How do you measure PaO2

The alveolar gas equation is of great help in calculating and closely estimating the partial pressure of oxygen

What is PaO2 and How Is It measured?

PaO2 is a measurement of the partial pressure of oxygen dissolved in the plasma only. It is measured in mm Hg (millimeters of mercury). The PaO2 does not tell us about the body’s total oxygen content, but it does indicate how much oxygen was available in the alveoli to dissolve in the blood.

How is PaCO2 measured?

The partial pressure of carbon dioxide (PaCO2) is one of several measures calculated by an arterial blood gases (ABG) test often performed on people with lung diseases, neuromuscular diseases, and other illnesses. PaCO2 specifically evaluates carbon dioxide (CO2) levels in the blood.

Does pulse oximetry measure PaO2?

Pulse oximetry is one obvious monitoring tool to identify hypoxemia and hypoxia. I find that one frequent area of confusion relates to understanding the important difference between arterial partial pressure of oxygen (PaO2) and oxygen saturation (O2 sat).

How do you find pO2?

P divided by F = P/F ratio. Example: PaO2 = 90 on 40% oxygen (FIO2 = 0.40): 90 / 0.40 = P/F ratio = 225. A P/F ratio of 225 is equivalent to a pO2 of 45 mmHg, which is significantly < 60 mmHg on room air.

What is difference between spo2 and PAO2?

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.

How do you calculate ABG from PAO2?

1. PaO2 should = FiO2 x 500 (e.g. 0.21 x 500 = 105 mmHg)
2. see caveats below.

How do you check ABG?

Blood for an ABG test is taken from an artery. Most other blood tests are done on a sample of blood taken from a vein, after the blood has already passed through the body’s tissues where the oxygen is used up and carbon dioxide is produced.

What should PAO2 be on 100 oxygen?

For example, at sea level with no additional supplemental oxygen and a normal physiological state, the PO2 inside the alveoli calculates at approximately 100 mm Hg. But, if a patient is given 100% oxygen in the same situation the PO2 can be as high as 663 mm Hg.

How do you do ABG analysis?

Uncap the ABG syringe, and hold it with two fingers of the dominant hand. The needle bevel should be facing upward. Insert the needle just under the skin at a 45º angle, aiming in the direction of the artery, while palpating the radial pulse proximal to the puncture site with the nondominant hand (see the image below).

Article first time published on

How do I check my ABG report?

1. Look at pH – < 7.40 – Acidosis; > 7.40 – Alkalosis.
2. If pH indicates acidosis, then look at paCO2and HCO3-
3. If paCO2is ↑, then it is primary respiratory acidosis. …
4. If paCO2↓ and HCO3- is also ↓→ primary metabolic acidosis. …
5. If HCO3-is ↓, then AG should be examined.

How do you calculate AA ratio?

Information regarding the alveolar/arterial (A/a) gradient can be estimated indirectly using the partial pressure of oxygen (Po2) (obtained from blood gas analysis) in a simple mathematical formula: A/a gradient = Po2 in alveolar air (estimated from the alveolar gas equation) – Po2 in arterial blood (measured from a …

What is PAO2 normal range?

Normal Results Partial pressure of oxygen (PaO2): 75 to 100 millimeters of mercury (mm Hg), or 10.5 to 13.5 kilopascal (kPa) Partial pressure of carbon dioxide (PaCO2): 38 to 42 mm Hg (5.1 to 5.6 kPa)

What is PAO2 and PaCO2?

PaO2 = measured the partial pressure of oxygen in arterial blood. PaCO2 = measured the partial pressure of carbon dioxide in arterial blood.

How do you calculate alveolar co2?

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 a PF ratio?

The P/F ratio is a simple way to assess the severity of hypoxemia. It’s the ratio of the PaO2 (arterial oxygen partial pressure obtained from an arterial blood gas) to the FiO2 (fraction of inspired oxygen expressed as a decimal).

What does PF ratio tell you?

Knowing the P/F ratio lets you: Recognize severity of hypoxemic respiratory failure in a patient on oxygen therapy. Easily calculate the predicted PaO2 on room air in a patient receiving oxygen— without having to remove that patient from oxygen to test.

What is the difference between ABG and pulse oximeter?

Arterial blood gas tests are invasive, requiring a blood sample, and provide information at a specific moment in time. Pulse oximetry is not invasive. It uses a sensor attached to the person’s finger. It can also provide continuous measurements of the amount of oxygen in the blood.

Is SpO2 the same as SaO2?

The mean difference between SpO2 and SaO2 was -0.02% and standard deviation of the differences was 2.1%. From one sample to another, the fluctuations in SpO2 to arterial saturation difference indicated that SaO2 could not be reliably predicted from SpO2 after a single ABG.

How do you calculate Aa gradient?

The A-a gradient has important clinical utility as it can help narrow the differential diagnosis for hypoxemia. The A-a gradient calculation is as follows: A-a Gradient = PAO2 – PaO2.

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 SpO2?

Example: Suppose a patient on 40% oxygen has a pulse oximetry SpO2 of 95%. Referring to the Table above, SpO2 of 95% is equal to a pO2 of 80mmHg. The P/F ratio = 80 divided by 0.40 = 200.

What is a good pO2 level?

Most healthy adults have a PaO2 within the normal range of 80–100 mmHg. If a PaO2 level is lower than 80 mmHg, it means that a person is not getting enough oxygen . A low PaO2 level can point to an underlying health condition, such as: emphysema.

How do you calculate SpO2 FiO2 ratio?

In general , Spo2/Fio2 (SF) ratio could be predicted well from pao2/fio2(PF) ratio, using the linear regression equation: SF =57+0.61 PF. Based on this equation a PF ratio of 300 corresponds to SF ratio of 235 and PF ratio of 200 to SF ratio of 181( P <0.001).

What are the parameters required to calculate blood pH?

As previously explained, the denominator in this equation (S x pCO2) is the amount of dissolved carbon dioxide (dCO2) mmol/L. Thus pH of blood is dependant on the ratio of plasma bicarbonate concentration (the metabolic component) to pCO2 (the respiratory component).

What is HCT in ABG test?

Hct: Hematocrit (% or volume fraction) ctHb: Concentration of total hemoglobin (g/dL, g/L or mmol/L) RBC: Red blood cell (erythrocyte) (× 1012/L)

What size needle is used for ABG?

Standard arterial blood gas kits typically contain 22- to 25-gauge needles. To assess whether smaller needles might decrease the pain of ABG draws, researchers conducted a randomized, controlled crossover trial in 50 healthy adult volunteers.

Can a nurse draw an ABG?

Most ABG samples can be drawn by a respiratory technician or specially trained nurse. Collection from the femoral artery, however, is usually performed by a doctor. Before attempting a radial puncture, you should perform Allen’s test.

How much blood do you need for ABG?

Collect 2ml arterial/venous blood in this heparinised syringe (filling the syringe completely is very important).

How can you tell the difference between metabolic and respiratory acidosis?

The main difference between metabolic and respiratory acidosis is that the metabolic acidosis occurs due to the production of organic acids such as lactic acid and ketone bodies whereas the respiratory acidosis occurs when lungs have failed to remove excess carbon dioxide from the blood.

What is a normal Aa gradient?

A normal A–a gradient for a young adult non-smoker breathing air, is between 5–10 mmHg.