Prenatal and Neonatal Adaptations with a Focus on the Respiratory System

Abstract

Contents Among the modifications that occur during the neonatal period, pulmonary development is the most critical. The neonate's lungs must be able to perform adequate gas exchange, which was previously accomplished by the placenta. Neonatal respiratory distress syndrome is defined as insufficient surfactant production or pulmonary structural immaturity and is specifically relevant to preterm newborns. Prenatal maternal betamethasone treatment of bitches at 55 days of gestation leads to structural changes in the neonatal lung parenchyma and consequently an improvement in the preterm neonatal respiratory condition, but not to an increase in pulmonary surfactant production. Parturition represents an important challenge to neonatal adaptation, as the uterine and abdominal contractions during labour provoke intermittent hypoxia. Immediately after birth, puppies present venous mixed acidosis (low blood pH and high dioxide carbon saturation) and low but satisfactory Apgar scores. Thus, the combination of physiological hypoxia during birth and the initial effort of filling the pulmonary alveoli with oxygen results in anaerobiosis. As a neonatal adaptation follow‐up, the Apgar analysis indicates a tachypnoea response after 1 h of life, which leads to a shift in the blood acid–base status to metabolic acidosis. One hour is sufficient for canine neonates to achieve an ideal Apgar score; however, a haemogasometric imbalance persists. Dystocia promotes a long‐lasting bradycardia effect, slows down Apgar score progression and aggravates metabolic acidosis and stress. The latest data reinforce the need to accurately intervene during canine parturition and offer adequate medical treatment to puppies that underwent a pathological labour.

The influence of the obstetrical condition on canine neonatal pulmonary functional competence

“…Regarding the obstetrical condition, we have previously shown in dogs that dystocia compromises neonatal vitality (ie, Apgar score) as a consequence of persistent metabolic acidosis. 22 Therefore, in the DYS group, we can infer that respiratory alterations were due to prolonged exposure to uterine contractions, which may lead to intrapartum hypoxia, metabolic acidosis and, consequently, impaired surfactant synthesis and pulmonary clearance.…”

Radiographic assessment of pulmonary fluid clearance and lung aeration in newborn calves delivered by elective Caesarean section

“…To the best of our knowledge, there are no previous studies using serial radiographic recordings to examine extrauterine respiratory adaptation in neonatal calves. On the other hand, there are some reports focusing on radiography to predict lung fluid clearance in other species such as lambs and foals (Fletcher, Sachs, & Kotas, ; Kutasi et al., ; Lamb et al., ; Vannucchi et al., ).…”

“…The delay in lung aeration may also be attributed to the lack of compression stimuli along the vaginal birth canal in surgically born neonates, causing a diminution of the respiratory reflex. This leads to a failure of activation of the mechanisms required for appropriate final pulmonary maturation (Vannucchi et al., ). Diminished synthesis and increased absorption of the pulmonary fluid as well as surfactant secretion in healthy neonates are important events for post‐natal pulmonary maturation and appropriate alveolar expansion, and for preventing the occurrence of increased post‐natal soft tissue opacity in the lungs (Vannucchi et al., ).…”

“…Pulmonary adaptation to extrauterine life in newborn calves is an important example of changes in cardiopulmonary physiology at birth, as it has a significant role in the rapid, smooth transition from a fluid‐filled foetal lung to an air‐breathing organ (Vannucchi et al., ; Varga, Mester, Börzsönyi, Lekeux, & Szenci, ). The compensation of neonatal respiratory and metabolic acidosis and the improvement in lung mechanics occur mainly during the first 6 hr of life in newborn calves (Varga et al., ).…”

“…Thoracic radiographs are a valuable tool for the diagnosis of disorders related to foetal pulmonary fluid clearance after birth. It was found to be preferable to use thoracic radiographs as an adjuvant diagnostic tool in conjunction with clinical assessment and blood gas measurements during routine diagnosis of post‐natal respiratory abnormalities in the dog (Silva, Lucio, Veiga, Rodrigues, & Vannucchi, ; Vannucchi et al., ). Digital thoracic radiography is also a valuable diagnostic imaging technique of the post‐natal equine lung where 6 hr after birth is the earliest time when normal foals consistently have clear, radiolucent lung fields on the radiographs (Kutasi, Horvath, Harnos, & Szenci, ).…”