# How do you calculate alveolar air?

The alveolar gas equation is a formula used to approximate the partial pressure of oxygen in the alveolus (PAO2):PAO2=(PB−PH2O)FiO2−(PaCO2÷R)where PB is the barometric pressure, PH2O is the water vapor pressure (usually 47mmHg), FiO2 is the fractional concentration of inspired oxygen, and R is the gas exchange ratio.

## How do you calculate alveolar o2?

It is not possible to collect gases directly from the alveoli. The alveolar gas equation is of great help in calculating and closely estimating the partial pressure of oxygen inside the alveoli. The alveolar gas equation is used to calculate alveolar oxygen partial pressure: PAO2 = (Patm – PH2O) FiO2 – PACO2 / RQ.

## How do you calculate alveolar gas from PAO2?

The alveolar gas equation is a way to estimate the PAO2, and is calculated with the following formula: PAO2=FiO2 (PATM – PH2O) – PaCO2/RQ.

## How is alveolar concentration calculated?

For you to achieve Mac or two percent sevoflurane would have to be measured in the alveolus. For you to achieve 2% of the mixture would have to be sevoflurane.

## How is PO2 calculated?

The P/F ratio equals the arterial pO2 (“P”) from the ABG divided by the FIO2 (“F”) – the fraction (percent) of inspired oxygen that the patient is receiving expressed as a decimal (40% oxygen = FIO2 of 0.40).

## What is alveolar air?

3.1.

Alveolar gas is a mixture of inspired air, fully saturated with water vapor, and carbon dioxide that diffuses from the blood. At the end of each expiration about 2000–2500 ml of air remain in the lung.

## How do you calculate alveolar pco2?

Alveolar Carbon Dioxide Equation

1. PACO2 = V’CO2/V’A
2. PACO2 = Alveolar Partial Pressure of CO2
3. V’CO2 = Metabolic Rate of CO2 production.
4. V’A = Alveolar Ventilation (ml/min)

## What is alveolar PO2?

1) PO2 in alveoli is 104 mmHg vs. 40 mmHg for the deoxygenated blood of the pulmonary arteries. So after . 25 seconds, equilibrium is reached. That means that PO2 in the pulmonary capillary blood = 104 mmHg.

## How do you calculate oxygen content?

The constant, 1.36, is the amount of oxygen (ml at 1 atmosphere) bound per gram of hemoglobin.

Oxygen Content.

CaO2 = 1.36 * Hgb * SaO2 + 0.0031 * PaO2
100

## How is the alveolar gas equation derived?

I a corollary to dalton's law can be quickly derived from simple algebra that the partial pressure of a gas X is equal to the fractional concentration of that gas multiplied.

## Is PaO2 and PO2 the same?

PO2 , SaO2 , CaO2 are all related but different.

If the lungs are normal, then PaO2 is affected only by the alveolar PO2 (PAO2), which is determined by the fraction of inspired oxygen, the barometric pressure and the PaCO2 (i.e., the alveolar gas equation).

## How do you calculate PaCO2?

III. Calculation: Calculated PaCO2 in Metabolic Conditions

1. PaCO2 = 1.5 x HCO3 + 8 (+/- 2)
2. PaCO2Delta = 1.2 x BicarbDelta.
3. PaCO2 will not typically drop below 10 mmHg in respiratory compensation.

## Is PaO2 and spo2 the same?

PaO2 values are always much lower than oxygen saturation values. This is simply a reflection of the oxygen saturation curve (figure above). For example, a saturation of 88% correlates to a PaO2 of ~55mm. We’re generally comfortable with a saturation of 88%, but a PaO2 of 55mm may cause concern.

## What is SaO2 vs SpO2?

Conclusion: Oxygen saturation results determined of different ways are often not identical. The difference between SaO2 and SpO2 are often more 3 pp when SpO2 results obtained from fingertip less than 94%.

## Which is more important SaO2 or PaO2?

PaO2 is the most important (but not the only) determinant of SaO2. Other determinants of SaO2 for a given PaO2 are conditions that shift the position of the oxygen dissociation curve left or right, such as temperature, pH, PaCO2 and level of 2,3-DPG in the blood.

## How do you calculate PaO2 from FiO2?

PaO2 should = FiO2 x 500 (e.g. 0.21 x 500 = 105 mmHg)

## How do you calculate desired PAO2?

At sea level, the alveolar PAO2 is: PaO2 = (760 – 47) 0.21 – 40/0.8 = 99.7 mm Hg.

## What does FiO2 0.5 mean?

Oxygen-enriched air has a higher FIO2 than 0.21; up to 1.00 which means 100% oxygen. FIO2 is typically maintained below 0.5 even with mechanical ventilation, to avoid oxygen toxicity, but there are applications when up to 100% is routinely used.

## How is SF ratio calculated?

SF values were examined as a substitute of PF ratio for diagnosis ARDS and ALI. Results: The relationship between SF and PF ratio was described by the following regression equation: SF=57+0.61 PF (P<0.001). SF ratios of 181 and 235 corresponded of PF ratio .