ABSTRACT
The alternative ventilation system is a time-cycled, volume preset respirator which will deliver a set tidal volume at a preselected rate. In certain machines, the operator chooses the minute volume and ventilatory rate and the tidal volume can be calculated from these two settings. Alternatively, in other types of respirators the tidal volume and rate are selected and the minute volume calculated. As with the pressure-type respirator, the duration of the inspiratory and expiratory time can be adjusted according to conditions within the thorax. A fall in compliance or rise in airway resistance will not result in a fall in alveolar ventilation as the machine will merely increase the pressure in order to overcome these changes. The respirator however will not compensate for leaks around the ET tube and a significant proportion of the preset volume will be vented around the tube when there is a large leak. These ventilators are most commonly used for ventilating adult patients where cuffed ET tubes are used, but are increasingly used in children and newborns.
