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Different patterns of ventilation affect also CO 2 elimination in fact, end-inspiratory pause prolongation reduces dead space, increasing respiratory system compliance plateau pressure and consequently driving pressure increase accordingly. Dead space guided recruitment allows avoiding regional overdistension or reduction in cardiac output in critical care patients with ALI or ARDS. Lung recruitment is a dynamic process that combines recruitment manoeuvres (RMs) with positive end expiratory pressure (PEEP) and low Vt to recruit collapsed alveoli. Different dead space indices can provide useful information in acute lung injury (ALI) and acute respiratory distress syndrome (ARDS) patients, where changes in microvasculature are the main determinants for the increase in dead space and consequently a worsening of the outcome. Dead space is not routinely measured in critical care practice, because the difficulties in in interpreting capnograms and the different methods of calculations.

Anatomic dead space is age dependent and is > 3 ml/kg in early infancy.Dead space is the portion of each tidal volume that does not take part in gas exchange and represents a good global index of the efficiency of the lung function. The following relationship between total anatomic dead space (DStotal in ml/kg) and age (in yr) is derived: DStotal = 3.28 - 0.56, with r = 0.95 and P = 0.0001. Mean intrathoracic anatomic dead space was 1.03 ml/kg and was not related to age. Extrathoracic dead space per kilogram decreased exponentially with increasing age, ranging from 2.3 ml/kg in early infancy to 0.8 ml/kg in children older than 6 yr. Intrathoracic dead space was measured by continuous analysis of end-tidal and mixed-expired PCO2 and minute ventilation in 10 patients, aged 18 days to 14.7 yr. Extrathoracic dead space was measured by a "water displacement" technique in 40 patients aged 7 days to 14.2 yr who were intubated with cuffed endotracheal tubes. Because of the relatively large head size of infants and children, we hypothesized that extrathoracic and, therefore, total dead space would be relatively larger in pediatric subjects. In adults, anatomic dead space is 2.2 ml/kg.