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The Alveolar–arterial gradient (A-aO 2, [1] or A–a gradient), is a measure of the difference between the alveolar concentration (A) of oxygen and the arterial (a) concentration of oxygen. It is a useful parameter for narrowing the differential diagnosis of hypoxemia. [2] The A–a gradient helps to assess the integrity of the alveolar ...
The alveolar gas equation is the method for calculating partial pressure of alveolar oxygen (p A O 2). The equation is used in assessing if the lungs are properly transferring oxygen into the blood. The alveolar air equation is not widely used in clinical medicine, probably because of the complicated appearance of its classic forms.
The alveolar oxygen partial pressure is lower than the atmospheric O 2 partial pressure for two reasons. Firstly, as the air enters the lungs, it is humidified by the upper airway and thus the partial pressure of water vapour (47 mmHg) reduces the oxygen partial pressure to about 150 mmHg.
Carbon dioxide is a by-product of food metabolism and in high amounts has toxic effects including: dyspnea, acidosis and altered consciousness. [8] Arterial blood carbon dioxide tension. P a CO 2 – Partial pressure of carbon dioxide at sea level in arterial blood is between 35 and 45 mmHg (4.7 and 6.0 kPa). [9] Venous blood carbon dioxide tension
Arterial carbon dioxide tension, or partial pressure: P A CO 2: Alveolar carbon dioxide tension, or partial pressure: P v O 2: Oxygen tension of mixed venous blood: P (A-a) O 2: Alveolar-arterial oxygen tension difference. The term formerly used (A-a D O 2) is discouraged. P (a/A) O 2: Alveolar-arterial tension ratio; P a O 2:P A O 2 The term ...
Key to understanding whether the lung is involved in a particular case of hypoxemia is the difference between the alveolar and the arterial oxygen levels; this A-a difference is often called the A-a gradient and is normally small. The arterial oxygen partial pressure is obtained directly from an arterial blood gas determination. The oxygen ...
Carbon dioxide is produced continuously as the body's cells respire, and this CO 2 will accumulate rapidly if the lungs do not adequately expel it through alveolar ventilation. Alveolar hypoventilation thus leads to an increased PaCO 2 (a condition called hypercapnia). The increase in PaCO 2 in turn decreases the HCO − 3 /PaCO 2 ratio and ...
For F I O 2 values equal to or greater than 0.5, the alveolar–arterial gradient value should be used in the APACHE II score calculation. Otherwise, the PaO 2 will suffice. [4] The ratio between partial pressure of oxygen in arterial blood and F I O 2 is used as an indicator of hypoxemia per the American-European Consensus Conference on lung ...