What is the purpose of the alveolar-arterial oxygen tension gradient?

The A-a gradient, or the alveolar-arterial gradient, measures the difference between the oxygen concentration in the alveoli and arterial system. The A-a gradient has important clinical utility as it can help narrow the differential diagnosis for hypoxemia.

What does a high alveolar-arterial gradient mean?

A high A–a gradient could indicate a patient breathing hard to achieve normal oxygenation, a patient breathing normally and attaining low oxygenation, or a patient breathing hard and still failing to achieve normal oxygenation.

How do you use the A-a gradient?

V. Interpretation: Calculating a normal A-a Gradient

A-a Gradient = (Age/4) + 4.
Young person at sea level. A-a increases 5 to 7 mmHg for every 10% increase FIO2. Room Air: 10 to 20 mmHg.
Increased age affects A-a Gradient (at sea level, on room air) Age 20 years: 4 to 17 mmHg. Age 40 years: 10 to 24 mmHg.

What is a good A-a gradient?

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

What is alveolar oxygen tension?

Qualitatively, the partial pressure of oxygen within the alveoli is determined by two opposing processes. The alveolar oxygen tension is of significant physiological importance as it largely determines the partial pressure of arterial oxygen.

What is oxygen gradient?

The alveolar to arterial (A-a) oxygen gradient, which is the difference between the amount of the oxygen in the alveoli (the alveolar oxygen tension [PAO2]) and the amount of oxygen dissolved in the plasma (PaO2), is an important measure to help narrow the cause of hypoxemia.

Does asthma cause high A-a gradient?

Results The A-a oxygen gradient was higher in severe asthma compared with controls (mean difference 2.15 KPa, p=0.01 [95% CI 0.95 to 3.3]) and was also higher in mild/moderate asthma compared with normal controls (mean difference 1.29 KPa, p=0.024 [95% CI 0.17 to 2.4]).

Why does the A-a gradient increase?

The A-a gradient is increased as deoxygenated blood enters the arterial (systemic) circulation, which decreases the PaO2. Since venous blood does not oxygenate in the pulmonary shunt, increasing the oxygen concentration does not correct the hypoxemia.

How do you calculate the gradient?

To calculate the gradient of a straight line we choose two points on the line itself. The difference in height (y co-ordinates) ÷ The difference in width (x co-ordinates). If the answer is a positive value then the line is uphill in direction.

What is a normal P AA O2?

Normal P(A-a)O2 = 12 mm Hg in the young Adult to 20 mm Hg at age 70 yo; In pure Ventilatory Failure the P(A-a)O2 will remain 12 to 20 mm Hg; in oxygenation failure it will increase; Interpretation of alveolar-arterial oxygen tension difference.

What is the A-a gradient in ARDS?

What is a normal gradient?

Normal Pressure Gradient. Definition – What does Normal Pressure Gradient mean? Normal Pressure Gradient is the normal pore pressure in a column of fluid within a wellbore. The unit of normal pressure gradient is generally psi/ft or kPA/m (kPA = kilo Pascals). This gradient varies from area to area but generally considered to be around 0.465 psi/ft.

How are the concentration gradients in the alveoli maintained?

Ventilation is the process of bringing fresh air into the alveoli and removing the stale air. It maintains the concentration gradient of carbon dioxide and oxygen between the alveoli and the blood in the capillaries (vital for oxygen to diffuse into the blood from the alveoli and carbon dioxide out of the blood into the alveoli).

What is elevated gradient?

An elevated A–a gradient could indicate a patient breathing hard to achieve normal oxygenation, a patient breathing normally and attaining low oxygenation, or a patient breathing hard and still failing to achieve normal oxygenation. If lack of oxygenation is proportional to low respiratory…

How does an arterial line measure?

ARTERIAL LINES An arterial line is a cannula placed into an artery so that the actual pressure in the artery can be measured. This provides continuous measurement of systolic blood pressure (SBP), diastolic blood pressure (DBP) and mean arterial pressure (MAP). The cannula is connected to an infusion set fitted with a transducer.