the gap

Hi guys,

when reading ABGs, have you come across the term "anion gap"? well, i've always wondered what it meant and how it relates to our patient so i thought i'd share it with you guys so you guys can get a better picture of our patients status.

The anion gap represents the concentration of all the unmeasured anions in the plasma. It is calculated from the following formula:

either [Na]-[Cl]-[HCO3] or [Na]+[K]-[Cl]-[HCO3]

The optimum value is about 10-12mmol/L. Some of the major clinical uses of the anion gap include signalling the presence of a metabolic acidosis, helping to differentiate between causes of a metabolic acidosis and to assist in the assessment of the biochemical severity of the acidosis and following the response to treatment.

An elevated anion gap is commonly die to ketoacid overproduction due to fat metabolism (diabetes, alcohol, starvation), lactic acid overproduction due to respiratory failure, inability to excrete acids due to renal disease and dehydration.

A decreased anion gap then might be due to hyponatremia, primary hypothyroidism and hypoalbuminemia.

I think this is a pretty useful number as by working backwards from the ABGs then we would be able to detect the associated problems with the patient and thus adjust our treatment and approach accordingly.

Also, i think knowledge of this gap gave me a better understanding of why my patient (whose anion gap is abnormal ) was so lethargic. In fact, i think that the reason could possibly be attributed to insufficiency of the electrolytes which in turn compromises energy production and cellular function.