The Modified Alveolar Gas Equation2

The value of PaO2 (the partial pressure of O2 in the arterial blood) cannot be interpreted in isolation. A PaO2 which is low relative to the PAO2 (the partial pressure of O2 in alveolar air) implies a significant deficiency in the gas exchange mechanisms of the lung. The alveolar gas equation makes it possible to calculate the PAO2. The difference between the PAO2 (which is a calculated value) and the PaO2 (which is measured in the laboratory) helps quantify the pulmonary pathology that is...

Timing the ABG

How long should you wait editorial Chest 1975 67 253 2.53 A-aDO2 on Intermediate Levels of FIO2 The A-a DO2 normally increases with age. The following formula predicts the A-aDO2 for a given age A - aDO2 2.5 +(0.25 x Age in years) The norntti A-a D02 gradient wklcnswith higher fractions of inspired 02-Tliis A-a difference leaches a maximum when PA02 exceeds 350-450 mmHg and tiien decreases at higher POj's thus describing a hell shaped curve. Therefore, between the two extremes of...

Metabolic Alkalosis Maintenance Factors

Bicarbonate absorption is increased by the following factors 2. Hypochloremia (this is the most common mechanism) Volume conlrancfion (this is alio true of conditions such as CCF and hepatic cirrhosis, where the patient may be in apparent fluid overload, but in reality has (issue hypoperfusion) The kidneys attempt to conserve sodium, especially if the dietary sodium is also km Secondary hypoaldosteroism this is the principal mechanism Intercalated cells of the collecting tubules Increased...

The Determinants of PaCO

The level of PaCO depends on the balance between C02 production and C02 elimination CO production is dependent upon the rate of tissue metabolism CO j production almost never influences PaC02 in the presence of intact ventilatory mechanisms. Hyperventilation or hypoventilation in response to increased or decreased C02 production respectively, promptly results in normalization of the PaCOj. C02 elimination is dependent upon the amount of alveolar ventilation CO elimination is much more important...