RADIOGRAPHIC LUNG-DISEASE AND RESPONSE OF PERSISTENT PULMONARY-HYPERTENSION TO MEAN AIRWAY PRESSURE AND ALKALOSIS

Persistent pulmonary hypertension of the newborn (PPHN) is associated with multiple cardiopulmonary diseases. Therapy often includes hyperventilation/alkalosis despite little evidence as to its efficacy in diverse conditions. To determine (1) if part of the improvement of arterial oxygen tension (P-aO2) attributed to alkalosis is actually related to increased mean airway pressure (P-aw) and (2) if the presence of radiographic pulmonary disease predicts the response to alkalosis or mean airway pressure, we reviewed records of 19 newborns with well-documented PPHN. Arterial blood gases and corresponding ventilator settings were recorded during the first day of life. To adjust for lower F-iO2 corrected P-aO2 (cP(aO2)) was calculated when the F-iO2<1.0, such that cP(aO2)=calculated arterial/alveolar oxygen ratio x (713-P-aCO2/0.8). Regression equations were obtained and mean slopes of these were compared for P-aw vs. cP(aO2), and pH vs. cP(aO2) by one group t-tests (with assumed population slope of zero). There was no correlation between Paw and cP(aO2) (mean slope+/-SD=-8.4+/-30.8, P=0.25), but there was a moderate correlation between pH and cP(aO2) (mean slope=333.1+/-480.5, P=0.007). Patients were then classified by chest radiographs as having severe or minimal/no lung disease. Relationships of Paw and pH to cP(aO2) were then re-examined. No correlation was present between Paw and cP(aO2) in 11 patients with PPHN and severe radiographic disease (mean slope=-7.4+/-26.9, P=0.38) or in eight patients with PPHN and minimal/no lung disease (mean slope=-9.8+/-37.5, P=0.48). There was no correlation between pH and cP(aO2) in patients with severe radiographic lung disease and PPHN (mean slope=92.1+/-399.5, P=0.46), but patients with PPHN and minimal/lung disease showed a strong correlation (mean slope=664.5+/-385.8, P=0.002). We conclude that Paw (less than or equal to 18 cm H2O) with conventional mechanical ventilation has no apparent effect on oxygenation in patients with PPHN regardless of lung disease; however, severe radiographic lung disease may be a predominant variable predicting a poor response to alkalosis. We speculate that different diseases cause pulmonary hypertension by different mechanisms. (C) 1994 Wiley-Liss, Inc.