Continuous Positive-Pressure Ventilation in Acute Respiratory Failure

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Abstract
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-pressure ventilation. In four patients subcutaneous emphysema or pneumothorax developed. Weighed against the effects of prolonged hypoxemia, these complications were not severe enough to warrant cessation of continuous positive-pressure ventilation.