Assessment of Postnatal Pulmonary Adaption in Bovine Neonates Using Electric Impedance Tomography (EIT)

SIMPLE SUMMARY: The lungs of the neonate must oxygenate the blood and eliminate carbon dioxide at birth. Efficient gas exchange requires ventilation of the pulmonary alveoli to meet rapidly increasing oxygen demands. It is not entirely clear how quickly the different regions of the lungs become ventilated and when ventilation of all lung regions is achieved. We used electric impedance tomography (EIT) to measure lung stretch and aeration in 20 non-sedated neonatal calves born without difficulty. For EIT measurement, an electrode belt was placed around the thorax of each calf positioned in sternal recumbency immediately after birth and at various other times until 3 weeks of age to measure aeration and ventilation in different regions of the lungs. Standard EIT variables describing distribution of ventilation, respiratory rate, and several blood gas variables were determined. Most lung regions were ventilated immediately after birth. Ventilation of the ventral regions increased during the first hour, after which it decreased. Dorsal lung regions and the right lung had the greatest ventilation. The respiratory rate decreased, and the tidal impedance change as a surrogate for tidal volume increased in the first 3 weeks of life. The study showed that most regions of the lungs are ventilated immediately after birth. However, this is followed by a reduction in ventilation of ventral regions of the lungs, presumably because of gravity-driven ventral movement of residual amniotic fluid. These findings may allow identification of calves with insufficient lung expansion and ventilation after birth. ABSTRACT: Several aspects of postnatal pulmonary adaption in the bovine neonate remain unclear, particularly the dynamics and regional ventilation of the lungs. We used electric impedance tomography (EIT) to measure changes in ventilation in the first 3 weeks of life in 20 non-sedated neonatal calves born without difficulty in sternal recumbency. Arterial blood gas variables were determined in the first 24 h after birth. Immediately after birth, dorsal parts of the lungs had 4.53% ± 2.82% nondependent silent spaces (NSS), and ventral parts had 5.23% ± 2.66% dependent silent spaces (DSS). The latter increased in the first hour, presumably because of gravity-driven ventral movement of residual amniotic fluid. The remaining lung regions had good ventilation immediately after birth, and the percentage of lung regions with high ventilation increased significantly during the study period. The centre of ventilation was always dorsal to and on the right of the theoretical centre of ventilation. The right lung was responsible for a significantly larger proportion of ventilation (63.84% ± 12.74%, p < 0.00001) compared with the left lung. In the right lung, the centrodorsal lung area was the most ventilated, whereas, in the left lung, it was the centroventral area. Tidal impedance changes, serving as a surrogate for tidal volume, increased in the first 3 weeks of life (p < 0.00001). This study shows the dynamic changes in lung ventilation in the bovine neonate according to EIT measurements. The findings form a basis for the recognition of structural and functional lung disorders in neonatal calves.