PH 2O is the water vapor pressure (47 mmHg at 37☌). Pb is the barometric pressure (760 mmHg at sea level). PAO 2 is the mean alveolar oxygen pressure.įiO 2 is the fractional concentration of inspired oxygen. Unlike PaO 2, PAO 2 is not measured but calculated by using the alveolar gas equation: The difference between alveolar and arterial oxygen tensions is due to other factors: (1) V/Q imbalance in various parts of the lungs, (2) small right to left shunt (bronchial vein, thebesian vein, and small pulmonary arteriovenous anastomosis), and (3) resistance to the diffusion of oxygen across the alveolar membrane. The word gradient is a misnomer, and ideally, it should be referred to as A-a oxygen difference as the difference between alveolar and arterial oxygen is not due to any diffusion gradient. Therefore, hypoxemia due to V/Q mismatch, diffusion limitation, and shunt will have widened gradient, whereas hypoxemia due to hypoventilation would have normal gradient. Pathology of the alveolocapillary unit widens the gradient. The A-a oxygen gradient indicates the integrity of the alveolocapillary membrane and effectiveness of gas exchange. Some apparatus dead space may actually reduce total dead space, as an ETT bypasses the majority of anatomical dead space of the patient (nasopharynx).ĭead space from the patient.It is the difference between alveolar oxygen level (PAO 2) and arterial oxygen level (PaO 2) and is represented by the following equation: Alveolar to arterial (A-a) oxygen gradient = PAO 2 – PaO 2. Types of Dead Spaceĭead space from equipment, such as tubes ventilator circuitry. Glomerular Filtration and Tubular Functionĭead space is the proportion of minute ventilation which does not participate in gas exchange. Functional Anatomy and Control of Blood Flow
0 Comments
Leave a Reply. |
AuthorWrite something about yourself. No need to be fancy, just an overview. ArchivesCategories |