The movement of air into the lungs is responsible for bringing with it a fresh supply of oxygen, while the movement of air out of the lungs is responsible for removing carbon dioxide from within the body. In order to get oxygen into the lungs and carbon dioxide out of the lungs, the physical movement of air in and out of the lungs is required. Therefore, it is important to have adequate perfusion through the pulmonary vasculature to ensure there is a fresh blood supply passing the alveoli within the lungs to allow this to happen. Before the VQ Mismatch, There Was a VQ Matchįor normal gas exchange to occur, oxygen within the lungs has to move into the bloodstream and carbon dioxide within the bloodstream has to move into the lungs. The difference in pathophysiology between a shunt and dead space is essentially why oxygen therapy works wonders in some patients but has a minimal effect on others. But how hypoxemia reacts to oxygen therapy is different based on whether the patient has a shunt or dead space the two problems associated with a VQ mismatch. The management for hypoxemia seems easy enough provide oxygen therapy as quick band-aid therapy to counteract the problem. Anatomic dead space is age dependent and is > 3 ml/kg in early infancy.Hypoxemia is an abnormally low concentration of oxygen in the blood which can lead to dire consequences when left untreated. 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.
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