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The P ETCO 2/PaCO 2, measured at 5 cmH 2O airway pressure, significantly decreased from mild to mild–moderate moderate–severe and severe ARDS.

The source was a database in which we collected since 2003 all the patients enrolled in different CT scan studies. We retrospectively studied 200 patients with ARDS. Our aim is to investigate if and at which extent the P ETCO 2/PaCO 2, a comprehensive meter of the “gas exchanger” performance, is related to the anatomo physiological characteristics in ARDS. Therefore, in the perfect gas exchanger (alveolar dead space = 0, venous admixture = 0), the P ETCO 2/PaCO 2 is 1, as P ETCO 2, P ACO 2 and PaCO 2 are equal. The “ideal” alveolar PCO 2 equals the end-tidal PCO 2 (P ETCO 2) only in absence of alveolar dead space. As it cannot be measured, it is surrogated by arterial PCO 2 which, unfortunately, may be far higher than ideal alveolar PCO 2, when the right-to-left venous admixture is present. The “ideal” alveolar PCO 2, in equilibrium with pulmonary capillary PCO 2, is a central concept in the physiological dead space measurement. Positive pressure ventilation (i.e.The physiological dead space is a strong indicator of severity and outcome of acute respiratory distress syndrome (ARDS).Neck extension and jaw protrusion (can increase it twofold).General anesthesia – multifactorial, including loss of skeletal muscle tone and bronchoconstrictor tone.The ratio of physiologic dead space to tidal volume is usually about 1/3. Alveolar dead space is the volume of gas within unperfused alveoli (and thus not participating in gas exchange either) it is usually negligible in the healthy, awake patient. Anatomic dead space is the volume of gas within the conducting zone (as opposed to the transitional and respiratory zones) and includes the trachea, bronchus, bronchioles, and terminal bronchioles it is approximately 2 mL/kg in the upright position. Physiologic or total dead space is the sum of anatomic dead space and alveolar dead space.

Dead space is the volume of a breath that does not participate in gas exchange.