Simple SummaryThe aim of this study was to analyze the spatial and temporal progress of the aeration of lung tissue in vital canine neonates during the first day post natum (p.n.). To this end, computed tomography (CT) was used, and histopathology was applied to quantify the area of aerated neonatal lung tissue. It was shown that, within the first 10 min p.n., the degree of ventilation in vital born pups reached about 75% of the final values obtained 24 h p.n. The dorsal lung areas were always significantly better ventilated than the ventral regions. The results of this study are clinically relevant and suggest that resuscitation measures should be performed already within the first 10 min p.n., preferably with the pup in the chest–abdomen position, to achieve the best ventilation of the lungs.AbstractBackground: The lung tissue in newborn canine neonates is still in a morphologically and functionally immature, canalicular–saccular stage. True alveoli are only formed postnatally. The aim of this study was to analyze the spatial and temporal development of the ventilation of the lung tissue in vital canine neonates during the first 24 h post natum (p.n.). Methods: Forty pups (birth weight Ø 424 g ± 80.1 g) from three litters of large dog breeds (>20 kg live weight) were included in the studies. Thirty-three pups (29 vital, 2 vitally depressed, 2 stillborn neonates) originated from controlled, uncomplicated births (n= 3); moreover, six stillborn pups as well as one prematurely deceased pup were birthed by other dams with delivery complications. Computed tomography (CT) was used in 39 neonates, and histopathologic tissue classification techniques (HALO) were used in 11 neonates (eight stillborn and three neonates died early post natum, respectively) to quantify the degree of aerated neonatal lung tissue. Results: It was shown that, in vital born pups, within the first 10 min p.n., the degree of ventilation reached mean values of −530 (±114) Hounsfield units (HU) in the dorsal and −453.3 (±133) HU in the ventral lung area. This is about 75–80% of the final values obtained after 24 h p.n. for dorsal −648.0 (±89.9) HU and ventral quadrants −624.7 (±76.8) HU. The dorsal lung areas were always significantly better ventilated than the ventral regions (p= 0.0013). CT as well as histopathology are suitable to clearly distinguish the nonventilated lungs of stillborns from neonates that were initially alive after surviving neonatal respiratory distress syndrome but who died prematurely (p= 0.0398). Conclusion: The results of this study are clinically relevant since the lung tissue of canine neonates presents an aeration profile as early as 10 min after birth and continues progressively, with a special regard to the dorsal lung areas. This is the basis for resuscitation measures that should be performed, preferably with the pup in the abdomen–chest position.