Index of pulmonary expansion: a new method to estimate lung hypoplasia in congenital diaphragmatic hernia.

In order to find a simple method for assessing the degree of lung hypoplasia in congenital diaphragmatic hernia (CDH), we measured an index of pulmonary expansion (V/P: expiratory tidal volume over inspiratory pressure) in 23 pulmonary normal and 16 CDH neonates. We also measured V/P in 9 newborn lambs, 6 with experimentally induced CDH and 3 controls, and compared V/P values with fractional lung masses (FLM: lung weight over body weight). In animals, the correlation between V/P and FLM was significant (P less than .05), whereas there was a very significant inverse correlation between pulmonary interstitial emphysema found at postmortem and FLM (P less than .01). These findings suggest that V/P could be an indicator of lung hypoplasia and, therefore, of sensitivity to barotrauma. In neonates with CDH, this index could be useful to make comparisons between series and to separate infants who cannot be ventilated at usual pressures without significant barotrauma.