The tidal volume can be divided in two major compartments: the alveolar volume, which is the volume of gas that reaches the alveolar membrane and contributes to gas exchange, and the dead space, which corresponds to the fraction of the tidal volume which does not take part in gas exchange. The total or physiological dead space is the aggregate of the anatomical and the alveolar dead space. The anatomical dead space consists of the upper airways and the intrathoracic large airways and is larger in relation to the total body weight in smaller and more premature infants. The alveolar dead space refers to the areas of the lung which are ventilated but not perfused by the pulmonary vessels. The alveolar dead space is of a smaller magnitude compared to the anatomical dead space, and a sensitive index of parenchymal lung damage and respiratory disease severity. Although the actual values of the dead spaces currently cannot be calculated and displayed in real-time in neonatal ventilators, their actual values and dynamic changes over time can be inferred by indirect parameters such as the difference between the arterial and the end-tidal carbon dioxide and they can influence the delivery of targeted parameters during invasive ventilation such as the targeted tidal volume.