Application of PAP increases intraluminal pressure and prevents the collapse of the bronchioles and alveoli. The increased pressure provides better conditions for the functioning of the diaphragm. The optimum level of PAP has not been clearly defined.
EPAP (exhalation against a threshold resistor) increases the work of the diaphragm, permitting the patient to recover normal diaphragmatic function more rapidly. When the transmural pressure gradient is increased, bronchiolar collapse is limited. Slow inspiratory flow provides better ventilation in the parts of the lung with a low time constant.
During CPAP therapy the patient breathes from a pressurized circuit against a threshold resistor that maintains constant airway pressure (from 1 to 15-20 cmH 2O) during both inspiration and expiration. The main aim is to increase the functional residual capacity.
The side-effects are hypercapnia, increase in intracranial pressure, hemodynamic failure, vomiting, pulmonary barotrauma, and patient discomfort. There are no absolute contraindications, but the indications should be carefully weighed in the following conditions: esophageal or cephalic surgery, chronic obstructive pulmonary disease, acute sinusitis, epistaxis or hemoptysis, nausea, tympanic rupture, and undrained pneumothorax. In the ICU, this therapy can be administered at intervals of 1 to 6 h and pressures of 5 to 20 mmHg.
These techniques are used to prevent or treat atelectasis and sputum retention in patients on spontaneous ventilation. The indication follows clinical examination revealing hypoxemia associated with bronchial obstruction, sputum retention that is not responsive to spontaneous or directed coughing, or radiological signs of atelectasis. The various clinical studies in the literature are often encouraging but have yet to clearly demonstrate the advantage of one technique over another. However, CPAP appears to be the best tolerated technique.
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