Minimum artificial lung expansion necessary for resuscitation of the newborn lamb

In a group of seven lambs, pressure-volume relationships were obtained for the initial artificial expansion of the lungs in the intact chest and subsequent re-expansion afer the lungs had been excised and collapsed. In a second group, of 12 severely asphyxiated lambs, the lungs were expanded in steps and circulatory resuscitation was achieved at pressures ranging from 1.75 to 3.5 kPa, geometric mean 2.3 kPa, with estimated corresponding volumes of 3--24 ml kg-1, geometric mean 5.8 ml kg-1. In a third group, of 24 severely asphyxiated lambs (mean pH 6.84), 22 were successfully resuscitated in the same manner and nine of these survived in apparent good health for more than 6 months. Any resuscitation regime for human neonates should take account of the finding that resuscitation occurred at pressures less than those necessary for full expansion and that, after the first sign of an increase in heart rate, there was a delay of 17--45 s before full circulatory improvement and of 3 min before full improvement in PaO2.