| Research Abstract |
Recently, prone positioning was introduced as a new method for treatment of hypoxemia of acute respiratory failure (ARF). We already reported that this position could increase PaO2 and improve lung injury it self in acute respiratory distress syndrome.
The purpose of this study was projected to analyze the effects of prone position on respiratory mechanics, and the effects of the manual breathing assist technique (MBAT) on respiratory pattern in ARF.
The results are as follows :
With turning to prone position from supine position, PaO2 (FIO2=1.0) was sinificantly increased 30%, and simultaneously patients'work of beathing (WOBp) was significantly decreased 17%. These observations have not been previously reported to our knowledge. Moreover, airway resistence and dynamic plumonary compliance were significantly improved, 17% and 25% respectively.
One of the generally accepted model of decreasing PaO2 in ARF,based on the fact that pulmonary edema increases the gravitational pleural pressure (
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Ppl) gradient in the dorsal lung regions of supine, predicts that this decreases in ventilation resulting from the compression of alveoli and small airways. The reduction of this gravitational Ppl gradient occurs on turning prone predicts that the regional ventilation in the dosal area increases and ventilation/perfusion ratio improves, then hypoxemia improved. Our data of WOBp and other respiratory mechanicsare completely consistent with this explanation. The MBAT,one of the basic maneuvers in respiratory physiotherapy, controlled the respiratory pattern, rapid and shallow respiration (or tachpnea) was changed to slow and deep respiration, namely tidal volume was increased and respiratory rate was deceased dramatically. This phenomenon was augmented of combining with patients'respiratory effort. Forced expiration by the MBAT was followed by the augmented inspiration which might create larger negative Ppl. Negative Ppl promotes recruiting collapsed alveoli and peripheral small airways by the pulmonary interdependence. The combination of MBAT and prone position could create larger negative Ppl to improve effectively alveolar ventilation in dorsal injured lung region. Interpreting our data along with other studies in the literature indicates that prone positioning and MBAT are useful strategies for the non-invasive respiratory support (lower grade ventiratory support without tracheal intubation), and the negative pressure ventilation and/or the helium inhalation method should be revived and used withthem for the treatement of ARF. Less
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