THE PRONE POSITION IN ARDS - A SUCCESSFUL THERAPEUTIC STRATEGY

As early as 1974, Brian advocated the prone position for ventilated pa tients [5]. He suggested that this position might enhance ventilation of the dorsal parts of the lungs, thereby improving oxygenation. These considerations have been confirmed by several experimental and clinic al studies [1, 6, 13, 17]. Better secretion removal, decreased intrapu lmonary shunting, and an increased FRC are thought to be responsible f or the observed improvement of oxygenation. However, the prone positio n never became very popular in the clinical treatment of the adult res piratory distress syndrome (ARDS). Routine performance of thoracic CT scans in ARDS patients demonstrated preferential distribution of patho logical densities in the dependent lung areas. The prone position ther efore could possibly benefit these patients, as shown by two recent st udies [8, 11]. The aim of our study was to evaluate the influence of r epeatedly turning the patient to the prone position on gas exchange an d thoracic CT findings in multiple-trauma patients. Methods. Seven ven tilated intensive care patients with severe ARDS (Murray Score > 2.5 [ 9], Quotient >0.7 [4], mean airway pressure > 18 cm H2O, thoracic CT s can showing dorsal atelectases) were included in the study. Patients w ere turned from the supine to the prone position at 12-h intervals usi ng an air-cushion bed (Mediscus, Austria). Redistribution of dystelect atic or atelectatic dependent lung areas was verified by means of repe ated thoracic CT scans (Figs. 1, 8). Results. The patients were interm ittently turned for 6.5 +/- 1.1 days. The course of gas exchange is sh own in Figs. 2 and 3. Initially, improvement of the respiratory quotie nt could only be achieved during prone positioning, from the 2nd day i n the supine position as well. Intrapulmonary shunting showed a simila r trend (Figs. 4 and 5). No significant changes in cardiovascular para meters could be observed. Control thoracic CT scans showed uniform red uction of atelectases in dependent lung areas (Figs. 1 and 8). The ins piratory fraction of oxygen could be reduced significantly as of the 2 nd day (Fig. 7). Constant levels of positive end-expiratory pressure a nd tidal volume were associated with decreasing mean and plateau airwa y pressures (Fig. 6). Discussion. Repeatedly turning the patient to th e prone position produced long-lasting improvement of arterial oxygena tion, which persists up to the end of the weaning process. This is in good accordance with other studies [1, 2, 6, 8, 11, 13, 17], however, this is the first study to report an observation period of more than 6 days of repeatedly turning the patient. These positive effects on gas exchange can be attributed to sudden improvement of the ventilation-p erfusion ratio within the lung areas that become dependent after turni ng to the prone position. Due to reduced hydrostatic pressure [11] and relative hyperventilation [7, 16], previously collapsed alveoli are r ecruited in the lung areas that become non-dependent after turning to the prone position.