Category: Learning

Anion Gap & Metabolic Acidosis

The anion gap (AG) represents the amount of unmeasured anions in the plasma.

AG =([Na]+[K]) – ([HCO3]+[Cl])

The main contributor to the AG is albumin (decreasing albumin by 1g/l reduces the AG by 0.25) so hypoalbuminaemia can falsely reduce the AG.

Corrected AG = AG + (0.25*(40-[albumin]))

(However, this relies on getting LFT’s back about 1 hour) Read more

A-a gradient

A-a gradient = Alveolar Oxygen – arterial Oxygen

This is “relatively” simple way of working out if the paO2 on a ABG is normal, and demonstrates V/Q mismatch well. V/Q mismatch is simple terms is either an area of the lung either under ventilated(pneumonia) or under perfused (PE). Read more