Neonatal Liquid Ventilation
Over the past three decades significant advances in neonatal respiratory care have led to decreased mortality in smaller and premature infants as well as critically ill term infants. However, many of the survivors went on to develop bronchopulmonary dysplasia (BPD), a chronic lung disease first reported in 1967 by Northway.
The introduction of antenatal steroids, surfactant replacement, high frequency ventilation, volume-targeted ventilation, and non-invasive ventilation has decreased severe lung injury in babies born more than 28 to 30 weeks gestation. These advances in technology and management have also increased the survival of extremely preterm infants born during the canalicular and early saccular phase (< 28 weeks) of lung development. This is the stage when alveolar and distal vascular development is rapidly occurring. When babies are born during these phases of lung development, it is done at the expense of interrupting normal gestational growth and development and subsequent reparative processes of impaired (not arrested) alveolization, dysmorphic microvascular and minimal alveolar wall fibroproliferation. The pathogenesis of this evolving or “new” BPD is a function of extreme lung prematurity, treatment-induced oxygen, volutrauma, and inflammatory responses.
Despite optimal treatments with prenatal steroids, early treatment with surfactant, gentle ventilatory strategies and oxygen saturation targeting the outcome of babies born during the canalicular and early saccular phase of lung development is BPD with a histopathologic appearance that is different than the BPD of babies born in the late saccular and alveolar phases (> 28 weeks) of lung development. Jacqueline Coalson describes the new BPD as large and simplified alveoli (alveolar hypoplasia, decreased acinar complexity); decreased, dysmorphic capillaries; variable interstitial fibroproliferation; less severe arterial/arteriolar vascular lesions; negligible airway epithelial lesions; and variable airway smooth muscle hyperplasia.
An alternative to gas ventilation is the use of oxygenated fluids to protect the lungs and effect gas exchange. With oxygenated fluids, physiologic gas exchange occurs at a normal functional residual capacity, lower minute ventilation and low alveolar pressures. This is due, to the elimination of the air-liquid interface at the alveolar-capillary surface, reducing pressure requirements to inflate the lung. To date, perfluorochemicals are the most promising breathing media liquids because of their specific physiochemical properties of low surface tension and high solubility for respiratory gases, as well as their chemically and biologically inert nature. After more than 30 years of neonatal and adult animal studies of liquid ventilation, the clinical investigations have yielded promising results.