Anything mssing w Alveolar Ventilation? - goodman - Printable Version +- USMLE Forum - Largest USMLE Community (https://www.usmleforum.com) +-- Forum: USMLE Forum (https://www.usmleforum.com/forumdisplay.php?fid=1) +--- Forum: Step 1 (https://www.usmleforum.com/forumdisplay.php?fid=2) +--- Thread: Anything mssing w Alveolar Ventilation? - goodman (/showthread.php?tid=843825) |
Anything mssing w Alveolar Ventilation? - goodman - ArchivalUser - 08-28-2017 The equation AV = VC02 / PACO2. doubling AV will cause PACO2 to halve. If we need to Calculate PAO2 can be calculated using the alveolar gas equation: PAO2 = PIO2 - (PACO2/R) where PAO2 = alveolar PO2 and PIO2 = inspired PO2 Is AV double, the exchange ratio R of 1.0 and PACO2 of 40 mm Hg the Alveolar PO2 will increase by 20 mmHg The explanation of this problem in USMLE is. Before Hyperventilation PAO2 = 150 mm Hg - (40 mm Hg/1) = 110 mm Hg After Hyperventilation PAO2 = 150 mm Hg - (20 mmHg/1) = 130 mm Hg. Therefore, PAO2 will increase by 20mm Hg It is very important also to know the Alveolar Oxygen/Arterial Oxygen gradient = A/A gradient. Normal volume are: 5% or 30 mmHg. Alteration in the A/A gradient = LUNG DAMAGE. Remember Perfusion is better in lower lobes and Ventilation is better in upper lobes Pt w/ hypoxemia remember the A/A gradient. Any disease w/ normal A/A gradient the problem is not in the LUNGS Another Formula: Alveolar Ventilation = Respiratory Rate x (Tidal Volume (OUTPUT) - dead space). |