![]() ![]() pH is an indicator of the relative acidity or alkalinity of a solutionĭead space is the volume of air that is inhaled that does not take part in the gas exchange, because it either remains in the conducting airways or reaches alveoli that are not perfused or poorly perfused. Symbol relating the hydrogen ion concentration or activity of a solution to that of a standard solution approximately equal to the negative logarithm of the hydrogen ion concentration. Oxygen saturation as measured by pulse oximetry Oxygen saturation of the hemoglobin of arterial blood ![]() The term formerly used ( A-a D O 2) is discouraged.Īlveolar-arterial tension ratio P aO 2: P AO 2 The term oxygen exchange index describes this ratio. ![]() By these definitions, healthy subjects are those whose physiological dead space and shunt do not exceed their anatomical dead space and shunt.Inhaled air not part of gas exchange Blood gas, acid-base, and gas exchange terms P aO 2Īrterial oxygen tension, or partial pressureĪlveolar oxygen tension, or partial pressureĪrterial carbon dioxide tension, or partial pressureĪlveolar carbon dioxide tension, or partial pressureĪlveolar-arterial oxygen tension difference. 7) that allow systemic blood to bypass the pulmonary circulation plus any pulmonary arterial blood flowing through alveoli with inadequate ventilation, that is, V̇ A/Q̇ <0.01 ( Table 8.1). 9 includes actual extra-pulmonary anatomical defects like PDA or PFO (Chap. Likewise, a calculated physiological shunt as detailed in Chap. 4) plus the volume of all alveoli whose ventilation vastly exceeds their blood flow, that is V̇ A/Q̇ >100 ( Table 8.1). Thus, a calculated physiological dead space includes the anatomical dead space of conducting zone airways (Chap. It is important to emphasize that such physiological estimates are made on living subjects and include any anatomical defects that are only quantifiable by autopsy. ![]() 9 present equations to calculate a patient’s physiological dead space and physiological shunt. ![]()
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