Positive pressure ventilation is sometimes accomplished with a facemask that forms a tight seal around the mouth and nose or just the nose. CPAP is applied through a mask, in this instance usually over both the nose and mouth, that forms a tight seal. Positive pressure is applied by a machine with inspiration and expiration, causing fluid to be pushed out of the alveolar space and opening alveoli or keeping them from collapsing. Lying on the stomach increases gas exchange in the alveoli. Inverse ratio ventilation is reserved for severe cases of ARDS, when it is impossible to oxygenate the patient adequately.
Treatment involves increasing the amount of time that the ventilator is inspiring versus expiring.
Increasing the amount of time spent inhaling re-expands more collapsed alveoli than positive pressure alone. This is an uncomfortable technique and usually requires sedation and a muscle-paralyzing drug that keeps the respiratory muscles from resisting the unnatural inverse ratio ventilation. Complications of mechanical ventilation Volutrauma , over expansion of the alveoli, can contribute to lung injury and is one of the most common complications of mechanical ventilation. Recent studies have shown that decreasing the amount of air pushed into the lungs can reduce the risk for volutrauma. Weakened lungs, high pressures from the ventilator, and the high volume of air increase the risk for pneumothorax.