Category: Resus

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

COPD think VBG

Why VBG instead of ABG?

  • Pain – we all know and warn our patients ABG’s are painful. Patients know it to and delay presentation.
  • Number of bloods taken – patients attending with COPD will generally have venous bloods taken at triage. Would you want stabbing again if it could be avoided?

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