilators sustain ventilation and oxygenation in the presence of large airway disruptions. The frequency-dependent mechanism is based on variations in the pneumatic equivalent to capacitive reactance. The pressure-dependent mechanism models lung defects on a voltage-controlled resistor. The electrical circuit model is also used to explain the factors leading to gas trapping and inadvertent positive end-expiratory pressure during high-frequency jet ventilation.

The consensus of available studies indicates that high-frequency jet ventilation (HFJV) can adequately ventilate animals in respiratory failure, although a clear superiority to volume-cycled ventilation (VCV) cannot be established. HFJV is probably useful in the presence of airway disruption and in tracheal or pulmonary surgery. Clinical trials and additional bench and animal studies must be performed, to reach a full understanding of the potential benefits of this technique.