Tissue Oxygen Available (O2a) as a Criterion for the Effectiveness of Continuous Positive Pressure Breathing (CPPB)
Since Gregory’s report (I) on the effectiveness of Continuous Positive Airway Pressure for treatment of infants with the Idiopathic Respiratory Distress Syndrome (IRDS), the method has been widely accepted throughout the world. This method provides increased proximal airway pressure (Ppa) sufficient to prevent alveolar collapse at the end of expiration, while the subject is breathing spontaneously. In the normal lung, as little as 3–5 cm H2O Ppa may reduce cardiac output (Q̇). Contrary to this, it is postulated that in IRDS, decreased pulmonary compliance (SCL) acts as a barrier and minimizes this effect. Pulmonary compliance varies widely between normal subjects and those with IRDS of varying severity. Therefore, a wide range of Ppa is required to provide optimal oxygenation without reducing Q̇. Since Q̇ is not routinely measured, a reduction in Q̇ could follow an excessive increase in Ppa; in addition, excessive reduction in Q̇ could accompany regression of the disease while Ppa is unchanged.
KeywordsContinuous Positive Airway Pressure Normal Lung Damage Lung Normal Compl Iance Pulmonary Compl Iance
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