Maximum Ventilatory Capabilities of Four Current-Generation Mechanical Ventilators

Abstract

Patients with severe adult respiratory distress syndrome, burns, or multisystem failure may have such high minute ventilation requirements and such low respiratory system compliance (C) that older ventilators such as the MA-1 are incapable of ventilating them. Materials and Methods: Using an MA-1 for comparison and employing a test lung with variable C, we determined the maximum ventilatory capabilities of four currently manufactured, state-of-the-art ventilators: the Bear 5, the Puritan-Bennett 7200a, the Siemens Servo 900C, and the Hamilton Veolar. We incrementally increased dialed minute volume (V) by manipulating ventilator rate, and we measured actual V output with a pneumotachometer at three different tidal volumes and three settings of C and positive end-expiratory pressure. Inspiratory (I) and expiratory times (E) were determined from strip-chart recordings, and each ventilator's maximum ventilatory capability was considered to be its greatest V output before the I:E ratio exceeded 1.0. Results: The capabilities of the 7200a, 900C, and Veolar varied somewhat under individual test settings but were similar, with none of the three clearly outperforming the others; the Bear 5 had maximum ventilatory capabilities much greater than those of the MA-1 but somewhat lower than those of the other test machines. Conclusions: Current ventilators are far superior to their ancestors in ventilatory capabilities, and the clinical importance of the differences among them is uncertain. (Respir Care 1986;31:1054-1058.)