Nine consecutive patients with flail chest injuries were treated with mechanical ventilation and positive end-expiratory pressure (PEEP). Twenty-eight studies were performed, beginning on the day of admission. Blood and gas samples were evaluated during ZEEP and again after 30 min of PEEP of 10 or 15 cm H2O. In 24 studies, the Pao2 increased with PEEP. The lower the Pao2 at ZEEP, the greater the improvement with PEEP. The D/T ratio showed no significant change with either PEEP or ZEEP. Seven studies also included (a-v)Do2 and S/T. The S/T was reduced following the application of PEEP. A reduced Pao2 was associated with an in-crease in (a-v)Do2 in four of these studies. Improvement in oxygenation in patients treated with mechanical ventilation and PEEP is attributed to a change in FRC toward the normal. Etiologic factors causing a reduction in FRC in patients with flail chest injuries are discussed. Use of this technique improved oxygenation and allowed the Fio2 to be reduced in the majority of these patients.

Continuous positive-pressure ventilation was used in eight patients with severe acute respiratory failure. Cardiac output and lung function were studied during continuous positive-pressure ventilation (mean end-expiratory pressure, 13 cm of water) and a 30-minute interval of intermittent positive-pressure ventilation. Although the mean cardiac index rose from 3.6 to 4.5 liters per minute per square meter of body-surface area, the mean intrapulmonary shunt increased by 9 per cent with changeover to intermittent positive-pressure ventilation. Satisfactory oxygenation was maintained in all patients during continuous positive-pressure ventilation with 50 per cent inspired oxygen or less. With intermittent positive-pressure ventilation arterial oxygen tension promptly fell by 161 mm of mercury, 79 per cent occurring within one minute. Prevention of air-space collapse during expiration and an increase in functional residual capacity probably explain improved oxygenation with continuous positive-pressur...