08-28-2017, 03:16 PM
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).
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).