Mechanical ventilation. Physiology, equipment design, and management.

The major goals of mechanical ventilation are the prevention of significant respiratory acidosis and the correction of arterial hypoxemia. Ventilators are categorized as negative- or positive-pressure types, depending on their effect on airway pressure. Positive-pressure ventilators, which are used in the treatment of acute respiratory failure, may be subclassified as pressure-, volume-, or time-cycled. Volume types provide stable tidal volumes and inspiratory oxygen concentrations over the range of changing ventilatory conditions seen in acute respiratory failure. Ventilation may be provided in a number of modes. No clear-cut advantage of intermittent mandatory ventilation over assisted mechanical ventilation has been demonstrated. By following simple guidelines, the clinician can initiate mechanical ventilation that provides an ideal ventilatory pattern.