INTRODUCTION: We compared performance characteristics and clinical efficacy of the Nellcor Puritan Bennett 335 and the Respironics BiPAP S/T pressure support ventilators (PSV). METHODS: In the laboratory, triggering capabilities of the ventilators were assessed in 3 normal subjects, using changes in esophageal pressure. Determinants of delivered tidal volume (VT) and leak compensation were evaluated during controlled breathing on the 335 and in the spontaneous/time (S/T) mode on the BiPAP. In the clinical phase, day-time blood gas values, pulmonary function, nocturnal gas exchange, and sub-jective evaluations were compared after 2 weeks of use by patients with chronic respiratory failure due to restrictive diseases previously stabilized using the BiPAP S/T. RESULTS: The 335 at the most sensitive setting (1 for most, 5 for least) was more sensitive both for inspiratory triggering and expiratory cycling than the BiPAP S/T. During controlled breathing in the A/C mode on the 335 or the S/T mode on the BiPAP, determinants of expiratory cycling differed substantially, causing marked differences in breathing pattern, deliv-ered VT, and air leak compensation at certain settings. Clinical evaluation showed the ventilators to be equally efficacious in supporting nocturnal and daytime gas exchange, except that oxygenation improved slightly when patients resumed BiPAP use. Daytime vital signs and pulmonary function remained stable throughout. Patients judged the ventilators to be equally comfortable in terms of airflow and triggering, but deemed the 335 quieter and the BiPAP more portable. Of the 6 patients, 4 preferred the 335 ventilator at the end of the study. CONCLUSIONS: The 335 is a portable PSV that is as effective in supporting patients with chronic respiratory failure as is the BiPAP S/T. Because it offers adjustable triggering and cycling, it may be preferred by some patients. However, close attention must be paid to the differing mechanisms for expi-ratory cycling that determine delivered VT, before switching between ven-tilators or ventilator modes. [Respir Care 1996;41(10):885-894]
