COMPARISON OF LUNG-VOLUME MEASUREMENTS BY ANTERO-POSTERIOR CHEST-X-RAY AND THE SF6 WASHOUT TECHNIQUE IN MECHANICALLY VENTILATED INFANTS

While anterior/posterior chest x-rays (CXR) are routinely performed to estimate lung volume (LV) and adjust ventilator settings, the precise measurement of LV requires additional sophistication. In 31 infants v entilated because of surfactant deficiency (n = 23), bronchopulmonary dysplasia (n = 7), or pulmonary hypoplasia (n = 1) with either intermi ttent positive pressure (n = 18) or high frequency oscillation (n = 13 ) (gestational age 23-39 weeks (median 26 weeks); birthweight 550-2780 g (median 840 g); age at measurement 1-91 days (median 6 days); weigh t at study time (WST) 675-3000 g (median 938 g)), we investigated whet her LV, as measured by the sulfur hexafluoride (SF6) washout technique , could by estimated from CXR by: 1) the sum (A+B) of the right (A) an d left (B) lung fields areas; 2) the product (LxW) of the distances fr om the right apex to the right costophrenic angle (L) and between both costophrenic angles (W); 3) the diaphragm position relative to the po sterior parts of the ribs (DP); and 4) the lung radiolucency (RL, grad es 0-4). Correlations between A+B (r = 0.44) or LxW (r = 0.37) and LV were poor, but improved when A+B, LxW, and LV were normalized to WST: (A+B)/WST vs. LV/WST (r = 0.74), and LxW/WST vs. LV/WST (r = 0.67). DP (r = 0.13) and RL (Spearman's rho = 0.17) did not correlate with LV/W ST. A multiple linear regression analysis led to the following best-fi t equation: LV/WST = 2.58 (A+B)/WST - 5.47 DP + 42.2 (r = 0.83). We co ncluded that an estimate of LV from CXR lacked sufficient accuracy. DP and RL did not correlate with LV measured by SF, washout. Pediatr Pul monol, 1998; 26:265-272, (C) 1998 Wiley-Liss, Inc.